278 A CENTURY OF GEOLOGY. 



to answer this question by estimates based on the rates of sedimenta- 

 tion and erosion, or else on the rate of changes of organic forms by 

 struggle for life and survival of the fittest. Physicists have attempted 

 to answer the same question by calculations based on known laws of 

 dissipation of energj^ in a cooling body, such as the sun or the earth. 

 The results of the two methods ditfer widely. The estimates of the 

 geologists are enormous, and growing ever greater as the conditions 

 of the problem are better understood. Nothing less than several 

 hundred million years will serve their purpose. The estimates of the 

 physicists are much more moderate, and apparently growing less with 

 each revision. The latest results of King and Kelvin give only twenty 

 to thirty millions.^ This the geologist declares is absurdly inadequate. 

 He can not work freely in so narrow a space — he has not elbow room. 



The subject is still discussed very earnestly, but with little hope of 

 definite conclusion. One thing, however, must be remarked. Both 

 parties assume — the geologist tacitly, the physicist avowedly — the 

 nebular hypothesis of the origin of the solar system, and therefore 

 the early incandescent fluid condition of the earth as the basis of all 

 his reasonings. Now, while this is probably the most reasonable view, 

 it is not so certain that it can be made the basis of complex mathemat- 

 ical calculation. There is a possible alternative theory, viz, the 

 meteoric theory, which is coming more and more into favor. Accord- 

 ing to this view the planets may have been formed l>y aggregation of 

 meteoric swarms and the heat of the earth produced ))y the collision 

 of the meteors in the act of aggregation. According to the one view 

 (the nebular) the heat is all primal, and the earth has been only losing 

 heat all the time. According to the other, the aggregation and the 

 heating are both gradual, and may have continued even since the earth 

 was inhabited. According to the one, the spendthrift earth wasted 

 nearly all its energ}' before it became habitable or even a crust was 

 formed, and therefore the habitable period nuist be comparatively 

 short. According to the other, the cooling and the heating, the 

 expenditure and the income, were going on at the same time, and 

 therefore the process may have lasted much longer. 



The subject is much too complex to be discussed here. Sufiice it 

 to say that on this latter view not only the age of the earth, but many 

 other fundamental problems of dynamical geology, would have to be 

 recalculated. The solution of these great questions must also be left 

 to the next century. In the meantime we simply draw attention to 

 two very recent papers on the subject, viz. that of Lord Kelvin,'^ 

 and criticism of the same by Chamber lin.^ 



^Clarence King, American Journal of Science, pp. 45-51, 1893; Kelvin, Science, 

 Vol. IX, p. 665, 1899. [Smithsonian Report, 1898.] 

 -Science, Vol. IX, p. 665, 1899. [Smithsonian Report, 1898.] 

 ^Ibid., p. 889, and Vols. X and XI, 1899. [Smithsonian Report, 1899.] 



