THE FUTURE OF IVIAN AS AN INHABITANT OF THE 



EARTH ' 



By BDcBTLEY F. Mather 

 Professor of Geology, Harvard University 



During the first decade or two of the current century, geologists, 

 astronomers, and physicists engaged in many discussions concerning 

 the future of the earth as an abode for life. Some believed that "the 

 end of the world" was relatively close at hand ; others, that the pros- 

 pect for the future was to be measured in terms of hundreds of thou- 

 sands if not of millions of years. As usual in scientific circles, there 

 has emerged from the conflict of ideas during the years of discussion a 

 general unanimity of opinion, and today the geologic outlook for the 

 future of the earth is quite clear. 



Since the turn of the century new methods of measuring the length 

 of geologic time have been discovered and applied. New concepts of 

 the nature and sources of energy have been proposed and tested. New 

 data concerning astronomic space and the distribution of the stars 

 have been obtained. Innumerable details of earth history have been 

 deciphered to give a trustworthy record of the changes that the earth 

 and its inhabitants have undergone in the past. The key to unlock 

 the secrets of the future is now available in this knowledge of the past, 

 and with our present understanding of the processes of nature that 

 key may be intelligently used. All the evidence combines to lead us 

 unmistakably to the conclusion that for many scores, if not for hun- 

 dreds of millions of years to come, the earth will continue to be a 

 comfortably habitable abode for creatures like ourselves. 



Surface temperatures of the earth, the most important item in any 

 consideration of its long-range habitability, are detennined by the 

 receijot of solar energy distributed through atmospheric agencies. 

 For any given area of land the annual contribution of heat from the 

 earth's interior, hot though it may be, is just about equal to the warmth 

 received from the sun in 20 minutes by an equal area in equatorial 



^ Eighteenth Annual Sigma Xi Lecture, Columbus, Ohio, December 28, 1939. Reprinted 

 by permission, with slight revision, from Sigma Xi Quarterly, vol. 28, No. 1, Spring, 1940. 



215 



