The Origin of Organic Molecules 3 



elements would necessarily be so vastly simpler in behavior that we 

 would not recognize it as such. 



The liquid in which all terrestrial life exists is water. It is intereM- 

 ing to inquire whether other liquids might be suitable. Only two seem 

 possible candidates, namely, ammonia and hydrocarbons. It is difficult 

 to imagine circumstances that would supply liquid ammonia to a 

 planet without water being present, but its chemical properties might 

 not rule it out. The hydrocarbons might be present on a planet but 

 the generally slow reactions occurring in hydrocarbon solvents look 

 less likely as substitutes for moderately lively reactions of living 

 things. 



Living organisms do grow in petroleum products, though these or- 

 ganisms are of the hydrophilic variety and depend for their energy 

 on the oxidation of petroleum by atmospheric oxygen. Free oxygen 

 should be nonexistent on a planet with excess hydrocarbon rather 

 than an excess of water. The sulfur deposits of the world have been 

 produced by the reduction of CaS0 4 by petroleum through the action 

 of bacteria, but again sulfate has been produced on earth by oxidation 

 due to free atmospheric oxygen. These arguments may not exclude the 

 possibility of life on a planet having excess hydrocarbon compounds 

 but no oxidizing atmosphere, and any conclusion to this effect may 

 only indicate a prejudice arising from our terrestrial experience. It 

 seems likely to the writer that only a water solvent could lead to any 

 reasonable approximation to compounds and chemical reactions of 

 sufficient complexity to be regarded as constituting a living organism. 



Primitive conditions on the earth 



Hydrogen is the most abundant element in the cosmos. In particular 

 the sun contains 80 per cent H 2 , and it can be confidently supposed 

 that the earth and other planets evolved from matter in which hydro- 

 gen was equally abundant initially. Also, carbon is reported to be 

 about equally as abundant as oxygen. The abundances of some of the 

 relevant elements in solar and terrestrial material are given in Table 1. 



It is evident that solar material is highly reducing, with about 1,100 

 times as many atoms of hydrogen as of oxygen, and that the relative 

 abundances of these elements are quite different in terrestrial matter 

 at the present time. Metcoritic matter is in general very reducing also, 

 i.e., it contains iron in the elementary and ferrous states. (However, 

 the carbonaceous chondrites contain carbon compounds which are 

 partially oxidized and also highly oxidized sulfur as magnesium sul- 



