Oxygen is the second most common component of the earth's atmosphere (20.947% by volume). It is a major component of air. Oxygen is very important for breathing. We start yawing when there is a lack of oxygen in the room. We try to go at the weekend to the country or to the forest to breathe fresh air rich with oxygen, produced by plants during photosynthesis. One of oxygen derivatives is ozone. Ozone layer protects the earth from harmful UV rays. Protection of ozone layer against depletion is one of the main environmental concerns of the modern mankind.
Now you see how oxygen is important for us. To make its role in our life even more vivid, I will give you the following example showing the relation between oxygen and how our skin looks like. Oxygen depletion is one of the things that happen to older skin. Unfortunately, delivering extra oxygen to the skin doesn't reverse it. Oxygen on the surface may affect the very top layer of skin, but so what? How much extra oxygen does skin need? No one knows. Can it be absorbed? No.
What is oxygen from chemical point of view? Its atomic number is 8. Oxygen is very common, found not only on the Earth but throughout the universe, usually bonded with other elements. Unbound oxygen (usually called molecular oxygen) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago). The name "oxygen" was chosen because, at the time it was discovered in the late 18th century, it was believed that all acids contained oxygen. Michal Sedziwoj who first discovered oxygen thought of it as "the elixir of life".
Oxygen depletion is an urgent question as well as ozone layer depletion. Oxygen depletion is also called hypoxia.
Hypoxia occurs in aquatic environments as dissolved oxygen (DO; molecular oxygen dissolved in the water) becomes reduced in concentration to a point detrimental to aquatic organisms living in the system. Dissolved oxygen is typically expressed as a percentage of the oxygen that would dissolve in the water at the prevailing temperature and salinity (both of which affect the solubility of oxygen in water). An aquatic system lacking dissolved oxygen, in other words, system with low DO concentration-in the range between 1 and 30% DO saturation-is called hypoxic. Most fishes cannot live below 30% DO saturation. A "healthy" aquatic environment should seldom experience DO less than 80%.
T o understand what it means in real life I will give an example. The lack of oxygen in the water is the number 1 stressor that causes fish death in garden or other fish habitats. Two major factors contributing to fish-pond oxygen loss concern blooming algae. During daylight hours, algae make oxygen; during the night, however, the plants take oxygen. If algae are profusely blooming, the plants deplete all the pond's oxygen during the night, which in turn, causes fish inhabiting the pond to die. Another way that algae trigger oxygen loss is by dying suddenly.
Oxygen depletion could be the result of a number of factors including natural ones, but is of most concern as a consequence of pollution and as a highly detrimental outcome of a process known as eutrophication.
Scientists work under the problems of oxygen and ozone depletion. Some international and national measures are taken to stop ozone depletion. For example, Vienna Convention of Ozone Depletion created a framework for international actions to limit production and uses of substances that might contribute to depletion of the stratospheric ozone layer.