Which biochemical is most abundant in our atmosphere

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. Ice ages developed when Northern Hemisphere summers cooled and ice built up on land, which in turn slowed the carbon cycle. Meanwhile, a number of factors including cooler temperatures and increased phytoplankton growth may have increased the amount of carbon the ocean took out of the atmosphere.

The drop in atmospheric carbon caused additional cooling. Similarly, at the end of the last Ice Age, 10, years ago, carbon dioxide in the atmosphere rose dramatically as temperatures warmed. Levels of carbon dioxide in the atmosphere have corresponded closely with temperature over the past , years. Antarctic ice-core data show the long-term correlation until about Today, changes in the carbon cycle are happening because of people. We perturb the carbon cycle by burning fossil fuels and clearing land.

When we clear forests, we remove a dense growth of plants that had stored carbon in wood, stems, and leaves—biomass.

By removing a forest, we eliminate plants that would otherwise take carbon out of the atmosphere as they grow. We tend to replace the dense growth with crops or pasture, which store less carbon. We also expose soil that vents carbon from decayed plant matter into the atmosphere. Humans are currently emitting just under a billion tons of carbon into the atmosphere per year through land use changes. The burning of fossil fuels is the primary source of increased carbon dioxide in the atmosphere today.

Without human interference, the carbon in fossil fuels would leak slowly into the atmosphere through volcanic activity over millions of years in the slow carbon cycle. By burning coal, oil, and natural gas, we accelerate the process, releasing vast amounts of carbon carbon that took millions of years to accumulate into the atmosphere every year.

By doing so, we move the carbon from the slow cycle to the fast cycle. In , humans released about 8. Emissions of carbon dioxide by humanity primarily from the burning of fossil fuels, with a contribution from cement production have been growing steadily since the onset of the industrial revolution.

About half of these emissions are removed by the fast carbon cycle each year, the rest remain in the atmosphere. Since the beginning of the Industrial Revolution, when people first started burning fossil fuels, carbon dioxide concentrations in the atmosphere have risen from about parts per million to parts per million, a 39 percent increase.

If 14 C is present at atmospheric levels, the molecule must derive from a recent plant product. The pathway from the plant to the molecule may have been indirect or lengthy, involving multiple physical, chemical, and biological processes. Levels of 14 C are affected significantly only by the passage of time.

If a molecule contains no detectable 14 C it must derive from a petrochemical feedstock or from some other ancient source. Intermediate levels of 14 C can represent either mixtures of modern and dead carbon or carbon that was fixed from the atmosphere less than 50, years ago.

Signals of this kind are often used by chemists studying natural environments. A hydrocarbon found in beach sediments, for example, might derive from an oil spill or from waxes produced by plants.

If isotopic analyses show that the hydrocarbon contains 14 C at atmospheric levels, it's from a plant. If it contains no 14 C, it's from an oil spill. If it contains some intermediate level, it's from a mixture of both sources. What is Carbon Dating? How does Radiocarbon work? Scientific American Editor Michael Moyer explains the process of radiocarbon dating.

However, denitrification in wastewater treatment plays a very beneficial role by removing unwanted nitrates from the wastewater effluent, thereby reducing the chances that the water discharged from the treatment plants will cause undesirable consequences e.

When an organism excretes waste or dies, the nitrogen in its tissues is in the form of organic nitrogen e. Various fungi and prokaryotes then decompose the tissue and release inorganic nitrogen back into the ecosystem as ammonia in the process known as ammonification. The ammonia then becomes available for uptake by plants and other microorganisms for growth.

Many human activities have a significant impact on the nitrogen cycle. Burning fossil fuels, application of nitrogen-based fertilizers, and other activities can dramatically increase the amount of biologically available nitrogen in an ecosystem. And because nitrogen availability often limits the primary productivity of many ecosystems, large changes in the availability of nitrogen can lead to severe alterations of the nitrogen cycle in both aquatic and terrestrial ecosystems.

Industrial nitrogen fixation has increased exponentially since the s, and human activity has doubled the amount of global nitrogen fixation Vitousek et al. In terrestrial ecosystems, the addition of nitrogen can lead to nutrient imbalance in trees, changes in forest health, and declines in biodiversity. With increased nitrogen availability there is often a change in carbon storage, thus impacting more processes than just the nitrogen cycle.

In agricultural systems, fertilizers are used extensively to increase plant production, but unused nitrogen, usually in the form of nitrate, can leach out of the soil, enter streams and rivers, and ultimately make its way into our drinking water. The process of making synthetic fertilizers for use in agriculture by causing N 2 to react with H 2 , known as the Haber-Bosch process, has increased significantly over the past several decades.

Much of the nitrogen applied to agricultural and urban areas ultimately enters rivers and nearshore coastal systems. In nearshore marine systems, increases in nitrogen can often lead to anoxia no oxygen or hypoxia low oxygen , altered biodiversity, changes in food-web structure, and general habitat degradation.

One common consequence of increased nitrogen is an increase in harmful algal blooms Howarth Toxic blooms of certain types of dinoflagellates have been associated with high fish and shellfish mortality in some areas. Even without such economically catastrophic effects, the addition of nitrogen can lead to changes in biodiversity and species composition that may lead to changes in overall ecosystem function.

Some have even suggested that alterations to the nitrogen cycle may lead to an increased risk of parasitic and infectious diseases among humans and wildlife Johnson et al. Additionally, increases in nitrogen in aquatic systems can lead to increased acidification in freshwater ecosystems. Nitrogen is arguably the most important nutrient in regulating primary productivity and species diversity in both aquatic and terrestrial ecosystems Vitousek et al.

Microbially-driven processes such as nitrogen fixation, nitrification, and denitrification, constitute the bulk of nitrogen transformations, and play a critical role in the fate of nitrogen in the Earth's ecosystems. However, as human populations continue to increase, the consequences of human activities continue to threaten our resources and have already significantly altered the global nitrogen cycle.

Galloway, J. Year Consequences of population growth and development on deposition of oxidized nitrogen. Ambio 23 , — Howarth, R. Coastal nitrogen pollution: a review of sources and trends globally and regionally. Harmful Algae 8 , 14— Johnson, P.

Linking environmental nutrient enrichment and disease emergence in humans and wildlife. Ecological Applications 20 , 16—29 Koenneke, M.

Isolation of an autotrophic ammonia-oxidizing marine archaeon. Nature , — Kuypers, M. Massive nitrogen loss from the Benguela upwelling system through anaerobic ammonium oxidation. Risgaard-Petersen, N. Evidence for complete denitrification in a benthic foraminifer. Nature , 93—96 Strous, M. Missing lithotroph identified as new planctomycete. Vitousek, P. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7 , — Towards an ecological understanding of biological nitrogen fixation.

Biogeochemistry 57 , 1—45 Ward, B. Denitrification as the dominant nitrogen loss process in the Arabian Sea. Nature , 78—81 Introduction to the Basic Drivers of Climate. Terrestrial Biomes. Coral Reefs. Energy Economics in Ecosystems. Biodiversity and Ecosystem Stability. Biological Nitrogen Fixation. Ecosystems Ecology Introduction. Factors Affecting Global Climate.

Rivers and Streams: Life in Flowing Water. The Conservation of Mass. The Ecology of Carrion Decomposition. Causes and Consequences of Biodiversity Declines. Earth's Ferrous Wheel. Alternative Stable States. Recharge Variability in Semi-Arid Climates. Secondary Production. Food Web: Concept and Applications. Terrestrial Primary Production: Fuel for Life. Citation: Bernhard, A.