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Hidden Mantle Layer of Earth

2023 MAR 4

Preliminary   > Geography   >   Geomorphology   >   Geomorphology

Why in news?

  • According to two new studies, the mantle of the earth has been hiding two new layers.

More about the news:

  • The first layer is a low viscosity zone in the upper mantle, approximately 100 kilometres thick, which was discovered by studying deep earthquakes (2018 Fiji earthquake of 8.2 magnitude) using GPS sensors.
  • The second layer is a partially molten layer that extends from 90 km to 150 kilometres and sits below the tectonic plates.
  • This layer was discovered by analysing seismic waves from earthquakes and suggests a higher temperature.

Structure of the Earth:

  • Crust:
    • The crust is the outermost solid part of the earth.
    • It is fragile.
    • The thickness of the crust varies under the oceanic and continental areas.
    • Oceanic crust is thinner as compared to the continental crust.
    • The continental crust is thicker in the areas of major mountain systems.
    • The crust is made up of heavier rocks having a density of 3 g/cm3.
    • The kind of rock seen in the oceanic crust is basalt.
    • The mean density of material in the oceanic crust is 2.7 g/cm3.
    • Silica (Si) and Aluminium (Al) are major constituent minerals. Hence it is often termed as SIAL. Also, sometimes SIAL is used to refer to the Lithosphere.
  • Mantle:
    • The portion of the interior beyond the crust is called the mantle.
    • It is in a solid-state.
    • It has a density higher than the crust portion.
    • The thickness ranges from 10-200 km.
    • The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
    • The asthenosphere is the upper portion of Mantle.
    • It is the chief source of magma that finds its way to the surface during volcanic eruptions.
    • The crust and the uppermost part of the mantle are called the lithosphere.
    • The major constituent elements of the mantle are Silicon and Magnesium and hence it is also termed as SIMA
  • Core:
    • The core-mantle boundary is positioned at the depth of 2,900 km.
    • The inner core is in the solid-state whereas the outer core is in the liquid state.
    • The core is made up of very heavy material mostly constituted by nickel and iron. Hence it is also called the “nife” layer.


In the context of structure of earth, consider the following statements:

1. The asthenosphere is the upper portion of Mantle

2. Mantle has a lower density than the crust portion

3. Mantle is made up of very heavy material mostly constituted by nickel and iron

Which of the statements given above is/are correct?

(a) 2 and 3 only

(b) 1 only

(c) 3 only

(d) 1 and 2 only