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Geological Time
| Term | Definition |
|---|---|
| fossil | the preserved remains of an organism, or traces of an organism such as a mark or print left by an animal |
| carbon films | a thin film coatings which consist predominantly of the chemical element carbon |
| mold | a fossil that forms when the remains of an organism leave an imprint in the sediment after the organic material has been completely replaced |
| casts | a type of fossil formed when sediment fills a mold of an organic object such as a fossil shell, creating a replica of that object made of sediment |
| trace fossils | fossilized evidence of plant existence or animal movements such as root channels, footprints, and burrows |
| paleontologist | scientist who studies fossils and the fossil record |
| relative age | the dating of events based solely upon the order in which they occurred |
| absolute age | the age given in years, of a fossil, a rock, a feature, or an event; usually determined through radiometric dating |
| superposition | the ordering of sedimentary layers of rock with the oldest on the bottom and the youngest on top |
| index fossils | fossils of organisms belonging to species that existed in large numbers for a relatively short amount of geologic time; used to date the rocks in which they are found |
| radioactive decay | a process by which an unstable atom loses energy by emitting ionized particles over a period of time |
| half-life | the time in which half the atoms of a radioactive material disintegrate |
| eon | the longest division of time in the geologic time scale |
| era | the second-longest division in the geologic time scale, measured in tens- to hundreds-of-millions of years |
| epoch | a division of the geologic time scale that is smaller than a period and measured in hundreds of thousands to millions of years |
| mass extinction | the loss of many species throughout the world in a short period of time |
| Paleozoic era | the earliest of three geologic eras |
| Mesozoic era | includes the Triassic, Jurassic, and Cretaceous Periods and is characterized by the development of flying reptiles, birds, and flowering plants and by the appearance and extinction of dinosaurs. |
| Cenozoic era | pertaining to the present era, beginning 65 million years ago and characterized by the ascendancy of mammals. |
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amauri.021
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