Abiotic Oil; Abiogenic Petroleum origin; Origin of natural hydrocarbons (oil and gas); Inorganic Petroleum Origin; Primordial Hydrocarbons
Origem de hidrocabonetos naturais (petróleo e gás). Origem Inorgânica do Petróleo; Origem do Petróleo; Dmitri Y. Mendeleev; Marcelin Berthelot; Nikolai A. Kudryavtsev; Thomas Gold; Robert Robinson; Emmanuil B. Chekaliuk; J. F. Kenney; P. Szatmari; G. A. Kutcherov;
Sunday, January 23, 2011
Hidrocarbonetos e suas relações com a origem da vida na Terra e além
Poster publicado na American Geophysical Union AGU, August 2010, Meeting of the Americas, Foz do Iguassu, Brazil
Hydrocarbons And Their Relationship To The Origin Of Life In The Earth And Beyond
Vasconcelos, C. S and Szatmari, P.
Life as we know it is based primarily on carbon. Carbon is the fourth element in the order of cosmic abundances, after hydrogen, helium and oxygen. Many astrobiologists try to evaluate the possibility of life on other planets, based on hypotheses about the conditions on the surface, such as the presence of liquid water, favorable temperatures and the composition of atmospheric gases, among other factors, even including life in extreme environments. However, there is the possibility that life in the planetary bodies could develop first underground, at depths of several kilometers below the surface, within the pores of the rocks. There the presence of abiogenic hydrocarbons, mainly primordial methane, oxygen compounds associated with iron oxide minerals, and even water, all at appropriate temperatures, could provide ideal conditions for the emergence of life. The conquest of the planet's surface by life would become possible only at a later stage when prokaryotic bacteria (Archaea) arise and move away from the declining hydrocarbon resources, adapt to surface conditions and develop internally catalyzed complex photosynthetic reactions permitting autotrophy. The detection of a deep biosphere in other planets is not simple and probably beyond the capabilities of our technology of telescopes and space probes. On the other hand, it would be relatively less complex to identify life on planets where photosynthesis does occur and has become exuberant.
A vida tal como a conhecemos é baseada principalmente em carbono. O carbono é o quarto elemento da ordem de abundância cósmica, depois de hélio, hidrogênio e oxigênio. Muitos astrobiólogos tentam avaliar a possibilidade de vida em outros planetas com base em hipóteses sobre as condições na superfície, como a presença de água líquida, temperatura favorável e da composição dos gases atmosféricos, entre outros fatores, incluindo até mesmo a vida em ambientes extremos. No entanto, existe a possibilidade de que a vida nos corpos planetários poderia desenvolver primeiro no interior dos mesmos, em profundidades de vários quilômetros abaixo da superfície, dentro dos poros das rochas. A presença de hidrocarbonetos abióticos, principalmente o metano primordial, compostos de oxigênio associados com minerais de óxido de ferro e, até mesmo água, em temperaturas adequadas, poderia proporcionar condições ideais para o surgimento da vida. A conquista da superfície do planeta pela vida seria possível apenas numa fase posterior, quando as bactérias procarióticas (Archea) surgem e distanciam-se dos recursos de hidrocarbonetos em declínio, adaptando-se às condições de superfície e desenvolvendo internamente complexas reações catalisadoras permitindo tornarem seres autótrofos, através da fotossíntese. A detecção de uma biosfera profunda em outros planetas não é simples e, provavelmente, além da capacidade da nossa tecnologia de telescópios e sondas espaciais. Por outro lado, seria relativamente menos complexo identificar vida em planetas onde a fotossíntese ocorreu e tornou-se exuberante.
(Clique nas figuras paraampliar) (Click pictures to enlarge, text in english)
A figura acima mostra que o carbono é o quarto elemento em ordem de abundância cósmica. Materiais primordiais do sistema Hidrogênio-Carbono são complexados em compostos policíclicos aromáticos PAH (Polycyclic Aromatic Hydroarbons) nas nebulosas e nos processos de acreção planetária juntamente com outros voláteis.
A figura mostra relações dos hidrocarbonetos aromáticos com a química pré-biótica, ressaltando que as porfirinas de níquel e vanádio podem estar relacionadas com moléculas catalisadoras de bactérias primitivas que consomem hidrocarbonetos e morrem em meio a esses últimos. As moléculas de asfaltenos são extremamente complexas e não possuem nenhuma relação com a vida. Sua formação sugere ser primordial através dos compostos PAH.
As figuras demonstram que os hidrocarbonetos são compostos primordiais, abióticos, com grande estabilidade termodinâmica. As teorias e proposições de Thomas Gold para a origem dos hidrocarbonetos (The Deep-Earth Gas Theory) são adequadas e possuem base científica, como se observa no gráfico de estabilidade termodinâmica para os hidrocarbonetos, de Chekaliuk, 1976. Também nos estudos do Massachussets Institute of Technology, MIT, que mostram que o carbono é extremamente abundante no manto da Terra em comparação com os níveis mais superficiais.
Os diagramas mostram que os hidrocarbonetos como o petróleo e gás natural migram de grandes profundidades do interior da Terra (manto) para níveis de baixa pressão e temperatura tal como nas bacias sedimentares, conduzidos por gases como Hélio e Nitrogênio, podendo haver acumulação em reservatórios. Nesse contexto, bactérias primitivas alimentam-se desses hidrocarbonetos primordiais e deixam seus traços, como exemplo, hopanóides. Essa contaminação causada pelos microrganismos conduz um antigo paradoxo para a origem do petróleo, caso não se compreenda que os hidrocarbonetos são primordiais e abióticos. Os trabalhos de Kutcherov (2009) em experimentos de alta pressão e temperatura comprovam a formação de hidrocarbonetos gasosos a partir de materiais inorgânicos assim como os trabalhos de J.F.Kenney e colaboradores.
Na figura a árvore filogenética da vida. Notar que o domínio das archeas está na base, próximo ao ancestral comum. Ver as moléculas de hopanóides, muito comuns no petróleo, que são fracamente oxigenadas e estão relacionadas com partes de paredes celulares de bactérias que vivem e morrem em meio ao petróleo. A clorofila é uma molécula de porfirina com núcleo de magnésio. No petróleo inexistem porfirinas de magnésio, apenas de níquel e vanádio.
A figura mostra a distribuição global de clorofila no planeta Terra, a partir de dados de satélites NASA. Notar a abundância nas regiões polares, onde há mais oxigênio dissolvido na água. Torna-se óbvio que um planeta com vida baseada em clorofila seria de fácil identificação por refletir a cor verde no espectro. A fotossíntese é um processo complexo e posterior à biosfera que existe no interior da Terra. O estudo dessa biosfera profunda e quente deve ser o objetivo principal dos astrobiólogos caso queiram entender melhor onde pode haver vida e como ela pode se originar.
Also available in Deep Carbon Observatory - Carnegie Institution, Washington, USA.
His book, "The Deep Hot Bioshpere" (Copernicus, An Imprint of Springer-Verlag, New York, ISBN 0-387-98546-8) is available in bookstores in the USA and United Kingdom. It can also be obtained on the Internet from Barnes & Noble or Amazon.com. It discusses most of the items listed below.
The basic idea that a large amount of microbial life exists in the pore spaces of the rocks down to depths of between 6 and 10 kilometers arose in the following way: natural petroleum almost always contains elevated levels of the chemically inert gas helium and at the same time it contains molecules that are unquestionably of biological origin. How these two different substances meet up in oil has long been a puzzle. If there exists microbial life, down to all levels that can be reached by the drill, then the biological molecules can be explained. The association with helium can then be explained adequetely if the hydrocarbons have come up from much deeper levels and thereby swept up the diffusely distributed helium that exists in the rocks.
The evidence that such a deep biosphere exists has now been strongly supported by microbial studies in deep bore holes.
Drilling deep into the crystalline granite of Sweden between 1986 and 1993 revealed substantial amounts of natural gas and oil. 80 barrels of oil were pumped up from a depth between 5.2 km and 6.7 km.
Russian petroleum geologists followed this operation closely. Dr. P.N. Kropotkin reported at a meeting in Moscow that the discovery of oil deep in the Baltic Shield may be considered a decisive factor in the hundred year old debate about the biogenic or abiogenic origin of oil. This discovery was made in deep wells that were drilled in the central part of the crystalline Baltic Shield, on the initiative of T. Gold.
Drilling into crystalline bedrock is now underway in Russia on a large scale. More than 300 wells have been drilled to a depth of more than 5 km and are productive, as also is the giant White Tiger field offshore Vietnam, mostly producing also from basement rock.
Outgassing processes of the Earth are discussed, and the relation they may have to:
• sub-surface biology
• origin of petroleum
• earthquakes and volcanic eruptions
• deposits of certain metal ores
• chemical processing of the crust
Sub-surface life on Earth may give an indication that similar life exists on other planetary bodies, and suggests means of looking for that. The material is presented in the form of assorted papers from the following menu.
• The most important information for estimating the value of a field: Recharging of oil and gas fields.
• The origin of petroleum
Natural Gas and Oil
The Origin of Methane (and oil) in the Crust of the Earth— This is a major paper, outlining the reasons why an origin from non-biological materials accounts better for the facts, than an origin from buried biomass (approximately 31 printed pages).
• Can There Be Two Different Processes Responsible for Commercial Oil?
• Evidence for a primordial origin of hydrocarbons
On the History of Science - Excerpts from a paper by P.N. Kropotkin
Depth Effects of Petroleum
• Association of hydrocarbons with helium and with biological molecules
Association of Petroleum with Helium and Biological Molecules
• Causes of Earthquakes and Earthquake Prediction
Earthquakes, Gases, and Earthquake Prediction
Eye-witness Accounts of Several Major Earthquakes
• Sub-surface life on Earth and possibly on other planetary bodies
The Deep, Hot Biosphere — Reason for suspecting massive microbial life in the crust of the Earth.
Life on other Planets — Sub-surface life on Earth suggests that similar life may exist on other planetary bodies.
• The deposition of certain metal ores
Metal Ores and Hydrocarbons
• T. Gold Vita
Natural Gas and Oil
Natural gas and oil are widely considered to originate on Earth from the chemical evolution of biological debris. A view, widespread in earlier times and entertained by Mendeleev among others, was instead that these substances originated in materials laid down in the formation process of the Earth, and later percolated towards the surface.
Similar hydrocarbons are widespread on many other planetary bodies, as well as on comets and generally in deep galactic space, clearly not related to biological materials there.
Thermodynamic considerations show that in the high-pressure, high-temperature regime of the outer mantle of the Earth, hydrogen and carbon will readily form hydrocarbon molecules, and some of those will be stable during ascent into the outer crust. There is no reason now for invoking the unique origin of biology for the Earth's hydrocarbons, different from the origin of similar materials on the other planetary bodies.
The many molecules of unquestionably biological origin in petroleum - hopanes, pristine, phytane, steranes, certain porphyrins - can all be produced by bacteria, and such microbial life at depth is indeed now seen to be widespread. The presence of these molecules can no longer be taken to be indicative of a biological origin of petroleum, but merely of the widespread presence of a microflora at depth. The presence of helium and of numerous trace metals, often in far higher concentrations in petroleum than in its present host rock, has then an explanation in the scavenging action of hydrocarbon fluids on their long way up. Many mineral deposits may be due to the formation and transportation of organo-metallic compounds in such streams, often interacting with microbial life in the outer crust.
A 6.6 km deep well drilled in the granite of Sweden shows petroleum and gas, and bacteria that can be cultured, all in the complete absence of any sediments, and hence of any biological debris. Combustible gas in large sample containers has been brought to the surface from a depth of more than 6.5 km. It will readily burn, and it shows a composition which includes methane and heavier hydrocarbons up to C-7, as well as free hydrogen. The greatest concentrations of this gas are in and close to the various intrusions of volcanic rocks (dolerite), indicating that the gases have used the pathways from depth that the volcanic rock created or used in its ascent.
The Origin of Methane (and Oil) in the Crust of the Earth
U.S.G.S. Professional Paper 1570, The Future of Energy Gases, 1993
The deposits of hydrocarbons in the crust of the Earth have long been regarded by many investigators as deriving from materials incorporated in the mantle at the time of the Earth's formation. Outgassing processes, active in all geological epochs, then transported the liquids and gases liberated there into porous rocks of the crust. The alternative viewpoint, that biological debris was the source material for all crustal hydrocarbons, gained widespread acceptance when molecules of clearly biological origin were found to be present in most commercial crude oils.
Modern information re-directs attention to the theories of a non-biological, primeval origin. Among this information is the prominence of hydrocarbons—gases, liquids and solids—on many other bodies of the solar system, as well as in interstellar space. Advances in high-pressure thermodynamics have shown that the pressure-temperature regime of the Earth would allow hydrocarbon molecules to be formed and to survive between the surface and a depth of 100 to 300 km. Outgassing from such depth would bring up other gases present in trace amounts in the rocks, thus accounting for the well known association of hydrocarbons with helium. Recent discoveries of the widespread presence of bacterial life at depth point to this as the origin of the biological content of petroleum. The carbon budget of the crust requires an outgassing process to have been active throughout the geologic record, and information from planets and meteorites, as well as from mantle samples, would suggest that methane rather than CO2 could be the major souce of surface carbon. Isotopic fractionation of methane in its migration through rocks is indicated by numerous observations, providing an alternative to biological processes that have been held responsible for such fractionation. Information from deep boreholes in granitic and volcanic rock of Sweden has given support to the theory of the migration of gas and oil from depth, to the occurrence of isotopic fractionation in migration, to an association with helium, and to the presence of microbiology below 4 km depth.
The gas methane, CH4, the principal component of natural gas, does not contain sufficient evidence in itself from which to deduce its origin on the Earth. There is some evidence from its isotopic composition, but interpretations of that are not unique. Information, however, exists in the mode of occurrence of natural gas reservoirs, in the geographic and geological relationships, in associated chemicals, and, above all, in the frequent association with other hydrocarbons, specifically crude petroleum and bituminous coal. Although there are numerous occurrences of natural gas without the heavier hydrocarbons, the association is generally so clear that one cannot contemplate an origin for the natural gas deposits independent of those of petroleum. We shall therefore first consider the origin of the whole set of hydrocarbons, including natural gas, and then discuss aspects that are specific to methane.
Debate about the Origin of Petroleum
It is remarkable that in spite of its widespread occurrence, its great economic importance, and the immense amount of fine research devoted to it, there perhaps still remain more uncertainties concerning the origin of petroleum than that of any other commonly occurring natural substance. (H.D.Hedberg, 1964)
Actually it cannot be too strongly emphasized that petroleum does not present the composition picture expected from modified biogenic products, and all the arguments from the constituents of ancient oils fit equally well, or better, with the conception of a primordial hydrocarbon mixture to which bio-products have been added. (Sir Robert Robinson, President, Royal Society, 1963)
The capital fact to note is that petroleum was born in the depths of the Earth, and it is only there that we must seek its origin. (D. Mendeleev, 1877)
The origin of petroleum has been a subject of many intense and heated debates, ever since this black fluid was first discovered to be present in large quantities in the pore spaces of many rocks. Is it something brought in from space when the Earth was formed? Or is it a fluid concentrated from huge amounts of vegetation and animal remains that may have been buried in the sediments over hundreds of millions of years?
Arguments have been advanced for each viewpoint, and although they conflict with each other, each line of argument sounds strangely convincing. In favor of the biogenic origin of petroleum, the following four observations have been advanced:
(1) Petroleum contains groups of molecules which are clearly identified as the breakdown products of complex, but common, organic molecules that occur in plants, and that could not have been built up in a non-biological process.
(2) Petroleum frequently shows the phenomenon of optical activity, i.e. a rotation of the plane of polarization when polarized light is passed through it. This implies that molecules which can have either a right-handed or a left-handed symmetry are not equally represented, but that one symmetry is preferred. This is normally a characteristic of biological materials and absent in fluids of non-biological origin.
(3) Some petroleums show a clear preference for molecules with an odd number of carbon atoms over those with an even number. Such an odd-even effect can be understood as arising from the breakdown of a class of molecules that are common in biological substances, and may be difficult to account for in other ways.
(4) Petroleum is mostly found in sedimentary deposits and only rarely in the primary rocks of the crust below; even among the sediment, it favors those that are geologically young. In many cases such sediment appears to be rich in carbonaceous materials that were interpreted as of biological origin, and as source material for the petroleum deposit.
On the other side of the argument, in favor of an origin from deeply buried materials incorporated in the Earth when it formed, the following observations have been cited:
(1) Petroleum and methane are found frequently in geographic patterns of long lines or arcs, which are related more to deep-seated large-scale structural features of the crust, than to the smaller scale patchwork of the sedimentary deposits.
(2) Hydrocarbon-rich areas tend to be hydrocarbon-rich at many different levels, corresponding to quite different geological epochs, and extending down to the crystalline basement that underlies the sediment. An invasion of an area by hydrocarbon fluids from below could better account for this than the chance of successive deposition.
(3) Some petroleums from deeper and hotter levels lack almost completely the biological evidence . Optical activity and the odd-even carbon number effect are sometimes totally absent, and it would be difficult to suppose that such a thorough destruction of the biological molecules had occurred as would be required to account for this, yet leaving the bulk substance quite similar to other crude oils.
(4) Methane is found in many locations where a biogenic origin is improbable or where biological deposits seem inadequate: in great ocean rifts in the absence of any substantial sediments; in fissures in igneous and metamorphic rocks, even at great depth; in active volcanic regions, even where there is a minimum of sediments; and there are massive amounts of methane hydrates (methane-water ice combinations) in permafrost and ocean deposits, where it is doubtful that an adequate quantity and distribution of biological source material is present.
(5) The hydrocarbon deposits of a large area often show common chemical or isotopic features, quite independent of the varied composition or the geological ages of the formations in which they are found. Such chemical signatures may be seen in the abundance ratios of some minor constituents such as traces of certain metals that are carried in petroleum; or a common tendency may be seen in the ratio of isotopes of some elements, or in the abundance ratio of some of the different molecules that make up petroleum. Thus a chemical analysis of a sample of petroleum could often allow the general area of its origin to be identified, even though quite different formations in that area may be producing petroleum. For example a crude oil from anywhere in the Middle East can be distinguished from an oil originating in any part of South America, or from the oils of West Africa; almost any of the oils from California can be distinguished from that of other regions by the carbon isotope ratio.
(6) The regional association of hydrocarbons with the inert gas helium, and a higher level of natural helium seepage in petroleum-bearing regions, has no explanation in the theories of biological origin of peroleum.
Advocates of the Abiogenic Theory
Among the early advocates of a non-biological origin of petroleum was the great Russian chemist Mendeleev, the originator of the periodic table of the elements. His arguments, presented in a paper on the origin of petroleum (Mendeleev, 1877) are still valid today. He already knew of the large-scale patterns of hydrocarbon occurrence, but his information on the processes that shaped the Earth was not our present understanding, and made his explanations much more complex than would need to be the case now.
Sokoloff (1889) discussed the "cosmic origin of bitumina" (carbonaceous substances from petroleum to pitch and tar), and he related these to the meteorites, knowing then already about their hydrocarbon content. He stressed that oil and tar occur in basement rocks, such as in the gneiss of Sweden. He could find no relationship to the fossil content of rocks, and he stressed that porosity was the sole circumstance which relates to the accumulation of bituminous substances.
Vernadsky (1933) gave reasons why he considered that with increased pressure and deceased oxygen availability with depth, hydrocarbons would be stable and largely replace carbon dioxide as the chief carbon-bearing fluid.
Kudryavtsev (1959) the most prominent and strongest advocate of the abiogenic theory in modern times, argued that no petroleum resembling the chemical composition of natural crudes has ever been made from genuine plant material in the laboratory, and in conditions resembling those in nature. He gave many examples of of substantial and sometimes commercial quantities of petroleum being found in crystalline or metamorphic basements, or in sediments directly overlying those. He cited cases in Kansas, California, Western Venezuela and Morocco. He pointed out that oil pools in sedimentary strata are often related to fractures in the basement directly below. The Lost Soldier Field in Wyoming has oil pools, he stated, at every horizon of the geological section, from the Cambrian sandstone overlying the basement to the upper Cretaceous deposits. A flow of oil was also obtained from the basement itself.
Hydrocarbon gases, he noted, are not rare in igneous and metamorphic rocks of the Canadian Shield. Petroleum in Precambrian gneiss is encountered in wells on the eastern shore of Lake Baikal. He stressed that petroleum is present, in large or small quantity, but in all horizons below any petroleum accumulation, apparently totally independent of the varied conditions of formation of these horizons. This statement has since become known as "Kudryavtsev's Rule" and many examples of it have been noted in different parts of the world. Commercial accumulations are simply found where permeable zones are overlaid by impermeable ones, he concluded.
Kudryavtsev introduced a number of other relevant considerations into the argument. Columns of flames have been seen during the eruptions of some volcanoes, sometimes reaching 500 meters in height, such as during the eruption of Merapi in Sumatra in 1932. (We since know of several other instances.) The eruptions of mud-volcanoes have liberated such quantities of methane, that even the most prolific gasfield underneath should have been exhausted long ago. Also the quantities of mud deposited in some cases would have required eruptions of much more gas than is known in any gasfield anywhere. The water coming up in some instances carries such substances as iodine, bromine and boron that could not have been derived from local sediments, and that exceed the concentrations in seawater one hundred fold. Mud volcanoes are often associated with lava volcanoes, and the typical relationship is that where they are close, the mud volcanoes emit incombustible gases, while the ones further away emit methane. He knew of the occurrence of oil in basement rocks of the Kola Peninsula, and of the surface seeps of oil in the Siljan Ring formation of Central Sweden (which we shall discuss later). He noted that the enormous quantities of hydrocarbons in the Athabasca tar sands in Canada would have required vast amounts of source rocks for their generation in the conventional discussion, when in fact no source rocks have been found.
Beskrovny and Tikhomirov (1968) noted, as did Anders, Hayatsu and Studier (1973), that of the many possible isomers of petroleum molecules, the particular sub-set found in natural petroleum is also the one singled out in artificial oil production from hydrogen and carbon rather than from biological substances.
Porfir'ev (1974) argued that so-called source rocks have no identification that proves their hydrocarbons to be primarily biogenic. He also discounted the hypothesis, often advanced, that the transport and deposition of oil from supposed source rocks to the final reservoir was accomplished by solution in gas: the quantities of gas that would be required would exceed by orders of magnitude the quantities that could be derived from the supposed source materials.
Levin (1958) concerned himself with the formation process of the Earth, claiming that the class of meteorites called carbonaceous chondrites, a low-temperature condensate that was probably responsible for bringing in solids that contained water, could have brought to the forming Earth several times larger quantities of carbonaceous materials than all the ocean water.
Kravtsov (1975) presented much observational material. He showed that the natural seepage of methane in many areas was far more than could be supplied by any kind of gasfield known. If the volcanic gases of the Kurile Islands, for example, are typical of the gases emitted over the time-span of the volcanic activity there, the amount of methane emitted would far exceed the conventional estimate of the present-day total world reserves. He also gave many examples of "Kudryavtsev's Rule."
Kropotkin and Valyaev (1976, 1984) and Kropotkin (1985) developed many aspects of the theory of deep-seated, inorganic origin of hydrocarbons. They concluded that petroleum deposits were formed where pressure conditions permitted the condensation of heavier hydrocarbons, transferred from great depth by rapidly rising streams of compressed gases. In volcanic regions, they noted, decomposition of hydrocarbons would be favored, resulting in the formation of carbon dioxide and water, while in "cool" regions hydrocarbons would be preserved, and could accumulate in alluvial cover and highly fractured beds, depending on the presence of adequate reservoirs and covers. According to these authors "vertical migration of hydrocarbons from levels far below formations rich in biogenic organic matter, which have been considered the source material for the oil, can be demonstrated in a majority of deposits." Kropotkin also presented numerous examples where Kudryavtsev's Rule is satisfied in a striking way.
There were several voices also outside Russia (or the Soviet Union), who argued for a non-biogenic origin. Most notable among them was Sir Robert Robinson (1963, 1966) who, like Mendeleev, can be considered among the most distinguished chemists of his day. He studied the chemical make-up of natural petroleums in great detail, and concluded that they were mostly far too hydrogen-rich to be a likely product of the decay of plant debris. Olefins, the unsaturated hydrocarbons, would have been expected to predominate by far in any material that was derived in that way.
Sylvester-Bradley (1964, 1972) discussed that the meteorites have hydrocarbons, and that hydrocarbons on the Earth derived in major part from such material. He proposed that hydrocarbons streaming up through the crust from great depth would have provided energy sources for simple forms of life. He knew about the biological materials in petroleum, but, like Robert Robinson, he thought that they were due to contaminating additions from microbiology in such locations.
Before discussing further the possible origins of hydrocarbons on the Earth, it is necessary to discuss the present state of knowledge of the formation process of the Earth and the planetary system, and the materials that contributed to the formation.
The Formation Process of the Earth
The Earth is a body with a most complex history. None of its sister planets display signs of the processes that appear to have been the major ones to shape this planet of ours. On all the other solid bodies of the Solar System the effects of impact cratering can be seen very clearly. Craters spanning a range of size from a few kilometers to several thousand can be clearly recognized. Impacts of solid objects upon all the planetary bodies in the process of their formation must have been a common occurrence.
Strangely, on our Earth similar cratering events can only be seen, if at all, in a very subdued form. We see arcs of circles appearing in the midst of a topography shaped by other effects. It seems reasonable to interpret such circular features as the remains of impacts, now deeply buried but affecting the outer crust at a later stage in some way that makes the buried impacts recognizable again. One has to suppose that other events occurred here that obscured most of the evidence of this early bombardment.
Nevertheless, it is now quite clear that the Earth, like the other solid planetary bodies, also formed by the accretion of solid objects, probably largely in the form of small grains, but interspersed with occasional major pieces. It appears that then a partial melting took place, causing materials of lower density to make their way to the surface, while presumably melts of high density sank down towards the center. The heat for this melting was the result of radioactivity contained in the material, as well as just the heat resulting from compression. Once partial melting occurred, two other sources of heat came into play: firstly the gravitational energy that is released as materials can move and sort themselves out according to density. Secondly there is the chemical energy that results from all the chemical reactions that can then take place, either between different liquids or between liquids and solids. The original diverse materials accreted as cold objects would certainly not have been chemically equilibrated with each other, but would be left in an uneven distribution by the chances of the impact events. After gaining mobility by melting, many chemical reactions would take place that would, on average, release energy and thus provide more heat, as well as giving rise to volatile substances.
Both these last two sources of energy have the interesting property that they make the heating unstable: where more heating has occurred and more melt produced, more of these actions can take place and therefore still more heat will be produced there. One may well speculate that the very uneven distribution of internal heat sources which we recognize at the surface, derives from such an instability. The circumpacific "belt of fire" is the most striking example, but there are also many other lanes characterized by high heat flow and volcanic activity. They are also characterized by the outflow of fluids, gases and liquids, that are thought to have a deep origin. Deposits of hydrocarbons frequently show a clear association with such patterns. (An example is shown in Figure 3.)
If the major volume of the Earth has never been molten, the mantle of the Earth underneath the crust must still contain the diversity of chemistry, the chemical energy sources and the sources of gases and liquids that would be the legacy of an accretion process from diverse and initially cold solids. Major impacts would have thrown up ring patterns of mountains, which, as on the Moon, would convert vertical patterns of chemical inhomogeneity into regional patterns. Many arcuate patterns on the Earth of present surface topography and of chemical features or of heat flow may be a consequence of this.
The Theory of the Biological Origin of Hydrocarbons on Earth
Oil, hydrocarbon gases and coal on the Earth were thought to have derived entirely from biological debris for the following reasons: One reason was the belief in earlier times that hydrocarbons were specifically organic substances: hence the name "organic carbon" for all forms of unoxidized carbon. The knowledge that hydrocarbons are abundant in the universe, and on many of the other planetary bodies of our solar system, was not available at that time. Now we know that carbon, the fourth most abundant element in the Universe after hydrogen, helium and oxygen, is almost certainly also the fourth most abundant in the planetary system; there it is predominantly in the form of hydrocarbons. The major planets Jupiter, Saturn, Uranus and Neptune, have large amounts of methane and other hydrocarbon gases in their atmospheres. Titan, a large satellite of Saturn, has methane and ethane in its atmosphere, and these gases form clouds and behave much like water does in the atmosphere of the Earth. Triton, a large satellite of Neptune, appears to have hydrocarbons mixed with water ices on its surface, as does the outermost planet known at this time, Pluto. A large fraction of all the asteroids show a surface reflectance closely resembling that of tar, and the comets have hydrocarbons among the gases they emit. The surface of the core of Comet Halley, recently observed by spacecraft, is most reasonably interpreted as one of tar. Complex, polycyclic hydrocarbon molecules, similar to those in natural petroleum have been observed to be a prominent component of interplanetary dust grains that currently enter the Earth's upper atmosphere (Clemett and others, 1993).
