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Atmosphere – Structure and Composition (UPSC Geography Notes)
Overview: The atmosphere is the thin blanket of gases surrounding the Earth, essential for life and climate regulation. It protects us from harmful solar radiation, maintains temperature balance, and enables weather and rainfall. Understanding its structure and composition is vital for UPSC Geography and environmental studies.
Table of Contents
- 1. Introduction
- 2. Composition of the Atmosphere
- 3. Variable Components
- 4. Structure (Layers) of the Atmosphere
- 5. Significance of Each Layer
- 6. Importance of the Atmosphere
- 7. UPSC Quick Revision Notes
- 8. Previous Year Question
1. Introduction
The atmosphere is a mixture of gases surrounding the Earth and held by its gravity. It extends up to about 10,000 km but most weather and life-supporting gases are found within the first 100 km. The atmosphere interacts continuously with the lithosphere and hydrosphere, forming the Earth’s climate system.
2. Composition of the Atmosphere
The atmosphere is made up of a mixture of permanent and variable gases. The proportions of the permanent gases remain nearly constant up to about 100 km (homosphere).
Permanent Gases (by volume)
| Gas | Percentage by Volume | Importance |
|---|---|---|
| Nitrogen (N₂) | 78.08% | Maintains atmospheric stability; used by plants indirectly. |
| Oxygen (O₂) | 20.95% | Essential for respiration and combustion. |
| Argon (Ar) | 0.93% | Inert gas with minimal role in weather or life processes. |
| Carbon Dioxide (CO₂) | 0.04% | Absorbs heat; plays a key role in greenhouse effect and photosynthesis. |
| Neon, Helium, Krypton, Xenon, Hydrogen | Traces | Found in small quantities; some are used in scientific applications. |
3. Variable Components
These components vary from place to place and time to time, but they play a crucial role in weather and climate regulation.
- Water Vapour (0–4%) – Controls humidity and rainfall; major greenhouse gas.
- Ozone (O₃) – Found mainly in the stratosphere; absorbs harmful UV radiation.
- Dust Particles – Serve as condensation nuclei for cloud formation.
- Carbon Dioxide (CO₂) – Although small in amount, it strongly influences global temperature.
4. Structure (Layers) of the Atmosphere
The atmosphere is divided into several layers based on temperature and composition. Each layer has unique features and functions.
(a) Troposphere
- Lowest layer of the atmosphere; extends up to 8 km at poles and 18 km at equator.
- Contains almost all weather phenomena — clouds, rainfall, storms.
- Temperature decreases with height at an average rate of 6.5°C per 1000 m.
- Upper boundary: Tropopause.
(b) Stratosphere
- Extends from tropopause to about 50 km.
- Contains the ozone layer that absorbs harmful ultraviolet (UV) rays.
- Temperature increases with height due to ozone absorption (temperature inversion).
- Favorable for aircraft flights due to stable conditions.
- Upper boundary: Stratopause.
(c) Mesosphere
- Extends from 50 to 80 km.
- Temperature again decreases with height.
- Meteors burn in this layer due to friction.
- Upper boundary: Mesopause – the coldest part of the atmosphere.
(d) Thermosphere (Ionosphere)
- Extends from 80 to about 700 km.
- Temperature increases sharply with height due to absorption of solar radiation.
- Contains charged particles (ions), making it crucial for radio communication.
- Auroras (Northern and Southern Lights) occur here.
(e) Exosphere
- Outermost layer, extending beyond 700 km.
- Contains very thin gases (hydrogen and helium).
- Gradually merges into outer space.
5. Significance of Each Layer
- Troposphere: Supports weather, water cycle, and life processes.
- Stratosphere: Ozone layer protects life from UV rays.
- Mesosphere: Burns meteors and prevents them from reaching Earth.
- Thermosphere: Enables radio communication and satellite orbits.
- Exosphere: Transitional zone to space; low-density gases escape Earth’s gravity.
6. Importance of the Atmosphere
- Maintains Earth’s temperature balance.
- Protects from harmful solar radiation.
- Enables cloud formation and rainfall.
- Supports respiration and photosynthesis.
- Facilitates weather and climate processes.
7. UPSC Quick Revision Notes
Variable Gases: Water vapour, ozone, dust.
Layers: Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.
Boundaries: Tropopause, Stratopause, Mesopause.
Ozone layer – Stratosphere.
Meteors burn – Mesosphere.
Auroras occur – Thermosphere.
8. Previous Year Question
Q. The ozone layer is mainly found in which layer of the atmosphere?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
(d) Thermosphere
Answer: (b) Stratosphere
Related Keywords
Structure of Atmosphere UPSC Notes, Composition of Atmosphere, Layers of Atmosphere, Ozone Layer, Troposphere, Stratosphere, Physical Geography NCERT Notes, UPSC Geography Preparation.
Sources: NCERT – Fundamentals of Physical Geography, Goh Cheng Leong, NASA Atmospheric Studies, Geological Survey of India
