10 The Nature of Biological Diversity 



tissues were secured. They were not optically active and a number of 

 unidentified substances were produced. 



These experiments were repeated and extended by others, notably 

 by Abelson (1957) in this country. Also the more difficult experiments 

 using ultraviolet light have been done and very similar results ob- 

 tained. Abelson's experiment showed that various mixtures always gave 

 amino acids if the mixture was reducing, i.e., if excess hydrogen was 

 present in amounts over that required to form water, and that amino 

 acids were not produced if the mixture was on the oxidizing side, i.e., 

 if free oxygen or its equivalent was present. We can conclude that it 

 is most improbable that life would appear in an oxidizing atmosphere. 

 In particular, if all life were destroyed on earth, the oxygen of the 

 atmosphere would probably disappear by combining with carbona- 

 ceous compounds. The amount of reduced carbon in living organisms 

 and in soils is very small but the great deposits of shales contain some 

 10 or 12 times as much carbon as could be oxidized by atmospheric 

 oxygen. This would be brought only very slowly into contact with 

 atmospheric oxygen, and hence the atmosphere would probably re- 

 main somewhat oxidizing. Life would probably never evolve again 

 on this planet if it were completely destroyed. Also, if a planet evolved 

 into the oxidized state before well-organized life had appeared, it is 

 probable that no life would evolve on that planet. 



Miller's experiments and those of others who have extended this 

 work carry us only a very small way along the long and involved road 

 to the origin of well-organized life. There are many elementary 

 problems which might be mentioned at this point, but possibly one 

 of the most puzzling and also most essential is the introduction of 

 phosphate into effective organic compounds. All inorganic phosphorus 

 compounds are highly unstable except the phosphates, and the cal- 

 cium, magnesium, and ferrous phosphates are highly insoluble in 

 water (see Table 1). These are mentioned particularly because cal- 

 cium and magnesium are present in water solution, i.e., in the oceans, 

 as bicarbonates and hence phosphates would be precipitated. In the 

 absence of elementary oxygen, ferrous iron would also be present. 

 Probably organic compounds of some kind which are able to hold 

 phosphate in solution existed in the primitive oceans. 



In general, living organisms are excellent chemists and they have 

 found routes for metabolic process which are beautifully adapted to 

 their needs. The production of proteins, chlorophyll, enzymes, and 

 the intricate implicative systems are amazing triumphs of the most 

 skillful of chemists. The mind of man will be able to follow these to 

 some extent in the future. 



