Structure of the Earth

Structure of the Earth – The Earth is made of several concentric layers. The outer layer of the Earth is known as the lithosphere. The interior of the Earth is divided into three layers—core, mantle, and crust.

Structure of the Earth

Crust (Lithosphere)

  • It is the uppermost layer of the Earth and is a sphere of solid rocks.
  • It is the thinnest of all the layers. It is about 35 km on the continental masses and only 5 km on the ocean floor.
  • 3.Two main mineral constituents of the continental mass are silica and alumina. Therefore, it is also called SIAL.
  • The oceanic crust consists mainly of silica and alumina. Therefore, it is known as SIMA.

Mantle ( Barysphere )

  • This layer of the Earth lies underneath the crust. It extends up to a depth of 2,900 km below the Earth’s crust.
  • The mantle is further divided into upper mantle and lower mantle. At the depth of 100–250 km, the mantle is in the semi-molten state and is known as asthenosphere.


  • It is the innermost layer of the Earth with a radius of about 3500 km. The boundary between the mantle and the core is known as Gutenberg Discontinuity.
  • It is called NIFE (NI–nickel; FE–ferrous/iron) as it is made of nickel and iron.
  • There is very high temperature and pressure in the Earth’s core.

The discontinuity between the crust and the mantle is known as Mohorovicic Discontinuity. It forms the boundary between the crust and the mantle.

Isostasy is a state of gravitational equilibrium between the lithosphere and the asthenosphere. There is a difference in the densities of continental and oceanic crusts. The continental crust lies above the ocean basin. It goes deeply into the asthenosphere than the ocean basin. However, both continents and ocean basins float on the asthenosphere which is in the semi-molten form. This state of balance is known as isostasy.

Also, Read Landforms of the Earth