EQ1: How does the carbon cycle operate to maintain planetary health?

6.1 Most global carbon is locked in terrestrial stores as part of the long-term geological cycle

Explain how the biogeochemical carbon cycle consists of carbon stores of different sizes (terrestrial, oceans and atmosphere), with annual fluxes between stores of varying size (measured in Pg/Gt), rates and on different timescales.

Explain why most of the earth's carbon is geological, resulting from the formation of sedimentary carbonate rocks (limestone) in the oceans and biologically derived carbon in shale, coal and other rocks.

Explain how geological processes release carbon into the atmosphere through volcanic out-gassing at ocean ridges/subduction zones and chemical weathering of rocks.).

6.2 Biological processes sequester carbon on land and in the oceans on shorter timescales

Explain how phytoplankton sequester atmospheric carbon during photosynthesis in surface ocean waters; carbonate shells/tests move into the deep ocean water through the carbonate pump and action of the thermohaline circulation.

Explain how terrestrial primary producers sequester carbon during photosynthesis; some of this carbon is returned to the atmosphere during respiration by consumer organisms.

Explain how biological carbon can be stored as dead organic matter in soils, or returned to the atmosphere via biological decomposition over several years.

6.3 A balanced carbon cycle is important in sustaining other earth systems but is increasingly altered by human activities

Explain how the concentration of atmospheric carbon (carbon dioxide and methane) strongly influences the natural greenhouse effect, which in turn determines the distribution of temperature and precipitation.

Explain why ocean and terrestrial photosynthesis play an important role in regulating the composition of the atmosphere.

Explain how soil health is influenced by stored carbon and why this is important for ecosystem productivity.

Explain how the process of fossil fuel combustion has altered the balance of carbon pathways and stores with implications for climate, ecosystems and the hydrological cycle.