MILLIONS ' 



AGE OF MAN 



AGE 



OF 



MAMMALS - 



QUARTEHNARY 



u 



o 



N 



o 



U) 



u 



LOWER 

 CRETACEOUS 

 ■ (COMANCHEAN) 



AMPHIBIANS 



MILLIONS ' 



INVERTEBRATES 



EVOLUTION 



OF 



INVERTEBRATES 



EVOLUTION 



UNICELLULAR 



LIFE 



u 





 N 



o 

 < 



< 



(L 



PENNSYLVANtAN 



(UPPER 

 CARBONIFEROUS) 



MISSISSIPPIAN ' 



(LOWER 



CARBONIFEROUE) 



DEVONIAN 



ORDOVICIAN 



CAMBRIAN 



KEWEENAWAN 



SUDSURIAN 



GRENVILLE 



(KEEWATIN) 

 (COUTCHICHINO) 



UQU 



"Ed 



X Mm 



Q tU J 



u q: II) 



a: u) 



0- 7 P 



gis 



liS 



l-£ 



u^o 



OUlL 



o<o 



EDO 



uzo 

 zu z 



Fig. 5.— Total Geologic Time Scale, estimated at sixty million years. 

 Osborn's " Origin and Evolution of Life " [Charles Scribner's Sons].) 

 26 



(After 



