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Learn how carbon moves through Earth's ecosystems and how human activities are altering the carbon cycle.
Key points
Carbon is an essential element in the bodies of living organisms. It is also economically important to modern humans, in the form of fossil fuels.
Carbon dioxide—
—from the atmosphere is taken up by photosynthetic organisms and used to make organic molecules, which travel through food chains. In the end, the carbon atoms are released as in respiration.Slow geological processes, including the formation of sedimentary rock and fossil fuels, contribute to the carbon cycle over long timescales.
Some human activities, such as burning of fossil fuels and deforestation, increase atmospheric
and affect Earth's climate and oceans.
Carbon: building block and fuel source
About 18% of your body consists of carbon atoms, by mass, and those carbon atoms are pretty key to your existence!
Carbon is part of our bodies, but it's also part of our modern-day industries. Carbon compounds from long-ago plants and algae make up the fossil fuels, such as coal and natural gas, that we use today as energy sources. When these fossil fuels are burned, carbon dioxide—
Let's take a look at the carbon cycle and see how atmospheric
The carbon cycle
The carbon cycle is most easily studied as two interconnected subcycles:
One dealing with rapid carbon exchange among living organisms
One dealing with long-term cycling of carbon through geologic processes
Although we will look at them separately, it's important to realize these cycles are linked. For instance, the same pools of atmospheric and oceanic
As a brief overview, carbon exists in the air largely as carbon dioxide—
Longterm storage of organic carbon occurs when matter from living organisms is buried deep underground or sinks to the bottom of the ocean and forms sedimentary rock. Volcanic activity and, more recently, human burning of fossil fuels bring this stored carbon back into the carbon cycle. Although the formation of fossil fuels happens on a slow, geologic timescale, human release of the carbon they contain—as
The biological carbon cycle
Carbon enters all food webs, both terrestrial and aquatic, through autotrophs, or self-feeders. Almost all of these autotrophs are photosynthesizers, such as plants or algae.
Autotrophs capture carbon dioxide from the air or bicarbonate ions from the water and use them to make organic compounds such as glucose. Heterotrophs, or other-feeders, such as humans, consume the organic molecules, and the organic carbon is passed through food chains and webs.
How does carbon cycle back to the atmosphere or ocean? To release the energy stored in carbon-containing molecules, such as sugars, autotrophs and heterotrophs break these molecules down in a process called cellular respiration. In this process, the carbons of the molecule are released as carbon dioxide. Decomposers also release organic compounds and carbon dioxide when they break down dead organisms and waste products.
Carbon can cycle quickly through this biological pathway, especially in aquatic ecosystems. Overall, an estimated 1,000 to 100,000 million metric tons of carbon move through the biological pathway each year. For context, a metric ton is about the weight of an elephant or a small car!
The geological carbon cycle
The geological pathway of the carbon cycle takes much longer than the biological pathway described above. In fact, it usually takes millions of years for carbon to cycle through the geological pathway. Carbon may be stored for long periods of time in the atmosphere, bodies of liquid water—mostly oceans— ocean sediment, soil, rocks, fossil fuels, and Earth’s interior.
The level of carbon dioxide in the atmosphere is influenced by the reservoir of carbon in the oceans and vice versa. Carbon dioxide from the atmosphere dissolves in water and reacts with water molecules in the following reactions:
The carbonate—
On land, carbon is stored in soil as organic carbon from the decomposition of living organisms or as inorganic carbon from weathering of terrestrial rock and minerals. Deeper under the ground are fossil fuels such as oil, coal, and natural gas, which are the remains of plants decomposed under anaerobic—oxygen-free—conditions. Fossil fuels take millions of years to form. When humans burn them, carbon is released into the atmosphere as carbon dioxide.
Another way for carbon to enter the atmosphere is by the eruption of volcanoes. Carbon-containing sediments in the ocean floor are taken deep within the Earth in a process called subduction, in which one tectonic plate moves under another. This process forms carbon dioxide, which can be released into the atmosphere by volcanic eruptions or hydrothermal vents.
