UPSC Prelims Special – Geography Synopsis | English | Page 1

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1. Origin and Structure of the Earth

The Earth is believed to have formed around 4.5 billion years ago. It consists of multiple layers including the crust, mantle, and core.

Major Layers of the Earth

• Crust – Outer solid layer
• Mantle – Semi-molten middle layer
• Core – Innermost metallic layer

The Earth’s crust is the thinnest layer of the Earth.

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2. Types of Rocks

Rocks are naturally occurring solid materials that form the Earth’s crust. They are classified into three major categories.

Major Types of Rocks

• Igneous Rocks
• Sedimentary Rocks
• Metamorphic Rocks

Examples

• Granite – Igneous Rock
• Sandstone – Sedimentary Rock
• Marble – Metamorphic Rock

Igneous rocks are known as primary rocks.

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3. Earthquakes and Volcanoes

Earthquakes occur due to sudden movements within the Earth’s crust, while volcanoes are openings through which magma erupts to the surface.

Important Terms

• Focus – Point inside the Earth where earthquake originates
• Epicenter – Point on the Earth’s surface directly above the focus
• Magma – Molten material inside the Earth

The Pacific Ring of Fire is highly prone to earthquakes and volcanoes.

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4. Interior Forces of the Earth

Internal forces continuously shape the Earth’s surface through processes such as folding, faulting, volcanism, and earthquakes.

Major Endogenic Forces

• Folding
• Faulting
• Volcanic Activity
• Earthquake Activity

Fold mountains are formed due to compressional forces.

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5. Mountains and Plateaus

Mountains and plateaus are important landforms formed through geological processes over millions of years.

Types of Mountains

• Fold Mountains
• Block Mountains
• Volcanic Mountains

Examples

• Himalayas – Fold Mountains
• Black Forest – Block Mountain
• Deccan Plateau – Plateau Region

The Himalayas are young fold mountains.

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Quick Revision Points

• Crust – Outer layer of the Earth
• Granite – Igneous Rock
• Epicenter – Surface point above focus
• Pacific Ring of Fire – Earthquake zone
• Himalayas – Young Fold Mountains

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Practice MCQ

Which layer of the Earth is the thinnest?

• A) Mantle
• B) Core
• C) Crust
• D) Lithosphere

Correct Answer: C) Crust

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