46 EVOLUTION OF THE EARTH 



Geologic time. 



Cenozoic era. Age of mammal dominance. 



Glacial or Pleistocene time. Last great ice age. 



Late Cenozoic or Pliocene and Miocene time. Rise of 



higher primates : apes and man. 

 Early Cenozoic or Ollgocene and Eocene time. Rise 

 of higher mammals, including primates. 

 Mesozolc era. Age of reptile dominance. 



Cretaceous period. Rise of archaic mammals. 

 Comanchlan period. Rise of flowering plants and 



higher Insects. 

 Jurassic period. Rise of birds and flying reptiles. 

 Triassic period. Rise of dinosaurs and primitive mam- 

 mals. 

 Paleozoic era. Age of fish dominance. 



Permian period. Rise of reptiles. Another great Ice 



age. 

 Pennsylvanian period. Rise of insects and first time 



of marked coal accumulation. 

 Mississlppian period. Rise of marine sharks. 

 Devonian period. First known amphibians and marine 



fishes. 

 Silurian period. First known land floras. 

 Ordovician period. First known fresh-water fishes. 

 Cambrian period. First abundance of marine fossils, 

 and dominance of trilobltes. 

 Proterozoic era. Age of invertebrate dominance. An 



early and a late ice age. 

 Archeozoic era. Origin of protoplasm and of simplest life. 

 Cosmic time. 



Formative era. Birth and growth of the earth out of 

 the spiral nebula of the sun. Beginnings of the atmos- 

 phere and hydrosphere, and of continental platforms 

 and oceanic basins. No known geological record. 



Origin of the sun and earth. Professor Barrell, In the pre- 

 vious lecture, pointed out that the sun Is a star, and one of the 

 smaller among the countless millions seen through the tele- 

 scope. It may have had Its origin in a diffuse nebula like 

 Orion, and, according to the disruption hypothesis of Cham- 