Human impacts on the carbon cycle
Global demand for Earth’s limited fossil fuel reserves has risen since the beginning of the Industrial Revolution. Fossil fuels are considered a nonrenewable resource because they are being used up much faster than they can be produced by geological processes.
When fossil fuels are burned, carbon dioxide—
Some of the extra
That is a great question, one whose answer we still don't fully know.
The changes in
For our purposes here, the key point is that the
Why does it matter that there is lots of
Also, while uptake of excess carbon dioxide by the oceans might seem good from a greenhouse gas perspective, it may not be good at all from the perspective of sea life. As we saw above,
The debate about the future effects of increasing atmospheric carbon on climate change focuses on fossils fuels. However, scientists must take natural processes, such as volcanoes, plant growth, soil carbon levels, and respiration, into account as they model and predict the future impact of this increase.
Attribution
This article is a modified derivative of the following articles:
"Biogeochemical cycles" by Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne, CC BY 4.0; download the original article for free at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.18
"Biogeochemical cycles" by OpenStax College, Concepts of Biology, CC BY 4.0; download the original article for free at http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10
"The carbon cycle - Advanced" by Douglas Wilkin and Jean Brainerd, CK-12 Foundation, CC BY-NC 3.0.
The modified article is licensed under a CC BY-NC-SA 4.0 license.
Works cited
"Composition of the Human Body," Wikipedia, last modified June 10, 2016, https://en.wikipedia.org/wiki/Composition_of_the_human_body.
"The Fast Carbon Cycle," NASA Earth Observatory, accessed June 10, 2016, http://earthobservatory.nasa.gov/Features/CarbonCycle/page3.php.
Colin Peters, "What Animal Weights a Metric Ton? [Answer]," Answers, accessed June 10, 2016, http://www.answers.com/Q/What_animal_weighs_a_metric_ton.
"What Is an Example of Something That Weighs a Metric Ton? [Answer]," Blurtit, accessed June 10, 2016, http://science.blurtit.com/1562903/what-is-an-example-of-something-that-weighs-a-metric-ton.
"The Slow Carbon Cycle," NASA Earth Observatory, accessed June 10, 2016, http://earthobservatory.nasa.gov/Features/CarbonCycle/page2.php.
"Deforestation and the Carbon Cycle," accessed June 10, 2016, http://ecosystems.wcp.muohio.edu/studentresearch/climatechange03/deforestation/index2.html.
Daniel Sigman and Edward A. Boyle, "Glacial/Interglacial Variations in Atmospheric Carbon Dioxide," Nature 407 (2000): 859, http://dx.doi.org/10.1038/35038000.
Intergovernmental Panel on Climate Change, "Projected Changes in the Climate System," in Climate Change 2014 Synthesis Report Summary for Policymakers (2014), 10. http://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf.
"Ocean Acidification," Wikipedia, last modified June 6, 2016, https://en.wikipedia.org/wiki/Ocean_acidification.
References
"Agriculture Sector Emissions." United States Environmental Protection Agency. Last modified on May 26, 2016. https://www3.epa.gov/climatechange/ghgemissions/sources/agriculture.html.
"Autotroph." National Geographic Society. Accessed June 10, 2016. http://nationalgeographic.org/encyclopedia/autotroph/.
"Carbon Cycle." Wikipedia. Last modified June 9, 2016. https://en.wikipedia.org/wiki/Carbon_cycle.
"Carbon Dioxide in Earth's Atmosphere." Wikipedia. Last modified June 5, 2016. https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere.
"Composition of the Human Body." Wikipedia. Last modified June 10, 2016. https://en.wikipedia.org/wiki/Composition_of_the_human_body.
"Deforestation and the Carbon Cycle." Accessed June 10, 2016. http://ecosystems.wcp.muohio.edu/studentresearch/climatechange03/deforestation/index2.html.
"Deforestation." Wikipedia. Last modified May 29, 2016. https://en.wikipedia.org/wiki/Deforestation.
"Effects of Changing the Carbon Cycle." NASA Earth Observatory. Last accessed June 10, 2016. http://earthobservatory.nasa.gov/Features/CarbonCycle/page5.php.
