Oxygen catastrophe. Oxygen catastrophe How the oxygen atmosphere of the earth was formed briefly

Accumulation of O 2 in the Earth's atmosphere:
1 . (3.85-2.45 billion years ago) - O 2 was not produced
2 . (2.45-1.85 billion years ago) O 2 was produced but absorbed by the ocean and seafloor rocks
3 . (1.85-0.85 billion years ago) O 2 leaves the ocean, but is consumed during the oxidation of rocks on land and during the formation of the ozone layer
4 . (0.85-0.54 billion years ago) all rocks on land are oxidized, accumulation of O 2 in the atmosphere begins
5 . (0.54 billion years ago - present) modern period, O 2 content in the atmosphere has stabilized

Oxygen disaster(oxygen revolution) - a global change in the composition of the Earth's atmosphere that occurred at the very beginning of the Proterozoic, about 2.4 billion years ago (the Siderian period). The result of the Oxygen Catastrophe was the appearance of free oxygen in the atmosphere and a change in the general character of the atmosphere from reducing to oxidizing. The assumption of an oxygen catastrophe was made based on a study of a sharp change in the nature of sedimentation.

Primary composition of the atmosphere

The exact composition of the Earth's primary atmosphere is currently unknown, but it is generally accepted that it was formed as a result of degassing of the mantle and was of a reducing nature. It was based on carbon dioxide, hydrogen sulfide, ammonia, and methane. This is supported by:

unoxidized sediments formed clearly on the surface (for example, river pebbles from oxygen-labile pyrite);
absence of known significant sources of oxygen and other oxidizing agents;
study of potential sources of the primary atmosphere (volcanic gases, composition of other celestial bodies).

Causes of the oxygen catastrophe

The only significant source of molecular oxygen is the biosphere, or more precisely, photosynthetic organisms. Having appeared at the very beginning of the existence of the biosphere, photosynthetic archaebacteria produced oxygen, which was almost immediately spent on the oxidation of rocks, dissolved compounds and atmospheric gases. A high concentration was created only locally, within bacterial mats (so-called “oxygen pockets”). After the surface rocks and gases of the atmosphere became oxidized, oxygen began to accumulate in the atmosphere in free form.

One of the likely factors influencing the change in microbial communities was a change in the chemical composition of the ocean caused by the extinction of volcanic activity.

Consequences of the oxygen catastrophe

Biosphere

Since the overwhelming majority of organisms of that time were anaerobic, unable to exist at significant oxygen concentrations, a global change in 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”). Subsequently, the presence of molecular oxygen in the atmosphere led to the formation of an ozone screen, which significantly expanded the boundaries of the biosphere and led to the spread of more energetically favorable (compared to anaerobic) oxygen respiration.

Lithosphere

As a result of the oxygen catastrophe, virtually all metamorphic and sedimentary rocks that make up most of the Earth's crust are oxidized.

The marked increase in free oxygen in the Earth's atmosphere 2.4 billion years ago appears to have resulted from a very rapid transition from one equilibrium state to another. The first level corresponded to an extremely low concentration of O 2 - about 100,000 times lower than what is observed now. The second equilibrium level could have been achieved at a higher concentration, no less than 0.005 of the modern one. The oxygen content between these two levels is characterized by extreme instability. The presence of such “bistability” makes it possible to understand why there was so little free oxygen in the Earth’s atmosphere for at least 300 million years after cyanobacteria (blue-green “algae”) began to produce it.

Currently, the Earth's atmosphere consists of 20% free oxygen, which is nothing more than a by-product of photosynthesis by cyanobacteria, algae and higher plants. A lot of oxygen is released by tropical forests, which in popular publications are often called the lungs of the planet. At the same time, however, it is silent that during the year tropical forests consume almost as much oxygen as they produce. It is spent on the respiration of organisms that decompose finished organic matter - primarily bacteria and fungi. For that, In order for oxygen to begin to accumulate in the atmosphere, at least part of the substance formed during photosynthesis must be removed from the cycle- for example, get into bottom sediments and become inaccessible to bacteria that decompose it aerobically, that is, with the consumption of oxygen.

The total reaction of oxygenic (that is, “giving oxygen”) photosynthesis can be written as:
CO 2 + H 2 O + hν→ (CH 2 O) + O 2,
Where hν is the energy of sunlight, and (CH 2 O) is the generalized formula of organic matter. Breathing is the reverse process, which can be written as:
(CH 2 O) + O 2 → CO 2 + H 2 O.
At the same time, the energy necessary for organisms will be released. However, aerobic respiration is possible only at an O 2 concentration of no less than 0.01 of the modern level (the so-called Pasteur point). Under anaerobic conditions, organic matter decomposes through fermentation, and the final stages of this process often produce methane. For example, the generalized equation for methanogenesis through acetate formation looks like:
2(CH 2 O) → CH 3 COOH → CH 4 + CO 2.
If we combine the process of photosynthesis with the subsequent decomposition of organic matter under anaerobic conditions, then the overall equation will look like:
CO 2 + H 2 O + hν→ 1/2 CH 4 + 1/2 CO 2 + O 2.
It was precisely this path of decomposition of organic matter that apparently was the main one in the ancient biosphere.

