CHAPTER XII 



STAGES OF THE EARTH'S HISTORY PRIOR TO 

 THE KNOWN ERAS 



The conception of the history of the earth prior to the earliest 

 stage which can be read from the strata must depend upon the view 

 which is entertained as to its origin. The course of its early history 

 according to each hypothesis of its origin, will be sketched sepa- 

 rately. Though these sketches are necessarily hypothetical, their 

 study is important, for the great features of the earth and of the 

 earth-shaping processes were inherited from these early stages. 



I. STAGES UNDER THE LAPLACIAN HYPOTHESIS 



The hypothetical stages of the earth's early history, according 

 to the Laplacian view have been stated as follows, 1 and they must 

 have been essentially the same for any view of primitive conditions 

 that involves a molten globe. 



I. "The 1 Astral aeon, or that of the fluid globe having a heavy vaporous envelope 

 containing the future water of the globe or its dissociated elements, and other 

 heavy vupors or gases. 

 II. The Azoic aeon. Without life. 



1 . The Lithic Era: Commencing with the earth a solid globe, or at least 

 sold at the surface; the temperature at the beginning above 2,500 F.; the 

 atmosphere still containing all the water of the globe (estimated at 200 atmos- 

 pheres), all the carbonic acid now in limestone and that corresponding to the 

 carbon now in carbonaceous and organic substances (probably 50 atmos- 

 pheres), all the oxygen since shut up in the rocks by oxidation, as well as that 

 of the atmosphere and of organic tissues. The time when lateral pressure for 

 crustal disturbance and orographic work was begun; when "statical meta- 

 morphism," or that dependent on heat of a statical source the earth's 

 mass and the vapors about it, began. 



2. The Oceanic Era: Commencing with the waters condensed into an ocean 

 over the earth, or in an oceanic depression, with finally some emerging lands, 

 the temperature perhaps about 500 F., if the atmospheric pressure was still 

 50 atmospheres. The first of tides and the beginning of the retardation of 

 the earth's rotation. Oceanic waves and currents and embryo rivers begin 

 work about the emerged and emerging lands; the large excess of carbonic 

 acid and oxygen in the air and water a source of rock-destruction; before the 



I 1 Dana, Manual of Geology. 

 307 



