asthenosphere | A region of Earth's outer shell beneath the lithosphere. The asthenosphere is of indeterminate thickness and behaves plastically.
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continental drift | A concept suggesting that continents move over Earth's surface.
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convergent boundary | A boundary between two plates that are moving toward each other.
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core | The central zone of Earth.
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crust | The outer layer of rock, forming a thin skin over Earth's surface.
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divergent plate boundary | Boundary separating two plates moving away from each other.
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equilibrium | Material is in equilibrium if it is adjusted to the physical and chemical conditions of its environment so that it does not change or alter with time.
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erosion | The physical removal of rock by an agent such as running water, glacial ice, or wind.
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hypothesis | A tentative theory.
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igneous rock | A rock formed or apparently formed from solidification of magma.
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isostatic adjustment | Concept of vertical movement of sections of Earth’s crust to achieve balance or equilibrium.
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lithosphere | The rigid outer shell of Earth, 70 to 125 or more kilometers thick.
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magma | Molten rock, usually mostly silica. The liquid may contain dissolved gases as well as some solid minerals.
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mantle | A thick shell of rock that separates Earth’s crust above from the core below.
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metamorphic rock | A rock produced by metamorphism.
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mid-oceanic ridge | A giant mountain range that lies under the ocean and extends around the world.
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plate tectonics | A theory that Earth's surface is divided into a few large, thick plates that are slowly moving and changing in size. Intense geologic activity occurs at the plate boundaries.
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scientific method | A means of gaining knowledge through objective procedures.
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sediment | Loose, solid particles that can originate by (1) weathering and erosion of preexisting rocks, (2) chemical precipitation from solution, usually in water, and (3) secretion by organisms.
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sedimentary rock | Rock that has formed from (1) lithification of any type of sediment, (2) precipitation from solution, or (3) consolidation of the remains of plants or animals.
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subduction zone | Elongate region in which subduction takes place.
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tectonic forces | Forces generated from within Earth that result in uplift, movement, or deformation of part of Earth’s crust.
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theory | An explanation for observed phenomena that has a high possibility of being true.
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transform plate boundary | Boundary between two plates that are sliding past each other.
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