Geologic time scale
| Years Ago3 | Epoch | Period/Age4 and 5 | Era | Eon | Major Events | |
|---|---|---|---|---|---|---|
| Present day | Holocene | Quaternary | Cenozoic | Extinction of many large mammals. Humans evolve | ||
| 10,000 | Pleistocene | |||||
| 1.6 million | Pliocene | Tertiary | Neogene | |||
| 5 | Miocene | |||||
| 23 | Oligocene | Paleogene | ||||
| 38 | Eocene | |||||
| 55 | Paleocene | |||||
| 64.3* | Cretaceous | Mesozoic | Dinosaurs reach peak, go extinct. Primitive placental mammals | |||
| 146 | Jurassic | Marsupial mammals | ||||
| 208 | Triassic | Egg-laying mammals | ||||
| 251.1* | Permian | Paleozoic | ||||
| 286 | Carboniferous1 | Pennsylvanian | Abundant insects, first reptiles | |||
| 325 | Mississippian | Large primitive trees | ||||
| 360 | Devonian | First amphibians | ||||
| 408.5* | Silurian | First land plant fossils | ||||
| 443.5* | Ordovician | Invertebrates dominant; first fishes | ||||
| 490* | Cambrian | Major diversification in the Cambrian explosion | ||||
| 545* | Neoproterozoic2 | Proterozoic | Precambrian | |||
| 900 | Mesoproterozoic | |||||
| 1600 | Paleoproterozoic | |||||
| 2500 | Archaean | |||||
| 3800 | Hadean | |||||
1) In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods
2) Discoveries in the past quarter century have substantially changed the view of geologic and paleontologic events immediately prior to the Cambrian. The nomenclature has not stabilized. The term Neoproterozoic is used here, but other writers might equally well have used one or more of the terms 'Ediacarian', 'Vendian', 'Varangian', 'Precambrian', 'Protocambrian', 'Eocambrian', or might have extended the Cambrian further back in time. All of these terms are usually treated as a subset of the Proterozoic rather than a period between the Paleozoic and the Proterozoic.
3) Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where we would most like to have them. Dates with an * are radiometrically determined based on internationally agreed to GSSPs.
4) Paleontologists often refer to faunal stages rather than geologic Periods. The Stage Nomenclature is quite complex. See http://flatpebble.nceas.ucsb.edu/public/harland.html for an excellent time ordered list of faunal stages. Also see the article on GSSPs.
5) In common usage the Tertiary-Quaternary and Paleogene-Neogene-Quaternary Periods are treated as equivalents to the Mesozoic and Paleozoic Periods. The term 'Age' (e.g. 'Neogene Age') is sometimes used instead of 'Period'.