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Earth Science Regents Review Unit 5
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Sequence of Events Principle of Superposition: older layers are on the bottom Law of Original Horizontality: sedimentary layers are all horizontal before crustal movement Law of Cross Cutting Relationships: whatever cuts across a layer is younger than the layer Principle of Uniformitarianism: the way geologic events happened in the past happen in the same way today.
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An unconformity is a buried erosional surface. It is usually represented by a squiggly line in between layers. The steps are as follows: uplift and emergence weathering and erosion subsidence and submergence deposition of _______________
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How did this form?
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1) _________________is the matching of strata through fossils or characteristics of the layers to prove that they were once part of the same outcrop.
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What are index fossils? These are fossils found in many locations but only existed for one geologic time period. They are excellent time markers.
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Volcanic Ash Useful because volcanic ash could cover large areas in a very small period of time (days to weeks) and each volcano has a mineral “fingerprint” it is very useful in correlation
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The diagram below shows a fossil found in the surface bedrock of New York State. Which other fossil is most likely to be found in the same age bedrock? 1.Phacops 2.condor 3.Coelophysis 4.Tetragraptus
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1. 2. 3. 4. Which fossil may be found in the surface bedrock near Ithaca, NY?
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3) Define radioactive decay: The breakdown of an unstable atom into a more stable atom which is a completely different element.
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5) Parts of radioactive decay Parent isotope The unstable isotope Decreases during decay Daughter isotope The stable isotope Increases during decay A.k.a. decay product
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5) Define half life: It is the time needed for half of a substance to decay into its stable form.
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6) Why is the half life so useful for accurate dating? Nothing can change the half life.
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7) Which isotope should we use? Carbon- 14 Short half-life Dates living things Recent events of less than 50,000 years (Pleistocene to Holocene) Potassium-40 Looooong half-life Can be used on rocks Dates very old events
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# of half- lives # of years passed fraction remaining amount of C-14 amount of N-14 0 1 2 3 4
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How old is a substance that has 100g of Carbon-14 and 100 g of Nitrogen- 14? How old is a fossil that contains 25g of Potassium-40 and 175 g of Argon-40?
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