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Hydrogen Sulfide

Hydrogen sulfide

:For an alternative meaning of H2S, see H2S radar. Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs. It often results when bacteria break down organic matter in the absence of oxygen, such as in swamps and sewers. It also occurs in volcanic gases, natural gas and some well waters. Hydrogen sulfide is also known as sulfane, sulfur hydride, dihydrogen monosulfide, sulfurated hydrogen, sewer gas and stink damp. IUPAC accepts the names "hydrogen sulfide" and "sulfane"; the latter one is used exclusively when naming more complicated compounds.

Chemistry

Hydrogen sulfide is a covalent hydride chemically similar to water (H2O) since oxygen and sulfur occur in the same periodic table group. The gas is weakly acidic, dissociating in solution into hydrogen cations H+ and the hydrosulfide anion HS−: ::H2S → HS− + H+ :::Ka = 1.3×10−7 mol/L; pKa = 6.89. The sulfide ion, S2−, is known in the solid state but not in aqueous solution (c.f. oxide). The second dissociation constant of hydrogen sulfide is often stated to be around 10−13, but it is now clear that this is an error caused by oxidation of the sulfur in alkaline solution. The current best estimate for pKa2 is 19±2. Hydrogen sulfide reacts with alkalis and metals to produce sulfides, the salts of hydrogen sulfide (not to be confused with sulfites, which are certain compounds that contain sulfur and oxygen.) Metal sulfides are often black; silver jewelry turns black over time because hydrogen sulfide from the air reacts with the silver to produce silver sulfide. Hydrogen sulfide penetrates the lattice of some steels and makes them brittle, leading to sulphide stress cracking - a concern especially for handling acid gas and sour crude in the oil industry. Small amounts of hydrogen sulfide can be disposed by burning it to sulfur dioxide, which is also corrosive but less toxic.

Occurrence

Hydrogen sulfide occurs naturally in crude petroleum, natural gas (even up to 28%), volcanic gases, and some hot springs. Sulfate-reducing bacteria obtain their energy by using sulfates to oxidize organic matter or hydrogen, thereby reducing the sulfates to hydrogen sulfide. They are especially efficient in low-oxygen environments, such as in swamps and standing waters. Sulfur-reducing bacteria and some archaea obtain their energy by using elemental sulfur to oxidize organic matter or hydrogen, thus also producing hydrogen sulfide. Some other anaerobic bacteria liberate hydrogen sulfide when they digest sulfur-containing amino acids, for instance during the decay of organic matter. Hydrogren sulfide producing bacteria also operate in the human colon, and the odor of flatulence is largely due to trace amounts of the gas. They can also be found in the mouth and contribute to bad breath. Hydrogen sulfide can also result from industrial activities, such as food processing, sewage treatment, coke ovens, paper mills (using the sulphate method), tanneries, and petroleum refineries, in coal mines (as iron sulfides such as pyrite decompose) and anywhere where sulfur comes in contact with organic material at high temperatures. Anthropogenic emissions of hydrogen sulfide are however just 10% of total global emissions. Normal average concentration in clean air is about 0.0001-0.0002 ppm. Hydrogen sulfide can be present naturally in well water. In such cases, ozone is often used for its removal. An alternative method uses a filter with manganese dioxide. Both methods oxidize sulfides to fairly non-toxic sulfates.

Manufacture and use

Hydrogen sulfide used to have importance in analytical chemistry for well over a century, in the qualitative chemical analysis of metal ions. For such small-scale laboratory use the gas is made as needed in a Kipp generator (also known as Kipp's aparatus, named after its inventor Petrus Johannes Kipp) by reaction of sulfuric acid with ferrous sulfide FeS. Industrial production focuses on separation of hydrogen sulfide from sour gas - natural gas with high content of H2S. The most important industrial use of hydrogen sulfide is as a source of about 25% of the world production of elemental sulphur. The manufacturing process is based on burning about 1/3 of hydrogen sulfide to sulphur dioxide, then letting the resulting SO2 react with H2S. Other uses are in metallurgy for the preparation of metallic sulfides. It also finds use in preparation of phosphors and oil additives, in separation of metals, removal of metallic impurities, and in organic chemical synthesis. Hydrogen sulfide is also used in nuclear engineering, in the Girdler Sulfide process of manufacturing heavy water.

Dangers

The gas is highly toxic and can kill or seriously injure exposed persons. It is heavier than air, so tends to concentrate at the bottom of poorly ventilated spaces - deep wells, sewers, underground tanks. It is also highly flammable, forming explosive mixture with air over a wide range of concentrations (4.3-46%, or 43000-460000 ppm). Hydrogen sulfide created in sewage has an insidious behavior. When the sewage is allowed to stand for long time, hydrogen sulfide can build up in high concentration - up to 6000 ppm, and then gets quickly released when the liquid is disturbed, rapidly building up fatal concentration. This can happen even in open spaces, when opening manhole covers; a stream of escaping gas can be - and often is - deadly. Due to the fast action of the gas in high concentration loss of consciousness is possible even after a single breath. Attempts to rescue unconscious people from spaces with high concentration of hydrogen sulfide often lead to the death of rescuers (so called "second man fatalities").

Health effects

Hydrogen sulfide is considered a broad-spectrum poison, meaning it can poison several different systems in the body, in particular the nervous system. Its toxicity is comparable with hydrogen cyanide. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thereby blocking oxygen from binding and stopping cellular respiration. Poisoning can happen by inhalation of hydrogen sulfide or ingestion of soluble sulfides; absorption through skin is low. Breathing hydrogen sulfide may paralyze the olfactory nerve (making it impossible to smell the gas) and can cause death within just a few breaths. There could be loss of consciousness after one or more breaths. Cases of acute hydrogen sulfide poisonings are rare, occurring mostly in industrial settings; however, emergency physicians should be aware of its symptoms, as quick identification and treatment is critical. An interesting diagnostic clue is discoloration of copper coins in the pockets of the patient. Treatment involves immediate inhalation of amyl nitrite, injections of sodium nitrite, inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm, and in some cases hyperbaric oxygen therapy. Exposure to lower concentrations can result in eye irritation (because of the high alkality of the SH- anion), a sore throat and cough, shortness of breath, and fluid in the lungs. These symptoms usually go away in a few weeks. Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. Higher concentrations of 700-800 ppm tend to be fatal.
- 0.0047 ppm is the recognition threshold, the concentration at which 50% of humans can detect the characteristic rotten egg odor of hydrogen sulfide [http://www.extension.iastate.edu/Publications/PM1963A.pdf]
- 10-20 ppm is the borderline concentration for eye irritation.
- 50-100 ppm leads to eye damage.
- At 150-250 ppm the olfactory nerve is paralyzed after a few inhalations, and the sense of smell disappears, often together with awareness of danger,
- 320-530 ppm leads to pulmonary edema with the possibility of death.
- 530-1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing;
  - 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposition (LC50).
- Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath. Animal studies showed that pigs that ate food containing hydrogen sulfide had diarrhea after a few days and weight loss after about 105 days. According to Lee R. Kump, a geoscientist from Penn State University, a buildup of hydrogen sulfide in the atmosphere could have caused the Permian-Triassic extinction event 252 million years ago. There is some evidence that hydrogen sulfide produced by sulfate-reducing bacteria in the colon may cause or contribute to ulcerative colitis.

