l68 ABIOGENIC ORGANIC-CHEMICAL EVOLUTION 



low temperatures, but yield hydrocarbons when heated to 

 temperatures such as might easily be reached in the litho- 

 sphere. Under these conditions the formation of hydro- 

 carbons could also take place by the direct reduction of 

 carbides by hydrogen. 



Even now hydrogen is given off by the lithosphere in 

 considerable amounts ; it is an important constituent of 

 inflammable volcanic gases. ^^^ Of course, the hydrogen given 

 off now may be partly of secondary origin, arising as the result 

 of the breakdown of biogenic substances. Its formation by 

 inorganic means is, however, by no means excluded. G. 

 Stadnikov,®* for example, put forward the possibility that 

 hydrogen might be formed thermally in the interior of the 

 Earth by the action of water vapour on red-hot solutions of 

 carbides in ferromanganese. A. Gaedicke®^ invoked the action 

 of the a-particles of the radioactive elements on the water of 

 the deep geological formations 



(n + i)h20 — >2(n + i)h + (n+i)o 



The hydrogen arising from this reaction might escape 

 directly into the atmosphere or might form hydrocarbons 

 by reacting with carbon (e.g. with graphite) according to 

 the equation: 



nc + 2{n+ i)h >c„H(2„^,) 



Under the strongly reducing conditions which were present 

 on the primaeval Earth the opportunities for the formation 

 of free hydrogen must have been far greater than they are 

 now. 



S. C. Schuman®® has calculated the equilibrium constants 

 for the reactions : 



FeoC + (2/2 - i)H2 + {n - l)cO >C„H2„ -f 2Fe + {u - i)H20 



Fe2C + 2«H2 + {n - l)C0 ^C„H(2„+2) + 2Fe + {u - i)H20 



The results of these calculations showed that the forma- 

 tion of hydrocarbons from iron carbide by direct reduction 

 is perfectly possible thermodynamically, at temperatures of 

 250° - 350° C, that is to say, under conditions which may 

 easily obtain in the lithosphere. 



The hydrocarbons which appeared during the formation 



