86 Lord Kelvin on the Age of the 



to present conditions was realized in the first hundred cen- 

 turies after consolidation of the surface ? 



§ 40. We may consider it as quite certain that nitrogen 

 gas, carbonic acid gas, and steam, escaped abundantly in 

 bubbles from the mother liquor of granite, before the primi- 

 tive consolidation of the surface, and from the mother liquor 

 squeezed up from below in subsequent eruptions of basaltic 

 rock ; because all, or nearly all, specimens of granite arid 

 basaltic rock, which have been tested by chemists in respect 

 to this question *, have been found to contain, condensed in 

 minute cavities within them, large quantities of nitrogen, 

 carbonic acid, and water. It seems that in no specimen of 

 granite or basalt tested has chemically free oxygen been dis- 

 covered, while in many, chemically free hydrogen has been 

 found ; and either native iron or magnetic oxide of iron in 

 those which do not contain hydrogen. From this it might 

 seem probable that there was no free oxygen in the primitive 

 atmosphere, and that if there was free hydrogen, it was due 

 to the decomposition of steam by iron or magnetic oxide of 

 iron. Going back to still earlier conditions we might judge 

 that, probably, among the dissolved gases of the hot nebula 

 which became the earth, the oxygen all fell into combination 

 with hydrogen and other metallic vapours in the cooling of 

 the nebula, and that although it is known to be the most 

 abundant material of all the chemical elements constituting 

 the earth, none of it was left out of combination with other 

 elements to give free oxygen in our primitive atmosphere. 



§ 41. It is, however, possible, although it might seem not 

 probable, that there was free oxygen in the primitive atmo- 

 sphere. With or without free oxygen, however, but with 

 sunlight, we may regard the earth as fitted for vegetable life 

 as now known in some species, wherever water moistened the 

 newly solidified rocky crust cooled down below the tempera- 

 ture of 80° or 70° of our present Centigrade thermometric 

 scale, a year or two after solidification of the primitive lava 

 had come up to the surface. The thick tough velvety coating 

 of living vegetable matter, covering the rocky slopes under 

 hot water flowing direct out of the earth at Banff (Canada) |, 

 lives without help from any ingredients of the atmosphere 

 above it, and takes from the water and from carbonic acid or 

 carbonates, dissolved in it, the hydrogen and carbon needed 

 for its own growth by the dynamical power of sunlight ; thus 



* See, for example, Tilden, Proc. R. S. February 4th, 1897. "On the 

 Gases enclosed in Crystalline Rocks and Minerals." 



f Rocky Mountains Park of Canada, on the Canadian Pacific Railway. 



