40 THE ORIGIN AND EVOLUTION OF LIFE 



atmosphere^ is whether or no it contained free oxygen. The 

 earliest forms of hfe were probably dependent on atmospheric 

 oxygen, although certain existing bacterial organisms, known 

 as "anaerobic," are now capable of existing without it. 



The primordial atmosphere was heavily charged with water 

 vapor (HoO) which has since been largely condensed by cooling. 

 In the early period of the earth's history volcanoes- were also 

 pouring into the atmosphere much greater amounts of car- 

 bon dioxide (CO2) than at the present time. At present the 

 amount of carbon dioxide in the atmosphere averages about 

 three parts in 10,000, but there is little doubt that the primor- 

 dial atmosphere was richer in this compound, w^hich next to 

 water and nitrogen is by far the most important both in the 

 origin and in the development of living matter. The atmos- 

 pheric carbon dioxide is at present continually being withdrawn 

 by the absorption of carbon in living plants and the release of 

 free oxygen; it is also washed out of the air by rains. On the 

 other hand, the respiration of animals, the combustion of car- 

 bonaceous matter, and the discharges from volcanoes are con- 

 tinually returning it to the air in large quantities. 



As to carbon, from our present knowledge we cannot con- 

 ceive of organisms that did not consist, from the instant of 

 initial development, of protoplasm containing hydrogen, oxygen, 

 nitrogen, and carbon. Probably carbon dioxide, the most likely 

 source of carbon from the beginning, was reduced in the pri- 

 mordial environment by other than chlorophyllic agencies, by 

 simple chemical influences. 



Since carbon is a less dominant element^ than nitrogen in 

 the life processes of the simplest bacteria, we cannot agree 

 with the theory that carbon dioxide was coequal with water 



1 Becker, George F., letter of October 15, 1915. 

 - Henderson, Lawrence J., 1913, p. 134. 

 3 Jordan, Edwin O., 1908, p. 66. 



