36 THE ORIGIN AND EVOLUTION OF LIFE 



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. 



Age of the Ocean Calculated from its Sodium Content - 



1S76. T. Mellard Reade. 



1899. J. Joly 80- 90 million years. 



1900. J. Joly 90-100 million years. 



1909. Sollas 80-150 million years. 



1910. Becker 50- 70 million years. 



1911. F. W. Clarke and Becker 94,712,000 years. 



1915. Becker 60-100 million years. 



1916. Clarke somewhat less than loo million years. 



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 100,000,000 years. The 63,000,000 

 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 sulphates as well 

 as its chlorides of sodium and of magnesium, its potassium, 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 



1 Becker, George F., 1015, p. 201; igio, p. 12. 



-After Becker, George F., 1910, pp. 3-5; and Clarke, F. W., 1916, pp. 150, 152. 



^ Becker, George F., 1910, pp. 7, 8, 10, 12. 



