SOURCES OF ENERGY l73 



arisen secondarily and have been laid down in the crust of 

 the Earth as a result of the activities of living organisms. 

 At present ^\e can see in many places the transformation of 

 secondary organic compounds in the lithosphere. A particu- 

 lar example of this is the formation of petroleum. In this, 

 the organic remains of animals and plants which have been 

 heated in the depths of the crust of the Earth undergo re- 

 actions involving the breakdown of those large, complicated 

 molecules, rich in oxygen and nitrogen, which have previ- 

 ously been synthesised by living things. On the whole these 

 phenomena are proceeding in the opposite direction from 

 the reactions which have been described above. Compounds 

 of high molecular weight are broken down and new ones 

 are formed in place of them. Compounds containing oxygen, 

 nitrogen, phosphorus and sulphur are almost completely 

 decomposed, their hydrogen content is inCTeased and new 

 cyclic and polycyclic hydrocarbons, etc., emerge.^* It is only 

 on rare and isolated occasions that these phenomena of the 

 degradation of pre-formed organic substances can be used 

 directly to form an estimate of the primitive synthetic pro- 

 cesses which occurred on the Earth before the appearance 

 of life. 



A study of the formation of petroleum and, in particular, 

 of that of natural gas can, however, make a great contribution 

 towards the solution of the problem before us. It shows that 

 the results which are obtained under artificial conditions 

 in the laboratory are completely confirmed in nature. This 

 applies both to the influence of temperature and pressure on 

 the complicated processes of transformation of organic sub- 

 stances in the crust of the Earth, and also to the effects of 

 various artificial and natural catalysts on these processes. 

 The remarkable geochemical ideas on this subject put 

 forward by N. Zelinskii"' on the basis of his laboratory 

 experiments have been completely confirmed by the investi- 

 gations of the formation of petroleum by many scientists in 

 Russia and other countries.^" According to S. N. Obryad- 

 chikov" and A. V. Frost, *^ petroleum is formed at compara- 

 tively low temperatures, about ioo-300°C. V. Porfir'ev,*^ 

 on the other hand, suggests the figure of 500° C. Even higher 

 temperatures may certainly be encountered in different zones 



