The Earth’s atmosphere is divided into five main layers based on temperature variation with altitude. Each layer has distinct physical characteristics and functions.
1. Troposphere
Lowest and most important layer for life
Altitude
- From Earth’s surface up to:
- ~8 km at poles
- ~18 km at equator
- Average: ~12 km
Key Characteristics
- Temperature decreases with height at ~6.5°C per km.
- Contains 75% of atmospheric mass and almost all water vapour and dust.
- All weather phenomena occur here: clouds, rain, storms, cyclones.
- Strong vertical air movement.
Upper Boundary
- Tropopause: acts as a barrier limiting vertical movement of weather systems.
2. Stratosphere
Stable layer above the troposphere
Altitude
- From ~12 km to ~50 km.
Key Characteristics
- Temperature increases with height due to absorption of UV radiation by ozone.
- Very stable air; no weather disturbances.
- Contains the ozone layer, which protects life by absorbing harmful UV rays.
- Commercial jet aircraft fly in lower stratosphere to avoid turbulence.
Upper Boundary
- Stratopause
3. Mesosphere
Coldest atmospheric layer
Altitude
- From ~50 km to ~80–85 km.
Key Characteristics
- Temperature decreases sharply with height.
- Coldest layer (temperatures can drop below –90°C).
- Meteors burn up due to friction with atmospheric gases.
- Very thin air; no aircraft can fly here.
Upper Boundary
- Mesopause (coldest point in atmosphere)
4. Thermosphere
Layer of extremely high temperatures
Altitude
- From ~80 km to ~600–700 km.
Key Characteristics
- Temperature rises rapidly, reaching 1500–2500°C.
- High temperature due to absorption of X-rays and UV radiation.
- Extremely low air density, so it does not feel hot.
- Auroras occur here.
- International Space Station (ISS) orbits in this layer.
Special Feature
- Overlaps significantly with the ionosphere.
5. Exosphere
Outermost atmospheric layer
Altitude
- From ~700 km to ~10,000 km.
Key Characteristics
- Air is extremely thin; atmosphere gradually merges into outer space.
- Dominated by hydrogen and helium.
- Minimal gravitational pull; particles can escape into space.
- Many communication and weather satellites orbit here.
Ionosphere (Functional Layer)
The ionosphere is not a separate temperature-based layer.
Extent
- Roughly from 60 km to 1000 km, overlapping:
- Upper mesosphere
- Entire thermosphere
- Lower exosphere
Key Characteristics
- Ionisation caused by solar radiation creates free electrons and ions.
- Divided into D, E, and F layers based on electron density.
- Reflects radio waves, enabling long-distance communication.
- Highly affected by solar storms, impacting GPS and satellites.
Summary Table
| Layer | Altitude | Temperature Trend | Key Importance |
| Troposphere | 0–12 km | Decreases | Weather, life |
| Stratosphere | 12–50 km | Increases | Ozone protection |
| Mesosphere | 50–80 km | Decreases | Meteor burning |
| Thermosphere | 80–700 km | Increases sharply | Auroras, ISS |
| Exosphere | 700+ km | Nearly constant | Satellites |
| Ionosphere | 60–1000 km | — | Radio communication |
