IndexSteps of the Carbon CycleExamples of the Carbon CycleAtmosphereLithosphereBiosphereOceansNitrogen CycleAll living things are made of carbon. Carbon is also part of the ocean, air and even rocks. Because the Earth is a dynamic place, carbon does not stay still. It's on the move! In the atmosphere, carbon is bonded to some oxygen in a gas called carbon dioxide. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original EssayPlants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and become buried can turn into carbon-based fossil fuels such as coal and oil over millions of years. When humans burn fossil fuels, most of the carbon quickly enters the atmosphere in the form of carbon dioxide. Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without this and other greenhouse gases, the Earth would be a frozen world. But humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than about 150 years ago, and the Earth is becoming a warmer place. In fact, ice cores show us that there is more carbon dioxide in the atmosphere now than there has been in the last 420,000 years. Carbon dioxide in the atmosphere prevents solar energy from escaping into space, much like the glass walls of a greenhouse. . This isn't always a bad thing: a certain amount of carbon dioxide in the atmosphere is helpful in keeping the Earth warm and its temperature stable. But Earth has experienced catastrophic warming cycles in the past, such as the Permian extinction, which is believed to have been caused by a drastic increase in the level of greenhouse gases in the atmosphere. No one is sure what caused the change that led to the Permian extinction. Greenhouse gases may have been added to the atmosphere by an asteroid impact, volcanic activity, or even massive forest fires. Whatever the cause, during this warming episode, temperatures rose dramatically. Much of the Earth became deserted, and over 90% of all living species became extinct at that time. This is a good example of what can happen if the essential cycles of our planet undergo a major change. Another important variable influenced by the carbon cycle is the acidity of the ocean. Carbon dioxide can react with ocean water to form carbonic acid. This has been an important stabilizing force of the carbon cycle over the years, as the chemical balance between carbon dioxide and carbonic acid means that the ocean can absorb or release carbon dioxide as atmospheric levels rise and fall. However, as you might imagine, increasing ocean acidity can spell trouble for marine life – and this could eventually pose a problem for other parts of the carbon system. Many marine life with shells, for example, can extract carbon from the water to create the calcium carbonate from which they make their shells. If these species suffer, the ocean could lose some of its ability to remove carbon from the atmosphere. Finally, of course, there is the role of living things in the carbon cycle. Plant and animal activity has been a major force influencing changes in the carbon cycle over the past billions of years. Photosynthesizers have dramatically changed the Earth's atmosphere and climate by taking huge amounts of carbon from the atmosphere andtransforming that carbon into cellular materials. These activities created free oxygen and the ozone layer, and generally set the stage for the evolution of animals that obtain their energy by breaking down organic materials created by photosynthesizers and extracting the energy that the photosynthesizers used to produce those molecules. With one particular species of animal – humans – making major changes, the future of Earth's carbon cycle is uncertain. All of these cycles in closed systems eventually correct themselves, but sometimes this occurs through drastic population reduction of the offending species through starvation. The Phases of the Carbon Cycle Atmospheric Carbon To become part of the carbon cycle, carbon atoms start out in gaseous form. Carbon dioxide gas – CO2 – can be produced by inorganic processes or by the metabolism of living things. Before Earth hosted life, carbon dioxide gas likely came from volcanic activity and asteroid impacts. Today, carbon is also released into the atmosphere through the activities of living beings, such as animal fumes, the actions of decomposer organisms and the burning of wood and fossil fuels by humans. Regardless of how carbon dioxide enters the atmosphere, CO2 gas is the starting point of the carbon cycle. Carbon absorbed by producers “Producers” – organisms that make food from sunlight, such as plants – absorb carbon dioxide from the atmosphere and use it to build sugars, lipids, proteins and other essential elements of life. For plants, CO2 is absorbed through pores in leaves called “stomata”. Carbon dioxide enters the plant through the stomata and is incorporated into carbon-containing compounds with the help of solar energy. Plants and other producing organisms such as cyanobacteria are critical to life on Earth because they can transform atmospheric carbon into living matter. Carbon transfer through producers being eaten “Consumers” are organisms that eat other living things. Animals are the most visible type of consumer in our ecosystems, although many types of microbes also fall into this category. Consumers incorporate carbon compounds from plants and other food sources when they eat them. They use some of these carbon compounds in foods to build their bodies, but much of the food they eat is broken down to release energy, in a process that is almost the reverse of what producers do. While producers use the energy of sunlight to create bonds between carbon atoms, animals break these bonds to release the energy they contain, ultimately turning sugars, lipids and other carbon compounds into single-carbon units. These are ultimately released into the atmosphere in the form of CO2. This process of “cellular respiration” – in which oxygen is inhaled and carbon dioxide is exhaled – is a major source of carbon release into the atmosphere. But it's not always the last step in the carbon cycle. What about carbon compounds that are not eaten or broken down by animals? Carbon released by decomposers Plants and animals that die without being eaten by other animals are broken down by other organisms, called "decomposers". Decomposers include many bacteria and some fungi. They usually only break down already dead matter, rather than catching and eating a living animal or plant. Just like animals, decomposers destroy chemical bonds in food molecules. They create many chemicals, including CO2 in some cases. The carbon that doesn't comereleased into the atmosphere in this way can also be released by…Combustion caused by humans Humans are the only animals we know of that can create fire on