1.
Meteorite classification
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The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, asteroid, Moon, or other current Solar System object, as such information comes to light, the classification system will most likely evolve. Beyond the assignment of meteorites into groups, which essentially universally accepted and it is also fairly common for groups that seem to be closely related to be referred to as clans. In turn, groups or clans that appear to be loosely related are often referred to as chondrite classes, but higher order terms for aggregating groups of meteorites tend to be somewhat chaotic in the scientific and popular literature. There is little agreement on how to fit nonchondritic meteorite groups into an overall scheme, several other classification terms are in widespread use, Type, a historic top level of classification that grouped all meteorites into one of four types, chondrite, achondrite, iron or stony-iron. Anomalous, meteorites that are members of well-established groups that are different enough in some important property to merit distinction from the other members, grouplet, a provisional group with less than 5 members. Duo, a group with only 2 members. Ungrouped, meteorites that do not fit any known group, though they may fit into a clan or class, meteorites are often divided into three overall categories based on whether they are dominantly composed of rocky material, metallic material, or mixtures. These categories have been in use since at least the early 19th century but do not have much significance, they are simply a traditional. In fact, the term stony iron is a misnomer as currently used, one group of chondrites has over 50% metal by volume and contains meteorites that were called stony irons until their affinities with chondrites were recognized. Some iron meteorites also contain silicate inclusions but are rarely described as stony irons. Nevertheless, these three categories sit at the top of the most widely used classification system. Stony meteorites are then divided into two other categories, chondrites, and achondrites. Stony–iron meteorites have always been divided into pallasites and mesosiderites. g, E. Rubin classification scheme, Two alternative general classification schemes were recently published, illustrating the lack of consensus on how to classify meteorites beyond the level of groups. In the Krot et al. scheme the following hierarchy is used, modern meteorite classification was worked out in the 1860s, based on Gustav Roses and Nevil Story Maskelynes classifications. Gustav Rose worked on the collection of the Museum für Naturkunde, Berlin and Maskelyne on the collection of the British Museum. Rose was the first to make different categories for meteorites with chondrules, story-Maskelyne differentiated between siderites, siderolites and aerolites. In 1872 Gustav Tschermak published his first meteorite classification based on Gustav Roses catalog from 1864, further modifications were made by Aristides Brezina
2.
Allende meteorite
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The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01,05 on February 8,1969, after breaking up in the atmosphere, an extensive search for pieces was conducted and it is often described as the best-studied meteorite in history. The Allende meteorite is notable for possessing abundant, large calcium-aluminium-rich inclusions, carbonaceous chondrites comprise about 4 percent of all meteorites observed to fall from space. Prior to 1969, the carbonaceous chondrite class was known from a number of uncommon meteorites such as Orgueil. Meteorites similar to Allende were known, but many were small, the original stone is believed to have been approximately the size of an automobile traveling towards the Earth at more than 10 miles per second. The fall occurred in the morning hours of February 8,1969. At 01,05 a huge, brilliant fireball approached from the southwest and lit the sky and it exploded and broke up to produce thousands of fusion crusted individuals. This is typical of falls of large stones through the atmosphere and is due to the braking effect of air resistance. The fall took place in northern Mexico, near the village of Pueblito de Allende in the state of Chihuahua. Allende stones became one of the most widely distributed meteorites and provided an amount of material to study. Stones were scattered over a huge area – one of the largest meteorite strewnfields known and this strewnfield measures approximately 8 by 50 kilometers. The region is desert, mostly flat, with sparse to moderate low vegetation, hundreds of meteorites were collected shortly after the fall. Approximately 2 or 3 tonnes of specimens were collected over a period of more than 25 years, some sources guess that an even larger amount was recovered, but there is no way to make an accurate estimate. Even today, over 40 years later, specimens are occasionally found. Fusion crusted individual Allende specimens ranged from 1 gram to 110 kilograms, Allende is often called the best-studied meteorite in history. There are several reasons for this, Allende fell in early 1969 and this was a time of great excitement and energy among planetary scientists. The field was attracting many new workers and laboratories were being improved, as a result, the scientific community was immediately ready to study the new meteorite. A number of museums launched expeditions to Mexico to collect samples, including the Smithsonian Institution, the CAIs are billions of years old, and help to determine the age of the Solar System
3.
Chondrule
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Chondrules are round grains found in chondrites. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids, different kinds of the stony, non-metallic meteorites called chondrites contain different fractions of chondrules. Chondrules can range in diameter from just a few micrometers to over 1 centimetre, other chondrite groups are intermediate between these. Most chondrules are composed primarily of the minerals olivine and pyroxene. Small amounts of minerals are often present, including Fe sulfide, metallic Fe-Ni, oxides such as chromite. Less common types of chondrules may be composed of feldspathic material, silica, or metallic Fe-Ni. Chondrules display a variety of textures, which can be seen when the chondrule is sliced open. Some show textural evidence for rapid cooling from a molten or nearly completely molten state. Pyroxene-rich chondrules that contain extremely fine-grained, swirling masses of fibrous crystals only a few micrometers in size or smaller are called cryptocrystalline chondrules. When the pyroxene fibers are coarser, they may appear to radiate from a single site on the surface. Other observed textural features that are clearly the result of rapid cooling are dendritic and hopper-shaped olivine grains. More commonly, chondrules display what is known as a porphyritic texture, in these, grains of olivine and/or pyroxene are equidimensional and sometimes euhedral. They are named on the basis of the dominant mineral, i. e. porphyritic olivine, porphyritic pyroxene and it seems likely that these chondrules cooled more slowly than those with radial or barred textures, however they still may have solidified in a matter of hours. The composition of olivine and pyroxene in chondrules varies widely, although the range is usually narrow within any single chondrule, some chondrules contain very little iron oxide, resulting in olivine and pyroxene that are close to forsterite and enstatite in composition. These are commonly called Type I chondrules by scientists, and often contain amounts of metallic Fe. Other chondrules formed under more oxidizing conditions and contain olivine and pyroxene with large amounts of FeO, such chondrules are called Type II. Most chondrites contain both Type I and Type II chondrules mixed together, including those with both porphyritic and nonporphyritic textures, although there are exceptions to this. Chondrules are believed to have formed by a heating and melting of solid dust aggregates of approximately Solar composition under temperatures of about 1000 K
4.
Chondrite
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Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the solar system accreted to form primitive asteroids. They are the most common type of meteorite falls to Earth with estimates for the proportion of the total fall that they represent varying between 85. 7% and 86. 2%. Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life or the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, chondrites can be differentiated from iron meteorites due to their low iron and nickel content. Other non-metallic meteorites, achondrites, which lack chondrules, were formed more recently, there are currently over 27,000 chondrites in the worlds collections. The largest individual stone ever recovered, weighing 1770 kg, was part of the Jilin meteorite shower of 1976, chondrites were formed by the accretion of particles of dust and grit present in the primitive Solar System which gave rise to asteroids over 4.55 billion years ago. These asteroid parent bodies of chondrites are small to medium-sized asteroids that were never part of any body large enough to undergo melting, dating using 206Pb/204Pb gives an estimated age of 4,566.6 ±1.0 Ma, matching ages for other chronometers. Another indication of their age is the fact that the abundance of elements in chondrites is similar to that found in the atmosphere of the Sun. Many chondritic asteroids also contained significant amounts of water, possibly due to the accretion of ice along with rocky material. As a result, many chondrites contain hydrous minerals, such as clays, in addition, all chondritic asteroids were affected by impact and shock processes due to collisions with other asteroids. These events caused a variety of effects, ranging from simple compaction to brecciation, veining, localized melting, and formation of high-pressure minerals. Chondrites also contain inclusions, which are among the oldest objects to form in the solar system, particles rich in metallic Fe-Ni and sulfides. The remainder of chondrites consists of fine-grained dust, which may either be present as the matrix of the rock or may form rims or mantles around individual chondrules and refractory inclusions. Embedded in this dust are presolar grains, which predate the formation of our solar system, the chondrites have distinct texture, composition and mineralogy and their origin continues to be the object of some debate. Chondrites are divided into about 15 distinct groups on the basis of their mineralogy, bulk chemical composition, the various chondrite groups likely originated on separate asteroids or groups of related asteroids. Each chondrite group has a mixture of chondrules, refractory inclusions, matrix, and other components. Other ways of classifying chondrites include weathering and shock, chondrites can also be categorized according to their petrologic type, which is the degree to which they were thermally metamorphosed or aqueously altered
5.
