1.2 - Slow Carbon Cycle Extra Detail

Question 1

How are hydrocarbons formed?

Answer 1

• remains of living organic material decays under anaerobic conditions
• chains of hydrogen and carbon form and are stored as crude oil in the pore spaces of clastic sedimentary basins (eg. Vienna/Molasse basin)
• Gaseous hydrocarbons are also formed during decay process
  
  • moves upwards through shale until it reaches a cap rock
• Coal is formed from plant remains
  
  • organic material in swamps starts as peat
  • is converted to coal due to heat and pressure experienced over time

Question 2

How is shale rock made?

Answer 2

• Clay, silt and mud is compacted over time

Question 3

How are sedimentary carbonate rocks formed as part of the slow cycle?

Answer 3

• shells and skeletons of dead coral and marine animals contain carbon
  
  • due to absorption of carbon when alive through photosynthesis
• cementation and accumulation of shells under heat and pressure creates limestone under the ocean floor
• tectonic folding and uplifting results in limestone being lifted and folded into mountain ranges
  
  • rock is then chemically weathered by carbonic acid in rainfall and returns to oceans as calcium ions to form calcium carbonate rock when reacting with carbonate ions already present in water through ocean-atmosphere exchange

Question 4

How many main types of coal are there?

Answer 4

• 4
• Anthracite: most carbon rich, thus higher energy content
• Bituminous coals: less carbon rich and energy dense than anthracite
• Soft coals: even lower in carbon content (25-35%), emit more CO₂ than more carbon rich coals
• Peat: stage before coal, is also used as an energy source itself