||Duration||Biologic and Climatic Changes
||Periodic glaciations. Dawn of social life and industry
among men. Extinction of large mammals.
||Age of Man|
||Cooling climate. Changing of man ape into man.
||Age of Mammals|
||Culmination of mammals and land floras.|
|Oligocene (Epoch)||2%||Rise of Anthropoids.
Last of archaic mammals.|
|Eocene (Epoch)||Spread of modernized mammals.
Dawn of modern life. Rise of grasses, cereals, fruits. Expansion of
||Last of the Ammonites. Extinction of Dinosaurs, Pterodactyls, and
toothed birds. Rise of archaic mammals and birds. Spread of flowering
plants and modern insects.||Age of Reptiles and Ammonites|
|Jurassic||2%||Rise of toothed birds and spread
of Pterodactyls. Spread of primitive mammals. Culmination of ammonites.|
|Triassic||1%||Rise of Dinosaurs, Pterodactyls, and
primitive mammals. Spread of cycads and conifers.|
||Periodic glaciations in southern hemisphere. Extinction of
Trilobites and Paleozoic corals. Primitive insects.
||Age of Amphibians|
||2%||Warm humid climate with extensive coal making.
Dominance of spore floras. Spread of reptiles|
|Mississsippian||2%||Spread of ancient sharks and
culmination of crinoids.|
|Devonian||2%||Rise of amphibians, marine
fishes, and primitive ammonites. First spread of forests.
||Age of Fishes|
|Silurian||1%||Rise of air-breathing invertebrates.
Spread of Paleozoic reef-corals. First known occurrence of land plants.|
|Ordovician||3%||Rise of fresh-water fishes
and of corals. Spread of molluscs. Culmination of trilobites.
||Age of Marine Invertebrates|
|Cambrian||4%||Rise of shell-bearing
molluscs. Dominance of trilobites. First appearance of well-known
||Era of primitive marine life. An early and late glacial period.|
|Archeozoic Era||Era of the oldest known life.
Geologic history very obscure.||Age of Larval Life|