1(B) The Formation of Geological Carbon Stores
Most of the Earth's carbon is geological, resulting from the formation of sedimentary carbonate rocks (limestone) in oceans and biologically derived carbon in shale, coal and other rocks.
Key Points:
- MOST carbon in the world is geological in ROCKS
- It comes from CARBONATE rocks
- It's mainly LIMESTONE, formed in the OCEAN
- There's also SHALE and CLAY, which is created BIOLOGICALLY
Carbon Stores
- The largest carbon store is geological
- There is over 100 million Pg of carbon in the lithosphere
- Most lithospheric carbon is concentrated in the sedimentary rocks of the crust
- There is over 100 million Pg of carbon in the lithosphere
Formation of Sedimentary Rocks
- Sediment is deposited in layers in a low-energy environment
- E.g. lake
- E.g. sea bed
- Further layers are deposited and sediment undergoes diagenesis
- Diagenesis - /ˌdʌɪəˈdʒɛnɪsɪs/ - the physical and chemical changes that occur during the conversion of sediment to sedimentary rock
- The lower layers become compressed and chemical reactions cement particles together
- The conversion of loose, unconsolidated sediment into solid rock is known as lithification.
Limestone
- Composed 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.
There are two types of ways:
- limestone formed in the oceans
- The Himalayas form one of the Earth's largest carbon stores. This is because the mountains started life as ocean sediments rich in calcium carbonate derived from crustaceans, corals and plankton. Since these sediments have been upfolded, the carbon they contained has been weathered, eroded and transported back to the oceans.
- carbon derived from plants and animals in shale, coal and other rocks
- these rocks were made up to 300 million years ago from the remains of organisms. These remains sank to the bottom of rivers, lakes and seas and were subsequently covered by silt and mud. As a consequence, the remains continued to decay anaerobically and were compressed by further accumulations of dead organisms and sediment. The subsequent burning of these fossil fuels has released the large amounts of carbon they contained back into the atmosphere.