Atmospheric Composition and Layers

Describe the composition and layered structure of the atmosphere

  • Atmosphere: The gaseous mixture surrounding the surface of the Earth.
  • The dry atmosphere is composed of the following gases:

Gas% by volume
Oxygen 20.95
Carbon dioxide0.036
Other 0.004
Atmospheric composition

  • The dried atmospheric composition varies little with altitude.
  • The percentage of carbon dioxide in the atmosphere has been increasing over the last 150 years, largely due to the burning of fossil fuels.
  • The percentage of water vapour in the atmosphere varies considerable, particularly in the troposphere, where it ranges from 0.5 % to 5 %.
  • The atmosphere consists of a series of layers, the boundaries between which are defined by marked changes in the rate of change of temperature.

LayerExtent (Altitude)
Troposphere    Earth’s surface to ~15 kmTemperature decreases with altitude
Stratosphere    ~15 km to ~50 km• Temperature increases with altitude
• Contains ozone layer, with maximum concentration at altitude of ~25 km
Mesosphere    ~50 km to ~85 km
Temperature decreases with altitude
Thermosphere    ~85km to ~500 km
Temperature increases with altitude
Exosphere    ~500 km outwards• Particles can overcome the Earth’s gravity an escape into space
• Diffuses into space
Ionosphere    ~60 km outwards
• Incorporates the thermosphere and part of the mesosphere
• Contains free ions, atoms and electrons

Easychem - Atmospheric Composition and Layers