Meteorite
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When the object enters the atmosphere, various factors like friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy. It then becomes a meteor and forms a fireball, also known as a shooting/falling star, meteorites that survive atmospheric entry and impact vary greatly in size. For geologists, a bolide is a large enough to create a crater. Meteorites that are recovered after being observed as they transit the atmosphere or impact the Earth are called meteorite falls, all others are known as meteorite finds. As of April 2016, there were about 1,140 witnessed falls that have specimens in the worlds collections, there are more than 38,660 well-documented meteorite finds. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition, meteorites smaller than 2 mm are classified as micrometeorites. Extraterrestrial meteorites are such objects that have impacted other celestial bodies and they have been found on the Moon and Mars. Meteorites are always named for the places they were found, usually a town or geographic feature. In cases where many meteorites were found in one place, the name may be followed by a number or letter, the name designated by the Meteoritical Society is used by scientists, catalogers, and most collectors. Most meteoroids disintegrate when entering the Earths atmosphere, usually, five to ten a year are observed to fall and are subsequently recovered and made known to scientists. Few meteorites are large enough to create large impact craters, instead, they typically arrive at the surface at their terminal velocity and, at most, create a small pit. Large meteoroids may strike the ground with a significant fraction of their escape velocity, the kind of crater will depend on the size, composition, degree of fragmentation, and incoming angle of the impactor. The force of such collisions has the potential to cause widespread destruction, the most frequent hypervelocity cratering events on the Earth are caused by iron meteoroids, which are most easily able to transit the atmosphere intact. In contrast, even relatively large stony or icy bodies like small comets or asteroids, up to millions of tons, are disrupted in the atmosphere, and do not make impact craters. Although such disruption events are uncommon, they can cause a concussion to occur. Very large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons or more, can reach the surface and cause large craters, such events are generally so energetic that the impactor is completely destroyed, leaving no meteorites. Several phenomena are well documented during witnessed meteorite falls too small to produce hypervelocity craters, various colors have been reported, including yellow, green, and red. Flashes and bursts of light can occur as the object breaks up, explosions, detonations, and rumblings are often heard during meteorite falls, which can be caused by sonic booms as well as shock waves resulting from major fragmentation events
6.
Meteorite fall
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Meteorite falls, also called observed falls, are meteorites collected after their fall from space was observed by people or automated devices. All other meteorites are called finds, there are more than 1,100 documented falls listed in widely used databases, most of which have specimens in modern collections. As of early 2017, the Meteoritical Bulletin Database has 1,149 confirmed falls, observed meteorite falls are interesting for several reasons. Material from observed falls has not been subjected to weathering, making the find a better candidate for scientific study. Historically, observed falls were the most compelling evidence supporting the extraterrestrial origin of meteorites, furthermore, observed fall discoveries are a better representative sample of the types of meteorites which fall to Earth. For example, iron meteorites take much longer to weather and are easier to identify as unusual objects and this may explain the increased proportion of iron meteorites among finds, over that among observed falls. There is also detailed statistics on falls such as based on meteorite classification, the German physicist Ernst Cladni, sometimes considered as the father of meteoritics, was the first to publish the then audacious idea that meteorites were rocks from space. There were already several documented cases, one of the earliest was the Aegospotami meteorite of 467 BC, below is a list of 8 confirmed falls pre-1600 AD. However, unlike the Loket and Ensisheim meteorites, not all are as well-documented, while most confirmed falls involve masses between less than one kg to several kg, some reach 100 kg or more. A few are more than one metric ton. The six largest falls are listed below and five occurred during the 20th century, presumably, events of such magnitude may happen a few times per century but, especially if it occurred in remote areas, may have gone unreported. These 14 have been found in 2010 and after, since in the modern period around half a dozen falls are normally found each year, the table needs some updating. These have all been found between 1610-2010 and arranged alphabetically, glossary of meteoritics Meteorite fall statistics
7.
Murchison meteorite
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The Murchison meteorite is a large meteorite that fell to earth near Murchison, Victoria, in Australia, in 1969. It is one of the most studied meteorites due to its mass, the fact that it was a fall. About 30 seconds later, a tremor was heard, many fragments were found over an area larger than 13 km², with individual mass up to 7 kg, one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg, the meteorite belongs to the CM group of carbonaceous chondrites. Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth, CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites. Like other CM chondrites, Murchison contains abundant CAIs, over 15 amino acids, some of the basic components of life, have been identified in the meteorite by multiple studies. Murchison contains common amino acids such as glycine, alanine and glutamic acid as well as unusual ones like isovaline and pseudoleucine, a complex mixture of alkanes was isolated as well, similar to that found in the Miller–Urey experiment. Serine and threonine, usually considered to be earthly contaminants, were absent in the samples. A specific family of amino acids called diamino acids was identified in the Murchison meteorite as well, the initial report stated that the amino acids were racemic and therefore formed in an abiotic manner because amino acids of terrestrial proteins are all of the L-configuration. In 1997, L-excesses were also found in an amino acid, isovaline. At the same time, L-excesses of alanine were again found in Murchison but now with enrichment in the isotope 15N, however, the list of organic materials identified in the meteorite was extended to polyols by 2001. Although the meteorite contained a mixture of left-handed and right-handed amino acids, most amino acids used by living organisms are left-handed in chirality, and most sugars used are right-handed. A team of chemists in Sweden demonstrated in 2005 that this homochirality could have triggered or catalyzed. Several lines of evidence indicate that the portions of well-preserved fragments from Murchison are pristine. A2010 study using high resolution analytical tools including spectroscopy, identified 14,000 molecular compounds including 70 amino acids in a sample of the meteorite, measured purine and pyrimidine compounds were found in the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ13C = +44. 5‰ and +37. 7‰, respectively and this specimen demonstrates that many organic compounds were delivered by early Solar System bodies and may have played a key role in lifes origin. Cosmochemistry Glossary of meteoritics Rosenthal, Anne M. Murchisons Amino Acids, meteorite That Fell in 1969 Still Revealing Secrets of the Early Solar System. This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration
8.
Orgueil (meteorite)
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Orgueil is a scientifically important carbonaceous chondrite meteorite that fell in southwestern France in 1864. It fell on May 14,1864, a few minutes after 20,00 local time, about 20 stones fell over an area of several square miles. He wrote that it contained carbon, hydrogen, and oxygen, an intense scientific discussion ensued, continuing into the 1870s, as to whether the organic matter might have a biological origin. Orgueil is one of five known meteorites belonging to the CI chondrite group and this group is remarkable for having a composition that is essentially identical to that of the sun, excluding gaseous elements like hydrogen and helium. Because of its extraordinarily primitive composition and relatively large mass, Orgueil is one of the most-studied meteorites, one notable discovery in Orgueil was a high concentration of isotopically anomalous xenon called xenon-HL. The carrier of this gas is extremely fine-grained diamond dust that is older than the system itself. In 1962, Nagy et al. announced the discovery of organised elements embedded in the Orgueil meteorite that were purportedly biological structures of extraterrestrial origin and these elements were subsequently shown to be either pollen and fungal spores that had contaminated the sample, or crystals of the mineral olivine. Despite great initial excitement, the capsule was shown to be that of a European rush, glued into the fragment. The outer fusion layer was in fact glue, richard B. Hoover of NASA has claimed that the Orgueil meteorite contains fossils, some of which are similar to known terrestrial species. Hoover has previously claimed the existence of fossils in the Murchison meteorite, however, NASA has formally distanced itself from Hoovers claims and his lack of expert peer-reviews. Glossary of meteoritics Nagy B, Claus G, Hennessy DJ Organic Particles Embedded in Minerals in Orgueil, nature 193 p.1129 Fitch FW, Anders E Organized Element - Possible Identification in Orgueil Meteorite
9.