"Fossil Fuel." Wikipedia. Last modified June 10, 2016. https://en.wikipedia.org/wiki/Fossil_fuel.
Intergovernmental Panel on Climate Change. "Projected Changes in the Climate System." In Climate Change 2014 Synthesis Report Summary for Policymakers, 10-13. 2014. http://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf.
Marsh, Gerald E. "Interglacials, Milankovitch Cycles, and Carbon Dioxide." Argonne National Laboratory. Accessed July 10, 2016. https://arxiv.org/pdf/1002.0597.pdf.
"Ocean Acidification." Wikipedia. Last modified June 6, 2016. https://en.wikipedia.org/wiki/Ocean_acidification.
"Oceanic Carbon Cycle." Wikipedia. Last modfied April 20, 2016. https://en.wikipedia.org/wiki/Oceanic_carbon_cycle.
Peters, Colin. "What Animal Weights a Metric Ton? [Answer]." Answers. Accessed June 10, 2016. http://www.answers.com/Q/What_animal_weighs_a_metric_ton.
Raven, Peter H., George B. Johnson, Kenneth A. Mason, Jonathan B. Losos, and Susan R. Singer. "Biogeochemical Cycles." In Biology, 1209-1214.1 0th ed., AP ed. New York: McGraw-Hill, 2014.
Sigman, Daniel and Edward A. Boyle. "Glacial/Interglacial Variations in Atmospheric Carbon Dioxide." Nature 407 (2000): 859-869. http://dx.doi.org/10.1038/35038000.
"Soil Carbon." Wikipedia. Last modified June 4, 2016. https://en.wikipedia.org/wiki/Soil_carbon.
"The Fast Carbon Cycle." NASA Earth Observatory. Accessed June 10, 2016. http://earthobservatory.nasa.gov/Features/CarbonCycle/page3.php.
"The Slow Carbon Cycle." NASA Earth Observatory. Accessed June 10, 2016. http://earthobservatory.nasa.gov/Features/CarbonCycle/page2.php.
"What Is an Example of Something That Weighs a Metric Ton? [Answer]." Blurtit. Accessed June 10, 2016. http://science.blurtit.com/1562903/what-is-an-example-of-something-that-weighs-a-metric-ton.
Log in Isaac D. Cohen 6 years agoPosted 6 years ago. Direct link to Isaac D. Cohen's post “The article says in the s...” The article says in the section entitled "Human Impacts on the Carbon Cycle" that more carbon dioxide dissolving in water is not a good thing because it produces bicarbonate along with H+ ions which can in turn reduce the levels of bicarbonate. Am I missing something? The only way increased carbon dioxide will lead to more H+ ions in the water is through producing bicarbonate. All that will happen is that same bicarbonate will be taken out by its own H+ ions, which if they weren't there, the bicarbonate wouldn't be there either. So what's the big deal? Also, why can't the H+ ions dissolve into the atmosphere? • (6 votes) samuelyung758 2 years agoPosted 2 years ago. Direct link to samuelyung758's post “when carbon dioxide disso...” when carbon dioxide dissolves in water it produces hydrogen ion. the water becomes acidic because of the hydrogen ions dissolved in it (2 votes) 🎆M🎆A🎆R🎆I🎆A🎆P🎆A🎆U🎆L🎆A🎆 4 years agoPosted 4 years ago. Direct link to 🎆M🎆A🎆R🎆I🎆A🎆P🎆A🎆U🎆L🎆A🎆's post “what will happen if we di...” what will happen if we did not had athmosphere? • (4 votes) Ivana - Science trainee 4 years agoPosted 4 years ago. Direct link to Ivana - Science trainee's post “We probably wouldn't able...” We probably wouldn't able to breathe - not just humans but other oxic and anoxic organisms. Also, Earth would look like it looked way before atmosphere formed - full fo craters, volcanoes, extreme thunderstorms, extreme drought, UV light from the sun, etc... Eroded lithosphere and unfriendly environment. (7 votes) iyanapierre2003 6 years agoPosted 6 years ago. Direct link to iyanapierre2003's post “how many carbon dioxide a...” how many carbon dioxide are there in the atmosphere • (2 votes) tyersome 6 years agoPosted 6 years ago. Direct link to tyersome's post “According to NASA§ the to...” According to NASA§ the total mass