Interior of the Earth: Sources & Compositions

The study of the interior of the earth is not possible by direct observations because of the huge size and changing nature of its interior composition. Thus, it is not possible to go deep into the earth due to huge pressure and temperature.  

Fig: Layers of the Earth

• The structure of the earth surface is largely a product of the processes operating in the interior of the earth. Endogenic as well as Exogenic processes are constantly shaping the landscape.

Source of the Interior of the Earth

• To understand the interior of the earth, the direct source and indirect source is the prominent factor. These are as follows-

• Direct Source:
  • Surface rock or the rocks widely available as solid earth material in mining areas can be a direct source of the interior of the earth.
  • Volcanic eruption is another source for the interior of the earth. As molten material (magma) is thrown onto the surface of the earth, during volcanic eruption it becomes available for laboratory analysis.
• Indirect Source:
  • During mining activity, temperature and the pressure increase with the increasing distance from the surface towards the interior of the earth. Further, it is known that the density of the material also increases with depth. Thus, change of rock characteristics. 
  • Another source is meteors that reach on the earth. However, the material is not from the interior of the earth. The structure and the material observed in the meteors are similar to that of the earth. 
  • They are solid bodies developed out of materials the same as our planet. Hence, source of the earth’s interior.

Other Indirect Sources – The other indirect sources include gravitation, magnetic field, and seismic activity. Gravity Anomaly – The gravitational force at different places is influenced by many factors. These readings fluctuate from the expected values. This difference is called a gravity anomaly.  – Gravity Anomalies give us evidence about the distribution of mass of the material in the crust of the earth. Magnetic Surveys – It provides evidence about the distribution of magnetic materials in the crust portion and further provides information about the distribution of materials on the earth. Seismic Activity – The study of seismic waves provides information of the layered interior. The sudden shaking of the earth is called an earthquake. It is a natural event. It is caused due to the release of energy and generates waves that travel in all directions. – Thus, provide information about the interior of the earth.

Composition of the Interior of the Earth:

The Crust 

• It is brittle in nature and the outermost solid part of the earth. 
• The crust varies in the thickness of the oceanic and continental areas. The crust of the ocean is thinner as compared to the continental crust. 
• Ocean crust mean thickness is 5 km whereas that of the continental is approx. 30 km. 
• The crust of the continent is thicker in the mountain regions of the world. For instance, it is approx. 70 km wider in the Himalayan region.

The Mantle 

• The next layer is the mantle extends from Moho’s discontinuity to a depth of 2,900 km. 
• Asthenosphere, is the upper portion of the mantle extending upto 400 km. The word ‘astheno’ means weak, hence in liquid state.
• It is the significant source of magma that finds its way to the surface during volcanic eruptions. 
• The crust and the uppermost part of the mantle are called lithosphere (thickness ranges from 10-200 km). 
• The lower part of the mantle extends beyond the asthenosphere which is in solid state.

The Core 

• The core-mantle boundary is located at the depth of 2,900 km and from crust is approx. 6,378 km.
• The earthquake wave velocities helped in understanding the existence of the core of the earth and signifies-
  • Outer core is in liquid state 
  • Inner core is in solid state. 
• The core is made up of extremely heavy material constituted by nickel and iron and can be referred as the nife layer.

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