2.3C Carbon in lithosphere (HL) Notes

Carbon Stores in the Lithosphere

1. The lithosphere is the solid outer layer of the Earth composed of the crust, upper mantle, and soils.
2. It is one of the most significant long-term carbon reservoirs in the global carbon cycle.
3. It stores carbon in both organic and inorganic forms
4. These stores hold carbon for long periods, often hundreds of millions of years.

1. Fossil Fuels as Carbon Stores

1. Fossil fuels (coal, oil, and natural gas) are carbon-rich deposits formed from the remains of ancient plants and animals.
2. Over millions of years, organic material buried under heat and pressure transformed into these fuels, which now store large amounts of carbon.
3. When coal is burned for energy, the carbon that was stored in the Earth's lithosphere is quickly released, contributing to global carbon emissions.

2. Carbonate rocks

1. Rocks such as limestone and dolomite store carbon in the form of calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃).
2. These rocks are formed through biological processes (e.g., coral reef deposition) and chemical precipitation in oceans.

Carbon Residence Time

1. Carbon in the atmosphere and biomass has short residence times (years–decades).
2. Carbon in limestone and fossil fuels has extremely long residence times (hundreds of millions of years).

Biological Deposition of Calcium Carbonate

1. Marine organisms such as reef-building corals and molluscs contribute to long-term carbon storage through the formation of calcium carbonate structures.
2. Their process involves:
   1. Ion absorption: organisms take in Ca²⁺ and HCO₃⁻ ions from seawater.
   2. Calcification reaction: formation of CaCO₃ skeletons or shells.
   3. Sedimentation: upon death, remains settle on the seafloor.
   4. Lithification: compaction and cementation over millions of years form limestone.

Limestone as the Largest Carbon Store

1. Limestone is the largest store of carbon on Earth due to its ability to trap large amounts of carbon in the form of calcium carbonate.
2. This carbon can remain stored for hundreds of millions of years in geological formations.
3. Geological processes like sedimentation and burial lead to the accumulation of carbon-rich limestone.
4. Over time, the carbon in limestone remains locked away, making it an important long-term carbon store in the Earth’s lithosphere.

Formation of Limestone

1. Reef-building corals and mollusks use calcium from seawater to create hard parts (e.g., coral skeletons, mollusk shells) made of calcium carbonate.
2. When these organisms die, their remains accumulate on the ocean floor.
3. Over time, these remains are compressed and compacted, eventually forming limestone.
4. Biological fossilization occurs when large amounts of calcium carbonate from the shells and skeletons of marine life accumulate and are preserved in the rock layers.

Formation of Fossil Fuels

1. In past geological eras, organic matter from plants and marine organisms became fossilized to form the major fossil fuels we use today: coal, oil, and natural gas.
2. This process, which occurred over tens of millions of years, is responsible for the significant carbon stores that are now extracted and burned, contributing to carbon emissions.

1. Formation of Coal

1. Originates from terrestrial plants (ferns, mosses, trees) in swampy, low-oxygen environments.
2. Organic matter accumulates in peat bogs, is buried by sediments, and exposed to pressure and heat.
3. Over millions of years, it converts into lignite, then bituminous, and finally anthracite coal.

2. Oil and Natural Gas

1. Formed from marine organisms (plankton, algae) that settled on the sea floor.
2. In the Mesozoic era (252-66 million years ago), marine environments led to the accumulation of organic material that eventually turned into oil and gas.
3. The oil and gas are stored in porous rocks like sandstone or limestone.

Time Scale and Irreversibility

1. Fossil fuel formation is extremely slow, taking tens to hundreds of millions of years.
2. This makes them non-renewable on human timescales, as the rate of extraction far exceeds their natural replacement rate.