52 EVOLUTION OF THE EARTH 



umes of this gas to 10,000 of air, and there is as much more 

 in living things as there is in the atmosphere. On the other 

 hand, there is in the oceans of today, according to F. W. 

 Clarke, the geochemist, from 18 to 27 times more carbon 

 dioxide than in the air (Johnston and Williamson say that 

 at 15 C. there is about 70 times more), while the still vaster 

 volumes locked up in the sedimentary rocks and in the fuels 

 and carbonaceous deposits of the earth are computed to be 

 30,000 times greater than the volume in the present atmos- 

 phere. These facts are brought forward at this time to show 

 that the constituents of the atmosphere have always varied 

 because of the constant loss of carbon dioxide and oxygen to 

 the sedimentary rocks, but that at the same time there has 

 always been a resupply of carbon dioxide through the ever 

 active volcanoes and the mineral springs, and of oxygen 

 through the life activities of plants. Holmes says: 1 "Even 

 now, the outer 70 miles of the earth's crust would be competent 

 to supply all the nitrogen of the atmosphere, the water of the 

 oceans and the vast quantity of carbon dioxide represented by 

 limestones and carbonaceous deposits." 



It has been well said that if volcanism should cease it would 

 not be long before the existence of life would be impossible 

 because of the absence of carbon. We should add here that 

 if there were again as much life as there is at present, all the 

 carbon of the atmosphere would be in the living plants and 

 animals, and, if such a condition were possible, death would 

 come to them all. Therefore life and its abundance at any 

 time are conditioned by the amount of this gas present in the 

 atmosphere. 



Climates of the past. The quantity of carbon dioxide in 

 the atmosphere is to a certain extent also a climatic regulator, 

 though the greater factor in this matter is water-vapor, which 

 is also the most variable constituent of the atmosphere. With 



1 Holmes, A., "The Age of the Earth," 1913, p. 30. 



