||Characteristic life.||Duration according to various estimates.|
|Millions of years.|
|Cenozoic (recent life).
(Great Ice Age).
|"Age of man." Animals and plants of modern types.
||1 to 5.|
|"Age of mammals." Possible first appearance of man. Rise and
development of highest orders of plants.|
|Mesozoic (intermediate life).||Cretaceous.
||"Age of reptiles." Rise and culmination of huge land reptiles
(dinosaurs), of shellfish with complexly partitioned coiled shells
(ammonites), and of great flying reptiles. First appearance (in Jurassic)
of birds and mammals; of cycads, an order of palmlike plants (in
Triassic), and of angiospermous plants, among which are palms and
hardwood trees (in Cretaceous).
||4 to 10.|
||"Age of amphibians." Dominance of club mosses (lycopods) and plants of
horsetail and fern types. Primitive flowering plants and earliest
cone-bearing trees. Beginnings of backboned land animals (land
vertebrates). Insects. Animals with nautilus-like coiled shells
(ammonites) and sharks abundant.||17 to 25.|
||"Age of fishes." Shellfish (mollusks) also abundant. Rise of amphibians
and land plants.|
||Shell-forming sea animals dominant, especially those related to the
nautilus (cephalopods). Rise and culmination of the marine animals
sometimes known as sea lilies (crinoids) and of giant scorpion-like
crustaceans (eurypterids). Rise of fishes and of reef-building
||Shell-forming sea animals especially cephalopods and mollusk-like
brachiopods, abundant. Culmination of the buglike marine crustaceans
known as trilobites. First trace of insect life.|
||Trilobites and brachiopods most characteristic animals. Seaweeds (algae)
abundant. No trace of land animals found.|
||First life that has left distinct record. Crustaceans, brachiopods, and
|No fossils found.||50+.|