Topic 13 Interpreting Geologic History Vocabulary

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inclusion
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Body of older rock within igneous rock
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extrusion
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Lava flows on the Earth’s surface and solidifies
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volcanic ash
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Consisting of sand sized and clay sized particles of extrusive igneous rocks shot into the air
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intrusion
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Magma squeezes into preexisting rocks and crystallizes
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absolute age
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Actual age of the rock or an event in years
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evolution
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States that life forms change through time
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bedrock
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An area’s local rock covered by soil and other loose materials
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radioactive decay
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Emission of particles and electromagnetic energy
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index fossils
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Fossils used in correlation that have lived over a wide geographic area and are short lived
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principle of superposition
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Rocks are deposited in layers with youngest on top, oldest on the bottom
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relative dating
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Determination of the age of a rock in relation to other rocks or events
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unconformities
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Evidence of buried eroded surfaces
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carbon-14
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Useful isotope with a half life of 5700 years that is used to date fossils or organic remains
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fossils
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Remains or evidence of former living things (bones, shells, footprints…)
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outgassing
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Gases from the Earth’s interior seeped out of the crust through cracks in the crust and volcanoes
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half-life
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Time required for half of the atoms in a given mass of an isotope to decay
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isotopes
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Elements exist in several different varieties
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radioactive dating
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Method used to estimate the absolute age of a rock
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geologic time scale
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Divisions of geologic time (Eons, Eras, Periods, Epochs) make up this chart
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uranium-238
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Important radioactive isotope used in dating very old rocks

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