294 ATMOSPHERIC FACTOR IN EVOLUTION. 



an animal lives, the more sluggish is the life of the animal, but 

 the longer. Gradual increase of carbon dioxide in the air then 

 means (i) a longer life, (2) diminished need for food and {3) a more 

 sluggish life. Now have we any signs of these three results 

 being brought about? I think we have, (i) We have the 



average of human life getting longer. But some may say 



that this is due to advances in sanitation and medical science 

 rather than to the increase of carbon dioxide in the air. (2) 

 Are there any signs of animals needing less food nowadays? 

 We have the growing conviction that we all eat too much, and 

 a growing plea for a return to the simple life. May this need 

 for less food not be in part an explanation of the growth of 

 Vegetarianism. (3) Are there any signs of life becoming more 

 sluggish? May we not take as a sign of this, the shorter hours' 

 movement of the present day, a movement which seems to grow 

 pari passu with the coal output, that is with the increase of 

 carbon dioxide? 



(3) At the end. We all know that the huge outpat 

 of coal is merely a short episode in the world's future history. 

 The available coal will in a few thousand years, at most, be at 

 an end. Now as soon as the coal output is reduced to a certain 

 point then there will begin again that process that has been 

 going on from the beginning till recently, namely : the gradual 

 diminution of the air's carbon. This process cannot go on 

 for ever ; a point will ultimately be reached when the carbon in 

 the air has been so reduced that plant life will no longer be able 

 to subsist. 



We thus see that at the end of organic life there will be much 

 oxygen and little or no carbon dioxide; while at the beginning 

 there was much carbon dioxide and little or no oxygen. 



Now for the question "When will the end of all living 

 things come?" 



Sir Robert Ball, in his "In the High Heavens," tries to 

 show that the conditions on this earth cannot always remain 

 such as are consistent with life. He says a time must come 

 when, due to loss of heat of the sun by radiation, life will be 

 no longer possible on our globe. He gives organic life here 

 from four to ten millions more years. This estimate was made 

 before the days of radio-activity. Nowadays it is recognised 

 that, due to this newly recognised source of heat, the Sun's heat 

 may continue as at present for countless millions of vears in the 

 future. 



Now from considerations such as I have been making with 

 regard to the steady withdrawal of carbon from the air, can 

 any approximate estimate be made of the time that must elapse 

 before the end of all living things? Any such estimate must 

 be of the vaguest. Still a vague estimate may be attempted. 

 There Ls the reason, I hold, for beUeving that at the beginning 

 the quantity of carbon in the air was at least 500 times (it may 

 be 1,000 times) the amount now present. There is also good 

 reason for believing that for long years all through the oldest 

 geological period, very Uttle carbon would be abstracted from 

 the air; and that this earth's atmosphere began the Carboniferous 



