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Geological Time
| Term | Definition |
|---|---|
| fossil | any remains, impression, or trace of a living thing of a former geologic age, as a skeleton, footprint, etc. |
| index fossil | a widely distributed fossil, of narrow range in time, regarded as characteristic of a given geological formation, used especially in determining the age of related formations |
| Permineralized remains | a process of fossilization in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue |
| molds & casts | a print of a fossil or footprint |
| original remains | the evidence in rock of the presence of a plant or an animal from an earlier geological period. Fossils are formed when minerals in groundwater replace materials in bones and tissue, creating a replica in stone of the original organism or of their tracks |
| trace fossils | a fossilized track, trail, burrow, boring, or other structure in sedimentary rock that records the presence or behavior of the organism that made it |
| relative age | the science of determining the relative order of past events without necessarily determining their absolute age |
| superposition | the order in which sedimentary strata are superposed one above another. |
| horizontally | of material on a printed page |
| absolute age | the true age of a rock or fossil |
| half life | Physics. the time required for one half the atoms of a given amount of a radioactive substance to disintegrate |
| isotopes | any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights |
| radioactive decay | disintegration of a nucleus that occurs spontaneously or as a result of electron capture. One or more different nuclei are formed and usually particles and gamma rays are emitted Sometimes shortened to decay Also called disintegration |
| geologic time | the succession of eras, periods, and epochs as considered in historical geology |
| eon | on billion years |
| era | a period of time marked by distinctive character, events, etc. |
| period | any specified division or portion of time |
| epoch | a particular period of time marked by distinctive features, events, etc. |
| pangaea | the hypothetical landmass that existed when all continents were joined, from about 300 to 200 million years ago |
| trilobite | any marine arthropod of the extinct class Trilobita, from the Paleozoic Era, having a flattened, oval body varying in length from 1 inch (2.5 cm) or less to 2 feet (61 cm) |
| precambrian | noting or pertaining to the earliest era of earth history, ending 570 million years ago, during which the earth's crust formed and life first appeared in the seas |
| Mesozoic era | the 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. See Table at geologic time |
| Cenozoic era | The most recent era of geologic time, from about 65 million years ago to the present. The Cenozoic Era is characterized by the formation of modern continents and the diversification of mammals and plants. Grasses also evolved during the Cenozoic. |
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