Plate Boundaries

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Plate Tectonics Noun

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[playt tek-ton-iks]

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Plate Tectonics

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The scientific theory that Earth's outer shell is divided into several plates that glide over the mantle.

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Example: This diagram shows a divergent plate boundary where two oceanic plates move apart, allowing magma to rise and form new crust at a mid-ocean ridge.

Front

Convection Currents Noun

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[kon-vek-shun kur-ents]

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Convection Currents

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The movement of fluid in the mantle, caused by differences in temperature and density, that drives plate tectonics.

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Example: Hot material in the Earth's mantle rises, cools, and sinks, creating circular convection currents that push and pull the tectonic plates on the surface.

Front

Seafloor Spreading Noun

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[see-flor spred-ing]

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Seafloor Spreading

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The process at mid-ocean ridges where new oceanic crust is formed through volcanic activity and then moves away.

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Example: This diagram shows how two oceanic crust plates move apart, allowing magma to rise from below and create new seafloor at a divergent boundary.

Front

Lithosphere Noun

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[lith-o-sfeer]

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Lithosphere

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The rigid outer part of the Earth, consisting of the crust and upper mantle, which is broken into plates.

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Example: This diagram shows the lithosphere as the rigid outer layer of the Earth, including the crust and upper mantle, which sits above the asthenosphere.

Front

Continental Crust Noun

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[kon-ti-nen-tal krust]

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Continental Crust

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The thick, less dense layer of rock which forms the continents and is too buoyant to subduct.

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Example: This diagram shows the thick continental crust, where land and cities are, overriding the thinner oceanic crust at a convergent plate boundary.

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Oceanic Crust Noun

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[oh-shee-an-ik krust]

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Oceanic Crust

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The thin, dense layer of rock that underlies the ocean basins and is composed primarily of basalt.

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Example: This diagram shows how new oceanic crust is formed by rising magma at a mid-ocean ridge and then moves away, eventually sinking under a continent.

Front

Plate Boundary Noun

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[playt bown-duh-ree]

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Plate Boundary

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The region where two of the Earth's tectonic plates meet, characterized by significant geological activity.

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Example: This diagram shows a convergent plate boundary, where two tectonic plates collide, causing one to slide under the other and form a volcano.

Front

Convergent Boundary Noun

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[kon-vur-jent bown-duh-ree]

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Convergent Boundary

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A tectonic boundary where two plates are moving toward each other, often resulting in one plate sliding under another.

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Example: This diagram shows an oceanic plate colliding with and sliding under a continental plate, a process called subduction, which forms deep ocean trenches and volcanic mountains.

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Subduction Noun

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[sub-duk-shun]

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Subduction

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The geological process in which one tectonic plate moves under another and is forced to sink into the mantle.

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Example: This diagram shows a dense oceanic plate sliding beneath a less dense continental plate, a process called subduction, which can cause volcanoes to form.

Front

Subduction Zone Noun

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[sub-duk-shun zohn]

Back

Subduction Zone

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The entire region at a convergent boundary where one tectonic plate is being forced down into the mantle.

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Example: This diagram shows a dense oceanic plate sinking beneath a continental plate, forming a trench and a volcanic arc, which defines a subduction zone.