i8 THE SCIENTIFIC MONTHLY
salt in the ocean might afford a means of computing its age. Assuming a primitive fresh-water sea^ Becker*^ in 1915 estimated the age of the ocean as between 50 and 70 million years, probably closer to the upper limit. The accumulation of sodium was probably more rapid in the early geologic periods than at the present time, because the greater part of the earth's surface was covered with the granitic and igneous rocks which have since been largely covered or replaced by sedimentary rocks, a diminution causing the sodium content from the earth to be constantly decreasing.** This is on the assumption that the primitive ocean had no continents in its basins and that the continental areas were not much greater than at the present time, namely, 20.6 per cent to 25 per cent, of the surface of the globe.
Agb of ths Ooxan Oaloxtlated from its SoDmic Content**
1876. T. MeUard Beade
1899. J. Joly 80-90 mUlion years.
1900. J. Jolj 90-100 miUion yean.
1909. SoUas 80-150 mUlion yean.
1910. Becker 50- 70 mUUon yean.
1911. P. W. Clarke and Becker 94,712,000 yean.
1915. Becker 60-100 mimon yean.
1916. Clarke Boxnewhat less than 100 million yean.
From the mean of the foregoing computations it is inferred that the age of the ocean since the earth assumed its present form is somewhat less than 100 million years. The 63 million tons of sodium which the sea has received yearly by solution from the rocks has been continually uniting with its equivalent of chlorine to form the salt (NaCl) of the existing seas.^^ So with the entire present content of the sea, its sul- phates as well as its chlorides of sodium and of magnesium, its potas- sium, its calcium as well as those rare chemical elements which occasion- ally enter into the life compounds, such as copper, fluorine, boron, barium — all these earth-derived elements were much rarer in the pri- mordial seas than at the present time. Yet from the first the air in sea- water was much richer in oxygen than the atmosphere.** The primal sea was also devoid of those nitrogen compounds which are chiefly derived from the earth through the agency of the nitrifying bacteria. Those who hold to the hypothesis of the marine origin of protoplasm fail to account for the necessary proportion of nitrogenous matter there to begin with.
•7 Becker, George P., 1910, pp. 16, 17. •8 Becker, George F., 1915, p. 201; 1910, p. 12.
M After Becker, George F., 1910, pp. 3-5; and Clarke, F. W., 1916, pp. 150, 152.
«o Becker, George F., 1910, pp. 7, 8, 10, 12.
41 Pirsson, Louis V., and Schuchert, Charles, 1915, p. 84.
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