Chapter V 



THE TWO ATMOSPHERES: ANOXYGENIC AND 



OXYGENIC, PRE-ACTUALISTIC 



AND ACTUALISTIG 



AEROBIC AND ANAEROBIC, OXYGENIC AND ANOXYGENIC 



The difference between the primeval anoxygenic atmosphere and the 

 present oxygenic one is as clear-cut as between black and white. 

 Admittedly, there will have been a long period of transition. But 

 before that time, and after that time, there is complete antithesis 

 between the two. 



In the literature, this difference has not always been sufficiently 

 stressed. For one thing, most authors speak of 'anaerobic' conditions 

 prevailing in the primeval atmosphere. This results from the fact 

 that our present anaerobic life forms live under conditions which, 

 in a superficial way, are comparable biochemically. That is, they live 

 under the exclusion of free oxygen. But this is at present an ex- 

 ceptional environmental niche, depending on the exclusion of air, of 

 the atmosphere, which now contains free oxygen. Hence they are 

 properly named 'anaerobic'. 



Life in the primeval atmosphere and in the contemporary hydro- 

 sphere was, however, far from anaerobic, although the absence of free 

 oxygen led to a superficial biochemical resemblance. Life was indeed 

 aerobic; it could follow its functions in the free atmosphere; it was 

 exposed to the air. But, the atmosphere at that time did not contain 

 free oxygen. 



Although life in the primeval atmosphere will have been largely 

 aerobic, just as it is now, this does not, of course, alter the fact that 

 aerobic in the primeval atmosphere was diametrically opposed to 

 what the aerobic environment is now. Consequently, one had better 

 speak of the early anoxygenic atmosphere, of anoxygenic aerobic life 

 under the primeval atmosphere, as opposed to the oxygenic aerobic 

 life of today. 



