Layers of Earth: The Crust, the Mantle and the Core for Competitive Exams 2021

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Layers Of Earth: The Crust, The Mantle and The Core (Environmental Science)

The Crust

Thickness of crust

  • Oceanic areas – 5 - 10 Km (More Iron)
  • Continental areas – 35 Km (Less Iron)
  • Orogenic belts- 55 - 70 Km

Density of crust is 2.6 - 3 gm/cm3

  • Sub-divisions of crust:
    • Sial- Al and Silica
    • Sima- Mg and Silica

Conrad Discontinuity- Separates Sial layer from the underlying Sima layer

The Mantle

  • Thickness is about 2865 km
  • Density of mantle is 3 gm/cm3
  • Temperature of upper mantle is 870°C and lower mantle is upto 4470°C
    • Upper mantle has pyrolite (3 parts of ultramafic rock + 1 part of Basalt) .
    • Lower Mantle extends from 1000 Km to the core boundary.
  • Repetiti Discontinuity- At 950 Km depth- It marks the lower limit of the very rapid rise in the velocity of seismic vibrations.

The Core

  • Thickness of 3500 Km
  • Density is 9 – 12 gm/cm3
  • Consists of three parts:
    • Outer Core- Homogeneous fluid
    • Middle Core- transition layer
    • Inner Core- metallic Ni and Fe


  • Central Temperature of core- 6000°C
  • Central Pressure of core- 392 × 108 bars
  • Density of centre of core- 18gm/cm3
  • Core is separated from the Mantle by the Guttenberg Weichert Discontinuity
  • Mohorovicic Discontinuity- This Boundary separates crust (low density silicates) from mantle (high density silicates) .

Multiple Choice Questions

1. Which among the following discontinuity separates the Sial layer from Sima layer?

  1. Conrad Discontinuity
  2. Mohorovicic Discontinuity
  3. Repetiti Discontinuity
  4. None of the above

Answer: a

2. Metallic Iron and Nickel is found at

  1. Inner core
  2. Crust
  3. Mantle
  4. Earth՚s surface

Answer: a

3. Central temperature of the core is

  1. 2000°C
  2. 4000°C
  3. 5000°C
  4. 6000°C

Answer: d

4. Which among the following statement is true?

  1. Mantle is the upper region of lithosphere
  2. Inner core is the transition layer
  3. Oceanic crust is denser than continental crust
  4. All of the above

Answer: c

#Layers of Earth





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