Our air is a mixture of gases and contains various gases of use to us. The major constituents of our air are nitrogen and oxygen. While the nitrogen constitutes almost 78% (78.084% to be precise) of our air, oxygen constitutes about 21% (20.947% to be precise) of our air. Other components include argon, carbon dioxide, methane, hydrogen, etc. Each of these other components are present in very minuscule quantities compared to nitrogen and oxygen.
Oxygen is required for our survival, because of its role in cellular respiration. The majority of oxygen in our air has been (and is continuously being) generated by green plants, through the process of photosynthesis. This process also removes carbon dioxide that is generated as a by-product of cellular respiration.
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