Geology and Dating Methods

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Relative dating

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Any method of determining whether an event or object is older or younger than other events or objects.

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Absolute dating

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Any method of measuring the age of an event or object in years.

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Radiometric dating

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Method used to determine the age of rocks using the rate of decay of radioactive isotopes.

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Half-life

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Length of time required for half of the radioactive atoms in a sample to decay.

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Index fossil

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A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found.

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Fossil

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The preserved remains or traces of an organism that lived in the past.

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Geologic time scale

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A record of the geologic events and life forms in Earth's history.

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Precambrian Era

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Earth's first era that began 4.6 billion years ago, including the creation of the Sun, Earth, the atmosphere, oceans, and life; longest era due to Earth's formation.

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Paleozoic Era

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Second era on the geologic time scale; explosion of life including when animals began to invade land; ended with the largest mass extinction ever.

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Mesozoic Era

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Era 245-144 million years ago; rise of mammals and dinosaurs; the rise of birds; extinction of dinosaurs.