Interior of the Earth

Interior of the Earth (UPSC Geography Notes)

Overview: The Earth’s interior is not uniform. It is made up of several layers that differ in composition, temperature, and density. Understanding the Earth’s internal structure is crucial for studying earthquakes, volcanoes, and plate tectonics — important topics for UPSC Geography.

Table of Contents

• 1. Introduction
• 2. Sources of Information about Earth’s Interior
• 3. Structure of the Earth
• 4. Crust
• 5. Mantle
• 6. Core
• 7. Temperature, Pressure, and Density Variation
• 8. Importance of Studying Earth’s Interior
• 9. UPSC Quick Revision Notes
• 10. Previous Year Question

1. Introduction

The Earth looks solid from the outside, but its interior is made of different layers with varying chemical compositions and physical states. Scientists study these layers to understand phenomena like volcanic eruptions, earthquakes, and mountain formation.

2. Sources of Information about Earth’s Interior

We cannot directly observe the Earth’s deep interior, so scientists use indirect methods to study it.

Main sources include:

• 1. Direct Sources: Rocks and materials from mining, drilling, and volcanic eruptions. The deepest mine (South Africa) is about 12 km deep — very shallow compared to Earth’s total radius (~6371 km).
• 2. Indirect Sources:
  • Seismic waves generated by earthquakes.
  • Gravitational force variations.
  • Magnetic field studies.
  • Meteorite composition (believed to represent early Earth material).

3. Structure of the Earth

The Earth is divided into three main layers based on composition and density:

• 1. Crust – Outer solid layer.
• 2. Mantle – Layer beneath the crust, made of molten and solid rock.
• 3. Core – Central part, composed mainly of metals (iron and nickel).

4. Crust

• It is the outermost and thinnest layer of the Earth.
• Average thickness: 5–10 km (oceanic) and 30–40 km (continental).
• Composition: Oxygen, silicon, aluminum (often called SIAL – silica + alumina).
• Below the crust lies a discontinuity called the Mohorovičić Discontinuity (Moho), separating it from the mantle.

5. Mantle

• Lies below the crust and extends up to about 2900 km depth.
• Constitutes about 84% of Earth’s volume.
• Composition: Silicon, magnesium (known as SIMA – silica + magnesia).
• Upper mantle (up to 400 km) contains a semi-molten zone called the asthenosphere — this is where magma originates.
• The boundary between mantle and core is called the Gutenberg Discontinuity.

6. Core

• The innermost layer of the Earth, extending from about 2900 km to 6371 km.
• Composition: Iron and nickel (called NIFE – nickel + ferrous).
• Divided into:
  • Outer Core: Liquid layer responsible for generating Earth’s magnetic field.
  • Inner Core: Solid due to immense pressure, despite very high temperature.
• Temperature at the center may reach 5000–6000°C.

7. Temperature, Pressure, and Density Variation

• Temperature: Increases by about 1°C for every 32 m of depth in the upper crust, but the rate decreases with depth.
• Pressure: Increases with depth due to overlying rocks, reaching millions of atmospheres near the core.
• Density: Increases from 2.7 g/cm³ in the crust to about 13 g/cm³ at the core.

8. Importance of Studying Earth’s Interior

• Explains the causes of earthquakes and volcanic activity.
• Helps in locating minerals, oil, and natural gas deposits.
• Provides understanding of plate tectonics and continental drift.
• Essential for building disaster-resilient infrastructure.

9. UPSC Quick Revision Notes

Crust – Outer, thin, solid layer (SIAL).
Mantle – Thickest layer, semi-molten (SIMA).
Core – Central metallic layer (NIFE), source of magnetic field.
Moho – Boundary between crust and mantle.
Gutenberg – Boundary between mantle and core.
Asthenosphere – Semi-molten layer under crust, source of magma.
Temperature, pressure, and density increase with depth.

10. Previous Year Question

Q. The layer of the Earth responsible for generating the magnetic field is —
(a) Crust
(b) Mantle
(c) Outer Core
(d) Inner Core
Answer: (c) Outer Core

Related Keywords

Interior of the Earth UPSC Notes, Layers of the Earth, Earth’s Structure, Mohorovicic Discontinuity, NIFE SIAL SIMA, Geography NCERT Class 11 Notes, UPSC Physical Geography.

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Sources: NCERT – Physical Geography, Geological Survey of India, Britannica