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Geological Time
| Question | Answer |
|---|---|
| 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 type of fossilization where the physical characteristics of organisms are impressed onto rocks, especially coarse porous rocks such as sandstones. |
| original remains | hardened animal remains such as shells, bones, and teeth. |
| 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 geologic age of a fossil organism, rock, or geologic feature or event defined relative to other organisms, rocks, or features or events rather than in terms of years. |
| superposition | the order in which sedimentary strata are superposed one above another. |
| horizontality | at right angles to the vertical; parallel to level ground. |
| absolute age | the true age of a rock or fossil. Absolute age tells scientists the number of years ago a rock layer formed. |
| half-life | 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 | decay |
| geologic time | a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history. |
| eon | one billion years |
| era | a major division of geologic time composed of a number of periods. |
| period | the basic unit of geologic time, during which a standard rock system is formed: comprising two or more epochs and included with other periods in an era. |
| epoch | any of several divisions of a geologic period during which a geologic series is formed. |
| 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 lasted about 180 million years, and is divided into three periods, the Triassic, the Jurassic, and the Cretaceous. |
| cenozoic era | The Cenozoic spans only about 65 million years, from the end of the Cretaceous Period and the extinction of non-avian dinosaurs to the present. |
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