502 The Age of the Earth [Feb. 24, 



ture within must go on till the present epoch succumbs to the 

 accumulated energy. Then must ensue a period of vulcanicity 

 which will end life upon the globe, and probably reverse the 

 chemical work stored up by ages of denudative and organic activity. 

 The whole sequence of events — rapid cooling by radiation, re- 

 storation of the oceans, and, possibly, re-birth of life and of its 

 evolutionary history — would begin all over again. On this view the 

 age we have been studying may be one of many, and will inevitably 

 attain its three score and ten, terminating in labour and sorrow. 

 But there must come a rejuvenation, and the rejuvenation, possibly, 

 may one day be pondered by other minds than ours. Remember 

 that after some ten thousand millions of years there still survives 

 50 per cent, of the heat-generating elements, and the effect of their 

 diminution is only to lengthen out the recurring geological ages. 

 Our planetary companions may be in various stages of such cyclical 

 changes. 



[j. j.] 



