Atmosphere of Earth

The Earth's atmosphere (from Greek ἀτμός Atmos, vapor ',' Dunst ',' touch ' and σφαῖρα sphaira, ball '), the Earth's atmosphere is the gaseous envelope above the earth's surface. It represents one of the Erdsphären and their gas mixture is characterized by a high content of nitrogen and oxygen and thus oxidizing conditions.

For optical phenomena in the atmosphere, see the article Atmospheric Optics.

Composition

The near-surface layers to about 90 km altitude have a fairly uniform composition, so this section is also referred to as Homo sphere. What we call air, consists in ignoring the changing water vapor content (ie, steam-free air ) consists essentially of ( by volume ) 78.084 % nitrogen ( N2) 20.946 % Oxygen ( O2) and 0.934 % argon ( Ar), to aerosols and trace gases, including carbon dioxide ( CO2) with currently 0.04 %, for water vapor, the most important causes of the greenhouse effect, methane ( CH4 ), ozone (O3 ), chlorofluorocarbons substances, sulfur dioxide ( SO2) and nitrogen compounds.

For the emergence of the weather, the water vapor content is next to the power supply by solar radiation mainly responsible. This comes in varying concentration of 0% by volume to about 4% by volume in the air before, see humidity.

The upper layers consist of very thin gas into which the high-energy radiation from the sun penetrates and molecules dissociated and ionized. Furthermore, it also leads to a separation of the components according to their different molar mass, which is why the altitude increases the proportions of lighter particles such as hydrogen and helium increase. These two elements with very low escape rate to space, both thermally and by photoionization and charge transfer.

Development

The development of earth's atmosphere is a part of the chemical evolution of the earth and also an important element of climate history. It is now divided into four main stages of development.

At the beginning of the creation of the earth in front of about 4.56 billion years. They possessed very early on a presumably of hydrogen (H2) and helium ( He) existing gas envelope, but again lost.

The slow cooling of the Earth and volcanism occurring, there was an extensive outgassing from the Earth's interior. Created an atmosphere consisted of about 80 % water vapor (H2O ), to 10% of carbon dioxide (CO2) and 5 to 7% hydrogen sulfide. It is precisely those products of volcanism, as we can still watch them today. The high percentage of water vapor due to the fact that the atmosphere at that time was still too hot to form precipitates can. So there was no water on the earth. The actual origin of the water is controversial.

After the temperature of the atmosphere dropped below the boiling point of water, there was an extremely long duration rain, after the end of which the oceans were formed and, accordingly, the other atmospheric gases were enriched relative to water vapor.

The high UV - radiation -induced photochemical decomposition of water, methane and ammonia molecules, resulting in carbon dioxide and nitrogen relative accumu. The light gases such as hydrogen or helium faded away into space. Carbon dioxide was dissolved in large quantities in the oceans and consumed by C- autotrophic microorganisms in part. Remained unchanged, the inert nitrogen. This was relatively enriched in the time, and formed approximately 3.4 billion years ago the main component of the atmosphere.

The oxygen O2 plays the leading role in the further development of today's atmosphere. Oxygen photosynthetically active cyanobacteria led as C- autotrophs to a further decrease in the concentration of carbon dioxide, but were mainly ( possibly as early as 3.5 billion years ago starting ) oxygen. However, the oxygen concentration of the atmosphere was low at first, since the oxygen formed in the ocean in the oxidation of iron ( II) ions and hydrogen sulfide was consumed. Only about two billion years ago, oxygen began to escape into the atmosphere, namely, as the reacting with oxygen materials were scarce. A billion years, the oxygen concentration of the atmosphere exceeded three percent, which over the next 400 million years could gradually form a first Ozone layer. Before 500-600 million years ago, the oxygen content increased, due to the first mass occurrence of land plants, rapidly, reaching 350 million years ago the first time the current level. After several strong fluctuations during the Mesozoic era, the atmospheric oxygen eventually settled at the present value of 21%.

Structure and gradients

The Earth's atmosphere has a mass of about 5.15 · 1018 kg and consists in relation to their vertical temperature profile, in particular its gradient, composed of several layers:

• Troposphere from sea level to between 7 km ( polar regions) and 17 km ( tropics), bounded by the tropopause
• Stratosphere up to the stratopause at 50 km altitude
• Mesosphere up to the mesopause at 80-85 km altitude
• Thermosphere over

The troposphere is also referred to as the lower atmosphere, stratosphere and mesosphere together as a middle atmosphere and thermosphere as the upper atmosphere. In addition, is particularly evident in the troposphere - the weather sphere - a dynamic within the temperature stratification, which is why there also the respective stratification stability plays a major role.

This outline is only a rough classification again and it is also possible not to divide the atmosphere according to the temperature profile, but according to other factors, such as

• The radio- physical state of the atmosphere: Neutrosphere (gases predominantly in the neutral, ie non- ionized state )
• Ionosphere ( ionized gases, placed in the thermosphere )
• Plasmasphere (> 1000 km, complete ionization of all particles )
• Magnetosphere

• Ozonosphere / ozone layer ( 16-50 km )
• Chemosphere ( 20-600 km )

• Prandtl layer ( about 0-50 m)
• Ekman layer ( about 50-1000 m)
• Prandtl layer Ekman layer = planetary boundary layer ( Peplosphäre )
• Free atmosphere ( > 1 km)

Edge of space

The transition between exosphere and space is continuous and can therefore draw no sharp upper limit of the earth's atmosphere.

By the Fédération Aéronautique Internationale therefore the homo pause or a height of about 100 km ( the Kármán line) is considered as a boundary. This definition is widely accepted internationally, even if they have no absolute validity. For example, by the NASA Mesopause (about 80 km) is defined as a boundary.

Research

The lower atmosphere, the troposphere, in particular, is the research field of meteorology, whereas the middle and upper atmosphere ( stratosphere, mesosphere ) belong to the realm of Aerology. Measurements are made near the ground with the full range of meteorological instruments. In height, especially in terms of height profiles that make radiosondes, meteorological rocket, lidar, radar and weather or environmental satellites, the most important measurement method dar. In the future are expected to level platforms, such as the High Altitude and Long Range Research Aircraft play a greater role.