Carbon Stores (HL) (DP IB Environmental Systems & Societies (ESS)): Revision Note

Carbon stores

Lithosphere carbon stores

• The lithosphere contains significant carbon stores in fossil fuels and carbonate rocks

  • Fossil fuels: carbon stored in coal, oil, and natural gas

  • Limestone: carbon is stored as calcium carbonate (CaCO₃) in certain rocks, e.g. limestone

    • Residence time: carbon in these stores can remain for hundreds of millions of years

Formation of fossil fuels

• Fossil fuels are formed from partially decomposed organic matter

• Coal: mainly formed from dead plant material (trees and ferns) in swampy areas. This process peaked during the Carboniferous period (around 300 million years ago)

• Oil and natural gas: mainly formed from marine microorganisms like plankton

  • When they died, their bodies settled on the seafloor

  • Over time, they were buried and fossilised in porous rocks

• These processes took tens of millions of years to accumulate significant carbon stores

Biological carbon stores

Reef-building corals and molluscs

• The hard parts of organisms such as reef-building corals and molluscs (e.g. clams and snails) contain calcium carbonate

  • Calcium carbonate can become fossilised in limestone

  • The largest carbon store in Earth's systems is limestone

  • Both biological and non-biological processes can produce limestone

Methane

• Methane (CH₄) is a store of carbon because it contains one carbon atom bonded to four hydrogen atoms

  • When methane is produced from organic matter in anaerobic conditions (when very little or no oxygen is available), carbon from that organic material is stored in the methane molecule

• Methane production (methanogenesis):

  • Methanogenic bacteria produce methane in anaerobic conditions

  • Anaerobic conditions occur in places like swamps, rice paddies, landfills, and in the stomachs of cattle (ruminants)

    • Swamps and wetlands are major natural sources of methane because of the presence of large amounts of organic material and anaerobic conditions

• Methane as a greenhouse gas:

  • Methane is a potent greenhouse gas

    • It has a global warming potential that is about 25 times higher than carbon dioxide over a 100-year period

  • It has a residence time of about 10 years

    • It takes about 10 years for atmospheric methane to oxidise to carbon dioxide