Atmosphere of earth
Atmosphere - a gaseous shell of a celestial body held near it by gravity.
The Earth's atmosphere contains oxygen usedmost living organisms for respiration, and carbon dioxide consumed by plants and cyanobacteria during photosynthesis. The atmosphere is also the planet's protective layer, protecting its inhabitants from solar ultraviolet radiation and meteorites.
All massive bodies—gas giants and most terrestrial planets in the Solar System, except Mercury—have an atmosphere.
- Atmosphere boundaries
The atmosphere is considered to be that area aroundEarth, in which the gaseous medium rotates with the Earth as a whole. It passes into interplanetary space gradually, in the exosphere, starting at an altitude of 500–1000 km from the Earth's surface.
According to the definition proposed by the InternationalAviation Federation, the boundary of the atmosphere and space is drawn along the Karman line, located at an altitude of 100 km, above which aviation flights become completely impossible.
NASA uses the 122 km (400,000 ft) mark as the boundary of the atmosphere, where the shuttles switched from engine-powered maneuvering to aerodynamic maneuvering.
- Composition
The Earth's atmosphere is the result of twoprocesses: evaporation of the substance of cosmic bodies when they fall to the Earth and the release of gases during volcanic eruptions (degassing of the earth's mantle). With the release of the oceans and the emergence of the biosphere, the atmosphere changed due to gas exchange with water, plants, animals and their decomposition products in soils and swamps.
At present, the Earth's atmosphere consists mainly of gases and various impurities (dust, water droplets, ice crystals, sea salts, combustion products).
The history of the formation of the atmosphere
According to the most common theory,The Earth's atmosphere has had three different compositions throughout its history. Initially, it consisted of light gases (hydrogen and helium) captured from interplanetary space. This is the so-calledprimary atmosphere.
At the next stage, active volcanic activity led to the saturation of the atmosphere with gases other than hydrogen (carbon dioxide, ammonia, water vapor). This is how it was formedsecondary atmosphere... The atmosphere was restorative. Further, the formation of the atmosphere was determined by the following factors:
- leakage of light gases (hydrogen and helium) into interplanetary space;
- chemical reactions in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually these factors led to the formationtertiary atmosphere, characterized by a much lower hydrogen content and a much higher nitrogen and carbon dioxide content (formed as a result of chemical reactions from ammonia and hydrocarbons).
Oxygen in the atmosphere
The composition of the atmosphere began to change radically with the appearance of living organisms on Earth, as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide.
Initially, oxygen was spent on the oxidation of reduced compounds - ammonia, hydrocarbons, ferrous form of iron contained in the oceans, etc.
At the end of this stage, the oxygen content inthe atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties was formed. Since this caused serious and abrupt changes in many processes occurring in the atmosphere, lithosphere and biosphere, this event was called the Oxygen Catastrophe.
Why is oxygen disappearing from the atmosphere?
It turned out that during this time from the Earththere is a fairly stable oxygen leak at a rate of about 8.4 ppm per million years. In particular, over the past 800 thousand years, the atmosphere in the atmosphere has become about 0.7% less oxygen.
The diagram on the left shows how differentresults of scientific modeling of atmospheric O2 / N2 ratio and partial pressure. The diagram on the right shows the change in the partial pressure based on the results of measuring air bubbles in ice cores for 800 thousand years.
Reducing the amount of oxygen in the atmospherehappens quite slowly. It probably won't threaten human life for millions of years. But information about the nature of such cycles is very important for science.
You need to know under the influence of what factorschanges are taking place. This information can be used, among other things, when terraforming Mars, when people begin to populate the Red Planet. We will probably have to increase the amount of oxygen in the Martian atmosphere.
Why is oxygen disappearing?
Scientists have not yet come to a consensus as to why the Earth's atmosphere is slowly losing oxygen. There are two hypotheses.
- Increasing the rate of erosion, which removes more rock from the soil, which oxidizes and binds more oxygen.
- Changing of the climate.Temperatures have dropped slightly over the past several million years, despite sharp increases in recent decades. Due to the decrease in temperature, a chain of ecological reactions could be initiated, as a result of which more oxygen began to dissolve and bind in the oceans.
Will the oxygen disappear completely?
Yes, at least this is the conclusion reached by a Japanese scientist from Toho University Kazumi Ozaki and his American colleague Christopher Reinhard from the Georgia Institute of Technology.
Experts have modeled the evolution of the atmosphereour planet, taking into account geological, biological and climatic factors. As a result, they found out that the earth's atmosphere will remain relatively stable for about a billion years, and after that, within a few thousand years, it will turn into practically oxygen-free.
According to scientists, the cause of the disaster will beconsist in the increased activity of the Sun, due to which the content of carbon dioxide in the atmosphere will decrease. When this indicator reaches a critical point, the process of photosynthesis will be disrupted on the planet, and oxygen will cease to enter the atmosphere.
The biosphere will not have time to adapt to such significant environmental changes. The world of primitive anaerobic microbes, which today lurks in the shadows, will again prevail.
Conclusion of the authors of the work
How will the Earth be without oxygen?
This state of affairs already existed on our planet before the oxygen catastrophe.
The exact composition of the primary atmosphere of the Earth onthe present date is unknown, however, as a rule, scientists believe that it was formed as a result of degassing of the mantle and was of a regenerative nature. It was based on carbon dioxide, hydrogen sulfide, ammonia, methane. This is evidenced by:
- unoxidized deposits that have formed clearly on the surface (for example, river pebbles from pyrite not resistant to oxygen);
- lack of known significant sources of oxygen and other oxidants;
- study of potential sources of the primary atmosphere (volcanic gases, the composition of other celestial bodies).
Since the overwhelming majority of organismstime was anaerobic, unable to exist at significant oxygen concentrations, a global change of communities occurred: anaerobic communities were replaced by aerobic ones, previously limited only to “oxygen pockets”. Anaerobic communities, on the contrary, were pushed into “anaerobic pockets” (figuratively speaking, “the biosphere turned inside out”).
In the future, the presence of molecular oxygen inatmosphere led to the formation of an ozone screen, which significantly expanded the boundaries of the biosphere, and to the spread of more energetically favorable (in comparison with anaerobic) oxygen respiration.
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