THE AGE OF THE EARTH.* 



By Clarence King. 



Among the vari(»us attempts to estimate geological time none lias 

 ofleied a more attractive field for lurtlier develoi)ment than Lord Kel- 

 vin's mode of limiting the eartii's age from considerations of its prob- 

 able rate of refrigeration, pnblished in 186U.+ At that time the conse- 

 quences of his physical reasoning could not be fully applied to the con- 

 ditions within the earth, so as to test the probability of his hyi)othet- 

 ical case, for want of positive knowledge of certain properties of rocks, 

 particularly the volume changes of melted rock in approaching and 

 experiencing congelation, and the qualitative and quantitative effects 

 of pressure upon the fusion and freezing points. Data then lacking are 

 for the first time available, and with them it is proposed to apply a new 

 criterion to the gradient of Lord Kelvin and to compare with it other 

 cases of more probable earth-temperature distribution, which should 

 have the effect of advancing his method of determining the earth's age 

 to a further order of importance. 



Accepting the hitherto unshaken results of Kelvin and G. A. Darwin 

 as to the tidal effective rigidity of the earth, and the further argument 

 for rigidity advanced by Prof. S. Newcombf from the data of the lately 

 ascertained periodic variation of terrestrial latitude, as together war- 

 ranting a firm belief in the rigid earth, it follows that solidity may be 

 used as a criterion to test the probable truth of many cases of earth 

 temperature distribution; at least so far as to justify the rejection of 

 such as involve considerable liquidity of the upper couches. In an 

 earth of which the superficial quarter of radius is composed of mate- 

 rials that contract from the fluid condition toward and in the act of 

 congelation, any temperature gradient in which the downward heat 

 augmentation exceeds the rate by which advancing pressure raises the 

 fusion point, would obviously reach a fused couche, and all such distri- 

 butions may be rejected as violating the requirements of rigidity. 



* From American Journal of Science, January, 1893, 3d series, vol. xlv, pp. 1-20. 

 t Treatise on Natural I'hilofiopliij, Thomsou & Tait, Part 2, A])pt'ii(lix D. 

 \ Monthly Notices of the I\oyal As1rono)iiicol Societij, 1892, vol. lii, No. 5. 



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