Function in the body

Hydrogen sulfide is produced in small amounts by some cells of the mammalian body and has a number of biological functions. (Only two other such gases are currently known: nitric oxide NO and carbon monoxide CO.) It is produced from cysteine by various enzymes. It acts as a vasodilator and is also active in the brain, where it increases the response of the NMDA receptor and facilitates long term potentiation, which is involved in the formation of memory. Eventually the gas is converted to sulfites and further oxidized to thiosulfate and sulfate. In Alzheimer's disease, the concentration of hydrogen sulfide in the brain is abnormally low; in trisomy 21 the body produces an excess of hydrogen sulfide.

Induced hibernation

In 2005, Mark Roth and other scientists from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle demonstrated that mice can be put into a state of suspended animation by applying a low dosage of hydrogen sulfide (80 ppm H2S) in the air. The breathing rate of the animals sank from 120 to 10 breaths per minute and their temperature fell from 37 °C to 2 °C above ambient temperature (in effect, they had become cold-blooded). The mice survived this procedure for 6 hours and afterwards showed no negative health consequences. Such a hibernation occurs naturally in many mammals and also in toads, but not in mice. (Mice can fall into a state called clinical torpor when food shortage occurs). If the H2S-induced hibernation can be made to work in humans, it could be useful in the emergency management of severely injured patients, and in the conservation of donated organs. As mentioned above, hydrogen sulfide binds to cytochrome oxidase and thereby prevents oxygen from binding, which apparently leads to the dramatic slowdown of metabolism. Animals and humans naturally produce some hydrogen sulfide in their body; researchers have proposed that the gas is used to regulate metabolic activity and body temperature, which would explain the above findings.

Participant in the sulfur cycle

Hydrogen sulfide is a major participant in the sulfur cycle, the biogeochemical cycle of sulfur on Earth. As mentioned above, sulfur-reducing and sulfate-reducing bacteria derive energy from converting sulfur or sulfate into hydrogen sulfide by oxidizing hydrogen or organic molecules. Other bacteria liberate hydrogen sulfide from sulfur-containing amino-acids. Several groups of bacteria can use hydrogen sulfide as fuel, oxidizing it to elemental sulfur or to sulfate by using oxygen or nitrate as oxidant. The purple sulfur bacteria and the green sulfur bacteria use hydrogen sulfide as electron donor in photosynthesis, thereby producing elemental sulfur. (In fact, this mode of photosynthesis is older than the mode of cyanobacteria, algae and plants which uses water as electron donor and liberates oxygen.)

Reference

# Giggenbach, W. (1971). Inorg. Chem. 10:1333. Meyer, B.; Ward, K.; Koshlap, K.; & Peter, L. (1983). Inorg. Chem. 22:2345. Myers, R. J. (1986). J. Chem. Educ. 63:687.

External links


- [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc01/icsc0165.htm International Chemical Safety Card 0165]
- [http://www.inchem.org/documents/cicads/cicads/cicad53.htm Concise International Chemical Assessment Document 53]
- [http://www.cdc.gov/niosh/npg/npgd0337.html NIOSH Pocket Guide to Chemical Hazards]
- [http://ptcl.chem.ox.ac.uk/MSDS/HY/hydrogen_sulfide.html MSDS safety data sheet]
- [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15329822&query_hl=7 Abstract of survey article on H2S as used by the body], by P. Kamoun
- [http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4469793.stm BBC about suspended animation by H2S]
- [http://www.compchemwiki.org/index.php?title=Hydrogen_sulfide Computational Chemistry Wiki] Category:Sulfides Category:Hydrogen compounds ja:硫化水素

H2S radar

 area]] The H2S radar was used in bombers of RAF Bomber Command. It was designed to identify targets on the ground for night and all-weather bombing. On January 30 1943, H2S radar was used by RAF bombers for navigation for the first time and so became the first ground mapping radar to be used in combat. Initially it was fitted to Stirling and Halifax bombers and provided a ground mapping capability for both navigation and night bombing. This develoment, using ten-centimeter radar, (actually 9.1 cm) was possible thanks to the development of the cavity magnetron. Later versions of H2S reduced the wavelength used, first to 3 cm and then 1.5 cm, at which wavelength the system was capable of detecting rain clouds. Later in World War II the Luftwaffe night fighters used Naxos radar detectors to home in on the transmissions of H2S. The Americans adapted the X-Band version of H2S (H2S Mk VI) as H2X radar which they regarded as a significant improvement and which was tested by the RAF Bomber Command in 1945.

