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The rocks of the crust fall into two major categories – sial (aluminium silicate) and sima (magnesium silicate). [13] It is estimated that sima starts about 11 km below the Conrad discontinuity , [ 14 ] though the discontinuity is not distinct and can be absent in some continental regions.
Because of the large pressures, over geologic time, the sima flows like a very viscous liquid, so, in a real sense, the sial floats on the sima, in isostatic equilibrium. [9] Mountains extend down as well as up, much like icebergs on the ocean; [ 9 ] so that on the continental plates , the sial runs between 5 km and 70 km deep.
The thickness of Earth's crust (km). The continental crust consists of various layers, with a bulk composition that is intermediate (SiO 2 wt% = 60.6). [5] The average density of the continental crust is about, 2.83 g/cm 3 (0.102 lb/cu in), [6] less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm 3 (0.12 lb/cu in).
Sima often takes the form of basalt when on the surface. In geology, sima (/ ˈ s aɪ m ə /) is an antiquated [1] blended term for the lower layer of Earth's crust. This layer is made of rocks rich in magnesium silicate minerals. Typically, when the sima comes to the surface, it is basalt, so sometimes this layer is called the 'ocean layer' of ...
Sial – Rocks rich in aluminium silicate minerals; Sima – Rocks rich in magnesium silicate minerals; Hydrosphere – Total amount of water on a planet; Lithosphere – Outermost shell of a terrestrial-type planet or natural satellite; Ocean – Body of salt water covering most of Earth; Plate tectonics – Movement of Earth's lithosphere
Therefore, the seismologists of that time considered that the Conrad discontinuity should correspond to a sharply defined contact between the chemically distinct two layers, sial and sima. [2] Despite the fact that sial and sima are two solid layers, the lighter sial is thought to "float" on top of the denser sima layer.
Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust , or sial , generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams ...
Physiographic diagram of the South Atlantic, the Caribbean, the Scotia Sea, and the eastern margin of the South Pacific Ocean. Boulder, CO: The Geological Society of America. Heezen, B. C.; Tharp, M. (1964). Physiographic diagram of the Indian Ocean, the Red Sea, the South China Sea, the Sulu Sea, and the Celebes Sea.