Geologic Time Scale

Proterozoic Eon

Division of the Geologic Timescale from 2.5 billion years to 542 million years ago.

Silurian Period

Division of the Geologic Timescale from 440 to 420 million years ago.

Triassic Period

A division of the Geologic Time Scale from 252 to 201 million years ago; first period in of the Mesozoic Era; the start and end are marked by mass extinctions. Dinosaurs (e.g. Coelophysis and Herrerasaurus) and mammals first appeared in this division.

Phanerozoic Eon

Division of the Geologic Timescale from 542 million years ago to the present.

Permian Period

Division of the Geologic Timescale from 300 to 252 million years ago; ended in the largest mass extinction in Earth's history.

Paleozoic Era

Division of the Geologic Timescale from 542 to 252 million years ago that includes six geological periods.

Ordovician Period

Division of the Geologic Timescale from 490 to 440 million years ago; during this time the first jawed fish evolved; ended with a mass extinction.

Mesozoic Era

Division of the Geologic Timescale from 252 to 66 million years ago; contains the Triassic, Jurassic, and Cretaceous periods; during this time dinosaurs, birds, and mammals evolved; commonly called "the Age of Dinosaurs".

Archean Eon

Division of the Geologic Timescale from 4 to 2.5 billion years ago; during this time, the atmosphere likely lacked free oxygen and stromatolites first appeared.

Cambrian Period

Division of the Geologic Timescale from 542 to 490 million years ago. Huge explosion of life; sponges, molluscs, worms, first vertebrate relatives, and many kinds of arthropods (including trilobites) evolved.

Carboniferous Period

Division of the Geologic Timescale from 355 to 300 million years ago. Amphibians were widespread in the abundant

swamps, and reptiles, the first amniotes,

evolved. Much of the coal that is mined today

formed from rotting plants in swamps.

Cenozoic Era

Division of the Geologic Timescale from 66 million years ago to the present; often called "The Age of Mammals"

Devonian Period

Division of the Geologic Timescale from 420 to 355 million years ago. Huge jawed

fishes, like Dunkleosteus, evolved in the seas,

and the first true sharks appeared. Lobe-finned

'fishapods', like Tiktaalik, ventured onto land,

and give rise to the tetrapods.

Ediacaran Period

Division of the Geologic Timescale from 635 to 541 million years ago. The oldest fossil evidence of multicellular life comes from this time.

Hadeon Era

Division of the Geologic Timescale from 4.6 billion to 4 billion years ago; the first geologic eon

Jurassic Period

Division of the Geologic Timescale from 201 to 145 million years ago; the second period of the Mesozoic Era. Dinosaurs present include the Allosaurids, while the first birds, like Archaeopteryx, also evolve.

Cretaceous Period

Division of Geologic Timescale from 146-65 million years ago; the third period of the mesozoic Era. Dinosaurs present include Tyrannosaurs and Pachycephalosaurs.