Hydrocarbons in our planetary system are certainly very abundant, and in all the extraterrestrial examples mentioned almost certainly not related to biology. Also hydrocarbons are prominent among the gases identified in the molecular clouds of the galaxy, and it is from such clouds that the solar system formed initially. The presence and great abundance of hydrocarbons is universal, and no special mechanism for their generation on the Earth needs to be invoked, unless one knew with certainty that they could not have survived the formation process here, although they did so on many of the other planetary bodies. (No evidence of hydrocarbons has yet been seen on Mars, Moon, Venus and Mercury. The atmosphere of Venus is too hot to have maintained gaseous or liquid hydrocarbons; the other three bodies lack an adequate protective atmosphere to have maintained them on their surfaces.)
In earlier times there was the belief that the Earth had formed as a hot, molten body. In that case no hydrocarbons or hydrogen would have survived against oxidation, nor would any of these substances have been maintained in the interior after solidification. With that belief, there seemed no other possibility of accounting for the hydrocarbons embedded in the crust than by the outgassing of carbon in the form of CO2, produced by materials that could have survived in a hot Earth, and subsequent photosynthesis by plants that converted this CO2 into unoxidized carbon compounds. This consideration is irrelevant now that we know that a cold formation process assembled the Earth and that hydrocarbons could have been maintained, and could be here for the same reasons as they are on the other planetary bodies.
The common existence of molecules of clearly biological origin in most petroleum and bituminous coal is no longer an argument for a biological origin of hydrocarbons, now that we know of the wide reach of microbiology in the crust (Jannasch, 1983; Yayanos, 1986; Gold, 1992). Before this had been identified, the possibility of widespread biological contamination at depth had not been considered. Now, especially after the discovery of the volcanic vents on the ocean floors and the profuse chemosynthetic life that exists there, the outlook is different. It is now seen as not only possible, but very likely, that microbiology is common in the crust down to depths of between 5 and 10 kilometers, a level below which the temperature will reach values too high for any microbial life we know, thought to be between 110 and 150 °C. This deep microbial life uses as its energy source the various chemical imbalances that the outgassing process creates as gases and liquids stream up through rocks with which they have never been chemically equilibrated. Knowing now of the occurrences of such deep microbial life, it seems likely that no location that could support such life has been kept sterile from it for the long periods of geologic time. Hydrocarbons, together with oxygen donors such as sulfates or metal (principally iron) oxides, substances that are common in the rocks or water, would provide a usable energy source for microorganisms. Hydrocarbon deposits would therefore acquire biological debris in the course of time. The molecules which are commonly regarded as proof of the biological origin of petroleum and of bituminous coal have all been found to be also produced by subsurface bacteria; indeed some of them can only be produced by bacteria (Ourisson and others, 1984). Pristane, phytane, steranes, hopanes are unquestionably of biological origin, but do not certify the biological origin of either petroleum, coal, kerogen or whatever other deposits in which they are seen. With the photosynthetic theory of their origin, they seemed to certify that these materials were all once at the surface. But this is no longer a valid inference. Many other conclusions in geology were based on this, and should also be reconsidered now.
Origin of the Carbon on the Earth
The surface and surface sediment on the Earth contain approximately one hundred times as much carbon as would have been derived from the grinding up of the basement rocks that contributed to the sediment. The surface is enormously enriched in carbon, and this needs an explanation.
The carbon we have on the surface or in the sediment of the Earth is estimated to be 4/5 in the form of carbonate rocks, and 1/5 in unoxidized form, frequently referred to as "organic." (The word "organic" given then to all unoxidized carbon, is of course now a misleading misnomer.) The quantities are large: if expressed as the mass of the element carbon per square centimeter of total Earth surface area, the estimate is about 20 kilograms. (I will be referring to this quantity again later.)
During formation of the Earth by the accumulation of cold solids, very little gaseous material was incorporated. The knowledge of this comes from the extremely low level of the non-radiogenic noble gases in the atmosphere of the Earth. Among those, only helium could have escaped into space, and only xenon could have been significantly removed by absorption into rocks. Neon, argon, krypton would have been maintained as an atmospheric component. The noble gas proportions in the Sun and in space are known. Any acquisition of such a mix of gases in the formation process would not have been able to selectively exclude noble gases that have no significant chemical interactions. One is forced to conclude that the acquisition of gases, or substances that would be gaseous at the pressures and temperatures that ruled in the region of formation of the Earth, was limited to the small value implied by the low noble gas values. The carbon supply the Earth received initially could not have been in the form of hydrocarbon gases, high volatility hydrocarbon liquids, or CO or CO2.
Could meteoritic infall of carbon at later times be held responsible for the surface carbon excess? Such a massive infall would have left much other evidence in the geologic record, and this is absent. The only alternative is that carbon came up from the interior as a liquid or gas, just as is also true for the water of the oceans (approximately 300 kg/cm2) the nitrogen of the atmosphere (1 kg/cm2 approximately) and the (largely radiogenic) argon of the atmosphere.
Perhaps one might consider the possibility that the Earth once had a massive atmosphere of carbon dioxide that evolved early on, from materials that could have survived the formation process, and that these then became converted in into the carbon deposits we now have; but that also does not seem an acceptable explanation, for in that case we should see incomparably more very early carbonate rocks than the amounts laid down later. This is not what the geologic record shows. What it does show is a reasonably continuous process of laying down carbonate rocks; no epoch having enormously more per unit time, nor enormously less. If outgassing from depth is responsible, then one has to discuss what the source material in the Earth might have been, what liquids or gases might have come from them, and what their fate would have been as they made their way up through the crust.
The meteorites represent some samples of leftover material from the formation of the planets. While they may not be representative of the quantities of the different types that made up the Earth, they appear to represent at least samples of all the major components. Only one type, the carbonaceous chondrites, contain significant amounts of carbon, and they contain it mainly in unoxidized form, a substantial fraction in the form of solid, heavy hydrocarbons. This material, when heated under pressure as it would be in the interior of the Earth, would indeed release hydrocarbon fluids, leaving behind deposits of solid carbon.
The quantitative information on carbonaceous chondrites is difficult to evaluate. They are much more friable than most other meteorites, and therefore survive the fall through the atmosphere less often than the others. Carbonaceous chondrites also are destroyed by erosion on the ground much more rapidly. The result must be that far fewer than the original proportion are ever discovered. They may well represent even now the largest quantity of meteoritic material still available for collection by the Earth; the infall of interplanetary dust to which I have referred, contains similar carbonaceous material.
By contrast, carbonates, which would be a source material for CO2, exist in meteoritic materials only in very small concentrations, so that an origin of the carbon from an initial CO2 source seems unlikely. If the carbonaceous chondrite material is the principal source of the surface carbon we have, then the initial material that could be mobilized in the Earth at elevated temperatures and pressure would be a mix of carbon and hydrogen. What would be the fate of such a mix? Would it all be oxidized with oxygen from the rocks, as some chemical equilibrium calculations have suggested? Evidently not, for we have clear evidence that unoxidized carbon exists at depths between 150 km and 300 km in the diamonds. We know they come from there, because it is only in this depth range that the pressures would be adequate for their formation. Diamonds are known to have high-pressure inclusions that contain CH4 and heavier hydrocarbons, as well as CO2 and nitrogen (Melton and Giardini, 1974). The presence of at least centimeter-sized pieces of very pure carbon implies that carbon-bearing fluids exist there, and that they must be able to move through pore-spaces at that depth, so that a dissociation process may deposit selectively the pure carbon; a process akin to mineralization processes as we know them at shallower levels. The fluid responsible cannot be CO2, since this has a higher dissociation temperature than the hydrocarbons that co-exist in the diamonds; it must therefore have been a hydrocarbon that laid down the diamonds.
Diamonds will only survive a transport to the low pressure at the surface, if it is accompanied by rapid cooling; if they are taken through a slow cooling process they will turn to graphite, the equilibrium form of carbon at low pressure. Diamond is a metastable form of carbon at the low surface pressure, but the temperature is too low for a relaxation to the stable form. Indeed, diamonds are found predominately in the vicinity of sites of explosive gas eruptions, diamond pipes, where rapid gas expansion caused quick cooling. There is also evidence for pure carbon transported up from depth at a slow rate: pseudomorphs of diamonds. Spaces showing the octahedral symmetry of diamond have been found filled with graphite, in mantle rocks that have come to the surface in Morocco (Pearson and others, 1989). These rocks came up presumably in a slow ascent, and contained a dense array of octahedral spaces filled with graphite, clearly fitting the interpretation as pseudomorphs of diamond. This discovery suggests that a very high density of diamonds exists at least in some locations in the mantle, and that their rarity on the surface is to be attributed to the rarity of the explosive events that could bring them up sufficiently quickly. It is noteworthy that hydrocarbons are found in diamond pipes together with the diamonds, suggesting that the gases involved in the explosive events were not oxidizing (Kravtsov and others, 1976; 1981).
The Surface Carbon Budget
The deposition of carbonate rocks has been an ongoing process throughout the times of the geologic record. Most, but not all of this carbonate has been an oceanic deposit, deriving the necessary CO2 from the atmospheric-oceanic CO2 store. The amount that is at present in this store is, however, only a very small fraction of the amount required to lay down the carbonates present in the geologic record. The atmospheric-oceanic reservoir holds at present only about 0.01 kg of carbon per cm2 of the Earth's surface area. If we take the figure quoted, of about 20 kg of carbon per cm2 laid down over the time of the identified geologic record, there must have been a supply renewing the atmospheric-oceanic CO2 gradually, but by an amount 2,000 times the present content. This amount of carbon, if calculated as a continuous and steady outgassing rate and initially all coming up as methane, would translate into a one meter deep layer of methane (at STP) being created all over the Earth every 2,700 years. If the rate is regionally variable so that, for example, one tenth of the area produces nine tenths of the amount, then in the gas-prone areas one meter STP methane would come up every 300 years. If natural gas fields are filled from outgassing methane, such a supply rate would be much more than adequate in the timespans available to create all the known fields.
If the supply of carbon from below ceased, the present rate of laying down carbon would deplete the atmosphere-ocean reservoir in something on the order of 500,000 years, a very short fraction of geologic time. Outgassing of carbon in some form must have been a continuous process; it is not likely that humans evolved just in the last period, just before the death of all plant life. We must therefore inquire what quantities of carbon would have been available at deep levels, in what form this was, and in what manner this resupply of the atmospheric-oceanic CO2 reservoir could have taken place. It is also clear that one cannot discuss the man-made additions to the atmospheric carbon gases without regard to the large and surely variable natural carbon emission that has taken place throughout geologic time.
The resupply of carbon must be from juvenile sources. Recycling of sediments cannot account for it, both for reasons of the quantities involved and for reasons of the isotopic composition. If the repeated subduction of carbonate rocks occurred on the necessary massive scale, it would seem that old carbonates should have disappeared almost completely. This is not the case. The isotopic information, to which we shall return later, also would say that in a process of continuous recycling the proportion of 13C would continuously increase in the atmosphere, and hence the younger carbonates should be isotopically heavier than the old ones; this also is not the case. Marine carbonates of all ages back to the Archaean show the same narrow range of the carbon isotopic ratio (Schidlowski and others, 1975, see also Figure 4).
How much carbonaceous chondrite material would have been required to provide the supply of the surface carbon? Let us make a simple calculation for this. Suppose that in the depth range between 100 and 300 kilometers we have a patchwork in which the carbonaceous chondrite material comprises 20 percent on an average. In this material, carbon amounts to 5 percent. This means, on an average, each square centimeter column through the 200 kilometer layer would contain 1 percent of carbon (5% of 20%), which would translate into 660 kilograms per square centimeter. If one-thirtieth of this had been mobilized and reached the outer crust, it would suffice to account for all the carbon of the carbonate sediments and the sediments of unoxidized carbon. Of course the proportion of carbonaceous chondrite type of material may have been very much larger, and the producing layer much thicker. The fraction that needs to have been mobilized would then be much smaller. All one can really say at this stage is that there is no quantitative problem. Volatile-rich material of sufficient quantity to have supplied the water of the oceans, as discussed by Levin (1958), could quite easily have supplied the quantity of hydrocarbons for all the surface carbon.
As we have seen, the primary source material in the Earth that would send up a carbon-bearing fluid is likely to be a hydrocarbon mix, not a substance that would produce CO2 in the first place. On the way up, however, some unknown fraction would come on pathways held open by magma, where these fluids would largely be oxidized to CO2 and water. On other pathways, created by pressure fracturing in solid rock, the direct oxidation will be minimal and these fluids may arrive at the surface as methane and other hydrocarbon gases or liquids. However, even in the solid rock a substantial proportion is frequently oxidized at shallow levels, as is indicated by the common presence in oil and gas-rich regions, of carbonate cements. These cements derive from metal oxides initially present in the rocks, and CO2 derived apparently from the oxidation of methane with some oxygen supplied from the rocks; the carbon isotope ratio of these pore-filling cements is not compatible with a derivation from atmospheric CO2, and their distribution fills the pores in a vertical column, suggesting an origin from ascending fluids. This oxidation is probably due to the action of microorganisms that obtain oxygen from components of the rock, and it is then limited to the outer levels of the crust where the temperature is in the range in which microbial activity can take place. It can be presumed quite reasonably that only a fraction of the CO2 so produced will in fact remain in the ground as carbonate, and a substantial fraction, quite possibly the major amount, will escape into the atmosphere.
A supply of hydrocarbons at depth may thus provide CO2 into the atmospheric-oceanic reservoir in three different ways. One is through volcanic pathways and oxidation with oxygen supplied by the magma; another is by ascent of hydrocarbons through solid rocks and oxidation at shallow levels, most likely by bacterial action, with subsequent escape of CO2 to the atmosphere; a third process will be the escape of methane and other hydrocarbons into the atmosphere, where, in the presence of atmospheric oxygen, they would reside on average 10 years before oxidation to CO2. What fraction of carbon resupply comes by each of these pathways is still not known directly, but some limits can be placed by considerations of the maintenance of the atmospheric oxygen level within the bounds suggested by the geologic record, and possibly by some other more direct measurements.
Methane in the atmosphere is present at about 1.7 ppm by volume. Much or most of this represents a cycling of atmospheric carbon through biological processes, but the quantitative estimates of the magnitudes and speeds of these processes are not sufficiently precise to determine whether the observed concentration is the one to be expected. One may therefore inquire whether a contribution to this methane directly from outgassing sources is a possibility. Fortunately there is a clear possibility of distinguishing biologically recycled methane from juvenile methane: the radiocarbon (14C) proportion of the biological contribution should be the same as that of atmospheric CO2, since such recycling would almost all take place in a short time compared with the half-life of radiocarbon (5,700 years). Thus carbon from deep sources would be free from radiocarbon. A measurement of the fraction of radiocarbon in atmospheric methane can therefore supply the information. Several such measurements have been attempted, but there are difficulties and uncertainties connected with the sampling method and with the measurement itself. The latest measurements have given values of approximately 32% of non-radiocarbon bearing atmospheric methane (Lowe and others, 1988). Would such values be compatible with a supply of carbon from juvenile sources?
We may take, for a simple calculation, methane at 1.7 ppm (vol) and a lifetime of about 10 years against oxidation. Let us suppose that 30% of this is juvenile, and see how this compares with the requirements of the terrestrial carbon budget. The measurements quoted would give an amount of juvenile carbon at present in CH4 in the air of 2 x 10-7 kg carbon/cm2. If this were replenished on a ten year timescale, the lifetime of atmospheric methane, the average supply per year would have to be 2 x 10-8 kg/cm2 year. To lay down the carbon deposits of 20 kg/cm2 entirely from this source would therefore take 1 billion years, a figure compatible with the geologic record. While this cannot be taken to be a confirmation of the results that have been reported, nor of the proportion of the juvenile supply of CH4, it does demonstrate that such measurements are worth doing, and that a substantial fraction of the atmospheric methane may in fact be juvenile. If it is, one must suspect that such a contribution would have large time variations, as have all other tectonic processes, and that therefore much higher or much lower values could be registered at the present time, or at any one time, than the long-term average value. The time variations of atmospheric CH4 reported from ice cores should be seen in the light of these considerations.
Thermodynamics of Outgassing
With the carbonaceous chondrite type of material as the prime source of the surface carbon, the question arises as to the fate of this material under heat and pressure, and in the conditions it would encounter as buoyancy forces drove some of it it towards the surface.
This problem has been tackled by thermodynamicists, most thoroughly by Chekaliuk (1976). His conclusion was that at sufficient pressure, such as that at a depth of 200 km or so, a mix of hydrocarbon molecules would be the equilibrium configuration, despite a temperature which would be far in excess of the dissociation temperature for these molecules (Figure 1). The pressure would provide these molecules with some stability, although any one molecule may indeed have sufficient internal energy to fall apart at the elevated temperature. At high pressures the assembly as a whole does not have enough energy to generate the increased volume that the dissociated molecules would demand. Fragments will instantly be reformed in such a way as to satisfy the volumetric constraint. No molecule has permanent stability, but a statistical assembly of hydrocarbon molecules will represent an average equilibrium. The detailed mix of molecules will depend on pressure and temperature, and on the carbon - hydrogen ratio present. Other atoms that may be present also, such as oxygen and nitrogen, will form a variety of complex molecules with the carbon and hydrogen. Metal atoms that may be present in the surroundings will form a range of organo-metallic molecules in these circumstances.
Even with the knowledge that the diamonds and their high-pressure inclusions have provided, it has been argued that hydrocarbons could not come from these deep levels, because they could not survive at temperatures that are reached in the crust at a depth below 20 kilometers (Hunt, 1975); but these discussions in the petroleum literature have not included the effects of pressure.
Figure 1. Stability of hydrocarbons at temperatures and pressures in the Earth (from Chekaliuk, 1976). Pressure-temperature regime of Earth is indicated by the shaded region. Thermodynamic calculations indicate domains in which various hydrocarbon molecules are stable. The lines marked Paraffins, Naphthenes, and Aromatics enclose domains in which a mix of hydrocarbon molecules would be set up from hydrogen and carbon, and on crossing outward from these domains the percentages indicated would be retained. Methane is essentially stable to the left of the line marked 95 percent, and 10 percent would still be retained on crossing to the right of the line so marked (that is, 90 percent would dissociate into hydrogen and carbon). According to these calculations, most of the petroleum components would be present in equilibrium of a carbon-hydrogen mix at a depth between 100 and 300 km, and methane streaming up could bring a significant fraction of these petroleum components toward the surface. b, bar; kb, kilobar; km, kilometer; m, meter; T, temperature.
The statistical mix of hydrocarbon molecules expected from a carbonaceous chondrite source material, being less dense than the surrounding rock, would have buoyancy forces driving it towards the surface. If present in a locality in sufficient concentration, the fluid will fracture the solid rock, and ascend in such fracture porosity. (Molecular diffusion in rock over large distances is too slow a process to be of any significance, even on the long time-scales of geology.) In that upward travel, the temperature and the pressure would be decreasing, and the various molecules would reach levels where the temperature was low enough for them to achieve stability. Each one of these molecules would then cease the "musical chairs" game, and become effectively permanent. If there is a high ratio of hydrogen to carbon in the stream, saturated hydrocarbons would become a major component, and, with sufficient hydrogen, methane, the most stable of all the hydrocarbon molecules, may become by far the dominant component. At depth methane will behave chemically like a liquid, and it will dissolve the heavier hydrocarbons that may be present, and therefore greatly reduce the viscosity of the entire fluid.
The continuing upward stream would acquire more and more of such unchangeable molecules, and the final product that may be caught in the reservoirs we tap for oil and gas, is the end product of this process. The detailed chemistry of the oils in each region then represents this final phase of the oil molecules on their way up, and that chemistry will be determined by the pressure-temperature regime the flow has experienced, the initial hydrogen-carbon ratio of the mix, and possibly surface catalytic actions and contributions from the rocks through which the flow has gone.
At shallow levels and low pressures, methane, now a gas, will separate out from the heavier components, leaving those as fluids of higher viscosity, and therefore much more subject to retention in reservoir rocks: the quantities of methane that would need to have been in the stream to facilitate the transport of oils, would be many times larger than that of the oils, but because of the great mobility of methane gas, most of it would fail to be retained in the ground at shallow levels.
Horizontal and Vertical Patterns of Hydrocarbon Fields
Everyone now thinks of Arabia, the Persian Gulf, Iran and Iraq as being the oil region of the world. It is indeed one connected large patch that is oil-rich, stretching for 2,700 km from the mountains of Eastern Turkey down through the Tigris Valley of Iraq and through the Zagros Mountains of Iran into the Persian Gulf, into Saudi Arabia and further south into Oman (Figure 2). There is no feature that the geology or the topography of this entire large region has in common, and that would give any hint why it would all be oil and gas rich. The various oil deposits are in different types of rock, in rocks of quite different ages, and they are overlaid by quite different caprocks. They are in a topography of folded mountains in Turkey and the high Zagros mountains of Iran, in the river valley of the Tigris in Iraq, in the Persian Gulf itself, in the flat plains of Arabia and in the mountainous regions of Oman. It cannot have been a matter of chance that this connected region had so prolific a supply of oil and gas, but resulting from totally different circumstances in different parts of the region. These hydrocarbon-bearing formations represent times so different from each other that there would have been no similarity in the climate or in the types of vegetation that existed there during deposition, just as there is no similarity in the reservoir rocks or in the caprocks of the different regions now. Yet it is a striking fact that the detailed chemistry of these oils is similar over the whole of this large region (Kent and Warman, 1972). Surely this is an example of the need to invoke a larger scale phenomenon for the cause of the oil supply than any scale we can see in the geology of the outer crust.
Figure 2. Oil fields of the Middle East, showing continuous region from Turkey to Oman. The dots represent individual fields, and the size of each dot indicates the magnitude of the field.
The island arc of Indonesia, of which Java and Sumatra are the main components, belongs to a much larger pattern of an arc, that stretches from the western tip of New Guinea through these Indonesian islands into the Indian Ocean, through the Andaman Islands up into the Irrawaddi valley of Burma, and on into the high mountains of Southern China, over a total length of 6,000 km (Figure 3). That it is one connected arc all the way cannot be doubted because the frequency of earthquakes along the whole of this arc is hundreds of times greater than outside. Along the whole of this arc petroleum is very abundant. But at one end this arc is made up of volcanic islands; at the other end, in Burma and China, it is in continental material with folded mountains. Again there are great age differences and differences in every aspect of the geology in which the oilfields exist; but here we have a unifying feature, namely the belt of earthquakes and volcanoes which stretches over this entire length, and which points to causes in the deeper crust or in the mantle.
Many other examples can be quoted and they all point to the same conclusion: oil-rich regions seem to be defined by much larger-scale patterns than those we see in the surface geology or topography of the region.
Figure 3. Petroleum and tectonic map of Southeast Asia. The map shows the belt of hydrocarbon occurrence paralleling the volcanic and earthquake belt from New Guinea, through the southern islands of Indonesia, Java, and Sumatra, through the Andaman Islands and on into the Irrawaddy valley of Burma and the mountains of southern China. Data compiled from World Seismicity Map (Tarr, 1974) and from the Oil and Natural Gas Map of Asia (revised 1975), published by the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP). M, earthquake magnitude.
Another global observation of similar significance is the vertical stacking of hydrocarbons deposits, Kudryavtsev's Rule: "Any region in which hydrocarbons are found at one level will be seen to have hydrocarbons in large or small quantities, but at all levels down to and into the basement rock." The most common sequence is to find gas at the deepest levels, oil above, sometimes more gas above the oil, and coal at the shallowest. If one examines gas, oil and coal maps of different parts of the globe, one finds this rule repeated very frequently. It holds in most of the Middle East: many oil wells in Iran have penetrated through large coal deposits. Deep underneath the oil of the Gulf States, large gas fields have been discovered. Almost all the oil wells of Java and Sumatra have drilled through coal, and even the deep gas of Oklahoma is often underneath coal. What we are seeing is principally a succession of hydrocarbons with diminishing hydrogen content as one goes from the deepest to the shallowest. One presumes that bacterial action, which attacks the hydrogen rich hydrocarbons first, has been largely responsible for the progressive hydrogen depletion of upwelling hydrocarbons. For coal, the situation is more complex because biology can be involved in another way also. In a hydrocarbon outgassing area, the ground water is held strongly anoxic because hydrocarbon oxidizing bacteria are abundant there, and quickly remove atmospheric oxygen carried in that water. The result is that the normal processes of fermentation of plant material, which would turn the carbon back to the atmospheric CO2, will be interrupted. Hydrocarbon outgassing areas tend to become swamps filled with the insoluble carbon of plant material. What plant fossils there are in bituminous coal (frequently there are none) are often themselves filled with the same homogeneous coal as that which surrounds them, suggesting a carbon source different from the fossilized plant material itself. It would not seem possible that plant material was converted into the homogeneous coal, and yet that a fraction survived as fossils with a precise maintenance of detail; and that this was then filled by the homogeneous coal derived from similar material.
The huge gas deposits in the form of methane hydrates in the oceans may not have an adequate explanation in terms of the plant debris of the ocean mud. There is often little organic mud and its gaseous products would not have migrated downwards. Yet it has been said by the Russian investigators (Makogan, 1988) that, so far as they could see, in every location on the ocean floor and in the permafrost of the North where the temperature-pressure situation would make methane hydrates stable, they are found. As the deeper ocean regions are being investigated for hydrates, the inadequacy of a biological source material for them may become even more obvious, since the biological deposits there tend to be much smaller than in the continental shelf regions that have been the principal targets so far.
Every deep hole that has been drilled into the crystalline basement, by several Soviet deep drilling programs, by the German on-going deep drilling efforts, by the deep drilling into the Swedish granite, has shown the presence of hydrocarbons at depth. While the quantities vary regionally, the indications we now have would point to a ubiquitous presence of some amounts at deep levels everywhere. Even small amounts of methane or of hydrogen at the deeper levels in the rocks show that equilibration between the oxygen fugacity of the rocks and of the fluids has not taken place, since in chemical equilibrium these fluids could not be present. The explanation for this is that only a small fraction of the volume of the rocks could equilibrate by diffusive processes with the fluid streaming through pores; the pore fluids determine the oxygen levels in these cracks, the rest of the rock takes no part in this. Chemical equilibrium calculations are meaningful only in situations where the rocks and the fluids are much more tightly intermixed, such as in gases streaming through molten rocks. There each moving gas bubble keeps meeting new rock material to provide oxygen, and in these circumstances most carbon reaches the surface in oxidized form as CO2. In solid rock there is a mixture of various proportions of methane and CO2, frequently with methane as the major quantity.
Since methane hydrate formation is a very efficient means of retaining any upward streaming methane, even regions with low rates of methane emission would still build up hydrates in the long course of time. CO2 hydrates could exist also, but very little of this has so far been found, presumably because the cool, non-volcanic regions produce mainly methane, and the hot regions do not lay down hydrates. If plant debris were responsible, CO2 would be a major component of the gases produced, and CO2 hydrates should be common.
If hydrocarbon outgassing is in fact a major source of the surface carbon excess, then one must of course consider whether it is also a major source of all the carbonaceous deposits that are found in the crust. The frequent compliance with Kudryavtsev's Rule would have no explanation for any other mode of deposition.
It has often been argued that oil deposits are in the vicinity of "source-rocks", rocks that contain carbonaceous materials which have been assumed to come from biological deposits. Most commonly these rocks are shales, and their hydrocarbon content often shows a close chemical match to that of the oil pool in the vicinity. This has been taken to verify the source-rock concept; but it would only do so if these shales were generally particularly rich in discerible fossils. This is not the case, and there is no reason for attributing their hydrocarbon content to anything other than a supply from the same source as that of the neighboring oil. The so called "source-rocks" can be regarded as a further demonstration of Kudryavtsev's Rule.
