Besides argon, already mentioned, other noble gases, neon, helium, krypton, and xenon are also present. : 8 The remaining gases are often referred to as trace gases, among which are other greenhouse gases, principally carbon dioxide, methane, nitrous oxide, and ozone. The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by mole fraction in the coldest portions of the atmosphere to as much as 5% by mole fraction in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor). Water vapor accounts for roughly 0.25% of the atmosphere by mass. The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Numbers are mainly from 2000, with CO 2 and methane from 2019, and do not represent any single source. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations ). Main article: Atmospheric chemistry Composition of Earth's atmosphere by molecular count, excluding water vapor. The study of historic atmosphere is called paleoclimatology. Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The study of Earth's atmosphere and its processes is called atmospheric science (aerology), and includes multiple subfields, such as climatology and atmospheric physics. Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). 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. The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The atmosphere has a mass of about 5.15 ×10 18 kg, three quarters of which is within about 11 km (6.8 mi 36,000 ft) of the surface. Recently, human activity has also contributed to atmospheric changes, such as global warming, ozone depletion and acid deposition. The atmosphere changed significantly over time, affected by many factors such as volcanism, life, and weathering. Įarth's early atmosphere consisted of gases in the solar nebula, primarily hydrogen. Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere. Air composition, temperature, and atmospheric pressure vary with altitude. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention ( greenhouse effect), allowing life and liquid water to exist on the Earth's surface, and reduces temperature extremes between day and night (the diurnal temperature variation).Īs 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. 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. Not to be confused with Air quality.īlue 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).
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