Exosphere: >700 km (>440 miles) Thermosphere: 80 to 700 km (50 to 440 miles)[6] Mesosphere: 50 to 80 km (31 to 50 miles) Stratosphere: 12 to 50 km (7 to 31 miles) Troposphere: 0 to 12 km (0 to 7 miles)[7] atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earths gravity. The atmosphere protects life on Earth by 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. By volume, dry air contains 78.09% nitrogen, 20.95% oxygen,[1] 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, 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 Earths 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 Earths 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 Nitrogen (N2) 780,840 ppmv (78.084%) Oxygen (O2) 209,460 ppmv (20.946%) Argon (Ar) 9,340 ppmv (0.9340%) Carbon dioxide (CO 2) 397 ppmv (0.0397%) Neon (Ne) 18.18 ppmv (0.001818%) Helium (He) 5.24 ppmv (0.000524%) Methane (CH4) 1.79 ppmv (0.000179%) Not included in above dry atmosphere: Water vapor (H2O) ~0.25% by mass over full atmosphere, locally 0.001%–5% by volume [3]
Posted on: Mon, 30 Jun 2014 03:10:54 +0000
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