74 



SCIENCE 



[N. S. Vol. XXXVII. No. 941 



The above results show that the earth in its 

 present form must be many times a hundred 

 million years old. 



However, if we take the evidence as based 

 on the result that is obtained by dividing the 

 total amount of sodium in the ocean by the 

 annual additions of all the rivers of the globe, 

 we find that the age of the ocean can not 

 be more than one hundred million years. 

 Two of the most eminent geologists, Y. W. 

 Clarke' and J. Joly,* think 70,000,000 years to 

 be more nearly the correct age. It seems to 

 me that these estimations were not made with- 

 out due consideration of the largest sources 

 of error. According to Clarke the saline mat- 

 ter of the ocean if segregated would occiipy 

 nearly five million cubic miles, a quantity 

 compared to which all beds of rock salt become 

 insignificant. He also considered the salt of 

 marine origin in sedimentary rocks and he 

 figured that a correction of not more than 

 one per cent, was necessary to allow for sodium 

 disseminated in this way. If there is error 

 due to unequal annual additions by the rivers, 

 Becker" argues that it is altogether in favor 

 of making the age of the earth yet smaller 

 rather than larger, perhaps between 50 and 70 

 million years. There is therefore a discrep- 

 ancy between the age of the earth as deduced 

 by the two methods. Joly in the Philosoph- 

 ical Magazine for September, 1911, favors the 

 view that the radioactive constants are in 

 error, because these constants have not been 

 taken from data extending over a suificiently 

 long time and under proper circumstances free 

 from doubtful assumptions. 



I wish to suggest that there is another ex- 

 planation of the discrepancy that requires no 

 distrust of the radioactive constants as they 

 have been experimentally determined. In fact, 

 the explanation is merely an extension of our 

 knowledge in radioactivity. The discrepancy 

 may be made to disappear if sodium is sup- 

 posed to belong to a series of radioactive ele- 



» Bulletin 491, U. S. Geol. Surv. 

 *Phil. Mag., Ser. 6, 22, p. 357, 1911. 

 'Quart. Jmirn. Sci., May, 1909. 



ments. If we accept the present data of radio- 

 activity as authoritative, then it must be ad- 

 mitted that there is not enough sodium in the 

 ocean. Perhaps during geologic time elements 

 of higher atomic weight may have been disin- 

 tegrating into sodium, and therefore the an- 

 nual output of the rivers now is not the same 

 as the average annual output for all time in 

 the past. That is, the sodium over the land 

 has been increasing by radioactive production 

 while sodium in the ocean has been increasing 

 almost entirely by the annual river supply. 

 This would necessitate that the parent of 

 sodium should commonly exist in relatively 

 insoluble compounds. Otherwise we should 

 have had sodium produced radioactively also 

 in the ocean, and perhaps sodium deposits in 

 the bottom of the ocean. The above fact 

 should give us some clue as to the parentage of 

 sodium, if our whole argument is not faulty. 

 Obviously those elements that have been de- 

 posited in the ocean bed in appreciable quanti- 

 ties are eliminated. 



The second way for explaining the small 

 sodium content of the ocean is to assume that 

 the sodium in the ocean has disintegrated into 

 otlier elements. The theory of radioactivity 

 as it now stands, however, requires that the 

 rate of decay of an element shall not be altered 

 by its physical state or surroundings. Then 

 it is highly probable that the sodium in the 

 ocean has not decayed faster than has the 

 sodium on the land, and therefore any dimin- 

 ished quantity of sodium on the ocean would 

 have been offset by a diminished annual addi- 

 tion of the rivers. But the quantity of sodium 

 carried by the rivers is not known to vary 

 greatly with the amount in the earth's crust. 

 It seems then that this second explanation is 

 within the limits of possibility. 



The simplest explanation and one which re- 

 quires no apologies or additional assumptions 

 is based on the supposition that the sodium on 

 the land has been increasing by virtue of the 

 existence of the parent of sodium there and 

 the non-existence of the parent in the ocean 

 or the ocean bed. Perhaps there would be less 

 chance for error if it were stated that the pres- 