Many important details of how the modern balance between oxygen supply and removal from the atmosphere was established remain unclear. After all, a noticeable increase in oxygen content, the so-called “Great Oxidation of the Atmosphere,” occurred only 2.4 billion years ago, although it is known for sure that cyanobacteria carrying out oxygenic photosynthesis were already quite numerous and active 2.7 billion years ago, and they arose even earlier - perhaps 3 billion years ago. Thus, within for at least 300 million years, the activity of cyanobacteria did not lead to an increase in oxygen content in the atmosphere.

The assumption that, for some reason, there suddenly was a radical increase in net primary production (that is, the increase in organic matter formed during the photosynthesis of cyanobacteria) did not stand up to criticism. The fact is that during photosynthesis, the light isotope of carbon 12 C is predominantly consumed, and in the environment the relative content of the heavier isotope 13 C increases. Accordingly, bottom sediments containing organic matter must be depleted in the isotope 13 C, which accumulates in water and goes for the formation of carbonates. However, the ratio of 12 C to 13 C in carbonates and in organic matter of sediments remains unchanged despite radical changes in the concentration of oxygen in the atmosphere. This means that the whole point is not in the source of O 2, but in its, as geochemists put it, “sink” (removal from the atmosphere), which suddenly decreased significantly, which led to a significant increase in the amount of oxygen in the atmosphere.

It is usually believed that immediately before the “Great Oxidation of the Atmosphere,” all the oxygen then formed was spent on the oxidation of reduced iron compounds (and then sulfur), which were quite abundant on the Earth’s surface. In particular, the so-called “banded iron ores” were formed then. But recently Colin Goldblatt, a graduate student in the School of Environmental Sciences at the University of East Anglia (Norwich, UK), together with two colleagues from the same university, came to the conclusion that the oxygen content in the earth's atmosphere can be in one of two equilibrium states: it can be either very small - about 100 thousand times less than now, or already quite a lot (although from the position of a modern observer it is small) - no less than 0.005 of the modern level.

In the proposed model, they took into account the entry into the atmosphere of both oxygen and reduced compounds, in particular paying attention to the ratio of free oxygen and methane. They noted that if the oxygen concentration exceeds 0.0002 of the current level, then some of the methane can already be oxidized by methanotroph bacteria according to the reaction:
CH 4 + 2O 2 → CO 2 + 2H 2 O.
But the rest of the methane (and there is quite a lot of it, especially at low oxygen concentrations) enters the atmosphere.

The entire system is in a nonequilibrium state from the point of view of thermodynamics. The main mechanism for restoring the disturbed equilibrium is the oxidation of methane in the upper layers of the atmosphere by hydroxyl radical (see Fluctuations of methane in the atmosphere: man or nature - who wins, "Elements", 10/06/2006). The hydroxyl radical is known to be formed in the atmosphere under the influence of ultraviolet radiation. But if there is a lot of oxygen in the atmosphere (at least 0.005 of the current level), then an ozone screen is formed in its upper layers, which well protects the Earth from hard ultraviolet rays and at the same time interferes with the physicochemical oxidation of methane.

The authors come to the somewhat paradoxical conclusion that the existence of oxygenic photosynthesis itself is not a sufficient condition either for the formation of an oxygen-rich atmosphere or for the emergence of an ozone screen. This circumstance should be taken into account in cases where we are trying to find signs of the existence of life on other planets based on the results of a survey of their atmosphere.

According to the most common theory, the atmosphere
The earth has been in three different compositions over time.
Initially it consisted of light gases (hydrogen and
helium) captured from interplanetary space. This is true
called the primary atmosphere (about four billion
years ago).

At the next stage, active volcanic activity
led to the saturation of the atmosphere with other gases, except
hydrogen (carbon dioxide, ammonia, water vapor). So
a secondary atmosphere formed (about three billion
years to the present day). This atmosphere was restorative.
Next, the process of atmosphere formation was determined as follows:
factors:
- leakage of light gases (hydrogen and helium) into the interplanetary
space;
- chemical reactions occurring in the atmosphere under the influence of
mitigation of ultraviolet radiation, lightning discharges and
some other factors.
Gradually, these factors led to the formation of tertiary
atmosphere, characterized by much lower content
pressure of hydrogen and much greater - nitrogen and carbon dioxide
gas (formed as a result of chemical reactions from ammonia
and hydrocarbons).
The composition of the atmosphere began to change radically with the advent of
We eat living organisms on Earth as a result of photosynthesis, co-
accompanied by the release of oxygen and the absorption of carbon
chloride gas.
oxygen was initially consumed
for the oxidation of reduced compounds - ammonia, carbon
hydrogen, the ferrous form of iron found in the oceans
etc. At the end of this stage, the oxygen content
began to grow in the atmosphere. Gradually the modern
cold atmosphere with oxidizing properties.
Because it caused major and drastic changes
many processes occurring in the atmosphere, lithosphere and
biosphere, this event was called the Oxygen Catalyst
stanza.
Currently, the Earth's atmosphere consists mainly of
gases and various impurities (dust, water drops, crystals
ice, sea salts, combustion products). Gas concentration,
components of the atmosphere is practically constant, with the exception of
the concentration of water (H 2 O) and carbon dioxide (CO 2).

