The origins of the atmospheric oxygen of the earth are a global problem attracting natural scientists of all levels, from astrophysicists to microbiologists. Yet a key to the solution of this problem was found by the earth sciences on the basis of geological data.

According to Drs. V. Molchanov and V. Parayev of the Joint Institute of Geology, Geophysics and Mineralogy (Siberian Branch of the Russian Academy of Sciences), this problem has been conceptualized by three outstanding scientists of our country, Academicians V. Vernadsky, A. Vinogradov and A. Trofimuk. Academician Vernadsky has detected a dependence between the genesis of atmospheric oxygen and fossil organic deposits. Academician Vinogradov has proved that atmospheric oxygen, the product of photosynthesis, is that of water, not of carbon dioxide. And Academician A. Trofimuk has advanced a hypothesis on the carbon-hydrogen envelope of the stratosphere as the primary source of the globe's oil and gas deposits.

The sustainable development of the earth as an integral system is ensured by geobiological processes of different scale occurring in the atmosphere, biosphere, hydrosphere and lithosphere. These are the strata where various exogenic transformations are taking place, largely under the effect of solar energy. The atmo-, hydro- and lithosphere interact through material exchange which is effected via biosphere in the process of photosynthesis whereby solar energy is assimilated. The accumulation and expenditure of this energy always involves hydrogen, oxygen and carbon.

Photosynthetic processes in the biosphere concur with the consumption of water of the hydrosphere and carbon dioxide of the atmosphere. Organic residues are buried in the lithosphere, while biogenic oxygen is released into the atmosphere. These are synchronous processes within a single chain of interdependent events in the form of the material interchange of the above-named geospheres.

Free oxygen may be redundant if a certain amount of organic matter synthesized in the process of photosynthesis is withdrawn from circulation and deposited in the lithosphere. Consequently, the mass of atmospheric oxygen is proportional to the mass of organic fossils contained in sedimentary rock. Biospheric products are buried in the bowels of the lithosphere on such a significant scale that we may speak of an independent carbon-hydrogen envelope taking body and form in the stratosphere.

The gist of V. Molchanov's and V. Parayev's article is that atmospheric oxygen is equivalent to hydrogen buried in the lithosphere within organic fossils. Therefore the mass of oxygen released through photosynthesis should be calculated from the mass of hydrogen within the buried (fossilized) residues, but not from the mass of organic carbon.

The earlier attempts to compute the formative dynamics of the oxygen atmosphere (using a simplified photosynthetic reaction) proceeded from the following correlation: one atom of organic carbon within sedimentary rock caused two atoms of

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oxygen to escape into the atmosphere, that is in the ratio 12:32, or 3:8. But the mass of buried hydrogen is computed otherwise: each carbon atom in the lithosphere captures two hydrogen atoms to cause a release of only one atom of oxygen (12:16, or 3:4).

The formula used previously for computing photosynthesis from the buried carbon (simplified by one water molecule) led to a systematic error whereby the mass of free oxygen released is doubled; but we cannot strike a balance this way. Besides, there is yet another error made here, that of chemical and genetic origin: oxygen released during photosynthesis is generated from water, it is not a product of carbon dioxide reduction. Such kind of computation errs against physics and chemistry too, for solar light knocks out electrons, i.e. it is an oxidizing, not a reducing, agent of carbon dioxide. And last, a geo-chemical error. It is common knowledge that atmospheric oxygen is more rich in the heavy isotope than the oxygen of the hydrosphere (even though the oxygen of the air is the same thing as the oxygen of water). The computation formula (with a water molecule doubled) can explain the fractionation of isotopes. Biogenic water in the photosynthetic reaction is formed when most of the light isotopes of oxygen are consumed, while the heavy isotopes are ejected into the atmosphere.

The authors of the publication under review (V. Molchanov and V. Parayev) say it is absolutely impermissible from the standpoint of natural sciences to simplify the photosynthesis computation formula (though this is quite legitimate by the rules of arithmetic). Atmospheric oxygen evolves into an agent all-important for sedimentation genesis. In lithogenesis it is expended on the oxidation of mineral substances, above all iron monoxide and sulfide sulfur (we leave aside other substances for the time being). Knowing the total mass of sedimentary, volcanogenic and sulfate rocks making up the sedimentary shell of the earth, we can calculate how much of the oxygen has been consumed for the oxidation of mineral substances in a particular geological period.

To strike a balance of the interaction of external geospheres we should calculate: the mass of oxygen produced in the course of photosynthesis (input); the mass of oxygen expended on the oxidation of mineral substances in lithogenesis (output); the "input- output" difference is what the atmosphere will be getting. Biogenic oxygen released through photosynthesis is capable of oxidizing mineral substances in the course of lithogenesis and, simultaneously, it can accumulate in the atmosphere to a present- day level.

The accumulation of oxygen in the atmosphere is not a uniform process. In the Phanerozoic history of the earth (the last 570-600 million years) we may identify seven formative stages of the oxygen atmosphere. Clearly distinct are the

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recurring ups and downs in the generation of oxygen, and correlating global changes of the natural environment, climate, biota, sedimentation genesis, sedimentary rock formation and tectonic activity.

