At what elevation does the Earths atmospheric pressure fall to 50% of its sea-level value?
2007 Schools Wikipedia Selection. Related subjects: Climate and the Weather
Layers of Temper (NOAA)
Earth'due south temper is a layer of gases surrounding the planet Earth and retained by the Earth'due south gravity. It contains roughly 78% nitrogen, 21% oxygen, 0.97% argon, 0.04% carbon dioxide, and trace amounts of other gases, in add-on to water vapor. This mixture of gases is ordinarily known equally air. The temper protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between twenty-four hours and night.
The atmosphere has no abrupt cut-off. Information technology slowly becomes thinner and fades abroad into space. There is no definite boundary between the atmosphere and outer space. Three-quarters of the temper's mass is inside 11 km of the planetary surface. In the U.s., persons who travel in a higher place an altitude of 50.0 miles (80.5 km) are designated as astronauts. An altitude of 120 km (75 mi or 400,000 ft) marks the boundary where atmospheric furnishings become noticeable during re-entry. The Karman line, at 100 km (62 mi), is also frequently used as the boundary betwixt atmosphere and space.
Temperature and the atmospheric layers
The temperature of the Earth's atmosphere varies with altitude; the mathematical relationship between temperature and distance varies between the different atmospheric layers:
- troposphere: From the Greek discussion "tropos" pregnant to turn or mix. The troposphere is the lowest layer of the atmosphere starting at the surface going upwardly to between 7 km (four.4 mi) at the poles and 17 km (10.vi mi) at the equator with some variation due to atmospheric condition factors. The troposphere has a dandy deal of vertical mixing due to solar heating at the surface. This heating warms air masses, which then rise to release latent estrus equally sensible heat that further uplifts the air mass. This procedure continues until all h2o vapor is removed. In the troposphere, on average, temperature decreases with height due to expansive cooling.
- stratosphere: from that 7–17 km range to nearly l km, temperature increasing with height.
- mesosphere: from about 50 km to the range of lxxx km to 85 km, temperature decreasing with height.
- thermosphere: from 80–85 km to 640+ km, temperature increasing with height.
- exosphere: from 500-1000 km upwards to 10,000 km, free-moving particles that may migrate into and out of the magnetosphere or the solar air current.
The boundaries between these regions are named the tropopause, stratopause, mesopause, thermopause and exobase.
The average temperature of the atmosphere at the surface of world is fourteen °C.
Force per unit area
Atmospheric pressure is a direct result of the weight of the air. This means that air pressure varies with location and time, because the corporeality (and weight) of air in a higher place the earth varies with location and time. Atmospheric pressure drops by l% at an distance of about 5 km (equivalently, about 50% of the full atmospheric mass is inside the lowest 5 km). The average atmospheric pressure, at ocean level, is about 101.three kilopascals (nigh fourteen.seven pounds per square inch).
Thickness of the atmosphere
Even at heights of thousand km and above, the atmosphere is however present (every bit can be seen for example by the effects of atmospheric drag on satellites).
All the same:
- 57.8% of the temper by mass is below the summit of Mount Everest.
- 72% of the temper by mass is below the common cruising altitude of commercial airliners (about 10000 1000 or 33000 ft).
- 99.99999% of the atmosphere by mass is below the highest 10-fifteen plane flying on August 22, 1963, which reached an altitude of 354,300 ft or 108 km.
Therefore, most of the atmosphere (99.9999%) past mass is beneath 100 km, although in the rarefied region above this there are auroras and other atmospheric effects.
Limerick
Limerick of Earth'south temper. The lower pie represents the least common gases that compose 0.038% of the temper. Values normalized for analogy.
| ppmv: parts per 1000000 by volume | |
| Gas | Volume |
|---|---|
| Nitrogen (N2) | 780,840 ppmv (78.084%) |
| Oxygen (O2) | 209,460 ppmv (20.946%) |
| Argon (Ar) | nine,340 ppmv (0.9340%) |
| Carbon dioxide (CO2) | 381 ppmv |
| Neon (Ne) | 18.18 ppmv |
| Helium (He) | 5.24 ppmv |
| Methane (CH4) | one.745 ppmv |
| Krypton (Kr) | 1.14 ppmv |
| Hydrogen (H2) | 0.55 ppmv |
| Not included in above dry out atmosphere: | |
| Water vapor (H2O) | typically 1% to 4%(highly variable) |
Mean Atmospheric Water Vapor.
Source for figures above: NASA. carbon dioxide (updated 2006). Methane updated (to 1998) past IPCC TAR table six.1 . The NASA total was 17 ppmv over 100%, and COii was increased here past 15 ppmv. To normalize, N2 should be reduced past about 25 ppmv and O2 past about vii ppmv.
Small-scale components of air non listed above include:
| Gas | Volume |
|---|---|
| nitrous oxide | 0.5 ppmv |
| xenon | 0.09 ppmv |
| ozone | 0.0 to 0.07 ppmv |
| nitrogen dioxide | 0.02 ppmv |
| iodine | 0.01 ppmv |
| carbon monoxide | trace |
| ammonia | trace |
- The mean tooth mass of air is 28.97 g/mol.