Interpretations Based on the Carbon Stable Isotopes
Carbon has two stable isotopes; 12C (6 protons, 6 neutrons) and 13C (6 protons, 7 neutrons). The natural carbon on the Earth contains predominantly 12C , and 13C is mixed in at a level of approximately 1 percent. This mixing ratio must have been determined in the nuclear processes in the stars that cooked up the elements and eventually supplied them to form the planets. There are no processes that could occur on the planets that would be able to change this ratio greatly. Only small variations can be produced, not by any effects on the nuclei themselves, but only by processes that show a slight preference and select in favor of either the light or the heavy isotope.
The study of the distribution of the carbon isotopes in relation to petroleum and natural gas has a very extensive literature. We shall discuss here only one aspect of it: can isotope measurements determine whether a hydrocarbon compound was derived from biological material or whether it is primordial? Because many petroleum geologists have considered that such a distinction can be made, and that petroleum and natural gas appear on that basis to be usually of biological origin, it is clear that we must address this aspect here.
A selection process that enriches one or other isotope is usually referred to as a process of "fractionation." The resulting fractionated material is referred to as isotopically light or isotopically heavy, depending on the ratio of the lighter to the heavier isotope. Measurements of the slight variations in the carbon isotope ratio in different samples is usually not done in absolute terms, but by comparison with a norm, and the small departures from this norm are then the quantities noted. The norm that has been selected for this purpose is a marine carbonate rock called Pee Dee Belemnite, or PDB, and this norm has a carbon isotope value that is about in the middle of the distribution of all the marine carbonates. The measurements are then quoted as the departure of the 13C content of the sample from that of the norm, and the figure is usually given in parts per thousand (permil) and referred to as the d13C value of the sample.
Unoxidized carbon in plants derives from atmospheric carbon dioxide by the process of photosynthesis. In this process the light isotope is slightly favored. As a result this carbon is slightly depleted in 13C relative to atmospheric carbon dioxide, and the effect is larger than that occurring in any other single nonbiological chemical process recognized in nature. When it was found that most of the deposits of unoxidized carbon, like petroleum, methane, coal and kerogen, show also a marked depletion of 13C, it was considered that this confirmed their biological origin. d13C for plant organic carbon is generally in the range of -8 to -35 permil (PDB standard). The atmospheric carbon dioxide from which that carbon derived is at -6 per mil, showing the possibility of a large fractionation effect. Marine carbonates laid down from atmospheric carbon dioxide dissolved in ocean water have d13C values ranging from about +5 to -5 permil (average 0) and thus evidently a fractionation averaging 6 permil occurs in favor of the heavy isotope during that process.
In the production of methane from plant debris a further fractionation takes place that again favors the light isotope, and plant-derived methane is therefore isotopically even lighter and its d13C plots at -50 to -80 permil. In the literature we now find that some arbitrary division has generally been assumed, so that carbon with d13C values lighter than -30 permil is regarded as of biological origin, while heavier carbon is taken to be from some other source.
There is no clear division in the actual data. Carbonaceous materials have d13C values spanning the range from +20 to -110 permil on the Earth, and they span an even larger range in the carbonaceous meteorites. There is no natural dividing point in the data and the choice of a particular figure in this continuous distribution, for making the distinction between organic and inorganic origin seems very arbitrary. The question is of course what other fractionation processes can select in favor of the light isotope.
Figure 4. Distribution of ratio (expressed as d13C) of the stable isotopes 13C and 12C in different terrestrial materials. Methane and carbonate cements span a much larger range of these isotope ratios than all other forms of terrestrial carbon. PDB, Peedee belemnite.
A look at the distribution of the carbon isotope ratio in different natural forms of carbon gives immediately a strong suggestion (Figure 4). Just methane, the only carbon-bearing molecule that is light enough to suffer significant isotopic fraction, shows the largest spread of values. The atmospheric carbon dioxide from which marine carbonates have been deposited throughout geological time seems to have had a remarkably constant isotopic ratio, so that d13C values for nearly all these carbonates fall into the range of -5 to +5 permil. d13C in petroleum has a fairly narrow range, from -20 to -38 permil. Carbonate (calcite) cements in the rocks have d13C values spanning the second widest range. This fact by itself would suggest that the carbonate cements are generally produced from methane, and their shift of between 20 and 40 permil heavier than the range for methane suggests that a fractionation occurs when methane is oxidized in the ground and then combined with calcium oxide to produce the carbonate cement. Everything in the data points to such a process. These cements are found in great quantity overlying gas and oil fields. They are usually isotopically lighter than marine carbonates, the lightest among them as light as -65 permil. Where methane and carbonate cements are found in the same location the methane is usually isotopically lighter than the carbonate by between 20 to 60 permil. The overall isotopic distribution of methane and carbonate cements show a similar shift.
Figure 5. Carbon isotope ratios (expressed as d13C) of methane plotted against depth of occurrence (from Galimov, 1969). Although there is much variability in this relationship, it is almost always true that where methane is found at different levels in the same area, the methane is isotopically lighter (contains less 13C) the shallower the level.
Galimov (1969), a major contributor to the carbon isotope investigations, saw that in any vertical column methane tends to be isotopically lighter, the shallower the level. This appears to be true irrespective of the type or age of the formation from which the sample was taken.(Figure 5). It is most unlikely that in all those cases methane from two different sources mixed in such a fashion. A much better explanation is that a progressive fractionation of the methane had taken place in its upward migration. Some of this methane appears to be lost to oxidation, ending up as carbon dioxide (Figure 6), and a fraction of that in turn as calcite cements. This oxidation process seems to prefer the heavy isotope and so the remaining methane gets isotopically lighter on the way up. At each level the calcite thus derives from the already fractionated methane and so it also will become lighter, tracking the methane but always remaining heavier than the methane at that same level.
Figure 6. Comparison of the carbon isotope ratios (expressed as d13C) of methane and coexisting carbon dioxide in ocean-floor sediments (from Galimov and Kvenvolden, 1983). The carbon isotope ratios of the two gases seem to follow the same depth dependence, but with the CO2 always isotopically heavier than the methane. This is the pattern to be expected if progressive fractionation were happening, with the CO2 produced (probably by bacterial oxidation) from methane moving upward through the crust. Both the methane and the CO2 produced would become isotopically lighter on the way up, but the CO2 would be heavier by a constant amount than the methane from which it was derived. (This is not the interpretation given by the authors of the article.)
Progressive fractionation is an important process because it can drive the remaining material to a very much greater fractionation than could be done by any single chemical step. It is of course the technique used for commercial isotope separation, where extremely large fractionation factors are required. In our case two effects work in the same sense, helping to create the result. One is the tendency for the oxide to bind slightly more tightly with the heavier carbon isotope (in CO2), and in equilibrium conditions at a low temperature the heavy isotope will therefore be enriched in the oxide and depleted in the remaining methane. The other effect is the diffusion speed, which for methane with the heavier isotope and a mass number of 17, will be 3 percent slower than for the light methane with a mass number of 16. This means that in any circumstance where methane is diffusing through a barrier to fill a reservoir, the light isotope methane will enter initially with a 30 per mil enrichment. If this reservoir were to fill another, the light isotope enrichment would augment. Differential removal by oxydation, by different solubilities in water, by different adsorption on solids, by bacterial attack, will all affect the final result of a slow percolation of methane through diverse strata of rock. Since in any such progressive fractionation the final effect can be arbitrarily large, one cannot conclude that a large fractionation implies that of a single step process, namely the one that occurs in plants.
The constancy of the isotopic ratio of marine carbonates spanning all ages deserves further comment. If at any time between the Archean and the present a large change had taken place in the amount of plant debris that was buried, and if this plant debris was, as is usual, isotopically light, then more of the light isotope would have been taken out of the atmospheric-oceanic carbon dioxide reservoir. The remaining CO2 in that reservoir would have been driven to a slightly heavier composition. If as much as one-fifth of the buried carbon was in the form of such plant debris, then the shift in the remaining atmospheric carbon and the resulting shift in the carbonates laid down from it should have been readily observable. When land vegetation suddenly proliferated in Silurian times, for example, one might well think that twice as much unoxidized plant material was buried as before this event. Why is there no change in the isotopic ratio of marine carbonates in that epoch? An explanation that the primordial supply suffered a change in the isotopic ratio just sufficient to compensate is improbable. A more likely explanation is that the quantity of biological debris that is buried is a much smaller fraction than the one usually assumed. The reason for this may be that the identification of much of the buried carbonaceous material as plant debris is not correct and that a large proportion of this material derived directly from hydrocarbons ascending from the mantle. The extra contribution made by the time-variable burial of plant debris may then be so small an effect that it does not show in the isotopic ratio of the carbonates. Of course if all the dispersed kerogen and the oil shales, which have been regarded as source material for oil pools, were derived from the primary hydrocarbons, then this discrepancy would disappear. It is worth noting that the amount of carbon that would have been contained in certifiable fossils is a very small quantity by comparison.
The remarkable constancy of isotope values of marine carbonates also affects the question mentioned earlier, of the amount of carbon that may be coming up as a result of the heating of subducted sediment. In such a process some or all of the carbonates may be dissociated and the CO2 may come to the surface. Much of the unoxidized carbon that is in the same sediment, whether it derives from plants or from a primordial hydrocarbon supply, is known to be isotopically much lighter. Of that, only a fraction would be turned into liquids or gases, limited by the availability of hydrogen; the remainder would eventually turn into elemental carbon--graphite or anthracite--and in that form it would be insoluble and stable, and would not be returned to the atmosphere. A process of multiple recycling of sedimentary carbon would therefore always take away more of the light isotope than of the heavy, and this would drive the atmospheric-oceanic CO2 to a heavier isotope value. Recycling of sediments cannot account for a significant fraction of the resupply of atmospheric CO2 over geologic time.
The Helium Association with Petroleum
On the basis of hydrocarbon outgassing from great depth, we understand immediately why various trace elements, especially helium, should be so commonly associated with deposits of oil and gas. The long pathway through pressure created fracture porosity in the rocks will, of course, sweep up whatever helium was available in those pores. Helium is generated in the rocks by the radioactive decay of uranium and thorium, but at too low a concentration to create a fracture porosity or hold it open. Its transport is therefore dependent entirely on a carrier gas, such as the more abundant hydrocarbons may provide. Helium is not only strongly associated with hydrocarbon deposits, it has even been noted to be particularly enriched in gas-oil reservoirs, more so than in dry gas reservoirs (Nikonov, 1973). It is also particularly enriched in reservoirs having a high nitrogen content. Any chemical or biological cause for the enrichment can be ruled out for the chemically inert helium. Only variations in the concentrations of the parent radioactive elements, and variations in the the length of pathway through the rocks from which the helium has been swept, can come under consideration for an explanation of the great regional differences of the observed helium concentration. Where large variations have to be explained, such as by a factor of 100 or more from one location to another, the lenth of pathway through which the carrier gas has swept is likely to have been the dominant effect. If carrier gases from a depth of 300 km are involved in one case, while only gases from the depth of sediment are involved in another, then this variant will outweigh any likely variation in the concentration of the radioactive elements. The helium concentration in a gas is then mainly an indication of the depth from which this gas has come. With this explanation one would conclude that nitrogen frequently derives from the deepest levels of any of the volatiles, and oil from the next deepest; dry methane sometimes from shallower levels still, but all from levels far deeper than the sediment. Helium enrichment is not found in sediment in the absence of larger amounts of hydrocarbons or nitrogen, and ten percent helium in methane-nitrogen gases is the highest concentration that has been found. Yet if helium could flow without a carrier gas, there should be many locations where amounts of helium had accumulated that were similar to the amounts of helium in some gas-fields, but now, in the absence of methane or nitrogen, they would be pure helium fields. Such fields would have been discovered, and would be very valuable. Their absence thus certifies the carrier gas concept for helium transport.
Some information can be gained from a study of the isotopic composition of the helium. Helium has two stable isotopes, helium-4 and helium-3. Most of the helium found on Earth is helium-4, the result of the radioactive decay of uranium and thorium. In the atmosphere helium is present at a concentration of 5.24 ppm by volume. The helium-3 isotope, which is much less abundant, is present in the atmosphere at about 1.4 parts of helium-3 to a million parts of helium-4. In the surface of the Sun and in the Solar Wind one observes a ratio of helium-3 to helium-4 of 3 x 10 -4, or about 200 times higher than the ratio in our atmosphere.
The primordial helium that was incorporated in the Earth as a small impurity in the rock grains must have been more similar to the solar composition and thus much richer in helium-3 than any present day terrestrial helium. But the total quantity that was brought in by the grains was small and so the continuous production of helium-4 from the radioactive decay became the major contributor to helium in all locations on the Earth.
While a small proportion of helium-3 can also be produced by radioactivity in an interaction involving uranium and lithium, this is not thought to be a major contribution to the Earth's helium-3. The lithium production of helium-3 in the most ideal circumstances, where lithium and uranium are in close association, could be as high as to give 3He/4He ratios of 1.2 x 10 -5, or ten times the ratio in the atmosphere (Morrison and Pine, 1955). But this would occur only in some rare minerals, and the average production in the crust of the Earth of helium-3 has been estimated as at least a hundred times lower. This means that in any location where we find a helium-3 to helium-4 ratio of more than one-tenth the atmospheric value, it is probably due to a contribution of some primordial helium. In those cases we then know that we are dealing with a gas that has at least a component that must have come from deep rocks, since the crust in its formation process would have largely outgassed, and primordial helium would not have been maintained there.
However, we cannot assume the converse. Where the proportion of helium-3 is low, the gas may well have come from mantle depths also, since in a mantle that was never all liquid, the gas content could never have become a uniform mix, nor could it have remained a uniform mix if the rates of outgassing were different in different regions.
Where a carrier gas has washed through pore spaces that it has created, it will have transported the mix of primordial and radiogenic helium that happens to have been there. If such a flow has been going on for a long time, then the primordial component will have been depleted, while the continuously produced radiogenic component will still be present. The heliun-3 proportion will have suffered a dilution throughout the existence of this flow. Pore spaces that have been flushed for a long time would have low helium-3 values, but there would be no reason to assume that such gases derived from a smaller depth. While the presence of a high helium-3 value is indicative of young pathways from mantle depths, helium with low helium-3 values does not give a firm indication of its depth of origin. Great concentrations of any helium, however, suggest that sweeping by a carrier gas on long pathways has been responsible, and this in itself is an indication of a deep origin.
The partial pressure at which helium is found, whether as a collection under a caprock or anywhere else, may also serve as in indication of its depth of origin. As an inert gas, it cannot have had its partial pressure increased from that of its point of origin by any chemical action. In any flow, its partial pressure must always decrease; only the (unlikely) circumstance a mechanical pumping action could ever cause an increase. Helium must have derived generally from a location where the radioactive decay could produce the partial pressure at which it is found, or a yet higher one. This is an important consideration in estimating whether helium in a location could come from the radioactivity of the surrounding rocks or whether it has come from greater depths. For this calculation one has to take into consideration not only the local concentration of uranium and thorium, but the helium porosity that the rock has (the volume of pore spaces large enough to be occupied by the helium atom, which includes many imperfections in the rock crystals, and will therefore represent a larger volume than the porosity presented to a gas of larger molecular size). At deeper levels, where the rocks are subjected to a high lithostatic pressure, the helium porosity will be small, and a given radioactive concentration will send the resulting helium into smaller volumes, and therefore set up correspondingly higher partial pressures. This consideration shows that in many locations, even where natural gas has a comparatively high helium content, the local rock cannot have supplied it. It explains why helium measurements at or near the surface seem to be successful in finding hydrocarbons underneath (Roberts, 1980), but rarely successful as a means of prospecting for uranium deposits.
Regional patterns of helium abundance have been observed in which the helium concentration and the helium partial pressure are far higher than the sediments could have produced in their entire age (Pierce and others, 1964), but where the patterns of gas composition (ratios of components) stretch horizontally over distances very large compared with any particular gasfield of the region. The helium must certainly have come from below the sediment, and it must have arrived there already in regionally well-defined mixing ratios with methane and initrogen, so that the different fields of the region could all be filled with the same or a closely similar mix. Only a mix that had entered the sediment and its individual gas fields from below could achieve that (Gold and Held, 1987).
Relation of Outgassing of Hydrocarbons to Atmospheric Oxygen
The problem of the maintenance of the atmospheric oxygen levels within the bounds suggested by the geologic record has not yet been solved satisfactorily, but it is clearly closely related to the carbon supply. Photosynthesis in the plants produces free oxygen by the dissociation of water. If none of the products of photosynthesis escaped from the circulation of atmosphere and biosphere, if fermentation returned all the content of carbon and hydrogen in plant debris back to the atmosphere as carbon dioxide and water (the form in which it was taken up by the plants), then there would be no net gain or loss of atmospheric oxygen. If some hydrogen were to escape, however, as hydrogen does escape from the upper atmosphere into space, or if it were laid down in hydrides or other hydrogen compounds in the sediment, then for every two hydrogen atoms so removed, there would be one oxygen atom that would constitute a net addition to the atmosphere.
If all the fresh carbon supply that the atmosphere receives came in as CO2, and if all the carbon laid down in the sediment were in the form of carbonate rocks (i.e. CaO from rocks combinig with CO2 to make Ca CO3), then also this process would neither add nor subtract from the atmospheric oxygen. If, however, as is generally thought, about one-fifth of the carbon that is laid down is in the form of plant debris, then there would be constantly a large addition to the atmospheric oxygen. For each carbon atom that is so buried there would be at most one oxygen atom and at most two hydrogen atoms (polysaccharides like cellulose are (C6H10O5)x). Every carbon atom that came up in the form of CO2 provides two oxygen atoms, while the burial of that carbon atom would bury only one oxygen atom and take away possibly as many as two hydrogen atoms that had derived from the dissociation of water and would not now be available to reform a water molecule with its photosynthetically liberated oxygen atom. Thus, for every carbon atom laid down as biological debris, approximately two oxygen atoms would be liberated. For the figures given, of 20 kg/cm2 of total carbon laid down, one-fifth in biological materials, the total amount of oxygen left over to join the atmosphere would be 10.6 kg/cm2 of O2. That is more than 50 times the present atmospheric oxygen content. All carbon being supplied as CO2, and one-fifth laid down in plant debris, the rest as carbonate rocks, does not seem a possible scenario over long periods of geologic time.
If a fraction of the juvenile carbon was supplied as CH4, that would diminish the oxygen excess, as both the carbonates and the organic carbon would lay down some oxygen, and the left-over hydrogen would form water, using up more atmospheric oxygen. Of course this could make the balance towards no gain or loss of atmospheric oxygen. But to maintain the atmospheric oxygen level within the bounds given by the geologic record, the supply of carbon as methane and as CO2, and the laying down of carbon in the sediment would have to be balanced very precisely, since both involve such large quantities of oxygen compared to the atmospheric oxygen content. One could not attribute such constancy nor the chance of just producing the balance, to tectonically controlled events over long periods of time. Some powerful stabilizing effect would have to be at work.
What are the limits on the excursions of atmospheric oxygen content that the geologic record can provide? In all the times that forests have existed, oxygen levels cannot have been higher than the present by more than a few percent, for we are now not far from that concentration at which fires would make it impossible for forests and many other major land plants to survive. In earlier times, before the emergence of large land plants in the Silurian, there may have been periods of higher oxygen values, and such periods have been suggested to account for the oxidation states of iron in some ancient sediments. The other limit, that of low oxygen values, can only be estimated from the oxygen requirements of animals both in seawater and on land, and from the oxidation state of some sediments. Again this limit cannot be set very far below the present values for all the periods back to the Cambrian, in which oxygen-breathing fishes have existed. Before these epochs the limits may have been wider.
What could be the stabilizing influences that are at work? The laying down of inorganic sediments may have a stabilizing effect, as these sediments can become more highly oxidized than the basement rocks from which they derived. A large amount of sulfur may be present now in a more highly oxidized state than that in which it came to the surface. Another stabilizing effect may be the escape of hydrogen from the Earth into space. In the presence of smaller atmospheric oxygen values, more hydrogen liberated by photosynthesis could diffuse into the outer atmosphere without being caught by oxidation, thereby leaving more oxygen behind. It is doubtful, however, that such large quantities of oxygen could have been liberated or absorbed in these processes as would be required, or that the stabilizing effect could have the required strength to keep the atmospheric oxygen levels within the narow bounds.
Perhaps the strongest stabilizing effect would be the control that the atmospheric oxygen concentration must have on the amount of plant debris that will be buried before being re-oxidized. Higher oxygen levels in the air, and hence in groundwater, will diminish the areas of swamps and of anoxic lakes, ponds and seas, the locations in which plant material would escape the fermentation processes that would turn the carbon back to CO2, thereby taking away atmospheric oxygen. Conversely, low oxygen would favor anoxic deposition, leaving more oxygen behind. Possibly this effect could be sufficiently powerful. However with the imprecise knowledge of the amounts of plant material buried in different epochs, with the strong possibility that deposits of organic carbon are in significant part due to upwelling hydrocarbons and not all to plant debris, and with the inexact knowledge of the ratio of oxidized to unoxidized carbon in the primary carbon supply to the surface, no firm judgment can yet be made.
The Mechanics of the Ascent of Fluids through the Crust
There are two principal methods of ascent towards the surface of fluids that are liberated in the mantle and that are of lesser density than that of the rock, and hence buoyant relative to it. One is the ascent in volcanic regions, where magma, with its density closely similar to that of the surrounding rock, can hold open vertical pathways down to depths of a hundred kilometers or more. Any other fluids that can pressure fracture the rock and make their way through cracks into such lava channels can then move upward by buoyancy forces, and quickly reach the surface. Hydrogen and hydrocarbons would, as we have said, be largely oxidized in bubbling through magma, but the extent of this oxidation would of course depend on the relative proportions of hydrocarbons and magma at any time. There are strong indications that small amounts of gases coming out of volcanoes at quiet times are largely oxidized, while in violent eruptions the unoxidized gases--hydrogen and methane--are prominent. On many occasions flames have been reported during major eruptions, and have been seen as quite distinct from the ejection of hot material. During the episodes of the Krakatoa eruption below the sea surface, a large region of flames above the water were observed, in this case of course in the complete absence of any confusing sprays of lava. But even at quiet times some volcanoes emit enough combustible gases to burn above the lava lake. This has been observed in the Hawaiian volcanoes and also in volcanoes of the African Rift. Volcanic eruptions in Java have delivered ashes containing several percent of unoxidized carbon.
The other possible manner of ascent of fluids from the mantle is the build-up of sufficient fluid pressure to fracture the rock and create pathways (Gold and Soter, 1984, 1985). For such pathways to stay open, the pressure in the rock due to the overburden weight, and the fluid pressure in the pore spaces, have to be closely similar. Since rock is extremely weak in tension, a fluid pressure higher than the lithostatic value will quickly create more fractures. In compression rock is much stronger and pore spaces will only be crushed shut when the pore pressure deficit exceeds a certain value. If one considers fluids that are less dense than the rock, then any connected system of pore spaces filled with such fluids will have a smaller pressure gradient with depth than that of the surrounding rock. At the top of such a domain the pressure may be close to that in the rock (the lithostatic pressure). The bottom of such a domain will then have a deficit of pressure and since this cannot exceed a value defined by the compressive strength of the rock, there will be a limit to the vertical height that such a domain can occupy (Figure 7 ). In the volcanic case, the dense lava with its pressure gradient closely similar to that of the surrounding rock, can keep open a channel to a depth of a hundred kilometers or more. In the case where the fluid is a hydrocarbon or water, and hence of of much lower density, it is only an interval of a few kilometers that can be held open; an interval whose height can be calculated from a knowledge of the compressive strength of the rock, and vertical pressure gradients in rock and fluid, given by their respective densities.
Figure 7. Schematic diagram showing pressure of rock due to overburden and pressure of fluid (less dense than the rock) in connected pore spaces. Pc denotes critical pressure difference (between rock pressure and fluid pressure) at which the rock compressive strength is inadequate to maintain pores. Dashed lines indicate fluid pressures that are physically unrealizable because of the limited compressive strength of the rock.
These limitations do not mean that gases or liquids are prevented from making their way up. If fluids are evolving as a consequence of an increase of temperature or of chemical reactions taking place at depth, they may create fracture porosity, and increase the pressure in such a domain of pore spaces. As more fractures are being created, the vertical height of the domain will increase. As soon as the height spanned exceeds the critical value, the rock at the bottom of the domain will crush shut. Such a domain may then be unstable and migrate upwards, driven by the force of buoyancy, much like a bubble of gas in a liquid makes its way up. Only here, in the presence of solid rock, it is not a round bubble but a region of rock with interspaced but connected pore spaces. Just as the bubble would split the liquid above it while the liquid below it would close again, so in this case it will happen with the rock. The rock itself does not move upwards, but the domain of pore spaces with its fluid makes its way up through the rock. Above strongly outgassing regions in the mantle one may have a frequent dispatch of pore space domains towards the surface.
Another mode of upward flow is also possible. If the generation of fluid is continuous, a set of adjoining, stationary pore space domains may be set up, and the flow may be in the form of a continuous or intermittent leakage from one to the next one above. The stability of such a flow will require that the pressure drop from the top of one domain to the base of the next will occur as a result of the flow through the low permeability of the dividing layer. (Figure 7.) However the flow occurs, it must always adopt a stepwise pressure profile, with domains in which the fluid pressure gradient has almost precisely the static value, given by the density of the fluid, divided from the next domain by a region in which the fluid pressure gradient has a much higher value. (If the mass of fluid is small compared to the mass of rock, as would mostly be the case, then the average pressure gradient over a large vertical interval must be the lithostatic one in both rock and fluid.) Such a flow can be compared with a flow of a river from the mountains, which creates a system of cataracts. Consider the potential energy in the flow: pressure in one case, height in the other. In the case of the river, almost all loss of height occurs at the cataracts, the flow between them being almost quiescent and level. Similarly, in the former case, almost all the drop in pressure would occur not continuously but in a few sharply defined locations.
If we look at this situation from the surface down we may find a system of connected pore spaces frequently filled with water, and we therefore define a pressure in the pore spaces that is called hydrostatic, and a pressure in the rock, called lithostatic. As the two pressure gradients with depth are dissimilar, a point must be reached where the rock will close. I have referred to this as the "critical layer." Beneath that we can again have open pore spaces, but now only provided that they are filled with a fluid at a pressure exceeding the hydrostatic value that would be calculated for that depth, but not exceeding the lithostatic value. We may then have another domain of fluid-filled pores, but again only of a limited vertical height. The uppermost domain can be calculated to reach down to a depth of between 3 and 5 kilometers in soft rock, but possibly as much as 10 kilometers in hard rock. This is the domain in which most of the oil and gas exploitation has been done so far, but a comparatively small number of cases exist where the drill went through a sharp pressure transition, and where the secomd domain has been tapped.
It should be emphasized that such a critical layer is a necessity dictated by the finite compressive strength of rock. It is thus a caprock layer which must overlie any region in which outgassing is occurring. As the strength of the rock is of course regionally quite variable, this critical layer may be far from level. It may be of a complex shape with large variations in height, and there may even be locations where it doubles over on itself. The main thing is that it has to be a continuous sheet. This is not to say that there may not be other layers of caprock in an outgassing region where a material of low permeability was laid down, and presumably all shallow gasfields have required the presence of such a caprock. The importance of the critical layer is that an outgassing region will inevitably possess that type of caprock at a sufficiently deep level.
The critical layer, like other layers of caprock, will not have zero permeability and there will be some leakage through it, as we have discussed. In a long term steady state of a continuous upward flow, the leakage through the critical layer (and through all the similar layers at deeper levels) must occur at the mean supply rate. Nothing can change the flow rate of this upward stream: it is given by the production rate of the fluid below. All that any caprock or any critical layer can do is to increase the amount that is dammed up underneath it. The situation is similar to that of the flow of a river from the mountains to the sea, where, we may suppose, the rainfall producing the water all occurs up in the mountains. On the way down, the river will transport all the water that has been collected; and if the river is dammed up anywhere along its length, the steady state flow rate will not be changed. All that the dam will do is to create a lake on the upstream side of it, but finally the amount of water flowing over the dam will be exactly the same as that which would have flowed without the dam.
