Glossary of A First Look at Planet Earth

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A layer of soft but solid, mobile rock comprising the lower part of the upper mantle from about 100 to 350 kilometers beneath the Earth's surface.
continental drift
The initial theory that the continents broke off from the single supercontinent and plowed through the ocean floors into their present positions.
continental crust
The layer of low density material which form the continents.
convection cells
One of the main mechinisms that keep the plates in motion. As deep rocks and material are warmed they lighted and rise up. Near the surface they spread out laterally pulling the plates atop the athenosphere.
convergent plate boundary
When two plates collide with each other. Either through subduction or continental collision.
divergent plate boundary
When plates move apart and new plate material and new oceans grow.
igneous rocks
Rocks created from solidified molten material.
inner core
The solid most interior part of the Earth consisting primarily of metals like nickle and iron.
The rocky external outermost layer of the Earth consisting of the oceanic and continental crust as well as a portion of the upper mantle.
The middle layer of the Earth consisting of relatively dense rocks. There is an upper and lower mantle. It occupies most of the Earth.
metamorphic rocks
A rock that has changed structurally due to heat pressure or chemical reaction.
mid-ocean ridge
A divergent plate boundary that is located within the oceanic crust.
oceanic crust
Part of the lithosphere that is located at the bottom of the Earth's oceans. Its makeup is denser then that of the continental crust.
outer core
The liquid outer part of the Earth's core. Comprised of iron and nickle as well as some other metals. Possibly the mechinism that creates the Earth's magnetic field.
The single supercontinent that was believed to exist before plate tectonics tore it apart.
plate tectonics
The theory that superceded continental drift explaining the motion of the Earth's crust. Divided into plates, the Earths crust literally floats upon the athenosphere growing and colliding.
seafloor spreading
The process of plate growth at mid-ocean ridges where the plates are divergent.
sedimentary rocks
These rocks form when erosion breaks down preexisting rocks into minute fragments, sometimes accumulating with other biological and chemical material compacting together in layers
When two plates converge that have different densities. The one with the higher density will sink below the one that is lower in density.
transform plate boundary
Occur when two plates, continental or oceanic, slide against each other. Transform plate motion differs because in the process the plates neither collide nor grow.

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