Atmosphere of Earth

Blue light is scattered more than other wavelengths by the gases in the atmosphere, surrounding Earth in a visibly blue layer at the stratosphere, above the clouds of the troposphere, when seen from space on board the ISS at an altitude of 335 km (208 mi) (the Moon is visible as a crescent in the far background).[1]

The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention (greenhouse effect), and reduces temperature extremes between day and night (the diurnal temperature variation), maintaining conditions allowing life and liquid water to exist on the Earth's surface.

As of 2023, by mole fraction (i.e., by number of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.[8] Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. 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]

Earth's early atmosphere consisted of gases in the solar nebula, primarily hydrogen. The atmosphere changed significantly over time, affected by many factors such as volcanism, life, and weathering. Recently, human activity has also contributed to atmospheric changes, such as global warming, ozone depletion and acid deposition.

The atmosphere has a mass of about 5.15×1018 kg,[9] three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes 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), and includes multiple subfields, such as climatology and atmospheric physics. Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann.[10] The study of historic atmosphere is called paleoclimatology.

  1. ^ "Gateway to Astonaut Photos of Earth". NASA. Retrieved 2018-01-29.
  2. ^ Cox, Arthur N., ed. (2000), Allen's Astrophysical Quantities (Fourth ed.), AIP Press, pp. 258–259, ISBN 0-387-98746-0, which rounds N2 and O2 to four significant digits without affecting the total because 0.004% was removed from N2 and added to O2. It includes 20 constituents.
  3. ^ Haynes, H. M., ed. (2016–2017), CRC Handbook of Chemistry and Physics (97th ed.), CRC Press, p. 14-3, ISBN 978-1-4987-5428-6, which cites Allen's Astrophysical Quantities but includes only ten of its largest constituents.
  4. ^ "Trends in Atmospheric Carbon Dioxide", Global Greenhouse Gas Reference Network, NOAA, 2019, retrieved 2019-05-31
  5. ^ "Trends in Atmospheric Methane", Global Greenhouse Gas Reference Network, NOAA, 2019, retrieved 2019-05-31
  6. ^ National Aeronautics and Space Administration (1976), U.S. Standard Atmosphere, 1976 (PDF), p. 3
  7. ^ Allen, C. W. (1976), Astrophysical Quantities (Third ed.), Athlone Press, p. 119, ISBN 0-485-11150-0
  8. ^ Two recent reliable sources cited here have total atmospheric compositions, including trace molecules, that exceed 100%. They are Allen's Astrophysical Quantities[2] (2000, 100.001241343%) and CRC Handbook of Chemistry and Physics[3] (2016–2017, 100.004667%), which cites Allen's Astrophysical Quantities. Both are used as references in this article. Both exceed 100% because their CO2 values were increased to 345 ppmv, without changing their other constituents to compensate. This is made worse by the April 2019 CO2 value, which is 413.32 ppmv.[4] Although minor, the January 2019 value for CH4 is 1866.1 ppbv (parts per billion).[5] Two older reliable sources have dry atmospheric compositions, including trace molecules, that total less than 100%: U.S. Standard Atmosphere, 1976[6] (99.9997147%); and Astrophysical Quantities[7] (1976, 99.9999357%).
  9. ^ Lide, David R. Handbook of Chemistry and Physics. Boca Raton, FL: CRC, 1996: 14–17
  10. ^ Vázquez, M.; Hanslmeier, A. (2006). "Historical Introduction". Ultraviolet Radiation in the Solar System. Astrophysics and Space Science Library. Vol. 331. Springer Science & Business Media. p. 17. Bibcode:2005ASSL..331.....V. doi:10.1007/1-4020-3730-9_1. ISBN 978-1-4020-3730-6.