1)The earths atmosphere ontains many gases.
2)Some of these gases are elements, E.G. Oxygen, Nitrogen and Argon these contain only one type of Atom.
3) Other gases are compounds, eg. Carbon Dioxide these cintain more than one type of atom bonded together
4) There are different amounts of each of these gases: 78% Nitrogen, 21% Oxygen, 1% Argon, and 0.04% Carbon Dioxide