6.1b+a geological carbon cycle

• terrestrial carbon

  • held within the mantle and release into atmosphere as carbon dioxide when volcanoes erupt - outgassing
  • can happen at ocean ridges, hotspot volcanoes and subduction zones
  • also happens in areas with no volcanic activity e.g Yellowstone National Park
  • insignificant in comparison to human activity
• chemical weathering

  • atmospheric CO2 combines with rainfall to produce a weak acid - dissolves carbon rich rocks - producing bicarbonates
  • bicarbonates end up in ocean to form carbonate rock
• carbon in organic matter

  • shells and skeletons sink to ocean bed + builds up strata of chalk and limestone (sedimentary carbonate rock)
  • from organisms like coral and plankton - form layers in low energy environment (sea bed), becomes compressed, turning into limestone
• Limestone

  • Com​posed of calcium carbonate, and is 40% carbon by weight
  • 80% of lithospheric carbon is found in limestones
  • Limestone is formed when calcium carbonate is deposited on the ocean floor. 
• biological derived - shale, coal and other rocks

  • 20% of lithospheric carbon is found in shale, coal etc.
  • from organisms that are embedded in layers of mud and silt.
  • the remains continued to decay anaerobically - compressed by further accumulations of dead organisms and sediment
  • form sedimentary rock like shale
• Coal formation

  • formed from remains of organic matter over 300 million years ago
  • when organic matter accumulates faster than it decays -> layers of organic carbon develop into coal rather than shale.
• Subduction and metamorphosis

  • pressure and intense heating along subduction plate - leads to metamorphosis of sedimentary rocks
  • limestone becomes marble
  • shale becomes slate