What are the 3 layers of the earth & know about the Crust, Mantle & Core

Interior layers of the earth

Our earth is made of many things and it has several layers above the land and below the land. Let us know about the interior of the earth.  Firstly, understand the basic structure of the earth which is very important to learn higher concepts well. Also, the origin of many phenomena like earthquakes, volcanoes, tsunami etc. are linked with the structure of the earth’s interior.

layers of Earth

Basics about the interior of the earth:

  • Due to the huge size and the changing nature of its interior composition. It is very difficult to know about the earth’s interior by direct observations.
  • But still, through some direct and indirect sources, the scientists have a fair idea about how the earth’s interior looks like.
  • The earth’s radius is 6,370 km, which almost an impossible distance for the humans to reach till the centre of the earth.
  • The rapid increase in temperature below the earth’s surface is mainly responsible for setting a limit to direct observations inside the earth.

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Let us read about the layers:


  • It is the outermost solid part of the earth whose thickness is 8-40 km.
  • It is very soft and brittle in nature.
  • Nearly 1% of the earth’s volume and 0.5% of earth’s mass are made of the crust.
  • Areas like ocean and continent have different crust layer. Oceanic crust is thinner i.e. about 5km and the continental crust layer is about 30km.
  • The elements of crust are Silica (Si) and Aluminum (Al) and it is often called as SIAL (Sometimes SIAL is used to refer Lithosphere)
  • The lithosphere is the region consisting the crust and uppermost solid mantle.
  • The mean density of the materials in the crust is 3g/cm3.
  • The discontinuity between the hydrosphere and crust is termed as the Conrad Discontinuity.


  • The second layer or the interior beyond the crust is called as the mantle.
  • The discontinuity between the crust and mantle is called as the Mohorovicic Discontinuity or Moho discontinuity.
  • The thickness of mantle is about 2900kms.
  • Approx 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle layer.
  • The major constituent elements of the mantle are Silicon and Magnesium and hence it is also called as SIMA.
  • The density of the layer is higher than the crust and varies from 3.3 – 5.4g/cm3.
  • There is a layer below lithosphere termed as asthenosphere is in between 80-200km.
  • The asthenosphere is a highly viscous, mechanically weak and ductile, deforming region of the upper mantle.
  • The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
  • The discontinuity between the upper mantle and the lower mantle is known as RepettiDiscontinuity.
  • The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.


  • It is the innermost layer surrounding the earth’s centre.
  • The core is separated from the mantle by Guttenberg’s Discontinuity.
  • It is mainly formed by iron (Fe) and nickel (Ni) and called as NIFE.
  • The core consists of nearly 15% of the earth’s volume and 32.5% of earth’s mass.
  • The core has the highest density as compared to the other layer of the earth i.e. between 9.5-14.5g/cm3.
  • The Core consists of two sub-layers: the inner core and the outer core.
  • The inner core is in solid state and the outer core is in the liquid state (or semi-liquid).
  • The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.
  • Barysphere is sometimes used to refer to the core of the earth or sometimes the whole interior.

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