32 THE EiaHT HON. LOED KKLVIN, G.C.V.O., ON 



— Whence came our present atmosphere of nitrogen, oxygen^ 

 and carbonic acid ? Wlience came our present oceans and' 

 lakes of salt and fresh Avater? How near an approximation 

 to present conditions was reahsed in the first hundred cen- 

 turies after consohdation 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 

 primitive consolidation of the surface, and from tlie mother 

 liquor squeezed up frtmi below in subsequent eruptions of 

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

 and basaltic rock, which have been tested by chemists in 

 respect to this question,* have been found to contain, con- 

 densed in minute cavities ^vithin 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 discovered, while in many, chemically free 

 hydrogen has been found; and either native iron or 

 magnetic oxide of iron in those ^vhich 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 

 atmosphere. With or without free oxygen, however, hut 

 wWi siiulu/lif, we may regard the earth as fitted for vegetalile 

 life as now known in some species, wherever water moistened 

 the neAvly solidified rocky crust cooled down below the tem- 

 perature 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 



* See for example Tilden, Froc. U.S., February 4tli, 18l»T. " On the 

 Gases enclosed in Crystalline Eocks and Minerals." 



