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20 Cards in this Set
- Front
- Back
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Nicholas Steno |
Law of superposition (oldest rocks are on the bottom and youngest are on the top) |
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Principles of Relative Dating |
Law of Superposition, Principle of Original Horizontality, Principle of Cross-Cutting Relationships, Inclusions, Unconformity, Correlation of Rock Layers |
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Determining Geologic Ages |
Relative and Numerical Dating |
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Principle of Original Horizontality |
If it isn't flat, you know something happened to the rock layer after it was deposited |
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Principle of Cross-Cutting Relationships |
In the case of igneous intrusions/faults younger features cut across older ones Sometimes a feature does not cut through all the other ones, and you know that fault occurred before the other layers were deposited |
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Inclusions |
Pieces of rocks enclosed in younger ones Rock containing inclusion is younger than inclusion itself and younger than the parent rock |
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3 Types of Uncomformity |
Angular, Non-conformity, Disconformity |
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Uncomformity |
Some kind of break in the rock record produced by erosion or no deposition - represents "lost time" |
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Angular Unconformity |
Tilted rocks are exposed, eroded, and overlain by flat-lying ones |
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Disconformity |
Rocks below and above are similar and show little evidence of erosion but can actually be a huge gap in time When it cuts deeper it is easier to find You are missing almost entire layers |
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Non-conformity |
Intrusive igneous rocks exposed through weathering and get deposited again |
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Correlation of Rock Layers |
You can use fossils as a sort of "index" for geologic time periods i.e. you know when one fossil lived and therefore you know the era of the rock or vice versa |
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William Smith |
Widely separated strata could be correlated by distinctive fossil content |
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Principle of Fossil Succession |
Fossil organisms succeed one another in a definite, determinable order and therefore any time period can be recognized by the fossils Dinos are often eroded and do not make good index fossils |
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Principles of Absolute (Numerical Dating) |
Using radioactive decay, you can predict when the mineral was deposited in a rock because decay works on proportions, so you don't have to know the original amount Igneous rocks are good for this -> they are deposited in dykes, ash, sills, plutons |
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Difficulties of Absolute Dating |
In Clastic sediment - the rocks are not as old as the parent The age of the mineral may not represent the time it was deposited (due to metamorphism) |
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Geologic Time Scale |
Eon -> Era -> Period -> Epoch |
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Eons |
Hadean, Archaeon, Proterozoic, Phanerzoic |
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Eras |
Paleozoic, Mesozoic, Cenozoic |
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Periods |
Quanternary Neogene Paleogene Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrain |
