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Archaean Eon

Origin of Earth
Oldest known rocks on Earth's surface
Oldest fossils of cells (prokaryotes) appear
Concentration of atmospheric oxygen begins to increase

Proterozoic Eon/Ediacaran Period

Oldest fossils of eukaryotic cells appear/diverse algae and soft-bodied invertebrate animals appear

Cambrian Period

Sudden increase in diversity of many animal phyla (Cambrian explosion)

Ordovician Period

Marine algae abundant
Colonization of land by diverse fungi, plants, and animals


Diversification of early vascular plants


Diversification of bony fishes
First tetrapods and insects appear


Extensive forests of vascular plants form
First seed plants appear
Origin of reptiles
Amphibians dominant


Radiation of reptiles
Origin of most present-day groups of insects
Extinction of many marine and terrestrial organisms at end of period


Cone-bearing plants (gymnosperms) dominate the landscape
Dinosaurs evolve and radiate
Origin of mammals


Gymnosperms continue as dominant plants
Dinosaurs abundant and diverse


Flowering plants (angiosperms) appear and diversify
Many groups of organisms, including most dinosaurs, become extinct at the end of the period

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