History

After the Battle of Britain, RAF Bomber Command began to ramp up night attacks against German cities. Unfortunately, although Bomber Command reported grand results from the raids, an independent analysis based on daylight air reconnaissance performed in the summer of 1940 showed that half the bombs fell on open country. Only one bomb in ten actually hit the intended target. Radio electronics promised some relief. The British developed a radio navigation system called "GEE", and then a second long range navigation scheme known as "Oboe". Gee and Oboe were limited in range to a line of sight to the transmitters. A bomber carrying its own, self-contained night targeting system would not be limited in range to a UK-based transmitter. Taffy Bowen had noticed during his early AI experiments before the war that the radar returns from fields, cities, and other areas were distinctively different. He had suggested development of targeting radar, but the matter was forgotten in the chaos. The idea resurfaced in 1941. Philip Dee's group had got a 10 cm / 3 GHz AI flying in a Blenheim in March of that year. The experimental set was known as "AIS" in reference to its S-band operation. During tests of the AIS, Dee's team rediscovered that radar reflections could reveal different types of terrain. In October 1941, Dee attended a meeting of the RAF Bomber Command where the night targeting issue was discussed. After the meeting, on 1 November 1941, Dee performed an experiment in which he used an AIS radar mounted on a Blenheim to scan the ground. He was able to pick up the outline of a town 55 kilometers (35 miles) away. 1 November (bottom) on a Halifax]] The brass were impressed, and on the first day of 1942, the Telecommunications Research Establishment (TRE) set up a team under Bernard Lovell (who later went on to become a leading figure in radio astronomy) to develop an S-band airborne targeting radar, based on AIS. The new targeting radar was designed to fit in a blister on the belly of a bomber, where the antenna would rotate to scan the terrain and feed the reflections to a PPI display, producing a map of sorts of the land below the bomber. The targeting radar was originally designated "BN (Blind Navigation)", but quickly became "H2S". This acronym remains somewhat mysterious, with different sources claiming it meant "Height to Slope"; the smelly compound hydrogen sulfide, with the possible interpretation of "it stinks" (reputedly once used by Lord Cherwell to describe the device); or, with a little rearrangement, "Home Sweet Home". The "S" might have also had some connection to "S-band", but it is plausible the acronym was deliberately obscure and misleading as a security measure. There is also a rumour that it was named after this compound, because the inventor realised that had he simply pointed the radar DOWNWARD instead of towards the sky, he would have an entirely new application for radar, ground tracking instead of simply for identifying air targets, and that it was simply 'rotten' that he hadn't thought of it sooner! H2S performed its first experimental flight on 23 April, with the radar mounted in a Handley Page Halifax bomber. There was much still to be done. For example, in order to display as a uniform a "map" of the terrain as possible, the radar had to have low sensitivity or "gain" for targets directly underneath the bomber, with the gain increasing with the angle of the radar away from vertical. This scheme would become known as "cosecant-squared" scanning, after the mathematical function that defined the change in gain. H2S was the TRE's top priority, and Lovell's team had use of the brilliant Alan Blumlein and other top EMI engineers, but there were snags. Intelligence reports had revealed the Germans had stationed a company of paratroopers near Cherbourg, across the channel, suggesting the enemy might be planning to raid the TRE. On 25 May, the entire organization moved out in another mad, infuriating fire drill from Swanage to Malvern College, about 160 kilometers (100 miles) to the north. Fortunately, this would prove to be the last move. Malvern College As if this weren't bad enough, then an outright disaster occurred. On 7 June 1942, the Halifax performing H2S tests (right) crashed, killing everyone on board and destroying the prototype H2S. One of the dead was Alan Blumlein, and his loss was a major blow to the program. Furthermore, Churchill's science advisor Lord Cherwell wanted the design team to build H2S around the klystron rather than the magnetron. Cherwell was opinionated, obstinate, contrary, something like Churchill himself but without quite as many redeeming features. Most people who had to deal with Cherwell regarded him, with some justification, as an obstructionist who tried to create problems instead of figuring out how to overcome them. He was not always wrong by any means, but he was usually annoying. Lord Cherwell did not want the secret of the magnetron to fall into German hands. Once the Germans understood it, they would not only try to duplicate it, but could quickly develop countermeasures against it. The klystron wasn't as powerful as the magnetron, but it could be much more easily destroyed in an emergency. A magnetron's copper core could survive even large self-destruct charges. The H2S design team did not believe the klystron could do the job, and in fact tests of an H2S built with klystrons instead of the cavity magnetron showed a drop in output power by a factor of 20 to 30. The H2S team also protested that it would take the Germans two years to develop a centimetric radar once the cavity magnetron fell into their hands, and that there was no reason to believe they weren't working on the technology already. The first concern would prove correct; the second would fortunately be proven wrong, though given the widespread parallel development of the cavity magnetron, in hindsight it wasn't an unreasonable assumption. Despite all the problems, on 3 July 1942 Churchill held a meeting with brass and the H2S group, where he shocked the radar designers by demanding the delivery of 200 H2S sets by 15 October 1942. Bomber Command had to have H2S. The H2S design team was under extreme pressure, but they were given priority on resources. The pressure also gave them an excellent argument to convince Lord Cherwell that the klystron-based H2S program be finally dropped. Despite the extraordinary efforts of the TRE, there was no way to meet the 15 October deadline. By 1 January 1943, however, twelve Short Stirling and twelve Halifax bombers had been fitted with H2S. On the night of 30 January 1943, thirteen "Pathfinder" bombers, which dropped incendiaries or flares on a target to "mark" it for other bombers following in the bomber "stream", took off to give H2S its introduction to combat by marking the German city of Hamburg for a strike. Seven of the Pathfinders had to turn back, but six marked the target successfully, which was hit by a hundred Lancasters. The Germans did not know about H2S at the time. Unfortunately, on 2 February 1943, a Pathfinder Stirling was shot down near Rotterdam, and the Germans noticed the unusual gear in its wreckage. The British had been clever with electronics, and the Germans were careful to look for anything out of the ordinary in RAF aircraft forced down in the Reich. Most of the H2S set was recovered except for the display, and German engineers began to work on the "Rotterdam Gerät" (Rotterdam Device), as they called it, however the engineeers were puzzled as to what the equipment actually did. The equipment remained a puzzle, until about a year later a working display was recovered from another aircraft and the complete equipment set-up on one of Berlin's immense concrete flak-towers. When the equipment was switched on and the onlookers saw the display they were horrified, the display recognizably showing Berlin's other flak towers and surrounding area. When Hermann Göring was shown this, he is said to have exclaimed "My God! the British really can see in the dark". Bomber Command didn't use H2S in a big way until that summer. On the night of 24 July 1943, the RAF began Operation Gomorrah, a large-scale systematic attack on Hamburg. At that time, H2S was fitted also to Avro Lancaster, which became a backbone of RAF Bomber Command. With the target marked by Pathfinders using H2S, RAF bombers hit the city with high explosive and incendiary bombs. They returned on the 25th and the 27th, with the USAAF performing two daylight attacks in between the three RAF raids. Large parts of the city were burned to the ground by a terrifying cyclone of fire. About 45,000 people, mostly civilians, were killed. H2S was noteworthy for introducing the Plan Position Indicator, or PPI the rotating-map display that is now familiar to radar operators the world over. Adapted from [http://www.vectorsite.net/ttwiz4.html Microwave Radar At War (1)]. There is a open source verification for this text on the home page [http://www.vectorsite.net/index.html Greg Goebel / In The Public Domain].

See also


- List of World War II electronic warfare equipment

References


- A. P. Rowe: One Story of Radar - Camb Univ Press - 1948
- Dudley Saward, Bernard Lovell: A Biography - Robert Hale - 1984

External links


- [http://histru.bournemouth.ac.uk/Oral_History/Talking_About_Technology/radar_research/contents.html Bournemouth University Radar Recollections site] Category:Aircraft radars Category: World War II British electronics

Hydrogen

|- | Critical temperature || 32.19 K |- | Critical pressure || 1.315 MPa |- | Critical density || 30.12 g/L (Bohr radius) Hydrogen (Latin: hydrogenium, from Greek: hydro: water, genes: forming) is a chemical element in the periodic table that has the symbol H and atomic number 1. At standard temperature and pressure it is a colorless, odorless, nonmetallic, univalent, highly flammable diatomic gas. Hydrogen is the lightest and most abundant element in the universe. It is present in water, all organic compounds (rare exceptions exist, like buckminsterfullerene) and in all living organisms. Hydrogen is able to react chemically with most other elements. Stars in their main sequence are overwhelmingly composed of hydrogen in its plasma state. The element is used in ammonia production, as a lifting gas, as an alternative fuel, and more recently as a power source of fuel cells. Despite its ubiquity in the universe, hydrogen is surprisingly hard to produce in large quantities on the Earth. In the laboratory, the element is prepared by the reaction of acids on metals such as zinc. The electrolysis of water is a simple method of producing hydrogen, but is economically inefficient for mass production. Large-scale production is usually achieved by steam reforming natural gas. Scientists are now researching new methods for hydrogen production; if they succeed in developing a cost-efficient method of large-scale production, hydrogen may become a viable alternative to greenhouse-gas-producing fossil fuels. One of the methods under investigation involves use of green algae; another promising method involves the conversion of biomass derivatives such as glucose or sorbitol at low temperatures using a catalyst. Yet another method is the "steaming" of Carbon, whereby hydrocarbons are broken down with heat to release hydrogen.

Basic features

Hydrogen is the lightest chemical element; its most common isotope comprises just one negatively charged electron, distributed around a positively charged proton (the nucleus of the atom). The electron is bound to the proton by the Coulomb force, the electrical force that one stationary, electrically charged nanoparticle exerts on another. The hydrogen atom has special significance in quantum mechanics as a simple physical system for which there is an exact solution to the Schrödinger equation; from that equation, the experimentally observed frequencies and intensities of the hydrogen's spectral lines can be calculated. Spectral lines are dark or bright lines in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. At standard temperature and pressure, hydrogen forms a diatomic gas, H2, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under extreme pressures, such as those at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the extremely low pressure in space—virtually a vacuum—the element tends to exist as individual atoms, simply because there is no way for them to combine. However, clouds of H2 and singular hydrogen atoms are said to form in H I and H II regions and are associated with star formation, however the existence of singular hydrogen atoms is disputed.. Hydrogen plays a vital role in powering stars through the proton–proton and carbon–nitrogen cycle. These are nuclear fusion processes, which release huge amounts of energy in stars and other hot celestial bodies as hydrogen atoms combine into helium atoms. H2 is highly soluble in water, alcohol, and ether. It has a high capacity for adsorption, in which it is attached to and held to the surface of some substances. It is an odorless, tasteless, colorless, and highly flammable gas that burns at concentrations as low as 4% H2 in air. It reacts violently with chlorine and fluorine, forming hydrohalic acids that can damage the lungs and other tissues. When mixed with oxygen, hydrogen explodes on ignition. A unique property of hydrogen is that its flame is completely invisible in air. This makes it difficult to tell if a leak is burning, and carries the added risk that it is easy to walk into a hydrogen fire inadvertently. See also: hydrogen atom.

