The atmospheric air composition or atmosphere is defined by the proportion of the different gases contained in it, which has been in constant variation throughout the history of the Earth. The atmosphere of the forming planet contained mainly Htwo and other gases like COtwo and HtwoO. About 4.4 billion years ago, the composition of atmospheric air was enriched mainly with COtwo.
With the emergence of life on Earth, an accumulation of methane (CH4) in the atmosphere, since the first organisms were methanogens. Later, photosynthetic organisms appeared, which enriched the atmospheric air with Otwo.
The composition of atmospheric air today can be divided into two large layers, differentiated in their chemical composition; the homosphere and the heterosphere.
The homosphere is located from 80 to 100 km above sea level and is made up mainly of nitrogen (78%), oxygen (21%), argon (less than 1%), carbon dioxide, ozone, helium, hydrogen and methane , among other elements present in very small proportions.
The heterosphere is made up of low molecular weight gases and is located above 100 km in altitude. The first layer presents Ntwo molecular, the second atomic O, the third helium and the last is made up of atomic hydrogen (H).
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Studies of atmospheric air began thousands of years ago. The moment primitive civilizations discovered fire, they began to have a notion of the existence of air..
During this period, they began to analyze what air is and its function. For example, Anaxímades of Miletus (588 BC-524 BC) considered that air was essential for life, since living beings fed on this element.
For his part, Empedocles of Acragas (495 BC-435 BC) considered that there were four fundamental elements for life: water, earth, fire and air..
Aristotle (384 BC-322 BC) also considered that air was one of the essential elements for living beings.
In 1773 the Swedish chemist Carl Scheele discovered that air was composed of nitrogen and oxygen (igneous air). Later, in 1774 the British Joseph Priestley determined that the air was composed of a mixture of elements and that one of these was essential for life.
In 1776 the French Antoine Lavoisier called oxygen to the element that he isolated from the thermal decomposition of mercury oxide.
In 1804, the naturalist Alexander von Humboldt and the French chemist Gay-Lussac analyzed the air coming from different parts of the planet. The researchers determined that atmospheric air has a constant composition.
It was not until the late 19th and early 20th centuries that the other gases that are part of the atmospheric air were discovered. Among these we have argon in 1894, then helium in 1895, and other gases (neon, argon and xenon) in 1898.
Atmospheric air is also known as the atmosphere and is a mixture of gases that covers planet Earth..
Little is known about the origin of Earth's atmosphere. It is considered that after its separation from the sun, the planet was surrounded by an envelope of very hot gases.
These gases were possibly reducing and coming from the Sun, composed mainly of Htwo. Other gases were probably COtwo and HtwoOr emitted by intense volcanic activity.
It is suggested that part of the gases present cooled, condensed and gave rise to the oceans. The other gases remained forming the atmosphere and others were stored in rocks.
The atmosphere is made up of different concentric strata separated by transition zones. The upper limit of this layer is not clearly defined and some authors place it above 10,000 km above sea level..
The attraction of the force of gravity and the way in which gases are compressed influences their distribution on the earth's surface. Thus, the largest proportion of its total mass (approximately 99%) is located in the first 40 km above sea level..
Different levels or layers of atmospheric air have different chemical composition and temperature variations. According to its vertical arrangement, from the closest to the furthest from the earth's surface, the following layers are known: the troposphere, stratosphere, mesosphere, thermosphere and exosphere.
In relation to the chemical composition of atmospheric air, two layers are defined: the homosphere and the heterosphere..
It is located in the first 80-100 km above sea level, and its composition of gases in the air is homogeneous. In this are located the troposphere, stratosphere and mesosphere.
It is present above 100 km and is characterized by the fact that the composition of the gases present in the air is variable. Matches the thermosphere. The composition of gases varies at different heights.
After the formation of the Earth, approximately 4,500 million years ago, gases began to accumulate that formed the atmospheric air. The gases came mainly from the Earth's mantle, as well as from the impact with planetesimals (aggregates of matter that originated the planets).
The great volcanic activity on the planet began to release various gases into the atmosphere, such as Ntwo, COtwo and HtwoO. Carbon dioxide began to accumulate, as carbonation (the process of fixing COtwo atmospheric in the form of carbonates) was scarce.
Factors affecting CO fixationtwo at this time there were very low intensity rains and a very small continental area.
