Interior of Earth

Interior of the Earth

Understanding the basic structure of the earth is very important to learn higher concepts well. Also, the origin of many phenomena like earthquakes, volcanoes, tsunamis, etc is linked with the structure of the earth’s interior.
  1. It is not possible to know about the earth’s interior by direct observations because of the huge size and the changing nature of its interior composition.
  2. It is an almost impossible distance for humans to reach the center of the earth (The earth’s radius is 6,370 km).
But still, through some direct and indirect sources, the scientists have a fair idea about how the earth’s interior.

Direct Sources

  1. Rocks from the Mining Area
  2. Volcanic Eruptions
  3. Meteoroids
  4. Earthquake

Indirect Sources

  1. By analyzing the rate of change in temperature and pressure from the surface towards the interior.
  2. Meteors, as they belong to the same type of materials earth is made of.
  3. Gravitation is greater near the poles and less at the equator.
  4. Gravity anomaly, which is the change in gravity value according to the mass of material, gives us information about the materials in the earth’s interior.
  5. Magnetic sources.

Structure of the Earth’s Interior

The structure of the earth’s interior is fundamentally divided into three layers.
  1. Crust
  2. Mantle
  3. Core

Do you know?

Gravitation is greater near the poles and less at the equator.
Interior of Earth


  1. It is the outermost solid part of the earth, normally about 8-40 km thick.
  2. Nearly 1% of the earth’s volume and 0.5% of the earth’s mass are made of the crust.
  3. The thickness of the crust under the oceanic and continental areas are different. Oceanic crust is thinner (about 5kms) as compared to the continental crust (about 30kms).
  4. Major constituent elements of crust are Silica (Si) and Aluminum (Al) and thus, it is often termed as SIAL (Sometimes SIAL is used to refer to Lithosphere, which is the region comprising the crust and uppermost solid mantle, also).
  5. The mean density of the materials in the crust is 3g/cm3.
  6. The discontinuity between the hydrosphere and crust is termed the Conrad Discontinuity.


  1. The portion of the interior beyond the crust is called the mantle.
  2. The discontinuity between the crust and mantle is called the Mohorovich Discontinuity or Moho discontinuity.
  3. The mantle is about 2900 kms in thickness. Nearly 84% of the earth’s volume and 67% of the earth’s mass is occupied by the mantle.
  4. The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed SIMA.
  5. The density of the layer is higher than the crust and varies from 3.3 – 5.4g/cm3.
  6. The uppermost solid part of the mantle and the entire crust constitutes the Lithosphere.
  7. The asthenosphere (in between 80-200km) is a highly viscous, mechanically weak, and ductile, deforming region of the upper mantle which lies just below the lithosphere.
  8. 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 Repetti Discontinuity. The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.


  1. It is the innermost layer surrounding the earth’s center. Barysphere is sometimes used to refer to the core of the earth or sometimes the whole interior.
  2. The core is separated from the mantle by Guttenberg’s Discontinuity.
  3. It is composed mainly of iron (Fe) and nickel (Ni) and hence it is also called NIFE.
  4. The core constitutes nearly 15% of the earth’s volume and 32.5% of the earth’s mass.
  5. The core is the densest layer of the earth with its density ranging between 9.5-14.5g/cm3.
  6. The Core consists of two sub-layers: the inner core and the outer core.
  7. The inner core is in a solid state and the outer core is in the liquid state (or semi-liquid).
  8. The discontinuity between the upper and lower core is called Lehmann Discontinuity.

Temperature, Pressure, and Density of the Earth’s Interior


Due to an increase in pressure and the presence of heavier materials like Nickel and Iron towards the centre, the earth’s layers’ density also increases towards the centre. The average density of the layers gets on increasing from crust to core and it is nearly 14.5g/cm3 at the very centre.


The pressure is also increasing from the surface towards the centre of the earth. It is due to the huge weight of the overlying materials like rocks.


A rise in temperature with an increase in depth is observed in mines and deep wells. This evidence along with molten lava erupted from the earth’s interior supports that the temperature increases towards the centre of the earth. In the beginning, this rate of increase in temperature is at an average rate of 1°C for every 32m increase in depth