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LD ES - Ch 6
LD Earth Science - Chapter 6 - Interpreting Earth's History
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 Era |
Evolution | Principle that through Earth's history, living things have changed in form from a few simple organisms to a great diversity of organisms |
Extrusion | Rocks formed from lava that solidifies quickly at Earth's surface |
Fold | 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 form 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 a element with more or fewer neutrons then other forms of the same element |
Law of Superposition | Principle that the lowest layer in a sequence of rock strata must have been deposited before the layers above, unless the rock strata have been turned upside down |
Mass extinction | Extinction of a large number of species |
Original horizontally | 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 then something else |
Superposition | Principle that the lowest layer in a sequence of rock strata must have been deposited 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 geologic record caused by the erosion of sediments or rock followed by new deposition |
Uniformitarianism | Principal that most geologic events of the past are similar to processes that occur in the present |