Unlike the hot and cold planets of our solar system, there are conditions on planet Earth that enable life in a certain form. One of the main conditions is the composition of the atmosphere, which allows all living things to breathe freely and protects against the deadly radiation prevailing in space.
What the atmosphere consists of
Earth's atmosphere is made up of many gases. This is mainly nitrogen, which occupies 77%. Gas, without which life on Earth is unthinkable, occupies a much smaller volume, the oxygen content in the air is 21% of the total atmosphere. The last 2% is a mixture of various gases, including argon, carbon dioxide, helium, neon, krypton and others.
The atmosphere of the Earth rises to a height of 8 thousand km. Air suitable for breathing is found only in the lower atmosphere, in the troposphere, reaching at the poles - 8 km, up, and above the equator - 16 km. With increasing height, the air becomes more rarefied and the more noticeable lack of oxygen. To consider what oxygen content in the air is at different heights, we give an example. At the peak of Everest (altitude 8848 m), air contains this gas 3 times less than above sea level. Therefore, climbers of mountain peaks - climbers - can climb to its peak only in oxygen masks.
Oxygen - the main condition for survival on the planet
At the beginning of the Earth's existence, the air that surrounded it did not have this gas in its composition. This was quite suitable for the life of protozoa - unicellular molecules that floated in the ocean. They did not need oxygen. The process began about 2 million years ago, when the first living organisms as a result of the photosynthesis reaction began to emit small doses of this gas, obtained as a result of chemical reactions, first into the ocean, then into the atmosphere. Life has developed on the planet and has taken various forms, most of which have not survived to our times. Some organisms eventually adapted to life with new gas.
They learned how to use his power safely inside the cell, where it acted as a power station, in order to extract energy from food. This way of using oxygen is called breathing, and we do it every second. It was breathing that made it possible for more complex organisms and people to appear. Over millions of years, the oxygen content in the air soared to the current level - about 21%. The accumulation of this gas in the atmosphere contributed to the creation of the ozone layer at an altitude of 8–30 km from the earth’s surface. Along with this, the planet received protection from the harmful effects of ultraviolet rays. The further evolution of life forms on water and on land has rapidly increased as a result of increased photosynthesis.
Anaerobic life
Although some organisms have adapted to rising levels of released gas, many of the simplest forms of life that existed on Earth have disappeared. Other organisms survived by hiding from oxygen. Some of them today live in legumes, using nitrogen from the air to build amino acids for plants. The deadly organism of botulism is another “refugee” from oxygen. He calmly survives in vacuum packaging with canned foods.
What oxygen level is optimal for life
Prematurely born babies whose lungs are not yet fully open for breathing fall into special incubators. In them, the oxygen content in the air is higher in volume, and instead of the usual 21%, its level of 30-40% is established here. Babies with serious breathing problems are surrounded by air with 100% oxygen to prevent damage to the baby’s brain. Being in such circumstances improves the oxygen regime of tissues in a state of hypoxia, normalizes their vital functions. But its excessive amount in the air is as dangerous as its lack. Excessive oxygen in the baby’s blood can damage the blood vessels in the eyes and cause loss of vision. This shows the duality of gas properties. We must breathe it in order to live, but its excess can sometimes become a poison for the body.
Oxidation process
When oxygen is combined with hydrogen or carbon, a reaction called oxidation occurs. This process causes the organic molecules that are the basis of life to decay. In the human body, oxidation proceeds as follows. Red blood cells collect oxygen from the lungs and carry it throughout the body. There is a process of destruction of the molecules of food that we eat. This process releases energy, water and leaves carbon dioxide. The latter is excreted by blood cells back into the lungs, and we exhale it into the air. A person may suffocate if he is prevented from breathing for longer than 5 minutes.
Breath
Consider the oxygen content in the inhaled air. The atmospheric air that enters the lungs from the outside when inhaled is called respirable, and the air that exits through the respiratory system when exhaled is called exhaled.
It is a mixture of air filling the alveoli with that in the airways. The chemical composition of air, which a healthy person inhales and exhales in natural conditions, practically does not change and is expressed by such numbers.
Gas content (%)
- | Oxygen | Carbon dioxide | Nitrogen and other gases |
Inhaled air | 20.94 | 0,03 | 79.03 |
Exhaled air | 16.3 | 4.0 | 79.7 |
Alveolar air | 14.2 | 5.2 | 80.6 |
Oxygen is the main component of air for life. Changes in the amount of this gas in the atmosphere are small. If at the sea the oxygen content in the air holds up to 20.99%, then even in the very polluted air of industrial cities its level does not fall below 20.5%. Such changes do not reveal effects on the human body. Physiological disturbances occur when the percentage of oxygen in the air drops to 16-17%. In this case, there is a clear oxygen deficiency, which leads to a sharp drop in vital activity, and with an oxygen content of 7-8%, a fatal outcome is possible.
Atmosphere in different eras
The composition of the atmosphere has always influenced evolution. At different geological times, due to natural disasters, rises or drops in oxygen levels were observed, and this entailed a change in the biosystem. About 300 million years ago, its content in the atmosphere rose to 35%, while the planet was populated by gigantic insects. The greatest extinction of living things in the history of the Earth happened about 250 million years ago. During it, more than 90% of the inhabitants of the ocean and 75% of the inhabitants of the land died. One version of the mass extinction says that the reason was the low oxygen content in the air. The amount of this gas dropped to 12%, and this is in the lower atmosphere to an altitude of 5300 meters. In our era, the oxygen content in atmospheric air reaches 20.9%, which is 0.7% lower than 800 thousand years ago. These figures are confirmed by scientists from Princeton University, who studied samples of Greenland and Atlantic ice formed at that time. Frozen water saved air bubbles, and this fact helps to calculate the level of oxygen in the atmosphere.
What does his level in the air obey
Its active absorption from the atmosphere can be caused by the movement of glaciers. Moving away, they open huge areas of organic layers that consume oxygen. Another reason may be the cooling of the waters of the oceans: its bacteria actively absorb oxygen at lower temperatures. Researchers argue that the industrial leap and with it the burning of a huge amount of fuel do not have a special effect. The oceans have cooled for 15 million years, and the amount of vital in the atmosphere has decreased regardless of human exposure. Probably, some natural processes are taking place on Earth, leading to the fact that oxygen consumption becomes higher than its production.
Human exposure to atmospheric composition
Let's talk about the effect of man on the composition of air. The level that we have today is ideal for living creatures, the oxygen content in the air is 21%. The balance of it and other gases is determined by the life cycle in nature: animals exhale carbon dioxide, plants use it and release oxygen.
But there is no guarantee that this level will always be constant. The amount of carbon dioxide released into the atmosphere is increasing. This is due to the use of fuel by humanity. And it, as you know, was formed from fossils of organic origin and carbon dioxide enters the air. Meanwhile, the largest plants of our planet, trees, are being destroyed at an increasing rate. Kilometers of forest disappear in a minute. This means that part of the oxygen in the air is gradually falling and scientists are already sounding the alarm. Earth's atmosphere is not a limitless pantry and oxygen does not enter into it from the outside. It was constantly being developed along with the development of the Earth. It must be constantly remembered that this gas is produced by vegetation during photosynthesis due to the consumption of carbon dioxide. And any significant decrease in vegetation in the form of forest destruction will inevitably reduce the ingress of oxygen into the atmosphere, thereby upsetting its balance.