Carbon on Earth
Carbon (C) is a hugely important element and can be found in many different compounds. The word Carbon comes from Latin word carbo which means "coal".1
Carbon is important because it is found in many different compounds. Carbon can be found;
• In the clothes you wear
• The food you eat
• In You!
• The cosmetics and sanitary products you use
• In building materials
• In hydrocarbons which power many of the appliances you use. 3
Carbon is the sixth most abundant element in the Milky Way Galaxy2 and the fourth most abundant element found on planet Earth. Carbon is essential as it is found in all living beings on Earth. It is the second most abundant element in the human body by mass after Oxygen.
Carbon comes in many different forms from the hardest substance known on Earth – diamonds, to other useful softer substances such as graphite (which is soft enough to use to write on paper).
Uses of Carbon
1. Diamond is used in jewellery and also in drills.
2. Carbon is used in the iron and steel industries
3. Graphite combined with clays form the 'lead' used in graphite pencils.
4. Carbon fibre is finding many uses as a very strong, yet lightweight, material. It is currently used in tennis rackets, skis, fishing rods, rockets and aeroplanes.
5. Graphite carbon in a powdered, caked form is used as charcoal for cooking, artwork and other uses.
6. Charcoal pills are used in medicine in pill or powder form to adsorb toxins or poisons from the digestive system.
7. Carbon is used for control rods in nuclear reactors.3
Carbon moves through the various “spheres” of the Earth in what is known as the Carbon Cycle. These spheres include the lithosphere, hydrosphere, cryosphere, biosphere, atmosphere. It moves through these spheres in many different forms but some important compounds of carbon include;
• Methane (CH4) - is a gas - one molecule of methane contains one carbon atom, surrounded by four hydrogen atoms. Methane is found in rocks in the lithosphere, in the oceans, in soils but also in the atmosphere. Methane is a greenhouse gas, and is produced by cows and landfill sites. It is also being released from the cryosphere.
• Carbon Dioxide (CO2) – is also a gas, found in the oceans, soils and the atmosphere and is released when we breath out.
• Hydrocarbons – these are any compounds of carbon that are found in sedimentary rocks in gas, solid or liquid form. Crude oil and natural gas are both hydrocarbons.
• Calcium carbonate (CaCO3) is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of pearls and the shells of marine organisms, snails, and eggs.
• Bio molecules in living things – these organic macromolecules contain carbon and the four major classes of biological macromolecules include carbohydrates, lipids, proteins, and nucleic acids. 5 Together, all these forms of carbon account for approximately half of the total dry mass of living things.
The origin of Carbon
The primary source of carbon today comes from inside of the Earth and was stored there when the Earth formed. It is thought that this Carbon arrived here as the Earth formed and from subsequent meteorite strikes. 4 This carbon is held within the Earth’s interior but escapes at constructive and destructive plate margins as well as at hot spot volcanoes.
The Carbon Cycle
The carbon cycle is another of those that works within the Earth’s systems. Just like Water, Carbon moves between different SPHERES on planet Earth, these spheres include the atmosphere, the biosphere, the lithosphere, the hydrosphere and the cryosphere.
When carbon is held in these spheres we consider them to be carbon pools (also called stocks or reservoirs) because they act as storage houses for large amounts of carbon. Net Carbon sinks are those pools where more carbon is added than leaves. Net carbon sources are those pools where more carbon leaves than is added.
Carbon Sink = Inputs of carbon>Outputs of carbon
Carbon source = Inputs of carbon
Any movement of carbon between the reservoirs is called a flux. 6 These fluxes vary in timescale from seconds to thousands of years. They can also result in feedback loops just like within the water cycle. If all sources are equal to all sinks, the carbon cycle can be said to be in dynamic equilibrium (or in balance) and there is no change in the size of the pools over time.
For example, over long periods of geologic time carbon dioxide returns to the atmosphere by decomposition of limestones subducted to the Earth's deep interior, releasing the carbon dioxide through gases dissolved in magmas that rise to the surface. Tectonic uplifting of carbonate rocks also causes them to be exposed to the atmosphere. Weathering processes release the trapped carbon, which can then pass into the oceans within precipitation. This carbon can then be taken up by sea creatures who use it in their shells. Their shells sink to the ocean bed upon death and are compressed into calcium carbonate rocks and the cycle begins again.
