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3.5: Subdivisions of the Structure of the Solid Earth

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    Subdivisions of the Structure of the Solid Earth

    The Earth consist of several parts: a core, a mantle, and a crust. Other planets and moons in our Solar System share some of these characteristics:

    -The crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crust is mostly composed of relatively low-density silicates minerals rich in aluminum. The crust is a comparatively thin outer skin that ranges from about 2 miles (3 km) thick at the oceanic ridges to 40 miles (70 km) under some mountain belts. Gravity measurements show that the crust is separated into thin oceanic (3.0 gm/cc) and thicker continental crust (2.7 gm/cc). The crust is more rigid than the underlying mantle, it is brittle, and hosts earthquakes.
    -The mantle is an inner layer of a terrestrial planet or other rocky body large enough to have differentiated in composition by density. On Earth, the mantle is a highly viscous layer between the crust and the outer core.
    • Composed of higher-density silicates rich in iron and magnesium that extends to a depth of about 1800 miles (2900 km).
    • Large portions can flow slowly and are near melting.
    -The core is the innermost part of the earth is believed to be a magnetic iron-nickel rich sphere that consists of a 758 mile (1220 km) thick solid and very dense inner core that is overlain by 1400 miles (2250 km) of dense molten material in the outer core. The outer core is liquid, and heat convection here creates currents in the liquid metal that generate Earth’s magnetic field.

    Other rocky planets and moons have also cores, mantles, and crusts, hydrospheres, and atmospheres. So far, only Earth is known to have a biosphere.

    Structure of the earth showing the asthenosphereFig 3-7. The asthenosphere is a part of the upper mantle that behaves in a more fluid-like manner than the overlying lithosphere. The lithosphere is cooler, and behaves in a more rigid or brittle manner. The lithosphere includes uppermost part of the mantle and overlying crust. It is the region where all earthquakes take place. Rocks in the asthenosphere are hot and will deform rather than fracture under pressure.

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