The earth's atmosphere It is the gaseous layer that surrounds the planet from the earth's surface to a diffuse limit at approximately 10,000 km of altitude. This layer is kept around the planet due to Earth's gravity and is made up of a mixture of gases that we call air..
The most abundant component of the Earth's atmosphere is nitrogen (78%), followed by oxygen (21%) and argon (0.9%), as well as others in minute quantities, such as water vapor and carbon dioxide.
This gaseous mass is arranged in 5 fundamental layers around the planet and performs important functions, such as protecting the planet from the impact of small meteorites, filtering ultraviolet radiation, retaining heat and allowing the existence of liquid water..
Similarly, the atmosphere forms the climates of the Earth and allows the flight of various species, including the flight of airplanes. But the atmosphere was not always as it is today, since it originated with the formation of the planet and has evolved since then..
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Earth's atmosphere is made up of a combination of gases called air. The composition of air varies in the concentration gradient that goes from the Earth's surface to the limit with outer space..
When we talk about the composition of the atmosphere, we refer to the composition of the air in the troposphere, which is in contact with the planet's surface.In this layer there is the highest concentration of air, in whose mixture of gases is dominant nitrogen (Ntwo) and oxygen (Otwo).
Nitrogen accounts for 78% of the total, while oxygen occupies 21%, subtracting about 1% from various other gases. Among these, in the first place argon, which almost completes the missing 1%, leaving the other gases in extremely small quantities.
Among these other gases, carbon dioxide (CO₂), which, although it only reaches approximately 0.041%, is increasing due to human activity. Water vapor has a variable concentration, reaching up to 0.25%. These gases have oxidizing properties, which is why the earth's atmosphere has this quality.
The Earth's atmosphere has 5 layers:
The troposphere extends from ground level to about 12 to 20 km in altitude and its name derives from the prefix tropes = change, due to its changing character. It is thinnest at the poles and widest at the equator..
Three quarters of the mass of gases in the atmosphere is concentrated in the troposphere, due to the attraction exerted by the Earth's gravity. In this layer, life on Earth is possible and meteorological phenomena and commercial aircraft flights occur..
Atmospheric biogeochemical cycles also occur in the troposphere, such as the oxygen, water, and CO cycle.₂ and nitrogen. In this layer, the temperature decreases with altitude, and the limit between it and the next layer is called a tropopause..
It is located between 12 and 20 km above the earth's surface up to approximately 50 km and is separated into two layers by the density of the air. The lower one is where the heavier cold air collects, and the upper one where the lighter warm air is. Hence its name derived from the prefix strata= layers.
The boundary between this layer and the next is called the stratopause. In it is in turn a fundamental layer for life on Earth, such as the ozone layer.
As this layer absorbs heat, the stratosphere increases in temperature with altitude, unlike what happens in the troposphere..
It is a layer composed of ozone (O3), which is formed due to the biochemical dissociation of oxygen (Otwo) by ultraviolet solar radiation. Thus, when this radiation hits the oxygen molecule, it breaks into two oxygen atoms..
Then, taking into account that atomic oxygen (O) is very reactive, it binds with oxygen molecules (Otwo) and form ozone (O3).
Its name comes from meso = medium, because it is located between the stratosphere and the thermosphere, approximately between 50 and 80 km in altitude. It is the layer where the meteors burn creating the shooting stars.
In this area there is still enough gas to produce friction and generate heat, which is no longer the case in the upper layers. The boundary between this layer and the next is called the mesopause..
The name of this layer comes from thermos = heat, since the temperature is 4,500 degrees Fahrenheit (around 2,482 ºC). However, as there are not enough gas molecules, this heat is not transmitted, and neither is sound..
This layer extends between 80 and 700 km of altitude, and there are the International Space Station and many satellites of low orbit. The boundary between the thermosphere and the next layer of the thermopause flame atmosphere.
It bears the name derived from the prefix exo = outside, since it is the outermost layer of the earth's atmosphere; behind it lies outer space. It is located between 700 and 10,000 km of altitude, being the most extensive layer of the atmosphere.
Lighter gases such as hydrogen and helium predominate there, but in very low density. Therefore, its molecules are widely separated from each other, being a very cold area without oxygen. In the exosphere is where are the meteorological satellites and those of high orbit.
The atmosphere has a series of functions that make possible the conditions for the existence of life as we know it.
The atmosphere contains the essential gases for life as it exists today, which are mainly oxygen and CO.₂.
Thanks to the existence of a layer like the mesosphere, the earth's surface is protected from the impact of a large number of small meteors. In this layer the air, although it is scarce, is enough for there to be friction and the meteors burn and break down for the most part.
The existence of the ozone layer in the stratosphere filters most of the ultraviolet radiation, preventing it from reaching the earth's surface. This is of great importance for various terrestrial processes, including life, since this type of radiation causes mutations and causes cancer..
