Earth History – Flashcards
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Fossil
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the remains or traces of an organism preserved from the geologic past
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Index Fossil
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a fossil that is associated with a particular span of geologic time
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Superposition (Law of...)
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a law that states that in any undeformed sequence of sedimentary rocks, each bed is older than the layers above and younger than the layers below
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Relative Dating
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process by which rocks are placed in their proper sequence or order
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Absolute Dating
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the determination of the age of an object with reference to a specific time scale, such as a fixed calendar or in years before present (BP)
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Unconformity
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a surface that represents a break in the rock record, caused by erosion or lack of deposition
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Radioactivity
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the spontaneous decay of certain unstable atomic nuclei
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Radiometric Dating
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the procedure of calculating the absolute ages of rocks and minerals that contain radioactive isotopes
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Half-Life
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the time required for one half of the atoms of a radioactive substance to decay
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Geologic Time Scale
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the division of Earth's history into blocks of time—eons, eras, periods, & epochs
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Eon
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the largest unit of time on the geologic time scale (broken into smaller units called eras)
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Era
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a major division on the geologic time scale (broken into smaller units called periods)
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Period
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a basic unit of the geologic time scale that is a subdivision of an era (broken into smaller units called epochs)
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Epoch
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smallest unit of geologic time
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Ice Age
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a period of time when much of the Earth's land is covered by glaciers
