Citizendia
Your Ad Here

The thickness of the Earth's crust (km).
The thickness of the Earth's crust (km).

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. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change A continent is one of several large Landmasses on Earth. They are generally identified by Convention rather than any strict criteria with seven regions The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such This layer is sometimes called Sial due to its granitic rock, in contrast to the oceanic crust, called Sima due to its basaltic (also called mafic) rock. Sial or SiAl is also the name for the upper layer of the Earth's crust, which is also known as the Continental crust because Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins Sima is the name for the lower layer of the Earth's crust. This layer is made of rocks rich in silicates and Magnesium minerals Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" Due to the change in velocity of seismic waves it is believed that on continents at a certain depth sial becomes close in its physical properties to sima and the dividing line is called Conrad discontinuity. Seismic waves are Waves that travel through the Earth, most often as the result of a tectonic Earthquake, sometimes from an Explosion Consisting mostly of granitic rock, it has a density of about 2. 7g/cm^3 and is less dense than the material of the Earth's mantle, which consists of mafic rock. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Continental crust is also less dense than oceanic crust, though it is considerably thicker; mostly 35 to 40 km versus the average oceanic thickness of around 7-10 km. Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins About 40% of the Earth's surface is now underlain by continental crust.

Because continental crust mostly lies above sealevel, its existence allowed land life to evolve from marine life. Its existence also provide broad expanses of shallow water known as epeiric seas and continental shelves where complex metazoan life could become established during early Paleozoic time. The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such The Paleozoic or Palaeozoic Era (from the Greek palaio (παλαιο "old" and zoe (ζωη "life" meaning "ancient life" If Earth was like the other silicate planets and lacked the duality of oceanic and continental crust, our planet would be a very different place and the evolution of Homo sapiens and civilization would have been impossible. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus A Civilization is a society in which large numbers of people share a variety of common elements

In contrast to the relative permanence of continental crust, the size, shape, and number of continents is constantly changing, as different tracts rift apart, collide and recoalesce as part of a grand supercontinent cycle. The supercontinent cycle describes the quasi-periodic aggregration and dispersal of Earth 's Continental crust. Today there are ~7 billion cubic kilometers of continental crust, but in the past there may have been fewer or more. The relative permanence of continental crust contrasts with the short life of oceanic crust. As a consequence of the density difference, when active margins of continental crust meet oceanic crust in subduction zones, the oceanic crust is typically subducted back into the mantle. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Because of its relative low density, continental crust is only rarely subducted or re-cycled back into the mantle (for instance, where continental crustal blocks collide and overthicken, causing deep melting). For this reason the oldest rocks on Earth are within the cratons or cores of the continents, rather than in repeatedly recycled oceanic crust; the oldest continental rock is the Acasta Gneiss at 4. A craton ( Greek kratos / κρἀτος ( neut. "strength" is an old and stable part of the Continental crust that has survived Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins The Acasta Gneiss is a rock Outcrop of Archaean Tonalite Gneiss in the Slave craton in Northwest Territories 01 Ga, while the oldest oceanic crust is no older than Jurassic (~180 Ma). Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular The Jurassic is a geologic period and system that extends from about Ma (million years ago to  Ma that is from the end of the Triassic to the beginning Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular Continental crust and the rock layers that lie on and within it are thus the best archive of Earth history.

The height of mountain ranges is usually related to the thickness of crust. This results from the isostasy associated with orogeny (mountain formation). Isostasy (Greek isos = "equal" stásis = "standstill" is a term used in Geology to refer to the state of gravitational equilibrium between the Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and The crust is thickened by the compressive forces related to subduction or continental collision. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other The buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found. The thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. In Geology, a rift is a place where the Earth 's crust and Lithosphere are being pulled apart and is an example of Extensional tectonics In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins The edges of continental fragments formed this way (both sides of the Atlantic Ocean, for example) are termed passive margins. A Passive margin is the transition between oceanic and Continental crust which is not an active plate margin

The high temperatures and pressures at depth, often combined with a long history of complex distortion, mean that much of the lower continental crust is metamorphic - the main exception to this being recent igneous intrusions. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Igneous rock may also be "underplated" to the underside of the crust, i. e. adding to the crust by forming a layer immediately beneath it.

Today there are ~7 billion cubic kilometers of continental crust, but in the past there may have been less or more. Today continental crust is produced and destroyed mostly by plate tectonic processes, especially at convergent plate boundaries. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere In Plate tectonics, a convergent boundary – also known as a convergent plate boundary or a destructive plate boundary – is an actively deforming region New material can be added to the continents by the partial melting of oceanic crust at subduction zones, causing the lighter material to rise as magma, forming volcanoes. Also, material can be accreted "horizontally" when volcanic island arcs, seamounts or similar structures collide with the side of the continent as a result of plate tectonic movements. A volcanic arc is a chain of volcanic islands or Mountains formed by Plate tectonics as an oceanic Tectonic plate subducts under A seamount is a Mountain rising from the Ocean Seafloor that does not reach to the water's surface ( Sea level) and thus is not an Island Continental crust is also lost, due to erosion and sediment subduction, tectonic erosion of forearcs, delamination, and deep subduction of continental crust in collision zones. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Many aspects of crustal growth are controversial, including rates of crustal growth and recycling, whether the lower crust is recycled differently than the upper crust and over how much of Earth history plate tectonics has operated and so could be the dominant mode of continental crust formation and destruction. It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model indicates that at prior to 3. 7 Ga ago continental crust constituted less than 10% of the present amount. By 3. 0 Ga ago the amount was about 25% and following a period of rapid crustal evolution it was about 60% of the current amount by 2. 6 Ga ago (Taylor and McLennan, 1995). The growth of continental crust appears to have occurred in spurts of increased activity corresponding to five episodes of increased production through geologic time (see graphic at Butler). N

References

See also

External links

Sial or SiAl is also the name for the upper layer of the Earth's crust, which is also known as the Continental crust because Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins A craton ( Greek kratos / κρἀτος ( neut. "strength" is an old and stable part of the Continental crust that has survived A terrane in Geology is a fragment of crustal material formed on or broken off from one Tectonic plate and accreted — " sutured "
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic