ORIGIN AND DIFFERENTIATION 547 



question presents itself: What was the source or sources of heat that 

 kept the oceans of the globe so continuously warm during all or most of 

 early geologic time? x^ccording to H. F. Eeid/^ the earth's surface at 

 the present time receives from the sun at least 2,000 times as much heat 

 as from the interior of the earth itself ; yet, covering the period including 

 the Pleistocene and subsequent time, during which at least the sun is 

 admitted by all to have dominated earth temperatures, the heat supplied 

 from this source has not been sufficient to remove the polar ice-caps or 

 raise the surface temperature of polar waters even to 0° C, though it is 

 to be acknowledged that in many areas — perhaps everywhere — the re- 

 maining ice-covering is being very slowly reduced. 



In seeking a solution of this problem of source of supply of heat, let 

 us assume for the moment that it came from the sun and see what rea- 

 sonable conclusions can be reached on this basis. In the first place, the 

 whole matter is seemingly thrown out of court, as many times pointed 

 out in this paper, on the ground that if the sun had been the principal 

 source of heat in pre-Pleistocene time, terrestrial temperatures would of 

 necessity have been disposed in zones, whereas the whole trend of this 

 paper has been the presentation of proof that these temperatures were 

 distinctly non-zonal. Therefore it seems to follow that the sun — at 

 least the present small-angle sun — could not have been the sole or even 

 the principal source of heat that warmed the early oceans. 



Assuming again, for the sake of argument, that the conclusion regard- 

 ing the non-zonal disposition of temperatures was in error, and that the 

 heat for warming the early oceans actually did come from the sun, then 

 it must have been from a hotter, small-angle sun or from a diffuse, large- 

 angle sun. In either case the first eifect would be an increase in surface 

 temperatures, which would increase evaporation and thus make the cloud 

 envelope more complete and efficient; and this in turn would automatic- 

 ally, though perhaps intermittently, shut off the sun's rays from access 

 to the earth's surface. Considering the extreme slowness of the absorp- 

 tion of heat by water and the great amount that must have been necessary 

 to heat up and maintain the warmth of the oceans, it becomes increas- 

 ingly difficult — not to say impossible — to believe that it could have been 

 supplied by the sun under the conditions predicated. 



EVIDENCES OF GLACIATIOX 



By many it is thought that one of the strongest arguments against a 

 gradually cooling globe and a humid, non-zonally disposed climate in the 

 ages before the Pleistocene is the discovery of evidences of glacial action 



30 Science, new ser., vol. 29, 1909, p. 29. 



