Air is everywhere even if we cannot see, taste or touch it. It doesn't have its own smell, but it's full of smells and perfumes that it carries up to our nose: it's the air that allows us to smell the fragrance of flowers or the bad smell of car exhaust! The air has allowed the development of life on Earth. It contains the oxygen necessary for the respiration of men and animals and the carbon dioxide essential for plants to carry out chlorophyll photosynthesis. Furthermore, the air allows the Earth to retain part of the heat coming from the Sun and to reject the sun's rays harmful to living beings.