254 AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 



Wagner' reconsiders Sir John jSIurraj-'s estimate just quoted and 

 arrives at the result that the whole land surface of the globe is 

 55,814,000 square miles and that the oceanic area bears to this the 

 ratio of 2.54 to 1. On this estimate, and accepting Sir John Murray's 

 estimate of the mean depth of the ocean (2,076 fathoms = 2.393 miles), 

 the bulk of the ocean in cubic miles is 339,248.000. This gives a mass 

 of 1.460 X 10'^ of which the sodium constitutes 15,627 X 10'- tons, 

 and the period of denudation arrived at is 99.4 millions of j^ears. 



This is probabh^ the most ac(;urate basis on which to obtain this 

 quotient and will be accepted in what follows. The estimate will be 

 modified to some extent on further considerations. 



II. — THE ORIGINAL CONDITION OF THE OCEAN. 



The existence of primitive high temperature conditions affecting the 

 materials of which the earth is composed is inferred as the result of 

 many observations and analogies. These need not be referred to here. 



The globe, as we find it, possesses as its lithosphere siliceous and 

 aluminous compounds, which are volatile onl}" at temperatures prob- 

 ably much exceeding 2,000° C, and carbonates of the alkaline earths, 

 which at a much lower temperature dissociate into a gaseous oxide and 

 stable solid oxides. In the hydrosphere now enveloping a large part 

 of the lithosphere we find a vast bulk of water, gaseous at all pressures 

 above the temperature 370° C, and dissolved in it a quantity of a 

 halogen salt suflicient in amount, as may be easilj^ shown, to cover the 

 entire globe to a depth of 112 feet if crystallized out into solid sodium 

 chloride. 



The efi'ect of a temperature so elevated as 1,500^ C. upon the mate- 

 rials of the earth's surface will, then, result as follows, according to our 

 laboratoiy experiments: 



The carbonic anhj^dride will, if previously formed, exist in a stable 

 state. Free oxygen and hydrogen will represent the present ocean, 

 water gas ceasing to be stable at normal pressures at temperatures 

 somewhat over 1,200° C. The alkaline earths, the iron, and the alka- 

 lies will be silicated and exist as lime, magnesium, iron, sodium, and 

 potash aluminum silicates in a state of fusion. Quartz melts below 

 1,500° C, and the largely preponderating number of silicates possess 

 melting points ranging between 900° and 1,500° C 



The chlorine, now combined, as assumed, with the sodium in the sea, 

 will have entered most probably into combination with the hydrogen 

 and exist as hydrochloric-acid gas. This compound is stable up to 

 1,700° C, nearly.=^ 



'Scottish Geological Magazine, 1895, p. 185. 



^The Melting Points of Minerals, by J. Joly, Proc. R. I. A., 1891, II, p. 44. 

 •nSee^the investigation of the stability of the compounds referred to by Carl Langer 

 and Victor Meyer, Pyrochemische Untersuchungen, Braunschweig, 1885. 



