17.1 - The Earth's Atmosphere

Today's atmosphere

• The atmosphere is a mixture of gases held around the Earth by gravity.
• Today it's made up of two main gases:
  1. About 78% nitrogen
  2. About 21% oxygen
• The remaining 1% or so is a mixture of other gases in far smaller proportions:
  • Carbon dioxide (about 0.04%)
  • Water vapour
  • The noble gases - an unreactive group that make up a small but constant part of the air
• The most abundant noble gas is argon, at around 1% of the atmosphere. The rest of the noble gases are present only in tiny traces.