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Unit 6 Vocabulary

Science vocab about geologic time scale.

TermDefinition
geologic time scale the record of Earth's history from its origin 4.6 bya to present.
mass extinction occurs when an unusually large number of organisms disappear from the rock record at about the same time.
uniformitarianism the theory that geologic time processes occurring today have been occurring since Earth formed.
relative-age dating establishing the order of the past geologic events.
original horizontality the principle that sedimentary rocks are deposited in horizontal or nearly horizontal layers.
superposition the principle that, in an undisturbed rock sequence, the oldest rocks are on the bottom and each consecutive layer is younger than the layer beneath it.
correlation matching of rock outcrops of one geographic region to another.
absolute-age dating a method that enables scientists to determine the actual age of certain rocks and other objects.
radioactive decay the emission of radioactive particles and its resulting change into other isotopes over time.
half-life the period of time it takes for a radioactive isotope, such as carbon-14, to decay to 1 half of its original amount.
trace fossils indirect fossil evidence of an organism; traces of worm trails, footprints, and tunneling burrows.
index fossils remains of plants or animals that were abundant, widely distributed, and existed briefly that can be used by geologists to correlate or date rock layers.
stromatolite a large mat or mound compound composed of billions of photosynthesizing cyanobacteria; dominated shallow oceans during the Proterozoic.
cyanobacteria are microscopic, photosynthetic prokaryotes that formed stromatolites and changed early Earth's atmosphere by generating oxygen.
geologic map shows the distribution, arrangement, and types of rocks below the sail, and other geologic features.
Created by: JangoFett
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