EVOLUTION OP' LIFE ON THE EARTH 9 



happened in a billion or half a billion years! A thousand 

 years may be an enormous span of time in human history, 

 but in the history of the earth it is infinitesimal. It is not 

 unreasonable to assume then that all the plants and animals 

 of the earth have developed from one or a few very simple 

 forms of life. Within several hundred millions of years, 

 evolution might have passed through the whole range of 

 the development of the vertebrate animals from fish to men 

 (Fig. 3 see following pages). 



In bare outline we can thus grasp the essence of the well- 

 known theory of evolution. But it is extremely difficult 

 to investigate the causes of all the amazing variations of 

 life. The real problem is to determine by what mechanism 

 this great evolution came about. More important still, 

 how did life originate on the earth? Originally the surface 

 of the earth was red hot and could have borne nothing but 

 inert lifeless matter. How did life arise from it after it 

 cooled? 



There was probably some sort of development, perhaps 

 extending over millions of years before life appeared. We 

 may assume that the first primitive forms of life must have 

 arisen from non-living matter, although they did not persist. 

 Others may have been formed and vanished, until finally 

 those creatures arose which were sturdier, capable of re- 

 producing themselves and of developing themselves to 

 organisms of ever-increasing complexity. The development 

 in the very first period would be the most important part of 

 the history of life. Is there no way of finding out anything 

 about it? 



Something can be gained if we investigate how, in a life- 

 less world, lifelike processes might have started before the 

 beginning of life proper. Another point worth studying is 

 the power of lifeless matter to organize itself. Thus links 

 between non-living matter and life can perhaps be found. 



