Chemical cycling

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An example chemical cycle, a schematic representation of a Nitrogen cycle on Earth. This process results in the continual recycling of nitrogen gas involving the ocean. Marine Nitrogen Cycle.jpg
An example chemical cycle, a schematic representation of a Nitrogen cycle on Earth. This process results in the continual recycling of nitrogen gas involving the ocean.

Chemical cycling describes systems of repeated circulation of chemicals between other compounds, states and materials, and back to their original state, that occurs in space, and on many objects in space including the Earth. Active chemical cycling is known to occur in stars, many planets and natural satellites.

Contents

Chemical cycling plays a large role in sustaining planetary atmospheres, liquids and biological processes and can greatly influence weather and climate. Some chemical cycles release renewable energy, others may give rise to complex chemical reactions, organic compounds and prebiotic chemistry. On terrestrial bodies such as the Earth, chemical cycles involving the lithosphere are known as geochemical cycles. Ongoing geochemical cycles are one of the main attributes of geologically active worlds. A chemical cycle involving a biosphere is known as a biogeochemical cycle.

The Sun, other stars and star systems

In most hydrogen-fusing stars, including the Sun, a chemical cycle involved in stellar nucleosynthesis occurs which is known as a carbon-nitrogen-oxygen or (CNO cycle). In addition to this cycle, stars also have a helium cycle. [1] Various cycles involving gas and dust have been found to occur in galaxies. [2]

Venus

The majority of known chemical cycles on Venus involve its dense atmosphere and compounds of carbon and sulphur, the most significant being a strong carbon dioxide cycle. [3] The lack of a complete carbon cycle including a geochemical carbon cycle, for example, is thought to be a cause of its runaway greenhouse effect, due to the lack of a substantial carbon sink. [4] Sulphur cycles including sulphur oxide cycles also occur, sulphur oxide in the upper atmosphere and results in the presence of sulfuric acid [5] in turn returns to oxides through photolysis. [6] Indications also suggest an ozone cycle on Venus similar to that of Earth's. [7]

Earth

Earth's water cycle. Water cycle.png
Earth's water cycle.

A number of different types of chemical cycles geochemical cycles occur on Earth. Biogeochemical cycles play an important role in sustaining the biosphere. Notable active chemical cycles on Earth include:

Other chemical cycles include hydrogen peroxide. [9]

Mars

Possible sources of a hypothesized Martian Methane cycle. PIA19088-MarsCuriosityRover-MethaneSource-20141216.png
Possible sources of a hypothesized Martian Methane cycle.

Recent evidence suggests that similar chemical cycles to Earth's occur on a lesser scale on Mars, facilitated by the thin atmosphere, including carbon dioxide (and possibly carbon), [10] water, [11] sulphur, [12] methane, [13] oxygen, [14] ozone, [15] and nitrogen [16] cycles. Many studies point to significantly more active chemical cycles on Mars in the past, however the faint young Sun paradox has proved problematic in determining chemical cycles involved in early climate models of the planet. [17]

Jupiter

Jupiter's gas toruses generated by Io (green) and Europa (blue) PIA04433 Jupiter Torus Diagram.jpg
Jupiter's gas toruses generated by Io (green) and Europa (blue)

Jupiter, like all the gas giants, has an atmospheric methane cycle. [18] Recent studies indicate a hydrological cycle of water-ammonia vastly different to the type operating on terrestrial planets like Earth [18] and also a cycle of hydrogen sulfide. [19]

Significant chemical cycles exist on Jupiter's moons. Recent evidence points to Europa possessing several active cycles, most notably a water cycle. [20] Other studies suggest an oxygen [21] and radiation induced carbon dioxide [18] cycle. Io and Europa, appear to have radiolytic sulphur cycles involving their lithospheres. [22] In addition, Europa is thought to have a sulfur dioxide cycle. [18] In addition, the Io plasma torus contributes to a sulphur cycle on Jupiter and Ganymede. [23] Studies also imply active oxygen cycles on Ganymede [24] and oxygen and radiolytic carbon dioxide cycles on Callisto. [18]

Saturn

A graph depicting mechanisms of Titan's methanological cycle. Titan atmosphere detail narrow.svg
A graph depicting mechanisms of Titan's methanological cycle.

In addition to Saturn's methane cycle [18] some studies suggest an ammonia cycle induced by photolysis similar to Jupiter's. [25]

The cycles of its moons are of particular interest. Observations by Cassini–Huygens of Titan's atmosphere and interactions with its liquid mantle give rise to several active chemical cycles including a methane, [26] hydrocarbon, [27] hydrogen, [28] and carbon [29] cycles. Enceladus has an active hydrological, silicate and possibly a nitrogen cycle. [30] [31]

Uranus

Uranus has an active methane cycle. [32] Methane is converted to hydrocarbons through photolysis which condenses and as they are heated, release methane which rises to the upper atmosphere.

