216 ANNUAL REPORT SMITHSONIAN XNSTITUTION, 1940 



latitudes under a clear sky at midday. The niiieteenth-century pic- 

 ture of an earth, initially fiery hot but progressively cooling so that 

 yesterday it displayed a glacial climate and tomorrow it will be too 

 frigid to support life, may now be thrown into the discard. The earth 

 will "grow old and die" only as a result of failure to receive adequate 

 supplies of radiant energy from the sun. The prospect that the sun 

 will "burn itself out" in a decrepit old age is so remote as to bafl3e all 

 attempts to date that untoward event even by those who are expert in 

 manipulating astronomic figures. Nor is there any likelihood that 

 the space relations between earth and sun will change appreciably 

 within scores of millions of years and put the earth either too close to 

 the sun or too distant from it for comfort. 



The lurid pictures of a sudden catastrophic debacle resulting from 

 collision with some other heavenly body — comet, planet, star, or what 

 you will — are products of a vivid imagination wholly without founda- 

 tion in astronomic fact or theory. 



The only plausible alternative to the conclusion that earth and sun 

 will continue the even tenor of their ways for an inconceivably long 

 period of time is that the sun will some day imitate the supernovae 

 occasionally detected among the stars and terminate the existence of 

 the entire solar system by a gigantic explosion. Precisely one such 

 supernova has been observed within the galaxy of the Milky Way 

 and several such in all the other galaxies of stars during the past 

 few decades. The astronomers could, therefore, calculate for us the 

 chances on a statistical basis that any individual star — the sun, for 

 example — would suffer such a fate within any given period of time. 

 The result would be a figure so infinitesimal as to set at rest the 

 mind of even the most jittery of questioners. Pending the discovery 

 of the kind of premonitory symptoms displayed by stars about to 

 blow themselves to atoms, the best that can be done is to rest content 

 in history. Since the earliest records of living creatures were left as 

 fossils, if not indeed since the earliest sedimentary rocks were 

 formed, the sun has faithfully maintained its energy output within 

 a fairly narrow range and has given no evidence of any fluctuations 

 that might suggest any significant change in its behavior. 



The geologist may, therefore, turn with confidence from the long 

 perspective of geologic past with its 1^ to 2 billion years of recorded 

 earth history to a similarly long prospect for the future. Time is 

 one of the most overwhelming resources of our universe. 



It should not be inferred, however, that the earth will continue 

 in the future to display the same enviroimiental conditions as those 

 wliich we enjoy today. The history of mankind thus far has been 

 enacted against a background that in the full perspective of earth 

 history is truly extraordinary. The geologic period in which we live 



