;iAY 19, 1899.] 



SCIENCE. 



709' 



must have caused a rapid downpour of all 

 the vapors other than water, if any there 

 were ; and, a little later, rain of water out 

 of the air, as the temperature of the surface 

 cooled from red heat to such moderate tem- 

 peratures as 40° and 20° and 10° Cent, 

 above the average due to sun heat and radi- 

 ation into the ether around the earth. 

 What that primitive atmosphere was, and 

 how much rain of water fell on the earth in 

 the course of the first century after consoli- 

 dation, we cannot tell for certain ; but Katu- 

 ral History and Natural Philosophy give us 

 some foundation for endeavors to discover 

 much towards answering the great ques- 

 tions : Whence came our present atmos- 

 phere 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, cause 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 con- 

 tain, condensed in minute cavities withiu 

 them, large quantities of nitrogen, car- 

 bonic 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 

 contain hydrogen. From this it might 

 seem probable that there was no free oxy- 



*See, for example, Tilden, Proo. E. S. February 

 4, 1897 : ' On the Gases Enclosed in Crystalline 

 Hocks and Minerals. ' 



gen in the primitive atmosphere, and that 

 if there was free hydrogen ic was due to 

 the decomposition of steam by iron or mag- 

 netic 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 hy- 

 drogen and other metallic vapors in the cool- 

 ing of the neubla, and that, although it is 

 know a 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 iu 

 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 

 ivith sunligJd, we may regai'd 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 temperature of 80° or 70° of our 

 present Centigrade thermometric scale a 

 year or two after solidification of the primi- 

 tive lava had come up to the surface. The 

 thick, tough, velvety coating of living vege- 

 table 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 leaving free oxygen in the 

 water to pass ultimately into the air. Simi- 

 lar 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 Na- 

 tional Park of the United States. This vege- 

 tation, consisting of confervas, all grows 



* Rocky Jlountains Park of Canada, on the Cana- 

 dian Pacific Railway. 



