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Field Division of Education
Outline of the Geology and Paleontology of Scotts Bluff National Monument and the Adjacent Region
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GEOLOGIC TIME SCALE (Modified from Schuchert)

ErasPeriods DurationBiologic and Climatic Changes Ages
CenozoicPleistocene (Epoch)
Periodic glaciations. Dawn of social life and industry among men. Extinction of large mammals. Age of Man
Pliocene (Epoch)5% Cooling climate. Changing of man ape into man. Age of Mammals
Miocene (Epoch)5% Culmination of mammals and land floras.
Oligocene (Epoch)2%Rise of Anthropoids. Last of archaic mammals.
Eocene (Epoch)
Spread of modernized mammals. Dawn of modern life. Rise of grasses, cereals, fruits. Expansion of archaic mammals.
MesozoicCretaceous4% Last of the Ammonites. Extinction of Dinosaurs, Pterodactyls, and toothed birds. Rise of archaic mammals and birds. Spread of flowering plants and modern insects.Age of Reptiles and Ammonites
Jurassic2%Rise of toothed birds and spread of Pterodactyls. Spread of primitive mammals. Culmination of ammonites.
Triassic1%Rise of Dinosaurs, Pterodactyls, and primitive mammals. Spread of cycads and conifers.
PaleozoicPermian2% Periodic glaciations in southern hemisphere. Extinction of Trilobites and Paleozoic corals. Primitive insects. Age of Amphibians
CarboniferousPennsylvanian 2%Warm humid climate with extensive coal making. Dominance of spore floras. Spread of reptiles
Mississsippian2%Spread of ancient sharks and culmination of crinoids.
Devonian2%Rise of amphibians, marine fishes, and primitive ammonites. First spread of forests. Age of Fishes
Silurian1%Rise of air-breathing invertebrates. Spread of Paleozoic reef-corals. First known occurrence of land plants.
Ordovician3%Rise of fresh-water fishes and of corals. Spread of molluscs. Culmination of trilobites. Age of Marine Invertebrates
Cambrian4%Rise of shell-bearing molluscs. Dominance of trilobites. First appearance of well-known marine faunas.
Proterozoic Era75% Era of primitive marine life. An early and late glacial period.
Archeozoic EraEra of the oldest known life. Geologic history very obscure.Age of Larval Life


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