Introduction to the Earth’s Interior:

The Earth is composed of several layers, starting from the surface to the deep interior. Each layer is unique in its composition, temperature, and density. Understanding these layers helps in studying natural phenomena like earthquakes, volcanic eruptions, and the formation of landforms.

Structure of the Earth

The Earth is divided into three main layers:

A. Crust

1. The outermost and thinnest layer of the Earth.
   • Thickness: 5-30 km under oceans and 35-70 km under continents.
   • It forms less than 1% of the Earth’s volume.
2. Composition:
   • Made of rocks and minerals.
   • The upper part of the crust is called SIAL (Silica and Aluminium).
   • The oceanic crust contains SIMA (Silica and Magnesium).
3. Characteristics:
   • Solid and rigid.
   • Contains resources like soil, minerals, and fossil fuels.

B. Mantle

1. Located beneath the crust, extending to a depth of 2,900 km.
   • Makes up 84% of the Earth’s volume.
2. Composition:
   • Semi-molten rock (magma).
   • Rich in silicate minerals and iron.
3. Characteristics:
   • The upper mantle is partially molten and contributes to the movement of tectonic plates.
   • Temperature increases with depth.

C. Core

1. The innermost layer, extending from 2,900 km to the center of the Earth (6,371 km).
2. Divided into:
   1. Outer Core:
      • Liquid layer composed mainly of iron and nickel.
      • Responsible for generating the Earth’s magnetic field.
   2. Inner Core:
      • Solid due to immense pressure.
      • Made of iron and nickel, forming NIFE.
      • Extremely hot, with temperatures up to 6,000°C.

Types of Rocks

Rocks form the building blocks of the Earth’s crust. They are classified into three types based on their formation process:

A. Igneous Rocks

Formed by the cooling and solidification of magma (inside the Earth) or lava (on the surface).

1. Intrusive Igneous Rocks:
   • Formed when magma cools slowly beneath the Earth’s surface.
   • Example: Granite (hard and durable).
2. Extrusive Igneous Rocks:
   • Formed when lava cools quickly on the Earth’s surface.
   • Example: Basalt (fine-grained).

B. Sedimentary Rocks

1. Formation:
   • Created by the deposition and compression of sediments like sand, mud, and pebbles over time.
2. Characteristics:
   • Found in layers.
   • Often contain fossils of plants and animals.
   • Examples: Sandstone, limestone, shale.

C. Metamorphic Rocks

1. Formation:
   • Formed when existing igneous or sedimentary rocks undergo changes due to heat and pressure.
2. Characteristics:
   • Hard and compact.
3. Examples:
   • Marble (from limestone).
   • Slate (from shale).

Rock Cycle:

The rock cycle explains the continuous transformation of rocks:

1. Igneous Rocks break down into sediments, forming sedimentary rocks.
2. Sedimentary Rocks undergo heat and pressure to form metamorphic rocks.
3. Metamorphic Rocks melt into magma, which cools to form igneous rocks again.

This cycle ensures the recycling of Earth’s materials over millions of years.

Minerals:

1. Definition:
   • Naturally occurring substances with a definite chemical composition.
2. Characteristics:
   • Found in rocks.
   • Essential for industries, construction, and jewelry.
3. Examples:
   • Metallic minerals: Iron, gold, silver.
   • Non-metallic minerals: Limestone, mica, gypsum.

Importance of the Earth’s Interior

1. Source of Resources:
   • Provides minerals, fossil fuels, and construction materials.
2. Understanding Natural Phenomena:
   • Helps study earthquakes, volcanic eruptions, and plate tectonics.
3. Formation of Landforms:
   • Processes like folding, faulting, and volcanic activity shape the Earth’s surface.