crust (geology)
Information about crust (geology)
In geology, a crust is the outermost layer of a planet.
The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovicic discontinuity, a boundary defined by a contrast in seismic velocity. Earth's crust occupies less than 1% of Earth's volume.
The oceanic crust of the Earth is different from its continental crust. The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick[1] and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (0 mi) to 50 km (0 mi) thick, and it is mostly composed of less dense rocks than is the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust.
The temperature of the crust increases with depth, reaching values typically in the range from about 500 (0 ) to 1,000 (0 ) at the boundary with the underlying mantle. The crust and underlying relatively rigid mantle make up the lithosphere. Because of convection in the underlying plastic, although non-molten, upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move.
The Earth has likely always had some form of basaltic oceanic crust, but there is evidence it has also had continental style crust for as long as 3.8 to 3.9 billion years. The oldest crust on Earth is the Narryer Gneiss Terrane in Western Australia at 3.9 billion years, and certain parts of the Canadian Shield and the Fennoscandian Shield are also of this age.
The majority of the current Earth's continental crust was formed primarily between 4.6 billion years and 3.9 billion years ago, in the Hadean. The vast majority of rocks of this age are located in cratons where the crust is up to 70 km (0 mi) thick. The lower density of the continental crust as compared to the oceanic crust prevents it being destroyed by subduction. Crust formation is linked to periods of intense orogeny or mountain building; these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms not so much by accumulation of granite and metamorphic fold belts, but by depletion of the mantle to form buoyant lithospheric mantle.
All the other constituents occur only in very small quantities, and total less than 1%.[2]. Density for the upper crust varies between 2.69 g/cm3 and 2.74 g/cm3 and for lower crust between 3.0 g/cm3 and 3.25 g/cm3[1].
)
The crust of the Earth is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust is underlain by the mantle. The upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovicic discontinuity, a boundary defined by a contrast in seismic velocity. Earth's crust occupies less than 1% of Earth's volume.
The oceanic crust of the Earth is different from its continental crust. The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick[1] and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (0 mi) to 50 km (0 mi) thick, and it is mostly composed of less dense rocks than is the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust.
The temperature of the crust increases with depth, reaching values typically in the range from about 500 (0 ) to 1,000 (0 ) at the boundary with the underlying mantle. The crust and underlying relatively rigid mantle make up the lithosphere. Because of convection in the underlying plastic, although non-molten, upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move.
Origin of the Earth's crust
Earth is considered to have differentiated from an aggregate of planetesimals into its core, mantle and crust within about 100 million years of the formation of the planet, 4.6 billion years ago. The primordial crust was very thin, and was likely recycled by much more vigorous plate tectonics and destroyed by significant asteroid impacts, which were much more common in the early stages of the solar system. There is a theory that the Moon was formed by one such very large impact.The Earth has likely always had some form of basaltic oceanic crust, but there is evidence it has also had continental style crust for as long as 3.8 to 3.9 billion years. The oldest crust on Earth is the Narryer Gneiss Terrane in Western Australia at 3.9 billion years, and certain parts of the Canadian Shield and the Fennoscandian Shield are also of this age.
The majority of the current Earth's continental crust was formed primarily between 4.6 billion years and 3.9 billion years ago, in the Hadean. The vast majority of rocks of this age are located in cratons where the crust is up to 70 km (0 mi) thick. The lower density of the continental crust as compared to the oceanic crust prevents it being destroyed by subduction. Crust formation is linked to periods of intense orogeny or mountain building; these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms not so much by accumulation of granite and metamorphic fold belts, but by depletion of the mantle to form buoyant lithospheric mantle.
Composition of the crust
The common rock constituents of the Earth's crust are nearly all oxides; chlorine, sulfur and fluorine are the only important exceptions to this and their total amount in any rock is usually much less than 1%. F. W. Clarke calculated that a little more than 47% of the Earth's crust consists of oxygen. It occurs principally in combination as oxides, of which the chief are silicon, aluminium, iron, calcium, magnesium, potassium and sodium oxides. Silica is a major constituent of the crust occurring as the silicate minerals, which are the most common minerals of igneous and metamorphic rocks. From a computation based on 1672 analyses of all kinds of rocks Clarke arrived at the following as the average percentage composition by mass:)
Plates in the crust of the earth, according to the plate tectonics theory
| Oxide | Percent |
|---|---|
| SiO2 | 59.71 |
| Al2O3 | 15.41 |
| CaO | 4.90 |
| MgO | 4.36 |
| Na2O | 3.55 |
| FeO | 3.52 |
| K2O | 2.80 |
| Fe2O3 | 2.63 |
| H2O | 1.52 |
| TiO2 | 0.60 |
| P2O5 | 0.22 |
| total | 99.22 |
See also
References
1. ^ Structure and composition of the Earth. Australian Museum Online. Retrieved on 2007-09-14.
2. ^
2. ^
External links
Structure of the Earth |
|---|
| Crust • Upper mantle • Lithosphere • Asthenosphere • Mesosphere • Mantle • Outer core • Inner core • Plate tectonics |
Oceanic crust 0-20 Ma
..... Click the link for more information.
..... Click the link for more information.
planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion in its core, and has cleared its neighbouring region of
..... Click the link for more information.
..... Click the link for more information.
EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
..... Click the link for more information.
..... Click the link for more information.
Igneous rocks (etymology from latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
..... Click the link for more information.
..... Click the link for more information.
The term Metamorphic can be associated with a number of meanings:
..... Click the link for more information.
