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Earth - Earth's atmosphere From Wikipedia the free...

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Earth's atmosphere From Wikipedia, the free encyclopedia (Redirected from Earth’s atmosphere ) “Air” redirects here. For other uses, see Air (disambiguation) . Layers of Atmosphere—not to scale ( NOAA ) [1] Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity . It contains roughly (by molar content/volume) 78% nitrogen , 20.95% oxygen , 0.93% argon , 0.038% carbon dioxide , trace amounts of other gases , and a variable amount (average around 1%) of water vapor . This mixture of gases is commonly known as air . The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night. There is no definite boundary between the atmosphere and outer space . It slowly becomes thinner and fades into space. Three quarters of the atmosphere's mass is within 11 km of the planetary surface. In the United States , people who travel above an altitude of 80.5 km (50 statute miles ) are designated astronauts . An altitude of 120 km (400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry. The Kármán line , at 100 km (328,000 ft), is also frequently regarded as the boundary between atmosphere and outer space. Contents [ hide ] 1 Temperature and layers 2 Pressure and thickness 3 Composition o 3.1 Heterosphere 4 Density and mass 5 Evolution on Earth 6 Air pollution 7 See also 8 References 9 External links [ edit ]Temperature and layers Nitrogen 78.084% Oxygen 20.946% Argon 0.934% Carbon dioxide 0.038% Water vapor >1% Other 0.002%
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The temperature of the Earth's atmosphere varies with altitude ; the mathematical relationship between temperature and altitude varies among six different atmospheric layers: 1. Troposphere : From the Greek word "τρέπω" meaning to turn or mix. The troposphere is the lowest layer of the atmosphere; it begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (60,000 ft) at the equator, with some variation due to weather factors. The troposphere has a great deal of vertical mixing due to solar heating at the surface. This heating warms air masses, which makes them less dense so they rise. When an air mass rises the pressure upon it decreases so it expands, doing work against the opposing pressure of the surrounding air. To do work is to expend energy , so the temperature of the air mass decreases. As the temperature decreases, water vapor in the air mass may condense or solidify, releasing latent heat that further uplifts the air mass. This process determines the maximum rate of decline of temperature with height, called the adiabatic lapse rate . 2. Stratosphere : From the Latin word "stratus" meaning a spreading out. The stratosphere extends from the troposphere's 7 to 17 km (23 – 60,000 ft) range to about 50 km (160,000 ft). Temperature increases with height. The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. "Relatively high" means a few parts per million—much higher than the
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