1 6 Where did Life Begin f 



be cooled by polewlse radiation than by- 

 equatorial ; or, secondly, this difference of di- 

 ameters is equivalent to having had a layer 

 around the earth of molten matter to be cooled 

 thirteen miles in thickness at the equator, and 

 tapering off to nothing somewhere north of the 

 Tropic of Cancer and south of the Tropic of 

 Capricorn in excess of the molten matter to be 

 cooled by polewise radiation, and this would 

 have tended to keep the polar regions con- 

 stantly in advance of all other parts of the 

 earth in cooling. 



In addition to all this, it is obvious that the 

 shape given to the earth by this difference of 

 diameters — this flattening at the poles of itself 

 — would somewhat lessen the angles of inci- 

 dent and reflection of the sun's rays within the 

 polar regions, which would still more decrease 

 their effect, and so reduce the offset to loss of 

 heat by radiation within these polar regions. 



Can it then be doubted that the frigid zones 

 first became cool enouofh to maintain life as 

 we now see it on the earth ? 



To state the matter briefly, the polar regions 

 have received less heat from the sun, have had 