- Metamorphic rock: The term for rocks that have been transformed by extreme heat and pressure.
- Metamorphic Technique is a form of massage used in complementary and alternative medicine.
..... Click the link for more information.
Sedimentary rock is one of the three main rock groups (the others being igneous and metamorphic rock). Rock formed from sediments covers 75-80% of the Earth's land area, and includes common types such as chalk, limestone, dolomite, sandstone, conglomerate and shale.
..... Click the link for more information.
..... Click the link for more information.
mantle is a ~2,900 km thick rocky shell comprising approximately 70% of Earth's volume. It is predominantly solid and overlies the Earth's iron-rich core, which occupies about 30% of Earth's volume.
..... Click the link for more information.
..... Click the link for more information.
Peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica.
..... Click the link for more information.
..... Click the link for more information.
Seismology (from the Greek seismos = earthquake and λόγος,logos = knowledge ) is the scientific study of earthquakes and the propagation of elastic waves through the Earth.
..... Click the link for more information.
..... Click the link for more information.
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima. It is thinner than continental crust, or sial, generally less than 10 kilometers thick, however it is more dense, having a mean density
..... Click the link for more information.
..... Click the link for more information.
The continental crust is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves.
..... Click the link for more information.
..... Click the link for more information.
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima. It is thinner than continental crust, or sial, generally less than 10 kilometers thick, however it is more dense, having a mean density
..... Click the link for more information.
..... Click the link for more information.
Basalt (IPA: /ˈbæsɒlt, bəˈsɒlt/) is a common gray to black extrusive volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth's surface.
..... Click the link for more information.
..... Click the link for more information.
Diabase (IPA: /ˈdʌɪəbeɪs/) is a mafic, holocrystalline, igneous rock equivalent to volcanic basalt or plutonic gabbro. Diabase is also called dolerite in many older British references.
..... Click the link for more information.
..... Click the link for more information.
Gabbro (IPA: /ˈgabrəʊ/) is a dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt.
..... Click the link for more information.
..... Click the link for more information.
The continental crust is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves.
..... Click the link for more information.
..... Click the link for more information.
Granite (IPA: /ˈɡrænɪt/) is a common and widely occurring type of intrusive, felsic, igneous rock. Granites are usually medium to coarsely crystalline, occasionally with some individual crystals larger than the
..... Click the link for more information.
..... Click the link for more information.
lithosphere (IPA: [ˈlɪθ.ə.sfiɹ], from the Greek for "rocky" sphere) is the solid outermost shell of a rocky planet. On the Earth, the lithosphere includes the crust and the uppermost mantle which is joined to the crust across the Mohorovičić
..... Click the link for more information.
..... Click the link for more information.
Convection in the most general terms refers to the movement of currents within fluids (i.e. liquids, gases and rheids).
Convection is one of the major modes of heat and mass transfer.
..... Click the link for more information.
Convection is one of the major modes of heat and mass transfer.
..... Click the link for more information.
In engineering mechanics, deformation is a change in shape due to an applied force. This can be a result of tensile (pulling) forces, compressive (pushing) forces, shear, bending or torsion (twisting). Deformation is often described in terms of strain.
..... Click the link for more information.
..... Click the link for more information.
mantle is a ~2,900 km thick rocky shell comprising approximately 70% of Earth's volume. It is predominantly solid and overlies the Earth's iron-rich core, which occupies about 30% of Earth's volume.
..... Click the link for more information.
..... Click the link for more information.
asthenosphere (from an invented Greek ἀσθενός a + sthenos "without strength") is the region of the Earth between 100-200 km below the surface — but perhaps extending as deep as
..... Click the link for more information.
..... Click the link for more information.
Plate tectonics (from Greek τέκτων, tektōn "builder" or "mason") is a theory of geology that has been developed to explain the observed evidence for large scale motions of the Earth's lithosphere.
..... Click the link for more information.
..... Click the link for more information.
Aggregate may refer to:
..... Click the link for more information.
- Construction aggregate, materials used in construction, including sand, gravel, crushed stone, slag, or recycled crushed concrete.
- Aggregate (composite), in materials science, a component of a composite material used to resist compressive stress.
..... Click the link for more information.
Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks.
A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of dust grains that collide and stick to form
..... Click the link for more information.
A widely accepted theory of planet formation, the so-called planetesimal hypothesis of Viktor Safronov, states that planets form out of dust grains that collide and stick to form
..... Click the link for more information.
mantle is a ~2,900 km thick rocky shell comprising approximately 70% of Earth's volume. It is predominantly solid and overlies the Earth's iron-rich core, which occupies about 30% of Earth's volume.
..... Click the link for more information.
..... Click the link for more information.
Primordial may refer to: Primordial, in reference to memory, eternal, never changing, never dying
..... Click the link for more information.
- Primordial (band), Irish pagan metal band
- Primordial sea (aka primordial ocean, ooze or soup)
..... Click the link for more information.
Plate tectonics (from Greek τέκτων, tektōn "builder" or "mason") is a theory of geology that has been developed to explain the observed evidence for large scale motions of the Earth's lithosphere.
..... Click the link for more information.
..... Click the link for more information.
Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the solar system that orbit around the Sun.
..... Click the link for more information.
..... Click the link for more information.
Moon
The Moon as seen by an observer on Earth
Orbital characteristics
Periapsis: 363,104 km
0.0024 AU
Apoapsis: 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.
..... Click the link for more information.
The Moon as seen by an observer on Earth
Orbital characteristics
Periapsis: 363,104 km
0.0024 AU
Apoapsis: 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.