Air g dating

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity.The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

Air content and atmospheric pressure vary at different layers, and air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere and in artificial atmospheres.

The atmosphere has a mass of about 5.15 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 (aerology).Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.The three major constituents of Earth's atmosphere, are nitrogen, oxygen, and argon.Water vapor accounts for roughly 0.25% of the atmosphere by mass.The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by volume in the coldest portions of the atmosphere to as much as 5% by volume in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor).

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