The Carbon Cycle
The carbon cycle is nature's way of reusing carbon atoms, which travel from the atmosphere into organisms in the Earth and then back into the atmosphere over and over again. Most carbon is stored in rocks and sediments, while the rest is stored in the ocean, atmosphere, and living organisms. Nov 21, · The movement of carbon from reservoir to reservoir is known as the carbon cycle. Carbon can be stored in a variety of reservoirs, including plants and animals, which is why they are considered carbon life forms.
Carbon cyclein biology, circulation of carbon in various forms through nature. Carbon is a constituent of all organic compoundsmany of which are essential to life on Earth. The source of the carbon found in living matter is carbon dioxide CO 2 in the air or dissolved in water.
Algae and terrestrial green plants producers are the chief agents of carbon dioxide fixation through the process of photosynthesisthrough which carbon dioxide and water are converted into simple carbohydrates. These compounds are used by the producers to carry on metabolism, the excess being stored what is a carbon cycle fats and polysaccharides.
The stored products are then eaten by consumer organisms, from protozoans to man, which convert them into other forms. CO 2 is added directly to the atmosphere by cylce and some other q as a by-product of respiration. The carbon present in animal wastes and in the bodies of all organisms is released as CO 2 by decay, or decomposerorganisms chiefly bacteria and fungi wjat a series of microbial transformations.
If oxygen is scarce as in sewage, marshes, and swampssome carbon is released as methane gas. Carbon cycle. Videos Images. Additional Ix. More About Contributors Article History. Home Science Environment Carbon cycle ecology. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions.
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Know about carbon and why it is called the element of what should you do when a dog eats chocolate. Learn about carbon and how it forms the basis of life. Carbon is transported in various forms through the atmosphere, the hydrosphere, and geologic formations. Mollusk shells or mineral precipitates that form by the reaction of calcium or other metal ions with carbonate may become buried in geologic strata and eventually release CO 2 ix volcanic outgassing.
Carbon dioxide also exchanges through photosynthesis in plants and through respiration in animals. Dead and decaying organic matter may ferment and release CO 2 or methane CH 4 or may be incorporated into sedimentary rock, where it is converted to fossil fuels.
Burning of hydrocarbon fuels returns CO 2 and water H 2 O to the atmosphere. The biological and anthropogenic pathways are much faster than the geochemical pathways and, consequently, have a greater impact on the composition and temperature of the atmosphere. Read More on This Topic.
Carbon from atmospheric carbon dioxide is incorporated by photosynthetic or chemosynthetic organisms Learn More in these related Britannica articles:. Carbon from atmospheric carbon dioxide is incorporated by photosynthetic or chemosynthetic organisms and converted into carbohydrates through the process of autotrophy.
These carbohydrates are ultimately oxidized by heterotrophic organisms to extract useful energy locked in cyce chemical bonds. In the…. Another important set of climate feedbacks involves the global carbon cycle.
In particular, the two main reservoirs of carbon in the climate how to place a free ad on the internet are the oceans and the terrestrial biosphere. These reservoirs have historically taken up large amounts of anthropogenic CO 2 emissions. The carbon budget in the atmosphere is of critical importance to climate and to life.
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Oct 03, · Carbon Cycle is a biogeochemical cycle where various carbon compounds are interchanged among the various layers of the earth, namely, the biosphere, geosphere, pedosphere, hydrosphere and atmosphere. The element carbon is a part of seawater, the atmosphere, rocks such as limestone and coal, soils, as well as all living things. On our dynamic planet, carbon is able to move from one of these realms to another as a part of the carbon cycle. Carbon moves from the atmosphere to plants. Carbon cycle, in biology, circulation of carbon in various forms through nature. Carbon is a constituent of all organic compounds, many of which are essential to life on Earth. The source of the carbon found in living matter is carbon dioxide in the air or dissolved in water.
Carbon is the backbone of life on Earth. We are made of carbon, we eat carbon, and our civilizations—our economies, our homes, our means of transport—are built on carbon. We need carbon, but that need is also entwined with one of the most serious problems facing us today: global climate change.
Carbon is both the foundation of all life on Earth, and the source of the majority of energy consumed by human civilization.
