How Carbon Dioxide Decreased (AQA GCSE Chemistry): Revision Note

Removal of carbon dioxide

• Carbon dioxide is a water soluble gas (it is the gas used in fizzy drinks) and dissolves readily

• There were high concentrations of carbon dioxide in the early atmosphere 

• The levels of carbon dioxide have decreased because: 

  • 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

  • Green plants and algae began to evolve and absorbed considerable amounts of carbon dioxide during photosynthesis

  • Animals fed on the plants which transferred carbon to their tissues including bones and shells and when these organisms died, their remains formed sedimentary rocks

  • Dead organisms turn into fossil fuels, such as crude oil, natural gas and coal which 'locked up' the carbon