Geological Time

Eon/time Era Period / comment Epoch / comment

Hadean Eon : 4.6 - 3.8Ga

Archean Eon : 3.8 - 2.5 Ga

3.8-3.6 Ga Eoarchean





stromatolite reefs

3.6-3.2 Ga Paleoarchean
3.2-2.8 Ga Mesoarchean
2.8-2.5 Ga Neoarchean

Proterozoic Eon : 2.5 Ga ~ 542 Ma

2.5-1.6 Ga

Paleoproterozoic Era

Siderian 2.5-2.3

evolution of oxygenic photosynthesis

continents stabilized

Rhyacian 2.3-2.05
Orosinian 2.05-1.8
Stratherian 1.8-1.6
1.6-1.0 Ga Mesoproterozoic Era Calymmian 1.6-1.4

Rodinia starts to assemble

evolution of sexual reproduction

Ectasian 1.4-1.2
Stenian 1.2-1
1.0 Ga-542 Ma Neoproterozoic Era Tonian 1.0 Ga -850 Ma

glaciations dubbed "Snowball Earth"

earliest multicelled fossils

Cryogenian 850-635 Ma
Vendian or Ediacaran, 635-542

Phanerozoic Eon : 542 Ma - present

542-251 Ma Paleozoic Era Cambrian 542-488.3

Cambrian "explosion"


Ordovician 488.3-443.7

began and ended (2nd largest) with extinction events: graptolites, first jawed fish, land plants

Gondwana, Taconinc orogeny

Silurian 443.7-416

Named for Wales. Euramerica and Caledonian orogeny

graptolites, coral reefs, first bony fish, Myriapods were first terrestrial animals, first vascular plants; eurypterids; brachiopods, bryozoa, molluscs, and trilobites abundant in warm seas

Devonian 416-359.2 "Age of Fishes", first sharks, first ammonites; land - first tetrapods, insects, spiders, and seed-bearing plants
Carboniferous 359.2-299.0

Pangaea assembling, Hercynian and Alleghanian orogenies

Mississippian and Pennsylvanian separated by an unconformity: cyclothemic coal deposits, widespread epicontinental seas and carbonate depostion.

Insect and amphibian gigantism. Foraminifera prominent.

Permian 299-251


Permian-Triassic extinction event (largest) with loss of 90% to 95% of marine species and 70% of all land organisms

251-65.5 Mesozoic Era Triassic 251-199.6 starts and ends with extinction events, adaptive radiation after P-T extinction; angiosperms, pterosaurs
Jurassic 199.6-145.4

Pangaea break-up

"Age of Dinosaurs"

Cretaceous 145.4-65.5

Named for chalk (coccolith) deposits of France and South England

K-T boundary extinction event - Chicxulub impact crater

65.5-present Cenozoic Era Paleogene 65.5-23.03 Paleocene 65.5-55.8 (mammals)

Eocene 55.8-33.9 : ends with Grande Coupure extinction event

first modern mammals

Oligocene 33.9-23.03 : climate cooling begins by end of epoch
Neogene 23.03-present

Miocene 23.03-5.332

Horses, mastodons, first apes

Pliocene 5.332-1.806

Australopithecus, Homo habilis

Pleistocene 1.506-.005

glaciations, megafauna, anatomically modern humans

.005- present

end of recent glaciation, rise of civilization

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