Source: class.rambler.ru

Consequently, the formation of the modern (oxygen) atmosphere of the Earth is unthinkable without living systems, i.e., the presence of oxygen is a consequence of the development of the biosphere. The brilliant vision of V.I. Vernadsky about the role of the biosphere transforming the face of the Earth is increasingly being confirmed. However, the path of origin of life is still unclear to us. V.I. Vernadsky said: “For thousands of generations, we have been faced with an unresolved, but fundamentally solvable riddle - the riddle of life.”

Biologists believe that the spontaneous emergence of life is possible only in a reducing environment, however, according to the ideas of one of them, M. Rutten, the oxygen content in a gas mixture of up to 0.02% does not yet interfere with the occurrence of abiogenic syntheses. Thus, geochemists and biologists have different concepts about reducing and oxidizing atmospheres. Let's call the atmosphere containing traces of oxygen neutral, in which the first protein accumulations could appear, which in principle could use (assimilate) abiogenic amino acids for their nutrition, perhaps for some reason only isomers.

However, the question is not how these aminoheterotrophs (organisms that use amino acids as food) ate, but how self-organizing matter, the evolution of which has negative entropy, could be formed. The latter, however, is not so rare in the Universe. Doesn't the formation of the Solar System and our Earth, in particular, go against the flow of entropy? Thales of Mitza wrote in his treatise: “Water is the root cause of all things.” Indeed, the hydrosphere had to form first in order to become the cradle of life. V.I. Vernadsky and other great scientists of our time spoke a lot about this.

It was not entirely clear to V.I. Vernadsky why living matter is represented only by left-handed isomers of organic molecules and why in any inorganic synthesis we obtain an approximately equal mixture of left-handed and right-handed isomers. And even if we obtain enrichment (for example, in polarized light) by certain techniques, we cannot isolate them in their pure form.

How could quite complex organic compounds such as proteins, proteins, nucleic acids and other complexes of organized elements consisting of only left-handed isomers be formed?

Source: pochemuha.ru

Basic properties of the Earth's atmosphere

The atmosphere is our protective dome from all kinds of threats from space. It burns up most of the meteorites that fall on the planet, and its ozone layer serves as a filter against ultraviolet radiation from the Sun, the energy of which is fatal to living beings. In addition, it is the atmosphere that maintains a comfortable temperature at the surface of the Earth - if not for the greenhouse effect, achieved through repeated reflection of the sun's rays from clouds, the Earth would be on average 20-30 degrees colder. The circulation of water in the atmosphere and the movement of air masses not only balance temperature and humidity, but also create the earth's diversity of landscape forms and minerals - such a wealth cannot be found anywhere else in the solar system.

The mass of the atmosphere is 5.2×10 18 kilograms. Although gaseous shells extend over many thousands of kilometers from the Earth, only those that rotate around an axis at a speed equal to the speed of rotation of the planet are considered its atmosphere. Thus, the height of the Earth’s atmosphere is about 1000 kilometers, smoothly transitioning into outer space in the upper layer, the exosphere (from the Greek “outer sphere”).

Composition of the Earth's atmosphere. History of development

Although air appears homogeneous, it is a mixture of various gases. If we take only those that occupy at least a thousandth of the volume of the atmosphere, there will already be 12 of them. If we look at the overall picture, then the entire periodic table is in the air at the same time!

However, the Earth did not manage to achieve such diversity right away. It is only thanks to the unique coincidences of chemical elements and the presence of life that the Earth's atmosphere became so complex. Our planet has preserved geological traces of these processes, allowing us to look back billions of years:

The first gases to blanket the young Earth 4.3 billion years ago were hydrogen and helium, fundamental constituents of the atmosphere of gas giants like Jupiter.
about the most elementary substances - they consisted of the remnants of the nebula that gave birth to the Sun and the surrounding planets, and they settled abundantly around the gravitational centers-planets. Their concentration was not very high, and their low atomic mass allowed them to escape into space, which they still do today. Today, their total specific gravity is 0.00052% of the total mass of the Earth’s atmosphere (0.00002% hydrogen and 0.0005% helium), which is very small.
However, inside the Earth itself lay a lot of substances that sought to escape from the hot bowels. A huge amount of gases were released from the volcanoes - primarily ammonia, methane and carbon dioxide, as well as sulfur. Ammonia and methane subsequently decomposed into nitrogen, which now occupies the lion's share of the mass of the Earth's atmosphere - 78%.

But the real revolution in the composition of the Earth's atmosphere occurred with the arrival of oxygen. It also appeared naturally - the hot mantle of the young planet was actively getting rid of gases trapped under the earth's crust. In addition, water vapor emitted by volcanoes was split into hydrogen and oxygen under the influence of solar ultraviolet radiation.

However, such oxygen could not linger in the atmosphere for long. It reacted with carbon monoxide, free iron, sulfur and many other elements on the planet's surface - and high temperatures and solar radiation catalyzed the chemical processes. This situation was changed only by the appearance of living organisms.