Studies by Grundy et al. (2006) indicate active carbon cycles operates on Titania, Umbriel and Ariel and Oberon through the ongoing sublimation and deposition of carbon dioxide, though some is lost to space over long periods of time. [33]

Neptune

Neptune's internal heat and convection drives cycles of methane, [18] carbon, [34] and a combination of other volatiles within Triton's lithosphere. [35]

Models predicted the presence of seasonal nitrogen cycles on the moon Triton, [36] however this has not been supported by observations to date.

Pluto-Charon system

Models predict a seasonal nitrogen cycle on Pluto [37] and observations by New Horizons appear to support this.

Related Research Articles

<span class="mw-page-title-main">Carbon monoxide</span> Colourless, odourless, tasteless and toxic gas

Carbon monoxide is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simplest carbon oxide. In coordination complexes, the carbon monoxide ligand is called carbonyl. It is a key ingredient in many processes in industrial chemistry.

A reducing atmosphere is an atmospheric condition in which oxidation is prevented by absence of oxygen and other oxidizing gases or vapours, and which may contain actively reductant gases such as hydrogen, carbon monoxide, methane and hydrogen sulfide that would be readily oxidized to remove any free oxygen. Although Early Earth had had a reducing prebiotic atmosphere prior to the Proterozoic eon, starting at about 2.5 billion years ago in the late Neoarchaean period, the Earth's atmosphere experienced a significant rise in oxygen and transitioned to an oxidizing atmosphere with a surplus of molecular oxygen (dioxygen, O2) as the primary oxidizing agent.

<span class="mw-page-title-main">Biogeochemical cycle</span> Chemical transfer pathway between Earths biological and non-biological parts

A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle. In each cycle, the chemical element or molecule is transformed and cycled by living organisms and through various geological forms and reservoirs, including the atmosphere, the soil and the oceans. It can be thought of as the pathway by which a chemical substance cycles the biotic compartment and the abiotic compartments of Earth. The biotic compartment is the biosphere and the abiotic compartments are the atmosphere, lithosphere and hydrosphere.

Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain.

<span class="mw-page-title-main">Tholin</span> Class of molecules formed by ultraviolet irradiation of organic compounds

Tholins are a wide variety of organic compounds formed by solar ultraviolet or cosmic ray irradiation of simple carbon-containing compounds such as carbon dioxide, methane or ethane, often in combination with nitrogen or water. Tholins are disordered polymer-like materials made of repeating chains of linked subunits and complex combinations of functional groups, typically nitriles and hydrocarbons, and their degraded forms such as amines and phenyls. Tholins do not form naturally on modern-day Earth, but they are found in great abundance on the surfaces of icy bodies in the outer Solar System, and as reddish aerosols in the atmospheres of outer Solar System planets and moons.

<span class="mw-page-title-main">Oxygen cycle</span> Biogeochemical cycle of oxygen

Oxygen cycle refers to the movement of oxygen through the atmosphere (air), biosphere (plants and animals) and the lithosphere (the Earth’s crust). The oxygen cycle demonstrates how free oxygen is made available in each of these regions, as well as how it is used. The oxygen cycle is the biogeochemical cycle of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. The word oxygen in the literature typically refers to the most common oxygen allotrope, elemental/diatomic oxygen (O2), as it is a common product or reactant of many biogeochemical redox reactions within the cycle. Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O2 production) or sink (O2 consumption).

<span class="mw-page-title-main">Biogeochemistry</span> Study of chemical cycles of the earth that are either driven by or influence biological activity

Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment. In particular, biogeochemistry is the study of biogeochemical cycles, the cycles of chemical elements such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space and time. The field focuses on chemical cycles which are either driven by or influence biological activity. Particular emphasis is placed on the study of carbon, nitrogen, oxygen, sulfur, iron, and phosphorus cycles. Biogeochemistry is a systems science closely related to systems ecology.

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.

<span class="mw-page-title-main">Iron cycle</span> Biogeochemical cycle of Fe2+/Fe3+

The iron cycle (Fe) is the biogeochemical cycle of iron through the atmosphere, hydrosphere, biosphere and lithosphere. While Fe is highly abundant in the Earth's crust, it is less common in oxygenated surface waters. Iron is a key micronutrient in primary productivity, and a limiting nutrient in the Southern ocean, eastern equatorial Pacific, and the subarctic Pacific referred to as High-Nutrient, Low-Chlorophyll (HNLC) regions of the ocean.

