The various gases present in the immediate atmosphere (troposphere) of the earth are oxygen, about 21% nitrogen about 78%, carbon dioxide about 0.03% and water vapours in variable amounts. In addition, there are traces of inert gases, like ozone, argon, xenon, neon, krypton and helium. Each of these gases serves as basic components of the living organisms.
For example, Carbon dioxide is the main component of the atmosphere, which is needed in the process of photosynthesis, while ozone protects the living organisms from the ultraviolet radiations.