Applications

Large quantities of hydrogen are needed in the chemical and petrolium industries, notably in the Haber process for the production of ammonia, which by mass ranks as the world's fifth most highly produced industrial compound. Hydrogen is used in the hydrogenation of fats and oils (into items such as margarine), and in the production of methanol. Hydrogen is used in hydrodealkylation, hydrodesulfurization, and hydrocracking. The element has several other important uses.
- The element is used in the manufacture of hydrochloric acid, in welding processes, and in the reduction of metallic ores.
- It is an ingredient in rocket fuels.
- It is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas.
- Liquid hydrogen is used in cryogenic research, including superconductivity studies.
- Since hydrogen is 14.5 times lighter than air, it was once widely used as a lifting agent in balloons and airships. However, this use was curtailed when the Hindenburg disaster convinced the public that the gas was too dangerous for this purpose.
- Deuterium, an isotope of hydrogen (hydrogen-2), is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.
- Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints. There are no "hydrogen wells" or "hydrogen mines" on Earth, so hydrogen cannot be considered a primary energy source like fossil fuels or uranium. Hydrogen can however be burned in internal combustion engines, an approach advocated by BMW's experimental hydrogen car. However, it is currently difficult and dangerous to store and handle in sufficient quantity for motor fuel use. Hydrogen fuel cells are being investigated as mobile power sources with lower emissions than hydrogen-burning internal combustion engines. The low emissions of hydrogen in internal combustion engines and fuel cells are currently offset by the pollution created by hydrogen production. This may change if the substantial amounts of electricity required for water electrolysis can be generated primarily from low pollution sources such as nuclear energy or wind. Research is being conducted on hydrogen as a replacement for fossil fuels. It could become the link between a range of energy sources, carriers and storage. Hydrogen can be converted to and from electricity (solving the electricity storage and transport issues), from bio-fuels, and from and into natural gas and diesel fuel. All of this can theoretically be achieved with zero emissions of CO2 and toxic pollutants.

History

Hydrogen was first produced by Theophratus Bombastus von Hohenheim (1493–1541)—also known as Paracelsus—by mixing metals with acids. He was unaware that the explosive gas produced by this chemical reaction was hydrogen. In 1671, Robert Boyle described the reaction between two iron fillings and dilute acids, which results in the production of gaseous hydrogen. In 1766, Henry Cavendish was the first to recognize hydrogen as a discrete substance, by identifying the gas from this reaction as "inflammable" and finding that the gas produces water when burned in air. Cavendish stumbled on hydrogen when experimenting with acids and mercury. Although he wrongly assumed that hydrogen was a compound of mercury—and not of the acid—he was still able to accurately describe several key properties of hydrogen. Antoine Lavoisier gave the element its name and proved that water is composed of hydrogen and oxygen. One of the first uses of the element was for balloons. The hydrogen was obtained by mixing sulfuric acid and iron. Harold C. Urey discovered Deuterium, an isotope of hydrogen, by repeated distilling the same sample of water. For this discovery, Urey received the Nobel prize for in 1934. In the same year, the third isotope, tritium, was discovered. Because of its relatively simple structure, hydrogen has often been used in models of how an atom works.

Electron energy levels

The ground state energy level of the electron in a Hydrogen atom is 13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm. With the Bohr Model the energy levels of Hydrogen can be calculated fairly accurately. This is done by modeling the electron as revolving around the proton, much like the earth revolving around the sun. Except the sun holds earth in orbit with the force of gravity, but the proton holds the electron in orbit with the force of electromagnetism. Another difference between the Earth-Sun system and the Electron-Proton system is that, in this model, due to quantum mechanics the electron is allowed to only be at very specific distances from the proton. Modeling the hydrogen atom in this fashion yields the correct energy levels and spectrum.

Occurrence

quantum mechanics.]] Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance in stars and gas giant planets. It is very rare in the Earth's atmosphere (1 ppm by volume), because being the lightest gas causes it to escape Earth's gravity, though when compounds are considered, it is the tenth most abundant element on Earth. The most common source for this element on Earth is water, which is composed two parts hydrogen to one part oxygen (H2O). Other sources include most forms of organic matter (currently all known life forms) including coal, natural gas, and other fossil fuels. Methane (CH4) is an increasingly important source of hydrogen. Throughout the Universe, hydrogen is mostly found in the plasma state whose properties are quite different to molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity, even when the gas is only partially ionised. The charged particles are highly influenced by magnetic and electric fields, for example, in the Solar Wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen can be prepared in several different ways: steam on heated carbon, hydrocarbon decomposition with heat, reaction of a strong base in an aqueous solution with aluminium, water electrolysis, or displacement from acids with certain metals. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (700–1100 °C), steam reacts with methane to yield carbon monoxide and hydrogen. :CH4 + H2O → CO + 3 H2 Additional hydrogen can be recovered from the carbon monoxide through the water-gas shift reaction: :CO + H2O → CO2 + H2

Compounds

The lightest of all gases, hydrogen combines with most other elements to form compounds. Hydrogen has an electronegativity of 2.2, so it forms compounds where it is the more nonmetallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H- ions or just as a solute within the other element (as in palladium hydride). The latter tend to be covalent, since the H+ ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. These both form acids. Thus even in an acidic solution one sees ions like hydronium (H3O+) as the protons latch on to something. Although exotic on earth, one of the most common ions in the universe is the H3+ ion. Hydrogen combines with oxygen to form water, H2O, and releases a lot of energy in doing so, burning explosively in air. Deuterium oxide, or D2O, is commonly referred to as heavy water. Hydrogen also forms a vast array of compounds with carbon. Because of their association with living things, these compounds are called organic compounds, and the study of the properties of these compounds is called organic chemistry. organic chemistry

Forms

Under normal conditions, hydrogen gas is a mix of two different kinds of molecules which differ from one another by the relative spin of the nuclei. These two forms are known as ortho- and para-hydrogen (this is different from isotopes, see below). In ortho-hydrogen the nuclear spins are parallel (form a triplet), while in para they are antiparallel (form a singlet). At standard conditions hydrogen is composed of about 25% of the para form and 75% of the ortho form (the so-called "normal" form). The equilibrium ratio of these two forms depends on temperature, but since the ortho form has higher energy (is an excited state), it cannot be stable in its pure form. In low temperatures (around boiling point), the equilibrium state is comprised almost entirely of the para form. The conversion process between the forms is slow, and if hydrogen is cooled down and condensed rapidly, it contains large quantities of the ortho form. It is important in preparation and storage of liquid hydrogen, since the ortho-para conversion produces more heat than the heat of its evaporation, and a lot of hydrogen can be lost by evaporation in this way during several days after liquefying. Therefore, some catalysts of the ortho-para conversion process are used during hydrogen cooling. The two forms have also slightly different physical properties. For example, the melting and boiling points of parahydrogen are about 0.1 K lower than of the "normal" form.

