The Origin of Life and Photosynthesis 103 



ultra-violet rays, as well as high speed particles (ionizing radiations), 

 which may well have been much more intense in the past than now. 

 These radiations are capable of breaking hydrocarbon molecules 

 into fragments called radicals, which can react with each other and 

 build up into long chain compounds. In the presence of ammonia a 

 great variety of nitrogenous compounds could also be formed in this 

 way. Experiments have been made by Miller in an attempt to repro- 

 duce these circumstances. A mixture of water vapour, carbon dioxide 

 and ammonia was exposed to electric discharges and it was found 

 that a variety of compounds including amino acids was formed. If 

 amino acids are formed in a concentrated condition, the effect of fur- 

 ther irradiation may well be to cause them to combine into long pep- 

 tide chains such as occur in proteins. This type of condensation can 

 be effected artificially. It involves (see p. 17) the elimination of water 

 molecules. The water can easily be removed from amino acids, 

 yielding compounds called amino acid anhydrides. Woodward and 

 Schramm have shown that these anhydrides hnk up spontaneously 

 into peptide chains. 



It is of course a long way from this to the exactly organized struc- 

 tures of the natural proteins and we do now know how this gap could 

 be bridged. But it no doubt would help a great deal if we could sup- 

 pose that at an early stage in the earth's history a surface layer rich 

 in carbon compounds were present. Certainly under such conditions 

 very complex compounds could be formed by the action of solar 

 radiation. Not only could we expect complicated hydrocarbons and 

 organic nitrogen compounds to be formed, but phosphorus too could 

 become activated and attached to organic residues and it might well 

 be that, out of the myriad possible combinations, eventually a simple 

 self-reproducing system would be formed, which would increase its 

 amount by making use of the organic material around it and would 

 thus impose its own pattern on the organic environment. 



We have no idea what this primitive self-reproducing system was 

 like or of its transformation towards living structures as we know 

 them. The living cell as we know it is the end of an enormous series 

 of developments, not the beginning. Life itself has entirely destroyed 

 the primitive environment from which it arose and all the inter- 

 mediate steps. The only possible and likely relic from this stage of the 

 evolution of life might be some of the petroleum deposits — but these 

 again are in sedimentary rocks and may have been formed by living 

 things at a much later date. 



(3) Steps leading to the creation of life from inorganic materials are 

 still going on in the present world, either in some unsuspected place 

 or on such a small scale that they have not been recognized. We can 



H 



