The Problem of Stages in Biopoesis 33 



made in accordance with these major conditions by considering first the essential 

 reactions on an atomic or micromolecular scale in their thermodynamic and 

 kinetic aspects; next the sequence of structures starting from atoms and building 

 up to polymers of colloidal dimensions ; and finally the way the mutual arrange- 

 ments of these impose a pattern of linked reactions which can be reproduced. 



On the first steps of emergence of simple organic molecules in the hydrosphere 

 there is still no agreement, but as this question will be largely debated here I will 

 not pursue it at any length. All I would like to say is that following Lyell's 

 principle it seems preferable to start by supposing substances and reactions 

 that still occur even though now modified by the action of life. It is not strictly 

 necessary to postulate the character of the original atmosphere of the Earth 

 because of the continual contributions which must have occurred from volcanic 

 sources. The character of these seems largely independent of organic sources 

 and to consist mainly of steam, carbon dioxide, ammonia, and hydrogen sulphide. 

 With regard to the supply of carbon dioxide I suspect it is derived from lower 

 layers of the crust where it may exist in the high pressure form of orthocarbonate 

 in such a mineral as fayalite Fe2 (C, Si)04. Ammonia is already known to exist 

 as ammonium felspar {K,(NH4)} AlSisOg. Both CO2 and NH3 in the form of 

 NH4CI are known to be hberated in volcanic gases, fumaroles etc. Probably a 

 far larger amount reaches the hydrosphere through the weathering of carbonate- 

 or ammonia-containing igneous rocks. The weathering of 100 km of igneous 

 rock already largely depleted of ammonia would provide all the nitrogen at 

 present in the atmosphere. 



The question as to whether primary or secondary inorganic hydrocarbons 

 were ever found in the primitive atmosphere is still an open one. They are hardly 

 ever detected in volcanic gases and their presence in carbonaceous meteorites 

 in my opinion points to the origin of these meteorites in a region further from the 

 sun than the Earth. In any case oxidation of methane at the top of the atmosphere 

 would relatively soon reproduce the condition in which carbon dioxide would be 

 the chief carbon compound in the atmosphere. 



It has been argued that CO2, the most oxidized form of carbon, is most un- 

 likely in the primitive atmosphere. If it was all derived from the oxidation of the 

 postulated earHer CH4 I would agree for, in that case, intermediates in the forms 

 of alcohols and carboxy acids would first have been formed. The situation would 

 be different if atmospheric CO2 is a product of the lithosphere as the existence, 

 admittedly rare, of carbonates of deep origin would seem to indicate. In any 

 case if CO2 was not a precursor of hfe it must have been one of its earUest pro- 

 ducts, as witnessed by the universal presence of limestone even in the early 

 pre-Cambrian rocks. Perhaps a study of carbon isotopes, in carbonatites and lime- 

 stones of various ages would resolve this problem. 



The major exergonic reactions occurring in the primitive hydrosphere would 

 be 



2NH3 ^ N2 + 3H2 or N2 + 2H2 + 2H etc. 

 8SH2 -> Sg + 8H2 



both of which, in the absence of free oxygen, would yield molecular hydrogen 



