LIFE WITHOUT OXYGEN 129 



demonstrated existence of absolutely anaerobic organisms is 

 evidence that we have not. 



Doubtless it would be a little hazardous to describe all meta- 

 cellular organisms simply as congeries or colonies of anaerobic 

 plastids, granules, biophores or " protomeres." 1 And yet 

 many facts are in favour of such a conception. If it can be 

 established and such is the present drift, we shall then have 

 a clear, simple, mechanical explanation of what is now wrapped 

 in fog. 



In any event, this much is sure : at the foot of the life-scale, 

 alike in the simplest of organisms and in the embryonic con- 

 ditions of all organisms, the need of oxygen is wholly lacking 

 or very slight. 



This must have been true historically, if evolution be true ; 

 else we shall for ever remain without the remotest clue to the 

 actual mode of the beginning of life, either in this or in any 

 other regard, for alone in the fact or conception that the living 

 world and each individual organism is, like the earth itself, a 

 mirror of its own history, is any kind of clue to be found. 

 We might manufacture life in the laboratory, as in the 

 laboratory we may, for example, make coal. But in neither 

 the one instance nor the other would there be any necessary 

 or positive indication of their natural origin. Here biology 

 and geology, biogeny and geogeny, are at one, for every 

 direct trace of the early history of life, like that of the 

 primitive history of the earth, 2 has been utterly and for ever 

 destroyed. 



Yet geology has its word on the special problem here under 

 consideration. There is oxygen in the present atmosphere : was 

 there any in eozoic time ? 



V. The Atmosphere of the Primitive Earth. — When we con- 

 sider the oxygen of the atmosphere in present and in former 

 times, we meet with the following facts : 



In the lower levels of the existing atmosphere oxygen forms 

 a little less than one-fourth of the air, by weight, the amount 

 decreasing as we ascend, so that in the upper levels of the 

 atmosphere there is no oxygen at all. 3 Even after including 



1 Heidenhain, I.e. p. 493. 



2 For a vivid presentation of this latter fact, cf. chaps. 11 and 14 of J. Walther's 

 Gesch. d. Erde (Leipzig, 1908). 



8 Hann, Lehr. d. Meteorologie, p. 8, 2te auf. (Leipzig, 1906). 



9 



