GK Chronicle GK Chronicle

World Geography / Earth

Interior Layers of the Earth and their Composition


    There are mainly three interior layers of the earth. The outermost layer is Crust and the layer below it is Mantle inside which lies the Core. Earth is the densest planet in the solar system. It is the only planet with life and having substantial atmosphere. It is located at 150 million km from the Sun. Diameter of Earth is 12742 km. Earth takes 23 hours 56 minutes 4 seconds for its complete Rotation about its axis and takes 365.25 days for completing one revolution in elliptical orbit around the Sun. Its axis is inclined to the orbital plane and is making an angle of 66 1/20.

    Crust Layer of the Earth

    • Crust is very thin and it is a lighter layer. It comprises of SiAl material. Rocks that are rich in Silicates and Aluminum minerals are called SiAl material. The lower portion of the crust has SiMa ( Silicates and Magnesium ) material.
    • Relative density of Crust is approximately 2.7. The average thickness of the Crust is around 30 km but it is not uniform across the Earth. It is thicker beneath the continents ( 50 km on an average ) and thinner below oceans ( 8-9 km on an average ). In high mountains and Tibetan Plateau, the crust extends up to 70 km. The higher the topography, the thicker is the crust. Continental crust is lighter and oceanic crust is denser.
    • It contributes 1% of earth's volume. Crust is crucial for ecological development.

    Mantle Layer of the Earth

    • Mantle is the thickest layer of Earth. The relative density of Mantle is 5.5 ( equal to average density of earth ). Mantle is made up of minerals like Olivine, Pyroxene, etc.
    • Mantle is being divided into two layers. The upper Mantle is a semi-viscous fluid layer, which is also regarded as Asthenosphere (molten rock). The inner Mantle is solid (rigid) layer. But the composition of both the layers is same.
    • The uppermost part of the Mantle coupled with the Crust is called Lithosphere. The discontinuity between the Crust and the Mantle is being known as Mohorovicic discontinuity. Mantle accounts for 16% in earth's volume.

    Core of the Earth

    • Core is having the highest density of Earth ranging from 17 to 19. It is made up of high density minerals like Iron, Nickel, Cobalt, etc. Sometimes, it is also known as NiFe ( Nickel Ferrous ) layer.
    • The Core is divided into two layers. The outer core is liquid in nature and the inner is solid but the composition is same and similarly the density is also same. The discontinuity between the inner core and outer core is called Lehmann discontinuity or Bullen discontinuity.
    • The Core-Mantle boundary is called Gutenberg discontinuity. Core accounts for 83% of earth's volume.