Chapter 2: INSIDE OUR EARTH

 🌍 Chapter 2: INSIDE OUR EARTH 

For Class 7 CBSE – Geography
Student: Subhangam

INTRODUCTION: THE EARTH – A DYNAMIC PLANET

The Earth, our homeland, is not just a static ball of land and water — it is a dynamic planet. This means that the Earth is always changing, both on the surface (like earthquakes, volcanoes) and deep inside. To understand these changes, we must first understand what lies beneath the surface of the Earth.

INTERIOR OF THE EARTH

Have you ever peeled an onion? Just like that, the Earth is made up of concentric layers — one inside another. These layers are:

1. Crust (The Outermost Layer)

2. Mantle (The Middle Layer)

3. Core (The Innermost Layer)

Let’s study each one in detail:

🟤 1. CRUST – The Outermost Layer

• Definition: The crust is the outer skin of the Earth.

• Thickness:

  • About 35 km on continental areas (land).

  • About 5 km on ocean floors (under the sea).

• Composition:

  • Continental Crust: Made of silica (Si) and alumina (Al) → called SIAL.

  • Oceanic Crust: Made of silica (Si) and magnesium (Mg) → called SIMA.

• It is the thinnest layer of all.

🟠 2. MANTLE – The Middle Layer

• Position: Located just below the crust.

• Depth: Extends to about 2900 km below the crust.

• Characteristics:

  • It is made of solid and semi-molten rocks.

  • Very hot, and this heat causes movements that lead to earthquakes and volcanic eruptions.

🔴 3. CORE – The Innermost Layer

• Depth: Begins at the bottom of the mantle and extends up to the center of the Earth.

• Radius: About 3500 km.

• Composition: Mainly made up of nickel (Ni) and iron (Fe) → called NIFE.

• Temperature and Pressure:

  • Extremely high temperature (like a furnace).

  • Immense pressure due to the weight of overlying layers.

SUMMARY TABLE: Layers of the Earth

Layer	Thickness	Main Elements	Nickname	Special Features
Crust	5–35 km	Silica, Alumina / Magnesium	SIAL / SIMA	Thinnest, outermost layer
Mantle	~2900 km	Silicate rocks	–	Hot, semi-molten, causes earthquakes
Core	~3500 km radius	Nickel, Iron	NIFE	Hottest layer, immense pressure

CONCLUSION

The Earth may seem solid and still, but deep inside, it is full of movement, heat, and activity. The structure of the Earth — from crust to core — plays a vital role in shaping the world we live in. From mountain formation to volcanic eruptions, everything is connected to the interior of our Earth.