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a large division of Earth's geologic time scale that is further divided into one or more periods.
preserved evidence of an organism, often found in sedimentary rock, that provides evidence of past life.
layer of iridium-rich material between rocks of the Cretaceous period and rocks of the Paleogene period that provides evidence of a meteorite impact.
law of superposition
states that the oldest layers of rock are found at the bottom and the youngest layers of rock are found at the top of a formation if the rock layers have not been disturbed.
geologic theory that Earth's surface is broken into several huge plates that move slowly on a partially molten rock layer.
method used to determine the age of rocks using the rate of decay of radioactive isotopes.
method used to determine the age of rocks by comparing the rocks with younger and older rock layers.
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