Firstly, they began to release so much oxygen that it not only oxidized all substances on the surface, but also began to accumulate - over a couple of billion years, its amount grew from zero to 21% of the total mass of the atmosphere.
Secondly, living organisms actively used atmospheric carbon to build their own skeletons. As a result of their activities, the earth’s crust was replenished with entire geological layers of organic materials and fossils, and carbon dioxide became much less

And finally, excess oxygen formed the ozone layer, which began to protect living organisms from ultraviolet radiation. Life began to evolve more actively and acquire new, more complex forms - highly organized creatures began to appear among bacteria and algae. Today, ozone takes up only 0.00001% of the Earth's total mass.

You probably already know that the blue color of the sky on Earth is also created by oxygen - of the entire rainbow spectrum of the Sun, it best scatters the short waves of light responsible for the blue color. The same effect operates in space - from a distance the Earth seems to be shrouded in a blue haze, and from a distance it completely turns into a blue dot.

In addition, noble gases are present in significant quantities in the atmosphere. Among them the most is argon, the share of which in the atmosphere is 0.9–1%. Its source is nuclear processes in the depths of the Earth, and it reaches the surface through microcracks in lithospheric plates and volcanic eruptions (this is how helium appears in the atmosphere). Due to their physical characteristics, noble gases rise to the upper layers of the atmosphere, where they escape into outer space.

As we can see, the composition of the Earth's atmosphere has changed more than once, and very strongly at that - but it took millions of years. On the other hand, vital phenomena are very stable - the ozone layer will exist and function even if there is 100 times less oxygen on Earth. Against the background of the general history of the planet, human activity has not left serious traces. However, on a local scale, civilization is capable of creating problems - at least for itself. Air pollutants have already made life dangerous for residents of Beijing, China - and huge clouds of dirty fog over big cities are visible even from space.

Atmospheric structure

However, the exosphere is not the only special layer of our atmosphere. There are many of them, and each of them has its own unique characteristics. Let's look at a few basic ones:

Troposphere

The lowest and densest layer of the atmosphere is called the troposphere. The reader of the article is now precisely in his “bottom” part - unless, of course, he is one of the 500 thousand people who are flying on a plane right now. The upper limit of the troposphere depends on latitude (remember the centrifugal force of the Earth's rotation, which makes the planet wider at the equator?) and ranges from 7 kilometers at the poles to 20 kilometers at the equator. Also, the size of the troposphere depends on the season - the warmer the air, the higher the upper limit rises.

The name "troposphere" comes from the ancient Greek word "tropos", which translates as "turn, change". This quite accurately reflects the properties of the atmospheric layer - it is the most dynamic and productive. It is in the troposphere that clouds gather and water circulates, cyclones and anticyclones are created and winds are generated - all those processes that we call “weather” and “climate” take place. In addition, this is the most massive and dense layer - it accounts for 80% of the mass of the atmosphere and almost all of its water content. Most living organisms live here.

Everyone knows that the higher you go, the colder it gets. This is true - every 100 meters up, the air temperature drops by 0.5-0.7 degrees. However, the principle only works in the troposphere - then the temperature begins to rise with increasing altitude. The zone between the troposphere and stratosphere where the temperature remains constant is called the tropopause. And with height, the wind speeds up - by 2–3 km/s per kilometer upward. Therefore, para- and hang gliders prefer elevated plateaus and mountains for flights - they will always be able to “catch a wave” there.

The already mentioned air bottom, where the atmosphere is in contact with the lithosphere, is called the surface boundary layer. Its role in atmospheric circulation is incredibly large - the transfer of heat and radiation from the surface creates winds and pressure differences, and mountains and other terrain irregularities direct and separate them. Water exchange occurs immediately - within 8–12 days, all the water taken from the oceans and surface returns back, turning the troposphere into a kind of water filter.

An interesting fact is that an important process in the life of plants, transpiration, is based on water exchange with the atmosphere. With its help, the planet's flora actively influences the climate - for example, large green areas soften the weather and temperature changes. Plants in water-saturated areas evaporate 99% of the water taken from the soil. For example, a hectare of wheat releases 2-3 thousand tons of water into the atmosphere over the summer - this is significantly more than lifeless soil could release.

Normal pressure at the Earth's surface is about 1000 millibars. The standard is considered to be a pressure of 1013 mbar, which is one “atmosphere” - you have probably already encountered this unit of measurement. With increasing altitude, the pressure rapidly drops: at the boundaries of the troposphere (at an altitude of 12 kilometers) it is already 200 mBar, and at an altitude of 45 kilometers it completely drops to 1 mBar. Therefore, it is not strange that it is in the saturated troposphere that 80% of the entire mass of the Earth’s atmosphere is collected.

Stratosphere

The layer of the atmosphere located between 8 km altitude (at the pole) and 50 km (at the equator) is called the stratosphere. The name comes from the other Greek word “stratos”, which means “flooring, layer”. This is an extremely rarefied zone of the Earth's atmosphere, in which there is almost no water vapor. The air pressure in the lower part of the stratosphere is 10 times less than the surface pressure, and in the upper part it is 100 times less.

In our conversation about the troposphere, we already learned that the temperature in it decreases depending on altitude. In the stratosphere, everything happens exactly the opposite - with an increase in altitude, the temperature increases from –56°C to 0–1°C. Heating stops in the stratopause, the boundary between the stratosphere and mesosphere.