This is an important consideration from a practical point of view. One has observed that over natural gas producing regions the amount of methane and other hydrocarbons in the soil is greatly enhanced, sometimes by a factor of one hundred or more, and any attempts at deducing a flow rate to account for this gives such high rates of methane seepage as to appear incompatible with a supply coming only from a gasfield below. The technique of surface chemical prospecting, such as measuring the soil methane, has been described by some as necessarily in error, since it was not conceivable that the outflow rate could be so high that the gasfield would be exhausted in a few thousand years. But of course if there is a continuous gas supply from below, and at rates that are in no way in conflict with the limits we can place on such outgassing processes, then it will make good sense to observe the surface concentrations of hydrocarbon gases. It would also make good sense to extend this technique and introduce tracer gases in a well at some depth, and observe the time it takes for the tracer gases to appear in the surrounding soil. From this, and the knowledge of the porosity of the ground, an actual flow rate can be established, and so one could evaluate for any region how much methane per day or per year is seeping out.
Regions that have a high seepage rate will in general be favorable ones for finding good reservoirs, since for a given quality seal or caprock a larger quantity is likely to be dammed up underneath that seal. Surface gas prospecting has been certified over many known gasfields, the outstanding example being the Cement Field of Oklahoma. The technique is yet to be used on a large scale in the search for more gas.
In several regions of the U.S. drilling to 5 kilometers (15,000 ft.) or deeper has demonstrated the sharp pressure discontinuity to which I have referred. All of the deep gas in the Anadarko Basin is below this discontinuity and there all the deep gas seems to form essentially one reservoir. In Louisiana and neighboring areas of the Gulf Coast, the pressure discontinuity is a little shallower and the continuous sheet represented by it has been carefully mapped (Jones, 1980), with the information available from a large number of wells and the interpolation between them from seismic data. In Oklahoma there is, in some instances, a dramatic increase in the porosity after penetrating the critical layer. Porosities as high as 18 percent have been found below 20,000 feet in the carbonate rocks. It is clearly not possible to account for this by any process of enclosing a rock volume tightly, and then compressing it to achieve the gas pressure in the pores. Since that gas pressure is roughly twice that above the critical layer, one would have to contemplate an initial gas-filled porosity of 36 percent. This is not a value that has ever been seen. The conclusion must be, therefore, that the gas has entered from even higher pressure regions deeper down, and that it has expanded pore spaces to these values. Investigations of the details of the fracture patterns in the rocks confirm such an explanation.
We may then describe how a flow of hydrocarbons from depth may take place. As we have discussed, a high proportion of saturated compounds would indicate that methane was a major component that dilutes the stream. But at shallow levels where the pressure is low, the heavier hydrocarbon molecules will be shed from the stream. The largest such effect will take place at the flow through the last pressure discontinuity on the way up, the shallowest critical layer. It is there that the oils are likely to be deposited, being now viscous and easily retained, while much or all of the gases can continue upwards and largely escape into the atmosphere. Oil deposits are concentrated laterally because major faults have facilitated their ascent and have caused a confluence towards them; and the oil deposits are concentrated vertically because of the sharp pressure changes in going from one pore-space domain to the next, at which oil and gas get separated.
Results in Sweden
The distinction between hydrocarbons derived from biological materials and hydrocarbons of primordial origin would be made most clearly by examining igneous or metamorphic rocks which could not have maintained either hydrocarbons or biogenic materials capable of producing them, before they froze to their present condition. If crude oil, methane and other hydrocarbon gases can be found in such locations, at depths that would exclude a seepage down from above, then this would demonstrate an origin from sources below.
Crude oil has been found and produced from crystalline and basement rocks in numerous locations, but mostly in places where a transport from neighboring sediments could be invoked as an explanation. The clearest example we have where a production from sedimentary materials can be excluded comes from two deep bore-holes in the granitic rock of central Sweden (Gold, 1991).
As we have noted, the granite and gneiss of Sweden has many signs of impregnation with hydrocarbons. Tar is frequently found during tunneling and mining operations as a substance filling cracks in the granite. Methane explosions and prominent shows of methane have been seen frequently. If hydrocarbons come from depth, one might judge that the large granitic block which makes up most of Sweden overlies an area of mantle that is particularly hydrocarbon rich, and one might think that the hydrocarbons of the Norwegian Trench or of the countries surrounding the Baltic signify an outflow from this area of the mantle. Fractures of the rock within Sweden may then have been conduits for hydrocarbons from the same source.
It is with this consideration in mind that I persuaded the Swedish Government to study the region of a giant meteoritic impact crater, the "Siljan Ring" in Central Sweden. An impact that left a circular formation 44 kilometers in diameter would undoubtedly have fractured the rock to great depth, and one might therefore have expected this to be a particularly favorable location for finding upwelling hydrocarbons.
It was quickly ascertained that just the area of the Siljan structure was quite anomalously rich in soil methane and other light hydrocarbons, that many ordinary water wells produced copious amounts of gas and that a number of stone quarries in the area had oil seeping out of the rocks and making oil pools in the ground. It is true that the stone quarries were in the sedimentary rock which fills a ring shaped depression, but those sediments are nowhere deeper than 300 meters. Oil seepage generated after 360 million years from such a small quantity of sediments seemed improbable. Aside from the ring shaped depression, the basement rock is very close to the surface in the whole area; there is barely enough soil for the trees to grow both inside and outside the Siljan Ring feature.
As a result of the clear demonstration that the area was quite anomalous for its hydrocarbon content, it was decided to engage in a major drilling operation. Since 1986 two wells have been drilled: one to a depth of 6.7 kilometers, the other to a depth of 6.5 kilometers. Both holes showed the presence of methane and of other hydrocarbon gases, as well as of crude oil. While in the first hole (Gravberg I) diesel oil was used for a time as a component of the drilling mud, only water-based mud was used in the second hole (Stenberg 1), which is situated in the center of the ring, and is 12 km distant from the ring sediments, and also from Gravberg 1. Although the detailed chemical makeup of the oil found at deep levels in Gravberg was not the same as diesel oil, many considered nevertheless that the diesel drilling oil could be held responsible. Some 15 tons of oil were pumped up, oil that had hydrocarbon components and organo-metallic compounds that are frequently in natural crude oils, but were absent or present only in very much lower abundance in any of the drilling fluids. Some biological molecules, steranes, were found to be from the same set and in closely similar ratios as had been seen in the surface seepage oils (Figure 8 ), and this strengthened the case that the two oils had a common origin. Steranes are thought to derive from sterol, a component of methane-oxidizing bacteria.
Figure 8. The four most prominent biomarker molecules, steranes, found in the oils of the Siljan region, Sweden. The steranes are present in similar proportions in surface-seep oil (Solberga quarry), local near-surface oil shale (Tretaspis Shale), and oil in black sludge obtained from 5.6 km depth in Gravberg 1 well. This similarity indicates a common origin of all three oils. The identity of the four sterane molecules is given in the usual notation by the number of carbon atoms and the right or left symmetry of the molecule.
In both holes the hydrocarbon content of the rocks increased with depth and in both holes high spots in methane (and in Gravberg 1 also in heavier hydrocarbons) were in the locations in which volcanic intrusive rock, dolerite, was present (Figure 9). (Heavier hydrocarbons were not measured during drilling in Gravberg 1).
Figure 9. Stenberg 1 well, Sweden: Methane content of drill cuttings as function of depth. Presence of intrusive volcanic rock, dolerite, is marked below graph, showing correlation with high spots of methane readings. Heavier hydrocarbons were also measured, and were largely in step with methane.
The carbon isotope ratio of the methane became heavier with increasing depth, and in the dolerite zones and their immediate surroundings it was as heavy as between -12 to -15 per mil in the Gravberg hole, and -7.2 to-7.8 per mil in the Stenberg hole. In both holes the helium concentrations were frequently as high as several percent of the total gas present, and possibly exceeding the highest concentration seen in any well.
The investigations during the drilling of Stenberg I gave the clearest indication that a range of hydrocarbon gases and liquids had indeed entered from deep levels. The content of hydrocarbon gases and liquids (aromatics) in the drilled out rock was carefully measured every five-foot interval during drilling. It showed very large increases in the dolerite and in the granite closely adjoining it (Figure 9). Since the dolerite has undoubtedly intruded from below, one has to conclude that the pathways which guided it up, or the pathways which it generated in the intrusion, are the pathways later used by the hydrocarbons. This relationship also confirms that contaminants introduced during drilling were not responsible for the observed hydrocarbon.
In both holes large amounts of a magnetite/oil sludge were discovered, the magnetite present as very small grains, mostly submicroscopic and highly concentrated in the sense that it formed more than 95 percent of the mineral content of the sludge. Twelve tons of this substance were pumped up from the Gravberg hole from a depth below 5.2 kilometers. It was suspected that the magnetite had been refined and concentrated by bacterial action, as has been seen in other oil-bearing regions at shallower levels (Sparks and others, 1990). Sample collection of liquids that entered the Gravberg wellbore below 5.2 kilometer depth was carried out by the Swedish State Bacteriological Laboratory in Stockholm and several strains of previously unknown thermophilic and anaerobic microorganisms were cultured from these samples (Szewzyk and others, 1993).
During the test procedure of the Stenberg well a gas cylinder was brought up containing free gas that would readily burn. Apart from a nitrogen contamination (due to nitrogen used to expel the drilling water), the gas consisted principally of methane with approximately 10 percent helium and 10 percent hydrogen. No continuous flow could be obtained, apparently due to the blocking effect of the entry of dense magnetite sludge into the wellbore.
The oil brought up with this sludge was investigated in detail by the Danish Geological Survey and considered to be a biodegraded crude oil. Chromatograms of it matched closely those obtained from the oil pumped up in Gravberg.
The scientific investigations carried out on products of the two holes have thus demonstrated that hydrocarbons are present deep in granitic rock in the complete absence or proximity of any sedimentary materials and in a distribution that leaves no reasonable doubt that they have come from deeper levels. The mix of the different hydrocarbon molecules, both of the gases and the oils, is quite a typical mix, as it is found in other oil and gas producing regions. The quantities of oil and gas that appear to be present in this 44 km diameter formation, tested in two distant locations, appear to be very large, as judged by the porosity measurements and the vertical intervals showing high concentrations. Production flow rates could not be achieved in either hole, apparently because in a confluent flow towards the wellbore, the sludge quickly concentrates and blocks the pores. The observed concentration of iron oxides in the rock is too low for the magnetite sludge to have been generated in the depth intervals in which it was found, and it must have been gathered and concentrated by a flow. We presume that this flow was that of the oil with which the magnetite is now associated. In that case, deeper levels than those that could be reached by the two boreholes (6.7 and 6.5 km ) would tap into liquids and gases that contain smaller concentrations of magnetite, and would therefore cause less obstruction to a flow.
If the main supply of the commercial quantities of hydrocarbons, both gas and oil, is indeed derived from mantle depths and from materials that were incorporated in the Earth at its formation, then many points in petroleum geology and in other aspects of geology will have to be reconsidered. The quantity and locations of gas and oil that can be found, the method of prospecting for them, and the technology involved will all be affected.
It was thought previously that gas could only be found where there was a particularly impermeable caprock, tight enough to hold gas, above sediments rich in biological debris. Now one would judge that gas can be found wherever a seepage of gas can be found at the surface, and where there is an adequate porosity at some depth below. If a low permeability layer exists over a porous region, then this may have dammed up the flow sufficiently for production. But at deeper levels the critical layer will in any case provide a caprock. Thus in searching for gas, the requirement of a special caprock and the requirement of biological debris have both disappeared. The porosity requirement may be satisfied in many more locations than was previously thought, since beneath the critical layer the fluids coming from high pressures will frequently have created fracture porosity (as was clearly seen in Oklahoma).
If hydrocarbons have been a major source of all the carbon supplied to the surface, then of course the quantities that would be involved are orders of magnitude larger than was previously estimated. The shallow zone above the shallowest critical layer, which is almost everywhere the only zone that has been the subject of oil and gas prospecting, will be seen to be the zone low in hydrocarbons, because they have largely escaped from these shallow levels. Oils, which became concentrated at shallow levels by the escape of the much more abundant gases, have been the chief object of the petroleum explorers. The deeper levels, which must be expected to have maintained the much more abundant gas, have not been explored at all outside of the United States, and in the U.S. the few areas that have been so explored have been found to be very productive.
Drilling to below 5 or 6 kilometers is still expensive and not much exploration to these levels will be done so long as the good prospects there are not recognized. But despite the expense of drilling, which would no doubt greatly decrease if more of it were done, the productivity from deep levels has frequently shown itself to be very high. Gas at depth below the critical layer tends to have a pressure approaching the lithostatic value, which may be on the order of 2,000 bar. The density is thus hundreds of times higher than it is in shallow wells, and may be as high as half the density of oils; therefore the content of gas in a given volume of pore spaces is hundreds of times greater than in shallow wells. The high pressure differentials into the well bore mean that very high flow rates can be obtained, even from rock which at shallower levels would be regarded as of insufficient permeability for production. The ultimate production from a given well is greater, because a greater pressure gradient drives gas to the wellbore, and the expansion of the gas will allow a large proportion of the initial gas in place to be produced. It is therefore by no means true that gas production from the deep horizons must be expensive, and many examples exist already that show that deep gas production can be quite competitive with shallow gas. The initial investment in an area will be higher, but so will be the returns.
Because deep gas does not have many of the special requirements for its accumulation that oil has, one may expect it to be in many more locations than oil. Many countries in all parts of the world will benefit from a more widely distributed fuel source.
Prospecting by the search for surface seepage of gas is a rational procedure, since large quantities of gas must constantly be escaping. Oil was found mainly by the attention that oil seeps drew to an area; gas seeps require instruments to be found, but, with more gas than oil coming up and escaping more readily, gas seeps are good indicators of the presence of gas underneath. The quality of available prospecting methods is a major economic item, especially for the deep horizons where exploratory drilling is expensive.
A flow of hydrocarbon fluids through the crust will have affected much of its chemical development. The concentration of many types of mineral deposits, especially of metal ores, has not had adequate explanations. The leaching out of particular components from the rocks requires fluids that can dissolve these components, and it requires large pressure differentials to drive these fluids through the pores of a sufficient quantity of rock to gain access to the materials. Hydrocarbons ascending from depth may provide these requirements. They will be present at a high temperature and pressure, where organo-metallic compounds can readily form. Such compounds are largely soluble in hydrocarbons, and may thus be transported upwards by them. These metals may include some that have quite inadequate solubilities to have been transported by aqueous fluids, but that can form organo-metallics. Silver, gold, and the platinum group are in that category, but many others may come under consideration for such processes. It is interesting to note that particularly gold has been found in many locations together with elemental carbon. Vanadium and nickel have shown a strong association with petroleum, both by the presence of compounds in the petroleum, and the deposition in or near oilfields. Several of the elements that would have a high vapor pressure at mantle temperatures have been found associated with hydrocarbons, not only helium but also mercury, and all the halides. A range of new processes will have to be investigated for the understanding of mineralization in the crust, and the search for hydrocarbons may become associated with the search for certain minerals. The microbiology in the ground which is fed by hydrocarbons may have contributed to highly selective processes; just as we saw concentrated magnetite in the boreholes in Sweden, apparently concentrated by microbial action, so perhaps all the large magnetite deposits of Sweden have a similar origin. Judging from the quantities of microbial material that have been identified in hydrocarbon regions (Ourisson and others, 1984), microbial processing may have been of major importance in the evolution of the crust.
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Further reading: Gold, T. Power from the Earth: Deep Earth Gas - Energy for the Future. Published by J. M. Dent & Sons, Ltd., London, 1987 (US distributer: The Bookery, 215 N. Cayuga Street, Ithaca, NY 14850)
Can There Be Two Independent Sources of Commercial Hydrocarbon Deposits, One Derived from Biological Materials, the Other from Primordial Carbon and Hydrogen, Incorporated into the Earth at its Formation?
In any discussion of the ultimate origin of hydrocarbons (oil and natural gas) that are commercially extracted, this is a major question: are there two pathways for generating these deposits, or is there evidence that there is only one? If it can be shown that there is only one, then a proof of the derivation of any one hydrocarbon deposit would constitute a proof that this represents the derivation of all.
The two pathways that are under discussion are a derivation from biological materials deposited in the sediments, or a derivation from carbonaceous materials incorporated into the Earth at its formation.
For the biological origin we have the evidence of the (unquestionably) biological origin of some sets of molecules found in all commercial oils.
For the second, the primordial origin of commercial hydrocarbons, we have the comparison with the abundance of similar hydrocarbons on many other planetary bodies, also in interplanetary grains, in comets, and also in the interstellar gas clouds thought to be similar to the cloud that formed the solar system. We also see abundance of methane in the volcanic ocean vents where there are no substantial biological sediments. Furthermore the common association of hydrocarbons with the inert gas helium has no explanation in a formation process from biological materials, but is readily understood as a consequence of the sweeping up of the trace gases by hydrocarbon fluids, if those have migrated up from a deep level, far below the sedimentary blanket.
The evidence for a biological origin, given by the presence of biological molecules in all oils, can be explained not only by a biological origin of the oils themselves, but equally well or better by a contamination with microbial materials in all oil wells. Microbial life at depth in the rocks was predicted on the basis that it would account for the biological molecules in oils, and such life has now been found to be widespread.
It has often been suggested that both modes of derivation may have occurred. There have been suggestions that the two different modes can be identified, and it has been said that "most" commercial oil and gas have come from biological materials, though there is some oil and gas, though commercially insignificant, that derived from deep sources in the mantle. Are there common features in all commercial crude oils that would rule out the dual origin theories?
The similarity of all commercial crude oils encompasses the following factors:
1.) Nickel and vanadium porphyrins are found in varying proportions, but in all petroleum deposits. Porphyrin molecules are complex molecules made up of carbon, hydrogen and nitrogen, together with a metal atom. Their presence in petroleum has been attributed to chlorophyll from photosynthesizing plants, and to the haem of the blood of animals, and both these will indeed produce porphyrin molecules. But those would contain the metal atoms of magnesium and iron. However no single case is known of magnesium or iron porphyrins having been found in petroleum anywhere. An explanation that on every occasion in all oils the original metal atoms had been exchanged for just nickel and vanadium from the rocks in their surroundings, seems extremely improbable. No explanation has been offered how plant debris would have produced the nickel and vanadium molecules, while, in the other explanation, nickel and vanadium complexes may well be expected, since these two metals are particularly prone to make organometallic compounds. This find therefore favors a deep origin, and at the same time a common origin for all oils.
2.) The heavier hydrocarbon molecules have a large variety of isomers (molecules of the same number of hydrogen and carbon atoms, but assembled in different geometrical configurations). The distribution of isomers of aromatic hydrocarbons has been demonstrated to depend upon the temperature range of their formation. Studies of the isomers of 322 oils from various oil fields of the world, have shown that they have a common set of isomers, a set that has been demonstrated to come from a formation temperature of between 700 and 1,100 °C. There is no significant difference in this range between oils coming from different tectonic settings. The overall hydrocarbon composition corresponds to the equilibrium state at temperatures 1,300 to 1,500 °C and pressures of 20 to 40 kb. The estimate is that this is the condition in the upper mantle at depths of 60 to 160 km. Temperatures and pressures in the sedimentary blanket are certainly far from the conditions necessary to account for the isomeric composition characteristic of all natural oils. (This information comes primarily from the publications of two chemists and thermodynamicists from the Ukraine, G.E. Boiko and E.B. Chekaliuk, over the years from 1950 to 1982. Although there is much reference to these publications in the Soviet scientific literature, and I have referred to them in my publications, I have found no other reference to these in the U.S., British, German or French literature.) This universal property of oils thus makes it extremely unlikely that two completely different modes of formation could have been responsible for such complex but similar products; at the same time the temperature range indicated is far too high for a sedimentary origin.
The depth range indicated is also that of the derivation of diamonds, whose formation required the presence of unoxidized carbon under a pressure in excess of 30 kb. Violent gas-driven eruptions from upper mantle depths were required to deliver the diamonds and other deep source materials to the surface.
3.) The common association of hydrocarbons with helium has no explanation in a biological origin theory; in a theory involving the ascent of hydrocarbons from deep levels, the physical process of sweeping up the gases in the pores of the rock, would be expected; and helium is a significant component of those. This also points to a derivation of the majority of oils from deep levels.
4.) The arguments of Robert Robinson still stand, that any biological debris would be quite unlikely to produce hydrogen-saturated hydrocarbons. The hydrogen/carbon ratio of biological materials is too low in the first place, and slow chemical processing in geologic settings would lead to a further loss of hydrogen. Yet most commercial hydrocarbon deposits contain methane and other high hydrogen components. The average hydrogen proportion is greater, the deeper the level from which the hydrocarbons are withdrawn, corresponding to a hydrogen loss during the upward migration of the fluids.
The overall conclusion is therefore that natural petroleum has detailed chemical features that are common to all, and that we must therefore consider that all derived from the same process. Moreover, most oils bear clear evidence of having had a deep origin, and a high temperature of formation.
Excerpts from the paper by P.N. Kropotkin, entitled "On the History of Science: Professor N.A. Kudryatsev (1893-1971) and the Development of the Theory of Origin of Oil and Gas"
Presented at a conference in Moscow in 1995, honoring Professor Kudryatsev's contributions to the field.
In the theory of an organic origin of petroleum it was considered that oil is formed in deposits rich in biogenic organic matter, the so-called "source rocks", at temperatures not exceeding 300 to 500 °C. A decisive fact against this theory came from the determination of the temperature of formation of oil from quantitative relations of isomers of identical chemical composition. Such studies were performed by G.E. Boiko, who considered the relations for the best studied isomers from 322 oils from various oil fields of the world, and the results of these analyses were published between 1950 to 1975. The relations for these isomers in the hydrocarbon system depend mainly on temperature. The results obtained have shown that in all oils of the world, the isomers of aromatic hydrocarbons are in relative proportions corresponding to the equilibrium at the temperature of approximately 1000 to 1400 °K. Oils of geosyncline and platform areas do not differ significantly in the temperatures corresponding to this equilibrium composition. The thermodynamic calculations of the complete hydrocarbon composition of oils has shown that it is the equilibrium state at temperatures of 1600 to 1800 °K and pressures of 2 to 4 x 103 MPa (Boiko, 1982). Based on experimental data and thermodynamic computations, G.E. Boiko came to the conclusion that the synthesis of oil takes place in the upper mantle at depths of 40-160 kilometers. In any case it could not be synthesized within the sedimentary blanket where temperatures and pressures certainly do not correspond to the isomeric relations characteristic of all oils.
A.S. Eigenson underscores the inconsistency of the argumentation for the biogenic origin of oils based on the presence in them of so-called molecular fossils. Hunt considers as a typical molecular fossil the porphyrins that are a closed bridge structure of four pyrol rings which can readily produce complexes (Eigenson, 1990). Such derivatives of porphyrin as a magnesium complex are contained in chlorophyll of green plants and as complexes of valence two iron are contained in hemoglobin and cytochrome. But many items regarding this assumed molecular fossil remain unconsidered. First of all, in no oils even traces of iron and magnesium complexes have been found, but only vanadium and nickel ones.
The discovery of oil, deep in the Baltic Shield, may be considered a decisive factor in the hundred year old debate about the biogenic or abiogenic origin of oil. This discovery was made in deep wells that were drilled in the central part of the crystalline Baltic Shield, on the initiative of T. Gold.
Boiko, G.E. Prognosis of the presence of oil and gas from genetic indices. Kiev, 1982. 252 pp.
Eigenson, A.S. On quantitative study of formation of technogenic and natural hydrocarbon systems using methods of mathematical modelling. Khimiya i tekhnologiya Topliv i Masel. 1990, No 9, pp. 3-8, No 12, pp. 19-254; 1991, No 5, pp. 1-26.
See complete text, with introduction by T. Gold, in Earth Sciences History (Fall 1997). Publ: History of Earth Sciences Society, Troy, New York.
Depth Effects of Petroleum
"Chirality" or Mirror Symmetry of Oils
The word "chirality" refers to the type of symmetry that the left hand has to the right hand. It can also be expressed as a mirror symmetry and an object possessing chirality will not be identical with its mirror image, instead it will have the sense of the chirality reversed. Two dimensional objects cannot possess chirality since looking at them from one side will make them identical with their mirror images seen from the other side. Three dimensions are necessary before chiral symmetry can come into play.
Molecules that are composed of four or more atoms may possess chirality, meaning that the same arrangements of the positions of the components of the molecule can be achieved in two different ways, one being the precise mirror image of the other. In chemistry this is important, since any given chiral molecule will act differently depending on the chirality of the partner in a reaction. However, the overall rule applies strictly: if you were to replace each molecule in a chemical system with one of the opposite chirality, then all the reactions would proceed exactly the same way. In other words chemical reactions do not favor one chirality over another.
A right-handed screw remains a right-handed screw from which ever side you look at it. Its mirror image is a left-handed screw. Complex molecules can exist in the two forms, one looking like the mirror image of the other. If they are in a liquid, tumbling around arbitrarily, they will still affect light traveling through the liquid and in fact plane polarized light may have the axis of its polarization rotated by the action of these molecules. If the right-handed and the left handed molecules are equally represented, there will be no net effect. However, if one type predominates over the other, then there will be an effect, which is in practice often readily observable. It is in liquids that this type of observation is important, because there is no long-range effect that would cause many of one kind to dominate over the optical path. A liquid containing equal numbers of each (to within the statistical expectation, if they had the same probability of being generated) would then be referred to as "racemic." A non-racemic liquid then requires an explanation for the preference of one sense of chirality over the other.
In biology, this is provided by saying that all these molecules were built up in a system that traces back to the very beginning of biology, and in all the evolution it has not changed the chirality on which it hit (with a 50/50 chance) in the first place. This may be the right explanation, but some people have doubted that this effect would really have prevented all digressions. It is clear, however, that on the Earth all amino acids that make up the proteins, rotate light in the left-handed sense. In principle we could suppose that some other planet had the same life forms as we have here, with everything working in just the same way, but in which all the amino acids were right-handed, and the opposite handedness to ours here applied also to each of the other complex molecules with which they may interact.
Figure 1 shows the rotation of plane polarized light passing through the oil. Different components of the oil as selected by the temperature at which they boil (boiling point fractions) show either a right-handed or a left-handed rotation. At deeper levels in the same petroleum bearing area, these effects are totally absent.
Non-racemic mixtures of chiral molecules occur naturally on Earth only in relation to biological activity. Figure 1, above (and many others like it that exist), show that oils acquire a non-racemic nature as they get from deep to shallower levels. I ascribe this to the presence of bacterial activity, which introduces a variety of non-racemic substances. It is only the amino acids that are all left-handers here, but the bacteria produce many other substances also, each of which will be a non-racemic mix, right-handed or left-handed. It is for this reason that the graph shows some components of the oil causing a left-handed rotation of the light, while other components show a right-handed one.
At deeper and hotter levels, these effects have completely disappeared, and I presume that this is due to the temperature there being too high for the particular set of microorganisms that produce the non-racemic additions. There may be many other microorganisms that can withstand higher temperatures, and they may be plentiful at the deeper levels, but they may be types that do not deliver significant amounts of chiral molecules to the fluid.
Sir Robert Robinson, who investigated the chemistry of natural petroleum in some detail, noted that the deeper one goes, the fewer are the signs of anything biological in the oil. This is clearly a case in point, but there are several others.
The complete absence of any optical rotation at the deeper levels is itself a strong argument against a biological derivation of the oil. If any oil could be generated from plant and animal debris, it would be very unlikely to be so accurately racemic; nor can one think that initially non-racemic oil lost this property by being exposed to a higher temperature for a long time. The boiling point fractions that show chirality go up to 240 °C and some even to 320 °C. It is clear that these temperatures have not destroyed the chiral molecules, even though they are temperatures much higher than those at the deep levels from which strictly racemic oil is extracted.
The presence of non-racemic oil has in the past been taken to prove a biological origin of the oil. Now when one sees to high accuracy the absence of such effects at deeper levels, the argument is reversed. The origin of oil must be strictly racemic, and it is only contamination by certain types of microbes, that can live only at the shallower and cooler levels, that has made the oil non-racemic.
It should be noted that different sources of natural petroleum all show a preference for one or other chirality at shallower levels, but in detail the sign and magnitude of effects are different. One has to presume that this represents differences in the microbial activity.