Major stores of carbon
The quantities of carbon in the Earth’s major carbon pools can be enormous so it is inconvenient to use familiar units such as pounds or kilograms. The United Nations Intergovernmental Panel on Climate Change (IPCC) use Gigatonnes of carbon dioxide equivalent (GtC) to measure the stores of carbon. One GtC is a billion (1,000,000,000) tonnes and can also be referred to as a Petagram.
The lithosphere includes the upper most part of Earth’s mantle and the crust – together these make up the hard sections of our Earth’s outer layer. The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The lithosphere contains both inorganic carbon such as shale gas, coal, oil, gas and limestone, and organic carbon such as organic matter in soils and leaf litter.
The lithosphere contains by far the largest amount of carbon on Earth, much of which is stored in sedimentary rocks within the planet’s crust. These carbon containing rocks are produced by;
1. The hardening of mud (containing organic matter) into shale over geological time or
2. The collection of calcium carbonate particles, from the shells and skeletons of marine organisms, into limestone and other carbon containing sedimentary rocks.
Together all sedimentary rocks on Earth store up to 100 million GtC, which represents a large mass of carbon!
Another 4,100 GtC is stored in the Earth’s crust as hydrocarbons formed over millions of years from ancient living organisms under intense temperature and pressure. These hydrocarbons are commonly known as fossil fuels such as coal, oil and gas. 6
The Hydrosphere & carbon
The hydrosphere consists of all of the water bodies on Earth. The Oceans are very important carbon source and store, there are many fluxes or exchanges or carbon between the ocean store and the atmosphere, and also with the deep oceans.
The Earth’s oceans contain 38,000 GtC 6, which can split into;
• 900 GtC in the surface layers of the ocean. Here the sunlight can penetrate into the water allowing photosynthesis to happen. This carbon is exchanged rapidly with the atmosphere through both physical processes, such as CO2 gas dissolving into the water, and biological processes, such as the growth, death and decay of plankton. Most of this surface carbon cycles rapidly, some of it can also be transferred by sinking to the deep ocean pool where it can be stored for a much longer time.
• 39,100GtC in the intermediate zone of the oceans – this makes up most of the carbon in the oceans and is in the form of dissolved inorganic carbon stored at great depths where it resides for long periods of time. 10
When organisms such as Coccoliths die in the oceans their shells sink to the bottom. These shells are rich in Calcium Carbonate and are slowly compressed over time into layers of Chalk. This locks up hydrospheric carbon in the lithosphere
The Cryosphere and carbon
The cold parts of our globe store a lot of carbon. The are 2 potential sources of carbon in the form of methane in the cryosphere;
1. Methyl clathrates are molecules of methane that are frozen into ice crystals. These molecules form under high pressure and low temperatures deep in the Earth or underwater. These are special conditions, and if the temperature rises or pressure changes, the ice that imprisons the methane will break apart, and the methane will escape.
2. Organic matter frozen in permafrost. Permafrost is permanently frozen ground, and it contains a lot of frozen organic matter. This organic matter is made of dead plants and animals that have been frozen deep in permafrost for thousands of years. The carbon in this organic matter is locked up because it is frozen. With global warming, if this permafrost melts the organic matter will decay, rand this will release carbon dioxide or methane into the atmosphere.
Both of these sources are problematic as it traps heat about twenty times as efficiently as carbon dioxide (however, there is much less methane in the atmosphere than carbon dioxide).
It is estimated that there are about 1,400 gigatons of carbon frozen in permafrost.12
The biosphere includes the regions of the surface and atmosphere of the earth or another planet occupied by living organisms. It contains all of the world’s ecosystems and is thought to contain 3170GtC. On Earth, the terrestrial ecosystems contain carbon in the form of plants, animals, soils and microorganisms (bacteria and fungi). Of these, plants and soils are by far the largest and, when dealing with the entire globe, the smaller pools are often ignored. Most of the carbon in terrestrial ecosystems exists in organic forms, unlike in the lithosphere and hydrosphere. The term “organic” refers to compounds produced by living things, including leaves, wood, roots, dead plant material and the brown organic matter in soils (which is the decomposed remains of formerly living tissues). 6
Within the biosphere;
1. The Earth’s plants store approximately 560 GtC, with the wood in trees being the largest fraction (woody stems have the greatest ability to store large amounts of carbon, because wood is dense and trees can be large). The pie chart shows the various percentages of the carbon that the world’s ecosystems have. This shows that forests do indeed store the most carbon.
