Evidence for chemical evolution

The recent discoveries of complex organic molecules associated with interstellar dust clouds have, of course, attracted great interest among students of chemical evolution. Inspection of Table IV will reveal several compounds which have been referred to with regard to the syntheses of biologically significant compounds HCN, formaldehyde and cyanoacetylene. It is perhaps unlikely that the processes which have produced these com- 

The organic material in carbonaceous chondrites is of more direct interest with regard to the problem of the origin of life on the Earth, not only because of the possible participation of similar material in the formation of the Earth, but because of the possibility that the mechanisms of formation of terrestrial and meteoritic organic compounds may be related. It has been suggested by Anders et al. (1974) that many of the organic compounds in meteorites may have been formed by Fischer—Tropsch-type reactions. There is reasonable agreement, for example, between certain hydrocarbon isomers 

Fischer Tropsch-type reactions have also been reported to synthesize 

Partial list of amino acids in the Murchison meteorite and formed in electric discharge and Fischer—Tropsch type experiments 

It is noteworthy that a portion of the amino acids, and many of the purines are only identifiable after acid extraction or hydrolysis. It is therefore unlikely that they exist in the free form. A polymeric precursor has been suggested for the purines (Hayatsu et al., 1975). It is interesting that HCN oligomerization leads to the formation of all of the purines which have been identified in carbonaceous chondrites. Although HCN may have played a role in the formation of some of the organic compounds in meteorites, it is unlikely that any one mechanism can account for all of the products of these remarkably complex and interesting samples of primitive material. 

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The signamres of long-lived radioactive isotope decay schemes provide some of the most unequivocal evidence for chemical evolution of the mantle. Excellent reviews of the application... 

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