158 ABIOGENIC ORGANIC-CHEMICAL EVOLUTION 



Later, the ultraviolet photolysis of water under a variety 

 of conditions was observed by A. Tian," H. Neuimin and 

 A. Terenin/^ and by several other workers. 



P. Harteck and J. H. D. Jensen^" tried to calculate the 

 total quantity of oxygen which might have been formed 

 photochemically in the upper layers of the atmosphere during 

 the entire period of existence of the Earth (which they 

 estimated as 3 x 10^ years) if hydrogen had been constantly 

 escaping into space. The calculated quantity of oxygen was 

 many tens of times that now present in the atmosphere. If 

 this were so, such extensive abiogenic photochemical produc- 

 tion of oxygen would speak against the idea that atmospheric 

 oxygen owes its origin exclusively to photosynthesis by plants. 



However, later determinations of the content of water 

 vapour in the cold upper layers of the atmosphere, particu- 

 larly those by G. M. B. Dobson,^^ failed to confirm the cal- 

 culations of Harteck and Jensen. The results of H. E. Moses 

 and Ta-You Wu^^ on the recombination of oxygen with 

 hydrogen were also in conflict with them. Thus, it appears 

 that, during the entire period of existence of the Earth, there 

 could not have been formed by inorganic, abiogenic means 

 a quantity of free oxygen vastly exceeding that present in 

 the atmosphere of to-day. 



Reducing conditions. 



It follows that it was the emergence of life itself and the 

 appearance of biogenic photosynthesis which established on 

 the surface of the Earth the markedly oxidising conditions 

 under which we now live. Up till this time reducing condi- 

 tions prevailed on the lifeless Earth, under which oxygen 

 can only be supposed to have occurred in the combined state, 

 in the form of water, metallic oxides, silicates, alumino- 

 silicates, etc. The following compounds were of special im- 

 portance": FeaSlOa, MgSiOg, Ca3(Al03) a-H-.O, Ai(oh)3. At the 



same time substantial amounts of metals and other substances 

 existed, in whole or in part, in the reduced state, since no 

 oxygen was available for combination with them. 



The comparatively small amounts of free oxygen formed 

 by the photolysis of water in the upper layers of the atmo- 



