710 



SCIENCE. 



[N\ S. Vol. IX. No. 229. 



under flowing water at various tempera- 

 tures, some said to be as high as 74° Cent. 

 We cannot doubt but that some such con- 

 fervse, if sown or planted in a rivulet or 

 pool of warm water in the early years of 

 the first century of the solid earth's history, 

 and, if favored with sunlight, would have 

 lived, and grown, and multiplied, and would 

 have made a beginning of oxygen in the air, 

 if there had been none of it before their 

 contributions. Before the end of the cen- 

 turj', if sun-heat, and sunlight, and rain- 

 fall were suitable, the whole earth not under 

 water must have been fitted for all kinds of 

 land plants which do not require much or 

 any oxygen in the air, and which can find, 

 or make, place and soil for their roots on 

 the rocks on which they grow ; and the 

 lakes or oceans formed by that time must 

 have been quite fitted for the life of many 

 or all of the species of water plants living 

 on the earth at the present time. The 

 moderate warming, both of land and water, 

 by underground heat, towards the end of 

 century, would probably be favorable rather 

 than adverse to vegetation, and there 

 can be no doubt but that if abundance of 

 seeds of all species of the present day had 

 been scattered over the earth at that time 

 an important proportion of them would have 

 lived and multiplied by natural selection 

 of the places where they could best thrive. 

 §42. But if there was no free oxygen in 

 in the primitive atmosphere or primitive 

 water several thousands, possibly hundreds 

 of thousands, of years must pass before 

 oxjrgen enough for supporting animal life, 

 as we now know it, was produced. Even 

 if the average activity of vegetable growth 

 on land and in water over the whole earth 

 was, in those early times, as great in re- 

 spect to evolution of oxygen as that of a 

 Hessian forest, as estimated by Liebig* 50 



* Liebig, 'Chemistry in its application to Agricul- 

 ture and Phj'siologj'. ' English, 2d ed., edited by 

 Play fair, 1843. 



years ago, or of a cultivated English hay- 

 field of the present day, a very improbable 

 supposition, and if there were no decay 

 {eremaccnms, or gradual recombination with 

 oxygen) of the plants or of portions, such 

 as leaves falling from plants, the rate of 

 evolution of oxygen, i-eckoned 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 li tons per 

 square meter per thousand years. At this 

 rate it would take only 1533 years, and, 

 thei'efore, in reality a much longer time 

 would almost certainly be required, to pro- 

 duce the 2.3 tons of oxygen which we have 

 at present resting on every square meter of 

 the earth's surface, land and sea.* But 

 probably quite a moderate number of hun- 

 dred thousand years may have sufficed. It 

 is interesting, at all events, to remark that, 

 at any time, the total amount of combus- 

 tible 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 M'ith what we assert when we 

 say that the free oxygen of the earth's at- 

 mosphere is augmented only by vegetation 

 liberating it from carbonic acid and water, 

 in virtue of the power of sunlight, and is 

 diminished only by virtual burningf of the 



* In our present atmosphere, in average conditions 

 of barometer and thermometer, we have, resting on 

 each square meter of the earth's surface, ten tons 

 total Aveight, of which 7.7 is nitrogen and 2.3 is 

 oxygen. 



t 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 regu- 

 lar animal economy of provision for heat and power. 



