History of Earth

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Fossils Noun

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[fos-uhls]

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Fossils

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The preserved remains or traces of living things, which are often found embedded in layers of sedimentary rock.

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Example: Fossils are shown in layers of sedimentary rock, demonstrating how they are preserved over time.

Front

Geologic record Noun

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[jee-uh-loj-ik rek-erd]

Back

Geologic record

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The history of Earth and the evolution of life as inferred from the information contained within layers of rock.

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Example: The image shows rock layers in the Grand Canyon, illustrating Earth's history through labeled strata.

Front

Relative age Noun

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[rel-uh-tiv eyj]

Back

Relative age

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The age of a rock or geologic feature determined by comparing it to the ages of other rocks or features.

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Example: This diagram shows how rock layers are stacked over time, with the oldest at the bottom and the newest at the top, illustrating relative age.

Front

Absolute age Noun

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[ab-suh-loot eyj]

Back

Absolute age

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The specific number of years that have passed since a rock or geologic feature was formed.

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Example: The image shows rock layers with numerical ages, explaining how absolute age is determined.

Front

Law of superposition Noun

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[law uv soo-per-puh-zish-uhn]

Back

Law of superposition

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The principle that in undisturbed rock layers, the oldest layer is at the bottom and the youngest is at the top.

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Example: The image shows rock layers with the oldest at the bottom and youngest at the top, explaining the law of superposition.

Front

Igneous extrusion Noun

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[ig-nee-uhs ik-stroo-zhuhn]

Back

Igneous extrusion

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A type of igneous rock that forms when molten lava cools and solidifies on the Earth's surface.

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Example: The image shows lava flowing through a conduit and forming an igneous extrusion on the surface.

Front

Igneous intrusion Noun

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[ig-nee-uhs in-troo-zhuhn]

Back

Igneous intrusion

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A body of igneous rock formed when magma pushes into existing rock layers and hardens beneath the surface.

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Example: Magma pushes into existing rock layers, forming igneous rock beneath the surface.

Front

Fault Noun

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[fawlt]

Back

Fault

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A fracture or break in Earth's crust along which blocks of rock have moved relative to each other.

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Example: Sponges represent Earth's crust layers with a visible fault line showing movement.

Front

Index fossil Noun

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[in-deks fos-uhl]

Back

Index fossil

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A fossil of a widespread organism that lived for a short geologic time, used to date rock layers.

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Example: The image shows how index fossils help determine the age of rock layers by displaying fossil succession.

Front

Unconformity Noun

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[uhn-kuhn-fawr-mi-tee]

Back

Unconformity

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A surface that represents a gap in the geologic record, where rock layers have been lost due to erosion.

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Example: The image shows an unconformity where rock layers are interrupted, indicating a gap in the geologic record.