ORIGIN OF LIFE OX THE SHORES OF THE OCEAN 99 



Now, with these considerations one can proceed to build a 

 picture of the world without Hfe which would lead rationally on 

 to the occurrence of living processes. First of all, however, I should 

 say something to modify previous views of my own and of others 

 as to the dates of these stages. In Table I the stages are just put 

 in logical order, and they are not attached to any particular dates 

 but I have in the past imagined that the closing dates, so to speak, 

 of number seven, the first definite organism, must be well before 

 the base of the Cambrian, and indeed well before the appearance 

 of anything that could be called a fossil in the pre-Cambrian. Let 

 us take, therefore, a final date of about one billion years before 

 now. If we consider the time required for the very complicated 

 organic processes in the early stages of life and remember, further, 

 that the evolution of life all the time we have known it has been 

 going on at an accelerated pace, we must imagine that the early 

 stages took a very long time. I had given them another billion 

 years, placing the origin of life, let us say, between two and three 

 billion years ago. I have now come to the conclusion that the 

 origin of life may be considerably earlier. It may even antedate 

 any of the rocks that we have on the surface of the earth today, 

 even in the most ancient parts of the Archean, that is, dates of 

 the order of three to three and a half billion years. I base this idea 

 on the observations of the geochemists who have shown that 

 fundamental types of rock, such as granites and gneisses of the 

 oldest shields, have been formed from clay rocks derived from the 

 detritus of earlier rocks. It is something of a puzzle that we do 

 not see on the surface of the earth any rocks older than three 

 billion years. To explain this I have formed a theory, which is 

 much reinforced by the evidence brought forward at this congress, 

 on the nature of the mid-oceanic ridges and the great lineations 

 in the Pacific. My belief is that what we observe in the earth's 

 crust may be only the later stages of a process of what might be 

 called revolutionary movement in the crust, in which new crust is 

 formed in the centers of oceans and is gradually pushed over to 

 create new continents and then is pushed under again and de- 

 stroyed (Bernal, 1959; Blackett, 1960). The motive force for such 

 vast changes I find in subcrustal convection currents. 



