Principles of Geologic History

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What is a trilobite?

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A trilobite is one of the oldest known organisms, a type of marine arthropod that existed during the Paleozoic era.

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What does the Law of Inclusions state?

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The Law of Inclusions states that if one rock layer contains fragments of another rock layer, the fragments are older than the surrounding rock.

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What does the Law of Superposition state?

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The Law of Superposition states that in undisturbed rock layers, younger rocks lie above older rocks.

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What is absolute age?

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Absolute age is the actual age of a rock or fossil, often determined through radiometric dating.

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What is relative age?

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Relative age is the age of a rock or fossil in comparison to other rocks or fossils, without determining its exact age.

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What is the significance of fossils in geologic history?

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Fossils provide evidence of past life and can help date rock layers and understand the environment of the time.

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What are unconformities in geology?

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Unconformities are gaps in the geological record that occur when rock layers are eroded or not deposited for a period of time.

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What is the principle of Original Horizontality?

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The principle of Original Horizontality states that layers of sediment are originally deposited horizontally under the action of gravity.

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What is cross-cutting relationships?

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Cross-cutting relationships state that if a rock or fault cuts through other rocks, it must be younger than the rocks it cuts.

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What is a cast and mold fossil?

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A cast and mold fossil is a type of fossil that forms when an organism leaves an impression in sediment, which later hardens.