lithosphere

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Lithosphere

The word lithosphere is derived from the word sphere, combined with the Greek word lithos which means rock. The lithosphere is the solid outer section of Earth which includes Earths crust (the outermost layer of rock on Earth), as well as the underlying cool, dense, and fairly rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44-62 mi (70-100 km). This relatively cool and rigid section of Earth is thought to float on top of the warmer, non-rigid, and partially melted material directly below.

Earth is made up of several layers. The outermost layer is called Earths crust. The thickness of Earths crust varies. Under the oceans the crust is only about 3-5 mi (5-10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is believed to be made up of denser material with a different chemical composition. This layer is called the upper part of the upper mantle, and varies in depth from about 31 mi (50 km) to 62 mi (100 km) below Earths surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.

Below the lithosphere, the temperature is thought to reach 1,832°F (1,000°C) which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone directly below the lithosphere is called the asthenosphere, from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earths crust, is carried on top of the weaker and less rigid asthenosphere, which is in continual motion. This motion creates stress in the rigid rock layers above it, and the plates of the lithosphere are forced against each other. This motion of the lithospheric plates is known as plate tectonics, and is responsible for many of the movements that we see on Earths surface today including earthquakes, certain types of volcanic activity, and continental drift.

See also Earths interior; Magma.

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Lithosphere

The word lithosphere is derived from the word sphere, combined with the Greek word lithos, meaning rock . The lithosphere is the solid outer section of Earth, which includes Earth's crust (the "skin" of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 4462 mi (70100 km). This relatively cool and rigid section of Earth is believed to "float" on top of the warmer, non-rigid, and partially melted material directly below.

Earth is made up of several layers. The outermost layer is called Earth's crust. The thickness of the crust varies. Under the oceans , the crust is only about 35 mi (510 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is assumed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 3162 mi (50100 km) below Earth's surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.

Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C), which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere , from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid asthenosphere, which seems to be in continual motion. This motion creates stress in the rigid rock layers above it, forcing the slabs or plates of the lithosphere to jostle against each other, much like ice cubes floating in a bowl of swirling water . This motion of the lithospheric plates is known as plate tectonics , and is responsible for many of the movements seen on Earth's surface today including earthquakes, certain types of volcanic activity, and continental drift.

See also Continental drift theory; Earth (planet); Earth, interior structure

views updated

Lithosphere

The word lithosphere is derived from the word "sphere," combined with the Greek word "lithos" which means rock. The lithosphere is the solid outer section of Earth which includes Earth's crust (the "skin" of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and fairly rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44-62 mi (70-100 km). This relatively cool and rigid section of Earth is believed to "float" on top of the warmer, non-rigid, and partially melted material directly below.

Earth is made up of several layers. The outermost layer is called Earth's crust. The thickness of Earth's crust varies. Under the oceans the crust is only about 3-5 mi (5-10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is believed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 31 mi (50 km) to 62 mi (100 km) below Earth's surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.

Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C) which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere , from the Greek word "asthenes," meaning "weak." The lithosphere, including both the solid portion of the upper mantle and Earth's crust, is carried "piggyback" on top of the weaker, less rigid asthenosphere, which seems to be in continual motion . This motion creates stress in the rigid rock layers above it, and the plates of the lithosphere are forced against each other. This motion of the lithospheric plates is known as plate tectonics , and is responsible for many of the movements that we see on Earth's surface today including earthquakes, certain types of volcanic activity, and continental drift .

See also Earth's interior; Magma.

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lithosphere The upper (oceanic and continental) layer of the solid Earth, comprising all crustal rocks and the brittle part of the uppermost mantle. It is generally considered to deform by brittle fracture and if subjected to stresses of the order of 100 MPa. It comprises numerous blocks, known as tectonic plates, which have differential motions giving rise to plate tectonics. The concept was originally based on the requirement for a rigid upper layer to account for isostasy. Its rigidity is variable, but much greater than 1021P, which corresponds with the underlying asthenosphere. Its thickness is variable, from 1–2 km at mid-oceanic ridge crests, but generally increasing from 60 km near the ridge to 120–140 km beneath older oceanic crust. The thickness beneath continental crust is uncertain, probably some 300 km beneath the cratonic (see CRATON) parts of the continental crust, but the absence of the asthenosphere in these regions makes definition difficult. Compare ATMOSPHERE; and HYDROSPHERE.

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lithosphere (lĬth´əsfēr´), brittle uppermost shell of the earth, broken into a number of tectonic plates. The lithosphere consists of the heavy oceanic and lighter continental crusts, and the uppermost portion of the mantle. The crust and mantle are separated by the Moho or Mohorovicic discontinuity (see earth and seismology). The thickness of the lithosphere varies from to around 1 mi (1.6 km) at the mid-ocean ridges to approximately 80 mi (130 km) beneath older oceanic crust. The thickness of the continental lithospheric plates is probably around 185 mi (300 km) but is uncertain due to the irregular presence of the Moho discontinuity. The lithosphere rests on a soft layer called the asthenosphere, over which the plates of the lithosphere glide. See plate tectonics.

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lithosphere Solid, upper layer of the Earth which includes the crust and the uppermost mantle. Its thickness varies, but is c.60km (40mi); it extends down to a depth of c.200km (125mi). It is made up of a number of tectonic plates that move independently, giving rise to plate tectonics.

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lith·o·sphere / ˈli[unvoicedth]əˌsfi(ə)r/ • n. Geol. the rigid outer part of the earth, consisting of the crust and upper mantle. DERIVATIVES: lith·o·spher·ic / ˌli[unvoicedth]əˈsferik; -ˈsfi(ə)r-/ adj.

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lithosphere The upper (oceanic and continental) layer of the solid Earth, comprising all crustal rocks and the brittle part of the uppermost mantle. Its thickness is variable, from 1–2 km at mid-oceanic ridge crests, but generally increasing from 60 km near the ridge to 120–140 km beneath older oceanic crust. The thickness beneath continental crust is uncertain, but is probably some 300 km in places.