Law of Superposition

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Relative Age Noun

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[rel-uh-tiv eyj]

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Relative Age

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The age of a rock or geological feature in comparison with other rocks, determining if it is younger or older.

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Example: This diagram shows that older rock layers are found below younger ones, and features like faults (E) or intrusions (D) are younger than the layers they cut through.

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Absolute Age Noun

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[ab-suh-loot eyj]

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Absolute Age

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The specific age of a geological material given in years, often determined through methods like radioactive dating.

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Example: This diagram shows a rock cross-section where specific layers, like volcanic ash, are given a numerical age (e.g., 495 million years ago), defining their Absolute Age.

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Radioactive Dating Noun

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[rey-dee-oh-ak-tiv dey-ting]

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Radioactive Dating

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A method used to determine the absolute age of materials by measuring the decay of their radioactive isotopes.

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Example: This graph shows that with each passing 'half-life' (time), the amount of a radioactive substance decreases by half, a principle used for dating materials.

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Stratigraphy Noun

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[struh-tig-ruh-fee]

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Stratigraphy

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The scientific study of rock layers, also known as strata, and their formation, sequence, and relationships to one another.

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Example: This diagram shows rock layers, or strata, stacked on top of each other. According to the Law of Superposition, the bottom layer (C) is the oldest, and the top layer (A) is the youngest.

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Strata Noun

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[strah-tuh]

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Strata

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Distinct layers of rock, sediment, or other geological material that are stacked on top of one another over time.

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Example: This cross-section shows rock layers, called strata, stacked on top of each other. The numbering demonstrates the Law of Superposition: older layers are at the bottom.

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Law of Superposition Noun

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

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Law of Superposition

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The geological principle stating that in an undisturbed sequence of rock layers, the oldest layers are at the bottom.

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Example: This diagram shows that in undisturbed layers of rock, the oldest layers are at the bottom and the youngest layers are at the top.

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Superposition Noun

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[soo-per-puh-zish-uhn]

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Superposition

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The principle that new rock layers are always deposited on top of existing rock layers, indicating their relative ages.

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Example: This diagram shows layers of rock (strata), where the oldest layers like shale are at the bottom and the youngest layers are at the top.