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Composition of air
The air a mixture of many gases, but its two main components are:
- dioxygen (21%)
- dinitrogen (78%)
dioxygen is often called oxygen in everyday life but this term is not
chemically correct (the explanation is given in the study of
microscopic constituents of matter)
remains 1% of other gases: argon, neon, carbon dioxide, ozone etc..
This composition was not the same when the Earth formed and has been
deeply changed by the emergence of life: the blue-green algaes, also
called cyanobacterias, were the first forms of life that produced
dioxygen 8 billion years ago
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