Interior of the earth for UPSC

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03 Jul Interior of the earth for UPSC

Posted at 03 Jul 2025 in Geography for UPSC, geography optional, Geomorphology by
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Interior of the Earth – UPSC Geography Notes

Earth Interior Layers Diagram

Relevant for: UPSC CSE Prelims (Geography) and GS Paper 1 (Mains)

 Introduction

The study of the interior of the Earth helps us understand natural phenomena such as earthquakes, volcanoes, plate tectonics, and more. Since direct observation is not possible beyond a few kilometers, scientists rely on indirect sources like seismic data, volcanic material, and meteors.

 Sources to Study Earth’s Interior

  • Direct Sources: Mining and deep drilling (Kola Superdeep Borehole, ~12 km deep)
  • Indirect Sources:
    • Seismic waves (P-waves and S-waves)
    • Meteorites (nickel-iron composition)
    • Volcanic eruptions (magma from mantle)
    • Gravitational and Magnetic field data

 Layers of the Earth

1. Crust

  • Outermost solid layer
  • Continental Crust: 30-70 km thick; granitic (sial)
  • Oceanic Crust: ~5 km thick; basaltic (sima)
  • Density: 2.7 g/cm³ (continental), 3.0 g/cm³ (oceanic)

2. Mantle

  • Lies below the crust (~2900 km thick)
  • Upper Mantle: Includes Asthenosphere (plastic, semi-molten)
  • Lower Mantle: More rigid and denser
  • Main elements: Magnesium, iron, silicates
  • Density: ~3.3 to 5.5 g/cm³

3. Core

  • Also known as Barysphere
  • Outer Core: Liquid (generates Earth’s magnetic field)
  • Inner Core: Solid (iron and nickel)
  • Depth: 2900 km to 6371 km
  • Temperature: Up to 6000°C
  • Density: ~9.5 to 13 g/cm³

Structure of the Earth

 Discontinuities within the Earth

Discontinuity Between Description
Mohorovičić (Moho) Crust and Mantle Identified by a sudden increase in seismic velocity
Repetti Upper and Lower Mantle Less clearly defined
Gutenberg Mantle and Core P-waves slow down, S-waves disappear (liquid core)
Lehmann Outer Core and Inner Core Inner core is solid; discovered by Inge Lehmann

 Seismic Waves and Earth’s Interior

Seismic waves generated by earthquakes provide crucial data about the interior:

  • P-waves (Primary): Travel through solids and liquids; fastest
  • S-waves (Secondary): Travel only through solids; stop at outer core
  • Shadow Zones: Help identify the liquid outer core (S-waves don’t reach)

Seismic Shadow Zone

 Composition of Earth’s Interior

  • Crust: Oxygen, Silicon, Aluminium, Iron, Calcium
  • Mantle: Silicate minerals rich in Mg and Fe
  • Core: Iron (Fe) and Nickel (Ni) – called NIFE

 Importance for UPSC Exam

  • Frequently asked in UPSC Prelims
  • Helps in understanding related topics: Plate tectonics, Earthquakes, Volcanoes
  • Static portion of Geography – high return for effort

Sample UPSC Prelims MCQs

  1. Which seismic waves can travel through both solids and liquids?
    A. P-waves
  2. The Moho discontinuity separates:
    C. Crust and Mantle
  3. Which part of the Earth is responsible for generating the magnetic field?
    D. Outer Core

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 Summary

  • The Earth is made up of three main layers: Crust, Mantle, and Core.
  • Seismic waves are the most reliable source of information about Earth’s interior.
  • Each layer has unique properties, and the study of these layers is crucial for understanding geophysical phenomena.

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