Heterosphere
Below the turbopause at an altitude of about 100 km, the Earth's atmosphere has a more than-or-less uniform composition (apart from h2o vapor) equally described in a higher place; this constitutes the homosphere. All the same, higher up about 100 km, the Earth's temper begins to accept a composition which varies with altitude. This is essentially considering, in the absence of mixing, the density of a gas falls off exponentially with increasing altitude, but at a rate which depends on the tooth mass. Thus college mass constituents, such as oxygen and nitrogen, fall off more than quickly than lighter constituents such as helium, molecular hydrogen, and diminutive hydrogen. Thus there is a layer, called the heterosphere, in which the globe's atmosphere has varying limerick. As the altitude increases, the temper is dominated successively past helium, molecular hydrogen, and atomic hydrogen. The precise altitude of the heterosphere and the layers it contains varies significantly with temperature.
Density and mass
The density of air at sea level is about 1.two kg/g3. Natural variations of the barometric pressure level occur at any one altitude as a effect of weather. This variation is relatively small for inhabited altitudes but much more pronounced in the outer temper and infinite due to variable solar radiation.
Temperature and force per unit area confronting altitude from the
NRLMSISE-00
standard temper model
The atmospheric density decreases every bit the altitude increases. This variation can be approximately modeled using the barometric formula. More sophisticated models are used by meteorologists and infinite agencies to predict weather and orbital decay of satellites.
The average mass of the atmosphere is about five,000 trillion metric tons. According to the National Eye for Atmospheric Research, "The total mean mass of the temper is 5.1480×10eighteen kg with an annual range due to h2o vapor of 1.2 or one.5×xfifteen kg depending on whether surface pressure or water vapor information are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27×10xvi kg and the dry air mass as five.1352 ±0.0003×ten18 kg."
The above composition percentages are done by volume. Assuming that the gases act like ideal gases, we tin add the percentages p multiplied past their molar masses m, to become a full t = sum (p·m). Whatever element'due south percent past mass is then p·grand/t. When we do this to the above percentages, nosotros become that, by mass, the composition of the atmosphere is 75.523% nitrogen, 23.133% oxygen, i.288% argon, 0.053% carbon dioxide, 0.001267% neon, 0.00029% methyl hydride, 0.00033% krypton, 0.000724% helium, and 0.0000038 % hydrogen.
Evolution of the Globe'due south temper
Diagram of chemical and ship processes related to atmospheric composition.
The history of the Earth's atmosphere prior to one billion years agone is poorly understood, simply the following presents a plausible sequence of events. This remains an active area of enquiry.
The modernistic atmosphere is sometimes referred to as Earth'south "third temper", in order to distinguish the electric current chemical limerick from two notably unlike previous compositions. The original atmosphere was primarily helium and hydrogen. Heat from the still-molten crust, and the dominicus, plus a probably enhanced solar wind, dissipated this atmosphere.
Near 4.4 billion years ago, the surface had cooled enough to course a crust, yet heavily populated with volcanoes which released steam, carbon dioxide, and ammonia. This led to the early on "second atmosphere", which was primarily carbon dioxide and water vapor, with some nitrogen but virtually no oxygen. This second atmosphere had approximately 100 times as much gas as the current atmosphere, just as it cooled much of the carbon dioxide was dissolved in the seas and precipitated out every bit carbonates. The later "second atmosphere" contained nitrogen, carbon dioxide, and very contempo simulations run at the University of Waterloo and University of Colorado in 2005 suggest that it may take had up to 40% hydrogen. It is mostly believed that the greenhouse outcome, acquired by high levels of carbon dioxide and methane, kept the World from freezing. In fact temperatures were probably very high, over lxx degrees C, until some 2.7 billion years agone.
One of the earliest types of bacteria were the cyanobacteria. Fossil bear witness indicates that leaner shaped like these existed approximately 3.3 billion years agone and were the outset oxygen-producing evolving phototropic organisms. They were responsible for the initial conversion of the earth's atmosphere from an anoxic state to an oxic state (that is, from a country without oxygen to a land with oxygen) during the period 2.seven to 2.two billion years ago. Being the first to deport out oxygenic photosynthesis, they were able to catechumen carbon dioxide into oxygen, playing a major role in oxygenating the atmosphere.
Photosynthesizing plants would subsequently evolve and convert more than carbon dioxide into oxygen. Over time, backlog carbon became locked in fossil fuels, sedimentary rocks (notably limestone), and brute shells. As oxygen was released, it reacted with ammonia to release nitrogen; in improver, leaner would besides catechumen ammonia into nitrogen. Simply nigh of the modern 24-hour interval level of nitrogen are due mostly to sunlight-powered photolysis of ammonia released steadily over the aeons from volcanoes.
Equally more plants appeared, the levels of oxygen increased significantly, while carbon dioxide levels dropped. At first the oxygen combined with various elements (such every bit iron), simply eventually oxygen accumulated in the atmosphere, resulting in mass extinctions and further evolution. With the appearance of an ozone layer (ozone is an allotrope of oxygen) lifeforms were better protected from ultraviolet radiations. This oxygen-nitrogen atmosphere is the "third atmosphere".
This modern atmosphere has a limerick which is enforced by oceanic bluish-green algae equally well every bit geological processes. O2 does not remain naturally free in an atmosphere, simply tends to be consumed (by inorganic chemic reactions, as well as by animals, leaner, and fifty-fifty land plants at dark), while CO2 tends to exist produced by respiration and decomposition and oxidation of organic thing. Oxygen would vanish within a few million years due to chemical reactions and COii dissolves easily in water and would be gone in millennia if non replaced. Both are maintained by biological productivity and geological forces seemingly working hand-in-paw to maintain reasonably steady levels over millions of years.
Source: https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/e/Earth%2527s_atmosphere.htm
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