6.1B Geological stores of carbon

• Geological Stores of Carbon:

  • The majority of the earth’s carbon is geological, originating from:
  • The formation of sedimentary carbonate rocks (limestone) in the ocean
  • Biologically derived carbon in shale, coal and other rocks
• Geological processes in the Carbon cycle:

  • weathering of rocks
  • decomposition
  • transportation
  • sedimentation
  • metamorphosis
• Weathering of rocks = Mechanical, chemical and biological weathering results in the breakdown of rocks
• decomposition = Plant and animal particles from decomposition after death store carbon
• transportation = Rivers can carry particles to the ocean, where they will be deposited
• sedimentation = Over time, sediments build up, burying older sediments below e.g. shale and limestone
• metamorphosis = Pressure builds over time in the layers of sediment which eventually leads to deeper sediment changing to rock

  -> e.g. limestone becomes marble, shale becomes slate
• Carbon in Limestone & Shale:

  • 80% of carbon containing rocks in the ocean is from shell-building organisms (corals) and plankton
  • When corals and plankton fall to the ocean floor, they form layers and cement together eventually turning into limestone (lithified)
  • The remaining 20% of rocks contain organic carbon originating from organisms that have been embedded in layers of mud
  • Heat and pressure compress the mud and carbon over millions of years to form sedimentary rock e.g. shale
• Carbon in Fossil Fuels:

  • Coal, oil and natural gas are known as fossil fuels because they have been formed from the remains of organic material over 300 million years ago from the remain
  • When organic matter builds up faster than it can decay, the layers of organic carbon develop into coal, oil or natural gas instead of shale