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46 Cards in this Set
- Front
- Back
Which type of fossil can be used for relative dating?
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Index fossils
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What is a varve?
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Bands of alternating light-and dark-colored sediments of sand, clay, and silt.
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Contrast relative-age dating and absolute-age dating.
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Relative-age dating compares past geologic events based on order of strata in the rock record.
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Define evolution.
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The change in species over time.
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What are altered hard parts?
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The soft organic material decays quickly. The remaining hard parts can become fossils with altered hard parts.
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What is original preservation?
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The remains are altered very little. They require extreme circumstances, such as freezing, arid, or oxygen-free environments.
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Describe recrystallization.
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A buried hard part is subject to changes in temperature and pressure over time. (similar to mineral replacement.)
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Compare and contrast a mold and a cast.
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A mold is a fossil that forms when a shelled organism decays in sedimentary rock and is removed by erosion or weathering, leaving a hollowed-out impression. A cast is formed when an earlier fossil of a plant or animal leaves a cavity that becomes filled with minerals or sediment. They are the same because neither of them contain any original or altered material of the original organism.
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Describe how the fossil record helps scientists understand Earth's history.
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They provide evidence of the past existence of a wide variety of life forms; most of which are now extinct. It provides evidence that species have evolved.
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What are trace fossils?
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Trace fossils are fossils that can provide information about how an organism lived, moved, and obtained food.
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Compare and contrast the use of U-238 and C-14 in absolute-age dating.
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You use U-238 to date inorganic materials, and C-14 with organic materials. You would use U-238 to date a rock that's hundreds of millions of years old. (Because it has a longer half-life.) C-14 has a much shorter half-life than other isotopes. You would use C-14 for younger artifacts.
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Explain how radioactive decay can provide more accurate measurements of age compared to relative-age dating.
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The rate of radioactive decay is constant regardless of pressure, temperature, or any other physical changes, scientists use it to determine the absolute-age of the rock or object in which it occurs.
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What is the link between uniformitarianism and absolute-age dating.
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elements decay today at the same rate that they always have.
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Describe the usefulness of varves to geologists who study lake deposits.
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The alternating bands of sediment in varves help scientists date the cycles of deposition in glacial lakes.
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What is dendrochronology?
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The science of using tree rings to determine absolute age.
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What is radiocarbon dating?
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In radiocarbon dating, scientists use C-14 to determine the age of organic materials, which contain abundant carbon.
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What is a half-life?
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The length of time it takes for one-half of the original isotope to decay.
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Describe radiometric dating?
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When scientists date an object using radioactive isotopes, they are using radiometric dating.
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What is radioactive decay?
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The emission of radioactive particles and the resulting change into other isotopes over time.
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What was James Hutton known for?
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He was a scottish scientist who thought that the Earth was much older than 4,000 years.
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How do geologists determine the relative ages of rock sequences?
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With original horizontality, superposition, cross-cutting relationships, and inclusions.
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What are disconformities?
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They form when a horizontal layer of sedimentary rock overlies another horizontal layer of sedimentary rock, the eroded layer is a disconformity.
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What is a nonconformity?
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They form when a layer of sedimentary rock overlies a layer of igneous or metamorphic rock, such as granite or marble, the eroded surface uneven. It indicates a gap in the rock record, during which the rocks are uplifted, eroded at Earth's surface, and new layers formed on top.
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Angular unconformity
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Layers of sedimentary rock are deformed during mountain building.
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Explain how geologists use fossils to understand the geologic history of a large region.
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The fossils indicate similar times of decomposition even though the layers might be made of entirely different material.
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Describe original horizontality.
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The principle that sedimentary rocks are deposited in horizontal or nearly horizontal layers.
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Describe superposition.
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As layers are layed upon Earth, the older ones will be on the bottom, with the youngest on the top, unless something happens to change it.
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What are cross-cutting relationships?
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States that an intrusion is younger than the rock it cuts across.
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What is the principle of inclusions?
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The fragments (inclusions), in a rock layer must be older than the rock layer that contains them.
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Explain how fossil correlation can be used in geographically distant locations.
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Fossils can indicate similar times of deposition even though the layers might be made of entirely different material.
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What is a key bed?
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A rock or sediment layer used as a marker.
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What is a correlation?
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The matching of unique rock outcrops or fossils exposed in one geographic region to similar outcrops exposed in other regions.
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What is relative-age dating?
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A way to study the order in which geologic events occurred
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Explain why the geologic time scale is divided into eras and smaller divisions.
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They depend on the rock and species present at a certain time period.
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Name the geologic time divisions from largest to smallest.
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Eon, era, period, epoch.
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Why do scientists know more about the Cenozoic than they do about any other era?
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There has been less erosion, because it is the most recent era.
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Why do scientists know so little about Precambrian Earth?
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The organisms were soft-bodied, and therefore difficult to preserve-they wore away. The periods of the Precambrian were long.
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What is the oldest era of the Phanerozoic eon?
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Paleozoic. The order from oldest to youngest-- Paleozoic, Mesozoic, then the Cenozoic.
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What is the importance of extinction events to geologists.
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When something extincts, something else appears.
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How long do periods generally last?
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10,000,000 years or so.
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How long do epochs generally last?
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100,000 to 1,000,000s of years
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How long do eras generally last?
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10,000,000 to 100,000,000s of years
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What is mass extinction?
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When many groups of organisms disappear from the rock record at the same time.
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what is the purpose of the geologic time scale?
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The geologic time scale enables scientists to find relationships among the geologic.
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Geologic time scale
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A record of Earth's history from its origin (4.6 billion years ago.) to the present.
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Precambrian
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The 3 earliest eons make up 90% of geologic time... known together as Precambrian.
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