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The age of an object in relation to the ages of other objects.
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A principle that geological processes that occurred in the past can be explained by current geological proccesses.
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The principle that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed.
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A break in the geological record created when sediment is not deposited for a long time.
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The principle that a fault or body of rock is younger than any other body of rock that it cuts through.
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The numeric age of an object or event, often stated in years before the present, as established by an absolute dating process, such as radiometric dating.
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A pair of sedimentary layers that is deposited in an annual cycle, commonly in glacial lakes, and that can be used to determine the absolute age.
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A method of determining the absolute age of an object by comparing the relative percentage of radioactive parent and stable daughter isotope.
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The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope.