AGE OF EARTH AND OCEAN KNOPF 199 



table gives the present status of the geologic time scale as expressed in 

 lead ratios. 



Despite the fact that at present many of the lead ratios listed in Table 

 LXXXII ^ are individually weak, they are nevertheless so consistently compat- 

 ible with each other from end to end that as a whole they provide a most 

 convincing demonstration of the method. 



In Part V ^ Brown discusses the age of the earth from the point of 

 view of the astronomer. The conclusion is reached that there are 

 no known methods derived from astronomical data alone for esti- 

 mating the age of the earth. The estimate based on atomic disin- 

 tegration (2X10^ years) is consistent, however, with the astronom- 

 ical probabilities. 



II. THE AGE OF THE OCEAN 

 THE PROBLEM 



The age of the ocean is usually estimated by dividing the total 

 sodium content of the ocean by the amount of sodium newly brought 

 to it each year by the rivers of the world. The assumptions that 

 underlie this procedure are : (1) There was no sodium in the primeval 

 ocean; (2) the sodium washed into the ocean has been steadily accu- 

 mulating, the amount lost by precipitation being negligible; and 

 (3) the annual increment determined from present-day data has been 

 constant throughout geologic time. 



THE SODIUM OF THE PRIMEVAL OCEAN 



No definitive answer can be given as to the amount of sodium in the 

 primeval ocean. In fact, the problem is linked with our ideas on the 

 origin of the planet. If the earth grew by the accretion of cold 

 planetesimals according to the hypothesis of Chamberlin, the ocean 

 must have grown slowly in size and probably in salinity. If, how- 

 ever, it condensed from a gaseous state, the ocean was born when 

 the temperature fell below the critical temperature of water, 374° C, 

 and may have contained chlorides that were condensed or formed by 

 the attack of hot h3^drochloric acid on the crust at that time. 



Joly (1899) has attempted to evaluate the amount of sodium 

 chloride present in the " primeval " ocean, that is, the salt present 

 in the ocean at the time it formed from the condensation of the 

 gaseous envelope of the globe. The subtractive correction thus ob- 

 tained amounted to 12.5 per cent of his estimate of the age of the 

 ocean. F. W. Clarke, distinguished for his work on the age of the 

 ocean by the sodium method, ignores this phase of the problem. 



The great chemist, Lavoisier, considered the ocean to be the wash 

 water of the globe. Many, however, including most German au- 



^ Of the bulletin referred to in the footnote 1 on the first page of this article. 



