Earth as an Abode fitted for Life. 87 



leaving free oxygen in the water to pass ultimately into the 

 air. Similar vegetation is found abundantly on the terraces 

 of the Mammoth hot springs and on the beds of the hot water 

 streams flowing from the Geysers in the Yellowstone National 

 Park of the United States. This vegetation, consisting of 

 confervas, all grows under flowing water at various tempera- 

 tures, some said to be as high as 74° Cent. We cannot doubt 

 but that some such confervas, 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 favoured 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 

 century, if sun-heat, and sunlight, and rainfall, 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 ail 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 the century, would probably be favourable 

 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 im- 

 portant 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 the primitive 

 atmosphere or primitive water, several thousands, possibly 

 hundreds of thousands, of years must pass before oxygen 

 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 respect to evolution of oxygen as that of 

 a Hessian forest, as estimated by Liebig* 50 years ago, or 

 of a cultivated English hayfield of the present day, a very 

 improbable supposition, and if there were no decay (erema- 

 causis, or gradual recombination 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 



* Liebig', ' Chemistry in its application to Agriculture and Physio- 

 logy,' English, 2nd ed., edited by Playfair, 1842. 



