English: This diagram is a mnemonic for teaching students that, by volume, the Earth's atmosphere is composed basically of 4 parts nitrogen and 1 part oxygen. The more precise composition for dry atmosphere is 78.1% nitrogen, 20.9% oxygen, with the other 1% being mostly argon (depicted in blue) along with carbon dioxide and other trace elements (purple). Not depicted is another important component of the atmosphere: water vapor (H2O), and its proportion varies considerably though it averages roughly 1% in the troposphere.

With each of the five fingers representing roughly 20% and the finger tips roughly 1%, the nitrogen can be seen as: 80% minus ~2% = 78.1%. The oxygen is 20% plus ~1% = 20.9%. The argon is ~1%. Carbon dioxide and the other trace gases are a small fraction of 1%. A table of the exact composition is listed here. And a pie chart representation is also available:



File:Atmosphere gas proportions.svg