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13 Cards in this Set
- Front
- Back
Uniformitarianism
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the forces and processes that we observe today have been at work for a very long time
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Relative dating
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identifying which rocks formed 1st, 2nd, 3rd, and so on. tells us the sequence in which events occured, NOT when they occurred.
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Law of superposition
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in sedimentary rocks, this law says that each bed is older than the one above it and younger than the one below it.
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Principle of original horizontality
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means that layers of sediment are usually deposited in a horizontal position
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Principle of cross-cutting relationships
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when a fault cuts through rock layers or when magma goes through rock, we can say that the fault is younger than the rocks affected
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Unconformity
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break in the rock record when sediment deposits have been interrupted again and again.
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Correlation
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rocks of same age in different places are matched up to develop a geologic time scale for the whole Earth.
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Fossil
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remains of prehistoric life.
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Index fossil
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fossils in many places, limited to a short span of time, and occur in large numbers. they provide an important method of matching rocks of the same age.
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Radioactivity
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when nuclei are unstable, they break apart or decay
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Half-life
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amount of time for 1/2 of the nuclei to decay to its stable isotope
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Radiometric dating
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provides a way to calculate the ages of rocks that contain radioactive isotopes
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Radiocarbon dating
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used to date recent events (up to 75,000 years ago) by measuring the carbon-14 that decreases in living thing as it decays.
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