10.3 - 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 (roughly four-fifths)
  2. About 21% oxygen (roughly one-fifth)
• The remaining 1% or so is a mixture of other gases in far smaller proportions:
  • Carbon dioxide
  • Water vapour
  • The noble gases - an unreactive group that make up a small but constant part of the air