8th grade Science The Rock Record–Chapter 8 – Flashcards
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The age of an object in relation to the ages of other objects is
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relative age
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The boundary between two sedimentary rock layers is called a(n)
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bedding plane
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Younger layers of undisturbed sedimentary rock are above older layers according to
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law of superposition
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The principle that Earth's history can be explained by current geologic processes is
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uniformitariansim
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If an igneous intrusion is observed through a layer of sedimentary rock, what geological law applies?
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the law of cross-cutting relationships
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A varve is most like a(n)
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a tree ring
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Almost all fossils are discovered in
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sedimentary rocks
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Index fossils found in rock layers in different areas of the world indicate that the rock layers were
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formed during the same time period
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Rates of erosion are not used to date geographical features over a million years old because
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the rate of erosion may greatly vary over a million of years
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How many years of deposition are represented by a single varve?
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one
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Carbon-14 is an isotope
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used to date objects less than 70,000 years old
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How much sedimentary rock is deposited over 1,000 years?
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30 cm
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The numeric age of an object is called
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absolute age
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A fault or body or rock is younger than any other body of rock it cuts through according to the law of:
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cross cutting relationships
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Using rates of erosion to determine the absolute age of a geologic feature is practical only for features formed within the past
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10,000 years to 20,000 years
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Why is radioactive decay used to determine the absolute age of rocks?
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radioactive decay happens at a relatively constant rate
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How is radioactive decay used to determine the absolute age of rocks?
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parent isotope is compared to daughter isotope
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The principle of uniformitarianism states that
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current geological processes can explain past processes
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How many half-lifes would be necessary for a sample of parent isotopes to decay to the point that only one-fourth of the sample is composed of parent isotopes?
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2
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In radiometric dating, scientist compare the proportion of a radioactive parent isotope to a stable
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daughter isotope
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One method used to estimate the absolute age of a stream is to
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measure the rate at which the stream erodes its bed
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Geologist estimate the Earth to be
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4.6 billions years old
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Atoms of the same element that have different numbers of neutrons are called
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isotopes
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The physician and farmer who has a keen observer of geologic changes taking place on his farm
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James Hutton