Carbon Isotope Ratio Depending on Depth
Similar indications concerning microbial life in oil are given by the distribution of the ratio of the two stable isotopes of carbon, carbon-12 and Carbon-13, dependent on the depth from which the oil was obtained, as shown in Figure 2.
Figure 2, "The Galimov Curve." The carbon isotope ratio as a function of depth from the surface is shown for many different locations and in a variety of containment rocks. The ratio follows a similar pattern indicating that a fractionation process is occurring and that this process is most effective at the shallowest levels.
The isotope ratio is given in parts per thousand from a norm (pdb) negative values representing a depletion of the heavy isotope (Galimov, 1969).
The Russian carbon-isotope investigator Galimov has assembled many measurements of the carbon isotope ratios in oils from different levels. A clear depth dependence emerges, quite independent of the nature of the containment rocks or their ages, and, as we shall see, a depth-dependent microbial alteration must be invoked.
If methane is diffusing upwards through the ground as one would expect, then the diffusion speeds of the methane with the heavier carbon atom will be a little slower than that of the lighter one. The comparison of the molecular weight would be 16 to 17. Diffusion speeds will be changed quite markedly, in fact by approximately three percent.
If we were to simulate the diffusion effects that would be present in nature, we might, for example, take a vertical glass tube and fill it with very fine sand. If we connected a source of methane of a certain ratio of its carbon isotopes to the bottom of that tube, then we would expect that after turning on the supply, we would first see the lighter methane arrive at the top. If we leave the system running, then the heavier molecules will also make their way up through it, and eventually a steady condition will be reached in which just as many of the two types of molecules will emerge on top per unit time, as were in the mix that was fed in at the bottom. There would be no selection effect according to the molecular weight.
If we were to look in detail how this could happen, we would find that at the bottom of the tube, the heavier molecule will become progressively enriched in this flow, until this enrichment will just compensate for the lower diffusion speed. This means that if we were to take out a certain amount of the mixed gas from the lower levels, (for example by a tube out of the side of the column) in a way that does not select in favor of either isotope, we would be taking out a mix enriched in the heavy isotope, and therefore the gas that is left to stream up the column will show a depletion of the heavy isotope. But at levels above that from which we removed some gas, the same process will occur, only now it will start with a lower ratio of the heavy to the light isotope. Some way up in the diffusion column, we could again take some gas away with the result that the gas entering the next higher section would be further depleted in the heavy isotope. We could set all this up in such a way that at each removal point gas is taken out at a steady rate, and a steady flow pattern will result. Now the output of gas at the top will have a different isotopic ratio from that which was put in at the bottom. The number of stages in this process can be arbitrarily large, and the isotopic selection (called "fractionation") can also be made arbitrarily large. Only the larger we make the number of stages, the more gas will have been withdrawn, and the quantity of gas which arrives at the top of the column per unit time will diminish.
How can this apply to the diffusion of methane from depth towards the surface of the Earth? Upward diffusion would certainly occur; but what are the side channels of this diffusion column that take away the components that have become enriched in the heavy isotope?
There may well be several mechanisms that take away non selectivity some gas from various levels in the natural diffusion column. The most evident mechanism is the conversion of methane to CO2, with oxygen available from the rocks. This process occurs mainly by bacterial action that can reduce sulfates and highly oxidized iron and use the oxygen so gained to turn methane into CO2 and water, or it may use atmospheric oxygen at shallow levels where this is available in groundwater. The CO2 may either emerge on the surface, bringing up an excess of the heavy carbon isotope, or it may form carbonates by combining with calcium or magnesium oxides. Results of both these processes have been observed. Carbonate pore filling cements are frequently seen in hydrocarbon areas, as is also the emission of CO2 at the surface. On this basis, the CO2 derived from any particular level in the diffusion column will contain a higher proportion of the heavier isotope than the gas continuing up in the column. The CO2 molecule is too heavy (molecular mass 44 or 45) to suffer significant fractionation, and what emerges at the top will contain the isotopic mix derived from various levels in the methane column from which it originated. All the time as some methane is taken over to CO2, the remaining methane in the column above will have a greater deficiency of the heavy isotope. The next step of removal will thus start with a greater deficiency of the heavy isotope, and the CO2 produced higher in the column will reflect that. A part of the carbon isotope ratios as a function of depth should therefore show the carbon-13 deficiency in the methane increasing with height in the column, and at each level, the CO2 will also become depleted in the heavy isotope, but at each level it will show less depletion than the methane. This has been seen in several locations, and Figure 3 gives a particularly accurate observation of the effect.
Figure 3 shows isotope measurements in the same vertical column in methane and of co-existing CO2. Both components are progressively depleted from deep to shallower levels. The CO2 tracking the methane quite accurately but with the methane depleted in the heavy isotope by some 40 points per thousand (from Galimov et al., 1983).
The Galimov Curve indicates a more rapid fractionation, the shallower the level of the measurement. This can be ascribed to atmospheric oxygen carried in the groundwater, that allows a more rapid oxidation of methane by bacterial action. Since the CO2 cannot suffer significant fractionation, it is clear that its carbon must have derived from the methane.
It used to be assumed that fractionation depleting the heavy isotope occurred mainly or only by the preferential absorption of the light isotope of surface plants, and that the greater depletion seen in methane than in CO2 certified that the methane had derived from buried biological materials. But if that had been the relevant fractionation mechanism without the diffusive separation discussed here, then there should be no change with depth in the column, nor could one expect the parallel tracking seen in Figure 3. A fractionation by plants favoring the light isotope is certainly commonly seen, but plants do not have any way of selecting in favor of one isotope except by the difference in speed of diffusion processes through membranes. The process discussed here can and evidently does produce a much greater degree of fractionation than occurs in the carbon uptake of plants (a deviation of nearly 90 parts per thousand from a standard norm, compared with plants that generally fractionate 20 to 30 parts per thousand).
Galimov, E.M. (1969) Isotopic composition of carbon in gases of the crust. Internat. Geology Rev. v. 11, no 10, 1092-1104.
Galimov, E.M and Kvenvolden, K.A. (1983) Concentrations and carbon isotopic compositions of CH4 and CO2 in gas from sediments of the Blake Outer Ridge, Deep Sea Drilling Project Leg 76: Initial Reports of the Deep Sea Drilling Project, v. 76, p. 403-407.
On the Association of Petroleum with Helium and with Biological Molecules
The regional and local association of terrestrial natural petroleum with helium has been clearly verified in thousands of locations.
So has the association of petroleum with specifically biological molecules.
An origin of petroleum from sedimentary biological materials could not account for the helium association, as no chemical interaction exists that would cause biological materials to concentrate the noble gas. But equally, the association of petroleum with biological molecules ("biomarkers") cannot be doubted, and has been explained as arising from the origin of hydrocarbons from biological deposits. This creates a paradox.
The only circumstance I could see that would account for the hydrocarbon-helium association, was that the hydrocarbons have ascended from deep levels far below any sediments, from materials similar to those of carbonaceous chondrite meteorites, which were a major component of the materials that formed the Earth. After all, we know that hydrocarbons of non-biological origin are common on many other planetary bodies, and must have had such a derivation there. At the high temperatures and pressures to which these materials will be subjected at depth, some components will be liquefied and, being less dense than the rocks, buoyancy forces will drive them upwards. On the long pathways of their ascent they will wash up any trace gases in the rocks, helium being a major component among these.
With this explanation for the helium association, the presence of biological molecules in all oils could no longer be regarded as due to an origin in biological debris. The association with biological molecules would have to be due to the existence of a truly gigantic quantity of subterranean micro-biological life, which had been so pervasive that it had produced the biological components seen in all oils. This would be in accord with the opinion of the chemist Sir Robert Robinson:
Actually it cannot be too strongly emphasized that petroleum does not present the composition picture expected from modified biogenic products, and all the arguments from the constituents of ancient oils fit equally well, or better, with the conception of a primordial hydrocarbon mixture to which bio-products have been added. (1963)
These considerations prompted me to write the paper: "THE DEEP, HOT BIOSPHERE", (Proc Nat. Ac. Sci. July 1992). In this I suggested that sub-surface microbiology is so widespread that every oil-bearing region has been subjected to biological alteration, down to the deepest wells from which oils have been extracted. The microbial life forms involved must then be hyperthermophilic, living at temperatures up to 120°C, possibly as much as 150°C. The quantities in terms of mass or volume would be comparable with all the surface life we know. This would solve the sharp paradox that had split petroleum geology into two camps, and had stymied progress of the discussion of the origin of petroleum for many decades.
Earthquakes, Gases, and Earthquake Prediction
Many reports about earthquakes have suggested that the escape of gases was a major effect, both before, during and after the quakes.
The modern theory has it that some subterranean forces, of unknown origin, gradually build up strains in the crustal rocks, up to the breaking point. The earthquake is then supposed to denote the moment of fracture of that rock.
Many features of earthquakes seem to have no explanation in this theory.
Why would there be many occasions of multiple large quakes over a period of a few days to months? Would the rock not break in all the locations in which it is already stressed to near breaking point, at the time it is violently shaken? Why would the ground shake sometimes for periods longer than a minute? Why would quakes cause tsunamis, the massive ocean waves? A brief tremor, however fierce, would not have such an effect. Perhaps the modern earthquake research had omitted the consideration of effects due to the sudden movements and the rapid large changes of volume that gases may cause. We shall therefore discuss the huge eruptions that have brought up diamonds, and we might well ask whether there may not be smaller ones much more frequently. Are they the initiating events for earthquakes as well as for volcanic eruptions?
Eye-witness accounts strongly suggest that gas eruptions are the initiating events, but in modern times not much attention is paid to such information, because it is considered too uncertain. Instead the effects that can be measured with accuracy, such as a gradual increase of the strains in rocks and the relation of this to earthquakes, has now become the main subject of research in this field in the US. The overriding importance of this research would lie in finding a method for the prediction of earthquakes, but no such method has so far been found.
One city has been successfully evacuated two hours before a massive earthquake, and thereby probably many thousands of lives were saved. This was the city of Haicheng in China, in February of 1975. That prediction was based almost entirely on gas-related phenomena. (See the description in "Eye-witness Accounts of Several Major Earthquakes," this Web site.)
In the modern geological literature the movement of gases in the crust is rarely considered. Perhaps this is still due to the widespread misconception that no pore-spaces could exist deeper than about 10 km. Even when a most violent volcanic gas explosion has occurred, this is often discussed as due to gases that have come out of solution as the lava is exposed to lower pressure. Why would one not consider that a massive bubble of gas had entered the lava channel and raced to the top?
Diamonds, a very pure form of carbon, tell us quite a detailed story about the physical and chemical conditions in the earth, below about 150 km, and this information bears on the origin of petroleum. Chemical theory and the experience in making artificial diamonds, show that high pressures of the order of 45 kilobars are needed to produce this dense crystal. Such pressures are found in the Earth only at a depth of 150 kilometers or more, and it is somewhere at such depths that natural diamonds must have been formed. The temperature there exceeds 1000°C.
The geologic situation in which diamonds occur shows that unusual gigantic eruptions were involved. Although many diamonds are found dispersed in river gravels, the only concentrated deposits are in the rare "pseudovolcanic" structures called "kimberlite pipes." These are deep, vertical shafts, usually filled with a mixture of rock types, including the diamond-bearing rock called kimberlite (Figure 1). Most of the known kimberlite pipes are in South Africa and Siberia, but there are some in North America, in Australia, and probably also in Brazil, where they may be well hidden under younger sediments.
Figure 1. Model of a Kimberlite pipe (from K.G. Cox, 1978).
The model is based on several South African pipes which have been exposed at various levels by erosion, not only on the one near the town of Kimberley, which gave this formation its name. The model was devised by J.B. Hawthorne of DeBeers Consolidated Mines, Ltd.
"The diamond pipes serve as a window that gives us a look into the Earth. There is probably no other group of rocks that originated from even remotely as great a depth as have these" (Kennedy and Nordly, 1968).
The pressure and temperature at a depth of 150 or 200 kilometers are in the right range for carbon to crystallize as diamond. But how did the carbon become concentrated? We cannot reasonably suppose that concentrations of large pieces of pure carbon were formed in the outer mantle by the diffusion through the rock of the dispersed individual carbon atoms.
Minerals of high purity are usually formed in the Earth by a process that involves the flow of some liquid through cracks and pore spaces in the rock. In some particular circumstance of pressure, temperature or chemical surroundings, a component of such a fluid precipitates, and thus builds up a concentrated deposit in the pore spaces. We then have to suppose that a fluid containing carbon, percolated through rock spaces and precipitated concentrated carbon. Veins of diamond would then be built up in these pore spaces, and a later eruption might bring fragments to the surface. What are the fluids that could be responsible for precipitating and concentrating the carbon?
The mere existence of the diamonds at these depths proves that unoxidized carbon exists there. The two types of fluids that one may consider for the concentration process would be carbon dioxide and methane, the latter possibly associated with heavier hydrocarbon molecules also. Tiny pore spaces in diamonds have been analyzed and found to contain small amounts of highly compressed gases, among which the carbon-containing ones were both carbon dioxide and methane (Melton and Giardini, 1974). It is clear, therefore, that not only unoxidized carbon, namely the diamond itself, but also methane, can exist down there. Thermodynamic calculations have shown that both these gases are stable in the upper mantle at diamond forming depth, and either could be responsible. The following indications would seem to favor methane. Methane is generally much more abundant in the crust than CO2, and appears to be streaming up from deeper levels. Secondly, of the gases contained in diamonds, nitrogen is by far the most abundant. One has to judge that nitrogen had something to do with the deposition of the diamond.
It follows that pore spaces in which fluids can flow exist at these depths, and that mineralization processes, leading to great concentrations of certain substances, can be active there, just as they are at shallower levels. Fluid pressures equaling the rock pressures seem to be widespread, at least in the crust and outer mantle, and this is a matter of great significance, both for the chemical processes and for the methods of ascent of fluids to the surface.
The existence of the kimberlite pipes shows that high concentrations of gas can build up, and have been building up, and these concentrations can explode a hole through 150 kilometers of overlying dense rock. Quite large bubbles of high-pressure gas must have been assembled to do this, and only an inhomogeneous mantle containing volatile-rich materials could be responsible.
A gas eruption, rather than a volcanic transport to the surface, is required to maintain the diamonds. The stable form of carbon at low pressures is graphite, but if diamonds are cooled sufficiently rapidly as they are brought to lower pressures, they are maintained as unstable but super-cooled crystals. At surface temperatures, they are then effectively stable. We see that the evidence from the diamonds is very simple and clear. Unoxidized carbon can and does exist in the outer mantle. It can be brought up without becoming oxidized; it is associated with a variety of hydrocarbon molecules, both within inclusions in diamond and also in other materials brought up in the eruptions. Volatile-rich regions exist in the mantle, so that high pressure gas bubbles become assembled there that can force their way violently through all the overlying rocks. This clearly shows that the Earth has an unmixed, inhomogeneous mantle, and that there is a high concentration of carbonaceous material in many areas of the globe.
I am presenting here a selection of eye-witness accounts of major quakes, showing that gases, and in particular combustible gases are frequently in evidence.
The great earthquake series in New Madrid (Mid Mississippi) in 1811 - 1812
The report by contains the following items:
On the 16th day of December, 1811, at two o'clock in the morning, the inhabitants of New Madrid were aroused from their slumbers by a deep rumbling noise like many thunders in the distance, accompanied with a violent vibratory or oscillating movement of the earth from the southwest to the northeast, so violent at times that men, women, and children caught hold of the nearest objects to prevent falling to the ground.
It was dangerous to stay in their dwellings, for fear they might fall and bury them in their ruins; it was dangerous to be out in the open air, for large trees would be breaking off their tops by the violence of the shocks, and continually falling to the earth, or the earth itself opening in dark, yawning chasms, or fissures, and belching forth muddy water, large lumps of blue clay, coal, and sand, and when the violence of the shocks were over, moaned and slept, again gathering power for a more violent commotion.
On this day twenty-eight distinct shocks were counted, all coming from the southwest and passing to the northeast, while the fissures would run in an opposite direction, or from the northwest to the southeast.
On a small river called the Pemiseo at that time stood a mill owned by a Mr. Riddle. This river ran a southeast course, and probably was either a tributary of the St. Francis or lost itself in those swamps. This river blew up for a distance of nearly fifty miles, the bed entirely destroyed, the mill swallowed up in the ruins, and an orchard of ten acres of bearing apple trees, also belonging to Mr. Riddle, nearly ruined. The earth, in these explosions, would open in fissures from forty to eighty rods in length and from three to five feet in width; their depth none knew, as no one had strength of nerve sufficient to fathom them, and the sand and earth would slide in or water run in, and soon partially fill them up.
Large forest trees which stood in the track of these chasms would be split from root to branch, the courses of streams changed, the bottoms of lakes be pushed up from beneath and form dry land, dry land blow up, settle down, and form lakes of dark, muddy water.
One family, in their efforts to reach the highlands by a road they all were well acquainted with, unexpectedly came to the borders of an extensive lake; the land had sunk, and water had flowed over it or gushed up out of the earth and formed a new lake. The opposite shore they felt confident could not be far distant, and they traveled on in tepid water, from twelve to forty inches in depth, of a temperature of 100 degrees, or over blood heat, at times of a warmth to be uncomfortable, for the distance of four or five miles, and reached the highlands in safety.
On the 8th of February, 1812, the day on which the severest shocks took place, the shocks seemed to go in waves, like the waves of the sea, throwing down brick chimnies level with the ground and two brick dwellings in New Madrid, and yet, with all its desolating effects, but one person was thought to have been lost in these commotions.
The morning after the first shock, as some men were crossing the Mississippi, they saw a black substance floating on the river, in strips four or five rods in breadth by twelve or fourteen rods in length, resembling soot from some immense chimney, or the cinders from some gigantic stove-pipe. It was so thick that the water could not be seen under it. On the Kentucky side of the river there empties into the Mississippi river two small streams, one called the Obine, the other the Forked Deer. Lieutenant Robinson, a recruiting officer in the United States army, visited that part of Kentucky lying between those two rivers in 1812, and states that he found numberless little mounds thrown up in the earth, and where a stick or a broken limb of a tree lay across these mounds they were all burnt in two pieces, which went to prove to the people that these commotions were caused by some internal action of fire.
About four miles above Paducah, on the Ohio River, on the Illinois side, on a post-oak flat, a large circular basin was formed, more than one hundred feet in diameter, by the sinking of the earth, how deep no one can tell, as the tall stately post-oaks sank below the tops of the tallest trees. The sink filled with water, and continues so to this time. The general appearance of the country where the most violent shocks took place was fearfully changed, and many farms were ruined.
After reading this and several reports about other earthquakes that are quite similar, I find it very hard to understand how there can be any opposition to the notion that the eruption of gases is connected with earthquakes, and possibly a major cause of them. I know of no way in which an area of land could suddenly sink by tens of feet, except by the release of large amounts of gases whose pressure had previously held open a large total volume of pore-spaces in the underlying rocks.
The same consideration applies to the creation of the earthquake-related ocean waves called tsunamis. A rapid and very large change in some volume is necessary to set up these waves, and that volumetric change has to be of a magnitude similar to the volume of ocean water that has been displaced to make either the negative or the positive phase of the great wave. Again sinking of an area of ocean floor due to the sudden escape of gases would be a possibility as would the rapid expansion of gases that make their way from the ocean floor to the surface. There are various reports of violent bubbling of areas of the ocean, and even of flames emerging out of the water.
Another feature of earthquakes that seems incompatible with the theory of shear strain in the rocks reaching breaking point are the deep source earthquakes. Earthquakes are known at depths down to 700 kilometers, and the pressure there is so great that sudden fracture cannot occur. The friction between two masses that slide against each other would be so great that this would far exceed any mechanical breaking strength of any rock. Any movement at such depths would occur only as a gradual adjustment proceeding in step with the driving force that causes the movement. This implied that another process must be going on down there and finding the answer to that may also then explain the features of shallower earthquakes that have so far remained unexplained, but that appear in seismic investigation quite similar to the deep ones.
We have two recent examples: on June 8, 1994, a very large earthquake registering 8.2 emanated from 600 kilometers below Bolivia. Not far away in time and space, in 1970, there was a powerful deep earthquake in Colombia.
The southern island arc of Indonesia and its continuation into Burma and the mountains of southern China is a very long belt that shows many features that show themselves along the whole length. Earthquakes make clear that it is related to an underlying structure of very large dimensions. The two other features that follow this same arc all the way are active volcanoes and the commercial production of oil and gas. While the belt was defined by the frequent occurrence of small quakes, it is also the region of the highest frequency of large quakes. In the 75 years between 1897 and 1972, there were ten earthquakes of magnitude eight or larger along this belt. There are no signs of a progressive shift of some land masses against others, and the rock stress situation is surely totally different in the folded mountains of Burma as in the volcanic island arc of Indonesia.
There are other features of earthquakes that have also to be considered. There are places that are distinctive "earthquake spots." There is a spot in northern Norway where for a long time one could almost be guaranteed to feel an earthquake in any 24 hour period. These were weak earthquakes, not much above the level at which one could feel them, but there was no faultline that was slipping, no accumulation of any deformation of the surface, it just kept shaking in an area that was about 12 kilometers across. A very similar story comes from two places in the United States, one is on the western tip of Flathead Lake in Montana, the other is in Arkansas, near the small town of Enola. Both of those have been active in recent times, and the one in Arkansas is known to have been active some 80 years ago.
Another earthquake spot is on the north shore of the St. Lawrence River, most interestingly just in a large meteorite impact structure ("astrobleme") called Charlevoix. The large meteorite struck there some 350 million years ago, and detailed evidence of this impact has been obtained. Despite the length of time that has elapsed since then, it seems that even now the area has not settled down and some activity is still clearly centered there. Some earthquakes that can be felt occur there every few days, and microquakes are registered extremely frequently. In this case, the proximity to the major faultline of the St. Lawrence River complicates the discussion somewhat but, nevertheless, the concentration of the seismic activity to the 30 mile diameter impact area is quite evident.
Such spots clearly need a different explanation from that of plates shearing against each other. Possibly the explanation has to do with gases forcing their way up and causing fractures in the rock to open and shut repeatedly.
We have investigated in some detail the Arkansas and the Charlevoix spots, and in the course of this discovered that they both contain a most intriguing feature which has shed further light on this type of occurrence. This is the presence of clusters of earth mounds that stand abruptly out of the alluvial plain. From a few feet to 40 feet in height and up to 200 feet or so in the horizontal dimensions, they are composed internally just of the clay and sand of the local alluvium, and no good reason has been offered to account for their origin.
The association in both areas of these strange mounds with locally concentrated seismic activity cannot reasonably be ascribed to chance. While such mounds do occur elsewhere, dense clusters of them are extremely rare, and an explanation for them is required. One cannot argue that the shaking of the ground of the earthquakes would itself cause what appears to be a substantial extrusion from below.
A class of a much larger type of feature is known and referred to as "mud volcano." It is also strongly related to earthquake activity. Mud volcanoes are mountains that are in the general shape of a volcano, sometimes but not always with an open hole on top and with steep sides sloping down to the plain below. The sides are made of rock debris, which presumably was ejected at the top as a mixture of such debris with water. Huge fields of mud volcanoes exist in several areas of the globe. The best known ones and the largest are in Azerbaijan on the north slopes of the Caucasus. Large eruptions of individual mud volcanoes are common there and the gases that propel the eruption are usually flammable and become ignited at the time, presumably by electrostatic sparks resulting from the friction of fast moving rock grains. Flames to a height of two kilometers have been photographed from one mud volcano whose orifice measures 120 meters across.
The gases coming out of mud volcanoes have often quite unusual composition and contain elements that are known to be at a high concentration in the mantle of the earth and at a much lower concentration in the sediments and in the outer crust. They clearly represent a very different chemical environment from that of the sedimentary cover.
The mounds on the earthquake spots in Enola, Arkansas and in Charlevoix on the St. Lawrence River, can be attributed to the same class of phenomenon as mud volcanoes, only on a much smaller scale.
Gases that stream up out of cracks during earthquakes are also frequently flammable. In the collection of eyewitness reports, flames are frequently a feature. Also in recent times, the great earthquake in San Francisco in 1906 was accompanied by large fires, and it was said at the time that this was due to the fracture of gas pipes in the ground. That may well have been the case; however flames were also seen on hills nearby that had no gas pipes and also on roads and fields in nearby San Jose. The Armenian earthquake of 1990 showed a line of burnt bushes along a visible faultline.
Large vertical displacements of areas of land can be understood if a mass of gas had previously held open pore spaces in the rocks below, and thereby raised the ground, and if these pore spaces had suddenly made connections to the surface and rapidly exhausted the gas. Such volumetric changes occurring in a matter of seconds can then account for the large tsunamis and for the flames often seen in earthquakes. As methane appears to be the most common gas in the rocks, it would seem reasonable to expect that methane would be the principal gas responsible, just as it is known in the case of mud volcanoes. The mud volcanoes merely show the locations in which earthquakes and gas eruptions are particularly frequent, and locations in which large amounts of underground mud have been generated by the frequent agitation of ground water in some fine-grained alluvial sediments.
Can the emission of gases be used for precursory information?
There were two observations before the earthquake at Loma Prieta on October 17, 1989 that seemed to be gas related and are clearly just prior to the earthquake (Reimer, 1990 and Fraser-Smith, 1989). But these observations were made for different purposes, unrelated to earthquake research, and yet they constitute the best earthquake-predictive observations. One was the observation of the amount of helium in a shallow well, which showed a sharp increase a day before the quake (Figure 2). I suppose that this represented an increased flow of gases upwards through the rocks, that had gathered up the helium that had accumulated in the pores.
Figure 2. From Reimer, 1990.
The other observation was that of a low radio frequency noise that is not normally present, also seen just before the quake (Figure 3); I attribute this to the interruption and reconnection of earth currents normally flowing in the groundwater, as these current paths are interrupted and re-connected by the bubbles of insulating gases that stream through the pores of the rock. Would these and other gas-related precursory effects not form the best line of earthquake investigation, to devise the most important of all, a predictive capability?
Figure 3. From Fraser-Smith, 1989.
The eye-witness stories of the past are all ignored or not even known to the present investigators; they are certainly not mentioned much in the modern earthquake literature. See the related documentation describing historical accounts of many large quakes (in "Eye-witness Accounts of Several Major Earthquakes," this Web site).
Cox, K. G. (1978). Kimberlite pipes. Scientific American 238 (4).
Fraser-Smith, A.C. et al. (1989). STAR Laboratory, Stanford University, Stanford, CA 94305.
Kennedy, G.C. and Nordly, B.E. (1968). The genesis of diamond deposits Econ. Geol. 63, 495-503.
Melton, C.E. and Giardini, A.A. (1974). The composition and significance of gas released from natural diamonds from Africa and Brazil. Amer. Mineralogist 59, 775-782.
To show how common the gas related effects have been in reports of earthquakes of the past, I am giving here a list of such reports. I do not believe that the individual authors had much information about other such reports, and therefore these reports can be taken to be free from suggestive influences.
I am grateful to my colleague Dr. Steven Soter for his library researches that found the samples given here and many more like these.
Norcia and Aquila (Italy), 14 January and 2 February 1703
"In Aquila and Norcia, and in other places . . . the earth was here and there observed to split in cracks, from which streamed the evil odors of sulfur and bitumen; and men in Aquila most worthy of trust write that in many places after the earthquake sulfur and fire issued from the opened earth." (Quoted by Galli, 1911)
Lisbon, 1 November 1755
". . . we began to hear a rumbling noise, like that of carriages, which increased to such a degree as to equal the noise of the loudest cannon; and immediately we felt the first shock, which was succeeded by a second and a third; on which, as on the forth, I saw several light flames of fire issuing from the sides of the mountains, resembling that which may be observed on the kindling of coal. . . . I observed from one of the hills called the Fojo, near the beach of Adraga [near Colares], that there issued a great quantity of smoke, very thick, but not very black/ which still increased with the fourth shock, and after continued to issue in a greater or less degree. Just as we heard the subterraneous rumblings, we observed it would burst forth at the Fojo; for the quantity of smoke was always proportional to the subterraneous noise." (Stoqueler, 1756)
Komarom (Hungary), 28 June 1763
"Ruptures in the soil originated in thousands of places. From almost all of them water and quicksand were emitted together with flames and stinking smoke. . . . The river Danube began to rise . . . and the water appeared to be steaming as though boiling. It had a sulphurous smell. The majority of the ruptures occurred near the river bank and from some of them flames emerged alternately with the sand and smoke. Fertö Lake, 100 km west of Komarom, began to rumble and foam very intensely. . . . Flames as big as a barrel were seen over the river itself. Many horned cattle perished in the terrible stinking vapour that came from the earth. . . . At the bank of another smaller river, the Vag, red-colored flames rushed up from the ruptures, followed by sulphurous waters. . . . At some places the waters that came from the earth were distinctly black. The water of the river Bag appeared to be boiling." (Quoted by Rethly, 1952)
Lima, 30 March 1828
Water in the bay "hissed as if hot iron was immersed in it," bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom. (Bagnold, 1829)
(The anchor chain is reported to be on display in the London Navy Museum.)
