Earth’s Layers – Crust, Mantle, Core | Delhi Police & SSC Exams

1. Introduction

The Earth is made up of several layers arranged like an onion. Each layer has unique composition, density, and temperature. Studying these layers helps us understand earthquakes, volcanoes, and the Earth's magnetic field.

Key Study Areas:

Layer composition and characteristics
Depth ranges and temperatures
Geological significance
Exam-focused memory tricks

Practical Importance:

Understanding Earth's structure helps explain natural phenomena and geological processes

2. Major Layers of the Earth

The internal structure of the Earth is divided into three main layers:

Layer	Depth (approx.)	Composition	Key Facts
Crust	0–35 km	Silica (Si) & Aluminium (Al) — "SIAL"	Outermost solid layer
Mantle	35–2900 km	Silica (Si) & Magnesium (Mg) — "SIMA"	Semi-molten rock called magma
Core	2900–6371 km	Nickel (Ni) & Iron (Fe) — "NIFE"	Hottest and densest layer

3. The Crust — The Skin of the Earth

Characteristics:

Thinnest layer of the Earth
Average temperature: ~500°C
Two types: Continental and Oceanic

Continental Crust

Thick (avg 35 km), granitic composition

Oceanic Crust

Thin (avg 5 km), basaltic composition

Composition Memory Aid:

"SIAL" = Si + Al → found in continents

"SIMA" = Si + Mg → found below oceans

4. The Mantle — The Middle Layer

Key Features:

Occupies most of Earth's volume (about 84%)
Made of semi-molten rock (magma)
Average temperature: ~1000–3000°C

Mantle Divisions:

Upper Mantle (Asthenosphere)

Semi-molten, causes plate movement

Lower Mantle (Mesosphere)

Solid due to high pressure

5. The Core — The Center of the Earth

Core Characteristics:

Temperature: >5000°C
Composition: Nickel + Iron (NIFE)
Extreme pressure conditions

Outer Core

Molten iron and nickel → causes Earth's magnetic field

Inner Core

Solid due to extreme pressure

Memory Tricks:

"C-M-C" = Crust–Mantle–Core

"SIAL–SIMA–NIFE" = Elements order

Earth's Internal Layers Diagram

CRUST (SIAL) - 0–35 km

MANTLE (SIMA) - 35–2900 km

OUTER CORE (Molten NIFE) - 2900–5150 km

INNER CORE (Solid NIFE) - 5150–6371 km

6. Quick Comparison Table

Feature	Crust	Mantle	Core
Depth	0–35 km	35–2900 km	2900–6371 km
Composition	Si, Al	Si, Mg	Ni, Fe
State	Solid	Semi-solid	Outer – liquid, Inner – solid
Temperature	~500°C	1000–3000°C	>5000°C
Importance	Surface layer, supports life	Plate movement	Magnetic field

PYQs (Previous Year Questions – Delhi Police & SSC)

1

The outermost layer of the Earth is called?

Options: (A) Mantle (B) Crust (C) Core (D) Asthenosphere

Category: Basic Layers

Show Answer

B. Crust

2

Which layer of the Earth is made up of Si and Al elements?

Options: (A) Crust (B) Mantle (C) Core (D) Lithosphere

Category: Composition