THE AGE OP THE EARTH. 35 



oxygen per square metre of surface, whicli our present 

 atraospliere contains. Hence it seems probable that the 

 earth's primitive atmosphere must have contained free 

 ox_ygen. 



§ 43. Whatever may have been the true history of our 

 atmosphere it seems certain that if sunhght was ready, 

 the eartJi was ready, both for vegetable and animal life, if 

 not v/ithin a century, at all events within a few liundred 

 centuries after the rocky consolidation of its surface. But 

 was the sun ready? The well founded dynamical theory 

 of the sun's heat carefully worked out and discussed by 

 Helmholtz, Newcomb, and myself,* says NO if the consoli- 

 dation of the earth took place as long ago as 50 million years ; 

 the solid earth must in that case have waited 20 or 30 million 

 years for the sun to be anything nearly as warm as he is 

 at present. If the consolidation of the earth was finished 

 20 or 25 million years ago, the sun was probably ready, — 

 though probably not then quite so warm as at present, yet 

 warm enough to support some kind of vegetable and animal 

 life on the earth. 



§ 44. My task has been rigorously confined to Avhat, 

 humanly speaking, we may call the fortuitous concourse of 

 atoms, in the preparation of the earth as an abode fitted for 

 life, except in so far as I have referred to vegetation, as 

 possibly having been concerned in the preparation of an 

 atmosphere suitable for animal life as we now have it. 

 ]\Iathematics and dynamics fail us when we contemplate 

 the earth, fitted for life but lifeless, and try to imagine the 

 commencement of life upon it. This certainly did not take 

 place by any action of chemistry, or electricity, or crystalline 

 grouping of molecules under the influence of force, or by any 

 possible kind of fortuitous concourse of atoms. We must 

 pause, face to face with the mystery and miracle of the 

 creation of living creatures. 



* See Popular Lectures and Addresses, voJ. 1, pp. 376-429, particularly 

 page 397. 



D 'J, 