Isotopes

Hydrogen is the only element that has different names for its isotopes. (During the early study of radioactivity, various heavy radioactive isotopes were given names, but such names are no longer used, although one element, radon, has a name that originally applied to only one of its isotopes.) The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, although this is not officially sanctioned. (The symbol P is already in use for phosphorus and is not available for protium.) ;1H The most common isotope of hydrogen, this stable isotope has a nucleus consisting of a single proton; hence the descriptive, although rarely used, name protium. The spin of a protium atom is 1/2+. ;2H The other stable isotope is deuterium, with an extra neutron in the nucleus. Deuterium comprises 0.0184%–0.0082% of all hydrogen (IUPAC); ratios of deuterium to protium are reported relative to the VSMOW standard reference water. The spin of a deuterium atom is 1+. ;3H The third naturally occurring hydrogen isotope is the radioactive tritium. The tritium nucleus contains two neutrons in addition to the proton. It decays through beta decay and has a half-life of 12.32 years. Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. Like ordinary hydrogen, tritium reacts with the oxygen in the atmosphere to form T2O. This radioactive "water" molecule constantly enters the Earth's seas and lakes in the form of slightly radioactive rain, but its half-life is short enough to prevent a buildup of hazardous radioactivity. The spin of a tritium atom is 1/2+. ;4H Hydrogen-4 was synthesized by bombarding tritium with fast-moving deuterium nuclei. It decays through neutron emission and has a half-life of 9.93696x10-23 seconds. The spin of a hydrogen-4 atom is 2-. ;5H In 2001 scientists detected hydrogen-5 by bombarding a hydrogen target with heavy ions. It decays through neutron emission and has a half-life of 8.01930x10-23 seconds. ;6H Hydrogen-6 decays through triple neutron emission and has a half-life of 3.26500-22 seconds. ;7H In 2003 hydrogen-7 was created ([http://physicsweb.org/articles/news/7/3/3 article]) at the RIKEN laboratory in Japan by colliding a high-energy beam of helium-8 atoms with a cryogenic hydrogen target and detecting tritons—the nuclei of tritium atoms—and neutrons from the breakup of hydrogen-7, the same method used to produce and detect hydrogen-5.

See also


- Antihydrogen
- Deuterium
- Fuel cell
- Hydrogen atom
- Hydrogen bomb
- Hydrogen bond
- Hydrogen car
- Hydrogen cycle
- Hydrogen economy
- Hydrogen line
- Hydrogen molecule
- Hydrogen spectral series
- Hydrogen station
- Liquid Hydrogen
- Periodic table
- Photohydrogen
- Tritium

References

# # # # # #
- [http://www.riken.go.jp/engn/r-world/research/lab/wako/ribeam/ RIKEN Beam Science Laboratory, Japan - Heavy hydrogen research]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes] Fourteenth Edition: Chart of the Nuclides, General Electric Company, 1989 ;Book references:
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External links


- [http://www.hydropole.ch/Hydropole/Intro/Phasediag.gif Hydrogen phase diagram.]
- [http://www.compchemwiki.org/index.php?title=Hydrogen Computational Chemistry Wiki] Category:Nonmetals Category:Fuels Category:Chemical elements ko:수소 ms:Hidrogen ja:水素 simple:Hydrogen th:ไฮโดรเจน

Toxic

Toxic may refer to:
- A state in which something is dangerously poisonous. A measure of this is its toxicity.
- A 2004 song by Britney Spears: see Toxic (song).
- [http://www.garageband.com/artist/toxic_circus Toxic Circus] is an experimental rock band. High energy music with a rock influence yet freely using elements of other styles such as dance, electronic, funk and more.

Egg (biology)

In some animals, an egg is the zygote, resulting from fertilization of the ovum. It nourishes and protects the embryo. Oviparous animals are animals that lay eggs, with little or no other development within the mother. This is the reproductive way of many fish, amphibians and reptiles, all birds, the monotremes, and most insects and arachnids. Reptile eggs, bird eggs, and monotreme eggs are surrounded by a protective shell, either flexible or inflexible. The 1.5 kg ostrich egg is the largest existing single cell currently known, though the extinct Aepyornis and some dinosaurs had larger eggs. The bee hummingbird produces the smallest known bird egg, which weighs half of a gram. The eggs laid by some reptiles and most fish are even smaller, and those of insects and other invertebrates are much smaller still. The study or collecting of eggs, in particular bird eggs, is called oology.

Bird eggs

After fertilization, the bird egg is laid by the female and is incubated for a time that varies according to the species; then a single young hatches from each egg. Average clutch sizes range from 1 (as in condors) to about 17 (the Grey Partridge).

Colors

Grey Partridge Different animals produce different colored eggs. The pigments protoporphyrin, biliverdin, and zinc chelate of biliverdin, are responsible for the diversity of egg color in birds. These pigments are secreted by cells in the oviduct wall, and can cause speckles if color is added right before the egg is laid. The eggs of modern reptiles are all white, and it is thought that this was true for all animals long ago. The markings of many birds' eggs may provide camouflage. Cavity-nesting birds such as woodpeckers and kingfishers do not need camouflaged eggs. Their eggs are often bright white, making it easy for the parent to locate them. In species such as the Common Guillemot, which nest in large groups, each female's eggs have very different markings, making it easier for females to identify their own egg.

Shell structure

Eggs are usually smooth, but there are exceptions. A cormorant's egg, for example, is quite rough and is very chalky. In contrast, tinamous have very shiny eggs, and ducks have oily and waterproof eggs. Another variation is the very heavily pitted eggs of cassowaries. There are tiny pores in the shells of eggs to allow the unborn animal to breathe. The domestic hen's egg has around 7500 pores.

Shape

Most bird eggs have a characteristic oval shape, with one end rounded and the other more pointy. This shape results from the egg being forced through the oviduct. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointy end develops at the back side.

Predation

oviduct There are numerous animals that feed on eggs. Principal predators of the Black Oystercatcher's eggs, for example, include raccoons, skunks, mink, river and sea otters, gulls, crows and foxes. The Stoat (Mustela erminea) and Long-tailed Weasel (M. frenata) steal ducks' eggs. The egg-eating snakes (genera Dasypeltis and Elachistodon) specialize in eating eggs.

Fish eggs

egg-eating snake, are often laid on the underside of leaves.]]

