30 JotyY—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. On 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 107, 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. 
IJ.—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 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 the temperature 5370°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 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 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.+ 
That the sodium chloride could not exist as such is shown in the every-day 
* «The Melting Points of Minerals.” By J. Joly. Proc. R.I.A., 1891, 11, p. 44. 
+ See the investigation of the stability of the compounds referred to by Carl Langer and Victor Meyer. 
‘“‘ Pyrochemische Untersuchungen.” Braunschweig, 1885. 
