Carbon 6.1 Flashcards
what is carbon?
- The building block of life – sustains life by moving around the Earth through the carbon cycle
- Found in oceans, rocks, soils, the atmosphere and all forms of life
- Carbon cycle is out of balance due to human activities (deforestation, car emissions)
the carbon cycle
the biochemical cycle by which carbon moves from one Earth sphere (atmosphere, hydrosphere, lithosphere, biosphere) to another.
what kind of system is the carbon cycle?
-It is a closed system but made up of interlinked subsystems which are open and have inputs and outputs.
What does complete decomposition of carbon result in?
Complete decomposition of organic matter results in carbon returning to inorganic forms such as CO2 and carbonates contained in rock and seawater.
What processes drive the fluxes?
-Process including photosynthesis and diffusion drive the fluxes between the stores, operating at both global and local stores
If sinks and sources are equal…
-If sinks and the sources are equal, the carbon cycle is balanced, with no change in the size of the stores
Fluxes
– movements of organic compounds through an ecosystem
Describe feedback in the carbon cycle
- The earth systems usually operate with negative feedbacks (stabilising) which helps it maintain a stable state
- Positive (amplifying) feedback loops occur when a small change in one component causes changes in other components
- This shifts systems away from its previous state and towards a new one
two main components of carbon cycle
- Stores – function as sources adding carbon to the atmosphere and sinks removing carbon from the atmosphere
- Fluxes – movements of carbon from one store to another, they provide the motion in the carbon cycle
How did the carbon cycle develop to create a habitable planet?
- Primitive bacteria (Cyanobacteria) started photosynthesising about 3 billion years ago (the earth has been around for 4.5 billion years according to scientists)
- This created more oxygen in the air, which allowed more complex organisms to develop around 2 billion years ago
- CO2 from the atmosphere started to dissolve in seawater in the early oceans and slowly became stored in sedimentary rocks
- This accelerated when land-based ecosystems developed about 400 million years ago
- Earth established its present carbon cycle around 290 million years ago
- The balance has been altered since 1800 by human activities (deforestation and burning fossil fuels)
What are the different stores of the carbon cycle?
- Atmosphere – as carbon dioxide and carbon compounds, such as methane
- Hydrosphere – dissolved carbon dioxide
- Lithosphere – as carbonate in limestones, chalk and fossil fuels, as pure carbon in graphite and diamonds
- Biosphere – as carbon atoms living in living and dead organisms (includes terrestrial and oceanic locations)
Anthropogenic
– processes and actions associated with human activity
Sizes of stores
Sedimentary rock store = 83,000,000 PgC
-Sedimentary rocks, very slowly cycling over millions of years
Ocean floor calcareous ooze store = 1,750 PgC
Terrestrial ecosystem store = 550 PgC
-CO2 is taken from the atmosphere by plant photosynthesis; carbon is stored organically, especially in trees; rapid interchange with atmosphere over seconds
sizes of fluxes
Respiration and fire = 118.7 = PgC/yr
Photosynthesis = 123 PgC/yr
Fossil fuel use and cement production = 7.8 PgC/yr
Rock weathering = 0.4 PgC/yr
What is the geological carbon cycle?
- Huge carbon stores in rocks and sediments
- Organic matter that is buried in deep sediments, protected from decay and takes millions of years to turn into fossil fuels
- Carbon is exchanged with the fast component through volcanic emissions of CO2, chemical weathering, erosion and sediment formation on the sea floor
Sequestering
the natural storage of carbon by physical or biological processes such as photosynthesis
Why are some fluxes fast and some slower?
- Photosynthesis and respiration is the quickest cycle which is completed in seconds – plants take carbon from atmosphere and release through respiration
- They are the fastest as they are happening continually
Factors affecting the speed of fluxes?
- Sunlight
- Temperature
- Moisture availability
- Levels of CO2
- Latitude
- Regional climates
- Carbon is an organic matter so can take a long time to flux into another store as some it may be frozen or stored in anaerobic conditions preventing decomposition – slowly converts to sedimentary rocks
- Dead organic material in soils may retain carbon for years as it waits to be broken down
- The carbon dioxide dead organisms eventually makes its way to the sea via the soil and decomposition
- Some organic materials may become buried so deeply they never decay and instead transform into sedimentary rocks (limestone or coal) or into hydrocarbons like oil and natural gas
- CO2 is only released from hydrocarbons when they are burned or when limestone is used industrially (cement)
How do fluxes vary with latitude?
-Levels are always higher in northern hemisphere – as it contains greater landmasses and greater temperature variations than in the southern hemisphere
Why is carbon important?
- Plays a key role in regulating the Earth’s climate by controlling the concentration of carbon dioxide in the atmosphere
- Carbon dioxide (CO2) is important because it contributes to the greenhouse effect, in which heat generated from sunlight at the Earth’s surface is trapped by certain gasses and prevented from escaping through the atmosphere.
- The greenhouse effect itself is a perfectly natural phenomenon and, without it, the Earth would be a much colder place.
