Atmosphere of Earth

The atmosphere of Earth is composed of a layer of <a href="/facts/Gas/hVVAoodV">gas</a> mixture that surrounds the <a href="/facts/Earth/HLLmDfj0">Earth</a>'s <a href="/facts/Planetary_surface/c3QVcQpV">planetary surface</a> (both <a href="/facts/Land/sYfevlh5">lands</a> and <a href="/facts/Ocean/8W8lYgjD">oceans</a>), known collectively as air, with variable quantities of suspended <a href="/facts/Aerosol/X1jXFLp2">aerosols</a> and <a href="/facts/Particulate/RleGr5E6">particulates</a> (which create <a href="/facts/Weather/f0qzFRVV">weather</a> features such as <a href="/facts/Cloud/KDgo0Wqu">clouds</a> and <a href="/facts/Haze/2Dfj4s2D">hazes</a>), all retained by <a href="/facts/Gravity_of_Earth/IXe9Bh8k">Earth's gravity</a>. The atmosphere serves as a protective buffer between the Earth's surface and <a href="/facts/Outer_space/R3LRKyFs">outer space</a>, shields the surface from most <a href="/facts/Meteoroid/5PexF2mR">meteoroids</a> and ultraviolet <a href="/facts/Solar_irradiance/SI26I7aD">solar radiation</a>, keeps it warm and reduces <a href="/facts/Diurnal_temperature_variation/nqz0KRKV">diurnal temperature variation</a> (temperature extremes between <a href="/facts/Daytime/nR7raDjV">day</a> and <a href="/facts/Night/aeJtffky">night</a>) through heat retention (<a href="/facts/Greenhouse_effect/LGdNYYj3">greenhouse effect</a>), redistributes heat and moisture among different regions via <a href="/facts/Air_current/no1jCKaF">air currents</a>, and provides the <a href="/facts/Atmospheric_chemistry/EbmISm33">chemical</a> and <a href="/facts/Climate/f57XrNFU">climate</a> conditions allowing <a href="/facts/Life/DNw7NUId">life</a> to exist and <a href="/facts/Evolution/qE5amP6a">evolve</a> on Earth.
By <a href="/facts/Mole_fraction/nW4EepmJ">mole fraction</a> (i.e., by quantity of <a href="/facts/Molecule/N9ljSfFq">molecules</a>), dry air contains 78.08% <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, 20.95% <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, 0.93% <a href="/facts/Argon/QX6NRH6d">argon</a>, 0.04% <a href="/facts/Carbon_dioxide_in_Earth%2527s_atmosphere/h6A4HSzy">carbon dioxide</a>, and small amounts of other <a href="/facts/Trace_gas/TC9E92BT">trace gases</a> (see Composition below for more detail). Air also contains a variable amount of <a href="/facts/Water_vapor/DX5IUFG0">water vapor</a>, on average around 1% at sea level, and 0.4% over the entire atmosphere. 
Earth's early atmosphere consisted of <a href="/facts/Accretion_(astrophysics)/atcWRsDP">accreted</a> gases from the <a href="/facts/Solar_nebula/cgElXHpM">solar nebula</a>, but the atmosphere changed significantly over time, affected by many factors such as <a href="/facts/Volcanism/0s6p1eFJ">volcanism</a>, <a href="/facts/Impact_event/fbWu9Q4p">impact events</a>, <a href="/facts/Weathering/uSYGlv0H">weathering</a> and the <a href="/facts/Evolution_of_life/TuWap5IK">evolution of life</a> (particularly the <a href="/facts/Photoautotroph/I1KGoVhw">photoautotrophs</a>). Recently, <a href="/facts/Human/rlcTENsr">human</a> activity has also <a href="/facts/Human_impact_on_the_environment/vIAWqfPB">contributed to atmospheric changes</a>, such as <a href="/facts/Anthropogenic_climate_change/rEN4BDE7">climate change</a> (mainly through <a href="/facts/Deforestation/L1TNhN9p">deforestation</a> and <a href="/facts/Fossil_fuel/BPgxAqB7">fossil fuel</a>-related <a href="/facts/Global_warming/rEN4BDE7">global warming</a>), <a href="/facts/Ozone_depletion/ssGWpcx3">ozone depletion</a> and <a href="/facts/Acid_deposition/f769GyNz">acid deposition</a>.
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 with increasing altitude, with no definite boundary between the atmosphere and <a href="/facts/Outer_space/R3LRKyFs">outer space</a>. The <a href="/facts/K%25C3%25A1rm%25C3%25A1n_line/CfvQ3fbp">Kármán line</a>, 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 <a href="/facts/Atmospheric_entry/p7TMk9sa">atmospheric reentry</a> 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, namely the <a href="/facts/Troposphere/JPDQq8cL">troposphere</a>, <a href="/facts/Stratosphere/taBra67V">stratosphere</a>, <a href="/facts/Mesosphere/JBPKmMuk">mesosphere</a>, <a href="/facts/Thermosphere/uhG50e2V">thermosphere</a> (formally the <a href="/facts/Ionosphere/mT9tTBE5">ionosphere</a>) and <a href="/facts/Exosphere/7vTtk7qC">exosphere</a>. Air composition, temperature and <a href="/facts/Atmospheric_pressure/wJLMSaVG">atmospheric pressure</a> vary with <a href="/facts/Altitude/B5eNVurK">altitude</a>. Air suitable for use in <a href="/facts/Photosynthesis/TMV7w693">photosynthesis</a> by <a href="/facts/Terrestrial_plant/lr1KGrQv">terrestrial plants</a> and <a href="/facts/Respiration_(physiology)/KKWAJIbd">respiration</a> of <a href="/facts/Terrestrial_animal/AhP2mont">terrestrial animals</a> is found within the troposphere.
The study of Earth's atmosphere and its processes is called <a href="/facts/Atmospheric_science/HKjTA3F4">atmospheric science</a> (aerology), and includes multiple subfields, such as <a href="/facts/Climatology/bYS7FktY">climatology</a> and <a href="/facts/Atmospheric_physics/r2eat5II">atmospheric physics</a>. Early pioneers in the field include <a href="/facts/L%25C3%25A9on_Teisserenc_de_Bort/wEDTEAKt">Léon Teisserenc de Bort</a> and <a href="/facts/Richard_Assmann/thpkDjvS">Richard Assmann</a>. The study of historic atmosphere is called <a href="/facts/Paleoclimatology/p3x22QaC">paleoclimatology</a>.

Atmosphere of Earth open-in-new

Atmosphere of Earth