Yolk in fish

egg-eating snake egg-eating snake, and because they are relatively heavy they have to swimm quite strong, burning down the yolk - then there is a "point of no return" after a few days, and if they don't learn how to hunt they die]]
egg-eating snake, in the lower right the blood vessels surround the yolk and in the upper left the black eyes are visible, even the lens]] egg-eating snake

See also


- Chicken sexer
- Egg yolk
- Egg white
- Incubate
- Nest
- Oology - the study or collecting of eggs.
- Trophic egg Category:Reproductive system ja:卵

Bacteria

Actinobacteria
Aquificae
Bacteroidetes/Chlorobi
Chlamydiae/Verrucomicrobia
Chloroflexi
Chrysiogenetes
Cyanobacteria
Deferribacteres
Deinococcus-Thermus
Dictyoglomi
Fibrobacteres/Acidobacteria
Firmicutes
Fusobacteria
Gemmatimonadetes
Nitrospirae
Planctomycetes
Proteobacteria
Spirochaetes
Thermodesulfobacteria
Thermomicrobia
Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. Most are microscopic and unicellular, with a relatively simple cell structure lacking a cell nucleus, and organelles such as mitochondria and chloroplasts. Their cell structure is further described in the article about prokaryotes, because bacteria are prokaryotes, in contrast to organisms with more complex cells, called eukaryotes. The term "bacteria" has variously applied to all prokaryotes or to a major group of them, otherwise called the eubacteria, depending on ideas about their relationships. In Wikipedia, bacteria is used specifically to refer to the eubacteria. Bacteria are the most abundant of all organisms. They are ubiquitous in soil, water, and as symbionts of other organisms. Many pathogens are bacteria. Most are minute, usually only 0.5-5.0 μm in their longest dimension, although giant bacteria like Thiomargarita namibiensis and Epulopiscium fishelsoni may grow past 0.5 mm in size. They generally have cell walls, like plant and fungal cells, but with a very different composition (peptidoglycans). Many move around using flagella, which are different in structure from the flagella of other groups.

History and taxonomy

The first bacteria were observed by Antony van Leeuwenhoek in 1683 using a single-lens microscope of his own design. The name bacterium was introduced much later, by Ehrenberg in 1828, derived from the Greek word βακτηριον meaning "small stick". Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described the role of bacteria as conveyors and causes of disease or pathogens.

Metabolism

Bacteria show a wide variety of different metabolisms and can accordingly be classified into primary nutritional groups. The most common division is between heterotrophs, which depend on an organic source of carbon, and autotrophs, which are able to synthesize organic compounds from carbon dioxide and water. Autotrophs that obtain energy by oxidizing chemical compounds are called chemotrophs, and those that obtain their energy from light, via photosynthesis, are called phototrophs. There are many variations on this terminology such as chemoautotrophs and photosynthetic autotrophs and so on. In addition, bacteria are distinguished based on the source of reducing equivalents they are using. Those using inorganic compounds (e. g. water, hydrogen, sulfide or ammonia) for this purpose are called lithotrophs and others needing organic compounds (e. g. sugars or organic acids) and are called organotrophs. The metabolic modes of energy metabolism (phototrophy or chemotrophy), reducing equivalent sources (lithotrophy or organotrophy) and carbon sources (autotrophy or heterotrophy) can be combined differently in any single microorganism, and even shifting between different modes frequently occurs in many species. Other nutritional requirements include nitrogen, sulfur, phosphorus, vitamins and metallic elements such as sodium, potassium, calcium, magnesium, manganese, iron, zinc, cobalt, copper and nickel for normal growth. For some species, additional trace elements such as selenium, tungsten, vanadium or boron are needed. Based on their response to oxygen, most bacteria can be placed into one of three groups: Some bacteria can grow only in the presence of oxygen and are called aerobes; others can grow only in the absence of oxygen and are called anaerobes; and some can grow in the presence or absence of oxygen and are called facultative anaerobes.

Movement

Motile bacteria can move about, either using flagella, bacterial gliding, or changes of buoyancy. A unique group of bacteria, the spirochaetes, have structures similar to flagella, called axial filaments, between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Bacterial flagella are arranged in many different ways. Bacteria can have a single polar flagellum at one end of a cell, clusters of many flagella at one end or flagella scattered all over the cell, as with Peritrichous. Many bacteria (such as E.coli) have two distinct modes of movement: forward movement (swimming) and tumbling. The tumbling allows them to reorient and introduces an important element of randomness in their forward movement. (see external links below for link to videos). Motile bacteria are attracted or repelled by certain stimuli, behaviors called taxes - for instance, chemotaxis, phototaxis, mechanotaxis and magnetotaxis. In one peculiar group, the myxobacteria, individual bacteria attract to form swarms and may differentiate to form fruiting bodies. The myxobacteria move only when on solid surfaces, unlike E. coli which is motile in liquid or solid media.

Groups and identification

myxobacteria Bacteria come in a variety of different shapes. Most are rod-shaped, sphere-shaped, or helix-shaped; these are respectively referred to as bacilli, cocci, and spirilla. An additional group, vibrios, are comma-shaped. Shape is no longer considered a defining factor in the classification of bacteria, but many genera are named for their shape (e.g. Bacillus, Streptococcus, Staphylococcus) and it is an important part in their identification. Another important tool is Gram staining, named after Hans Christian Gram who developed the technique. This separates bacteria into two groups, based on the composition of their cell wall. The first formal grouping of bacteria into phyla was based largely on this test:
- Gracilicutes - bacteria with a second cell membrane containing lipids, giving them Gram-negative stains
- Firmicutes - bacteria with a single membrane and thick peptidoglycan wall, giving them Gram-positive stains
- Mollicutes - bacteria with no second membrane or wall, giving them Gram-negative stains The archeabacteria were originally included as the Mendosicutes. As given, these phyla are no longer believed to represent monophyletic groups. The Gracilicutes have been divided into many different phyla. Most gram-positive bacteria are placed in the phyla Firmicutes and Actinobacteria, which are closely related. However, the Firmicutes have been redefined to include the mycoplasmas (Mollicutes) and certain Gram-negative bacteria.

Benefits and dangers

Bacteria are both harmful and useful to the environment, and animals, including humans. The role of bacteria in disease and infection is important. Some bacteria act as pathogens and cause tetanus, typhoid fever, pneumonia, syphilis, cholera, foodborne illness and tuberculosis. Sepsis, a systemic infectious syndrome characterized by shock and massive vasodilation, or localized infection, can be caused by bacteria such as streptococcus, staphylococcus, or many gram-negative bacteria. Some bacterial infections can spread throughout the host's body and become systemic. In plants, bacteria cause leaf spot, fireblight, and wilts. The mode of infection includes contact, air, food, water, and insect-borne microorganisms. The hosts infected with the pathogens may be treated with antibiotics, which can be classified as bacteriocidal and bacteriostatic, which at concentrations that can be reached in bodily fluids either kill bacteria or hamper their growth, respectively. Antiseptic measures may be taken to prevent infection by bacteria, for example, prior to cutting the skin during surgery or swabbing skin with alcohol when piercing the skin with the needle of a syringe. Sterilization of surgical and dental instruments is done to make them sterile or pathogen-free to prevent contamination and infection by bacteria. Sanitizers and disinfectants are used to kill bacteria or other pathogens to prevent contamination and risk of infection. In soil, microorganisms help in the transformation of nitrogen to ammonia with enzymes secreted by these microbes, which reside in the rhizosphere (a zone that includes the root surface and the soil that adheres to the root after gentle shaking). Some bacteria are able to use molecular nitrogen as their source of nitrogen, converting it to nitrogenous compounds, a process known as nitrogen fixation. Many other bacteria are found as symbionts in humans and other organisms. For example, the presence of the gut flora in the large intestine can help prevent the growth of potentially harmful microbes. The ability of bacteria to degrade a variety of organic compounds is remarkable. Highly specialized groups of microorganisms play important roles in the mineralization of specific classes of organic compounds. For example, the decomposition of cellulose, which is one of the most abundant constituents of plant tissues, is mainly brought about by aerobic bacteria that belong to the genus Cytophaga. This ability has also been utilized by humans in industry, waste processing, and bioremediation. Bacteria capable of digesting the hydrocarbons in petroleum are often used to clean up oil spills. Some beaches in Prince William Sound were fertilized in an attempt to facilitate the growth of such bacteria after the infamous 1989 Exxon Valdez oil spill. These efforts were effective on beaches that were not too thickly covered in oil. Bacteria, often in combination with yeasts and molds, are used in the preparation of fermented foods such as cheese, pickles, soy sauce, sauerkraut, vinegar, wine, and yogurt. Using biotechnology techniques, bacteria can be bioengineered for the production of therapeutic drugs, such as insulin, or for the bioremediation of toxic wastes.

