- Carbon dioxide is a water soluble gas (it is the gas used in fizzy drinks) and dissolves readily
- When the water vapour in Earth’s early atmosphere condensed large amounts of CO2 dissolved in the oceans
- Carbonates were precipitated during this process which later formed sediments on the seabed
- As marine life began to evolve sea creatures began to appear which used up the carbonates to form shells and skeletons
- Green plants and algae began to evolve and absorbed considerable amounts of carbon dioxide during photosynthesis
- When these organisms died, their remains locked the atmospheric carbon into the rocks
- This is how the large amounts of carbon dioxide in the early atmosphere were reduced
Exhaled air contains about 4% carbon dioxide and 16% oxygen which is why mouth-to-mouth resuscitation can save someone who has stopped breathing.