Geological Principles and Time Scale

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What is the Law of Superposition?

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The Law of Superposition is a geological principle that states in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layers below it.

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What is absolute dating?

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Absolute dating is precise and uses specific techniques (usually radioactive dating) to give a close exact age of rock layers or fossils.

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What is relative dating?

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Relative dating is an estimate that uses things like index fossils and the Law of Superposition to give a general age of older or younger based on the position of rock layers.

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What is a fault?

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A fault is what happens as a result of an earthquake that occurs and splits through layers of rock. A fault is always younger than the layers it goes through.

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What is an intrusion?

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An intrusion is when a layer of lava spreads through the earth but does not reach the surface. An intrusion is always younger than all the layers it passes through.

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What is an extrusion?

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An extrusion is when lava flows to the surface and hardens into an igneous rock layer. An extrusion is younger than any layers it passes through.

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What are index fossils?

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An index fossil is used to determine which layers of rock in the earth are closely related to each other and can be seen in different rock layers.

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What does it mean for something to go extinct?

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If something goes extinct, it means that the animal can no longer be found alive anywhere on Earth.

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What is the geological time scale used for?

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The geological time scale is used to help create an idea of what happened throughout the entire history of the planet.

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What are the 4 major Eras throughout all of history?

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The 4 major Eras are Precambrian, Paleozoic, Mesozoic, and Cenozoic.