Tagish Lake (meteorite)
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The Tagish Lake meteorite fell at 16,43 UTC on 18 January 2000 in the Tagish Lake area in northwestern British Columbia, Canada.7 kilotons. Following the reported sighting of a fireball in southern Yukon and northern British Columbia, Canada, post-event atmospheric photographs of the trail left by the associated fireball and U. S. Department of Defense satellite information yielded the meteor trajectory. Most of the stony, carbonaceous fragments landed on the Taku Arm of the lake, the passage of the fireball and the high-altitude explosion set off a wide array of satellite sensors as well as seismographs. The local inhabitants described the smell in the air following the airburst as sulfurous, the Tagish Lake meteoroid is estimated to have been 4 meters in diameter and 56 tonnes in weight before it entered the Earths atmosphere. However, it is estimated that only 1, of the 1.3 tonnes of fragmented rock, somewhat over 10 kilograms was found and collected. Tagish Lake is classified as a chondrite, type C2 ungrouped. The pieces of the Tagish Lake meteorite are dark grey to almost black in color with small light-colored inclusions, except for a greyish fusion crust, the meteorites have the visual appearance of a charcoal briquette. The fragments were transported in their state to research facilities after they were collected by a local resident in late January,2000. Initial studies of these fragments were done in collaboration with researchers from NASA. Snowfall covered the remaining fragments until April 2000, when an effort was mounted by researchers from the University of Calgary. Fragments of the fresh, pristine Tagish Lake meteorite totaling more than 850 g are currently held in the collections at the Royal Ontario Museum, degraded fragments from the April–May 2000 search are curated mainly at the University of Calgary and the University of Western Ontario. This meteorite shows some similarities to the two most primitive carbonaceous chondrite types, the CI and CM chondrites, it is quite distinct from either of them. Tagish Lake has a lower density than any other type of chondrite and is actually composed of two somewhat different rock types. The major difference between the two lithologies is in the abundance of minerals, one is poor in carbonates and the other is rich in them. The meteorite contains an abundance of materials, including amino acids. The organics in the meteorite may have formed in the interstellar medium and/or the solar protoplanetary disk. A portion of the carbon in the Tagish Lake meteorite is contained in what are called nanodiamonds—very tiny diamond grains at most only a few micrometers in size, in fact, Tagish Lake contains more of the nanodiamonds than any other meteorite. The age of the meteorite is estimate to be about 4.55 billion years thus being a remainder of the period when the system was formed
10.
Sutter's Mill meteorite
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The Sutters Mill meteorite is a carbonaceous chondrite which entered the Earths atmosphere and broke up at about 07,51 Pacific time on April 22,2012. The name comes from the Sutters Mill, the California Gold Rush site and this was the largest meteoroid impact over land since asteroid 2008 TC3. As of May 2014,79 fragments have been documented with a find location. The largest weighs 205 grams, and the second largest weighs 42 grams, the meteorite was found to contain some of the oldest material in the solar system. Two 10-micron diamond grains were found in the meteorite recovered before the rain fell, in primitive meteorites like Sutters Mill, some grains survived from what existed in the cloud of gas, dust and ice that formed the solar system. During the 2012 Lyrids meteor shower, a bolide and sonic boom rattled buildings in California, the bolide air burst was caused by a random meteoroid, not a member of the Lyrids shower. The bolide was so bright that witnesses were seeing spots afterward, the falling meteorites were detected by weather radar over an area centered on the Sutters Mill site in Coloma, between Auburn, California, and Placerville, California. Robert Ward found a small CM chondrite fragment in the Henningsen Lotus Park just west of Coloma, later that day, Peter Jenniskens found a crushed 4 g meteorite in the parking lot of that same park and Brien Cook found a 5 g meteorite off Petersen Road in Lotus. These were the only meteorites found before rain hit the area on 25 April, on 1 May 2012, the James W. Marshall Gold Discovery State Historic Parks Ranger Suzie Matin discovered two pieces of the meteorite in her front yard. The park contains what is now known as Sutters Mill, ground-based searches resulted in the additional recovery of two pristinely collected meteorites for scientific study. A consortium of over 50 scientists investigated the circumstances of the impact, the event was recorded by two infrasound monitoring stations of the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System. The preliminary analysis are indicative of energy yield of approximately 4 kilotons of TNT equivalent, hiroshimas Little Boy had a yield of about 16 kt. The air burst had approximate coordinates of 37. 6°N120. 5°W /37.6, before entry in Earths atmosphere, the meteoroid probably had an absolute magnitude of roughly 31. The meteoroid entered at a speed of 28.6 ±0.7 km/s. It broke apart at an altitude of 48 km, the highest breakup event on record resulting in meteorites on the ground, before entry, the meteoroid moved on an eccentric orbit, stretching from just inside the orbit of Jupiter to the orbit of Mercury. The orbit had an inclination and an orbital period suggesting that this meteoroid originated in the 3,1 mean motion resonance with Jupiter. The CM chondrite Maribo moved on an orbit, but rotated by 120 degrees in the direction of the line of apsides. The meteorite type is similar to that of the 1969 Murchison meteorite in Australia, the Sutters Mill meteorite originated from near the surface of its parent body
11.
Carbonaceous chondrite
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Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites, the C chondrites represent only a small proportion of meteorite falls. Some famous carbonaceous chondrites are, Allende, Murchison, Orgueil, Ivuna, Murray, Tagish Lake, Carbonaceous chondrites are grouped according to distinctive compositions thought to reflect the type of parent body from which they originated. Such meteorites are often named for the place where they fell, group CH, where H is for high metal is so far the only exception. See below for name derivations of each group, several groups of carbonaceous chondrites, notably the CM and CI groups, contain high percentages of water, as well as organic compounds. They are composed mainly of silicates, oxides and sulfides, with the olivine and serpentine being characteristic. Other groups of C chondrites, e. g. CO, CV, and CK chondrites, are poor in volatile compounds. This group, named after the Ivuna meteorite, have chemical compositions that are close to that measured in the solar photosphere, in this sense, they are chemically the most primitive known meteorites. CI chondrites typically contain a proportion of water, and organic matter in the form of amino acids. Aqueous alteration promotes a composition of hydrous phyllosilicates, magnetite, and olivine crystals occurring in a matrix. It is thought they have not been heated above 50 °C, five CI chondrites have been observed to fall, Ivuna, Orgueil, Alais, Tonk and Revelstoke. Several others have been found by Japanese field parties in Antarctica, in general, the extreme fragility of CI chondrites causes them to be highly susceptible to terrestrial weathering, and they do not survive on Earths surface for long after they fall. This group takes its name from Vigarano, most of these chondrites belong to the petrologic type 3. CV chondrites observed falls, Allende Bali Bukhara Grosnaja Kaba Mokoia Vigarano The group takes its name from Mighei, many falls of this type have been observed and CM chondrites are known to contain a rich mix of complex organic compounds such as amino-acids and purine/pyrimidine nucleobases. The group takes its name from Renazzo, the best parent body candidate is 2 Pallas. That makes them the most metal-rich of any chondrite group, the first meteorite discovered was ALH85085. Chemically, these chondrites are closely related to CR and CB groups, all specimens of this group belong only to petrologic types 2 or 3. The group takes its name from the most representative member, Bencubbin, although these chondrites contain over 50% nickel-iron metal, they are not classified as mesosiderites because their mineralogical and chemical properties are strongly associated with CR chondrites
12.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
13.
Organic compound
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An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry. Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. Vitalism survived for a while even after the rise of modern atomic theory and it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate, urea had long been considered an organic compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by others, in which increasingly complex organic substances were produced from inorganic ones without the involvement of any living organism. Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic. Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially
14.