Owens Valley (California), 26 March 1872
"People living near Independence . . . said [that] at every succeeding shock they could plainly see in a hundred places at once, bursting forth from the rifted rocks great sheets of flames apparently thirty or forty feet in length, and which would coil and lap about a moment and then disappear." (San Francisco Chronicle, 2 April 1872)
"Immediately following the great shock, men whose judgment and veracity is beyond question, while sitting on the ground near the Eclipse mine, saw sheets of flame on the rocky sides of the Inyo mountains but a half a mile distant. These flames, observed in several places, waved to and fro apparently clear of the ground, like vast torches; they continued for only a few minutes." (Inyo Independent, 20 April 1872)
Sonora (Mexico), 3 May 1887
"Another effect of the earthquake which terrified the frightened inhabitants of these places, was the fire upon all the mountains around the epicenter and even some situated in the territory of Arizona, among others the ridge of San Jose. Some of these, it is said, continued in flames for many days." (Aquilera, 1920)
Swabia (Southern Germany), 16 November 1911
The following are from among the many eyewitness accounts quoted by Schmidt and Mack (1913):
"We saw a sea of flames, gas-like and not electrical in nature, shoot up out of the paved market street. The height of the flames I can estimate at 8 to 12 cm; it was like when you pour petroleum or alcohol on the ground and light it."
"I observed very precisely how a bright fire, which had a bluish color, came out of the ground in the meadow. Its height was about 80 cm. . . . The first was present not only in the meadow but also in the whole surroundings of our house."
"Some people in the streets . . . noticed that for a while before the quake and particularly after it an evil stuffy air made breathing almost impossible."
Rumania, 10 November 1940
The following are phrases used in eyewitness accounts collected by Demetrescu and Petrescu (1941):
". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides."
Sungpan-Pingwu (China), 16, 22, and 23 August 1976
"From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists.
The San Francisco Earthquake
The earthquake that destroyed parts of San Francisco and virtually all of Santa Rosa occurred at 5:12 a.m. on 18 April 1906. It was most intense perhaps a hundred kilometers north of San Francisco. We will here list some excerpts from the numerous reports, all indicating violent gas emission from the ground, gases that contained the poisonous hydrogen sulphide and gases that were frequently flammable. It is the earthquake for with the most detailed reports exist, and which shows every type of phenomenon that we have noted in other cases.
(a) Effects in Air
An extensive list of noises heard at the time of the shock, compiled from witnesses by Lawson and others (1908), includes the following: From Santa Rosa, "Heard noises in SW; then felt breeze; then felt shock". From Cotati, "Sound as of a strong wind before the shock". From Point Reyes Station, "Heard roar, then felt wind on my face". From Calistoga, "A rushing noise before the shock came". From Pescadero, "Noise as of wind preceded the shock". And from Mount Hamilton, "Sound as of flight of birds simultaneously with shock".
Other clear evidence for gas is given by a report published on 23 April in the Santa Rosa Democrat-Republican (the first newspaper to appear after the devastation). It said:
J.B. Doda, who came over from Fort Ross on Monday, reports that the earthquake caused immense cracks in the earth there, from which strong gases are emitted which make men and cattle sick.
Also, according to Edgar Larkin (1906), who collected a great many accounts, the odour of hydrogen sulphide was noted in the area of Sausalito. He also reported that sulfurous odors were pungent in Napa County during the night of the 17th and 18th before the upheaval, and lasted all day. . . . From many of the letters it is clear that the entire region north and east of San Francisco is saturated with gases of sulfur origin. . . .
In Santa Rosa, according to Lawson and others (1908), a strong smell of sulphur had been noticed two days before the earthquake by one Charles Kobes. Since during an earthquake eight years previously, "sulfur fumes came up from under his house which almost drove his family from home", the recurrence of this phenomenon on 16 April 1906 caused Kobes to tell his family that there would be another earthquake.
(b) Effects in Water
Numerous indications of hydrogen sulphide in bodies of water were reported. According to Larkin (1906), "creeks became milky in several places as if gas escaped from the water". Hydrogen sulfide bubbling through water is known to give it a milky appearance. Another report in the San Jose Herald of 2 May 1906 states that in Monterey Bay, on the day of the quake, there were thousands of strange fish floating on the water a few miles offshore, none of which were known to old fishermen on the boat. Similar reports of massive fish kills at times of earthquakes, especially of bottom-dwelling fish, are known from Japan, in some cases also associated with the description of milkiness of the water. Again, hydrogen sulphide, which is highly toxic to fish, seems a likely explanation, and in each case it is bottom dwelling fish which are not normally caught that are the chief victims.
(c) Anomalous Animal Behaviour
Strange animal behaviour preceding earthquakes is well documented in many parts of the world. Dogs, pigs, horses, cows and many other animals seem to show signs of restlessness or extreme disturbance prior to major earthquakes, and I would attribute this to their ability to smell the outflow of ground gases much more readily than humans and to be altogether much more concerned about smells. In San Francisco the major reports of this nature concerned the behaviour of dogs (Lawson et al., 1908), which are reported to have been howling during the night preceding the earthquake.
(d) Earthquake Lights
Again, as in many other earthquakes, there are many reports of flames issuing from the ground, either seen close-by or seen as a glow of light in the distance. In fact, while it was reported that the great fire, which was initiated by the earthquake, was in part caused by broken gas mains in the streets of San Francisco, this may not have been the major cause. There are numerous reports of flames seen in neighboring areas where no gas mains existed. Thus, George Madeira, a veteran mining engineer from Healdsburg, reports in the Santa Rosa Republican for 4 April 1910:
While investigating the natural phenomena of the seismic disturbance of April 18, 1906, I visited the mountain ranch of Mr. and Mrs. Adams, a mile and one-half northeast of Cazadero. They stated that for two night preceding the earthquake they "had seen small streams of lightning running along the ground". Their attention was called to the phenomenon by the incessant barking of their dog.
Here, evidently some 30 hours before the shock, earthquake lights were reported in what was soon to be the epicentral region.
During the earthquake itself there were more such accounts, like that of J.E. Houser, and engineer in San Jose, California, quoted by Larkin (1906):
This report included the following:
We could see down Alameda Street ablaze with fire, it being of a beautiful rainbow color, but faint. We passed out into the street and met a man who asked, "Did you see the fire in Alameda Street?" An hour later a friend told me that the ground all around was a blaze of fire.
(e) Explosive Noises (Brontides)
According to George Madeira in a letter written on 5 May 1908, as quoted by Alippi (1911),
Explosions much resembling the discharge of heavy guns have for the past two years been heard at intervals in the West and Middle Coast range of mountains, particularly in Marin, Sonoma and Mendocino Counties. Heavy detonations and rumblings were heard near the base of Mt. Tamalpais, Marin County, during the winter months and previous to the great earthquake which destroyed San Francisco and Santa Rosa in Sonoma County April 18th, 1906, and have been heard at stated times up to this writing.
Some of these later explosions evidently accompanied earthquake aftershocks.
(f) Visible Waves
The phenomenon of slowly rolling waves, like the waves at sea, was reported from many places in the San Francisco earthquake. Lawson and others (1908) list over twenty such accounts distributed geographically from the vicinity of Eureka to Visalia, a distance of more than 600 kilometres. Several of these accounts explicitly compare the ground motion observed to that of waves in the ocean. Similar accounts are also in descriptions of other earthquakes, especially that in Lisbon. These waves were discussed by John Michell (1761), a brilliant scientist of the 18th century. What he presumed was happening was that soft alluvial deposits can be bent and do not fracture as readily as the hard rock beneath. If a great mass of gas suddenly comes from cracks in the rock, it may lift up this carpet and in that case, gravity waves quite similar to the waves in the ocean would be set up.
Can Earthquakes Be Predicted?
We see that these descriptions make major earthquakes look much like violent eruptions, quite similar to gas eruptions from volcanoes or mud volcanoes. The airborne noises, the flames, the air pollution are all similar, and while most of the intense effects take place at the time of the quake, some of the effects occur as precursors and cannot therefore be ascribed to secondary effects of the mechanical deformation of the ground. It seems very strange that in all the attempts to predict earthquakes, no gas observations are included. Highly accurate measurements of the distortion of the ground represent the main effort, since the current theory has earthquakes resulting from a gradually augmenting stress in the rocks until they reach the breaking strain and the earthquake occurs. It is therefore supposed that one can measure the building up of the stress by the slight deformation prior to a quake. However, as a means to predicting earthquakes, this method has been entirely unsuccessful. The ground does distort on occasions, but not by any unusual amount before an earthquake.
The evacuation of Haicheng two hours before a devastating quake is an example of a successful prediction, and it was based mainly on gas effects such as a cloud of warmer air and fog developing above the known faultline, strange and nauseating smells and changes in groundwater levels. The same effects have been mentioned in very many of the ancient records.
Gases can indeed have a lot to do with earthquakes. A large volume of gas entering the crust of the Earth from deeper levels and at a high pressure, will greatly change the mechanical properties of the rock. Pore-spaces will be inflated, and the overburden weight of the rock will be effectively relieved by the pressure of the gas. The great weight of the overburden would normally have resulted in high internal friction, opposing any slippage at all but the shallowest levels. But with gas effectively bearing the overburden, slippage can occur much more easily. Much smaller values of stress in the rock will then be sufficient to cause a quake.
The absence of high stresses along the San Andreas fault was indeed a surprise to the investigators, when they had a chance to make such measurements in the deep well drilled at Cajon Pass in Southern California. They also failed to find there the extra heat that the known past slippage should have left behind, had it taken place without gas levitation.
When gas has invaded an area of the crust, it generally shows some emission at the surface that can be observed, and that results in the various effects mentioned. Of course the gases that were in the pore-spaces to start with are pushed up first, before the "new" gas has got to the surface. This brings up smells which cause surprise or consternation among many animals; it brings up more carbon-dioxide and less oxygen than air has normally, and this drives animals out of burrows; it brings up humidity and temperature of the sub-surface and thus frequently makes a fog. This contains more of the heavy CO2 molecule than the average air, and can therefore make a warmer cloud that stays on the ground instead of rising rapidly. Radioactive gases that are normally generated in the ground make a prominent appearance as they are flushed from the ground.
These signs should be taken to mean that the rock underneath has now suddenly lost much of its strength, and even small stresses will allow it to break. There was no particular build-up of stress prior to the quake, and measurements of this are therefore useless as predictors. The sudden event was the gas invasion that weakened the rock, and it is on this that a prediction method has to be based. During earthquakes and after, a lot more gas escape can usually be observed, and by then the deep source gas may have made its way to the surface. This is often combustible, probably mainly methane as this is in most common gas in deep rocks, and it often catches fire.
In China, in Japan, in the Soviet Union, much more attention is paid to gas phenomena. Japan even has a "Laboratory of Earthquake Chemistry." The US is far behind in this field, not because it does not have the technology, but just because it took a wrong choice some time ago, and now does not wish to change course. But the citizens of earthquake-prone regions will be more concerned with obtaining a warning than to be party to a scientific controversy. Sub-surface gas observations are simple and comparatively inexpensive, such as changes in groundwater levels in water wells, or changes in gas pressure above a water table. It is high time that California and the Central Mississippi region obtained the knowledge and experience in this field that will be necessary to establish a meaningful prediction service. Instrumentation operated by scientists is one aspect of this; public earthquake education and a reporting network is another, to assure the widest possible coverage for the observation of the many phenomena that may be relevant for predictions. One wonders how many such observations go unreported because their relation to earthquakes is not generally known.
Alippi, T. (1911). The 1952 Fort Yuma earthquake—two additional accounts. Seismol. Soc. Amer. Bull. 68, 1761-1762.
Aquilera, J.G. (1920). The Sonora Earthquake of 1887. Seismol. Soc. Amer. Bull. 10, 31-44.
Bagnold, T. (1829). Extraordinary Effect of an Earthquake at Lima, 1828. Quart. J. Soc. Lit. Art 27, 429-430.
Demetrescu, G. and Petrescu, G. (1941). Sur les phénomènes lumineux qui ont accompagné le tremblement de terre de Roumanie de 10 Novembre 1940. Acad. Roumaine Bull. Sec. Sci. 23, 292-296.
Galli, I. (1911). Raccolta e classificazione di fenomeni luminosi osservati nei terremoti. Bol. Soc. Sismol. Ital. 14, 221-447.
Larkin, E.L. (1906). The great San Francisco earthquake. Open Court 20, 393-406.
Lawson, A.C., et al. (1908). the California Earthquake of April 18, 1906. Carnegie Institution, Washington, D.C.
Michell, J. (1761). Conjectures concerning the cause, and observations upon the Phaenomena, of Earthquakes. Phil. Trans. Roy. Soc. 51, 566-634.
Rethly, A. (1952). A Kárpámedencék Földrengesei 445-1918. Academic Publishing House: Budapest.
Schmidt, A. and Mack, K. (1913). Das Süddeutesches Erdbeben vom 16 November 1911. Württ, Jahrbücher f. Statist. u. Landeskde., Jahrg. 1912, Heft I, 96-139.
Stoqueler, Mr. (1756). Observations, Made at Colares, on the Earthquake at Lisbon, of the 1st of November 1755, by Mr. Stoqueler, Consul of Hamburg. Phil Trans. Roy. Soc. 49, 413-418.
The Deep, Hot Biosphere
Abstract: (Subject: microbiology)
There are strong indications that microbial life is widespread at depth in the crust of the Earth, just as such life has been identified in numerous ocean vents. This life is not dependent on solar energy and photosynthesis for its primary energy supply, and it is essentially independent of the surface circumstances. Its energy supply comes from chemical sources, due to fluids that migrate upwards from deeper levels in the Earth. In mass and volume it may be comparable with all surface life.
Such microbial life may account for the presence of biological molecules in all carbonaceous materials in the outer crust, and the inference that these materials must have derived from biological deposits accumulated at the surface is therefore not necessarily valid.
Subsurface life may be widespread among the planetary bodies of our solar system, since many of them have equally suitable conditions below, while having totally inhospitable surfaces. One may even speculate that such life may be widely disseminated in the universe, since planetary type bodies with similar sub-surface conditions may be common as solitary objects in space, as well as in other solar-type systems.
We are familiar with two domains of life on the Earth: the surface of the land and the body of the oceans. Both domains share the same energy source: namely sunlight, used in the process of photosynthesis in green plants and micro–organisms. In this process the molecules of water and of CO2 are dissociated, and the products of this then provide chemical energy that supports all the other forms of life. Most of this energy is made available through the recombination of carbon and hydrogen compounds concentrated in the plants, with the oxygen that became distributed into the atmosphere and oceans by the same photosynthetic process. The end product is again largely water and CO2, thereby closing the cycle.
This was the general concept about life and the sources of its energy until approximately twelve years ago, when another domain of life was discovered (1). This new domain, the "ocean vents", found first in some small regions of the ocean floor, but now found to be widespread (2), proved to have an energy supply for its life that was totally independent of sunlight and all surface energy sources. There the energy for life was derived from chemical processes, combining fluids - liquids and gasses - that came up continuously from cracks in the ocean floor, with substances available in the local rocks and in the ocean water. Such sources of chemical energy still exist on the Earth, because the materials here have never been able to reach the condition of the lowest chemical energy. The Earth formed by the accumulation of solid materials, condensed in a variety of circumstances from a gaseous nebula surrounding the sun. Much of this material had never been hot after its condensation, and it contained substances that would be liquid or gaseous when heated. In the interior of the Earth, heat is liberated by radioactivity, by compression, and by gravitational sorting; and this caused partial liquefaction and gasification. As liquids, gases and solids make new contacts, chemical processes can take place that represent, in general, an approach to a lower chemical energy condition. Some of the energy so liberated will increase the heating of the locality, and this in turn will liberate more fluids there, and so accelerate the processes that release more heat. Hot regions will become hotter, and chemical activity will be further stimulated there. This may contribute to, or account for the active and hot regions in the Earth's crust that are so sharply defined.
Where such liquids or gases stream up to higher levels into different chemical surroundings, they will continue to represent a chemical disequilibrium and therefore a potential energy source. There will often be circumstances where chemical reactions with surrounding materials might be possible and would release energy; but where the temperature is too low for the activation of the reactions. This is just the circumstance where biology can successfully draw on chemical energy. The life in the ocean vents is one example of this. There it is bacterial life that provides the first stage in the process of drawing on this form of chemical energy: for example, methane and hydrogen is oxidized to CO2 and water, with oxygen available from local sulfates and metal oxides. Hydrogen sulfide is also frequently present, and leads to the production of water and metal sulfides; there may be many other reactions of which we are not yet aware. Of all the forms of life that we now know, bacteria appear to represent the one that can most readily utilize energy from a great variety of chemical sources.
How widespread is life based on such internal energy sources of the Earth? Are the ocean vents the sole representatives of this? Or do they merely represent the examples that were discovered first? After all, the discovery of these is recent, and we may well expect that other locations that are harder to investigate would have escaped detection so far.
Bacteria can live at higher temperatures than any other known organisms; 110 °C has been verified, and some biologists consider that the upper temperature limit may be as high as 150 °C (providing always that the pressure is sufficient to raise the boiling point of water above this temperature).
There can be little doubt that venting of liquids and gases from areas of the Earth's mantle beneath the crust is not limited to a few cracks in the ocean floor. Indeed fossilized "dead" ocean vents have already been discovered (3), showing that the phenomenon is widespread and occurred in different geologic epochs. A similar supply of fluids seems to be widespread also in land areas, where it is much harder to investigate; but it has been noted that many areas of basement rocks contain methane and other hydrocarbons. This has been seen in numerous mining and tunnelling operations for a long time. Major fault-lines have been noted to be high-spots of hydrocarbon seepage (4). Hydrocarbons have also been encountered in deep drilling in basement rocks, as in the Soviet superdeep well in the Kola peninsula and in the pilot hole of the German Continental Deep Drilling Project (KTB). The large quantities of methane hydrates (methane-water ices) found in many areas of the ocean floor, and thought to contain more methane than all other known methane deposits (5,6), suggest a widely distributed methane supply from below.
In land areas, deep in the rocks, it would be much harder to discover and investigate biological activity than in the ocean vents,. The pore-spaces in the rocks are quite sufficient to accommodate bacterial life, and the rocks themselves may contain many of the chemicals that can be nutrients together with the ascending fluids. But, of course, there would be no space for larger life forms. Just as bacterial life in the ocean vents would not have been discovered had the secondary larger life forms not drawn attention to it, so any active bacterial life deep in the solid crust could have gone largely unnoticed.
The remains of bacteria in the form of molecules - "hopanoids" (derived from hopanes) - a material coming from bacterial cell-walls, have however been found in all of the several hundred samples of oil, coal and kerogen (distributed carbonaceous material in the crust) examined by by Ourisson et. al. (7). These authors note the widespread or apparently ubiquitous presence of these molecules in the sedimentary rocks, and they give an estimate of the total quantity as of the order of 1013 or 1014 tons, more than the estimated 1012 tons of organic carbon in all living organisms on or near the surface. They also note the virtually identical pattern of the chromatogram of these molecules in oil and in coal. Further they note that some of the molecules most commonly used to identify the presence of biological material in petroleum, such as pristane and phytane, are not necessarily derived from plant chlorophyll as is commonly believed, but could well be products of the same bacterial cultures as those that gave rise to the hopanoids. The presence of these bio-molecules can therefore not be taken to prove a derivation of the bulk substance from surface biological debris.
What are the depths to which active bacterial life may have penetrated? Could bacteria get down into the deep rocks? Would this represent just a minor branch of all the surface biological activity, or could it be comparable with it in the total amount of chemical processing caused by it? How important would such life have been for the chemical evolution of the crust of the Earth?
An upper limit of the temperature of 110 to 150 °C would place a limit to the depth of between 5 and 10 kilometers in most areas of the crust. The mere question of access to such depths for bacteria would be no problem. Even just the rate of growth of bacterial colonies along cracks and pore spaces in which the requisite nutrients are available, would take them down in a few thousand years - a very small fraction of the time spans available. In fact, fluid movements in pore spaces would provide still much faster transport. The tidal pumping of ground water alone would be sufficient to distribute bacteria down to 10 km in less than a thousand years. Probably longer times would have been required to allow for the adaptation to the high temperatures.
The total pore-space available in the land areas of the Earth down to 5 kilometer depth can be estimated as 2 x 1022 cm3, (taking 3% porosity as an average value). If material of the density of water fills these pore spaces, then this would represent a mass of 2 x 1016 tons. What fraction of this might be bacterial mass? If it were 1% or 2 x1014 tons, it would still be equivalent to a layer of the order of 1 1/2 meter thickness of living material if spread out over all of the land surface. This would indeed be more than the existing surface flora and fauna. We do not know at present how to make a realistic estimate of the subterranean mass of material now living, but all that can be said is that one must consider it possible that it is comparable to all the living mass at the surface.
Together with this consideration would go the consideration of the cumulative amount of chemical activity that could be ascribed to this deep biosphere, and with that the importance it may have had for the chemical evolution of the crust, the oceans and atmosphere, and the development of the surface biology.
The remarkable degree of chemical selection leading to concentrated deposits of certain minerals has long been an enigma. How can processes in the crust lead to the production of a nugget of gold or a crystal of galena, when the refining process had to concentrate these materials by a factor of more than 1011 from the original elemental mix? How much of the concentrated metal minerals found have so far been explained satisfactorily? What energy sources were available to produce such large local decreases of entropy, and how was the necessary energy applied? Is this not a field where the complexity of carbon chemistry and biology, with their ability to be highly selective and to mediate chemical processes, may have had a much larger share than had previously been thought? It is characteristic, after all, for biology to generate important local decreases of entropy at the expense of energy absorbed and entropy rejected elsewhere.
If there exists this deep, hot biosphere, it will become a central item in the discussion of many, or indeed most, branches of the Earth sciences. How much of the biological imprint of material in the sediments is due to surface life and how much to life at depth? Do the biological molecules of petroleum and coal indicate now merely the additions from the deep biosphere to materials of primordial origin, rather than indicate a biological origin of the bulk of the substances themselves? *
*Sir Robert Robinson, after studying the composition of natural petroleum, considered this possibility as likely. He wrote: "Actually it cannot be too strongly emphasized that petroleum does not present the composition picture expected from modified biogenic products, and all the arguments from the constituents of ancient oils fit equally well, or better, with the conception of a primordial hydrocarbon mixture to which bio-products have been added" (8). Although there has been much detailed work since, demonstrating the variety of biological molecules that exist in most petroleum, none of this can make the distinction between the two opposing viewpoints. This work was frequently cited to support the bio-origin theory rather than the bio-addition, as a widespread microbiology at depth was not put under consideration.
Many deductions that are firmly in the geological thinking of the present time may have to be reconsidered, if there is indeed such an abundance of life at depth.
One cannot discuss these possibilities without connecting them with the questions of the origin of life. Photosynthesis is an extremely complex process which must lie some considerable way down on the path of evolution. Energy sources that were simpler to tap had to sustain life for all the time from its origin to the perfection of the photosynthetic process. Presumably these were chemical energy sources, provided by the substances of the Earth. Now one will want to examine whether these were perhaps the same as the chemical energy sources providing the life in the ocean vents, and possibly the bacterial life in the rocks about which we are speculating here.
The rocks that have hydrogen, methane and other fluids percolating upwards would seem to be the most favorable locations for the first generation of self-replicating systems (9). Deep in the rocks the temperature, pressure, and chemical surroundings are constant for geologically long periods of time and, therefore, no rapid response to changing circumstances is needed. Ionizing radiations are low and unchanging. No defense is needed against all the photochemical changes induced by ultraviolet light or even by the broad spectrum of visible sunlight.
Bacteriologists have speculated that since a large sub-group of archaebacteria - the most primitive and judged to be the most ancient bacteria - are thermophiles, this may indicate that primitive life evolved at such high temperatures in the first place (10). If it did, and if the archaebacteria are the earliest forms of bacteria, evolved at some depth in the rocks, they may have spread laterally at depth, and they may have evolved and progressed upwards to survive at lower temperatures nearer the surface. Some combination of lateral spread at depth and spread over the surface with subsequent re-adaptation to the conditions at depth will have allowed them to populate all the deep areas that provided suitable conditions to support such life. Of course now, when the surface is replete with bacteria of all kinds, it may be difficult to unravel the evolution in each of the domains.
If the deep, hot biosphere of microbial life exists in the rocks as well as at the ocean vents, what would be the consequences? Could we expect to have seen any evidence already?
Many reports have been published in recent times, describing the discovery of bacteria in deep locations where they were not expected. The most striking example is the discovery deep in the granitic rock of Sweden. While drilling to a depth of 6.7 kilometers in an ancient meteorite impact crater called the "Siljan Ring", very large quantities of a fine-grained magnetite were encountered. Magnetite, a magnetic iron oxide, exists normally in the granite in the form of large crystals (~1 millimeter) and at a low mean concentration. What was found was quite different from this. Grains in the micron size range were found in a thick sludge or paste, with a liquid binder which was a light oil. This was seen first at a time when the drilling fluid was water, with only occasional small additions of a plant oil as a lubricant. This sludge contained oil to the complete exclusion of water, and the oil was largely a simple, light, hydrogen saturated petroleum, completely different from plant oils. (It is worth noting that no sediments of any kind had been encountered in the drilling, but only granitic and igneous rock). The magnetic grains were not only particularly small, but also had a different trace element content from the coarse magnetite grains in the granite. Neither the magnetite nor the oil had a simple explanation in terms of the material of the formation or of any of the drilling additives. The quantities of this sludge found in this first discovery were not small -- 60 kilograms of it filled a drillpipe to the almost complete exclusion of the water-based drilling fluid. Later a pump pumped up 15 tons of a similar oil, together with about 12 tons of the magnetite (11). Similar oil-magnetite pastes have been reported in several other oil drilling operations, and microorganisms have been identified that mediate the reduction of local ferric iron of the formation to the lesser oxidized magnetite, using the hydrocarbons as the reducing agent (12-14).
Later, when oil-based drilling fluid had been in use for several months, it was discovered that this had become loaded with many tons - at least 15 and possibly 30 - of this fine-grained magnetite. It became clear that there was a phenomenon that occurred on a large scale, and that was a major process in the rocks at a depth of between 5.5 and 6.7 kilometers.
It is very difficult to see how concentrations of this material could occur without bacterial action; and indeed samples of it taken from a depth of 4 km or deeper, have allowed several strains of previously unknown thermophilic, anaerobic bacteria to be cultured.*
*Dr. U. Szewzyk at the National Bacteriological Laboratory (Sweden) has cultured several strains of anaerobic, thermophilic bacteria from samples taken below 4,000 m in the Gravberg borehole , Siljan Ring, Central Sweden. Personal communication. Also Dr. K. Pedersen at the Department of Marine Biology of the University of Göteborg, reports: "Deep ground water microbiology in Swedish granitic rock" (15).
It will therefore be worthwhile to search for the presence of microorganisms in many other deep locations in the rocks where chemical energy is known to be available. The obvious location for this are the deep oil or gas wells. Bacterial cultures can be attempted from samples taken with the necessary precautions (maintenance of temperature, pressure, exclusion of oxygen) and using culturing media similar to the local chemical surroundings at the places of origin.