<span class="mw-page-title-main">Sulfur cycle</span> Biogeochemical cycle of sulfur

The important sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element (CHNOPS), being a constituent of many proteins and cofactors, and sulfur compounds can be used as oxidants or reductants in microbial respiration. The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes. Steps of the sulfur cycle are:

<span class="mw-page-title-main">Great Oxidation Event</span> Paleoproterozoic surge in atmospheric oxygen

The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis or Oxygen Holocaust, was a time interval during the Earth's Paleoproterozoic era when the Earth's atmosphere and shallow seas first experienced a rise in the concentration of free oxygen. This began approximately 2.460–2.426 Ga (billion years) ago during the Siderian period and ended approximately 2.060 Ga ago during the Rhyacian. Geological, isotopic and chemical evidence suggests that biologically produced molecular oxygen (dioxygen or O2) started to accumulate in the Archean prebiotic atmosphere due to microbial photosynthesis, and eventually changed it from a weakly reducing atmosphere practically devoid of oxygen into an oxidizing one containing abundant free oxygen, with oxygen levels being as high as 10% of modern atmospheric level by the end of the GOE.

<span class="mw-page-title-main">Atmosphere of Mars</span> Layer of gases surrounding the planet Mars

The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and noble gases. The atmosphere of Mars is much thinner and colder than Earth's having a max density 20g/m3 with a temperature generally below zero down to -60 Celsius. The average surface pressure is about 610 pascals (0.088 psi) which is 0.6% of the Earth's value.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

<span class="mw-page-title-main">Atmosphere of Venus</span> Gas layer surrounding Venus

The atmosphere of Venus is the very dense layer of gases surrounding the planet Venus. Venus's atmosphere is composed of 96.5% carbon dioxide and 3.5% nitrogen, with other chemical compounds present only in trace amounts. It is much denser and hotter than that of Earth; the temperature at the surface is 740 K, and the pressure is 93 bar (1,350 psi), roughly the pressure found 900 m (3,000 ft) under water on Earth. The atmosphere of Venus supports decks of opaque clouds of sulfuric acid that cover the entire planet, preventing optical Earth-based and orbital observation of the surface. Information about surface topography has been obtained exclusively by radar imaging.

<span class="mw-page-title-main">Mars general circulation model</span>

The Mars general circulation model is the result of a research project by NASA to understand the nature of the general circulation of the atmosphere of Mars, how that circulation is driven and how it affects the climate of Mars in the long term.

<span class="mw-page-title-main">Extraterrestrial atmosphere</span> Area of astronomical research

The study of extraterrestrial atmospheres is an active field of research, both as an aspect of astronomy and to gain insight into Earth's atmosphere. In addition to Earth, many of the other astronomical objects in the Solar System have atmospheres. These include all the giant planets, as well as Mars, Venus and Titan. Several moons and other bodies also have atmospheres, as do comets and the Sun. There is evidence that extrasolar planets can have an atmosphere. Comparisons of these atmospheres to one another and to Earth's atmosphere broaden our basic understanding of atmospheric processes such as the greenhouse effect, aerosol and cloud physics, and atmospheric chemistry and dynamics.

<span class="mw-page-title-main">Atmosphere of Titan</span>

The atmosphere of Titan is the dense layer of gases surrounding Titan, the largest moon of Saturn. Titan is the only natural satellite in the Solar System with an atmosphere that is denser than the atmosphere of Earth and is one of two moons with an atmosphere significant enough to drive weather. Titan's lower atmosphere is primarily composed of nitrogen (94.2%), methane (5.65%), and hydrogen (0.099%). There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene, propane, PAHs and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, acetonitrile, argon and helium. The isotopic study of nitrogen isotopes ratio also suggests acetonitrile may be present in quantities exceeding hydrogen cyanide and cyanoacetylene. The surface pressure is about 50% higher than on Earth at 1.5 bars which is near the triple point of methane and allows there to be gaseous methane in the atmosphere and liquid methane on the surface. The orange color as seen from space is produced by other more complex chemicals in small quantities, possibly tholins, tar-like organic precipitates.

<span class="mw-page-title-main">Carbonate–silicate cycle</span> Geochemical transformation of silicate rocks

The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.

Marine chemistry, also known as ocean chemistry or chemical oceanography, is the study of the chemical composition and processes of the world’s oceans, including the interactions between seawater, the atmosphere, the seafloor, and marine organisms. This field encompasses a wide range of topics, such as the cycling of elements like carbon, nitrogen, and phosphorus, the behavior of trace metals, and the study of gases and nutrients in marine environments. Marine chemistry plays a crucial role in understanding global biogeochemical cycles, ocean circulation, and the effects of human activities, such as pollution and climate change, on oceanic systems. It is influenced by plate tectonics and seafloor spreading, turbidity, currents, sediments, pH levels, atmospheric constituents, metamorphic activity, and ecology.

<span class="mw-page-title-main">Marine biogeochemical cycles</span>

Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substances and elements move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.

References

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