The Geotectonic 



Factor 



The products of organic evolution are the result of 

 the interplay between a spontaneously dynamic biota 

 and a spontaneously dynamic environment. Without 

 the dynamic nature of the biota, evolution would 

 not have occurred. Without the particular kind of 

 dynamics present in the environments on the earth, 

 either evolution would have followed an entirely 

 different course or life itself might not have evolved. 

 The environmental dynamics owe their ultimate 

 basis to geotectonic events which have been alluded 

 to only briefly in the preceding pages. 



The dynamics of the earth's crust produce dynamic 

 environments. Facets of this changing environment 

 affecting evolutionary processes include the rise and 

 subsidence of land bridges, changes in climatic zona- 

 tion and extremes, and the fomiation of new soils 

 and new climates. These changes are the product of 

 two great general forces which oppose each other 



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