Although it had often been said that the presence of bacteria in oil can be identified by the chemical signs of "biodegradation" of that oil, we believe that this is misleading. Oil showing none of the known signs of "biodegradation" may still be coming from a region rich in bacterial life, and the oil may still have gained biological molecules from this, without however having suffered any other changes. The reason for this is that microbial attack at depth is likely to be limited by the availability of oxygen and not by that of hydrocarbons; and in that case it seems to be the general rule that bacteria would use first the light hydrocarbons, the molecules from methane to pentane, before attacking any of the heavier hydrocarbons. If the light hydrocarbons are present in sufficient quantity to exhaust the locally available oxygen sources (iron oxides, sulfates, and perhaps other oxides with sufficiently low oxygen binding energy), then the liquid oils will not suffer any biodegradation. Under these circumstances, which are probably common at depth in petroleum provinces, oil will then commonly exist with additions of biomolecules, and yet without any signs of biodegradation. It is the finding of apparently undegraded oil that nevertheless contained biomolecules, that had been considered as the most compelling evidence for a biological origin of the oil itself. This consideration would no longer be valid, and a non-biological origin for the bulk of the terrestrial hydrocarbons, just as for all the abundant hydrocarbons on the other planetary bodies, then seems probable. This is one example where the recognition of the existence of abundant micobial life at depth may change major considerations in geology and geochemistry.
Where we find "biodegraded" oil, it must have been subjected to conditions of greater availability of oxygen and lesser availability of the hydrocarbon gases; presumably, this occurs generally nearer the surface where atmospheric oxygen is available in ground-water and where the concentration of the light hydrocarbons is low, as these are gases at the low ambient pressure.
It may be that we shall find a simple general rule to apply: that microbial life exists in all the locations where microbes can survive; that would mean all the locations that have a chemical energy supply and that are at a temperature below the maximum one to which microbes can adapt. There would be no locations on the Earth that have been protected from "infection" for the long periods of geologic time.
Chemical energy must be available, but it must not be liberated spontaneously without the intervention of the organisms. That means we have to be concerned with regions in which the chemical processes that can release energy would not run spontaneously; the temperature must be below the activation temperature for the reactions, or a set of reactions must be involved that give out energy on completion, but that require intermediate steps which absorb energy.
Research on the deep microbial life would allow one to judge the extent of it on the Earth, and with that one can expect to gain an insight into the extent to which microbial activity has contributed to the chemical evolution of the crust and its various mineral deposits. Prospecting techniques for minerals and for petroleum may be improved. The derivation of petroleum is a subject of great economic importance, and new information may profoundly influence the prospecting techniques and the estimates of the quantities of petroleum and natural gas that remain to be discovered.
The other planetary bodies in our solar system do not have favorable circumstances for surface life. The numerous bodies that have solid surfaces all have conditions of atmospheric pressure and temperature unfavorable for the presence of liquid water. Mars, deemed the least unfavorable in this respect, has been investigated (by the Viking landers) and no indications of any biological activity has been found. With this, it seemed that there was little or no chance of finding any other life in the solar system.
With the possibility of sub-surface life, the outlook is quite different. Many planetary bodies will have temperature and pressure regimes in their interiors that would allow liquid water to exist. Hydrocarbons clearly are plentiful not only on all the gaseous major planets, but also on the solid bodies: the large satellites, numerous asteroids, the planet Pluto, comets and meteorites; and there is every reason to believe that hydrocarbon compounds were incorporated in all of the planetary bodies at their formation. The circumstances in the interior of most of the solid planetary bodies will not be too different from those at a depth of a few kilometers in the Earth. The depth at which similar pressures and temperatures will be reached will be deeper, as the bodies are smaller than the Earth; but this fact itself does not constitute any handicap for microbial life. If in fact such life originated at depth in the Earth, there are at least ten other planetary bodies in our solar system that would have had a similar chance for originating microbial life.
Could the space program ever discover this? Is there a possibility of finding life of an independent origin on some of the other planetary bodies?
We shall have to see whether microorganisms exist at depths on the Moon, on Mars, in the asteroids, and in the satellites of the major planets. Such investigations may become central to that great question of the origin of life, and with that they may become a central subject in future space programs.
There is a chance that an independent origin could indeed be identified by a number of criteria - the discovery of opposite chiral asymmetries (50-50 chance in case of an independent origin, while the observation of the same chirality in just one other case would be uninformative); a different choice of basic molecules, or any of the criteria that have been used to show that all terrestrial life has one common origin. (Incidentally, as has often been discussed, this does not imply that there has been only one occurrence leading to an origin of life: if there had been several, the most successful would have supplanted all others and after that there would be no possibility for a fresh start in competition with evolved biology.)
It is difficult to foresee at the present time that the space program could proceed to the sophistication and power to perform very deep drilling operations on distant planets. However, there are other options. Deep rifts, such as the Valley Marinera on Mars, expose terrain that was at one time several kilometers below the surface. Samples from there, from the massive landslides in that valley, could be returned to Earth and analyzed for chemical evidence that living materials have existed there in the past. Similarly, one may sample lunar craters that have exposed deep materials fairly late in the lunar history; or deep rifts and young craters on any of the other solid planetary bodies.
Recognizing that even the seemingly most inhospitable bodies may harbor life, care would now be necessary to avoid contamination by terrestrial organisms. Manned expeditions, whatever other difficulties there might be with them, can certainly not be kept sterile, and would therefore spoil such researches for all future times. Only very clean unmanned space vehicles going to planetary bodies that have not previously been visited by contaminated vehicles would qualify to bring back meaningful samples of a biology that resembles that of the Earth.
If life was restricted to the proximity of the surface of planetary bodies, then "panspermia", the transport of living material through space over astronomical distances, would be very improbable, as such living material would have to remain viable in a dormant form for very long times; and in most of the suggested forms of panspermia, it would not be protected sufficiently well against the cumulative effects of the cosmic rays. Meteoritic impacts could well have exploded large chunks of rock from one planet and such chunks may have escaped complete vaporization and excessive heating both during expulsion from one body and accretion on another. But unless the living organisms were deep inside of a rock, so as to be shielded by many meters of solids from the cosmic ray bombardment of space, there would be little chance of transferring functional living materials. Panspermia becomes a much more realistic possibility if there is abundant life at depth in the planetary bodies. There would have been a vastly greater number of opportunities for a transfer between planets in earlier epochs, when the rates of bombardment were much higher than they are now.
Meteorites are being collected at the present time that are thought to have derived from Mars (16) and indeed are found to contain carbonaceous material. Can one find traces of biological substances in them?
The surface life on the Earth, based on photosynthesis for its overall energy supply, may be just one strange branch of life, an adaptation specific to a planet that happened to have such favorable circumstances on its surface as would occur only very rarely: a favorable atmosphere, a suitable distance from an illuminating star, a mix of water and rock surface, etc. The deep, chemically supplied life, however, may be very common in the universe. Astronomical considerations make it seem probable that planetary-sized, cold bodies have formed in many locations from the materials of molecular clouds, even in the absence of a central star, and such objects may be widespread and common in our and in other galaxies. It is therefore a possibility that they mostly support this or similar forms of life. Panspermia not only over interplanetary but over interstellar distances would then be a possibility, and it would take the form of the distribution from one body carrying active living forms for indefinite periods of time and in a protected environment, to another body capable of supporting similar life.
There is one further consideration that needs to be mentioned: the upper temperature limit of bacterial life may well be in the region of 120 to 150 °C. But the availability of chemical energy sources will go down to much greater depths and much higher temperatures. Many chemical mixtures will not spontaneously run down to chemical equilibrium until temperatures more in the neighborhood of a 1000 °C are reached. Therefore, underneath the type of biosphere which we have discussed here, there will generally lie a large domain that is too hot for the bacterial life we know, but that is nevertheless capable of supporting other systematic chemical processing systems that can mediate those energy reactions. Could there be such higher temperature systems that act in a way similar to life, even if we may not identify them as life? Perhaps their chemistry would not be based on carbon, like the life forms we know; the element silicon comes to mind as an element that can also form molecules of some complexity, and frequently with a higher temperature stability than similar carbon-based molecules. Perhaps there are chemical systems that lack some of the properties we use in our present definition of life. Self-replication is a property possessed by simple crystal growth: it is only when self-replication is associated with an adaptive capability that the complex forms develop that we identify as life. In the case of unfamiliar circumstances and materials we may fail to recognize these properties.
There is a lot of distance between plain crystallography and life. It is the bridging of this distance that forms the central piece of the theories of the origin of life. Should we perhaps look at this deeper, hotter domain to find the clues? This is a region where the conditions have remained constant for the longest periods, and where the chemical energy sources have perhaps been most plentuful. Thermodynamics teaches us that a high degree of organization can develop only where there is a supply of energy; but we do not yet understand whether the availability of energy will itself promote the formation of such organized systems.
Cairns-Smith (17), writing about the origin of life, has pointed out that once self-replicating adaptive systems have formed, they may well adapt gradually and change to a totally different chemistry. The chemistry of life we now know need not be the one associated with its essential origin. Thus if a higher temperature life (or pre-life) exists, based on a different chemistry, it may still have an evolutionary relationship with ours, and one cannot presume to know in which sense such an evolution may have taken place.
1. Corliss, J.B., Dymond, J., Gordon, L.I., Edmond, J.M., von Herzen, R.P., Ballard, R.D., Green, K., Williams, D., Bainbridge, A., Crane, K., VanAndel, T.H. (1979) SCIENCE 203, 1073-1083.
17. Cairns-Smith, A. G. (1971) The Life Puzzle. Oliver & Boyd, Edinburgh.
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Life on other Planets
Meteorites have been collected from the ice fields of Antarctica and several of them appear to have come from Mars. Trace element ratios such as the sequence of noble gases from neon to xenon, as well as the rather unusual nitrogen isotopic ratio of the Martian atmosphere, are so specific that it seems very improbable that any other body would match this so closely. Some of these meteorites contain unoxidized carbon, some of it in the form of hydrocarbons similar to molecules that are commonly found in petroleum on the Earth. One of the Martian carbon-bearing meteorites, denoted ALH84001, was analyzed and gave an indication that microbial activity had taken place in this material. Detailed examination made it seem very improbable that this evidence was due to contamination in Antarctica, but rather that the biological imprint had been present in the interior of the stone before it fell to the Earth.
For an object to be shot off from Mars into an orbit that could eventually end on the Earth, a very large meteorite impact on Mars would have to have been responsible. There are many large impact craters on Mars, so that this does not seem improbable. But in a large impact, most of the material excavated and possibly propelled to a high velocity, will have come from a considerable depth, and the contribution made by surface or near-surface materials is likely to be a very small one. In that case the past surface conditions on Mars are not significant factors for the evaluation of the evidence provided by this meteorite.
Mars, like the Earth, will have internal heat sources, and temperatures will be increasing with depth. Water is so common on planetary bodies that it seems almost certain it will be present in large quantity also on Mars, and there must then be a depth range in which it is liquid. If the surface temperature has decreased over geologic times, the depth range of liquid water would have moved a little lower. The surface itself and a thin layer below are cold, so that any water coming up from deeper levels would generally not spill over the surface, but freeze in the rocks. Very little would reach the surface; in contrast to the circumstances on the Earth, where a surface temperature above the freezing point of water allowed all the ocean water to come up and spill over the surface. Small amounts of water vapor have indeed been detected in the Martian atmosphere.
The surface materials will have had a very different chemical history on the Earth as on Mars; but below the surface there will be somewhat similar materials on the two bodies, as represented by a mix of the meteorites, the left-over debris of planetary formation.
A comparison of the Martian meteorites with terrestrial sub-surface materials may then be meaningful. Temperatures and pressures will generally increase with depth, but at different rates on the different bodies, rates that are not yet known for Mars.
The Widespread Presence of Hydrocarbons in the Solar System and in the Universe
The stability of hydrocarbon molecules against thermal dissociation is greatly increased by pressure, an effect frequently ignored in the Western petroleum literature. This has been studied by several thermodynamicists in the USSR., and the conclusion they reached was that on Earth there could be hydrocarbon molecules at a depth of as much as 300 km, at a temperature of 1,000°C and a pressure of 100 kilobar. In the Western literature no oils are expected to exist at deeper levels than 10 km, and hence a supply of petroleum from below seemed impossible.
Of all the materials in the crust, the hydrocarbons (natural petroleum liquids and gases) appear to be the carriers of a large fraction of the element carbon, percolating to the surface in thousands of locations. Once in our oxidizing atmosphere they would rapidly be converted to CO2. Atmospheric-oceanic CO2, which the plants use for their carbon, would be depleted in a small fraction of geologic time, chiefly by the deposition of carbonate rocks. A source of carbon must be provided by the interior of the Earth, throughout all of the time that carbonates have been laid down, and the geologic record shows this to have occurred in all geologic epochs.
Similar outgassing processes seem to have occurred on many other planetary bodies. Jupiter, Saturn, Uranus, and Neptune have hydrocarbons in their massive atmospheres. Titan, a satellite of Saturn, has a substantial atmosphere in which the hydrocarbons methane and ethane seem to play a role similar to that of water on Earth, forming clouds and probably rain, and as with water here, there must be evaporation from lakes or oceans on Titan to resupply the clouds. In addition to methane and ethane, a number of other hydrocarbon molecules are identified spectroscopically, and they are quite similar to the range of molecules in terrestrial natural petroleum.
Many of the asteroids, the small planetary objects in orbits between Mars and Jupiter, have a surface reflectance resembling that of solid hydrocarbons. Also, interplanetary dust grains have been captured and analyzed with great skill and have shown the larger hydrocarbon molecules [polycyclic aromatic hydrocarbons] to be present in them. Also, the molecular clouds in the galaxy, out of which solar systems like ours will have formed, contain carbon, the fourth most abundant element, largely as hydrocarbons. The meteorites show us a group called carbonaceous chondrites, containing a few percent of their mass in heavy hydrocarbon molecules.
The Hydrocarbon Association with Helium and with Biological Materials
When it was widely believed that natural petroleum had derived from very large deposits of plant and animal debris in the sedimentary cover of the crust, this seemed to provide the explanation for the existence of many specifically biological molecules found in all the oils. But not only biological molecules show a strong association with hydrocarbons, the noble gas helium is also seen closely associated with hydrocarbons all over the world. All commercial helium is produced from oil and gas wells. Although the literature contains hundreds of examples of this association, no mechanism has been suggested that would explain how it could have arisen.
Helium, being chemically quite inert, could not have been concentrated by plants or by any chemical action. This association of hydrocarbons with helium and with biological molecules is seen not only in major oil and gas fields, but also in the seepage of gases in many locations on the Earth's surface. Why would helium come up preferentially in petroleum-bearing zones?
The only possibility for concentrating helium is a purely mechanical action, a pump. Some pumping action must have driven helium specifically to the hydrocarbons area. But why and how?
The only solution to this puzzle that I have been able to see, would require a very deep origin of the hydrocarbons, a depth of 100 kilometers or more, where the temperature and pressure would liquefy some components of the solid hydrocarbons that were present in the building materials of the Earth. Buoyancy forces relative to the higher density rocks would drive these liquids upwards. On their long pathways through the fractures in the rocks, caused and held open by the fluid pressure, they would force up helium atoms that constantly accumulate from the radioactive decay of the widely distributed radioactive elements uranium and thorium. This pumping action enriches the hydrocarbons with helium. If hydrocarbons are the most abundant fluids coming up from great depths, then they would be the ones that pump up the most helium.
But if the hydrocarbons come from great depth, they will not be of biological origin (just as they are not of biological origin on the other planetary bodies mentioned). The explanation of the biological molecules as coming from plant debris is then not valid. How then can the presence of biological molecules found in all oils be explained?
The only way I could see of solving this puzzle was to suggest that a widespread microbiology exists down to moderate depths, including the depths of all oil wells (a depth of about 8 km). Such microbiology could provide the oils with all the biological molecules that are seen; in fact several of them can only be produced by microbiology.
The viewpoint that the main components of petroleum formed at depth and without the intervention of biology, from materials incorporated in the Earth at its formation, has been vigorously pursued in Russia [Soviet Union] since the days of Mendeleev, who wrote an important paper on the analysis of petroleum and concluded that it all came from deep down in the Earth.
Several hundred publications exist that support this viewpoint, some indeed present strong evidence for it. Sir Robert Robinson, a Nobel Laureate, made detailed studies of natural petroleum, and he concluded:
Actually it cannot be too strongly emphasized that petroleum does not present the composition picture expected from modified biogenic products, and all the arguments from the constituents of ancient oils fit equally well, or better, with the conception of a primordial hydrocarbon mixture to which bio-products have been added. (1963)
"A primordial hydrocarbon mixture to which bio-products have been added" is a good summary of the position presented here. If there was much microbial life below, and a good food supply for it, then this might have far-reaching consequences, not only for petroleum geology but also for many aspects of the evolution of the crust, and possibly for biology and the evolution of life.
These considerations prompted me to write the paper: "THE DEEP, HOT BIOSPHERE", (Proc Nat. Ac. Sci. July 1992). The microbial life forms involved must then be hyperthermophilic, living at temperatures up to 120°C, possibly as much as 150°C. And the quantities, in terms of mass or volume, would have to be comparable with all the surface life we know. This would solve the sharp paradox that had split petroleum geology into two camps and had stymied progress of the discussion of the origin of petroleum for many decades.
What Energy Sources Would There be for Such Life?
Microbial life could only flourish if there was a supply of the element carbon and a chemical energy source, a "food" for them. The heat that surrounds each microbe can supply no energy; energy can be derived only from the flow of heat from a hot body to a colder one, and the microbes in the rocks are far too small for any temperature differences across their bodies to arise. ("You can sit in a hot tub as much as you like, but you will still need to eat.") Hydrocarbons are a chemical energy source, but only in the presence of oxygen, so that it becomes possible for the microbiology to mediate the energy-giving process of oxidizing them. On the surface of the Earth this is easy, the atmosphere provides virtually unlimited amounts of free oxygen. But where is the oxygen deep down in the pores of the rocks where we find oil?
The rocks contain oxygen in abundance, only most of it is bound too tightly, and it would take more energy to free this oxygen than could be obtained by the oxidation of the hydrocarbons. There are just a few commonly occurring substances in the rocks that have sufficiently loosely bound oxygen to allow the oxidation of hydrocarbons to be an energy source. Highly oxidized iron is one of them, sulfates (oxidized sulfur compounds) are another. Microorganisms can then feed on the combination of hydrocarbons with some oxygen they can take off these substances. One must then expect to see the accumulation at least of the solid end- products of some or all of these processes in hydrocarbon-rich areas.
Search for Life on Other Planetary Bodies
The search for sub-surface life on other planetary solid bodies such as the Moon, Mars, and many asteroids and satellites of the major planets, will now become a high priority item in planetary research. The surface conditions on the other solid planetary bodies are all quite different from those we have here, where the conditions are remarkably favorable for the development of surface life. But the sub-surface conditions will be similar to ours on most of these bodies, though depth dependence of pressure and temperature will be different. The possibility of developing life in them may then be not too different from the circumstances here. Hydrocarbons on them are known, and sub-surface liquid water can be expected on many of them. The rocks will contain some oxidized components that will serve as oxygen donors. The scene would be set for the existence of microbiology there. The recommendations I made specifically for Mars (in the paper mentioned above) included the search for evidence of microbial life in the carbonaceous Martian meteorites that had been found in Antarctica (a search that is still in progress now). For future interplanetary missions that could return a sample back to Earth, I thought that it would be best to go to locations where material is exposed now, that must once have been at some depth. The outstanding case is the floor of the deep "Vallis Marineris," where massive landslides have exposed material that must once have been at a depth well into the liquid water domain.
What are the Solid Products of this Microbial Activity?
The liquid or gaseous products will generally escape in short times and would not be maintained in a small meteorite on a long space flight. Where iron oxides served as the oxygen donors, the end product will be iron in a less oxidized state in which it is magnetic. Magnetite is the most common form. A further removal of oxygen, such as the step to metallic iron, requires more energy than is available in the reaction. Where sulfur oxides were the oxygen donors, one must expect to see just sulfur or unoxidized sulfur compounds such as hydrogen sulfide or metal sulfides. The product of the oxidation of the hydrocarbons will be carbon dioxide and water, and in many rocks this will react with oxides of calcium or magnesium to make solid carbonates. Those are the carbonate cements that fill up small pore spaces, and must have been transported by a liquid before precipitating.
Hydrocarbon-rich Areas on Earth
Magnetite and sulfur or metal sulfides are often seen in great concentration in hydrocarbon-rich areas on Earth, as are carbonate cements that fills cracks and pore spaces in the rocks. The isotopic composition of their carbon suggests that the ultimate derivation was from the oxidation of methane. The clearest example of this of which I am aware (but not the first) was the discovery of many tons of highly concentrated grains of magnetite, together with isotopically anomalous carbonate cements and with crude oil, all at great depth in two boreholes in Sweden. From these same boreholes and depths, previously unknown microbes were sampled and successfully cultured by the Swedish National Bacteriological Laboratory. These microbes could be cultured only in the circumstances that prevailed at the depth from which they were collected, namely a temperature of around 60°C and an absence of free oxygen, making a contamination by surface microbes very improbable. By now many locations are known in which oil, magnetic iron compounds, sulfides, and carbonate cements are found together. In regions not bearing hydrocarbons, a close association of these three solids is not common.
Sub-surface Life on Mars Discovered?
Microbial life on Mars could be dependent on the same processes as we have discussed for sub-surface life here. Highly oxidized iron is abundant on Mars, and very small-grained magnetite can then be expected to be one of the accumulated residues of microbial processes; so can iron sulfide and methane-derived carbonates. Polycyclic aromatic hydrocarbons are the large molecules that might remain in a rock that originally contained crude oil but then was exposed for millions of years to the high vacuum of space. All these substances have been found in the discovery meteorite, closely packaged to each other, and this by itself would make a strong case for the microbial interpretation. In addition, there are small objects seen under scanning electron microscopy that may well be fossils of microbes. While the last item by itself would not be conclusive evidence, the combination of this together with oil and the three residue products make a strong case for the microbial explanation. It is true that each step can occur without biological intervention, but the chance of finding by chance the evidence for all three solids in a small volume, together with hydrocarbons, seems to be very low. Many terrestrial oil and gas wells show just such an association (but an association with helium also, which the meteorite could not have transported through space).
Past Life Fed by Photosynthesis on Mars?
A planetary surface without photosynthesis is in any case inhospitable for life. It is only the immense energy supply that photosynthesis provides here that may favor surface life over chemically fed life at depth. In all other respects such as radiation environment, temperature variation, and evaporation of liquids, the surface is less hospitable than the sub-surface.
It does not seem probable that Mars ever had surface life based on the energy supply of photosynthesis. Not only would a temperature regime be required that would maintain liquid water on the surface, but also a sufficient atmospheric pressure would be needed to prevent rapid evaporation of water and subsequent deposition as ice at the poles. The atmosphere would also have to be such as to prevent the continual loss of water, through dissociation by sunlight and the subsequent loss of hydrogen to space. A substantial atmosphere would also be required to protect the surface from the destructive ionizing radiations from the Sun and from space, more so because of the absence of a protective magnetic field. The small force of gravity on Mars is not likely to have maintained a sufficiently massive atmosphere that would satisfy all these requirements.
Origin of Life: Many Independent Beginnings or Panspermia?
Does microbial life evolve spontaneously in all locations that are favorable (reminiscent of pre-Pasteur views, but with an enormously longer evolutionary time scale)? Have all such independent origins of life a similar basic chemistry? Is panspermia, the transportation of living systems between different host bodies, a real possibility? These will be the important questions.
If on another planetary body we were to find a type of biology that used quite different basic steps of chemistry, outside the range of the variants we have observed here, then we would judge this to represent an independent origin (though even then not with complete certainty). We would then be led to believe that some variants of life arise with high probability in many other favorable locations. But if we saw life forms with a similar basic chemistry, could we then make a distinction between panspermia and a very closely parallel evolution? Perhaps our chemistry is the only one that could work to make functional organisms, so no other would be found; or perhaps ours is one of a small number of possible ones, and for this reason would be likely to be discovered elsewhere.
The Significance of Chirality or "Mirror Symmetry"
But even in the cases of a similar chemistry, there would still be a possibility of deciding between parallel evolution from independent beginnings, and a distribution of life from one source, such as panspermia would provide. This arises from the property of "chirality," the symmetry that the right hand has to the left hand, or that a right-handed screw has to a left-handed one. Chirality implies that an object is different from its mirror image, no matter from which side you look at it. (Remember, a right-handed screw is a right-handed screw from whichever side you look at it; but it is seen as a left-handed screw in a mirror.) Two-dimensional objects do not posses chirality; the outline of the right hand drawn on a sheet of paper will become the outline of the left hand if observed from the other side of the paper.
In chemistry, molecules can possess chirality if they are composed of four or more atoms. To visualize this, consider first three atoms, positioned at the corners of a triangle of three unequal sides. This is necessarily a two dimensional object and cannot possess chirality; it will look like its mirror image when it is turned over. But if a fourth point is added, out of the plane of the triangle, and identified by being (say) farther from any of the three points than these are from each other, then the object possesses chirality: No direction of viewing can make it look like its mirror image.
Chirality assumes a particular importance in relation to biology. While there are many chiral molecules in inanimate matter, in each case the two forms are present in equal numbers to within random statistical expectation. Inanimate chemistry has no preference for the right-handed or the left-handed form of any molecule. All chemical processes will be accurately the same in any grouping of different chiral molecules, as they would be for another such grouping of the same molecules, but with each of the first set replaced by its chiral opposite. Now, it is a remarkable fact that in all terrestrial biology the molecules that are concerned with the basic steps of genetics and that determine the construction of next generation of the organism, represent a choice of one chirality over the opposite one. For example, if you were to select any one of the chiral amino acid molecules that make up proteins, it will show the same chirality, whether it comes from a microbe, an insect, a fish, a plant or an elephant. The usual explanation for this is that there is a common origin of all terrestrial biology; the first beginnings involved an even chance for the choice of the chirality, but after that all that followed in all of evolution continued in that same pattern. Possibly this is the right explanation, but many scientists, including the great chemist Linus Pauling, have expressed doubts whether a single beginning could have enforced such a strict rule throughout all the diverse branches of evolution that followed. Perhaps genetic material is transferred occasionally between different species, so that there is much more interaction and more coherency in the evolution of the different species than we have yet recognized. If such interaction is beneficial to one or other of the species, this would tend to enforce a common pattern.
But whatever the correct explanation may be for this remarkable fact, we clearly have a large example in front of us. For this reason we will be inclined to attribute any observation of a large asymmetry (non-racemic chiral substances) of this nature that we might find on another planetary body as arising also from living systems. The search for such an effect will be one aspect of the search for life on other bodies. Transparent liquids like water or oils have been very useful for finding biological materials, even in small concentrations, since any such asymmetry causes plane polarized light to suffer a rotation of its plane of polarization, with the sense of this rotation depending on the sense of the chiral molecule involved. In the absence of biological materials no such rotation has been found. Liquids, or liquids derived from their frozen forms such as ices or bitumens, can be examined for any asymmetry in the content of chiral molecules. Possibly the massive ice covers of several satellites of major planets are good candidates for such an examination.
But the examination of chirality also offers the possibility of distinguishing between an origin of life that is common with ours and one that derived from an independent beginning.
If we found the same basic chemistry in biological molecules of another planetary body as the one we have here, we would investigate whether the molecules there had the same chirality as ours. If they had the opposite one, we would immediately know a lot more: We would then conclude that life, using the same basic chemistry, had a good probability of arising independently on other bodies that had similar sub-surface conditions as our planet. If, however, we found the same chirality there, all we could say is that they might derive from the same evolution as ours, or that an independent origin favoring the same basic chemistry, had hit (with a 50-50 chance) on the same chirality as ours. Panspermia could be responsible, but we could not know for sure.
If we repeated such observations on yet another planetary body and obtained the same result, we would conclude that the probability was beginning to point towards a common origin, since an independent origin would have given a chance of only one in four of providing the same sense in three independent cases. The investigations of yet more planetary bodies would then become essential for resolving the issue.