Life and man in the stratosphere

Passenger airliners and supersonic aircraft usually fly in the lower layers of the stratosphere - this not only protects them from the instability of air flows in the troposphere, but also simplifies their movement due to low aerodynamic drag. And low temperatures and thin air make it possible to optimize fuel consumption, which is especially important for long-distance flights.

However, there is a technical altitude limit for an aircraft - the flow of air, which is so small in the stratosphere, is necessary for the operation of jet engines. Accordingly, to achieve the required air pressure in the turbine, the aircraft has to move faster than the speed of sound. Therefore, only combat vehicles and supersonic aircraft like Concordes can move high in the stratosphere (at an altitude of 18–30 kilometers). So the main “inhabitants” of the stratosphere are weather probes attached to balloons - there they can remain for a long time, collecting information about the dynamics of the underlying troposphere.

The reader probably already knows that microorganisms - the so-called aeroplankton - are found in the atmosphere right up to the ozone layer. However, not only bacteria are able to survive in the stratosphere. So, one day an African vulture, a special type of vulture, got into the engine of an airplane at an altitude of 11.5 thousand meters. And some ducks calmly fly over Everest during their migrations.

But the largest creature to have been in the stratosphere remains man. The current height record was set by Alan Eustace, vice president of Google. On the day of the jump he was 57 years old! In a special balloon, he rose to a height of 41 kilometers above sea level, and then jumped down with a parachute. The speed he reached at the peak of his fall was 1342 km/h - more than the speed of sound! At the same time, Eustace became the first person to independently overcome the sound speed threshold (not counting the space suit for life support and parachutes for landing in its entirety).

An interesting fact is that in order to detach from the balloon, Eustace needed an explosive device - like the one used by space rockets when detaching stages.

Ozone layer

And on the border between the stratosphere and mesosphere there is the famous ozone layer. It protects the Earth's surface from the effects of ultraviolet rays, and at the same time serves as the upper limit of the spread of life on the planet - above it, temperature, pressure and cosmic radiation will quickly put an end to even the most persistent bacteria.

Where did this shield come from? The answer is incredible - it was created by living organisms, more precisely by oxygen, which various bacteria, algae and plants have released since time immemorial. Rising high in the atmosphere, oxygen comes into contact with ultraviolet radiation and enters into a photochemical reaction. As a result, the ordinary oxygen we breathe, O 2, produces ozone - O 3.

Paradoxically, the ozone created by the radiation of the Sun protects us from the same radiation! Ozone also does not reflect, but absorbs ultraviolet radiation - thereby heating the atmosphere around it.

Mesosphere

We have already mentioned that above the stratosphere - more precisely, above the stratopause, the boundary layer of stable temperature - is the mesosphere. This relatively small layer is located between 40–45 and 90 kilometers in altitude and is the coldest place on our planet - in the mesopause, the upper layer of the mesosphere, the air cools to –143°C.

The mesosphere is the least studied part of the Earth's atmosphere. Extremely low gas pressure, which is from a thousand to ten thousand times lower than the surface pressure, limits the movement of balloons - their lifting force reaches zero, and they simply hover in place. The same thing happens with jet aircraft - the aerodynamics of the wing and body of the aircraft lose their meaning. Therefore, either rockets or airplanes with rocket engines - rocket planes - can fly in the mesosphere. These include the X-15 rocket plane, which holds the position of the fastest aircraft in the world: it reached an altitude of 108 kilometers and a speed of 7200 km/h - 6.72 times the speed of sound.

However, the X-15's record flight was only 15 minutes. This symbolizes the general problem of vehicles moving in the mesosphere - they are too fast to conduct any thorough research, and they do not stay at a given altitude for long, flying higher or falling down. Also, the mesosphere cannot be explored using satellites or suborbital probes - even though the pressure in this layer of the atmosphere is low, it slows down (and sometimes burns) spacecraft. Because of these difficulties, scientists often call the mesosphere the “ignorosphere” (from the English “ignorosphere”, where “ignorance” is ignorance, lack of knowledge).

It is also in the mesosphere that most meteors falling to Earth burn up - it is there that the Perseid meteor shower, known as the “August meteor shower,” breaks out. The light effect occurs when a cosmic body enters the Earth's atmosphere at an acute angle at a speed of more than 11 km/h - the meteorite lights up due to the force of friction.

Having lost their mass in the mesosphere, the remains of the “aliens” settle on Earth in the form of cosmic dust - every day from 100 to 10 thousand tons of meteorite matter fall on the planet. Since individual dust grains are very light, it takes them up to one month to reach the Earth’s surface! When they fall into clouds, they make them heavier and sometimes even cause rain - just as volcanic ash or particles from nuclear explosions cause them. However, the influence of cosmic dust on rain formation is considered small - even 10 thousand tons is not enough to seriously change the natural circulation of the Earth's atmosphere.

Thermosphere

Above the mesosphere, at an altitude of 100 kilometers above sea level, passes the Karman line - the conventional border between the Earth and space. Although there are gases there that rotate with the Earth and technically enter the atmosphere, their amount above the Karman line is invisibly small. Therefore, any flight that goes beyond an altitude of 100 kilometers is already considered space.