Silicate
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A silicate is a compound containing an anionic silicon compound. The great majority of the silicates are oxides, but hexafluorosilicate, orthosilicate is the anion SiO4−4 or its compounds. Related to orthosilicate are families of anions with the formula 2n−, important members are the cyclic and single chain silicates n and the sheet-forming silicates n. Silicates constitute the majority of Earths crust, as well as the terrestrial planets, rocky moons. Sand, Portland cement, and thousands of minerals are examples of silicates, silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations, hence this class of compounds is very large. Both minerals and synthetic materials fit in this class, in the vast majority of silicates, including silicate minerals, the Si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. In these structures, the bonds to silicon conform to the octet rule. These tetrahedra sometimes occur as isolated SiO4−4 centres, but most commonly, commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. All these such species have negligible solubility in water at normal conditions, silicates are well characterized as solids, but are less commonly observed in solution. The anion SiO4−4 is the base of silicic acid, Si4. Instead, solutions of silicates are usually observed as mixtures of condensed, the nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites. Although the tetrahedron is the coordination geometry for silicon compounds. A well-known example of such a high number is hexafluorosilicate. Octahedral coordination by 6 oxygen centres is observed, at very high pressure, even SiO2 adopts this geometry in the mineral stishovite, a dense polymorph of silica found in the lower mantle of the Earth. This structure is formed by shock during meteorite impacts. In geology and astronomy, the silicate is used to denote types of rock that consist predominantly of silicate minerals. On Earth, a variety of silicate minerals occur in an even wider range of combinations as a result of the processes that form
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Oxide
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An oxide /ˈɒksaɪd/ is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Oxide itself is the dianion of oxygen, an O2– atom, Metal oxides thus typically contain an anion of oxygen in the oxidation state of −2. Most of the Earths crust consists of oxides, the result of elements being oxidized by the oxygen in air or in water. Hydrocarbon combustion affords the two principal carbon oxides, carbon monoxide and carbon dioxide, even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a skin of Al2O3 that protects the foil from further corrosion. Individual elements can form multiple oxides, each containing different amounts of the element. Certain elements can form many different oxides, such those of nitrogen, due to its electronegativity, oxygen forms stable chemical bonds with almost all elements to give the corresponding oxides. Noble metals are prized because they resist direct chemical combination with oxygen, two independent pathways for corrosion of elements are hydrolysis and oxidation by oxygen. The combination of water and oxygen is even more corrosive, virtually all elements burn in an atmosphere of oxygen, or an oxygen rich environment. In the presence of water and oxygen, some elements— sodium—react rapidly, even dangerously, in part for this reason, alkali and alkaline earth metals are not found in nature in their metallic, i. e. native, form. Caesium is so reactive with oxygen that it is used as a getter in vacuum tubes, the surface of most metals consists of oxides and hydroxides in the presence of air. A well-known example is aluminium foil, which is coated with a film of aluminium oxide that passivates the metal. The aluminium oxide layer can be built to greater thickness by the process of electrolytic anodising, though solid magnesium and aluminium react slowly with oxygen at STP—they, like most metals, burn in air, generating very high temperatures. Finely grained powders of most metals can be explosive in air. Consequently, they are used in Solid-fuel rockets. In dry oxygen, iron forms iron oxide, but the formation of the hydrated ferric oxides, Fe2O3−x2x. Free oxygen production by photosynthetic bacteria some 3.5 billion years ago precipitated iron out of solution in the oceans as Fe2O3 in the important iron ore hematite. Oxides have a range of different structures, from molecules to polymeric
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Sulfide
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Sulfide is an inorganic anion of sulfur with the chemical formula S2−. It contributes no color to sulfide salts, as it is classified as a strong base, even dilute solutions of salts such as sodium sulfide are corrosive and can attack the skin. Sulfide is the simplest sulfur anion, the systematic names sulfanediide and sulfide, valid IUPAC names, are determined according to the substitutive and additive nomenclatures, respectively. However, the sulfide is also used in compositional IUPAC nomenclature which does not take the nature of bonding involved. Examples of such naming are selenium disulfide and titanium sulfide, which contains no sulfide ions whatsoever, hydrogen sulfide is itself an example of a non-systematic name of this nature. However, it is also a name, and the preferred IUPAC name for sulfane. Sulfide does not exist in appreciable concentrations even in highly alkaline water, the sulfide anion can assimilate a proton by recombination, S2− + H+ → SH− Because of this capture of a proton, sulfide has basic character. In aqueous solution, it has a pKb value of less than 0, in aqueous solution, most sulfide ions are neutralized. S2− + H2O ↽ − ⇀ SH− + OH− Upon treatment with an acid, sulfide converts to hydrogen sulfide. Oxidation of sulfide gives sulfur or sulfate, metal sulfides react with nonmetals including iodine, bromine, and chlorine forming sulfur and metal salts. Such inorganic sulfides typically have low solubility in water. One famous example is the bright yellow species CdS or cadmium yellow, the black tarnish formed on sterling silver is Ag2S. Such species are referred to as salts. In fact, the bonding in transition metal sulfides is highly covalent, which rise to their semiconductor properties. Several have practical applications as pigments, in cells. Aspergillus niger plays a role in the solubilization of heavy metal sulfides, many important metal ores are sulfides. Significant examples include, argentite, cinnabar, galena, molybdenite, pentlandite, realgar, and stibnite, sphalerite, and pyrite, dissolved free sulfides are very aggressive species for the corrosion of many metals such as steel, stainless steel, and copper. Sulfides present in solution are responsible for stress corrosion cracking of steel
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Olivine
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The mineral olivine is a magnesium iron silicate with the formula 2SiO4. Thus it is a type of nesosilicate or orthosilicate and it is a common mineral in the Earths subsurface but weathers quickly on the surface. The ratio of magnesium and iron varies between the two endmembers of the solid solution series, forsterite and fayalite, compositions of olivine are commonly expressed as molar percentages of forsterite and fayalite. Forsterite has a high melting temperature at atmospheric pressure, almost 1,900 °C. The melting temperature varies smoothly between the two endmembers, as do other properties, olivine incorporates only minor amounts of elements other than oxygen, silicon, magnesium and iron. Manganese and nickel commonly are the elements present in highest concentrations. Olivine gives its name to the group of minerals with a structure which includes tephroite, monticellite and kirschsteinite. It has a structure similar to magnetite but uses one quadravalent. Olivine gemstones are called peridot and chrysolite, olivine is named for its typically olive-green color, though it may alter to a reddish color from the oxidation of iron. Translucent olivine is sometimes used as a gemstone called peridot, some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea. Olivine occurs in mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica and that magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be left after extraction of magmas. Olivine and high pressure structural variants constitute over 50% of the Earths upper mantle, the metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite. In contrast, Mg-rich olivine does not occur stably with silica minerals, Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth. Mg-rich olivine has also discovered in meteorites, on the Moon and Mars, falling into infant stars. Such meteorites include chondrites, collections of debris from the early Solar System, the spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets often have the signature of olivine
18.
Serpentine subgroup
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The serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite rocks. They are used as a source of magnesium and asbestos, the name is thought to come from the greenish color being that of a serpent. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group, owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine, antigorite, chrysotile and lizardite, the serpentine group of minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices. Chrysotile, which has a habit, is one polymorph of serpentine and is an important component of asbestos. Other polymorphs in the group may have a platy habit. Antigorite and lizardite are the polymorphs with platy habit, many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name false jade or Teton jade. Their olive green colour and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning serpent rock and they have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates, alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the surface, the soil is unusually high in clay. Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600 °C at depths of 60 km or so. In contrast, lizardite and chrysotile typically form near the Earths surface and break down at low temperatures. It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs, samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight, the flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees within otherwise forested areas, most serpentines are opaque to translucent, light, soft, infusible and susceptible to acids. All are microcrystalline and massive in habit, never being found as single crystals, lustre may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide, New Caledonia, Canada, US, Afghanistan, Britain, Greece, China, Ural Mountains, France, Korea, Austria, India, Myanmar, New Zealand, Norway and Italy are notable localities
19.