Are there bodies of planetary sizes that exist in abundance in the spaces between the stars? We would not have discovered them even if they were so numerous that their combined masses were an appreciable fraction of the total masses of all the stars. Molecular clouds may well be forming such objects constantly , and only a fraction would come to be associated with a star. Perhaps the frequent motion of such objects through the outer reaches of our solar system are the causes of the large perturbations that comets seem to suffer, and that bring them occasionally into the inner part of the solar system where they become evident to us. Such objects could contain and maintain for billions of years an active internal microbial life, just as seems to be the case on the Earth. Panspermia across galactic distances would then be a possibility, through impacts spalling off pieces like our Martian meteorite, when such an object had come, perchance, into the vicinity of a planetary system. In this case there would be no dependence on dormant life for long periods, nor on any long term resistance to the damage of cosmic rays, two problems that have made other galactic scale panspermia proposals seem improbable.
The Origin of Life
From the investigation of microbial life on other bodies of our solar system we may then be able to come closer to an answer to the basic questions of the origin of life. The microbes that are able to withstand the highest temperatures, and that therefore can live at the deepest levels, are found to be a very early type, judged by their genetic make-up. This may suggest that their early appearance and the evolution following them occurred underground, in the favorable circumstances of having a constant food supply, no problems of temperature changes, no radiation hazards, and minimal difficulty resulting from the evaporation of water. The deep life seems to be the best candidate for the early evolution.
It has been said that "nature abhors a vacuum." But what nature also abhors is free energy. All of biology is just a device for degrading energy available from chemical sources, and on the surface from the great temperature differential between the hot surface of the Sun and the cold of space. Perhaps biology is just a branch of thermodynamics, and there is no sudden beginning of life, but a gradual systematic development towards more and more efficient ways of degrading energy. The step to photosynthesis was no doubt a difficult one to achieve, and much evolution must have preceded it. The chemical energy available in a planetary body is then most likely to have been the first energy source, and surface creatures like the elephants and the tigers and humans and all, feeding indirectly on solar energy, are just a specific adaptation of that life to the strangely favorable circumstances on the surface of our planet.
Gold, T. 1993. The origin of methane in the crust of the Earth. In: The Future of Energy Gases, D. G. Howell (Ed.). USGS Professional Paper 1570. US Government Printing Office, Washington, 890 p.
Gold, T. 1992. The deep, hot biosphere. Proc. Natl. Acad. Sci. USA 89:6045-6049.
McKay, D.S, et al. 1996. Search for past life on Mars: Possible relic biogenic activity in martian meteorite ALH84001. Science 273:924-930.
Nikonov, V.F. 1969. Relation of helium to petroleum hydrocarbons. Dokl. Akad. Nauk SSSR, Earth Sci. Sect. 188:199-201.
Wright, I.P., M.M. Grady, and C.T. Pillinger. 1989. Organic materials in a martian meteorite. Nature 340:220-222.
Metal Ores and Hydrocarbons
The association of various metal ore deposits with hydrocarbons is a vast subject, but as yet very few people have worked on it. Many such associations have been seen, but as people did not recognize the possibility that hydrocarbons could come up from great depth, they could not see any reason for these effects. And people do not write papers to say they do not understand what they see.
The general problems about concentrated mineral deposits are the following:
1.) The Earth formed by the collection of solids, mostly small grains, that had the elements pretty much mixed up. There may have been some layers that had a little more of this or that, but except for iron and nickel, there were no "clean" substances in this infall. We judge this from the great array of meteorites which are samples of the various contributions the Earth received. Many detailed trace element and isotope ratios show that this is true.
What processes would single out a particular element and cause a deposition in a location which represents a concentration by a factor of one million or more from the original mix? A fluid that moved through a large amount of the mix, and picked up in solution the particular substance, and then shed it from solution as a result of changing circumstances such as temperature, pressure, ph, or the picking up into the solution of another substance that decreased the solubility of the first. All attempts at explanation assume processes of this kind and this seems inevitable. Water is generally considered the basic fluid, usually with aggressive contaminants like salts. But when it comes to the arithmetic of these processes, there is frequently serious trouble. Many metals , especially the heavy metals, are just not sufficiently soluble in brines. or in any aqueous fluids. The excerpt from Krauskopf (appended here) refers to this difficulty. Many other authors have also noted it.
In my view hydrocarbons come towards the surface from depths between 150 and 300 km. They therefore leach through a very large amount of rock as they are driven up by buoyancy forces. Effective leaching requires powerful pumping action to drive fluids though fine pores and for a large distance: fluids coming up from great depth have of course this advantage. By comparison surface waters running through some crustal rocks have an incomparably smaller driving force. The leaching has to be due to fluids that originate at depth, because only those have the pressure differentials that are required for effective leaching.
2.) Which fluids have the capability to take into solution such substances as heavy metals or metal compounds?
At high pressures and temperatures many metals will form organometallics, that means molecules that combine metal atoms with such elements as carbon and hydrogen, possibly with some nitrogen and oxygen also. Most organometallic compounds are soluble in hydrocarbon oils. Such oils, being forced through the rocks, will have a chance to combine with metals in the rocks to make organometallic compounds. In turn those that are soluble in the oils can then be transported by that same flow. This will be so also for many metals that have very low solubilities in aqueous liquids.
3.) What process can be so selective that it will deposit one metal ore in one location and another often nearby? What liquid stream will just leach out copper from the rocks, while another nearby stream will leach out zinc? Or why platinum here and gold there?
The hydrocarbon flow, on the way up, will make a large array of molecules, in detail depending on such things as the carbon-hydrogen ratio, the ratio to other elements like nitrogen and oxygen, the catalytic action of specific minerals in the rocks, and the pressure-temperature regime it finds on the way. Among those molecules may be a class that is particularly favourable for forming a particular organometallic compound with one metal, another class with another. The great diversity of hydrocarbon molecules is thus the reason for the selectivity in the metal deposits. Certain groups of metals occur in close association, presumably because there exists a hydrocarbon stream there, and similar hydrocarbons that were abundant in that location have selected that group because these respond similarly. Thus lead and zinc are found together, gold and silver, etc.
When these metal-laden streams come nearer to the surface, and reach lower pressures and temperatures, many of the compounds become unstable (many carbon compounds are stable at a high pressure only, like diamond). Also bacterial action may destroy them, as the bacteria will preferentially remove the hydrocarbon components. In this way the naked metal atoms remain.
The close association of gold with carbon is well recorded in the literature. Conventional wisdom gives no hint of an explanation either for the association with carbon, or even for the occurrence of metallic gold altogether. It seems that carbon is an essential component in the laying down of gold. The gold miners of olden days knew this very well, and followed the "black leader", a trail of carbon black that led frequently to a gold deposit.
It is interesting that the other substance that is commonly associated with gold is silicon dioxide. Silicon is in the same column, two below carbon, in Mendeleev's table of the elements and it has very similar properties. It will form oils that are quite similar to hydrocarbon oils, but frequently with higher thermal stability. I do not know (and possibly no one knows) whether at high temperatures and pressures, it will form silicon-metallic compounds, analogous to organometallics. An argument in favour of this would be the occurrence of gold in quartz veins rather than in quartz deposits, suggesting a common migration path. Mercury, found as the sulfide cinnabar, is often together with oil and tar.
Many metals will of course make sulfides, if sulfur is available. Thus mercury may come up in a gas stream as mercury vapor or as dimethyl-mercury, but have enough sulfur to be turned into cinnabar. It is the same for many other metals, they would not resist being turned into the sulfide. For mercury it is particularly clear that it has come from great depths, as it is strongly associated with helium, in particular with helium high in helium-3, which is the marker for primordial helium, caught in the formation process of the Earth, and not merely derived from the radioactivity of uranium and thorium.
In the drilling in the Siljan Ring structure in Sweden, large quantities of magnetite were found. Some twelve tons of a mix of very fine grained magnetite and natural petroleum were pumped up from one wellbore, and some kilograms of a similar paste were pulled up on the drillstring in a second hole. At the deeper levels, below 5 km, the magnetite paste impeded the drilling operation in both holes. It appears that it was this same paste that prevented any substantial inflow into the wellbores, necessary for any commercial production. Investigations by laboratories including that of the Danish Geological Survey, showed the oil to be an ordinary type of crude, somewhat biodegraded. In the second hole no drilling fluids were introduced that could possibly have resulted in the oils seen.
The origin of such clean, concentrated magnetite and its very small grain size, much of it in the micron size range, certainly present a puzzle. Moreover the entire Siljan Ring structure displayed a positive magnetic anomaly, quite accurately centered in the ring. It therefore seems very likely that this same magnetite paste was the source for the magnetic anomaly, and that it was present in sufficiently large amount to account for it. If this is considered a possibility, then one may well wonder whether the various other large magnetite deposits of Sweden have a similar origin.
The only clues we have about the origin of the Siljan magnetite come from the detailed trace element and isotope observations of it. Neutron activation analysis (done by the Los Alamos National Laboratory) showed a substantially different admixture of trace elements from the local granite or the much larger magnetite grains in it. For example the paste magnetite contained only 1/30th of the amount of Mg-27 as the magnetic grains of the granite; 1/7th of the Na-24; but 100 times as much Zn-65 (there is a commercial zinc mine in the region); 10 times as much Ba-131 and Ba-139; less than 1/10th the amount of Nd-148. Several other equally large differences were found. It does not seem probable that any iron oxide in the local granite can be the origin of the magnetite paste: no processes are known that could have separated these elements so sharply. One may therefore consider the possibility that all this magnetite has been brought up as an organometallic from a totally different chemical domain such as the mantle. It would be most illuminating to analyze some of the other magnetite deposits of Sweden for similar anomalies.
From Introduction to Geochemistry, Konrad B. Krauskopt, McGraw Hill, 1982, p. 395.
This is similar to the question we tried to answer in the last section, as to the minimum concentration of metal in a magmatic gas that would be significant for the formation of ore deposits. We proceed in the same way, using rough numbers to establish a limit of reasonableness. Suppose, for example, that an ore solution carried 10-7 g/liter of zinc. To deposit 1 ton of metal would require a minimum of 1010 cubic meters of solution, approximately the volume of water carried to the sea each year by the Hudson River (average flow approximately 10,000 sec-ft). Such a solution traversing a vein at a rate of 10 ft3/sec could deposit 1 ton of zinc in a thousand years, provided that all the dissolved zinc precipitates. The amount of water and the amount of time seem excessive, by comparison with scanty data on the flow of hot springs and on the geologic times required for the formation of ore bodies. Thus 10-7 g/liter can be taken as an absolute minimum, below which the concentration of metal is too small to be of interest. For most purposes a somewhat larger figure, say 10-5 g/liter, is a more reasonable minimum.
By this criterion the solubility of ZnS is barely high enough to be of interest at a temperature of 200° and a pH as low as 5. The calculated solubilities of the sulfides of some other common metals (Mn, Fe, Co, Pb) have a similar order of the amounts of metal that can be carried by hot sulfide solutions seem far too small, except for a few metals under the most favorable assumed conditions, to account for the origin of ore deposits. This is the long-standing difficulty with the classical hydrothermal hypothesis.
A natural phenomenon that may pose a severe aircraft hazard?
There have been many serious aircraft accidents in recent years that have not had a satisfactory explanation despite exhaustive researches, and that have certain features in common. Those features include apparently a situation of extreme urgency and danger, so that there was no time for the flight crew to communicate details to the flight controllers; in some cases there were circumstances that seemed quite unexpected and perplexing to the flight crew, suggesting an urgent need to override the usual automated control systems and manually put the plane into a steep dive. In several cases this was followed by actions to avoid excessive speed that would threaten the structural integrity of the aircraft. Several accidents have another feature in common: they occurred along the edge of the North-Eastern American continental shelf. These include, among others, TW 800 on July 17, 1996, Swissair 111 on September 2, 1998, Egypt Air 990 on October 1999, and also the crash of J. F. Kennedy Jr. The case of the EgyptAir crash has recently come under public debate again as some new information has become known, and the explanation tentatively offered by the National Transportation Safety Board (NTSB), suggesting a suicide attempt by a co-pilot, has come under strong attack by Egyptian authorities, and does not fit with the new information.
In view of the statistically quite improbable occurrence of these accidents, it seems prudent now to widen the search to causes that have so far not been included among possible aircraft hazards, and that have possibly a relationship to geographical features. Among such, the massive emission of gases from the seafloor (or land surface) seems to us most worthy of attention.
Massive sudden eruptions of gases have occurred in many locations, bursting up through the ground both from ocean floors and from dry land. They often occur repetitively in the same area, and on land create what is known as "mud volcanoes". The amounts of expelled material accumulated in some mud volcanoes in the last million years are as large as 10 or 20 billion tons, and the estimates of the amounts of gas responsible are several times larger than that. The erupting gases are usually dominated by methane. Since methane is lighter than air, it races upwards at high speed. Many cases are known where the gas spontaneously ignited, and flames to a height of 6,000 ft have been photographed from Baku, in the active mud volcano area on the West shore of the Caspian Sea. Much higher brief flashes have been reported, up to 30,000 ft but these were too brief to be photographed. Massive flammable gas eruptions at or near times of earthquakes (before, during or after) are reported in historical and in recent times from many parts of the world.
Similar eruptions are indicated on the sea floors, where large areas are densely covered with "pockmarks", quite characteristic circular features in the ocean mud, with diameters of between 10 and 200 meters. These features were first detected in the North Sea by Dr. Martin Hovland, of Statoil, (the Norwegian oil company), overlying known gas and oil fields. Similar fields have since been detected in many parts of the world by sonar, again often showing a relation to underlying hydrocarbon fields, and also there showing features of repetition of outbursts, with methane again the major component. Both in mud volcanoes and in pockmark fields the emitted quantities of gas in any single event may well amount to some millions of tons.
Another set of observations has now to be added: it is the occurrence of "mystery clouds" in the air. Satellite photography over a ten year period revealed more than two hundred clouds that rose up at a high speed from a small area of land or sea, forming an expanding funnel. Temperature observations showed a much lower temperature in the funnel cloud than in the outside air at the same height, and this implied that the rising gas must be one that is intrinsically much lighter than air. Only methane and hydrogen are candidates, and both are combustible. The largest such cloud on record was seen and reported by several airline pilots flying between Tokyo and Alaska, North-East of Japan, on April 9, 1984. They described it as a mushroom cloud that reached up to 50,000 ft, attaining a diameter of more than 200 miles.
Evidence of massive gas emissions have recently been reported by the Woods Hole Oceanographic Institute, who conducted a sonar survey of the mid-Atlantic US continental shelf edge. Along a major fault line they found many and very large pockmarks, similar to those described by Dr. Hovland, indicating that sudden almost explosive gas eruptions had taken place there. Also recent reports from the Province of Quebec, of frequent and large displays of lights in the sky, clearly related to the swarm of earthquakes between November 1988 and end of January 1989 in the region of Sanguenay and Quebec City, leave little doubt that massive gas eruptions occurred there, with some flames reaching high into the sky. Altogether 46 such sightings were recorded in that period, some but not all coincident with earthquake shocks. Earthquake-related lights have been well known and reported since antiquity, and indeed one very large event involving gas flames was reported in 1663, not far from the Sanguenay region, close to the St.Lawrence River.
I had investigated in 1982 a "near disaster" of a British Airways 747 plane flying at 37,000 ft over a volcanic region of Java. All four engines stopped shortly after it had entered a visible but tenuous volcanic cloud. After gliding down to 15,000 ft without power, and there apparently leaving the cloud, all engines could be started again immediately. The same sequence of events was experienced two weeks later by an Air Singapore 747 plane over a nearby region, and many years later by a KLM flight over the Aleutian Islands. A gas lighter than air, and hence combustible, must have been responsible in all three cases, to have carried small volcanic dust grains to these altitudes, and its combustion may have been responsible for the engine failures that were so sharply limited to the flight within the cloud, probably due to the fuel- rich and oxygen poor mixtures of the gas adding to the airplane fuel. Gas eruptions of volcanoes are known of either kind: eruptions of a ground-hugging heavy gas identified as carbon dioxide, but also eruptions of a light and flammable gas, probably methane, whose density is a little more than half that of air.
With three large planes having come so close to disaster, but yet able to give a precise account of the events, one has to take the threat of gas emission seriously. The belief that such emissions can come only from volcanoes has been voiced, but is clearly wrong in view of the facts already mentioned. What threats would massive gas emissions pose for aircraft?
One effect I have already described: the possibility of inducing failure of all engines. But several other aircraft hazards have also to be considered. One is due to the great upward speed the light gases would have, greatly in excess of the vertical speeds in ordinary atmospheric turbulence, and structural damage to the plane or serious injuries to persons may result from the ensuing violent vertical movement. The ignition and explosion of a large mass of gas external to the plane may be initiated by the engine exhausts and may be violently destructive, yet the recovered airplane skin would not show the shrapnel holes that would be the usual signs of explosions.
Other consequences of gas emissions are the dangerous and misleading indications that the flight instruments would provide. Air speed indicators and air pressure altimeters would give quite false and fluctuating readings. The autopilots, programmed for air, may have totally erroneous responses in the light gas, as indeed may the pilots themselves, who would be perplexed by a situation they had never encountered or contemplated before.
A further hazard is that clouds of low density gas may not support a plane, even at a flying speed that would be amply high enough in air. This would cause a stall of the aircraft, or be preceded by automatic stall-warning that requires the pilot to turn the nose down into a dive, and then confront the danger of excessive speed.
Then there are the various fire hazards resulting from combustible air-gas mixtures, especially in some confined spaces in the airplane where flames could be supported, even if the same gas-air mixture would readily be extinguished in the external high speed airflow. That danger may be highest in cable ducts where damage could destroy the airplane control system.
The North-Eastern coastline or edge of the continental shelf of the US and Canada, is the northward continuation of the line whose investigation I have already mentioned. This extension also has a history of earthquakes and gas emission from sand beaches and water surfaces beyond the shoreline. Such emissions had not ceased around the times of the aircraft disasters. A large number of reports were phoned in to police and emergency services in New Brunswick and Nova Scotia on October 27, about three days before the Egypt Air crash, stating that at 9:30 p.m. a large fireball had been seen streaking across the night sky. The details reported did not correspond to a meteorite, but included reports of flames and events much slower than those caused by meteors. A peak in the number of reports recorded prior to an event must be taken seriously, if the number greatly exceeds the number on other days, as was the case here. There were similar reports also before and after the TW 800 crash. There was also a report from Swiss Air 111 of a strange smell about three minutes before the declaration of emergency. This is particularly suggestive of gas effects, as a similar report was made in one of the near accidents over Java, where gas certainly was involved.
We may then wish to investigate whether some features of aircraft disasters along this region, the four disasters mentioned and several others that have also occurred along this corridor, could have an explanation in terms of the list of hazards I have mentioned, or others that have not yet been considered, that could be attributed to gas eruptions.
Mr. Jack Reed retired from the Sandia National Laboratory, an expert in sound propagation, has noted that the "loud" boom heard by many eye witnesses at the time of the TW 800 crash on a 25 mile stretch of Long Island, nearest point to the plane 15 miles away, was far too loud to have been caused by the proposed explosion of the empty central fuel tank. In his view a one ton bomb of TNT would have been the least required to make such a sound at that distance. Nor would such an explosion have caused the various external luminous phenomena that have been reported by many. Also it is doubtful that an explosion of such a small amount of fuel vapor could have had the power to tear off the entire front section of the fuselage. The absence of shrapnel holes in the recovered skin of TW 800 was taken to exclude a bomb explosion inside or outside the plane. However, a massive external gas explosion would produce no shrapnel.
The facts newly announced about the EgyptAir disaster make clear that a deliberate dive had seemed imperative to the pilot then at the controls, and that a dangerous overspeed situation had then arisen. After a brief recovery to level flight, again a dive seemed imperative, and the overspeed may then have destroyed the plane.
There are many steps that can be taken to find whether the sequence of disasters along this heavily traveled corridor may be due to gas emissions. As an immediate step I urge the continuation of the sonar search for pockmarks on the ocean floor along this coastline in the regions of the four disasters mentioned and others that occurred near this geographical line, since this will have a good chance of showing whether these accidents were indeed over locations at which strong gas outbursts had occurred. A routing change may then be indicated as the first step to avoid further disasters.
Ithaca NY 14853-6801
Recharging of oil and gas fields
There have been numerous reports in recent times, of oil and gas fields not running out at the expected time, but instead showing a higher content of hydrocarbons after they had already produced more than the initially estimated amount. This has been seen in the Middle East, in the deep gas wells of Oklahoma, on the Gulf of Mexico coast, and in other places. It is this apparent refilling during production that has been responsible for the series of gross underestimate of reserves that have been published time and again, the most memorable being the one in the early seventies that firmly predicted the end of oil and gas globally by 1987, a prediction which produced an energy crisis and with that a huge shift in the wealth of nations. Refilling is an item of the greatest economic significance, and also a key to understanding what the sources of all this petroleum had been. It is also of practical engineering importance, since we may be able to exercise some control over the refilling process.
The debate about the origin of all the petroleum on Earth lies in the center of the subject. If we really knew that it is only biological materials, which, in their decay, could produce hydrocarbons, then the quanities that could ever be produced would be limited by the biological content of the sediments. But then the clear and strong association of petroleum with the inert gas helium would have no explanation; the finding of hydrocarbon gases, liquids and solids on most other planetary bodies in our solar system which have surface conditions quite unsuitable for surface life, could not be understood; the presence of hydrocarbons which we now find in abundance in basement rocks would also remained unexplained.
If we accept the fact, now known full well, that hydrocarbons are a common constituent of the cosmos and the planetary condensations that formed in it, then we have a totally different viewpoint. Hydrocarbons are stable down to great depths and the high temperatures there, contrary to many statements that have been made that the temperature reached at depths between 30,000 and 40,000 ft would dissociate most of the hydrocarbons. But these calculations are seriously in error, because they ignored the strong stabilizing effect of pressure at depth, that had been calculated by Soviet (Ukrainian and Russian) thermodynamicists.
The existence of diamonds, crystals of pure carbon that form at pressures which are not reached on earth at depths of less than 140 kilometers, proves that unoxidized carbon exists at such depths, and also carbon-bearing liquids must flow there that can deposit carbon at high purity. High pressure fluid inclusions in diamonds prove that liquid or gaseous hydrocarbons were present at their formation. Present day meteorites give us examples of the solids responsible for the building up of the Earth; among those only one class, the carbonaceous chondrites, contain much carbon, mostly in unoxidized form. That this material is present in the Earth's interior in large abundance is shown by the distribution of noble gases and their isotopes that have emerged into our atmosphere and show distributions that are strikingly similar to those in carbonaceous chondrites, but dissimilar to those of any other class of meteorites. The presence of this type of material would account for a continuous supply of hydrocarbons to the atmosphere, as the outer layers of the mantle heat up over time and make fluids form from the solid hydrocarbons that were included in the forming Earth (as also in most of the other planets and their satellites, in the asteroids, comets and interplanetary dust grains). Such fluids are less dense than the rocks, and buoyancy forces will propel them upwards.
Rocks and lower density fluids can co-exist at any level in a solid planetary body, provided that the pressure of the pore fluids is sufficiently high to make the differential pressure between rocks and fluids less than the crushing strength of the rocks. For a static case (with no upward flow of the fluid), this would result in pressure domains, within which the fluid pressure shows a pressure gradient with depth given just by the density of the fluid (the "head"), and where the bottom of each domain is at the level at which the fluid pressure is insufficient to maintain pore spaces against the higher pressure of the rock. (See Figure 1.) It is assumed here (for the static case) that this makes a complete barrier. As for the top of any domain, this cannot be at a level higher than that at which the fluid pressure equals the rock pressure, since fluid pressures in excess of this value cannot be maintained in rocks that on a large scale and in long time-intervals, have no tensile strength and therefore cannot resist the intrusion of the fluids and the generation of new pores.
If we consider the case of a slow upward migration of fluids (liquids or gases), then this picture changes to one in which each domain
Idealized stacked pore pressure domains that make up a stepwise approximation to the rock pressure.
Pc is the critical pressure at which the pore fluid pressure cannot support the rock against crushing.
will be stacked on another one below, all the way down to the level of origin of the fluid. The fluid pressure would thus make a stepwise approximation to the pressure in the rocks. Now none of the barriers can be absolute, since they would be torn open by the fluids that arise from deeper and higher pressured domains. But the barriers would be torn open in each case only to the point at which the flow to the overlying domain causes it to suffer a pressure drop resembling that of the static case. This rule will apply whatever the nature of the rock. The heights of the domains will be determined by the rock and fluid densities and the crushing strength of the rocks; this height has been found to be between 10,000 ft and 15,000 ft in many sedimentary rocks, and in excess of 20,000 ft in granitic basement rocks. The upward seepage of methane is very widespread all over the Earth, as is shown by the great extent of methane hydrates on the ocean floors and in permafrost regions on land, where mostly no shallow source of methane can be invoked.
Vertically stacked domains of hydrocarbons have been found in all cases where drilling was sufficient to display them. The consistent tendency to find hydrocarbons below any producing region has been given the name of "Koudyavtsev's Rule", after the important Russian petroleum investigator who discovered this effect and collected a very large number of examples of it from all parts of the world. This rule would be the consequence of a deep origin of hydrocarbons and a steady process of outgassing.
With this picture in mind we would readily understand that refilling of hydrocarbon fields is possible and even probable. But if merely the steady upward flow from deep sources had been responsible, the refilling time scales would be much too slow to be of commercial interest, or to match the speed that appears to have been observed. A limit to the global average of that flow speed can be derived from the approximately known supply of carbon to the atmosphere over time. On that basis a large gas field may be recharging in times reckoned in tens of thousands of years, still very short compared with many millions of years, as had been the widespread belief. But observed refill times of just a few tens of years cannot be explained by this. However another effect will set in when a field is under production and the pressure in its domain is thereby diminished. The pressure difference between the producing domain and the one below it will then be increased, resulting in a higher rate of flow through the low permeability layer that divides these domains, or it may even result in a physical rupture of that layer.
There is an analogous case known in Kuwait. The extraction of goundwater at the shallow levels results in the disintegration of the barrier to the oil levels just below, and the water in the wells is suddenly replaced by oil. The delicate pressure balance that had established itself, just up to the level that the strength of the rock could bear, had been upset. Similarly in stacked domains of hydrocarbons, the lower domains will be opened quickly, once the upper ones had been depleted and the fluid pressure thereby reduced sufficiently. This process can be fast, just as it is in Kuwait, where we had the advantage that a different liquid (water) filled the upper domain, so that one could identify the rupture to the oil filled domain below.
This type of refilling process thus allows exploitation of the domain below that from which production had been obtained before. In turn, when this lower domain had suffered a sufficient pressure loss, the process may continue to the next lower domain. How much more than the original content of a hydrocarbon field can be produced in any one case will depend on numerous details of the formation, but present indications are that it is often at least double. The present global gas and oil glut appears to be due to this effect, and we have not yet seen the end of it, or any indication that it will end soon. Gas fields will be subject to faster refilling than oil fields, and moreover the volumes of gas in lower domains will in general be greater due to the higher pressures there and the higher compressibility of gas. Gas will thus become more plentiful than oil for this reason alone, but gas seems to be generally more plentiful and more widespread than oil. The environmental advantages of changing from coal or oil to gas, by far the cleanest of all combustible fuels, are very large, and the changeover is at present still handicapped by the mistaken belief that the supplies of gas will run out soon.
Thomas Gold (1920 – 2004)
Freeman Dyson on Tommy Gold, hearing mechanism,
and abiogenic oil (video)
Thomas Gold (1920 -2004)
Professor Emeritus of Astronomy at Cornell University;
founder and for 20 years director of Cornell Center for Radiophysics and Space Research.
Fellow, Royal Society (London)
Member, National Academy of Sciences (US)
Member, American Academy of Arts and Sciences
Member, American Philosophical Society
Fellow, American Geophysical Union
Honorary Fellow, Trinity College, Cambridge
Gold Medal, Royal Astronomical Society (UK)
Doctor of Science, Cambridge University
Honorary M.A. Harvard University
John L. Wetherill Professor of Astronomy, Cornell University; Chairman, Department of Astronomy
Assistant Vice President for Research, Cornell University
Robert Wheeler Willson Professor of Applied Astronomy, Harvard University
Chief Assistant to British Astronomer Royal
Lecturer in advanced physics, Cambridge University
Radar development work, British Admiralty during World War II
280 publications in various fields of science, including cosmology, mechanism of mammalian hearing, nature of pulsars as rotating neutron stars, aspects of solar system research, origin of planetary hydrocarbons. For 7 years a member of the President's Space Science Panel (US).