Air
Air is all around us, even though we cannot see it, taste it or touch it. It does not even have an odour, but it is full of perfumes and bad smells...
It is 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 humans and animals and the carbon dioxide essential for plants to carry out chlorophyll photosynthesis. The air also allows the Earth to retain part of the heat coming from the Sun and to reject the sun's rays that are harmful to living beings. The air that we breathe is made up of a mixture of gases and of solid and liquid particles. Nitrogen and oxygen, 78% and 21% by volume respectively, are the two main components of the atmosphere. Nitrogen is a colourless, odourless, inert gas that does not participate in vital processes in contrast with oxygen that is necessary for the respiration of living things. The oxygen present in the air is almost entirely of biological origin since it is produced by autotrophic organisms through photosynthesis. The remaining 1% is made up of water vapour, carbon dioxide and other gases.
The greenhouse effect
The amazing history of CO2