The first living beings that appeared on the planet used COtwo and Htwo to perform breathing. These early organisms were anaerobic and methanogenic (they produced large amounts of methane).
Methane accumulated in the atmospheric air, because its decomposition was very slow. It decomposes by photolysis and in an almost oxygen-free atmosphere, this process can take up to 10,000 years.
According to some geological records, about 3.5 billion years ago there was a decrease in COtwo in the atmosphere, which has been associated with air rich in CH4 intensified the rains, favoring carbonation.
It is considered that about 2.4 billion years ago the amount of Otwo on the planet it reached important levels in the atmospheric air. The accumulation of this element is associated with the appearance of photosynthetic organisms.
Photosynthesis is a process that makes it possible to synthesize organic molecules from other inorganic ones in the presence of light. During its occurrence, O is releasedtwo as a secondary product.
The high photosynthetic rate produced by cyanobacteria (first photosynthetic organisms) was changing the composition of the atmospheric air. Large amounts of Otwo that were released, returned to the atmosphere increasingly oxidizing.
These high levels of Otwo influenced the accumulation of CH4, since it accelerated the photolysis process of this compound. As methane in the atmosphere decreased dramatically, the planet's temperature decreased and glaciation occurred..
Another important effect of the accumulation of Otwo on the planet, it was the formation of the ozone layer. The Otwo Atmospheric dissociates under the effect of light and forms two atomic oxygen particles.
Atomic oxygen recombines with Otwo molecular and forms O3 (ozone). The ozone layer forms a protective barrier against ultraviolet radiation, allowing the development of life on the earth's surface.
Nitrogen is an essential component of living organisms, as it is necessary for the formation of proteins and nucleic acids. However, the Ntwo atmospheric cannot be used directly by most organisms.
Nitrogen fixation can be biotic or abiotic. It consists of the combination of Ntwo with Otwo or Htwo to form ammonia, nitrates or nitrites.
The contents of Ntwo in atmospheric air they have remained more or less constant in the earth's atmosphere. During the accumulation of COtwo, fixation of Ntwo it was basically abiotic, due to the formation of nitrogen oxide, formed by the photochemical dissociation of H moleculestwoO and COtwo which were the source of the Otwo.
When the decrease in CO levels occurredtwo In the atmosphere, the rates of nitrogen oxide formation decreased dramatically. It is considered that during this time the first biotic routes of N fixation originated.two.
Atmospheric air is made up of a mixture of gases and other quite complex elements. Its composition is mainly affected by altitude.
The chemical composition of dry atmospheric air at sea level has been found to be fairly constant. Nitrogen and oxygen make up about 99% of the mass and volume of the homosphere..
Atmospheric nitrogen (Ntwo) is in a proportion of 78%, while oxygen constitutes 21% of the air. The next most abundant element in atmospheric air is argon (Ar), which occupies less than 1% of the total volume.
There are other elements that are of great importance, even when they are in small proportions. Carbon dioxide (COtwo) is present in a proportion of 0.035% and the water vapor can vary between 1 and 4%, depending on the region.
Ozone (O3) is found in a proportion of 0.003%, but it forms an essential barrier for the protection of living beings. Also in this same proportion we find various noble gases such as neon (Ne), krypton (Kr) and xenon (Xe).
In addition, there is the presence of hydrogen (Htwo), nitrous oxides and methane (CH4) in very small quantities.
Another element that is part of the composition of atmospheric air is the liquid water contained in clouds. Likewise, we find solid elements such as spores, pollen, ashes, salts, microorganisms and small ice crystals..
At this level, altitude determines the predominant type of gas in atmospheric air. All gases are light (low molecular weight) and are organized in four different layers.
It is appreciated that as the height increases, the more abundant gases have a lower atomic mass.
Between 100 and 200 km of altitude, there is a greater abundance of molecular nitrogen (Ntwo). The weight of this molecule is 28.013 g / mol.
The second layer of the heterosphere is made up of atomic O and is located between 200 and 1000 km above sea level. Atomic O has a mass of 15,999, being less heavy than Ntwo.
Later, we find a helium layer between 1000 and 3500 km high. Helium has an atomic mass of 4.00226.
The last layer of the heterosphere is made up of atomic hydrogen (H). This gas is the lightest in the periodic table, with an atomic mass of 1.007.
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