EARTH-LIFE FORMATION. 379 



three elements together, while each has its 

 own process. 



There is a question about a change in the 

 character of the air, as well as about the 

 diminution of its quantity. Some scientists 

 maintain that the atmosphere is losing its 

 oxygen and its carbon dioxide, the one being 

 taken up by animals chiefly and the other by 

 plants, whereby both pass into the solid earth. 

 How these losses have been made good in the 

 past geologic ages, since the advent of or- 

 ganic life has been the subject of no little 

 speculation, and the question is still unsettled. 

 In both cases supplies have been supposed to 

 come to our globe from the outside, and pos- 

 sibly from the heated inside also. The mass 

 of air seems to have been constant and its 

 chemical constituents have not varied in pro- 

 portion since life began on our planet, say a 

 hundred million years ago. A small increase 

 in the proportions of oxygen and carbon diox- 

 ide has been shown by experiment to be fatal 

 to both Plant and Animal. 



On the other hand, it is stated that the land 

 of the globe is increasing. Not only is the 

 area extending at the expense of the water, 

 but certain chemical constituents held in so- 

 lution are continually deposited as solids, es- 

 pecially by marine organisms, like the coral 

 insect. Possibly in this case also there may 