Several of the atmospheric gases allow the entry of radiation that warms the Earth and provides energy for photosynthesis and other processes. While the heat generated (long-wave radiation), is partially retained and reflected back to the Earth.
This allows maintaining a temperature range favorable to life on the planet, with an average temperature of 15ºC. In the absence of the atmosphere, the average temperature of the planet would be -18 ºC.
The variation during the day of temperature is determined by the diurnal heating of the air layer directly above the ground by solar radiation and its nocturnal cooling. Although this variation is also influenced by other parameters such as altitude, the cloud layer present, humidity and atmospheric instability..
It is the force of attraction that gravity has on the air mass on Earth (weight of the air), which varies according to temperature, since the warmer the lighter the air. The combination of these factors contributes to the formation of the climate, by producing the winds and these in turn, the marine currents..
But additionally, the atmospheric pressure exerted by the air on the earth's surface is adequate for there to be liquid water on Earth..
The atmosphere concentrates the largest proportion of the air in its lower layer, the troposphere, which determines a certain density. This density of air is what allows the flight of birds, insects, flying mammals and the mechanized flight of humans..
The winds are caused by temperature differences that are generated in the atmosphere at the level of the troposphere, causing atmospheric pressure differences. This occurs thanks to the absorption of heat by some gases that compose it, such as oxygen, CO₂ and the water vapor.
When heated, these gases decrease their density, that is, their molecules move away from each other, becoming lighter and begin to rise. This lowers the atmospheric pressure in that area, creating a vacuum into which nearby air masses flow, forming winds..
These in turn cause surface currents that help distribute heat on Earth. On the other hand, the winds distribute the water vapor formed when the water evaporates, which cools and condenses when ascending, causing rains..
The formation and evolution of the Earth's atmosphere is part of the formation and evolution of the solar system from the big Bang.
It is argued that our system was formed due to a random concentration of matter moving and rotating in space. It was coming together in what would later become the center of the solar system by the force of gravity..
Subsequently, the matter furthest from the center cooled differentially and thus the coldest planets are those farthest from the sun, which occupies the central position. Later, the planets were formed by aggregation of particles at different distances from the center and, depending on their position, they present different characteristics..
The so-called ProtoTierra was formed by the aggregation of small rocky celestial bodies (called planetesimals), about 4.5 billion years ago. In this case, these planetesimals were made up of oxides, metals, and silicates..
Later, due to the lower mass of the Earth, our planet failed to retain most of the hydrogen and other light gases. The loss of gases was cooling the planet, consolidating a nucleus where the heaviest elements, iron and nickel, were concentrated..
While the lighter ones such as the silicates formed the mantle and crust, the gases were concentrated as the final layer. In this area, those gases that were so light that they escaped the force of gravity of the planet in formation were located.
It is considered that the atmosphere went through three basic stages in this evolution, which include the primordial atmosphere, the secondary atmosphere and the biotic atmosphere..
It is estimated that the planet formed its first atmosphere 4.45 billion years ago, after the impact that the piece that formed the Moon detached. From there, the planetary differentiation in nucleus, mantle, crust and atmosphere occurred..
The atmosphere was still very unstable due to the loss of light gases into space during the Earth's cooling process. These light gases such as neon, argon and others were lost in large proportions because they were very light..
In this phase, the dominant gases were those from the solar nebula, of a reducing nature such as hydrogen (Htwo). Like others from volcanic activity such as carbon dioxide (CO₂), nitrogen (Ntwo) and water vapor (H₂O), so this atmosphere was strongly reducing.
In a period of 100 to 500 million years the atmosphere evolved into a weak reducing condition, about 4,000 million years ago. This was due, among other things, to the so-called great late bombardment, in which asteroids rich in carbon and water hit the planet..
Meteorites and comets are proven to contain high content of water, CO₂, methane (CH4) and ammonia (NH3). On the other hand, volcanic activity expelled large amounts of CO into the atmosphere.₂ and Ntwo.
In this period the incidence of life on the atmosphere appears, with the activity of methanogenic protobacteria about 4,000 years ago. These organisms consumed COtwo and produced CH4, so the first was reduced and the second of these gases increased.
It is estimated that no more than 3.1 billion years ago the oxidizing biotic atmosphere began to form. This is due to the appearance of the first photosynthesizing organisms, that is, capable of producing chemical energy (food) from solar energy..
Originally they were cyanobacteria, which when carrying out their photosynthesis process produced oxygen as waste. This was incorporating large amounts of oxygen into the atmosphere, causing a qualitative change about 2.4 billion years ago known as the Great Oxidative Event..
In turn, the increase in oxygen caused the decrease in methane by photochemical recombination. Similarly, ultraviolet radiation caused the dissociation of Otwo, forming atomic oxygen (O), which combined with molecular oxygen (Otwo) forming ozone (O3).
Thus, an ozone layer was generated in the extratosphere, in addition to the Ntwo expelled the volcanoes that became the dominant gas, because it is not very reactive and does not form minerals easily, therefore it accumulated in the atmosphere.
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