THE AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 241 



of heat may hj^pothetieally have occupied a period many thue.s the 

 twenty or twenty-live million jenvs postulated. It seems altogether 

 necessary to determine specifically the distribution of the heat in time 

 before any approach to a satisfactory application to geological history 

 can be made. The period of twenty or twenty-five million years named 

 can have little moral guiding force until this problem is solved. But 

 the literature of the subject shows an almost complete neglect of this 

 consideration. While certain of the physicists and astronomers have 

 been instructing us "esuperiore loco," they seem, with very rare 

 exceptions, to have overlooked this vital factor in the case. ' Even in 

 computing the sum total of heat they have, for the most part, heretofore 

 neglected the central condensation of the sun and in their computations 

 have substituted a convenient homogeneit}". This is recognized in a 

 more recent number of Science (May 26), in the article by Dr. See, 

 in which he ofl^ers a correction which involves an extension of the pre- 

 viousl}' assigned output (eighteen million times the present annual radia 

 tion) to about thirty-two million times the annual radiation. But even 

 in making this correction he neglects to consider the distribution of this 

 heat in time, and leaves upon the reader the impression that the life 

 history of the earth was limited to thirty-two million years. Assuming 

 the correctness of his computations, the past thermal discharge of the 

 sun is merely limited to thirty-two million times the present annual 

 expenditure. For aught that appears to the contrary, the actual output 

 of this heat may have been spread over any assignable number of years. 

 It is obvious, upon consideration, that a certain distribution of this past 

 heat would favor longevity of life upon the earth, provided it could 

 exist with a more limited heat supph* than the sun is now yielding. On 

 the other hand, it is equally evident that if the supply be distributed 

 in certain other ways, either in the nature of excessive prolongation or 

 of excessive concentration, the life era will be shortened. Doubtless 

 the admonitory physicists have assumed that it was sufficient for the 

 gross purposes of restraining geologists within due limits to determine 

 the total amount of heat without assiduously considering the actual 

 facts relative to its distribution, but some of us are unwilling to accept 

 this loose method of dealing with the problem, since there are resources 

 of application of which our physical -friends have perhaps not taken 

 cognizance. For example: 



1. If at a certain stage in the evolution of the sun it occupied essen- 

 tially all the space within the earth's orbit, and was giA'ing forth one- 

 half as much heat per j^ear as now, it would possibly have sufficed for 

 the needs of life upon the earth essentially as well as at present, without 

 the assumption of any change in the constitution of the earth or of its 

 atmosphere. For, on this supposition, approximately one-half of the 

 space into which the earth radiated its heat would be blanketed by the 

 sun, and the heat thrown forth from the earth would be measurably 

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