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Geologic Time
Term | Definition |
---|---|
Molds and casts | Acids eat away the skeleton or shell and leave an impression in the rock. If the mold fills with minerals, it becomes a cast. |
Tracks and trails | Imprints are left in the mud, which later hardens. Dinosaur tracks are fairly common, |
Carbonization | Oils leave the plant and the remaining matter becomes a layer of carbo. In other cases nitrogen, hydrogen, and oxygen are distilled from the plant. Most common method of fossilizing plants. |
Petrifaction | Minerals in the plant cells crystalize; minerals enter openings or cavities in shells or bones. Common with plants. |
Replacement | Object buried in mud has its molecules replaced by minerals. It is rare. |
Recrystallization | Mineral aragorite in shells turns to calaite. Preserves the general shape of the animal. |
Soft tissue preservation | Mummification, frozen in ice. Fossils are relatively young and do not last long. |
Traps | Whole organismslocked in tar pits, asphalt, amber, ect. |
Fossils | Are the imprints or remains of organisms that were once alive. They provide evidence for the Geologic Time Scale. |
Cenozoic | Quaternary, teriary, halocane, pleistocane, pliocene, miocene, oligocene, eocene, palocene |
Mesozoic | Cretaceous, Jurassic, Triassic |
Palezoic | Permian, Carboniferous, Devonian, Silurian, Ordovician, Cambrian |
Proterozoic | Archaeon, Hadean, Precambrian |
Eon | The largest group; divided by the Cambrian Boundary (about 550 millions of years ago) when the variety of life forms exploded; billions of years long. |
Era | Mass extinctions mark the boundaries between the eras; hundreds of millions of years long. |
Period | Blocks of time when a unique rock series was laid down; tens of millions years long. |
Epoch | Divisions of the most recent periods; sereral million years long. |
Humans | Eon: Phanerozoic, Era: Cenozoic, Period: Quaternary, Epoch: Holocene, Years Ago: 11,000-Present |
Rise of Mammals | Eon: Phanerozoic, Era: Cenozoic, Period: Tertiary, Epoch: Paleocene, Years Ago: 65-54 |
Birds | Eon: Phanerozoic, Era: Mesozoic, Period: Jurassic, Years Ago: 208-146 |