Where does atmospheric oxygen come from?

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Earth's atmosphere consists of approximately 78% nitrogen and 21% oxygen with trace number of other gases. Oxygen is essential for the whole life of animals and for many other organisms. Because the gas is used on the life of breathing oxygen and also tends to react with many rocks and minerals, it must be constantly supplemented. About 98% of atmospheric oxygen come from photosynthesis, which is the process by which the plants produce sugars from carbon dioxide and water. The rest is the result of water decay with ultraviolet radiation.

photosynthesis

Plants and some bacteria use photosynthesis to produce food in the form of sugars and other energy -rich substances. Water and carbon dioxide are occupied by organism and sunlight provides energy that drives this process. Oxygen becomes a very useful by -product. As far as scientists are concerned, oxygen levels on Earth have remained relatively stable for several hundred million years. This is indicated by the oxygen production by photosynthesis was more or less balancedMi processes such as oxygen or aerobic breathing, life forms and chemical reactions.

Sources of atmospheric oxygen through photosynthesis are phytoplankton, such as cyanobacteria in the ocean, trees and other green plants on the ground. The amount that each source contributes is discussed: Some scientists suggest that more than half come from the oceans, for example, while others lay a number closer to one third. It is clear that the numbers fluctuated in geological time, depending on the balance of life on Earth. For example, when the atmosphere first evolved, cyanobacteria mostly contributed to oxygen.

increase oxygen levels

It is assumed that initially oxygen produced by cyanobacteria was used to respond with iron in soils, rocks and ocean, creating iron and minerals compounds. Geologists can estimate the amount of oxygen in an atmosphere in antiquity by looking at the species of iron withLoučenin in the rocks. In the absence of oxygen, iron tends to combine with sulfur and create sulfides such as pyrites. However, when it is present, these compounds disintegrate and iron combine with oxygen and form oxides. As a result, pyrite in ancient rocks indicates low oxygen levels, while oxides indicate the presence of a significant amount of gas.

As soon as most of the available iron was combined with oxygen, the gas was able to accumulate in the atmosphere. It is assumed that about 2.3 billion years ago the level increased from a small track to about 1% of the atmosphere. Things seemed to be equal for a long time, because other organisms have evolved to use oxygen to provide carbon oxidation energy and produce carbon dioxide (what _{2 ). They achieved this by eating organic plant material rich in carbon, eitje life or dead. This created a balance, with oxygen production through photosynthesis corresponding to its consumption by organisms by breathing oxygen.}

It seems that due to this balance, the photosynthesis itself cannot be responsible for the initial increase in oxygen. One explanation is that some dead organic matter was buried in mud or other sediment and was not available for aerobic organisms. This matter could not be combined with atmospheric oxygen, so not all elements produced were used in this way, allowing levels to rise.

At some point later in the history of the Earth, oxygen levels increased dramatically to their current level. Some scientists believe that this could have happened about 600 million years ago. Around this time there were many relatively large, complex, multicellular organisms that would require much higher oxygen levels. However, it is not clear what caused this change. Interestingly, it happened when the Earth seemed to appear from the massive ice of Age, during which most of the planet was covered with ice.

One theory is that the action of glaciers when progressing and recedingIt bumps the rock -rich rock and released its huge amounts into the oceans. Phosphorus is a necessary nutrient for phytoplankton, so it could cause an explosion of this form of life. This in turn would lead to increased oxygen production, with probably a very small life -based life. However, not all scientists have agreed with this theory and since 2012 the problem remains unresolved.

threats for atmospheric oxygen levels

The study showed that oxygen levels between 1990 and 2008 were constantly decreasing by 0.0317%. This is usually attributed to fossil fuel burning that uses oxygen for combustion. However, the decline is less than expected due to the amount of fossil fuels burned during this period. One possibility is that elevated levels of carbon dioxide, possibly combined using fertilizers, supported faster plant growth and more photosynthesis, partially compensated for loss. It is estimated that even if all the world's fossil fuel reserves should be burned, it shouldOnly a very small direct impact on the oxygen level.

deforestation is another popular problem. Although the destruction of large areas of the rainforest has many other serious environmental effects, it is considered unlikely to significantly reduce the oxygen level. In addition to trees and other green plants, rainforests support a variety of life breathing. These forests seem to contribute very little to the levels of atmospheric oxygen, because they consume almost as much oxygen as they produce.

A more serious threat may be the impact of human activities on phytoplankton, which, according to some sources, contributes to global oxygen levels. There are concerns that increased carbon dioxide in the atmosphere of fossil fuel combustion could make oceans warmer and more acidic, which could reduce the amount of phytoplankton. Since 2012, evidence has been unclear because different types of phytoplankton are affected differently. Some may drop in numbers while others can grow and photosynthetIzovat faster.