Age of the Earth 85 



of life. His plea for more time since the cooling of the 

 globe than physicists were willing to allow remains one 

 of the classics of geological literature. But he carried 

 the question much farther. The inference which was 

 widely drawn by the enemies of evolution from the 

 arguments of Sir William Thomson w^as that if geo- 

 logists had overestimated the age of the cooled earth 

 there was not time for the evolution of animals and 

 plants to have taken place. Huxley pointed out a fact 

 which should be quite obvious, but which even yet is 

 frequently neglected. The evidence for the gradual 

 appearance of life in the past history of the earth de- 

 pends simply on the fact that the successive forms 

 of life appear in successive strata, and the length of 

 time taken for these changes simply depends upon the 

 length of time which was taken up b}' the formation of 

 the strata. Our only reason for supposing the evolu- 

 tion of life, made plain by fossil records, to have taken 

 place very slowly is that geologists have stated that the 

 deposition of the strata took place very slowl3\ Whether 

 these strata were deposited slowl}' or less slowly, we 

 know that the forms of life changed at the same rate. 



" Biology takes her time from geology. The only reason we 

 have for believing in the slow rate of change in living forms is 

 the fact that they persist through a series of deposits which, 

 geology informs us, have taken a long while to make. If the 

 geological clock is wrong, all the naturalist will have to do is 

 to modify his notion of the rapidity of change accordingly ; and 

 I venture to point out that, when we are told that the limita- 

 tion of the period during which living beings have inhabited 

 this planet to one, two, or three hundred million years re- 

 quires a complete revolution in geological speculation, the 

 onus probandi rests on the maker of the assertion, who brings 

 forward not a shadow of evidence in its support." 



Perhaps, although this is now an old controversy, it is 



