In geology, a crust is the outermost layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than that of its deeper layers. The crust of the Earth is composed mainly of basalt and granite. It is cooler and more rigid than the deeper layers of the mantle and core.
On stratified planets, such as Earth, the lithosphere is floating on fluid interior layers. Because of convection in the plastic, although non-molten, upper mantle and asthenosphere the lithosphere is broken into tectonic plates that move. Oceanic crust is different from that of the continents. The oceanic crust (sima) is 5 to 10 km thick and is composed primarily of a dark, dense rock called basalt. The continental crust (sial) is 20-70 km deep and is composed of a variety of less dense rocks.
Origin of the Earth's Crust
The Earth is considered to have divided from a planetesimal into its core, mantle and crust within ~100 million years of the formation of the planet, at 4.4 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. Of particular note 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 that 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 3.9Ga, 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 3.4 billion years and 2.4 billion years before present, in the Archaean. The vast majority of rocks of this age are located in cratons where the crust is up to 70km thick, which 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.
2006-09-28 12:03:00
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answer #1
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answered by junaidi71 6
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Crust Of The Earth Facts
2016-11-15 09:28:30
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answer #2
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answered by ? 4
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The crusts' thickness can range between 5 and 40 km. The crust is divided into two sections, the continental crust and the oceanic crust.
The continental crust is composed mostly of granite, an igneous rock. It is thicker and less dense than oceanic crust with a density of 3.3 g/cm3.
The oceanic crust is composed mostly of basalt, and igneous rock. It is thinner and more dense than the continental crust with a density of 2.7 g/cm3.
2006-09-28 11:31:23
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answer #3
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answered by Adam L 1
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Earth suffered a planetary collision with another planet around the size of mars billions of years ago, this created our moon, and our modern Earth. the earth before the blast is not known simply as Earth it is reffered to as Potoearth
2016-03-26 21:51:49
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answer #4
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answered by Anonymous
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Mt. Everest is the highest point, sea mountains are not as high above sea level as it is because they start a lot lower(hence they are *sea* mountains.) The most abundant element is Oxygen and the most abundant compound is SiO2(Silicon Dioxide, quartz)
2006-09-28 20:34:05
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answer #5
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answered by Anonymous
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continetal crust is less dense than the oceanic crust and the highest point is not mount everest but a mountain under water
2006-09-28 11:23:31
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answer #6
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answered by kat 2
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the crust is basically the outside of earth
2006-09-28 12:18:46
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answer #7
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answered by Chuchie 1
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