Seafloor Spreading

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Seafloor Spreading Noun

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[see-flor spred-ing]

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Seafloor Spreading

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The process where new oceanic crust forms at mid-ocean ridges and slowly moves outward across ocean basins.

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Example: Magma rises at a mid-ocean ridge, creating new oceanic crust and pushing older crust away, which causes the seafloor to spread apart.

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Continental Drift Noun

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[kon-tuh-nen-tl drift]

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Continental Drift

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The theory that continents were once joined together in a single landmass and have since moved apart over time.

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Example: This diagram shows the North American and Eurasian tectonic plates moving apart, a process that drives continental drift, with Iceland located on the dividing line.

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Lithospheric Plates Noun

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[lith-o-sfer-ik pleyts]

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Lithospheric Plates

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The large, rigid sections of Earth's outer layer that move due to convection currents in the underlying mantle.

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Example: This diagram shows how convection currents in the Earth's mantle cause the rigid lithospheric plates to move, leading to seafloor spreading at divergent boundaries.

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Convection Currents Noun

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[kon-vek-shun kur-ents]

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Convection Currents

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The circular movement of fluid in the mantle caused by heat differences, which drives the motion of tectonic plates.

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Example: This diagram shows how heat from the Earth's core causes material in the mantle to rise, cool, and sink in a circular pattern, creating convection currents that move tectonic plates.

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Mid-ocean Ridge Noun

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[mid-oh-shun rij]

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Mid-ocean Ridge

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A continuous underwater mountain range where new ocean floor is created by volcanic activity at divergent plate boundaries.

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Example: This diagram shows magma rising from a chamber to form new crust at a central rift valley, while tectonic plates spread apart, creating a mid-ocean ridge.

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Magma Noun

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[mag-muh]

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Magma

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Molten rock material found beneath the Earth's surface that rises from the mantle and forms igneous rock upon cooling.

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Example: This diagram shows molten rock, called magma, forming deep underground and rising to the surface to erupt from a volcano.

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Basalt Noun

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[buh-sawlt]

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Basalt

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A dark, dense, fine-grained volcanic rock that constitutes the majority of the Earth's oceanic crust.

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Example: This image shows hot, molten lava cooling and hardening into dark-colored basalt rock, the same process that forms new ocean floor at mid-ocean ridges.

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Paleomagnetism Noun

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[pey-lee-oh-mag-ni-tiz-uhm]

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Paleomagnetism

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The study of the record of Earth's magnetic field in rocks, which provides evidence for seafloor spreading.

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Example: As new seafloor is created at a mid-ocean ridge, minerals in the cooling rock record the Earth's magnetic polarity, creating a symmetrical pattern.

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Deep-ocean Trench Noun

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[deep-oh-shun trench]

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Deep-ocean Trench

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A long, narrow, and very deep depression on the ocean floor where older oceanic crust is subducted into the mantle.

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Example: This diagram shows a deep-ocean trench forming where a dense oceanic plate sinks, or subducts, beneath a less dense continental plate.

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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 where 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 sinking below a less dense continental plate, a process called subduction, which can cause volcanoes to form.