Geologic time scale

Years Ago3,6	Epoch	Period/Age4,5		Era	Eon	Major Events
Present day	Holocene	Quaternary		Cenozoic	Phanerozoic
10,000	Pleistocene					Extinction of many large mammals. Evolution of fully modern humans
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
490*		Cambrian				Major diversification in the Cambrian explosion
545*		Neoproterozoic2		Proterozoic	Precambrian	First multi-celled animals
900		Mesoproterozoic
1600		Paleoproterozoic				First Complex single celled life
2500		Archaean				Simple single celled plants and animals
3800		Hadean				Formation of Earth

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. All dates given are for the end of the epoch in question.

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'.

6) The time shown in the "Years Ago" column is that of the end of the Epoch in the "Epoch" column.