| Era and Duration | Period | Epoch | Began (millions of years ago) |
Principal Events of the Era |
| CENOZOIC 65 million yrs |
Quaternary | Recent Pleistocene |
(11,000 yr) 1 |
Age of humans; end of last ice age; warmer climate. First human societies; large-scale extinctions of plant and animal species; repeated glaciation |
| Tertiary | Pliocene | 5 | Appearance of hominids; volcanic activity; decline of forest; grasslands spreading; cooling; glaciation. | |
| Miocene | 25 | Appearance of anthropoid apes; rapid evolution of mammals; formation of Sierra Mountains spread of grasslands. | ||
| Oligocene | 36 | Appearance of most modern genera of mammals and monocotyledons; warmer climate. | ||
| Eocene | 54 | Appearance of hoofed mammals and carnivores; heavy erosion of moutains. | ||
| Paleocene | 65 | First placental mammals. |
| MESOZOIC 160 million yrs |
Cretaceous | 135 | Appearance of monocotyledons; oak and maple forests; first modern mammals; beginning of extinction of dinosaurs; formation of Andes, Alps, Himalayas, and Rocky Mountains. | |
| Jurassic | 181 | Appearance of birds and mammals; rapid evolution of dinosaurs; first flowering plants; shallow seas over much of Europe and North America | ||
| Triassic | 220 | Appearance of dinosaurs; gymnosperms dominant; extinction of seed ferns; continents rising; desert conditions. |
| PALEOZOIC 360 million yrs |
Permian | 280 | Appearance of cycads; widespread extinction of animals; widespread glaciation; mountains rising; atmospheric carbon dioxide and oxygen reduced. | |
| Carboniferous | 345 | Appearance of reptiles; amphibians dominant; insects arise. Gymnosperms appear; vast forests; great life abundant. Climates mild, warm, and humid; low-lying land; extensive swamps; formation of enormous coal deposits. Many sharks and amphibians; large-scale trees and seed ferns. | ||
| Devonian | 405 | Appearance of seed plants; ascendance of bony fishes; first amphibians; small seas; higher, drier lands; glaciation. | ||
| Silurian | 425 | Atmospheric oxygen reaches second critical level. Explosive evolution of many forms of life over the land: first land plants and animals. Great continental seas; continents increasingly dry. | ||
| Ordovician | 500 | Appearance of vertebrates, but invertebrates and algae dominant. Land largely submerged; warm climates worldwide. | ||
| Cambrian | 600 | Atmospheric oxygen reaches first critical level. Explosive evolution of life in the oceans; first abundant marine fossils formed; trilobites dominant; appearance of most phyla of invertebrates. Low-lying lands; climates mild. |
| PRECAMBRIAN 2900 million yrs |
3500 | Life confined to shallow pools; fossil formation extremely rare; mountain building, erosion, and glaciation. Photosynthetic life. |
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