Miscellaneous

Two organelles, mitochondria and chloroplasts, are generally believed to have been derived from endosymbiotic bacteria. Microorganisms are widely distributed and are most abundant where they have food, moisture, and the right temperature for their multiplication and growth. They can be carried by air currents from one place to another. The human body is home to billions of microorganisms; they can be found on skin surfaces, in the intestinal tract, in the mouth, nose, and other body openings. They are in the air one breathes, the water one drinks, and the food one eats. The great antiquity of the bacteria has enabled them to evolve a great deal of genetic diversity. They are far more diverse than, say, the mammals or insects. For instance, the genetic distance between E. coli and Thermus aquaticus is greater than the distance between humans and oak trees.

See also


- Bacterial growth
- Bacteriocin
- Magnetotactic bacteria
- Microorganism
- Nanobacterium

References


- Some text in this entry was merged with the Nupedia article entitled Bacteria, written by Nagina Parmar; reviewed and approved by the Biology group (editor: Gaytha Langlois, lead reviewer: Gaytha Langlois, lead copyeditors: Ruth Ifcher and Jan Hogle)
-

Further reading


- Alcamo, I. Edward. Fundamentals of Microbiology. 5th ed. Menlo Park, California: Benjamin Cumming, 1997.
- Atlas, Ronald M. Principles of Microbiology. St. Louis, Missouri: Mosby, 1995.
- Holt, John.G. Bergey's Manual of Determinative Bacteriology. 9th ed. Baltimore, Maryland: Williams and Wilkins, 1994.
- Stanier, R.Y., J. L. Ingraham, M. L. Wheelis, and P. R. Painter. General Microbiology. 5th ed. Upper Saddle River, New Jersey: Prentice Hall, 1986.
- Hugenholtz P, Goebel BM, Pace NR. Impact of Culture-Independent Studies on the Emerging Phylogenetic View of Bacterial Diversity. J Bacteriol 1998;180:4765-4774. [http://jb.asm.org/cgi/content/full/180/18/4765?view=full&pmid=9733676 Fulltext] / PMID 9733676.

External links


- [http://www.dsmz.de/bactnom/bactname.htm Bacterial Nomenclature Up-To-Date from DSMZ]
- [http://www.sciencenews.org/pages/sn_arc99/4_17_99/fob5.htm The largest bacteria]
- [http://tolweb.org/tree?group=Eubacteria&contgroup=Life_on_Earth Tree of Life]
- [http://www.rowland.harvard.edu/labs/bacteria/index_movies.html Videos] of bacteria swimming and tumbling, use of optical tweezers and other fine videos.
- Category:Bacteriology ko:세균 ja:真正細菌 th:แบคทีเรีย

Swamp

:This article is about the wetland type (a landform). For other uses of the term "swamp", see swamp (disambiguation). A swamp is a wetland that features permanent inundation of large areas of land by shallow bodies of water, generally with a substantial number of hummocks, or dry-land protrusions. Swamps usually are regarded as including a large amount of woody vegetation. When a wetland area does not, it is usually termed a marsh. A mire (or quagmire) is a low-lying wetland of deep, soft soil or mud that sinks underfoot. Swamps are generally characterized by very slow-moving waters, often rich in tannins from decaying vegetation. They are usually associated with adjacent rivers or lakes. In some cases, rivers become swamps for a distance. Swamps are features of areas with very low topographic relief, although they may be surrounded by mountains. The most famous swamps in the United States are the Okefenokee Swamp (home to the cartoon characters of Pogo, by Walt Kelly) and the Great Dismal Swamp. The Okefenokee is located in extreme southeastern Georgia and extends slightly into northeastern Florida. The Great Dismal Swamp lies in extreme southeastern Virginia and extreme northeastern North Carolina. Both are National Wildlife Refuges. Another swamp area, Reelfoot Lake of extreme western Tennessee, was created by the New Madrid earthquake of 1812. Caddo Lake, the Great Dismal and Reelfoot are swamps that are centered at large lakes. Swamps are often called bayous in the southeastern United States. Swamps are characterized by rich biodiversity and specialized organisms. For instance, southeastern U.S. swamps, such as those mentioned above, feature trees such as the Bald cypress and Water tupelo, which are adapted to growing in standing water, and animals such as the American alligator. A common species name in biological nomenclature is the Latin palustris, meaning "of the swamp". Examples of this are Quercus palustris (pin oak) and Thelypteris palustris (marsh fern). marsh fern]]

List of Major Swamps

Africa


- Bangweulu Swamp, Zambia
- Okavango Swamp, Botswana
- Sudd, Sudan
- Niger Delta,Nigeria

Asia


- Asmat Swamp, Indonesia
- Vasyugan Swamp, Russia

North America


- Caddo Lake, United States
- Great Black Swamp, United States
- Great Dismal Swamp, United States
- Okefenokee Swamp, Georgia, United States
- Reelfoot Lake, United States
- Big Cypress National Preserve, Florida, United States
- Limberlost, Indiana, United States
- Honey Island Swamp, Louisiana, United States

South America


- Pantanal, Brazil

See also


- Will o' the wisp
- Marsh gas
- Slough
- Hydrogen sulfide
- Marsh
- Muck
- Peat
- Aquatic plant Category:Landforms

Volcano

:Eruption redirects here. For other meanings of the word eruption, see eruption (disambiguation) A volcano is a geological landform (usually a mountain) where a substance, usually magma (rock of the Earth's interior made molten or liquid by extremely high temperatures along with a reduction in pressure and/or the introduction of water or other volatiles) erupts through the surface of a planet. Although there are numerous volcanoes (some very active) on the solar system's rocky planets and moons, on Earth at least, this phenomenon tends to occur near the boundaries of the continental plates. However, important exceptions exist in hotspot volcanoes. hotspot volcanoes.]] The name "volcano" originates from the name of Vulcan, a god of fire in Roman mythology. The study of volcanoes is called vulcanology (or volcanology in some spellings). Mud volcanoes are formations which are often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano. This article describes igneous volcanoes.

Volcano classification

Erupted material

One way of classifying volcanoes is by the type of material erupted, which affects the shape of the volcano. If the erupting magma contains a high percentage (65%) of silica the lava is called felsic or acidic and tends to be highly viscous (not very fluid) and is pushed up in a blob that will solidify relatively quickly. Lassen Peak in California is an example. This type of volcano has a tendency to explode because it retains the volatiles or gases and easily plugs. Mount Pelée on the island of Martinique is another example. If, on the other hand, the magma contains a relatively low percentage of silica, the lava is called mafic or basic and will be very fluid as it erupts, capable of flowing for long distances. Due to the low viscosity the volatiles are able to escape. A good example of a mafic lava flow is the Great flow produced by an eruptive fissure almost in the geographical center of Iceland roughly 8,000 years ago; it flowed to the sea, a distance of 130 kilometers, and covered an area of 800 square km.

