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Geological Timescale

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Evolutionary Milestones

(544 mya to present)

Cenozoic Era
(65 mya to today)

Quaternary (1.8 ma to today)

Holocene (11,000 years to today)
Pleistocene (1.8 mya to 11,000 yrs) Homo erectus and Homo sapiens appear
Tertiary (65 to 1.8 mya) Pliocene (5 to 1.8 mya) Ape-like ancestors of modern humans (Hominids), the Australopithecines
Miocene (23 to 5 mya) Grazing horses, antelopes appear
Oligocene (38 to 23 mya)

Radiation of more modern animals: most modern bird forms have appeared; most modern mammals have appeared. First grasses appear.

Eocene (54 to 37 mya) Some modern mammals appear: advanced primates; camels, cats, dogs, horses & rodents
Paleocene (65 to 54 mya) Small mammals radiate
Mesozoic Era
(245 to 65 mya)

Cretaceous (146 to 65 mya)





Major extinction includes dinosaurs and ammonites (K-T)
Appearances include: flowering plants (angiosperms); lizards; snakes; social insects; marsupial and placental mammals
Modern insect forms radiate

Jurassic (208 to 146 mya) Appearances include: birds; crabs; frogs and salamanders

Dinosaurs radiate to dominate the land

Triassic (245 to 208 mya) Major extinction event: tabulate corals and conodonts disappear - ammonoids, reptiles and amphibians decimated
Appearances include: dinosaurs; crocodiles; marine reptiles; turtles and mammals
Major groups of seed plants appear


Paleozoic Era
(544 to 245 mya)

Permian (286 to 245 mya)

Major extinction of invertebrates (P-T). Trilobites fade away forever.
All but articulate crinoids disappear
Seed plants producing large trees

(360 to 286 mya)
Pennsylvanian (325 to 286 mya) Conifers and many winged insects appear
Mississippian (360 to 325 mya) Reptiles appear
Trilobites become scarce
Devonian (410 to 360 mya) Mass extinction (F-F)
Appearances include: insects; sharks; amphibians (tetrapods); lung fishes and earliest seed plants
Silurian (440 to 410 mya) Jawed fish and vascular plants appear
Ordovician (500 to 440 mya)
Mass extinction
First land plants; bryozoans appear. Trilobites begin to specialize.
Cambrian (544 to 500 mya) Tommotian (530 to 527 mya) Appearance of hard parts - fossils become common. Appearances include: vertebrates; jawless fish; small shelly animals; conodonts; trilobites radiate repeatedly and reach their peak diversity. First major radiation of animals

(4,500 to 544 mya)

Proterozoic Era
(2500 to 544 mya)

Vendian (650 to 544 mya) or Ediacaran

No Epochs
Extinction at end of Vendian
Macroscopic fossils of soft-bodied organisms.
Neoproterozoic (900 to 544 mya) - Late

Macroscopic fossils of soft-bodied organisms.
Stromatolites diminish

Mesoproterozoic (1600 to 900 mya) - Middle Eukaryotic organisms proliferate
Chloroplast endosymbiosis?
Paleoproterozoic (2500 to 1600 mya) - Early Eukaryotic organisms appear (acritarchs?)
Mitochondrion endosymbiosis?
Oxygen-releasing photosynthesizers appear, changing the atmosphere

(3800 to 2500 mya)

Early photosynthesis
Three domains' ancestors diverge
First life appears
(4500 to 3800 mya)
Earth possibly sterilized by heavy bombardment
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