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Interior of the Earth

The Interior of the Earth can be divided into one of two ways: mechanically or chemically. Mechanically (or rheologically) meaning the study of liquid state...

The Interior of the Earth can be divided into one of two ways: mechanically or chemically.

  • Mechanically (or rheologically) meaning the study of liquid states – it can be divided into the lithosphere, asthenosphere, mesospheric mantle, outer core, and the inner core.
  • But chemically or by composition, which is the more popular of the two, it can be divided into the crust, the mantle (which can be subdivided into the upper and lower mantle), and the core – which can also be subdivided into the outer core, and inner core.
  • It is the outermost solid part of the earth.
  • The crust is further divided into upper crust (continental crust) composed of silica and aluminium (sial) and lower crust (oceanic crust) made up of silica and magnesium (sima). The boundary between the upper crust and the lower crust is called the “Conorod boundary”.
  • The thickness of the crust varies under the oceanic and continental areas. Continental crust is thicker as compared to the oceanic crust. The mean thickness of the continental crust is about 32 km whereas that of oceanic crust is 5 km. The continental crust is thicker in the areas of major mountain systems. It is about 70 km in the Himalayan region.
  • The lithosphere is the rigid outer part of the earth with thickness varying between 10-200 km.
  • It is includes the crust and the upper part of the mantle.
  • The lithosphere is broken into tectonic plates (lithospheric plates), and the movement of these tectonic plates cause large-scale changes in the earth’s geological structure (folding, faulting).
  • The source of heat that drives plate tectonics is the primordial heat left over from the planet’s formation as well as the radioactive decay of uranium, thorium, and potassium in Earth’s crust and mantle.
  • The portion of the earth beyond the crust is called the mantle. It is made up of magnesium, silica and iron. It extends to a depth of about 2900 km.
  • The mantle is divided into upper mantle and lower mantle. The upper portion of the mantle is called the asthenosphere. The word “astheno” means weak. Asthenosphere extends up to 400 km and is the main source of magma which comes over to the surface during volcanic eruptions.
  • The boundary which divides the lower crust and the upper mantle is called the “Mohorovicic”.
  • The asthenosphere includes the soft layer of the mantle on which the lithosphere moves.
  • Depth- 100km to 350 km .
  • It is made of solid silicate materials, but the high temperature allows it to flow on very long timescales.
  • The lithosphere-asthenosphere boundary is where geophysicists mark the difference in ductility between the two layers.
  • The mesosphere is the layer below the asthenosphere but above the outer core. It is essentially the lower mantle.
  • Average depth-350-2900km
  • Despite its high temperature, the intense pressure in this region restricts the movements of the molecules of the silicate material despite being under high temperature, thus making it extremely rigid.

 Outer Core:
  • The outer core extends from the bottom of the mesosphere or the lower mantle and surrounds the inner core.
  • Composed of iron and nickel, the extreme temperature allows these metals to remain in their liquid phases.
  • It is the only layer of the Earth that is a true liquid.
  • Furthermore, its movement is responsible for generating the magnetic field.

 Inner Core: 
  • The inner core is also made of iron and some nickel.
  • However, unlike the outer core, it is a solid ball.
  • The solidity is due to the intense pressure from the upper layers.
  • Hence, although it is as hot as the surface of the Sun, there is speculation that the inner core is slowly growing as the liquid outer core at the boundary with the inner core cools and solidifies due to the gradual interior cooling.

Interior of the Earth,Interior of the Earth

Read More:Evolution of Atmosphere

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