Formation and evolution of the Solar System
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The formation of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. This model, known as the hypothesis, was first developed in the 18th century by Emanuel Swedenborg, Immanuel Kant. Its subsequent development has interwoven a variety of disciplines including astronomy, physics, geology. Since the dawn of the age in the 1950s and the discovery of extrasolar planets in the 1990s. The Solar System has evolved considerably since its initial formation, many moons have formed from circling discs of gas and dust around their parent planets, while other moons are thought to have formed independently and later been captured by their planets. Still others, such as Earths Moon, may be the result of giant collisions, collisions between bodies have occurred continually up to the present day and have been central to the evolution of the Solar System. The positions of the planets often shifted due to gravitational interactions and this planetary migration is now thought to have been responsible for much of the Solar Systems early evolution. In the far distant future, the gravity of passing stars will gradually reduce the Suns retinue of planets, some planets will be destroyed, others ejected into interstellar space. Ultimately, over the course of tens of billions of years, the first step toward a theory of Solar System formation and evolution was the general acceptance of heliocentrism, which placed the Sun at the centre of the system and the Earth in orbit around it. This concept had developed for millennia, but was not widely accepted until the end of the 17th century, the first recorded use of the term Solar System dates from 1704. The most significant criticism of the hypothesis was its apparent inability to explain the Suns relative lack of momentum when compared to the planets. However, since the early 1980s studies of stars have shown them to be surrounded by cool discs of dust and gas, exactly as the nebular hypothesis predicts. Understanding of how the Sun is expected to continue to evolve required an understanding of the source of its power, in 1935, Eddington went further and suggested that other elements also might form within stars. Fred Hoyle elaborated on this premise by arguing that evolved stars called red giants created many elements heavier than hydrogen, when a red giant finally casts off its outer layers, these elements would then be recycled to form other star systems. The nebular hypothesis says that the Solar System formed from the collapse of a fragment of a giant molecular cloud. The cloud was about 20 parsec across, while the fragments were roughly 1 parsec across, the further collapse of the fragments led to the formation of dense cores 0. 01–0.1 pc in size. One of these fragments formed what became the Solar System. The remaining 2% of the mass consisted of elements that were created by nucleosynthesis in earlier generations of stars
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Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
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Standard solar model
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The standard solar model is a mathematical treatment of the Sun as a spherical ball of gas. This model, technically the spherically symmetric quasi-static model of a star, has stellar structure described by differential equations derived from basic physical principles. The model is constrained by conditions, namely the luminosity, radius, age and composition of the Sun. The age of the Sun cannot be measured directly, one way to estimate it is from the age of the oldest meteorites, the composition in the photosphere of the modern-day Sun, by mass, is 74. 9% hydrogen and 23. 8% helium. All heavier elements, called metals in astronomy, account for less than 2 percent of the mass, the SSM is used to test the validity of stellar evolution theory. In fact, the way to determine the two free parameters of the stellar evolution model, the helium abundance and the mixing length parameter, are to adjust the SSM to fit the observed Sun. A star is considered to be at zero age when it is assumed to have a homogeneous composition, to obtain the SSM, a one solar mass stellar model at zero age is evolved numerically to the age of the Sun. The abundance of elements in the zero age solar model is estimated from primordial meteorites, the model is then evolved numerically up to the age of the Sun. Any discrepancy from the values of the Suns luminosity, surface abundances. For example, since the Sun formed, the helium and heavy elements have settled out of the photosphere by diffusion, a measure of heavy-element settling by diffusion is required for a more accurate model. The differential equations of stellar structure, such as the equation of equilibrium, are integrated numerically. The differential equations are approximated by difference equations, nuclear reactions in the core of the Sun change its composition, by converting hydrogen nuclei into helium nuclei by the proton-proton chain and the CNO cycle. This increases the molecular weight in the core of the Sun. This does not happen as instead the core contracts, by the Virial Theorem half of the gravitational potential energy released by this contraction goes towards raising the temperature of the core, and the other half is radiated away. By the ideal gas law this increase in temperature increases the pressure. The luminosity of the Sun is increased by the temperature rise, the outer layers expand to compensate for the increased temperature and pressure gradients, so the radius also increases. No star is completely static, but stars stay on the sequence for long periods. Thus the assumption of state is a very good approximation
22.
Amino acid
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Amino acids are organic compounds containing amine and carboxyl functional groups, along with a side chain specific to each amino acid. The key elements of an acid are carbon, hydrogen, oxygen. About 500 amino acids are known and can be classified in many ways, in the form of proteins, amino acids comprise the second-largest component of human muscles, cells and other tissues. Outside proteins, amino acids perform critical roles in such as neurotransmitter transport. In biochemistry, amino acids having both the amine and the acid groups attached to the first carbon atom have particular importance. They are known as 2-, alpha-, or α-amino acids and they include the 22 proteinogenic amino acids, which combine into peptide chains to form the building-blocks of a vast array of proteins. These are all L-stereoisomers, although a few D-amino acids occur in bacterial envelopes, as a neuromodulator, twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as standard amino acids. The other two are selenocysteine, and pyrrolysine, pyrrolysine and selenocysteine are encoded via variant codons, for example, selenocysteine is encoded by stop codon and SECIS element. N-formylmethionine is generally considered as a form of methionine rather than as a separate proteinogenic amino acid, codon–tRNA combinations not found in nature can also be used to expand the genetic code and create novel proteins known as alloproteins incorporating non-proteinogenic amino acids. Many important proteinogenic and non-proteinogenic amino acids also play critical roles within the body. Nine proteinogenic amino acids are called essential for humans because they cannot be created from other compounds by the human body, others may be conditionally essential for certain ages or medical conditions. Essential amino acids may also differ between species, because of their biological significance, amino acids are important in nutrition and are commonly used in nutritional supplements, fertilizers, and food technology. Industrial uses include the production of drugs, biodegradable plastics, the first few amino acids were discovered in the early 19th century. In 1806, French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated a compound in asparagus that was subsequently named asparagine, cystine was discovered in 1810, although its monomer, cysteine, remained undiscovered until 1884. Glycine and leucine were discovered in 1820, usage of the term amino acid in the English language is from 1898. Proteins were found to yield amino acids after enzymatic digestion or acid hydrolysis, in the structure shown at the top of the page, R represents a side chain specific to each amino acid. The carbon atom next to the group is called the α–carbon. Amino acids containing an amino group bonded directly to the alpha carbon are referred to as amino acids
23.
Polycyclic aromatic hydrocarbon
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Polycyclic aromatic hydrocarbons are hydrocarbons—organic compounds containing only carbon and hydrogen—that are composed of multiple aromatic rings. Formally, the class is defined as lacking further branching substituents on these ring structures. Polynuclear aromatic hydrocarbons are a subset of PAHs that have fused aromatic rings, the simplest such chemicals are naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. PAHs are neutral, nonpolar molecules found in coal and in tar deposits and they are produced as well by incomplete combustion of organic matter. The tricyclic species phenanthrene and anthracene represent the members of the PAHs. Smaller molecules, such as benzene, are not PAHs, PAHs with five or six-membered rings are most common. Those composed only of six-membered rings are called alternant PAHs, which include benzenoid PAHs, the following are examples of PAHs that vary in the number and arrangement of their rings, Examples of PAH compounds PAHs are nonpolar and lipophilic. Larger PAHs are generally insoluble in water, while some PAHs are soluble, the larger members are also poorly soluble in organic solvents as well as lipids. Although PAHs clearly are aromatic compounds, the degree of aromaticity can be different for each ring segment, according to Clars rule for PAHs the resonance structure with the largest number of disjoint aromatic п-sextets—i. e. Benzene-like moieties—is the most important for the characterization of the properties, in contrast, in anthracene the resonance structures have one sextet, which can be at any of the three rings, and the aromaticity spreads out more evenly across the whole molecule. Three Clar structures with two each are present in chrysene. Superposition of these reveals that the aromaticity in the outer rings is greater compared to the inner rings. Polycyclic aromatic hydrocarbons are found in natural sources such as creosote. They can result from the combustion of organic matter. PAHs can also be produced geologically when organic sediments are transformed into fossil fuels such as oil. Wild fires are another notable source, substantially higher outdoor air, soil, and water concentrations of PAHs have been measured in Asia, Africa, and Latin America than in Europe, Australia, and the U. S. /Canada. PAHs are typically found as complex mixtures, most PAHs are insoluble in water, which limits their mobility in the environment. Aqueous solubility of PAHs decreases approximately logarithmically as molecular mass increases, two-ring PAHs, and to a lesser extent three-ring PAHs, dissolve in water, making them more available for biological uptake and degradation
24.
Silicate minerals
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Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and they are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen. Nesosilicates, or orthosilicates, have the orthosilicate ion, which constitute isolated 4− tetrahedra that are connected only by interstitial cations and these exist as 3-member 6− and 6-member 12− rings, where T stands for a tetrahedrally coordinated cation. Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3,1,3 ratio, for single chains or Si4O11,4,11 ratio, for double chains. Nickel–Strunz classification,09. D Pyroxene group Enstatite – orthoferrosilite series Enstatite – MgSiO3 Ferrosilite – FeSiO3 Pigeonite – Ca0.251, all phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. Serpentine subgroup Antigorite – Mg3Si2O54 Chrysotile – Mg3Si2O54 Lizardite – Mg3Si2O54 Clay minerals group Halloysite – Al2Si2O54 Kaolinite – Al2Si2O54 Illite – 24O10 Montmorillonite –0 and this group comprises nearly 75% of the crust of the Earth. Tectosilicates, with the exception of the group, are aluminosilicates. Nickel–Strunz classification,09. F and 09. G,04. A, an introduction to the rock-forming minerals. Wise, W. S. Zussman, J. Rock-forming minerals, P.982 pp. Hurlbut, Cornelius S. Danas Manual of Mineralogy. Mindat. org, Dana classification Webmineral, Danas New Silicate Classification Media related to Silicates at Wikimedia Commons
25.
