Geologic Time Scale

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What is the Geologic Time Scale?

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A system of chronological dating that relates geological strata to time, used to describe the timing and relationships of events in Earth's history.

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What is an index fossil?

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A fossil that is used to define and identify a particular time period in the geologic time scale, typically widespread and existed for a short duration.

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Which fossil is considered the best index fossil?

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Frog, because it is a good indicator of a specific time period.

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What is relative age dating?

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A method of determining the age of rocks and fossils in relation to one another, without determining their exact age.

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What is absolute age dating?

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A method of determining the exact age of a rock or fossil, often using radiometric dating techniques.

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What does radiometric dating measure?

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The decay of radioactive isotopes in rocks and fossils to determine their age.

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What is the Precambrian supereon?

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The longest geologic time period, covering about 88% of Earth's history, before the Paleozoic era.

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What are the three main eras of the Phanerozoic eon?

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Paleozoic, Mesozoic, and Cenozoic.

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What is the law of superposition?

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In undisturbed rock layers, the oldest layers are at the bottom and the youngest are at the top.

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What does the law of crosscutting state?

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Any geological feature that cuts across another is younger than the feature it cuts through.