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18 Cards in this Set
- Front
- Back
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Correlation
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Establishing the equivalence of rocks of similar age in different areas
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law of superposition
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this law states thati n an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it
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unconformity
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represents along period during which deposition stopped erosion, removed previously formed rocks, and then deposition resumed. It is a surface that represents a break in the rock record, caused by erosion resumed.
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relative dating
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to identify which rock units formed first, second, third, and so on. It also tells us the sequence in which events occurred, not how long they occurred
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uniformitarianism
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simply states that the physical, chemical, and biological laws that operate today have laos operated in the geologic past. It means that the forces and processes that we observe today have been at work for a very long time
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fossil
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the remains or traces of prehistoric life. They are important components of sediment and sedimentary rocks
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index fossil
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a fossil that is associated wit ha particular span of geologic time
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half-life
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a common way of expressing the rate of radioactive decay. It is the amount of time necessary for one half of the nuclei in a sample to decay to its stable isotope
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radioactivity
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when nuclei are unstable, and they spontaneously break apart or decay
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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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radiocarbon dating
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method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample
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geologic time scale
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the divisions of earth's history in the blocks of time-eons, eras, periods, and epochs; the time scale was created using relative dating principles
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eon
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the largest time unit on geologic time scale, next in order of magnitude above era
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era
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a major division on the geologic time scale; eras are divided into shorter 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; it may be divided into smaller units called epochs
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epoch
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a unit of the geologic time scale that is a subdivision of a period
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principle of horizontality
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this is another one of stends observation that means that the layers of sediment are generally deposited in a horizontal position
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principle of cross-cutting relationships
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this relationship is an important principle used in relative dating. An intrusive rock body is younger than the rocks it intrudes. A fault is younger than the rock layers it cuts. This states that when a fault cuts through, or when magma intrudes other rocks and crystallizes we can assume that the fault or intrusion is younger than the rocks affected
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