Geologic Time and Dating Methods

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Geologic Time

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The huge span of time covering Earth’s history, broken into different sections.

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Precambrian

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The earliest and longest part of Earth’s history, before most life forms appeared.

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Paleozoic

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The era when the first fish, plants, and animals with shells and bones appeared.

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Mesozoic

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The “Age of Reptiles,” when dinosaurs and the first small mammals lived.

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Cenozoic

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The “Age of Mammals,” when mammals and humans became common.

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Pangaea

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A supercontinent that once included almost all the land on Earth, before it broke apart.

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Absolute Dating

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A method that tells the actual age of a rock, fossil, or object in years.

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Relative Dating

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A method that tells which rocks or fossils are older or younger, but not their exact age.

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Radiometric Dating

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A way to find the age of rocks by measuring how radioactive elements have changed over time.

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Radioactive Isotope

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An unstable isotope that slowly breaks down into a new element.