Our earth is made up of several concentric layers with one inside another. These layers are three in number—crust, mantle and core. Crust. It is the uppermost layer over the earth’s surface. It is the thinnest of all the layers. It is about 35 km on the continental masses and only 5 km on the ocean floors. The continental masses are made up of silica and alumina. It is thus called sial (si-silica and alalumina). The oceanic crust mainly consists of silica and magnesium. It is thus called sima (si-silica and ma-magnesium). Mantle:It is just beneath the crust.It extends up to a depth of 2900 km below the crust Core:It is the innermost layer. Its radius is about 3500 km. It is mainly made up of nickel and iron and is known as nife (ni-nickel and fe-ferrous, Le., iron). The central core has very high temperature and pressure.
