TRANSFORMATION OF HYDROCARBONS 155 



and more complicated organic compounds on the surface of 

 the Earth when it was still devoid of life. But when one 

 proceeds beyond asserting in principle the possibility of 

 organic-chemical evolution, it is indeed a difficult task to 

 trace the actual paths along which such evolution proceeded 

 during that remote epoch when the Earth was uninhabited 

 by living organisms. 



At first sight it might seem that a simple and reliable 

 approach to solving this problem would be through geologi- 

 cal and, especially, geochemical study. One could observe, 

 under natural conditions, the changes which carbon com- 

 pounds today undergo on the surface of the Earth in the 

 absence of living matter, and make detailed chemical study 

 of these changes. Such investigations could, indeed, give 

 valuable results in the long run. However, it must be 

 remembered that the emergence of life and, especially, of 

 photosynthesis, has markedly changed all the conditions 

 which exist on the surface of the Earth. At the present time, 

 under natm^al conditions, we cannot directly observe many 

 of those phenomena which manifested themselves in the past. 

 Moreover, new processes have now appeared which were 

 absent from the surface of the Earth when it was devoid of 

 life. Consequently we should be wrong to apply, in a simple 

 and mechanical fashion, the data of contemporary geo- 

 chemistry to the remote early period of the existence of the 

 Earth. We cannot use these data as they stand but must 

 amend them by making free use of laboratory experiments 

 in the attempt to reproduce artificially the various conditions 

 which have been postulated as occurring on the primaeval 

 Earth. We must then investigate the transformation which 

 organic substances undergo when they are exposed to these 

 conditions. 



As was pointed out in the previous chapter, the picture of 

 the formation of the Earth which is at present favoured by 

 scientists is that it took place at comparatively low tempera- 

 tures, of the same order as those at present prevailing here. 

 Even from the earliest period of its existence, the Earth had 

 a firm surface, an aqueous envelope (the hydrosphere) and a 

 gaseous envelope (the atmosphere). The temperature of the 

 firm surface will have depended very much on the radio- 



