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).
4 Billion Years Ago
First single-cell life forms emerge (bacteria).
3.6 Billion Years Ago
Oxygen producing bacteria appear.
1.8 Billion Years Ago
More complex single-cell life with cell nuclei begin to appear.
1 Billion Years Ago
Appearance of multi-celled eucaryotes.
485 Million Years Ago
First green plants and fungi begin to appear on land. Diversification of metazoans.
440 Million Years Ago
First vascular plants and millipedes appear on land.
420 Million Years Ago
First seed-bearing plants, ferns, and insects appear on land. First amphibians appear.
360 Million Years Ago
First land vertebrates, reptiles, large primitive trees and forests.
300 Million Years Ago
First true seed plants (gymnosperms) and mosses, formation of the Pangaea supercontinent, and dominance of mammal-like reptiles. Major extinctions.
250 Million Years Ago
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
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
First flowering plants and primates. Extinction of dinosaurs at the end of the period.
66 Million Years Ago
Modern plants appear and major diversification of mammals.
23 Million Years Ago
First apes appear. Australopithecines and Homo habilis appears. Cycles of ice ages. Carbon dioxide in atmosphere gradually reduced.
3 Million Years Ago
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
Appearance of modern humans.