Explosivity

The behaviour of volcanoes range from rare collossally explosive events to common cases of long term, gradual and gentle flow of magma. The Volcanic Explosivity Index is an attempt to categorise these into clear types, with low VEI values corresponding to gentle flows and high VEIs indicating a cataclysmic event with severe global consequences.

Shape

Shield volcanoes

Hawaii and Iceland are examples of places where volcanoes extrude huge quantities of lava that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, Mauna Loa, is 9,000 m tall (it sits on the sea floor), 120 km in diameter and forms part of the Island of Hawai. Olympus Mons is a shield volcano on Mars, and the tallest mountain in the known solar system. Smaller versions of the "lava shield" include the 'lava dome' (tholoid), 'lava cone', and 'lava mound'. Volcanic cones or cinder cones result from eruptions that throw out mostly small pieces of rock that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 300 m high.

Stratovolcanoes or composite volcanoes

These are tall conical mountains composed of both lava flows and ejected material, which form the strata that give rise to the name. Classic examples include Mt. Fuji in Japan and Mount Mayon in the Philippines. Volcanoes on land often take the form of flat cones, as the expulsions build up over the years, or in short-lived volcanic cones, cinder cones.

Supervolcanoes

Supervolcano is the popular term for large volcanoes that usually have a large caldera and can potentially produce devastation on a continental scale and cause major global weather pattern changes. Potential candidates include Yellowstone National Park and Lake Toba, but are hard to identify given that there is no formal definition of the term.

Submarine volcanoes

Submarine volcanoes are common features on certain zones of the ocean floor. Some are active at the present time and, in shallow water, disclose their presence by blasting steam and rock-debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them results in high, confining pressure and prevents the formation and explosive release of steam and gases. Even very large, deepwater eruptions may not disturb the ocean surface. Under water, volcanoes often form rather steep pillars and in due time break the ocean surface in new islands.

Active, Dormant, or Extinct?

Supervolcano Volcanoes are usually situated either at the boundaries between tectonic plates or over geology hotspots. Volcanoes may be either dormant (having no activity) or active (near constant expulsion and occasional eruptions), and change state unpredictably. Surprisingly, there is no consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of activity. Given the long lifespan of such volcanoes, they are very active. By our lifespans, however, they are not. Complicating the definition are volcanoes that become restless but do not actually erupt. Are these volcanoes active? Scientists usually consider a volcano active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in Hawaii, little more than 200 years. Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since calderas have lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. For example, the Yellowstone Caldera (considered a Supervolcano) in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years — although there has been some minor activity as relatively recent as 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera as extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be a very active volcano.

Notable Volcanoes

Volcanoes on Earth

:Main article: List of volcanoes List of volcanoes
- Mount Baker (Washington, USA)
- Cold Bay Volcano (Alaska, USA)
- El Chichon/El Chichonal, (Chiapas, Mexico)
- Citlaltépetl/Pico de Orizaba, (Veracruz/Puebla, Mexico)
- Cotopaxi (Ecuador)
- Mount Fuji (Honshu, Japan)
- Mount Hood (Oregon, USA)
- Mount Erebus (Ross Island, Antarctica)
- Etna (Sicily, Italy)
- Krafla (Iceland)
- Hekla (Iceland)
- Kick-'em-Jenny, (Grenada)
- Kilauea (Hawaii, USA)
- Kluchevskaya (Kamchatka, Russia)
- Krakatoa (Rakata, Indonesia)
- Mauna Kea (Hawaii, USA)
- Mauna Loa (Hawaii, USA)
- El Misti (Arequipa, Peru)
- Novarupta (Alaska, USA)
- Paricutín (Michoacán, Mexico)
- Mount Pinatubo (Luzon Island, Philippines)
- Popocatépetl (Mexico-Puebla state line, Mexico)
- Santorini (Santorini islands, Greece)
- Soufriere Hills volcano, (Montserrat)
- Stromboli (Aeolian Islands, Italy)
- Mount Rainier (Washington, USA)
- Mount Shasta (California, USA)
- Mount St. Helens (Washington, USA)
- Surtsey (Iceland)
- Tambora (Sumbawa, Indonesia)
- Teide (Tenerife, Canary Islands, Spain)
- White Island (Bay of Plenty, New Zealand)
- Mount Vesuvius (Bay of Naples, Italy)

Volcanoes elsewhere in the solar system

Italy, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.]] The Earth's Moon has no large volcanoes, but does have many volcanic features such as rilles and domes. The planet Venus is believed to be volcanically active, and its surface is 90% basalt, indicating that volcanism plays a major role in shaping its surface. Lava flows are widespread and many of its surface features are attributed to exotic forms of volcanism not present on Earth. Other Venusian phenomena, such as changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions. There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth:
- Arsia Mons
- Ascraeus Mons
- Hecates Tholus
- Olympus Mons
- Pavonis Mons These volcanoes have been extinct for many millions of years, but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well. Jupiter's moon Io is the most volcanic object in the solar system, due to tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, with the result that the moon is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1800 K (1500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io [http://www2.keck.hawaii.edu/news/archive/eruption/]. See the list of geological features on Io for a list of named volcanoes on the moon. list of geological features on Io In 1989 the Voyager 2 spacecraft observed ice volcanoes (cryovolcanism) on Triton, a moon of Neptune and in 2005 the Cassini-Huygens probe photographed fountains of frozen particles erupting from Saturn's moon Enceladus. The ejecta are believed to consist of liquid nitrogen, dust, or methane compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere. [http://www.newscientist.com/article.ns?id=dn7489] It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.

Volcanology

Volcano formation

Quaoar Like most of the interior of the earth, the movements and dynamics of magma are poorly understood. However, it is known that an eruption usually follows movement of magma upwards into the solid layer (the earth's crust) beneath a volcano and occupying a magma chamber. Eventually, magma in the chamber is forced upwards and flows out across the planet surface as lava, or the rising magma can heat water in the surrounding landform and cause explosive discharges of steam; either this or escaping gases from the magma can produce forceful ejections of rocks, cinders, volcanic glass, and/or volcanic ash also known as tephra. While always displaying powerful forces, eruptions can vary from effusive to extremely explosive. Most volcanoes on the land are formed at destructive plate margins: where oceanic crust is forced below the continental crust because oceanic crust is denser than continental crust. Friction between these moving plates will cause the oceanic crust to melt, and reduced density will force the newly formed magma to rise. As the magma rises through weak areas in the continental crust it may eventually erupt as one or more volcanoes. For example, Mount St. Helens is found inland from the margin between the oceanic Juan de Fuca Plate and the continental North American Plate. North American Plate A volcano generally presents itself to the imagination as a mountain sending forth from its summit great clouds of smoke with vast sheets of flame. The truth is that a volcano seldom emits either smoke or flame, although various combinations of hydrogen, carbon, oxygen, and sulfur do sometimes ignite. What is mistaken for smoke consists of vast volumes of fine dust, mingled with steam and other vapors, chiefly sulfurous. Most of what appears to be flames is the glare from the erupting materials, glowing because of their high temperature; this glare reflects off the clouds of dust and steam, resembling fire. Perhaps the most conspicuous part of a volcano is the crater, a basin of a roughly circular form within which occurs a vent (or vents) from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of vast depth. Very large features of this sort are termed calderas. Some volcanoes consist of a crater alone, with scarcely any mountain at all; but in the majority of cases the crater is situated on top of a mountain (the volcano), which can tower to an enormous height. Volcanoes that terminate in a principal crater are usually of a conical form. Volcanic cones are usually smaller features composed of loose ash and cinder, w