Crust

  • The crust is the outermost solid part and a thin layer of the Earth with an average thickness of 0-50 km.
  • The thickness of the crust varies under the oceanic (5 – 30 km) and continental areas (50 – 70 km).
  • Nearly 1% of the Earth’s volume and 5% of the Earth’s mass are made of the crust.
  • The temperature of the crust increases with depth, reaching levels of around 200°C to 400°C near the mantle-crust boundary.
  • Composition
    • The crust’s outer layer is made up of sedimentary material, and beneath it are acidic crystalline, igneous, and metamorphic rocks.
    • Basaltic and ultrabasic rocks make up the crust’s lowest layer.
  • Major Elements of the Crust of crust are  Oxygen (O (46.6 %), Silicon (Si) (27.7%), Aluminium (Al) (8.1 %), Iron (Fe) (5.0%), Calcium (Ca)(3.6%), Sodium (Na) (2.8%), Potassium (K) (2.6 %), Magnesium (Mg)(1.5%).
Lithosphere

  • The lithosphere is the earth’s rigid outer layer.
  • Thickness – 10 to 200 kilometres.
  • It consists of the crust as well as the upper part of the mantle.

Asthenosphere

  • Located below the lithosphere.
  • Thickness – 80-200 km
  • The asthenosphere is soft and plastic in nature.
  • It’s vicious, brittle, and ductile, and its density is higher than the crust.
  • It is the primary source of magma that rises to the surface.

 

Mantle

  • The portion of the interior beyond the crust is called the mantle.
  • The upper portion of the mantle is called the asthenosphere.
  • It is completely solid with a thickness of 10-200 km
  • Composition – The mantle has been formed largely of silicate minerals rich in iron and magnesium.

Core

  • It is composed of iron and nickel.
  • The core lies between 2900 km and 6400 km below the Earth’s surface.
  • Divided into
    • Outer Core
      • Located between a depth of 2900 and 5100km.
      • The outer core is liquid because it is not under enough pressure to solidify.
    • Inner Core
      • The inner core stretches from the Earth’s centre to 5100 kilometres below the surface.
      • This layer is solid in nature.
Discontinuity Between Layers

  • Conrad Discontinuity – Between upper and lower crust
  • Mohorovicic Discontinuity (Moho) – Between crust and mantle
  • Repetti Discontinuity – Between the upper and lower mantle
  • Gutenberg Discontinuity – Between the mantle and the outer core
  • Lehmann Discontinuity – Between inner and outer core

 

Source: The Hindu

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