Quick Revision Notes & Formula Sheet

Class: 7th
Subject: Social Science (Geography)
Chapter: Inside Our Earth

1. Introduction

The Earth is our dynamic home. It is constantly undergoing changes inside and outside. Just like an onion, the earth is made up of several concentric layers with one inside another.

2. Interior of the Earth

The earth's interior is divided into three main layers:

1. Crust (पपड़ी):

   • The uppermost layer over the earth’s surface.
   • It is the thinnest of all layers (about 35 km on the continental masses and only 5 km on the ocean floors).
   • Main components of Continental Mass: Silica and Alumina $\rightarrow$ Called Sial.
   • Main components of Ocean Floor: Silica and Magnesium $\rightarrow$ Called Sima.

2. Mantle (मैंटल / मेंटल):

   • Just beneath the crust.
   • Extends up to a depth of 2,900 km below the crust.

3. Core (क्रोड):

   • The innermost layer.
   • Radius is about 3,500 km.
   • Made of Nickel and Iron $\rightarrow$ Called Nife (Ni - nickel, fe - ferrous/iron).
   • Has very high temperature and pressure.

3. Rocks and Minerals

• Rock: Any natural mass of mineral matter that makes up the earth's crust. Rocks can be of different color, size, and texture.

Three Major Types of Rocks:

1. Igneous Rocks (आग्नेय चट्टानें):

   • Formed when molten magma cools and turns solid.
   • Also called Primary Rocks.
   • Types:
     • Intrusive Rocks: Magma cools deep inside the earth's crust (e.g., Granite).
     • Extrusive Rocks: Lava comes on the earth's surface and cools rapidly (e.g., Basalt).

2. Sedimentary Rocks (अवसादी चट्टानें):

   • Rocks roll down, crack, and hit each other (fragments are called sediments).
   • These sediments are transported and deposited by wind, water, etc., and compressed and hardened to form layers of rocks.
   • Example: Sandstone.
   • May contain fossils (प्राश्म / जीवाश्म) of plants, animals, and microorganisms.

3. Metamorphic Rocks (कायांतरित चट्टानें):

   • Igneous and sedimentary rocks change under great heat and pressure.
   • Example: Clay changes into slate; limestone changes into marble.

4. The Rock Cycle (चट्टान चक्र)

• Definition: The process of transformation of the rock from one form to another in a cyclic manner is known as the rock cycle.
• Flow: Molten Magma $\rightarrow$ Igneous Rocks $\rightarrow$ Sediments $\rightarrow$ Sedimentary Rocks $\rightarrow$ Metamorphic Rocks $\rightarrow$ Melts back into Magma.

5. Minerals (खनिज)

• Definition: Naturally occurring substances which have certain physical properties and a definite chemical composition.
• Importance:
  • Used as fuels (e.g., coal, natural gas, petroleum).
  • Used in industries (iron, aluminium, gold, uranium, etc.).
  • Used in medicines and fertilizers.