30 JoLY — An Estimate of the Geological Age of the Earth. 



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. Ou this estimate, and accepting Sir John Murray's 

 estimate of the mean depth of the ocean (2076 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 years. 



This is probably the most accurate 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 man}'' 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 only at temperatures probably much exceeding 

 2000° 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 tlie temperature 370° C, and dissolved in it a quantity of a 

 halogen salt sufficient in amount — as may be easily shown — to cover the entire 

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



The effect of a temperature so elevated as 1500° C. upon the materials of the 

 Earth's surface will then result as follows, according to our laboratory experi- 

 ments : — 



The carbonic anhydride will, if jireviously 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 1200° C. The alkaline 

 earths, the iron, and the alkalies will be silicated and exist as lime, magnesium, iron, 

 sodium, and potash aluminium silicates in a state of fusion. Quartz melts below 

 1500° C. and the largely preponderating number of silicates possess melting 

 points ranging between 900° and 1500° 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 1700° C. nearly. t 



That the sodium chloride could not exist as such is shown in the every-day 



* " The Melting Poiats of Minerals." By J. Joly. Proo. E.I.A., 1891, ii., p. 44. 

 f See ttc investigation of tlie stability of tlie compounds referred to by Carl Langer and Victor Meyer. 

 " Pyrocbeniische Untcrsucliiingen." Braunscliwcig, 1885. 



