Where did Life Begin? 57 



stant lowering temperature of the earth, the 

 constant loss of heat during its life-history, 

 with the concurrent effects thereof, has been 

 directly or indirectly the great and all-suffi- 

 cient exterminator of extinct species ? 



Of course heat and cold are comparative 

 terms. But notwithstanding, as the whole 

 globe was once too hot, and certain portions 

 of it are now too cold for life, it follows con- 

 clusively that there is a definite range of 

 temperature, a fixed number of degrees of 

 heat, which constitutes the gamut of life. No 

 organism known can exist an instant above 

 or below it. The numerous subdivisions of 

 this life-scale, both cause and define the con- 

 ditions most favorable to the development of 

 the several species and varieties of plants and 

 animals. But a portion of these subdivisions, 

 viz. : the higher heat lines of this great life- 

 range have passed from the earth forever, or 

 rather, the earth has passed through them, 

 dropping from time to time the extinct species 

 which were only fitted for hotter climates, 

 while the cooler subdivisions, the lower heat 

 lines within this gamut of life, we are now 



