Air

Air is the term how the layer of gases of the planet's atmosphere are known as. The layer of gases is retained by gravity and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the planet's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention, and reducing temperature extremes between day and night. Air can also refer to refer one of the four classical elements that describe matter, along with earth, water and fire.

Air composition, temperature, and atmospheric pressure vary with altitude. Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere.^{[citation needed]} The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition.

See also

• Fire

References

This article uses material from the Wikipedia article Atmosphere_of_Earth, which is released under the Creative Commons Attribution-ShareAlike 3.0 Unported License (view authors).