- absorbing ultraviolet solar radiation,
- warming the surface through heat retention (greenhouse effect), and
- reducing temperature extremes between day and night (the diurnal temperature variation).
The common name given to the atmospheric gases used in breathing and photosynthesis is air.
Composition of air
By volume, dry air contains:
- 78.09% nitrogen,
- 20.95% oxygen,
- 0.93% argon,
- 0.039% carbon dioxide, and small amounts of other gases.
Air also contains a variable amount of water vapour, on average around 1%.
Although air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and terrestrial animals currently is only known to be found in Earth's troposphere and artificial atmospheres.
The atmosphere has a mass of about 5.15×1018 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface.
The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.
The Kármán line, at 100 km (62 mi), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space.
Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi).
Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.
The study of Earth's atmosphere and its processes is called atmospheric science or aerology and includes meteorology. Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.