Magnetite
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Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron, Magnetite is ferrimagnetic, it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, today it is mined as iron ore. Small grains of magnetite occur in almost all igneous and metamorphic rocks, Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. The chemical IUPAC name is iron oxide and the chemical name is ferrous-ferric oxide. In addition to rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite, Magnetite has an inverse spinel crystal structure. As a member of the group, it can form solid solutions with similarly structured minerals, including ulvospinel. Titanomagnetite, also known as titaniferous magnetite, is a solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite, Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the pair forms a buffer that can control oxygen fugacity. Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite, Magnetite also is produced from peridotites and dunites by serpentinization. Lodestones were used as a form of magnetic compass. At low temperatures, magnetite undergoes a crystal structure phase transition from a structure to a cubic structure known as the Verwey transition. The Verwey transition occurs around 121 K and is dependent on size, domain state. An isotropic point also occurs near the Verwey transition around 130 K, the Curie temperature of magnetite is 858 K. Magnetite is sometimes found in large quantities in beach sand. Such black sands are found in places, such as Lung Kwu Tan of Hong Kong, California of the United States
26.
Cento
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Cento is a town and comune in the province of Ferrara, Emilia-Romagna, Italy. The name Cento is a reference to the centuriation of the Po Valley, centos growth from its origin as a little fishing village in the marshes to an established farming town took place in the first few centuries in the second millennium. South-east of the city lies the historic fortification of Pieve di Cento. Palazzo del Monte di Pietà, housing the Civic Gallery and it has paintings by the local artist Guercino. The Rocca, a square building with square towers. Built in 1378 by the bishop of Bologna, it was enlarged by Giulio della Rovere and it is home to the Galleria darte moderna Aroldo Bonzagni. Porta Pieve, the surviving gate of the four once existing. Cento is the Europeans city of Carnival and it is twinned with Rio carnival, Cento is twinned with, LAquila, Italy Székesfehérvár, Hungary Vicente Lopez, Argentina Official website Other information
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2 Pallas
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Pallas, minor-planet designation 2 Pallas, is the second asteroid to have been discovered, and is one of the largest asteroids in the Solar System. With an estimated 7% of the mass of the belt, it is the third-most-massive asteroid. It is 512 kilometers in diameter, somewhat smaller than Vesta and it is likely a remnant protoplanet. When Pallas was discovered by the German astronomer Heinrich Wilhelm Matthäus Olbers on 28 March 1802, it was counted as a planet, the discovery of many more asteroids after 1845 eventually led to their reclassification. Pallass surface is most likely composed of a material, its spectrum. It was formerly considered a dwarf planet for its size. In 1801, the astronomer Giuseppe Piazzi discovered an object which he believed to be a comet. Shortly thereafter he announced his observations of this object, noting that the slow, uniform motion was uncharacteristic of a comet, suggesting it was a different type of object. This was lost from sight for months, but was recovered later that year by the Baron von Zach and Heinrich W. M. Olbers after a preliminary orbit was computed by Carl Friedrich Gauss. This object came to be named Ceres, and was the first asteroid to be discovered, a few months later, Olbers was again attempting to locate Ceres when he noticed another moving object in the vicinity. This was the asteroid Pallas, coincidentally passing near Ceres at the time, the discovery of this object created interest in the astronomy community. Before this point it had been speculated by astronomers that there should be a planet in the gap between Mars and Jupiter, now, unexpectedly, a second such body had been found. When Pallas was discovered, some estimates of its size were as high as 3,380 km in diameter, even as recently as 1979, Pallas was estimated to be 673 km in diameter, 26% greater than the currently accepted value. The orbit of Pallas was determined by Gauss, who found the period of 4.6 years was similar to the period for Ceres, Pallas has a relatively high orbital inclination to the plane of the ecliptic. In 1917, the Japanese astronomer Kiyotsugu Hirayama began to study asteroid motions, by plotting the mean orbital motion, inclination and eccentricity of a set of asteroids, he discovered several distinct groupings. In a later paper he reported a group of three associated with Pallas, which became named the Pallas family, after the largest member of the group. Since 1994 more than 10 members of family have been identified. The validity of this grouping was confirmed in 2002 by a comparison of their spectra and these resulted in the first accurate measurements of its diameter
28.
Kaidun meteorite
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Kaidun is a meteorite that fell on 3 December 1980 on a Soviet military base near what is now Al-Khuraybah in Yemen. A fireball was observed travelling from the northwest to the southeast, and it contains a uniquely wide variety of minerals, causing some confusion as to its origin. It is largely made up of carbonaceous chondrite material of type CR2, but it is known to contain fragments of other types, such as C1, CM1, and C3. Of the nearly 60 minerals found within the meteorite, several have not been found elsewhere in nature, such as florenskyite, in March 2004 it was suggested that the meteorite originated from the Martian moon Phobos. The reason Phobos has been suggested is the existence of two extremely rare alkaline-rich clasts visible in the meteorite, each of which entered the rock at different times. This suggests that the parent body would have been near a source of an alkaline-rich rock and this points to Mars and one of its moons, and Phobos is more likely than Deimos because it is closer to Mars. However, mineralogical and noble gas work do not tie the lithic fragments to Mars, as has been done with other proven Martian meteorites, and this hypothesized link is tenable at best. Glossary of meteoritics Kaidun, A Meteorite with Everything but the Kitchen Sink, written by Linda M. V. Martel, Hawai‘i Institute of Geophysics and Planetology
29.
Mesosiderite
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Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with a texture, silicates and metal occur often in lumps or pebbles as well as in fine-grained intergrowths. The silicate part contains olivine, pyroxenes, and Ca-rich feldspar and is similar in composition to eucrites and diogenites and they are a rare type of meteorite, as of November 2014 only 208 are known and only 7 of these are observed falls. On the other hand, some mesosiderites are among the largest meteorites known, at Vaca Muerta in the Atacama Desert in Chile, many fragments with a total mass of 3.8 tons were found in a large strewnfield. They were first discovered in the 19th century by ore prospectors who mistook the shiny metal inclusions for silver, later when an analysis was made and nickel-iron was found, the true nature as a meteorite was established. The meteorite was called Vaca Muerta, the picture at right shows a cut and polished piece of Vaca Muerta. The most recent fall of a mesosiderite occurred at Dong Ujimqin Qi in China, on September 7,1995, the fall of the Estherville mesosiderite in Iowa, US occurred on May 10,1879. After a brilliant fireball had been seen, a shower of several large masses and many small fragments fell, the fall at Lowicz in Poland on March 12,1935 yielded many fragments with a total weight of 59 kilograms. The other observed mesosiderite falls occurred in 1842 at Barea, in 1880 at Varamin, in 1933 at Dyarrl Island, the legendary Chinguetti meteorite is also supposed to be a mesosiderite. The asteroid 16 Psyche is a candidate for the parent body of the mesosiderites, glossary of meteoritics Mesosiderite images from Northern Arizona University Mesosiderite images from Meteorites Australia
30.
Karoonda meteorite
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The Karoonda meteorite fell to earth on 25 November 1930 at 10,53 pm near the South Australian town of Karoonda. The CK chondrites were named for this meteorite, adelaide residents reported a huge ball of fire with a flaming tail shooting across the eastern sky. Some reported that the colour of the changed from brilliant red. Witnesses closer to Karoonda reported that a loud detonation followed by a low rumbling like thunder being heard shortly after the meteorite passed overhead. The meteorite was found nearly a month later by Professor Kerr Grant after collecting information from locals. The remains of the object were found buried in a crater, glossary of meteoritics Karoonda meteorite fragments in the R. A. Langheinrich meteorite collection An article from the American Museum of Natural History on the meteorite
31.
Moss meteorite
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Moss is a carbonaceous chondrite meteorite that fell over the communities of Rygge and Moss in Østfold county, southeast southern Norway in the morning of midsummer day, July 14,2006. The last time a type CO3 meteorite fell from the sky was in 1937 with Kainsaz, there are 6 known falls of a CO3 meteorite. Being of the rare carbonaceous subtype, meteorite man Robert Haag stated to the media that this was the most important meteorite fall since the Canadian Tagish Lake fall in January 2000, the summer of 2006 was the meteorite summer in Norway. The summer was very warm and dry and it was perfect weather to protect the valuable droppings that the skies let fall over Norway. It started in the beginning of June when on the 7th a very large explosion was seen. Although no meteorites was found from that event, its size stirred a whole world of meteorite aficionados, then on the 10th of July it was announced on NRK1, Norways number one TV channel, that a meteorite had been found in a mans driveway south of Stavanger. The story was soon denounced by the experts as being a rock from a nearby source. But then, incredible as it was, just four days later the skies opened for a meteorite fall event. This turned out to be the 13th find of a meteorite in Norway, at the same time its 9th fall. As if this was not enough, at the end of August a very large fireball was seen north from Troms county to south of Bergen, almost along the whole coast of the country, but no meteorites were found. At about 10,20 a. m. on the 14th of July a large meteor was seen in daylight by a large number of people heading north-northwest over Østfold county. It split into 4 or 5 smaller objects, over Rygge and Moss a loud explosion and a rumbling sound was heard. A man near his cabin in Rygge saw and heard a small piece of stone hit an aluminium sheet about 2 meter away. This was the only directly observed impacting stone from the fall, in all there were five separate finds of the Moss CO3.6 meteorite. They distributed over a strewnfield about 6 kilometres long from southeast in Rygge to northwest in parts of north Moss, the largest find, the main mass, was in several tens of pieces, part of it being smashed while hitting a fence. It was almost 2 kilograms in weight, the total weight of all the finds was over 4 kilograms. Several scientific papers have come out on the study of the meteorite. The first preliminary study of August 2006 showed that it contains numerous small chondrules, most <0. 2mm and small <1mm amoeboid olivine aggregates and it also contains isolated grains of olivine, troilite and kamacite in a gray matrix
32.
