ATMOSPHERIC FACTOR IX EVOLUTION. 295 



period with its orig-inal supply of carbon little reduced. Let us 

 assume, then, that at the beg^inning" of the Carboniferous period 

 there was still say 500 times the carbon now present, then we 

 should estimate that the end will come in about g^i of the 

 years since the Carboniferous period began. Geologists put 

 this period down as 30 . million years ag-o. This gfives us 60 

 thousand years as a probable estimate of the time before org-anic 

 life must come to an end from carbon hung^er. We have now 

 traced the atmospheric variation, and more especially the carbon 

 variation, from the dawn of organic life on this globe to its 

 close ; and we find that the birth of all things occurred in an 

 atmosphere with much carbon, and that the death of all things 

 will come when there is practically no carbon. Surely, then, 

 carbon has been well called "the food of life." 



Seeing what a stupendous change has been taking place 

 in the atmosphere, and especially the change with regard to 

 carbon, the food of life, we should expect to find a correspond- 

 ingly great change in the nature of the organisms which have 

 had to live in this changing medium, and which have had to 

 adapt themselves gradually to it. 



A few self-evident deductions may be made as to the effect 

 of this changing atmosphere on organic life. 



(i) Plant life must have been the first form of life, because 

 of the large quantity of carbon dioxide and lack of oxygen ia 

 the air. 



(2) Plants by their action on the carbon dioxide and the 

 formation of oxygen prepared the way for animal life. 



(3) At a certain stage the atmospheric conditions would become 

 an ideally perfect one for plant growth, with carbon, the special 

 plant food, hundreds of times more abundant than it is now, 

 and with sufficient oxygen. This time of plant luxuriance 

 began with the beginning of the Carboniferous period, and 

 lasted for a considerable time after. 



(4) As a result of the luxuriance of plant life, we would 

 expect later a rapid development and increase in size of animals, 

 first of the herbivorous and later of the carnivorous. 



(5) Later, after this age of luxuriance of plant and animal 

 life, we would expect a change in both, especially in the animal. 

 Carbon has been rapidly removed from the air, and oxygen 



added, that is with diminishing luxuriance in the growth of 

 plants, the animals' appetite is increasing owing to the increase 

 of oxygen. Thus we get a growing appetite and a diminishing 

 food supply. W'e would expect the largest animals to decrease 

 in size, if they did not die out altogether. 



Due to the diminishing carbon dioxide or plant food supply, 

 and increase of appetite of the animaJs due to increase of oxygen, 

 there would be (a) a general slow decline in plant luxuriance ; 

 (b) gradual reduction in the size of animals ; (c) increased animal 

 activity; (d) increased appetite of animals; and (e) shortening 

 of the average animal life. We see here a reason why the 

 ancient patriarchs lived much longer than ^'^. do now. 



