Conditions for Appearance of Life on Earth 91 



some of the clear light oils. Porphyrin enrichment is found especially in the 

 heavy, resinous, and sulphurous oils. According to available data, the same refers 

 to the dissolution in oil of admixture of organic matter of biogenic origin exhi- 

 biting optical rotation. 



In discussing the deposits of petroleum and combustible gases as the results 

 of ascension of hydrocarbons rising from the deep layers of the Earth's crust, 

 we would hke to emphasize that available facts agree with the hypothesis that 

 hydrocarbons are of inorganic origin, though not connected with magma. Dis- 

 integrating at high temperatures (especially when there is an acidic, i.e., granite 

 magma, comparatively richer in oxygen) in conditions when methane CH4 can 

 be spht off or oxidized, the petroleum hydrocarbons are preserved at a lower 

 temperature, in reducing conditions. This is in harmony with the fact that in 

 regions of the acidic or mediosilicic (andesitic) vulcanism, carbon compounds 

 in gases are represented chiefly by carbon dioxide CO2, and outside these regions 

 by CH4 (the Caucasus, the zones of mud-vulcanism, etc.). 



These conclusions about the abyssal but magma-independent origin of 

 petroleum and gas are in agreement with the modern conceptions of deep faults, 

 of the solid state of the Earth's mantle and the formation of the planet from cold 

 cosmic dust and gas (the hypotheses of O. Yu. Shmidt, H. Urey and others [36, 

 37]). Judging by the relative abtmdance of hydrocarbons in the cosmos, there was 

 a sufficient amount of these compounds in the original gas-and-dust nebula from 

 which the Earth and other planets of the solar system have arisen. The idea of 

 primary (cosmic) origin of petroleum hydrocarbons was first put forward by 

 V. Sokolov [38]. 



THE BIOGENIC (ORGANIC) THEORY 



OF ORIGIN OF PETROLEUM. 



CHANGES IN THE COMPOSITION OF 



ORGANIC MATTER IN THE EARTH'S CRUST 



Although the number of facts in favour of the inorganic origin of petroleum 

 increases every year, most specialists still adhere to the biogenic conception of 

 its origin (see, for instance, the review [39]). Different variations of the organic 

 theory can be divided into two groups. One trend proceeds from the idea that 

 petroleum hydrocarbons were formed imder the 'least severe' pressure and 

 temperature conditions, i.e. under conditions which exist in sediments imme- 

 diately after their deposition in a water basin or at the early stages of their 

 genesis [40, 41]. From this point of view it proves impossible to explain the 

 secondary nature of the petroleimi occurrence in most of the petroleum beds, 

 and the absence, outside the ou fields, of any signs of petroleum in sedimentary 

 rocks; in other respects these rocks may have exactly the same lithological 

 composition and geological age as those developed in the oil-field districts, or 

 may even be richer in biogenic organic matter, in comparison with them. 

 Discoveries of oil in the crystaUine basement mentioned here also exclude 

 the possibility of the origin of petroleum according to this scheme. 