Alanine
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Alanine is an α-amino acid that is used in the biosynthesis of proteins. It contains a group, an α-carboxylic acid group. It is non-essential in humans, meaning the body can synthesize it, the L-isomer of alanine is one of the 20 amino acids encoded by the human genetic code. L-Alanine is second only to leucine in rate of occurrence, accounting for 7. 8% of the structure in a sample of 1,150 proteins. The right-handed form, D-Alanine occurs in bacterial cell walls and in some peptide antibiotics, Alanine was first isolated in 1879 by Adolph Strecker. The amino acid was named Alanin in German, in reference to aldehyde, with the infix -an- for ease of pronunciation, the German ending -in used in chemical compounds being analogous to English -ine. The α-carbon atom of alanine is bound to a group, making it one of the simplest α-amino acids. The methyl group of alanine is non-reactive and is thus almost never directly involved in protein function, Alanine is an amino acid that cannot be phosphorylated, making it quite useful in a loss of function experiment with respect to phosphorylation. Alanine is an amino acid, meaning it can be manufactured by the human body. Alanine is found in a variety of foods, but is particularly concentrated in meats. Alanine can be manufactured in the body from pyruvate and branched chain amino acids such as valine, leucine, Alanine is most commonly produced by reductive amination of pyruvate. It also arises together with lactate and generates glucose from protein via the alanine cycle, in muscle and other tissues that degrade amino acids for fuel, amino groups are collected in the form of glutamate by transamination. Glutamate can then transfer its amino group through the action of alanine aminotransferase to pyruvate, the alanine formed is passed into the blood and transported to the liver. A reverse of the alanine aminotransferase reaction takes place in liver, pyruvate regenerated forms glucose through gluconeogenesis, which returns to muscle through the circulation system. Glutamate in the liver enters mitochondria and degrades into ammonium ion through the action of glutamate dehydrogenase, the glucose–alanine cycle enables pyruvate and glutamate to be removed from the muscle and find their way to the liver. Glucose is regenerated from pyruvate and then returned to muscle, the burden of gluconeogenesis is thus imposed on the liver instead of the muscle. All available ATP in muscle is devoted to muscle contraction, an international study led by Imperial College London found a correlation between high levels of alanine and higher blood pressure, energy intake, cholesterol levels, and body mass index. Alterations in the cycle that increase the levels of serum alanine aminotransferase is linked to the development of type II diabetes
33.
Glycine
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Glycine is the amino acid that has a single hydrogen atom as its side chain. It is the simplest possible amino acid, the chemical formula of glycine is NH2‐CH2‐COOH. Glycine is one of the amino acids. Its codons are GGU, GGC, GGA, GGG of the genetic code, Glycine is a colorless, sweet-tasting crystalline solid. It is unique among the amino acids in that it is achiral. It can fit into hydrophilic or hydrophobic environments since it exists as zwitterion at natural pH, Glycine was first isolated from gelatin in 1820. The name comes from the ancient Greek word γλυκύς sweet tasting, Glycine was discovered in 1820, by Henri Braconnot who boiled a gelatinous object with sulfuric acid. Glycine is manufactured industrially by treating chloroacetic acid with ammonia, ClCH2COOH +2 NH3 → H2NCH2COOH + NH4Cl About 15 million kg are produced annually in this way, in the USA and in Japan, glycine is produced via the Strecker amino acid synthesis. Glycine is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct. In aqueous solution, glycine itself is amphoteric, at low pH the molecule can be protonated with a pKa of about 2.4, the nature of glycine in aqueous solution has been investigated by theoretical methods. In solution the ratio of concentrations of the two isomers is independent of both the concentration and of pH. This ratio is simply the equilibrium constant for isomerization, K = / Both isomers of glycine have been observed by microwave spectroscopy in the gas phase. The solid-state structure has been analyzed in detail and this conversion is readily reversible, CO2 + NH+4 + N5, N10-Methylene tetrahydrofolate + NADH + H+ → Glycine + tetrahydrofolate + NAD+ Glycine is coded by codons GGU, GGC, GGA and GGG. Most proteins incorporate only small quantities of glycine, a notable exception is collagen, which contains about 35% glycine. Glycine is degraded via three pathways, the first step is the reverse of glycine biosynthesis from serine with serine hydroxymethyl transferase. Serine is then converted to pyruvate by serine dehydratase, in the third pathway of glycine degradation, glycine is converted to glyoxylate by D-amino acid oxidase. Glyoxylate is then oxidized by lactate dehydrogenase to oxalate in an NAD+-dependent reaction. The half-life of glycine and its elimination from the body varies significantly based on dose, in one study, the half-life was between 0.5 and 4.0 hours
34.
Beta-Aminobutyric acid
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β-Aminobutyric acid is an isomer of the amino acid aminobutyric acid with the chemical formula C4H9NO2. It has two isomers, alpha-aminobutyric acid and gamma-aminobutyric acid, a neurotransmitter in animals that is found in plants. All three are non-proteinogenic amino acids, not being found in proteins, BABA is known for its ability to induce plant disease resistance, as well as increased resistance to abiotic stresses, when applied to plants. Methods to synthesise BABA are known from at least 1857, early methods to produce BABA included from ammonia and crotonic acid under pressure, from the acetoacetic ester phenylhydrazone, or from malonic acid, acetaldehyde, and ammonia. In 1957, Zilkha reported a new simpler method based on adding amines to crotonic acid, since 2000, methods to produce only the S stereoisomer of BABA have also been reported. BABA was first found to increase the resistance of plants to disease in 1960, further tests were made in the 1960s, but it was not until the 1990s that interest in the compound was renewed. Since then, it has shown to be effective in many different pathosystems under controlled conditions. Pathogen groups that have shown a response include viruses, bacteria, nematodes, fungi and it has also been shown to be effective in the field at protecting potato and tomato plants from late blight, grape vines from Plasmopara viticola and melons Monosporascus cannonballus. Rather than having an effect on plant pathogens, it activates plant immune systems enabling them to resist infection more effectively. The effects that it has studied extensively using the model plant Arabidopsis thaliana. BABA induces defense responses in plants by both physical and biochemical means, the precise mechanism depends on the plant and pathogen species. It is unknown how BABA interacts with plant tissues to increase disease resistance and it does not directly activate defensive genes in isolation, but in combination with an infection, BABA treated plants respond more quickly and strongly to the pathogen. In some pathosystems, enhanced callose and lignin deposition is seen around the point of infection, if infected however, the level of PR proteins tends to increase further. PR proteins are not the mechanism of preventing infection however, as soil drenches of BABA that do not induce PR protein production. This may be due to differences between plant families, as the Solanaceae respond by producing PR proteins without any pathogen present, in other pathosystems, phytoalexins accumulate to higher levels in BABA treated plants when they are infected by pathogens, but not when the pathogen is not present. Foliar sprays of BABA can cause small necrotic spots to form on leaves 1 or 2 days after application and this has been suggested to be due to BABA inducing the hypersensitive response which plants normally use to kill infected cells to limit the spread of infection. BABA applied as a foliar spray causes the plant hormone salicylic acid to accumulate and this variation in the hormones required for BABA to confer resistance makes it differ from other synthetic activators of plant defence, which only operate through the SAR pathway of PR proteins
35.