The lower boundary of the longest layer of the atmosphere, the thermosphere, coincides with the Karman line. It rises to an altitude of 800 kilometers and is characterized by extremely high temperatures - at an altitude of 400 kilometers it reaches a maximum of 1800°C!

It's hot, isn't it? At a temperature of 1538°C, iron begins to melt - then how do spacecraft remain intact in the thermosphere? It's all about the extremely low concentration of gases in the upper atmosphere - the pressure in the middle of the thermosphere is 1,000,000 times less than the concentration of air at the surface of the Earth! The energy of individual particles is high - but the distance between them is enormous, and spacecraft are essentially in a vacuum. This, however, does not help them get rid of the heat that the mechanisms emit - to dissipate heat, all spacecraft are equipped with radiators that emit excess energy.

On a note. When it comes to high temperatures, it is always worth considering the density of hot matter - for example, scientists at the Hadron Collider can actually heat matter to the temperature of the Sun. But it is obvious that these will be individual molecules - one gram of star matter would be enough for a powerful explosion. Therefore, we should not believe the yellow press, which promises us the imminent end of the world from the “hands” of the Collider, just as we should not be afraid of the heat in the thermosphere.

Thermosphere and astronautics

The thermosphere is actually open space - it was within its boundaries that the orbit of the first Soviet Sputnik lay. There was also the apocenter - the highest point above the Earth - of the flight of the Vostok-1 spacecraft with Yuri Gagarin on board. Many artificial satellites for studying the Earth's surface, ocean and atmosphere, such as Google Maps satellites, are also launched at this altitude. Therefore, if we are talking about LEO (Low Reference Orbit, a common term in astronautics), in 99% of cases it is in the thermosphere.

Orbital flights of people and animals do not just happen in the thermosphere. The fact is that in its upper part, at an altitude of 500 kilometers, the Earth’s radiation belts extend. It is there that charged solar wind particles are caught and accumulated by the magnetosphere. Prolonged stay in radiation belts causes irreparable harm to living organisms and even electronics - therefore, all high-orbital vehicles are protected from radiation.

Auroras

In polar latitudes, a spectacular and grandiose spectacle often appears - auroras. They look like long glowing arcs of various colors and shapes that shimmer in the sky. The Earth owes its appearance to its magnetosphere - or, more precisely, to the holes in it near the poles. Charged particles from the solar wind burst through, causing the atmosphere to glow. You can admire the most spectacular lights and learn more about their origin here.

Nowadays, auroras are commonplace for residents of circumpolar countries such as Canada or Norway, as well as an obligatory item on the program of any tourist - but previously they were attributed supernatural properties. People of ancient times saw colorful lights as gates to heaven, mythical creatures and bonfires of spirits, and their behavior was considered to be prophecies. And our ancestors can be understood - even education and faith in their own minds sometimes cannot restrain their reverence for the forces of nature.

Exosphere

The last layer of the Earth's atmosphere, the lower boundary of which passes at an altitude of 700 kilometers, is the exosphere (from the other Greek measles "exo" - outside, outside). It is incredibly dispersed and consists mainly of atoms of the lightest element - hydrogen; There are also individual atoms of oxygen and nitrogen, which are highly ionized by the all-penetrating radiation of the Sun.

The dimensions of the Earth's exosphere are incredibly large - it grows into the Earth's corona, the geocorona, which stretches up to 100 thousand kilometers from the planet. It is very rarefied - the concentration of particles is millions of times less than the density of ordinary air. But if the Moon obscures the Earth for a distant spacecraft, then the crown of our planet will be visible, just as the crown of the Sun is visible to us during its eclipse. However, this phenomenon has not yet been observed.

Weathering of the atmosphere

It is also in the exosphere that weathering of the Earth’s atmosphere occurs - due to the large distance from the gravitational center of the planet, particles easily break away from the total gas mass and enter their own orbits. This phenomenon is called atmospheric dissipation. Our planet loses 3 kilograms of hydrogen and 50 grams of helium from the atmosphere every second. Only these particles are light enough to escape the general gas mass.

Simple calculations show that the Earth annually loses about 110 thousand tons of atmospheric mass. Is it dangerous? In fact, no - the capacity of our planet to “produce” hydrogen and helium exceeds the rate of losses. In addition, some of the lost matter returns back to the atmosphere over time. And important gases like oxygen and carbon dioxide are simply too heavy to leave the Earth en masse - so there's no need to worry about our Earth's atmosphere escaping.

An interesting fact is that the “prophets” of the end of the world often say that if the Earth’s core stops rotating, the atmosphere will quickly erode under the pressure of the solar wind. However, our reader knows that the atmosphere near the Earth is held together by gravitational forces, which will act regardless of the rotation of the core. A clear proof of this is Venus, which has a stationary core and a weak magnetic field, but its atmosphere is 93 times denser and heavier than the earth’s. However, this does not mean that stopping the dynamics of the earth’s core is safe - then the planet’s magnetic field will disappear. Its role is important not so much in containing the atmosphere, but in protecting against charged particles from the solar wind, which could easily turn our planet into a radioactive desert.

