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