Evolution of Lithosphere


Earth in the primordial stage was very volatile. Gradually, the density increased as the materials started to separate and get organized. Therefore, heavier metals sink towards the center (like iron) whereas, lighter ones moved towards the surface. As time passes materials solidify and condensed into smaller sizes. This outermost layer is known as the crust. This gave multiple layering in the interior of the earth i.e., Crust, Mantle, and Core.

CRUST- The crust is the outermost solid part of the earth. The crust is divided into two parts i.e., continental crust and oceanic crust. The thickness of the crust varies as the oceanic crust is thinner than the continental crust. The mean thickness of the oceanic crust is 5 Km whereas the mean thickness of the continental crust is 30 Km and it can reach up to 70 Km in the Himalayan Mountain region. The mean density of continental crust is 2.7 g/cm3 and it is majorly made up of granite rock whereas the oceanic crust is made up of basalt rock with a mean density of

3 g/cm3.

MANTLE- Crust, and Mantle separated from Moho’s discontinuity. The mantle can extend to a depth of 2900km with a mean density of 3.4 g/cm3. The upper part of the mantle is known as the asthenosphere. The word “astheno” means weak. It is a kind of liquid form on which plates move. It extends up to 400 Km. It is also the main source of magma that comes out from a vent during a volcanic eruption.

The crust and the asthenosphere combined are known as the lithosphere. The lower mantle is in a solid state.