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. Trans- 

 formation of apes into man. 

 Early Cenozoic or Oligocene and Eocene time. Rise 



of higher mammals. 

 Mesozoic era. Age of reptile dominance. 



Cretaceous period. Rise of archaic or primitive 



mammals. 

 Comanchian period. Rise of flowering plants and 



higher insects. 



Jurassic period. Rise of birds and flying reptiles. 

 Triassic period. Rise of dinosaurs. 

 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. 

 Mississippian period. Rise of marine fishes. 

 Devonian period. First known amphibians. 

 Silurian period. First known land floras. 

 Ordovician period. First known fresh-water fishes. 

 Cambrian period. First abundance of marine animals, 



and dominance of trilobites. 

 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- 



