Research by these methods indicates that the earth has a zoned interior, consisting of concentric shells differing from one another by size, chemical makeup, and density. The earth is undoubtedly much denser near the center than it is at the surface, because the average density of rocks near the surface is c.2.8 g/cc, while the average density of the entire earth is c.5.5 g/cc.
However, the earth is not an exact sphere, being slightly flattened at the poles and bulging at the equator. Khimicheskoe stroenie biosfery Zemli i ee okruzheniia.
Beneath the ocean basins and the sial of continents lie denser rock types called sima.
The sial and sima together form the crust, beneath which lies a shell called the mantle.
* * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
in geology and astronomy, 3rd planet of the solar system and the 5th largest, the only planet definitely known to support life.
Extending to a depth of c.1,800 mi (2,900 km), the mantle probably consists of very dense (average c.3.9 g/cc) rock rich in iron and magnesium minerals.