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



would be 0.8 of a degree warmer, and at tbe end of twenty five million 

 years it would be 0.016 of a degree warmer than if there were no under- 

 ground heat. 



39. When the surface of the earth was still white-hot liquid all round, 

 at a temperature fallen to about 1,200° C, there must have been hot 

 gases and vapor of water above it in all parts, and possibly vapors of 

 some of the more volatile of the present known terrestrial solids and 

 liquids, such as zinc, mercury, sulphur, i)hosphorus. The very rapid 

 cooling which followed instantly on the solidification at the surface 

 must have caused a rapid downpour of all the vapors other than water, 

 if any there wer6; and a little later, rain of water out of the air, as 

 the temperature of the surface cooled from red heat to such moderate 

 temperatures as 40° and 20° and 10° 0. above the average due to sun 

 heat and radiation into the ether around the earth. What that primi- 

 tive atmosphere was, and how much rain of water fell on the earth in 

 the course of the first century after consolidation, we can not tell for 

 certain ; but natural history and natural philosophy give us some founda- 

 tion for endeavors to discover much toward answering the great ques- 

 tions, Whence came our present atmosphere of nitrogen, oxygen, and 

 carbonic acid? Whence came our present oceans and lakes of salt and 

 fresh water"? How near an approximation to present conditions was 

 realized in the first hundred centuries 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 primitive 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 and 

 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 discovered, 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 vapors 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. 



'See, for example, Tilden, Proc. R. S., February 4, 1897; "On the Gases inclosed in 

 Crystalline Eocks and Minerals." 



