The air is a mixture of several gases. its composition is:-
1. 78% nitrogen- this gas is in abundance and is important for growth of plants.
2. 21% oxygen- it is very important as life can exist on earth due to it as living organism need oxygen for respiration. it also supports burning.
3. 0.04% - carbon dioxide which traps the heat and keep earth warm.
4. many other things are present like-
i) ozone gas which protects earth from uv rays of sun
ii) water vapour which condenses to form rain....etc.