THE AGE OF THE EARTH AND THE SALTNESS 

 OF THE SEA 



H. S. SHELTON 



Since the discovery of radioactivity, any estimation of geologic 

 time from the process of secular cooling, or from calculations of the 

 age of the sun's heat has become a process of very doubtful validity. 

 That being so, enhanced interest now accrues to any method not 

 based on these data. One of the most instructive of these is that 

 of Professor Joly' based on the saltness of the sea. But, standing as 

 it does on its own merits, and without collateral support, it is more 

 than ever necessary to examine carefully the foundations en which 

 it is based. 



The analysis of rocks shows clearly that the proportion of sodium 

 in the sedimentaries is much smaller than in the igneous rocks. The 

 natural inference from this is that the balance is to be found in the 

 ocean in the form of salt. Assuming these premises and a fairly 

 uniform rate of erosion, the estimation of geologic time is reduced 

 to a process of simple division. It is only necessary to find the total 

 quantity of sodium in the sea and the amount brought down by the 

 rivers each year. This, with some corrections, is Professor Joly's 

 method. The corrections, according to his estimate, are not con- 

 siderable and his calculation works out to something less than lOo 

 millions of years. 



The data for the two principal premises are derived from Sir 

 John Murray.^ This worker has carried out numerous investigations 

 on ocean depths and has also made estimates of the amount of solvent 

 denudation. That these are in the main fairly accurate can hardly 

 be disputed; but, as applied by Professor Joly to an entirely different 

 purpose, they are open to a number of criticisms. 



For our present purpose we will accept Sir John Murray's estimate 

 of the amount of the sodium in the sea; but the amount which enters 



1 Trans. Royal Society Dublin, Vol. VII, pp. 26 f. 



2 See Scottish Geographical Magazine (1887), and elsewhere. 



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