The falls in the intensity of oxygen generation and periods of inhibited photosynthesis concur with the epochs of global glaciations and other cold spells in the Cambrian, the late Ordovician-Silurian, Devonian, Permo-Triassic and in the Paleogene. The epochs of global cold snaps have come to be described in the literature as "winters of our planet", or "global geological winter". The cold spells, with rather sparse plant life - were then followed by periods of prolific organic life and active generation of oxygen (in the Ordovician, from the Upper Devonian to the Permian, in the Jurassic and in the Cretaceous period). By analogy such warm spells may be described as a "global geological summer".

The global summer and winter seasons are about equal in time, 50 to 70 million years each. They are separated by rather short (12 to 22 mln years) transition periods of oxygen generation ("global autumn", "global spring").

Now, the "global winter" should not be compared to Siberian winters with their steadily negative temperatures on the Centigrade scale and snow cover. For instance, the "Cenozoic winter", known for a dramatic cooling of the climate and ice-bound continents, also had warm spells, the interglacial periods.

As to the "global geological summer", we may get a good idea from the "Mesozoic summer" which is the nearest to our time. The peak of its efflorescence concurs with the Cretaceous period. Characteristic of this global summer were peneplanation (base- leveling) of continents, an immense shallow ocean, and no polar caps at all. The mean annual temperature was in the +18 to 25 ⁰ C range, and the difference of temperatures of the ocean surface in

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the poles and in the equator was much lower than at present.

Favorable conditions were obtained for the biosphere which saw a lush period of growth. Thermo-philic (heat-loving) plants moved far to the northern latitudes, with tropical forests found as far north as the Gulf of Finland, and dinosaurs living even on Alaska.

The last 570-600 mln years of the history of the earth have seen variations in the intensity of oxygen generation. Photosynthetic activity has been changing in a cyclic pattern, a phenomenon obviously related to astrophysical processes. The total length of one such cycle (the winter-spring-summer-autumn sequence) is estimated at 170 million years. These cycles are in strict correlation with the breakdown of the Phanerozoic: the Paleozoic contains two such cycles, the Mesozoic - one, while the Cenozoic corresponds to the onset of yet another cycle. This cyclicity reflects a law governing all geological processes, both exogenic and endogenic ones (in fact, such cycles tally with the division of geological history into eras).

It is remarkable that the synthesis of the ideas of Academicians Vernadsky and Trofimuk about the liberation of free oxygen into the atmosphere during the formation of the carbon/hydrogen envelope is added proof of the genetic connection of oil generation with the biosphere, and it warrants a revision of theoretical priorities of oil geology. Fluctuations in the intensity of oxygen generation and in the rates of accumulation of organic residues make it possible to identify epochs of enhanced accumulation of hydrocarbons in the lithosphere-epochs which Academician Trofimuk, proceeding from empirical data, called floors of oil-and- gas presence; besides, it will be possible to pinpoint strata of probable localization of deposits and estimate their reserves.

In a similar way, the synthesis of Vernadsky's and Trofimuk's ideas helps solving the problems of cyclicity and periodicity in the evolution of sedimentation genesis and sedimentary ore formation. The point is that the seasonal fluctuations of sediments accumulation in the course of global geological year are responsible for the localization of oil and many other deposits of sedimentation genesis. Autumn is the time when phosphorus, uranium and associated elements are accumulated in consequence of the wholesale dying away of organisms in the biosphere. Winter is the time when salts are accumulated as a result of precipitation in frozen bodies of water. In spring bauxites are accumulated due to the leaching of alumina by cold CO ₂ rich waters. And in summer caustobioliths (coal, oil and gas) are built up.

The computed balance of interaction among exogenous geospheres allows to make a long-term forecast for the development of the climate on earth and attack the all-important problem of self-regulation of global processes. For instance, in keeping with the pattern of "global annual cyclicity", we are now at the end of the "Cenozoic winter", and will be moving into a "global spring".

Widely discussed in the mass media now is the problem of global warming attributed to what is called "the hothouse effect". Yet analysis of geological events in the Phanerozoic, Drs. Molchanov and Parayev say, shows that the mechanisms of self-regulation, as they have evolved by now, will prevent disastrous changes. While not discounting the "hothouse effect", we should recognize that long-term global climatic changes are determined above all by astrophysical factors. As an integral thermodynamic system the earth has protective mechanisms of self-regulation which can compensate both an impermissible concentration of carbon dioxide in the atmosphere and a significant rise in the ocean level during ice melting.

A rise in the partial pressure of carbon dioxide in the atmosphere is immediately offset by dissolution of C02 in the cold polar regions. One consequence of this process-dissolution of carbonates-is now observed in the destruction of the Great Barrier Reef washed by a cold stream from the Bering Strait.

An increase in the mass of water and, consequently, a rise of the level of the World Ocean owing to climatic warming will be offset by an increase in the biosphere mass. Warm conditions will cause the tropical vegetation area to expand as far north as the arctic circle.

As we know, the synthesis of glucose and cellulose involves an active consumption of water and carbon dioxide. Globally, the masses of the present-day biosphere and of the hydrosphere are quite compatible. This correlation will hold by and large. It has been estimated that a doubling of the mass of flora will be sufficient enough to bind both "redundant" water from thawing ice and "redundant" carbon dioxide. The protective mechanisms of self-regulation operate through the biosphere for the most part (biosphere being the most sensitive element of the system). That is why geobiological factors are largely responsible for the evolution of terrestrial matter and our planet.

Nauka v Sibiri (Science in Siberia), 2001

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