- Intro to biogeochemical cycles
- Biogeochemical cycles overview
- The water cycle
- The water cycle
- The carbon cycle
- The carbon cycle
- The nitrogen cycle
- The nitrogen cycle
- The phosphorus cycle
- Phosphorus cycle
- Eutrophication and dead zones
- Biogeochemical cycles
The carbon cycle
Learn how carbon moves through Earth's ecosystems and how human activities are altering the carbon cycle.
- 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! Without carbon, you wouldn't have the plasma membranes of your cells, the sugar molecules you use for fuel, or even the that carries instructions to build and run your body.
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——is released into the air, leading to higher and higher levels of atmospheric . This increase in levels affects Earth's climate and is a major environmental concern worldwide.
Let's take a look at the carbon cycle and see how atmospheric and carbon use by living organisms fit into the bigger picture of carbon cycling.
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 that are utilized by organisms are also fed and depleted by geological processes.
As a brief overview, carbon exists in the air largely as carbon dioxide——gas, which dissolves in water and reacts with water molecules to produce bicarbonate—. Photosynthesis by land plants, bacteria, and algae converts carbon dioxide or bicarbonate into organic molecules. Organic molecules made by photosynthesizers are passed through food chains, and cellular respiration converts the organic carbon back into carbon dioxide gas.
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 —is on a very fast timescale.
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——released in this process combines with ions to make calcium carbonate——a key component of the shells of marine organisms. When the organisms die, their remains may sink and eventually become part of the sediment on the ocean floor. Over geologic time, the sediment turns into limestone, which is the largest carbon reservoir on Earth.
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——is released into the air. Increasing use of fossil fuels has led to elevated levels of atmospheric . Deforestation—the cutting-down of forests—is also a major contributor to increasing levels. Trees and other parts of a forest ecosystem sequester carbon, and much of the carbon is released as if the forest is cleared.
Some of the extra produced by human activities is taken up by plants or absorbed by the ocean, but these processes don't fully counteract the increase. So, atmospheric levels have risen and continue to rise. levels naturally rise and fall in cycles over long periods of time, but they are higher now than they have been in the past 400,000 years, as shown in the graph below:
Why does it matter that there is lots of in the atmosphere? is a greenhouse gas. When in the atmosphere, it traps heat and keeps it from radiating into space. Based on extensive evidence, scientists think that elevated levels of and other greenhouse gases are causing pronounced changes in Earth's climate. Without decisive changes to reduce emissions, Earth's temperature is projected to increase by 1 to 5C by the year 2100.
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, dissolved in seawater can react with water molecules to release ions. So, dissolving more in water causes the water to become more acidic. More acidic water can, in turn, reduce concentrations and make it harder for marine organisms to build and maintain their shells of . Both increasing temperatures and higher acidity can harm sea life and have been linked to coral bleaching.
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.
Want to join the conversation?
- 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?(5 votes)
- when carbon dioxide dissolves in water it produces hydrogen ion. the water becomes acidic because of the hydrogen ions dissolved in it(2 votes)
- what will happen if we did not had athmosphere?(4 votes)
- 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.(6 votes)
- how many carbon dioxide are there in the atmosphere(2 votes)
- 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:
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
§ https://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html(9 votes)
- Explain Carbon reservoirs(2 votes)
- There are four carbon reservoirs
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.(8 votes)
- Does the carbon cycle happen in human bones? (for example, after death)(3 votes)
- 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)
- What are the similarities and differences between carbon cycle and energy flow?(2 votes)
- 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)
- Hi! I just had a quick question:
Is calcium carbonate limestone?(2 votes)
- Limestone is largely made of the mineral forms of Calcium Carbonate , but also has few other particles such as clay and quartz.(2 votes)
- how does a carbon molecule from the deep ocean travel from an animal?(1 vote)
- 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)
- what is the humans affect in water why cant we breath in water(2 votes)
- What is biogeochemical cycle?(1 vote)
- A biogeochemical cycle is a pathway by which certain chemical (in this case Carbon) travels through Earth (abiotic and biotic).(2 votes)