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Chart of Geological Ages

Module by: Jack E. Maxfield. E-mail the author

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GEOLOGICAL AGES

Table 1: Geological Ages
**65 million years ago at the boundary between the geologic mesozoic and cenozoic periods, life in the oceans changed dramatically, with massive extinction of earlier life forms and explosive evolution of new ones. (Table references: 8, 202, 224)
ERA SUB-ERA YRS. BEFORE PRESENT PERIOD EPOCH CHARACTERIZED BY
Pre-Cambrian Archeozoic 5,000,000,000 to 1,000,000,000     Earth's crust. Unicellular organisms
Pre-Cambrian Proterozoic 1,000,000,000 to 600,000,000     Bacteria, algae, fungi and simple multicellular organisms
Phanerozoic** Paleozoic 600,000,000 to 220,000,000 From Cambrian thru Caroniferous & Permian   Development of animals from marine invertebrates up through insects and reptiles.
Phanerozoic Mesozoic (Warm & rather uniform global climate) 220,000,000 to 65,000,000 Triassic   Volcanic activity, marine reptiles, dinosaurs. As period started all continents were more or less locked together in a supercontinent (Pangaea_. A great bight Tethys extended between Asia and Africa and perhaps between Old and new Worlds. Number of marine species dropped by nearly 60% , but 40% of present land area became flooded. In No. Amer. sea over entire mid-continent region from Gulf deep into Canada & from Rockies to Appalachians. Africa split into large islands.
Phanerozoic Mesozoic (Warm & rather uniform global climate) 220,000,000 to 65,000,000 Jurassic   Dinosaurs, conifers.
Phanerozoic Mesozoic (Warm & rather uniform global climate) 220,000,000 to 65,000,000 Cretaceous   Extinction of giant reptiles. Insects and flowers.
Phanerozoic Cenozoic 65,000,000 to 38,000,000 Tertiary Paleocene Eocene Birds & Mammals.
Phanerozoic Cenozoic 38,000,000 Tertiary Oligocene Saber-tooth cats. Continents assumed approx. present position & a cold current circled Antarctica with relatively little water diverted northward, so temperature gradient from equator to So. Pole increased.
Phanerozoic Cenozoic 26 to 7,000,000 Tertiary Miocene Grazing mammals. First major Antarctic glaciations.
Phanerozoic Cenozoic 7 to 2,000,000 Tertiary Pliocene Mountains; climate cooling; increase in size and numbers of mammals. Man?
Phanerozoic Cenozoic 2,000,000 to 10,000 Quaternary PLEISTOCENE - ICE AGES. DEFINITE APPEARANCE OF MAN  
Phanerozoic Cenozoic 10,000 to present Quaternary HOLOCENE DEVELOPMENT OF MAN, THE SOCIAL ANIMAL.

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