purpose. And we often set things on fire. Our cars are powered by the burning of fossil fuels: oil and gasoline, which are made up of dead plant and animal material that has spent millions of years buried deep within the Earth. Many of our power plants are also powered by the burning of fossil fuels, including coal, which is another form of dead plant matter buried underground and transformed by geologic heat. Finally, humans also burn a lot of wood. We no longer burn wood to power our machines as we did in the 19th century, but now we often burn forests to clear land for agriculture, mining, and other purposes. To date, about half of Earth's forests have been burned or otherwise destroyed by human activities. The scientific community has been sounding the alarm that by making significant changes to Earth's carbon cycle, we could end up changing our climate or other important aspects of the planet's ecosystem that we rely on to survive. As a result, many scientists advocate decreasing the amount of carbon burned by humans by reducing car travel and electricity use and investing in non-burning energy sources such as solar and wind power. Carbon Cycle Examples The carbon cycle consists of many parallel systems that can absorb or release carbon. Together, these systems work to keep Earth's carbon cycle – and consequently the climate and biosphere – relatively stable. Atmosphere One of the major carbon sinks is carbon dioxide in the Earth's atmosphere. Carbon forms a stable gas molecule in combination with two oxygen atoms. In nature, this gas is released by volcanic activity and by the respiration of animals that attach carbon molecules from the food they eat to oxygen molecules before exhaling it. Humans also release carbon dioxide into the atmosphere by burning organic matter such as wood and fossil fuels. Carbon dioxide can be removed from the atmosphere by plants, which take atmospheric carbon and turn it into sugars, proteins, lipids and other molecules essential for life. Lithosphere The Earth's crust - called "lithosphere" from the Greek word "litho" for "stone" and "sphere" for globe - can also release carbon dioxide into the Earth's atmosphere. This gas can be created by chemical reactions in the Earth's crust and mantle. Volcanic activity can cause natural releases of carbon dioxide. Some scientists believe that widespread volcanic activity may be responsible for the warming of the Earth that caused the Permian extinction. While the Earth's crust can add carbon to the atmosphere, it can also remove it. Movements of the Earth's crust can bury carbon-containing chemicals, such as dead plants and animals, deep underground, where their carbon cannot return to the atmosphere. Biosphere Among living things, some remove carbon from the atmosphere, while others release it back. The most obvious participants in this system are plants and animals. Plants remove carbon from the atmosphere. They don't do it as an act of charity; Atmospheric carbon is actually the “food” that plants use to produce sugars, proteins, lipids and other molecules essential for life. Plants use the energy of sunlight, harvested through photosynthesis, to build these organic compounds from carbon dioxide and other trace elements. In fact, the term “photosynthesis”comes from the Greek words “photo” for “light” and “synthesis” for “to put together”. Oceans Earth's oceans have the capacity to both absorb and release carbon dioxide. When carbon dioxide from the atmosphere comes into contact with ocean water, it can react with water molecules to form carbonic acid – a dissolved liquid form of carbon. Like most chemical reactions, the rate of this reaction is determined by the equilibrium between the products and the reactants. When there is more carbonic acid in the ocean than carbon dioxide in the atmosphere, some of the carbonic acid can be released into the atmosphere as carbon dioxide. Nitrogen cycleAll life requires nitrogen compounds, for example proteins and nucleic acids. Air, composed of 79% nitrogen gas (N2), is the main nitrogen reservoir. But most organisms cannot use nitrogen in this form. Plants must secure their nitrogen in a "fixed" form, i.e. incorporated in compounds such as: nitrate ions (NO3−) ammonium ions (NH4+) urea (NH2)2CO Animals secure their nitrogen (and all other) compounds from plants (or animals) that fed on plants).Steps: Four processes participate or are involved in the cycling of nitrogen through the biosphere:Nitrogen fixationDecayNitrificationDentrificationMicroorganisms play an important role in all four of these.Nitrogen fixation The molecule of nitrogen (N2) is rather inert. Breaking it apart so that its atoms can combine with other atoms requires the input of significant amounts of energy. Three processes are responsible for most nitrogen fixation in the biosphere: atmospheric fixation by lightning industrial fixation biological fixation by some microbes - alone or in a symbiotic relationship with some plants and animals Atmospheric fixation The enormous energy of lightning breaks down molecules of nitrogen and allows their atoms to combine with oxygen in the air to form nitrogen oxides. These dissolve with rain forming nitrates, which are transported to the earth. Atmospheric nitrogen fixation probably contributes about 5-8% of the total nitrogen fixed. Industrial fixation Under great pressure, at a temperature of 600°C and with the use of a catalyst, atmospheric nitrogen and hydrogen (usually derived from natural gas or petroleum) can be combined to form ammonia (NH3). Ammonia can be used directly as a fertilizer, but most of it is further processed into urea and ammonium nitrate (NH4NO3). Biological fixation The ability to fix nitrogen is found only in some bacteria and archaea. Some live in a symbiotic relationship with plants in the legume family (e.g., soybeans, alfalfa). Some establish symbiotic relationships with plants other than legumes (for example, alders). Some establish symbiotic relationships with animals, for example, termites and "ship termites" (wood-eating bivalves). Some nitrogen-fixing bacteria live free in the soil. Nitrogen-fixing cyanobacteria are essential for maintaining the fertility of semi-aquatic environments such as rice paddies. Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP. Although the first stable product of the process is ammonia, this is rapidly incorporated into proteins and other organic nitrogen compounds. Decay Proteins produced by plants enter and pass through food webs just as carbohydrates do. At each trophic level, their metabolism produces nitrogenous organic compounds that return to the environment, mainly in the form of excretions. The ultimate beneficiaries of these materials are decaying microorganisms. They break down the2−).