Trilobyte fossil (photo: Judy and Ed).Geologic time periods are based on fossil and geologic evidence. Such evidence provides information on the earth’s climate, geology, and lifeforms since the formation of the earth.

Photo: Trilobytes were an early form of life. (Creative Commons: Judy_and_Ed).

Geologic Time Periods

4.5 Billion Years Ago

Precambrian/Hadean Eon

Formation of the earth and moon.

4 Billion Years Ago

4 Billion Years Ago

PreCambrian/Archean Eon

First single-cell life forms emerge (bacteria).

3.6 Billion Years Ago

PreCambrian/Archean Eon

Oxygen producing bacteria appear.

2 Billion Years Ago

2 Billion Years Ago

PreCambrian/Proterozoic Eon

Build-up of oxygen in the atmosphere.

1.8 Billion Years Ago

PreCambrian/Proterozoic Eon

More complex single-cell life with cell nuclei begin to appear.

1 Billion Years Ago

1 Billion Years Ago

PreCambrian/Proterozoic Eon

Appearance of multi-celled eucaryotes.

540 Million Years Ago

Paleozoic Era/Cambrian Period

Cambrian explosion with major growth and diversification of life forms occurs. First fishes and vertebrates appear.

500 Million Years Ago

485 Million Years Ago

Paleozoic Era/Ordovician Period

First green plants and fungi begin to appear on land. Diversification of metazoans.

440 Million Years Ago

Paleozoic Era/Silurian Period

First vascular plants and millipedes appear on land.

420 Million Years Ago

Paleozoic Era/Devonian Period

First seed-bearing plants, ferns, and insects appear on land. First amphibians appear.

360 Million Years Ago

Paleozoic Era/Carboniferous Period

First land vertebrates, reptiles, large primitive trees and forests.

300 Million Years Ago

Paleozoic Era/Permian Period

First true seed plants (gymnosperms) and mosses, formation of the Pangaea supercontinent, and dominance of mammal-like reptiles. Major extinctions.

250 Million Years Ago

250 Million Years Ago

Mesozoic Era/Triassic Period

Permian-Triassic extinction event that causes over 95% of life to become extinct. First mammals and dinosaurs appear.  Archosaurs (bird and crocodile groups) become the dominant species.

200 Million Years Ago

Mesozoic Era/Jurassic Period

First birds and lizards. Diverse dinosaur species and small mammals become common. Gymnosperms and ferns are common plant life. Pangaea breaks up into Laurasia and Gondwanaland.

150 Million Years Ago

Mesozoic Era/Cretaceous Period

First flowering plants and primates. Extinction of dinosaurs at the end of the period.

100 Million Years Ago

66 Million Years Ago

Cenozoic Era/Paleogene Period

Modern plants appear and major diversification of mammals.

23 Million Years Ago

Cenozoic Era/Neogene Period

First apes appear. Australopithecines and Homo habilis appears. Cycles of ice ages. Carbon dioxide in atmosphere gradually reduced.

10 Million Years Ago

3 Million Years Ago

Cenozoic Era/Quarternary Period

Growth then extinction of many large mammals. Modern humans with Stone Age cultures appear.  First apes appear. Australopithecines and Homo habilis appears. Cycles of ice ages. Carbon dioxide in atmosphere gradually reduced.

100,000 Years Ago

100,000 Years Ago

Cenozoic Era/Quarternary Period

Appearance of modern humans.

10,000 Years Ago

10,000 Years Ago

Cenozoic Era/Quarternary Period

Human civilization emerges. Stone, then Bronze, then Iron Age cultures appear. Industrial Revolution.

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