Atmosphere – Definition, Composition & Layers Explained

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Atmosphere – Definition, Composition, Layers, Characteristics, and Examples

Updated on November 2025 | Geography Notes

📚 Table of Contents

  1. Definition of Atmosphere
  2. Composition of Atmosphere
  3. Importance of the Atmosphere
  4. Layers of the Atmosphere
  5. 1. Troposphere
  6. 2. Stratosphere
  7. 3. Mesosphere
  8. 4. Ionosphere (Thermosphere)
  9. 5. Exosphere
  10. Satellites and Their Orbits
  11. PSLV and GSLV – India’s Satellite Launch Vehicles
  12. Conclusion

🌍 Definition of Atmosphere

The atmosphere is a thick layer of gases that surrounds the Earth and is held by gravity. It acts like a protective shield, preventing harmful solar radiation and maintaining a stable climate suitable for life. The term “atmosphere” comes from two Greek words: ‘atmos’ meaning vapor and ‘sphaira’ meaning sphere.

It extends hundreds of kilometers above the Earth’s surface but becomes thinner with height. Without the atmosphere, there would be no air to breathe, no clouds, and no life.

Example: On the Moon, where there is no atmosphere, the surface experiences extreme temperatures from +120°C to -170°C, showing how essential the atmosphere is for life.

🌬️ Composition of the Atmosphere

The atmosphere is a mixture of gases, water vapor, and dust particles. These gases are nearly constant up to 80 km from Earth’s surface. Beyond that, lighter gases dominate as heavier gases settle below.

Gas Percentage by Volume Function
Nitrogen (N₂)78.08%Maintains balance; essential for plant growth (via nitrogen cycle).
Oxygen (O₂)20.95%Required for breathing and combustion.
Argon (Ar)0.93%An inert gas that doesn’t react easily.
Carbon Dioxide (CO₂)0.04%Used by plants for photosynthesis; traps heat (greenhouse effect).
Others (Neon, Helium, Krypton, Hydrogen, etc.)TraceHelp in energy balance and radiation absorption.

Also present are water vapor (0–4%), dust particles, and smoke, which are essential for cloud formation and rainfall.

☀️ Importance of the Atmosphere

  • Provides essential gases like oxygen and carbon dioxide for living organisms.
  • Regulates the Earth’s temperature, keeping it suitable for life.
  • Protects from meteoroids — most burn up in the mesosphere.
  • Contains ozone that absorbs harmful ultraviolet rays.
  • Helps in communication by reflecting radio waves in the ionosphere.
  • Plays a key role in the water cycle — clouds, rain, and storms occur here.

Example Question: Why do astronauts wear spacesuits? → Because outer space has no atmosphere, so no air pressure or oxygen to breathe.

🌤️ Layers of the Atmosphere

The atmosphere is divided into five layers based on temperature variation, composition, and physical characteristics:

  1. Troposphere
  2. Stratosphere
  3. Mesosphere
  4. Ionosphere (Thermosphere)
  5. Exosphere

1. Troposphere

The Troposphere is the lowest and most important layer where all weather phenomena occur. It extends up to 8 km at poles and 18 km at the equator.

  • Contains 75% of air and almost all water vapor and dust.
  • Temperature decreases with altitude (6.5°C per km).
  • Clouds, winds, and rainfall are confined to this layer.
  • The upper boundary is called the Tropopause.

Example: Airplanes usually fly near the tropopause to avoid turbulence and clouds.

2. Stratosphere

The Stratosphere extends up to 50 km and is known for the Ozone Layer, which absorbs harmful ultraviolet radiation.

  • Temperature increases with height due to ozone heating.
  • Free from weather changes; ideal for jet aircraft and balloons.
  • Ozone layer lies between 15–35 km altitude.
  • The upper boundary is called the Stratopause.

Example: Supersonic jets like Concorde used to fly in the lower stratosphere for smooth travel.

3. Mesosphere

The Mesosphere extends from 50 to 80 km. It is the coldest layer, with temperatures reaching -90°C. Meteors burn up in this region due to friction.

  • Protects Earth by burning meteoroids.
  • Temperature decreases with height.
  • The upper boundary is called the Mesopause.
  • Contains thin air and noctilucent clouds.

4. Ionosphere (Thermosphere)

The Ionosphere extends from about 80 to 400 km. It contains electrically charged ions that reflect radio waves, enabling long-distance communication.

  • Temperature increases rapidly with height (up to 1500°C).
  • Useful for radio communication and satellite signals.
  • Auroras (Northern and Southern lights) appear here.
  • Upper part is known as the Thermosphere.

Example: HAM radio and GPS signals work efficiently due to the ionosphere’s reflective properties.

5. Exosphere

The Exosphere is the outermost layer, extending from around 400 km to 10,000 km. Air is extremely thin, and gas molecules gradually escape into outer space.

  • Composed mainly of hydrogen and helium.
  • Marks the boundary between atmosphere and space.
  • Satellites orbit within or above this layer.
  • No weather or breathable air exists here.

Example: The International Space Station orbits Earth within the lower exosphere.

🛰️ Satellites and Their Orbits

Satellites are objects that revolve around Earth. They are placed in different orbits depending on their function:

  • Low Earth Orbit (LEO): 200–2,000 km – used for Earth observation, mapping (e.g., Cartosat).
  • Medium Earth Orbit (MEO): 2,000–35,000 km – used for navigation (e.g., GPS, IRNSS).
  • Geostationary Orbit (GEO): 35,786 km – used for communication and weather satellites (e.g., INSAT, GSAT).

🚀 PSLV and GSLV – India’s Satellite Launch Vehicles

India’s ISRO has developed two major types of launch vehicles to send satellites beyond the atmosphere:

🔹 PSLV (Polar Satellite Launch Vehicle)

  • Launches satellites into Polar and Low Earth Orbits (up to 2,000 km).
  • Used for Earth observation and research (e.g., Chandrayaan-1, Cartosat).
  • Passes through the ionosphere and lower exosphere.

🔹 GSLV (Geosynchronous Satellite Launch Vehicle)

  • Launches satellites into Geostationary Orbits (~35,786 km).
  • Used for communication and weather satellites (e.g., GSAT, INSAT).
  • Goes far beyond the exosphere into outer space.

In short: PSLV and GSLV are not parts of the atmosphere but are advanced space vehicles that help India explore and connect with space.

🌎 Conclusion

The atmosphere acts as Earth’s life-support system. Each layer—from the troposphere to the exosphere—performs unique and vital functions such as protecting, communicating, and regulating temperature. Understanding these layers helps students answer exam questions and appreciate the scientific balance that sustains all life.

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