Term
| Principle of Superposition |
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Definition
| The oldest beds are on the bottom and the youngest are on top in a sequence of undeformed sedimentary rocks. |
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Term
| Principal of Original Horizontality |
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Definition
| Sedimentary layers are horizontal, or nearly so, when originally deposited. Strata that are not horizontal have been deformed by movements of Earth's crust. |
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Term
| Principle of Faunal Succession |
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Definition
| Groups of fossil plants and animals occur in the geological record in a definite and determinable order. |
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Term
| Principle of Crosscutting Relations |
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Definition
| Geologic features, such as faults, and igneous intrusions are younger than the rocks they cut. |
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Term
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Definition
| A rock body that contains inclusions of preexisting rocks is younger than the rocks from which the inclusions came from. |
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Term
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Definition
| A principle that geologic processes that occured in the past can be explained by current geologic processes. |
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Term
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Definition
| The age of an object in relation to the ages of other objects. |
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Term
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Definition
| A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. |
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Term
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Definition
| 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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Term
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Definition
| A banded layer of sand and silt that is deposited annually in a lake, especially near ice sheets or glaciers, and that can be used to determine absolute age. |
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Term
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Definition
| A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope. |
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Term
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Definition
| The time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope. |
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Term
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Definition
| The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock. |
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Term
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Definition
| The scientific study of fossils. |
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Term
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Definition
| A fossilized mark that formed in sedimentary rock by the movement of an animal on or within soft sediment. |
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Term
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Definition
| A fossil that is used to establish the ae of rock layers because it is distinct, abundant, and widespread and existed for only a short span of geologic time. |
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