Hidden Mantle Layer of Earth

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.

PRACTICE QUESTION:

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

Answer