Unlike the hot and cold planets of our solar system, planet Earth has conditions that allow life in some form. One of the main conditions is the composition of the atmosphere, which gives all living things the opportunity to breathe freely and protects from the deadly radiation that reigns in space.
What the atmosphere is made of
The Earth's atmosphere is made up of many gases. It 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 volume of the atmosphere. The last 2% is a mixture of various gases, including argon, carbon dioxide, helium, neon, krypton and others.
The Earth's atmosphere rises to a height of 8 thousand km. Breathable air is found only in the lower layer of the atmosphere.troposphere, reaching at the poles - 8 km, up, and above the equator - 16 km. As altitude increases, the air becomes thinner and the more oxygen is depleted. To consider what oxygen content in the air is at different heights, we will give an example. At the peak of Everest (altitude 8848 m), the air holds this gas 3 times less than above sea level. Therefore, the conquerors of high mountain peaks - climbers - can climb to its top only in oxygen masks.
Oxygen is 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 the simplest - single-celled molecules that floated in the ocean. They didn't need oxygen. The process began about 2 million years ago, when the first living organisms, as a result of the reaction of photosynthesis, began to release small doses of this gas obtained as a result of chemical reactions, first into the ocean, then into the atmosphere. Life evolved on the planet and took on a variety of forms, most of which have not survived to our times. Some organisms eventually adapted to life with the new gas.
They learned how to use his power safely inside the cell, where it acted as a power plant, in order to extract energy from food. This way of using oxygen is called breathing, and we do it every second. It was the breath that made it possible for morecomplex organisms and people. Over millions of years, the oxygen content in the air has skyrocketed to its current level of about 21%. The accumulation of this gas in the atmosphere contributed to the creation of the ozone layer at a height of 8–30 km from the earth's surface. At the same time, the planet received protection from the harmful effects of ultraviolet rays. The further evolution of life forms on water and on land has increased rapidly as a result of increased photosynthesis.
Anaerobic life
Although some organisms have adapted to the rising levels of the gas being released, many of the simplest life forms that existed on Earth have disappeared. Other organisms survived by hiding from oxygen. Some of them today live in the roots of legumes, using nitrogen from the air to build amino acids for plants. The deadly organism botulism is another "refugee" from oxygen. He quietly survives in vacuum packages with canned food.
What is the optimal oxygen level for life
Prematurely born babies, whose lungs are not yet fully opened for breathing, fall into special incubators. In them, the oxygen content in the air is higher by volume, and instead of the usual 21%, its level of 30-40% is set here. Toddlers with severe breathing problems are surrounded by air with 100% oxygen levels to prevent damage to the child's brain. Being in such circumstances improves the oxygen regime of tissues that are in a state of hypoxia, and normalizes their vital functions. Buttoo much of it in the air is just as dangerous as too little. Too much oxygen in a child's blood can damage the blood vessels in the eyes and cause vision loss. This shows the duality of the properties of the gas. We must breathe it in order to live, but its excess can sometimes become a poison for the body.
Oxidation process
When oxygen combines with hydrogen or carbon, a reaction called oxidation takes place. 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 the food that we eat. This process releases energy, water and carbon dioxide. The latter is excreted by the blood cells back into the lungs, and we exhale it into the air. A person may suffocate if prevented from breathing for more than 5 minutes.
Breathing
Consider the oxygen content in the inhaled air. Atmospheric air that enters the lungs from the outside when inhaled is called inhaled, and the air that goes out through the respiratory system when exhaled is called exhaled.
It is a mixture of air that filled the alveoli with that which is in the airways. The chemical composition of the air that a he althy person inhales and exhales under natural conditions is practicallyvaries and is expressed in numbers like this.
Gas content (in %)
| - | 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 the sea contains up to 20.99% oxygen in the air, 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 disorders appear when the percentage of oxygen in the air drops to 16-17%. At the same time, there is a clear oxygen deficiency, which leads to a sharp drop in vital activity, and with an oxygen content of 7-8% in the air, death 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 falls in the level of oxygen were observed, and this entailed a change in the biosystem. Approximately 300 million years ago, its content in the atmosphererose to 35%, while the planet was inhabited by insects of gigantic size. The largest extinction of living beings 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 low oxygen content in the air was to blame. The amount of this gas has dropped to 12% and it is in the lower atmosphere up to a height of 5300 meters. In our era, the oxygen content in the atmospheric air reaches 20.9%, which is 0.7% lower than 800 thousand years ago. These figures are confirmed by scientists at Princeton University who examined samples of the Greenland and Atlantic ice that formed at that time. The frozen water saved the air bubbles, and this fact helps to calculate the level of oxygen in the atmosphere.
What does its level in the air obey
Active absorption of it from the atmosphere may be caused by the movement of glaciers. As they move away, they reveal vast areas of organic layers that consume oxygen. Another reason may be the cooling of the waters of the oceans: its bacteria absorb oxygen more actively at low temperatures. The researchers argue that the industrial leap and with it the burning of a huge amount of fuel does not have a special impact. The world's oceans have been cooling for 15 million years, and the amount of vital matter in the atmosphere has decreased regardless of human impact. It is likely that some natural processes are taking place on Earth, leading to the fact that oxygen consumptionbecomes higher than its production.
Human impact on the composition of the atmosphere
Let's talk about the human impact on the composition of the air. The level that we have today is ideal for living beings, 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 mankind. And it, as you know, was formed from fossils of organic origin and carbon dioxide enters the air. Meanwhile, the largest plants on 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. The earth's atmosphere is not a limitless pantry and oxygen does not enter it from the outside. It has been developed all the time along with the development of the Earth. It must be constantly remembered that this gas is produced by vegetation in the process of photosynthesis due to the consumption of carbon dioxide. And any significant reduction in vegetation in the form of deforestation inevitably reduces the ingress of oxygen into the atmosphere, thereby upsetting its balance.
