p1 Flashcards
Why is carbon important?
Carbon is the main building block of life.
Carbon is held in stores e.g. the atmosphere and can have many forms. For example in the atmosphere, carbon is present as gases (carbon dioxide and methane).
Carbon Stores:
The atmosphere e.g. carbon dioxide and methane
The hydrosphere e.g. dissolved carbon
The lithosphere e.g. carbonates in limestone and fossil fuels such as coal, oil and gas
The biosphere - in both living and dead organisms.
Carbon moves from one sphere to another – this is the cycle of carbon.
Store/Reservoir –
where the carbon is held
Fluxes –
the flows of movement between the stores, which can operate at local and global scales.
Petagrams (Pg) or Gigatonnes (Gt):
The units used to measure carbon; one petagram (Pg), also known as a gigatonne (Gt), is equal to one billion tonnes.
long term stores (hundreds of years to millennia)
Crustal/terrestrial/ geological
Oceanic (deep)
Crustal/terrestrial/ geological
Store type (before anthropogenic influences):
Sedimentary rocks, very slow cycling over millennia
PgC (Petagrams average): 100 000 000 fossil fuels store an extra 4 000
oceanic (deep)
Most carbon is dissolved, inorganic carbon stored at great depths, very slowly cycled.
38 000
short term stores (seconds to decades)
Terrestrial soil
Oceanic (surface)
Atmospheric
Terrestrial ecosystems
terrestrial soil
From plant materials (biomass) microorganisms break most organic matter down into C02 in a process which can take days in a hot and humid climate to decades in colder climates
1 500
Oceanic (surface)
Exchanges are rapid with the atmosphere through physical processes such as C02 dissolving in the water and biological processes involving plankton. Some of this carbon sinks into the deeper ocean pool.
1 000
Atmospheric
C02 and CH4 store carbon as greenhouse gases with a lifetime up to 100 years
560
Terrestrial ecosystems
CO2 is taken from the atmosphere by photosynthesis, carbon is stored organically, especially in trees. Rapid exchange with the atmosphere- seconds/minutes.
560
Where does carbon come from?
Carbon can be created through a number of chemical reactions in the rock cycle. This is called geological carbon.
Carbon can also be present in organic matter as a result of processes such as respiration. This can later be stored in shale, coal and other sedimentary rocks. This is called biologically derived carbon.
Geological carbon
formed when rocks such as sedimentary rocks are created e.g. limestone and chalk.
This is a natural cycle that moves between land, oceans and the atmosphere.
It involves a number of chemical reactions that create new stores which trap carbon for significant periods of time.
There tends to be a natural balance between the amount of carbon being released and the amount being absorbed.
However, there can be occasional disruptions and short periods before this balance is restored, such as during a volcanic eruption.
Case Study Example of geological carbon
One of earth’s largest stores of carbon is the Himalayas which started off as oceanic sediments rich in calcium- this is now being weathered and returned back to the oceans.
Himalayas cover about 0.4 percent of the surface area of the Earth
Biologically derived carbon
created from dead organisms such as coal and shale.
These organisms absorb carbon during respiration and photosynthesis.
Once they die they (if they are in oceans) sink to the sea bed.
They are then buried under sinking sediments and form layers called strata.
Eventually, the strata are squeezed together as a result of the weight on top, and can create fossil fuels such as coal and oil.
formation of Oil and natural gas
- Formed from the remains of tiny aquatic animals and plants
- Gas and oil occur in ‘pockets’ in rocks, migrating up through the crust until meeting caprocks
- Natural gas, such as methane, is made up of the fractions of oil molecules, so small they are in gas form not liquid, and usually found with crude oil
- Other hydrocarbon deposits include oil shales, tar sands and gas hydrates
formation of Coal
Formed from the remains of trees, ferns and other plants There are four main types of coal:
* anthracite is the hardest coal; it has the most carbon and, hence, a higher energy content
* bituminous coals are next in hardness and carbon content
* soft coals such as lignite and brown coal are lower in carbon (25-35%) and energy potential; these are the major global source of energy supplies but emit more CO2 than hard coals
* peat is the stage before coal; it is an important carbon and energy source
six important stores and fluxes - geological carbon cycle
Terrestrial carbon, held within the mantle, is released into the atmosphere as carbon dioxide (CO2) when volcanoes erupt. This is known as out-gassing.
CO2 within the atmosphere combines with rainfall to produce a weak acid (acid rain) that dissolves carbon-rich rocks, releasing bicarbonates. This is chemical weathering.
Rivers transport weathered carbon and calcium sediments to oceans, where they are deposited.
Carbon in organic matter from plants and from animal shells and skeletons sinks to the ocean bed when they die, building up strata of coal, chalk and limestone.
Carbon-rich rocks are subducted along plate boundaries and eventually emerge again when volcanoes erupt.
The presence of intense heating along subduction plate boundaries metamorphoses (alters) sedimentary rocks by baking, creating metamorphic rock. CO2 is released by the metamorphism of rocks rich in carbonates during this process.
three ways carbon is released in the geological carbon cycle.
Volcanic Outgassing
Chemical Weathering
Metamorphism
Case Study Example of volcanic outgassing
In 2010, the Icelandic Eruption emitted between 150,000 and 300,000 tonnes of CO2 per day. It contributed less than 0.3% of global emissions that year.
Chemical weathering
The geological part of the carbon cycle interacts with the rock cycle, a series of constant processes through which Earth’s materials change from one form to another over millennia. These processes can be broken down into five phases:
These processes can be broken down into five phases:
- Chemical weathering: in the atmosphere, water reacts with atmospheric CO, and carbonic acid forms. Although only weakly acidic, once this water reaches the surface as rain, it reacts with some surface minerals, slowly dissolving them into their component ions.
- Transportation of calcium ions by rivers from the land into oceans. These combine with bicarbonate ions to form calcium carbonate and precipitate out as minerals such as calcite (CaCO3).
- Deposition and burial turns the calcite sediment into limestone.
- Subduction of the sea floor under continental margins by tectonic spreading.
- Some of this carbon rises back up to the surface within heated magma, then is ‘degassed’ as CO2 and returned to the atmosphere.
Diamonds, the purest form of carbon, have recently been discovered to be formed up to 435 miles (700 km) deep, proving that carbon is cycled between Earth’s surface and the lower mantle. Tectonic uplift can also expose previously buried limestone, as in the Himalayas and Alps.
Volcanic outgassing
Pockets of CO2 exist in the Earth’s crust. Disturbance by volcanic eruptions or earthquake activity may allow pulses or more diffuse fluxes into the atmosphere.
Outgassing occurs at:
Outgassing occurs at:
active or passive volcanic zones associated with tectonic plate boundaries, including subduction zones and spreading ridges
places with no current volcanic activity, such as the hot springs and geysers in Yellowstone National Park, USA
direct emissions from fractures in the Earth’s crust.
volcanoes vs humans
Volcanoes currently emit 0.15-0.26 Gt CO2 annually. In comparison, humans emit about 35 Gt, mainly from fossil fuel use, so volcanic degassing is relatively insignificant.