- But as is often the case, too much of a good thing can have negative consequences, and an unnatural build-up of greenhouse gasses can lead to a planet that gets unnaturally hot.
three forms of carbon found on earth
- Inorganic/ geologic – found in rocks such as limestone (calcium carbonate) – the largest store
- Organic/ biologically derived – found in plant material – trees
- Gaseous – found as CO2, CH4 and CO
chemical weathering
- In the atmosphere, water reacts with atmospheric CO2 and carbonic acid
- This water reaches the surface as rain which reacts with some surface minerals, slowly dissolving them into their component ions
transportation
- Of calcium ions by rivers from the land into the oceans
- These combine with bicarbonate ions to form calcium carbonate and precipitate out as minerals
deposition
-Deposition and the burial turns the calcite sediment into limestone
Subduction
- Subduction of the sea floor under continental margins by tectonic spreading
- Some of this carbon rises to surface within heated magma and then is degassed as CO2 and returned to atmosphere
Volcanic outgassing
- Pockets of CO2 exists in the Earth’s crust and disturbance by volcanic eruptions or earthquake activity may allow pulses into the atmosphere
- Occurs in these: subductions zones and divergent, fractures from earth’s crust, hot springs
Sedimentary rocks
- Shells and Skeletons of organisms sink to bottom and are collected in layers = calcareous ooze
- Sea became shallow and silt layer was formed, creating layers as they are compressed
What type of cycle occurs quickly?
The geological carbon cycle happens over a long time period compared to the biological one
Negative feedback mechanism regulates the natural carbon cycle:
- Increase volcanic activity
- Rise in CO2 emissions and loss of carbon from rocks
- Temperature rises
- More uplift of air, condensation and rain
- More chemical weathering and erosion of rocks
- More ions deposited on ocean floors
- More carbon stored in rocks
Types of outgassing
- Divergent and subduction zones – where outgassing occurs
- Mantle plumes – outgassing occurs – gas pitoning – biggest contribution to outgassing
- Mid ocean ridges
- Geothermal activity
- Fumaroles
- Rift valleys
What are the 2 ways that carbon gets released as a gas at a subduction zones?
- CO2 combines with water in the atmosphere to create carbonic acid
- This chemically weathers carbon rich rocks producing soluble bicarbonates
- This is washed into rivers and to the ocean
Metamorphosis
the layering and burial of sediment causes pressure to build, which eventually becomes so great that deeper sediments are changed into rock: shale becomes slate and limestone becomes marble.
How do carbon rich sedimentary rocks form?
-Sea life and vegetation dies and sinks to the bottom to be compressed and turn into limestone, chalk, coal, oil and gas
How is carbon is limestone and shale?
- One of the largest stores on earth is the Himalayas – this started off as oceanic sediments rich in calcium carbonate
- Folded up by mountain building, this carbon is being actively weathered, eroded and transported back to the oceans
- Most of the carbon containing rocks in the oceans is from shell-building (calcifying) organisms such as corals and planktons
- These are precipitated on to the ocean floor, forms layers and are cemented together and lithified into limestone
- Some of the rocks contain organic carbon from organisms that have been embedded in layers of mud
- Over millions of years heat and pressure compress the mud and carbon, forming sedimentrey rocks such as shale
How is carbon is fossil fuels?
- Dead organisms sink to the bottom of rivers and seas
- Covered in silt and mud and then start to decay anaerobically
- The deeper the deposit, the more heat and pressure is exerted
- When organic matter builds up faster than it can decay, layers of organic carbon become oil, coal or natural gas instead of shale
How is carbon in coal?
- Formed from the remains of trees, ferns and other plants
- Anthracite – the hardest – it has the most carbon and highest energy content
- Bituminous coals – next in hardness and carbon content
- Lignite and Brown coal – soft coals – lower content of coal and energy potential; these are the major global source of energy supplies but emit more CO2 than hard coals
- Peat – the stage before coal, it is an important carbon and energy source
- Combustible rock made by carbon
- Plants died and fell into swamps
- Swamp conditions – don’t allow it to decompose due to lack of oxygen
- Intense heat and pressure of these creates coal
Lithification
process of compaction and cementation to eventually form carbon rich rocks like Limestone over thousands of years
How is carbon in oil?
- Plankton in the sea die and settle to the bottom
- No oxygen available for decomposition – anaerobic conditions
- Sediment builds up on top and compresses
- Pressure converts it into a oil and the moisture is pushed out
- The liquid moves up through the permeable rock layer and collects underneath the impermeable rock layer (gases collect up that)
- Permeable rock – will collect underneath this rock and the gas will collect at the top
Sedimentary carbonate rocks
- Limestone rocks contain a high concentration of calcium carbonate which is formed partly from the shells and skeletons of marine creatures such as corals, that extracted the mineral from the seawater and also from the marine phytoplankton that absorb carbon through photosynthesis.
- Their remains accumulate on the seabed where over long periods of rime they are cemented and compacted into organic limestone rock.
- Limestone may also form from direct precipitation of calcium carbonate from salt or freshwater or from the evaporation of seawater, which leaves behind calcium carbonate deposits.
Why are limestone rocks are vulnerable to chemical weathering?
-Rain becomes a week carbonic acid when it falls through the air and it dissolves the calcium carbonate, allowing erosions processes to transfer dissolved carbon for deposition on the seabed