Clouds

Water on Earth exists not only in the vast ocean and numerous rivers. About 5.2 x 10 15 kilograms of water is in the atmosphere. It is present almost everywhere - the proportion of vapor in the air ranges from 0.1% to 2.5% of volume depending on temperature and location. However, most of the water is collected in the clouds, where it is stored not only as gas, but also in small droplets and ice crystals. The concentration of water in clouds reaches 10 g/m 3 - and since clouds reach a volume of several cubic kilometers, the mass of water in them amounts to tens and hundreds of tons.

Clouds are our Earth's most visible formation; they are visible even from the Moon, where the outlines of the continents blur before the naked eye. And this is not strange - after all, more than 50% of the Earth is constantly covered with clouds!

Clouds play an incredibly important role in the Earth's heat exchange. In winter, they capture the sun's rays, increasing the temperature underneath them due to the greenhouse effect, and in summer they shield the enormous energy of the Sun. Clouds also balance temperature differences between day and night. By the way, it is precisely because of their absence that deserts cool down so much at night - all the heat accumulated by sand and rocks freely flies upward, when in other regions it is held back by clouds.

The vast majority of clouds form near the Earth's surface, in the troposphere, but in their further development they take on a wide variety of shapes and properties. Their separation is very useful - the appearance of clouds of different types can not only help predict the weather, but also determine the presence of impurities in the air! Let's take a closer look at the main types of clouds.

Low clouds

Clouds that fall lowest above the ground are referred to as lower tier clouds. They are characterized by high uniformity and low mass - when they fall to the ground, meteorologists do not separate them from ordinary fog. However, there is a difference between them - some simply obscure the sky, while others can erupt in heavy rain and snowfall.

Clouds that can produce heavy precipitation include nimbostratus clouds. They are the largest among the lower tier clouds: their thickness reaches several kilometers, and their linear dimensions exceed thousands of kilometers. They are a homogeneous gray mass - look at the sky during a long rain and you will probably see nimbostratus clouds.
Another type of low-level cloud is stratocumulus, which rises 600–1500 meters above the ground. They are groups of hundreds of gray-white clouds, separated by small gaps. We usually see such clouds on partly cloudy days. It rarely rains or snows.
The last type of lower cloud is the common stratus cloud; They are the ones who cover the sky on cloudy days, when a light drizzle comes from the sky. They are very thin and low - the height of stratus clouds reaches 400–500 meters at maximum. Their structure is very similar to that of fog - descending at night to the very ground, they often create a thick morning haze.

Clouds of vertical development

The clouds of the lower tier have older brothers - clouds of vertical development. Although their lower boundary lies at a low altitude of 800–2000 kilometers, clouds of vertical development seriously rush upward - their thickness can reach 12–14 kilometers, which pushes their upper limit to the boundaries of the troposphere. Such clouds are also called convective: due to their large size, the water in them acquires different temperatures, which gives rise to convection - the process of moving hot masses upward and cold masses downward. Therefore, in clouds of vertical development, water vapor, small droplets, snowflakes and even whole ice crystals simultaneously exist.

The main type of vertical clouds are cumulus clouds - huge white clouds that resemble torn pieces of cotton wool or icebergs. Their existence requires high air temperatures - therefore, in central Russia they appear only in the summer and melt by night. Their thickness reaches several kilometers.

However, when cumulus clouds have the opportunity to gather together, they create a much more grandiose form - cumulonimbus clouds. It is from them that heavy downpours, hail and thunderstorms come in the summer. They exist for only a few hours, but at the same time they grow up to 15 kilometers - their upper part reaches a temperature of –10 ° C and consists of ice crystals. At the tops of the largest cumulonimbus clouds, “anvils” are formed - flat areas resembling a mushroom or an inverted iron. This happens in those areas where the cloud reaches the boundary of the stratosphere - physics does not allow it to spread further, which is why the cumulonimbus cloud spreads along the altitude limit.

An interesting fact is that powerful cumulonimbus clouds form in places of volcanic eruptions, meteorite impacts and nuclear explosions. These clouds are the largest - their boundaries even reach the stratosphere, reaching a height of 16 kilometers. Being saturated with evaporated water and microparticles, they emit powerful thunderstorms - in most cases this is enough to extinguish fires associated with the cataclysm. This is such a natural firefighter :)

Mid-level clouds

In the intermediate part of the troposphere (at an altitude of 2–7 kilometers in mid-latitudes) there are mid-level clouds. They are characterized by large areas - they are less affected by updrafts from the earth's surface and uneven landscapes - and a small thickness of several hundred meters. These are the clouds that “wind” around sharp mountain peaks and hover near them.

Mid-level clouds themselves are divided into two main types - altostratus and altocumulus.

Altostratus clouds are one of the components of complex atmospheric masses. They present a uniform, grayish-blue veil through which the Sun and Moon are visible - although the altostratus clouds are thousands of kilometers long, they are only a few kilometers thick. The gray dense veil that is visible from the window of an airplane flying at high altitude is precisely altostratus clouds. It often rains or snows for a long time.

