CHAPTER XIII 



STAGES OF THE EARTH'S HISTORY LEADING TO 

 THE KNOWN ERAS 



The conception of the development of the earth prior to the 

 earliest stage at which its history can be read directly from the 

 strata must depend upon the view which is entertained as to its 

 origin. The course of its early history, according to each hypoth- 

 esis of its origin, may be followed separately. These possible 

 courses are necessarily hypothetical at present, and should not be 

 entertained without due reserve; yet 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 



I. The 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 vapors or gases. 

 II. The Azoic aeon. Without life. 



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

 least solid at the surface; the temperature at the beginning above 

 2,500 F.; the atmosphere still containing all the water of the globe 

 (amounting to 200 atmospheres, according to Mallet, 1880), all 

 the carbonic acid now in limestone and that corresponding to 

 the carbon now in carbonaceous substances and organic sub- 

 stances (probably 50 atmospheres), 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 

 metamorphism," or that dependent on heat of a statical source 

 the earth's mass and the vapors about it, began. 

 1 Dana, Manual of Geology. 



426 



