The oxygen cycle is a biogeochemical cycle (the process by which elements in different chemical forms pass from the environment to living beings and back to the environment) that involves the element oxygen. This cycle features important processes such as photosynthesis and respiration .

Oxygen is one of the most abundant elements on the planet, constituting about 21% of the atmosphere Because it is very reactive , it influences several other biogeochemical cycles, such as the carbon cycle . We will present here how the oxygen cycle occurs, as well as the importance and origin of this chemical element.

Oxygen is an extremely important element. It is present in the ozone layer and is essential for the existence of life on Earth.

How does the oxygen cycle occur?

The oxygen cycle allows oxygen to circulate between the environment and living things . The main form of oxygen production is photosynthesis . Photosynthetic organisms assimilate carbon dioxide to produce organic matter and release oxygen, in its gaseous form (O 2 ), into the environment as one of the products of this process. Oxygen, present in the organic molecules produced, is transferred to other organisms through food chains .

In the oxygen cycle, oxygen is produced through photosynthesis and consumed by the process of respiration.

Atmospheric oxygen gas (O 2 ) is used by some organisms in the process of cellular respiration , an aerobic energy-producing process. In this process, oxygen bonds with hydrogen atoms, forming water (H 2 0). Part of this water is used in metabolic reactions and returns to the environment through the processes of respiration and decomposition . Another part is eliminated by perspiration and excretion . At the end of the breath, CO 2 (carbon dioxide) is also eliminated. It is for this reason that the oxygen and carbon cycles are intertwined.

origin of oxygen

Oxygen on Earth originated from its production by organisms that were able to use energy from solar radiation to produce sugars from water and carbon dioxide.

These organisms, cyanobacteria , produced oxygen, which reacted with iron ions present in the water, forming iron oxides. Only when the production of oxygen exceeded the oxidizing capacity of iron did it begin to accumulate in the atmosphere.

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The oldest cyanobacteria date back to about 3.5 billion years, however, the accumulation of oxygen in the atmosphere, which led to a major transformation in the atmosphere and allowed life to develop as we know it today, dates to about 2 billion years.

Oxygen and the ozone layer

Oxygen is part of the constitution of the ozone layer , a gaseous layer that protects the Earth by retaining part of the ultraviolet rays emitted by the Sun and protecting organisms against its harmful effects. In the stratosphere, part of the oxygen gas (O 2 ) is transformed into ozone (O 3 ) by the action of some wavelengths (less than 200 nm) of ultraviolet rays . A contrary reaction transforms ozone into oxygen, also through the action of ultraviolet rays, of different lengths (between 200 and 300 nm), which maintains an equilibrium in the layer.

However, some gases released into the atmosphere, such as chlorofluorocarbons (CFCs), react with this layer, transforming ozone into oxygen, destroying it. The destruction of the ozone layer allows the passage of ultraviolet rays, which can affect many organisms.

In view of this, in 1987, the Montreal Protocol was signed, which imposed certain obligations so that the production and consumption of products that depleted the ozone layer were reduced, until their elimination. Industrialized countries have already reduced these emissions by 97%. Some studies show that the destruction of the ozone layer is contained, with no expansion in the hole present in the layer.

The ozone layer acts as a barrier, retaining part of the ultraviolet rays, which are harmful to living beings.

Summary of the oxygen cycle

  • Oxygen is one of the most abundant elements on the planet. In the atmosphere, it can be found in the form of gaseous oxygen (O 2 ), ozone (O 3 ) and carbon dioxide (CO 2 );
  • Oxygen began to accumulate in the atmosphere about 2 billion years ago;
  • Oxygen is present in the constitution of the ozone layer and participates in important processes, such as photosynthesis, respiration, decomposition and combustion;
  • The oxygen cycle involves some processes. Its release into the environment occurs mainly through photosynthesis and its assimilation by organisms occurs through respiration.

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