Altocumulus clouds, resembling small pieces of torn cotton wool or thin parallel stripes, are found in the warm season - they are formed when warm air masses rise to a height of 2–6 kilometers. Altocumulus clouds serve as a sure indicator of an upcoming change in weather and the approach of rain - they can be created not only by natural convection of the atmosphere, but also by the onset of cold air masses. They rarely rain - however, the clouds can bunch together and create one large rain cloud.

Speaking of clouds near the mountains, in photographs (and maybe even in real life) you have probably seen round clouds resembling cotton pads that hang in layers above a mountain peak more than once. The fact is that middle-tier clouds are often lenticular or lens-shaped - divided into several parallel layers. They are created by air waves formed when the wind flows around steep peaks. Lenticular clouds are also special in that they hang in place even in the strongest winds. This is made possible by their nature - since such clouds are created at points of contact of several air currents, they are in a relatively stable position.

Upper clouds

The last level of ordinary clouds that rise to the lower reaches of the stratosphere is called the upper tier. The height of such clouds reaches 6–13 kilometers - it is very cold there, and therefore the clouds on the upper tier consist of small ice floes. Because of their fibrous, stretched, feather-like shape, high clouds are also called cirrus—though vagaries of the atmosphere often give them the shape of claws, flakes, and even fish skeletons. The precipitation they produce never reaches the ground - but the very presence of cirrus clouds serves as an ancient way to predict the weather.

Pure cirrus clouds are the longest among the upper tier clouds - the length of an individual fiber can reach tens of kilometers. Since the ice crystals in the clouds are large enough to feel the Earth’s gravity, cirrus clouds “fall” in whole cascades - the distance between the top and bottom points of a single cloud can reach 3-4 kilometers! In fact, cirrus clouds are huge “ice falls”. It is the differences in the shape of water crystals that create their fibrous, stream-like shape.

In this class there are also practically invisible clouds - cirrostratus clouds. They form when large masses of near-surface air rise upward - at high altitudes their humidity is sufficient to form a cloud. When the Sun or Moon shines through them, a halo appears - a shining rainbow disk of scattered rays.

noctilucent clouds

Noctilucent clouds - the tallest clouds on Earth - should be placed in a separate class. They climb to a height of 80 kilometers, which is even higher than the stratosphere! In addition, they have an unusual composition - unlike other clouds, they are composed of meteorite dust and methane, rather than water. These clouds are visible only after sunset or before dawn - the rays of the Sun penetrating from behind the horizon illuminate the noctilucent clouds, which remain invisible at altitude during the day.

Noctilucent clouds are an incredibly beautiful sight - but to see them in the Northern Hemisphere requires special conditions. And their mystery was not so easy to solve - scientists, powerless, refused to believe in them, declaring silvery clouds an optical illusion. You can look at unusual clouds and learn about their secrets from our special article.

Formation of the atmosphere. Today, the Earth's atmosphere is a mixture of gases - 78% nitrogen, 21% oxygen and small amounts of other gases, such as carbon dioxide. But when the planet first appeared, there was no oxygen in the atmosphere - it consisted of gases that originally existed in the solar system.

Earth arose when small rocky bodies made of dust and gas from the solar nebula, known as planetoids, collided with each other and gradually took the shape of a planet. As it grew, the gases contained in the planetoids burst out and enveloped the globe. After some time, the first plants began to release oxygen, and the primordial atmosphere developed into the current dense air envelope.

Origin of the atmosphere

A rain of small planetoids fell on the nascent Earth 4.6 billion years ago. Gases from the solar nebula trapped inside the planet burst out during the collision and formed the Earth's primitive atmosphere, consisting of nitrogen, carbon dioxide and water vapor.
The heat released during the formation of the planet is retained by a layer of dense clouds in the primordial atmosphere. "Greenhouse gases" such as carbon dioxide and water vapor stop the radiation of heat into space. The surface of the Earth is flooded with a seething sea of molten magma.
When planetoid collisions became less frequent, the Earth began to cool and oceans appeared. Water vapor condenses from thick clouds, and rain, lasting for several eons, gradually floods the lowlands. Thus the first seas appear.
The air is purified as water vapor condenses to form oceans. Over time, carbon dioxide dissolves in them, and the atmosphere is now dominated by nitrogen. Due to the lack of oxygen, the protective ozone layer does not form, and ultraviolet rays from the sun reach the earth's surface without hindrance.
Life appears in ancient oceans within the first billion years. The simplest blue-green algae are protected from ultraviolet radiation by seawater. They use sunlight and carbon dioxide to produce energy, releasing oxygen as a byproduct, which gradually begins to accumulate in the atmosphere.
Billions of years later, an oxygen-rich atmosphere forms. Photochemical reactions in the upper atmosphere create a thin layer of ozone that scatters harmful ultraviolet light. Life can now emerge from the oceans onto land, where evolution produces many complex organisms.

Billions of years ago, a thick layer of primitive algae began releasing oxygen into the atmosphere. They survive to this day in the form of fossils called stromatolites.

Volcanic origin

1. Ancient, airless Earth. 2. Eruption of gases.

According to this theory, volcanoes were actively erupting on the surface of the young planet Earth. The early atmosphere likely formed when gases trapped in the planet's silicon shell escaped through volcanoes.