NO. 6 AGE OF THE EARTH BECKER 11 



hypotheses each of which seems extreme, first that all of the questionable 

 amount of sodium is secular and second that two-thirds of it are juvenile. 



Before proceeding to these estimates, however, it is necessary to con- 

 sider other uncertainties. At the present day the continent of North 

 America stands above its average level, and this state of things appears 

 to prevail in the other continents as well. The effect is to increase the 

 potential of the streams and to hasten erosion. Again, the last glacial 

 period is recent; and the ice has laid bare great areas of feldspathic rocks, 

 which are thus more open to -weathering than they were during tlie Ter- 

 tiary. For this reason the yield of sodium per unit area must be above 

 the mean for drainage basins including glaciated areas. Corrections for 

 these conditions would tend to increase estimates of the earth's age. 

 Finally, marine erosion needs consideration. The abrasive effect of the 

 waves and tides on rock fragments and pebbles between high and low 

 water marks is intense and world-wide, but the average width of beach is 

 very small, much smaller than it would be were the continents to subside 

 even a couple of hundred feet, and smaller than the mean width for the 

 ocean's history. The sodium extracted by the waves is not represented in 

 the figures for the rivers and a correction for marine erosion would tend 

 to decrease estimates of the earth's age, or to offset the corrections for 

 glaciation and high level. It is to be hoped that means may be found of 

 evaluating the algebraic sum of these corrections, but I know of none ; I 

 cannot even guess its sign and must assume it to be zero. 



Supposing none of the river-borne sodium to be juvenile the annual 

 sodium increment is 98 x 10*' tons and the ratio of the total oceanic 

 sodium to this increment is 144.2 X 10^ This number of years would 

 be the corresponding age of the ocean if Mr. Joly's method of estimation 

 were adopted. Strictly speaking, the age should be somewhat greater, 

 because the whole of the secular sodium still remaining in the rocks ought 

 to be credited to the total oceanic sodium: but it is difficult to imagine 

 that this could have any substantial influence on so huge a total as 

 14 X 10^^ tons. On the second hypothesis, that 44 x 10" tons of sodium 

 are juvenile, the increment would be 142 x 10" tons and the ratio 

 99.5 X 10" provided that no allowance is made for juvenile additions to 

 the oceanic .sodium by submarine springs. Any such additions would be 

 equivalent to primitive salinity of the ocean and imply a further reduction 

 in age. 



Results of Asymptotic Accumulation 



To find the age of the ocean from the total oceanic sodium and its 

 annual increment, it is manifestly indispensable to know or to assume a 

 definite time relation between them. Mr. Joly's hypothesis is that the 

 total sodium of the ocean is the annual increment of sodium multiplied 

 by the age of the ocean in years; but another relation not less simple 