of earth's atmosphere is 5.1 x 10¹⁸ kg. As of 2018 the fraction of the atmosphere that is CO₂ is 622 parts per million by mass (409 ppm by volume). So, since the mass of CO₂ is ~44 g/mol and using Avogadro's number: § https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html (9 votes) Lamiaa Hatem 7 years agoPosted 7 years ago. Direct link to Lamiaa Hatem's post “Explain Carbon reservoirs” Explain Carbon reservoirs • (2 votes) Benjamin Hsieh 7 years agoPosted 7 years ago. Direct link to Benjamin Hsieh's post “There are four carbon res...” There are four carbon reservoirs (8 votes) Kaitlyn Hults 7 years agoPosted 7 years ago. Direct link to Kaitlyn Hults's post “Does the carbon cycle hap...” Does the carbon cycle happen in human bones? (for example, after death) • (3 votes) Hugo Lerming Lerminguez 7 years agoPosted 7 years ago. Direct link to Hugo Lerming Lerminguez's post “maybe to a tiny extent as...” maybe to a tiny extent as there is a lot of organic matter inside of bones (think marrow), but the main component of bone is hydroxylapatite (aka hydroxyapatite) and this has no carbon in the repeating formula unit (Ca5(PO4)3(OH)). this is probably why bones last a long time whereas the "meatier" parts of the animal essential disappear. (1 vote) andreancheng 5 years agoPosted 5 years ago. Direct link to andreancheng's post “What are the similarities...” What are the similarities and differences between carbon cycle and energy flow? • (2 votes) Ivana - Science trainee 5 years agoPosted 5 years ago. Direct link to Ivana - Science trainee's post “Comparison of different s...” Comparison of different scales. I'd understand comparisons of the Carbon cycle to the Nitrogen cycle, but the comparison to energy flow... Energy flow is something that happens and inseparable from element cycles in the biosphere. (2 votes) cookiemonster🍪 4 years agoPosted 4 years ago. Direct link to cookiemonster🍪's post “Hi! I just had a quick qu...” Hi! I just had a quick question: Is calcium carbonate limestone? • (2 votes) Arpit M. 4 years agoPosted 4 years ago. Direct link to Arpit M.'s post “Limestone is largely made...” Limestone is largely made of the mineral forms of Calcium Carbonate , but also has few other particles such as clay and quartz. (2 votes) maria.piplos 5 years agoPosted 5 years ago. Direct link to maria.piplos's post “how does a carbon molecul...” how does a carbon molecule from the deep ocean travel from an animal? • (1 vote) The Lone Fox 4 years agoPosted 4 years ago. Direct link to The Lone Fox's post “Deep sea oil drills take ...” Deep sea oil drills take it, an oil spill occurs, it winds up on and in the sea, and is absorbed by marine lifeforms. (1 vote) May Moe 2 years agoPosted 2 years ago. Direct link to May Moe's post “how the carbon present in...” how the carbon present in sugars in the plants is returned to the atmosphere in the carbon cycle • (2 votes) Davin V Jones 2 years agoPosted 2 years ago. Direct link to Davin V Jones's post “As per the article: "Orga...” As per the article: "Organic molecules made by photosynthesizers are passed through food chains, and cellular respiration converts the organic carbon back into carbon dioxide gas." (2 votes) Gwendolyn Davis 4 years agoPosted 4 years ago. Direct link to Gwendolyn Davis's post “what is the humans affect...” what is the humans affect in water why cant we breath in water • (2 votes)Want to join the conversation?
5.1 x 10²¹ g ⋅ 6.22 x 10⁻⁴ / 44 g/mol ⋅ 6.022 x 10²³ molecule/mol ≈ 4.3 x 10⁴⁰ molecules of CO₂
1. In rocks (this includes fossil fuels)
2. Dissolved in ocean water.
3. As plants, sticks, animals, and soil (which can be lumped together and called the land biosphere)
4. As a climate-warming gas in the atmosphere.