Crust density, pressure, gravity

This table gives the density p, pressure p, and acceleration due to gravity as a function of depth below the earth s surface, as calculated from the model of the structure of the earth in Reference 1. The model assumes a radius of 6371 km for the earth. The boundary between the crust and mantle (the Mohorovicic discontinuity) is taken as 21 km, while in reality it varies considerable with location. 

The planet Earth was thus formed. Heat was created as the coalescence (of planetesimals) proceeded due to gravity, and heat also came from radioactivity of several radioactive elements such as aluminum-26. So the newly formed body was heated and the core was melted. As the material becomes liquid (as a result of melting), the materials contained in the liquid separate out according to their densities. The more dense material would sink closer to the bottom (core). Thus, the present layer structure of the Earth formed. The innermost core is a dense solid of about 1,200 km radius, whose density is about 12.6 g per cubic centimeter (12.6 x 10 kg/m ). It is made of mostly iron metal and a small amount of nickel. By the way, the density of iron metal is only 7.8 x 10 kg/m under the ordinary pressure. The next layer is the outer core (up to 3,500 km from the center of the Earth), which is liquid and has a density of 9.5-12x10 kg/m. The chemical composition seems to be about the same as that of the inner core. There is an abrupt change in density in the next layer, mantle. The width of mantle is about 2,900 km (3,500-6,380 km from the center). Its density ranges from 4 to 5.5 x 10 kg/m. The mantle is made of mostly magnesium-iron silicates (silicon oxides). The outermost layer is the thin crust of about 35 5 km on the land portion, and about 6 km under the ocean portion. 

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