356 AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 



vated Bnglisli hayfield of the present day, a very improbable supposi- 

 tion, and if there were no decay (eremacausis, or gradual recombina- 

 tion with oxygen) of the plants or of portions such as leaves falling 

 from plants, the rate of evolution of oxygen, reckoned as three times 

 the weight of the wood or the dry hay produced, would be only about 6 

 tons per English acre per annum, or IJ tons per square meter per thou- 

 sand years. At this rate it would take only one thousand five hundred 

 and thirty-three years, and tberefore in reality a much longer time would 

 almost certainly be required, to produce the 2.3 tons of oxygen which 

 we have at present resting on every square meter of the earth's sur- 

 face, land and sea.^ But probably quite a moderate number of hundred 

 thousand years may have sufficed. It is interesting, at all events, to 

 remark that at any time the total amount of combustible material on 

 the earth, in the form of living plants or their remains left dead, must 

 have been just so much that to burn it all would take either the whole 

 oxygen of the atmosphere or the excess of oxygen in the atmosphere 

 at the time, above that, if any, which there was in the beginning. 

 This we can safely say, because we almost certainly neglect nothing 

 considerable in comparison with what we assert when we say that the 

 free oxygen of the earth's atmosphere is augmented only by vegeta- 

 tion liberating it from carbonic acid and water, in virtue of the power 

 of sunlight, and is diminished only by virtual burning^ of the vege- 

 table matter thus produced. But it seems improbable that the average 

 of the whole earth — dry laud and sea bottom — contains at j)resent coal, 

 or wood, or oil, or fuel of any kind originating in vegetation, to so 

 great an amount as 0.767 of a ton per square meter of surface, which 

 is the amount at the rate of 1 ton of fuel to 3 tons of oxygen that 

 would be required to i)roduce the 2.3 tons of oxygen i^er square meter 

 of surface which our present atmosphere contains. Hence it seems 

 probable that the earth's primitive atmosphere must have contained 

 free oxygen. 



43. Whatever may have been the true history of our atmosphere, it 

 seems certain that if sunlight was ready, the earth was ready, both for 

 vegetable and animal life, if not within a century, at all events within a 

 few hundred 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 consolidation of the earth took place as long ago 

 as fifty million years; the solid earth must in that case have waited 



^In our present atmosphere, in average conditions of barometer and thermometer, 

 we have, resting on each square meter of the earth's surface 10 tons total weight, of 

 which 7.7 is nitrogen and 2.3 is oxygen. 



-This ''virtual burning" includes eremacausis of decay of vegetable matter, if 

 there is any eremacausis of decay without the intervention of microbes or other 

 animals. It also includes the combination of a portion of the food with inhaled 

 oxygen in the regular auimal economy of provision for heat and power. 



3 See Popular Lectures and Addresses, Vol. I, pages 376-429, particularly page 397. 