2. The world’s soils carbon content is estimated to be 1500 GtC.
3. Peat contains over 250GtC. Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires and moors. It is created in anaerobic conditions and keeps carbon locked up.
4. Litter – the decaying remains of plants, contain carbon, and this can be released over time via decomposition.
The Atmosphere and carbon
The atmosphere is a small store of carbon relative to the other stores. It contains approximately 750 GtC 6, the majority of which is in the form of CO2, with much smaller amounts of methane (CH4) and various other compounds.
Despite the small size of the store, carbon in the atmosphere is of great importance because of its influence on the greenhouse effect and climate. The relatively small size of the atmospheric C pool also makes it more sensitive to disruptions caused by an increase in sources or sinks of C from the Earth’s other pools.
Carbon in the atmosphere is measured in parts per million. Deforestation and fossil fuel combustion have added to this store which has been monitored at the Mauna Loa Observatory (MLO) atmospheric research facility. It has been continuously monitoring and collecting data related to atmospheric change since the 1950's. The station has measured CO2 concentrations over 400ppm despite pre industrial revolution levels of less than 280ppm.
1 – Wikipedia, 2018, Carbon – retrieved 23rd November 2018 from https://en.wikipedia.org/wiki/Carbon
2 - Education for the Information Age, 1999, The Carbon Atom – retrieved 23rd November 2018 from http://www.edinformatics.com/math_science/c_atom.htm
3 – Royal Society of Chemistry, 2018, Periodic Table: Carbon – retrieved 23rd November 2018 from http://www.rsc.org/periodic-table/element/6/carbon
4 – George Shaw, 2006, A (Not So) Brief History of Carbon on Earth, NASA Astrobiology Institute. Retrieved 23rd November 2018 from https://nai.nasa.gov/seminars/featured-seminar-channels/university-of-washington-seminars/2006/10/24/a-not-so-brief-history-of-carbon-on-earth/
5 - Charles Molnar and Jane Gair, Concepts of Biology-1st Canadian Edition, retrieved 2nd December 2018 from https://opentextbc.ca/biology/chapter/2-3-biological-molecules/
6 – The University of New Hampshire, 2008, An introduction to the global carbon cycle - retrieved 2nd December 2018 from http://globecarboncycle.unh.edu/CarbonCycleBackground.shtml
7 – Andy Day & Tutor2U, Introduction to Carbon and Carbon Stores, retrieved 2nd December 2018 from https://www.tutor2u.net/geography/reference/carbon-and-carbon-stores-explained
8 - Kevin Schaefer, Hugues Lantuit, Vladimir E Romanovsky, Edward A G Schuur and Ronald Witt, 2014, The impact of the permafrost carbon feedback on global climate retrieved 2nd December 2018 from http://iopscience.iop.org/article/10.1088/1748-9326/9/8/085003/pdf
9 - “Geography for A-level and AS”, pages 27 to 29, Skinner et al, Hodder Education, 2016
10 - National Center for Atmospheric Research Staff (Eds). Last modified 31 Jan 2014. "The Climate Data Guide: GLODAP: GLobal Ocean Data Analysis Project for Carbon." Retrieved from https://climatedataguide.ucar.edu/climate-data/glodap-global-ocean-data-analysis-project-carbon
11 – Food and Agriculture Organisation, Climate change and forests, Retrieved from http://www.fao.org/docrep/003/y0900e/y0900e06.htm
12 - Kevin Schaefer of National Snow and Ice Data Center, 2018. Methane and Frozen Ground. Retrieved from https://nsidc.org/cryosphere/frozenground/methane.html
Written by Rob Gamesby