Forged in the heart of aging stars, carbon is the fourth most abundant element in the Universe. The rest is in the ocean, atmosphere, plants, soil, and fossil fuels. Carbon flows between each reservoir in an exchange called the carbon cycle, which has slow and fast components. Any change in the cycle that shifts carbon out of one reservoir puts more carbon in the other reservoirs.
Changes that put carbon gases into the atmosphere result in warmer temperatures on Earth. This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans. Yellow numbers are natural fluxes, and red are human contributions in gigatons of carbon per year.
White numbers indicate stored carbon. Diagram adapted from U. This thermostat works over a few hundred thousand years, as part of the slow carbon cycle. This means that for shorter time periods—tens to a hundred thousand years—the temperature of Earth can vary. And, in fact, Earth swings between ice ages and warmer interglacial periods on these time scales. Parts of the carbon cycle may even amplify these short-term temperature changes. The resulting drop in temperatures and the formation of ice sheets changed the ratio between heavy and light oxygen in the deep ocean, as shown in this graph.
Graph based on data from Zachos at al. Earth has undergone such a change over the last 50 million years, from the extremely warm climates of the Cretaceous roughly to 65 million years ago to the glacial climates of the Pleistocene roughly 1. Through a series of chemical reactions and tectonic activity, carbon takes between million years to move between rocks, soil, ocean, and atmosphere in the slow carbon cycle.
On average, 10 13 to 10 14 grams 10— million metric tons of carbon move through the slow carbon cycle every year. In comparison, human emissions of carbon to the atmosphere are on the order of 10 15 grams, whereas the fast carbon cycle moves 10 16 to 10 17 grams of carbon per year.
The movement of carbon from the atmosphere to the lithosphere rocks begins with rain. Atmospheric carbon combines with water to form a weak acid—carbonic acid—that falls to the surface in rain. The acid dissolves rocks—a process called chemical weathering—and releases calcium, magnesium, potassium, or sodium ions. Rivers carry the ions to the ocean. Rivers carry calcium ions—the result of chemical weathering of rocks—into the ocean, where they react with carbonate dissolved in the water.
The product of that reaction, calcium carbonate, is then deposited onto the ocean floor, where it becomes limestone. In the ocean, the calcium ions combine with bicarbonate ions to form calcium carbonate, the active ingredient in antacids and the chalky white substance that dries on your faucet if you live in an area with hard water.
In the modern ocean, most of the calcium carbonate is made by shell-building calcifying organisms such as corals and plankton like coccolithophores and foraminifera. After the organisms die, they sink to the seafloor. Over time, layers of shells and sediment are cemented together and turn to rock, storing the carbon in stone—limestone and its derivatives. Limestone, or its metamorphic cousin, marble, is rock made primarily of calcium carbonate.
These rock types are often formed from the bodies of marine plants and animals, and their shells and skeletons can be preserved as fossils. Carbon locked up in limestone can be stored for millions—or even hundreds of millions—of years. Only 80 percent of carbon-containing rock is currently made this way. The remaining 20 percent contain carbon from living things organic carbon that have been embedded in layers of mud. Heat and pressure compress the mud and carbon over millions of years, forming sedimentary rock such as shale.
In special cases, when dead plant matter builds up faster than it can decay, layers of organic carbon become oil, coal, or natural gas instead of sedimentary rock like shale. This coal seam in Scotland was originally a layer of sediment, rich in organic carbon. The sedimentary layer was eventually buried deep underground, and the heat and pressure transformed it into coal. Coal and other fossil fuels are a convenient source of energy, but when they are burned, the stored carbon is released into the atmosphere.
The slow cycle returns carbon to the atmosphere through volcanoes. When the plates collide, one sinks beneath the other, and the rock it carries melts under the extreme heat and pressure. The heated rock recombines into silicate minerals, releasing carbon dioxide.
When volcanoes erupt, they vent the gas to the atmosphere and cover the land with fresh silicate rock to begin the cycle again. At present, volcanoes emit between and million metric tons of carbon dioxide per year. For comparison, humans emit about 30 billion tons of carbon dioxide per year—— times more than volcanoes—by burning fossil fuels.
