U
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ultramafic
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A type of igneous rock that contains more than 90% mafic minerals.
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ultraviolet (UV)
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Electromagnetic radiation having wavelengths shorter than the violet.
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ultraviolet (UV) radiation
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High energy radiation from the Sun that can be dangerous to Earth’s life.
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umbra
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Inner cone shaped part of a shadow when all light is blocked during an eclipse.
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unconformity
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A gap between rocks of very different ages. Unconformities are often marked by an erosional surface.
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uniformitarianism
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Natural processes operated the same way throughout Earth’s history as they do today.
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universe
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Everything that exists; all matter and energy; also includes all of space and time.
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uplift
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The upward rise of rock material.
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upwelling
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Cold, nutrient-rich water that rises from oceanic depths.