The<unk>  is a layer of gases surrounding the planet<unk>  and retained by the<unk> 's gravity. It contains roughly (by molar content/volume) 78.08% 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<unk>  protects life on<unk>  by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
There is no definite boundary between the<unk>  and outer space. It slowly becomes thinner and fades into space. Three quarters of the<unk> '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 (~75 miles or 400,000 ft) marks the boundary where<unk> c effects become noticeable during re-entry. The Kármán line, at 100 km (62 miles or 328,000 ft), is also frequently regarded as the boundary between<unk>  and outer space.
Earth's atmosphere
Ionic liquid
Atom
Dead space
Fluid compartments
Syngas
Boil
Wound