Uniformitarianism / Geologic Dating

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Uniformitarianism

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The idea that the geological processes that happen today (volcanoes, faulting, erosion) have always happened on Earth.

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Original horizontality

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When sediments are laid down, they are horizontal. If rock layers are not horizontal, something happened to them.

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Law of Superposition

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In undisturbed rock layers, the oldest is at the bottom and the youngest is on the top.

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Folding

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Convergent boundary squeezes the rock and bends it.

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Faulting

Back

Break in the rock.

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Uplifting

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When some layers of rock are lifted from below.

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Intrusions

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Cracks in rock fill with magma which hardens.

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Unconformity

Back

When layers are eroded leaving a jagged top layer.

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Cross Cutting Relationship

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When layers of rock are cut across by folding, faulting, uplifting, or erosion.

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Radiometric Dating

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Finding the absolute age by testing how much of a radioactive element is still present.