Chemistry regulates this dance between ocean, land, and atmosphere. If carbon dioxide rises in the atmosphere because of an increase in volcanic activity, for example, temperatures rise, leading to more rain, which dissolves more rock, creating more ions that will eventually deposit more carbon on the ocean floor. It takes a few hundred thousand years to rebalance the slow carbon cycle through chemical weathering.
Carbon stored in rocks is naturally returned to the atmosphere by volcanoes. However, the slow carbon cycle also contains a slightly faster component: the ocean. At the surface, where air meets water, carbon dioxide gas dissolves in and ventilates out of the ocean in a steady exchange with the atmosphere.
Once in the ocean, carbon dioxide gas reacts with water molecules to release hydrogen, making the ocean more acidic. The hydrogen reacts with carbonate from rock weathering to produce bicarbonate ions. Before the industrial age, the ocean vented carbon dioxide to the atmosphere in balance with the carbon the ocean received during rock weathering. However, since carbon concentrations in the atmosphere have increased, the ocean now takes more carbon from the atmosphere than it releases.
In the meantime, winds, currents, and temperature control the rate at which the ocean takes carbon dioxide from the atmosphere. It is likely that changes in ocean temperatures and currents helped remove carbon from and then restore carbon to the atmosphere over the few thousand years in which the ice ages began and ended.
The time it takes carbon to move through the fast carbon cycle is measured in a lifespan. The fast carbon cycle is largely the movement of carbon through life forms on Earth, or the biosphere.
Between 10 15 and 10 17 grams 1, to , million metric tons of carbon move through the fast carbon cycle every year. Carbon plays an essential role in biology because of its ability to form many bonds—up to four per atom—in a seemingly endless variety of complex organic molecules.
Many organic molecules contain carbon atoms that have formed strong bonds to other carbon atoms, combining into long chains and rings. Such carbon chains and rings are the basis of living cells. For instance, DNA is made of two intertwined molecules built around a carbon chain. The bonds in the long carbon chains contain a lot of energy. When the chains break apart, the stored energy is released.
This energy makes carbon molecules an excellent source of fuel for all living things. During photosynthesis, plants absorb carbon dioxide and sunlight to create fuel—glucose and other sugars—for building plant structures.
This process forms the foundation of the fast biological carbon cycle. Illustration adapted from P. Sellers et al. Plants and phytoplankton are the main components of the fast carbon cycle. Phytoplankton microscopic organisms in the ocean and plants take carbon dioxide from the atmosphere by absorbing it into their cells. Using energy from the Sun, both plants and plankton combine carbon dioxide CO 2 and water to form sugar CH 2 O and oxygen.
The chemical reaction looks like this:. Four things can happen to move carbon from a plant and return it to the atmosphere, but all involve the same chemical reaction.
Plants break down the sugar to get the energy they need to grow. Animals including people eat the plants or plankton, and break down the plant sugar to get energy. Plants and plankton die and decay are eaten by bacteria at the end of the growing season. Or fire consumes plants. In each case, oxygen combines with sugar to release water, carbon dioxide, and energy.
The basic chemical reaction looks like this:. In all four processes, the carbon dioxide released in the reaction usually ends up in the atmosphere. The fast carbon cycle is so tightly tied to plant life that the growing season can be seen by the way carbon dioxide fluctuates in the atmosphere.
In the Northern Hemisphere winter, when few land plants are growing and many are decaying, atmospheric carbon dioxide concentrations climb. During the spring, when plants begin growing again, concentrations drop. It is as if the Earth is breathing.
The ebb and flow of the fast carbon cycle is visible in the changing seasons. As the large land masses of Northern Hemisphere green in the spring and summer, they draw carbon out of the atmosphere.
This graph shows the difference in carbon dioxide levels from the previous month, with the long-term trend removed. This cycle peaks in August, with about 2 parts per million of carbon dioxide drawn out of the atmosphere.
In the fall and winter, as vegetation dies back in the northern hemisphere, decomposition and respiration returns carbon dioxide to the atmosphere.
Left unperturbed, the fast and slow carbon cycles maintain a relatively steady concentration of carbon in the atmosphere, land, plants, and ocean. But when anything changes the amount of carbon in one reservoir, the effect ripples through the others.
See Milutin Milankovitch.