Key learning points

1. Earth’s atmosphere is mostly within 7 to 15 km of its surface.
2. Earth's atmosphere is 78% N₂ and 21% O₂, with very small amounts of other gases and particles of liquids and solids.
3. Greenhouse gases keep Earth’s temperature warm enought for human life.
4. The test for oxygen gas is that it relights a glowing splint.
5. The test for carbon dioxide gas is that it forms a white precipitate that turns limewater milky.

Keywords

• Atmosphere - a layer of gases that surrounds a planet and may contain small amounts of solid and liquid particles

• Mixture - a combination of two or more substances that are physically mixed and can be separated

• Respiration - a chemical process that uses oxygen from the air and glucose to provide energy for life processes

• Precipitate - an insoluble solid formed when two solutions react together

Common misconception