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FCSDGeo-Earth Hist
Interpreting Earth's History vocabulary (6)
| Term | Definition |
|---|---|
| absolute age | age of a rock unit, a fossil, or an event expressed in units of time, such as years |
| absolute time scale | geologic time that uses numerical time units (years) |
| carbon-14 | radioactive form of the element carbon that has been used to determine the absolute age of recent fossils & geologic events |
| correlation | matching rock layers in different locations by age or by rock types |
| decay product | element produced by the decay of a radioactive isotope |
| decay-product ratio | ratio between the mass of a radioactive element & its decay product |
| era | large division of geologic time such as the Mesozoic |
| evolution (organic) | principle that through Earth's history, living things have changed in form from a few simple organisms to a great diversity of organisms |
| extrusion | molten, liquid rock (lava) flowing out onto Earth's surface, forming a fine-grained igneous rock |
| folds | layers of rock that have been bent by forces within Earth |
| geologic time scale | divisions of Earth's history originally based on observations of fossil evidence; now, through the use of radioactive isotope measurements, it has changed from a relative scale to an absolute scale |
| half-life | time for half the atoms in a radioactive sample to change to the decay product |
| index fossil | fossil found over a large geographic area but which existed for a brief period of geologic time |
| intrusion | molten, liquid rock (magma) pushed into cracks within Earth's crust; a body of coarse grained igneous rock formed by slow cooling within Earth |
| isotope | form of an element with more or fewer neutrons that other forms of the same element |
| mass extinction | extinction of a large number of species |
| original horizontality (law of) | principle that all sedimentary layers were originally flat |
| orogeny | process of mountain building caused by forces within Earth |
| period | subdivision of an era |
| radioactive | emission of energy rays or nuclear particles due to the breakdown of an unstable isotope |
| relative age | comparative age; age expressed as before or after other events without specifying the age in units |
| relative time scale | time scale that indicates whether the object in question is older or younger than something else |
| superposition (law of) | principle that the lowest layer in a sequence of rock strata must have been depositied before the layers above, unless the rock strata have been turned upside down |
| tilted sedimentary layers | beds of rock (usually sedimentary) thought to have been deposited horizontally that have been pushed into a different inclination (angle), usually by motions of Earth's crust |
| unconformity | gap in the geologic record caused by the erosion of sediments or rock followed by new deposition |
| uniformitarianism | principle that most geologic events of the past are similar to processes that occur in the present |
| cross-cutting (law of) | an igneous intrusion, folded or faulted layers are younger than the rock layers it cuts across, shifts or bends - layers form first before they are changed |
| included fragments (law of) | pieces of one rock found in another must be older that the rock in which they are found |
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