2-Aminoisobutyric acid
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2-Aminoisobutyric acid, or α-aminoisobutyric acid or α-methylalanine or 2-methylalanine, is an amino acid with the structural formula is H2N-C2-COOH. It is contained in some antibiotics of fungal origin, e. g. alamethicin and it is not one of the proteinogenic amino acids and rather rare in nature. α-Aminoisobutyric acid is a strong helix inducer in peptides, oligomers of AIB form 310 helices. In the laboratory, 2-aminoisobutyric acid may be prepared from acetone cyanohydrin, BAIBA is found as a normal metabolite of skeletal muscle in 2014. The plasma concentrations are increased in human by exercise, the production is likely a result of enhanced mitochondrial activity as the increase is also observed in the muscle of PGC-1a overexpression mice. BAIBA is proposed as protective factor against metabolic disorder since it can induce brown fat function
36.
Isovaline
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Isovaline is a rare amino acid transported to earth by the Murchison meteorite, which landed in Australia in 1969. The discovery of isovaline in the biosphere demonstrates an extraterrestrial origin of amino acids and has linked to the homochirality of life on earth suggesting a role in the origin of life. The structure of isovaline is similar to the amino acids GABA and glycine, isovaline acts as an analgesic in mice by activating peripheral GABAB receptors. In a mouse model of osteoarthritis isovaline restored mobility, suggesting inhibition of nociception by isovaline in the membrane of the mouse knee. Isovaline does not cross the barrier and does not enter into the brain or spinal cord. Drugs such as opioids cross the barrier to produce analgesia. Isovaline acts downstream to the system that NSAIDs inhibit, suggesting a means to avoid adverse effects such as irritation of the gastrointestinal system. This novel first-in-class compound has potential for treatment of acute and chronic pain, without the negative side effects associated with other commonly used analgesics
37.
Carbon
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Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically resistant and require high temperature to react even with oxygen, the most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond. It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature. Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies,1086.5,2352.6,4620.5 and 6222.7 kJ/mol, are higher than those of the heavier group 14 elements. Carbons covalent radii are normally taken as 77.2 pm,66.7 pm and 60.3 pm, although these may vary depending on coordination number, in general, covalent radius decreases with lower coordination number and higher bond order. Carbon compounds form the basis of all life on Earth
38.
Allan Hills 84001
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Allan Hills 84001 is a meteorite that was found in Allan Hills, Antarctica on December 27,1984 by a team of U. S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs, ALH84001 is thought to be from Mars, however, it does not fit into any of the previously discovered SNC groups. On discovery, its mass was 1.93 kilograms. S, president Bill Clinton giving a speech about the potential discovery. This rock is considered to be one of the oldest Martian meteorites, based on chemical analyses, it is thought to have originated on Mars from a period when liquid water existed on the now arid planets surface. According to the analysis, Eos Chasma in the Valles Marineris canyon appears to be the source of the meteorite, the analysis was not conclusive, in part because it was limited to areas of Mars not obscured by dust. The theory holds that ALH84001 was blasted off from the surface of Mars by an impact about 17 million years ago. These dates were established by a variety of dating techniques, including samarium-neodymium, rubidium-strontium, potassium-argon. Other meteorites that have potential biological markings have generated less interest because they do not contain rock from a wet Mars, ALH84001 is the only meteorite collected from such a time period. In October 2011 it was reported that isotopic analysis indicated that the carbonates in ALH84001 were precipitated at a temperature of 18 °C with water and carbon dioxide from the Martian atmosphere. On August 6,1996, ALH84001 became newsworthy when it was claimed that the meteorite may contain evidence of traces of life from Mars, under the scanning electron microscope structures were revealed that some scientists interpreted as fossils of bacteria-like lifeforms. The structures found on ALH84001 are 20–100 nanometres in diameter, similar in size to theoretical nanobacteria, the announcement of possible extraterrestrial life caused considerable controversy. David S. McKay at NASA argued that likely microbial terrestrial contamination found in other Martian meteorites does not resemble the shapes in the ALH84001. In particular, the shapes within the ALH84001 look intergrown or embedded in the indigenous material, while likely contamination does not. While it has not yet conclusively been shown how the features in the meteorite were formed, David McKay says these results were obtained using unrealistically pure raw materials as a starting point, and will not explain many of the features described by us in ALH84001. According to McKay, a plausible inorganic model must explain all of the properties that we. The rest of the community disagreed with McKay. However, the consensus is that morphology alone cannot be used unambiguously as a tool for primitive life detection. Interpretation of morphology is notoriously subjective, and its use alone has led to errors of interpretation
39.
Martian meteorite
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A Martian meteorite is a rock that formed on the planet Mars and was then ejected from Mars by the impact of an asteroid or comet, and finally landed on the Earth. Of over 61,000 meteorites that have found on Earth,132 were identified as Martian as of 3 March 2014. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks, the term does not refer to meteorites found on Mars, such as Heat Shield Rock. The meteorite was determined to have formed 2.1 billion years ago during the Amazonian geologic period on Mars, by the early 1980s, it was obvious that the SNC group of meteorites were significantly different from most other meteorite types. Several scientists suggested these characteristics implied the origin of SNC meteorites from a large parent body. Then in 1983, various trapped gases were reported in impact-formed glass of the EET79001 shergottite and these trapped gases provided direct evidence for a Martian origin. In 2000, an article by Treiman, Gleason and Bogard gave a survey of all the used to conclude the SNC meteorites were from Mars. They wrote, There seems little likelihood that the SNCs are not from Mars, if they were from another planetary body, it would have to be substantially identical to Mars as it now is understood. As of January 9,2013,111 of the 114 Martian meteorites are divided into three groups of achondritic meteorites, shergottites, nakhlites, chassignites, and ones otherwise. Consequently, Martian meteorites as a whole are referred to as the SNC group. They have isotope ratios that are said to be consistent with each other, the names derive from the location of where the first meteorite of their type was discovered. Roughly three-quarters of all Martian meteorites can be classified as shergottites and they are named after the Shergotty meteorite, which fell at Sherghati, India in 1865. Shergottites are igneous rocks of mafic to ultramafic lithology and they fall into three main groups, the basaltic, olivine-phyric and lherzolitic shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their rare-earth element content and these two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas that the shergottites formed from. Because of this, some have advocated the idea that the shergottites are much older than this and this Shergottite Age Paradox remains unsolved and is still an area of active research and debate. The 3-million-year-old crater Mojave,58.5 km in diameter, nakhlites are named after the first of them, the Nakhla meteorite, which fell in El-Nakhla, Alexandria, Egypt in 1911 and had an estimated weight of 10 kg. Nakhlites are igneous rocks that are rich in augite and were formed from basaltic magma about 1.3 billion years ago and they contain augite and olivine crystals. It has been shown that the nakhlites were suffused with liquid water around 620 million years ago and they fell to Earth within the last 10,000 years
40.
Achondrite
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An achondrite is a stony meteorite that does not contain chondrules. As a result, achondrites have distinct textures and mineralogies indicative of igneous processes, achondrites account for about 8% of meteorites overall, and the majority of them are HED meteorites, possibly originating from the crust of asteroid 4 Vesta. Other types include Martian, Lunar, and several types thought to originate from as-yet unidentified asteroids and these groups have been determined on the basis of e. g. the Fe/Mn chemical ratio and the 17O/18O oxygen isotope ratios, thought to be characteristic fingerprints for each parent body. To this group belong, Acapulcoites Lodranites Winonaites Asteroidal achondrites, also called evolved achondrites, are called in this way because have been differentiated on a parent body and this means that their mineralogical and chemical composition was changed by melting and crytallization processes. They are divided several groups, HED meteorites and they may have originated on the asteroid 4 Vesta, because their reflection spectra are very similar. They are named after the letters of the three subgroups, Howardites Eucrites Diogenites Angrites Aubrites Ureilites Brachinites Lunar meteorites are meteorites that originated from the Moon. Martian meteorites are meteorites that originated from Mars
41.
Carboxylic acid
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A carboxylic acid /ˌkɑːrbɒkˈsɪlɪk/ is an organic compound that contains a carboxyl group. The general formula of an acid is R–COOH, with R referring to the rest of the molecule. Carboxylic acids occur widely and include the amino acids and acetic acid, salts and esters of carboxylic acids are called carboxylates. When a carboxyl group is deprotonated, its conjugate base forms a carboxylate anion, carboxylate ions are resonance-stabilized, and this increased stability makes carboxylic acids more acidic than alcohols. Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide, carboxylic acids are commonly identified using their trivial names, and usually have the suffix -ic acid. IUPAC-recommended names also exist, in system, carboxylic acids have an -oic acid suffix. For example, butyric acid is butanoic acid by IUPAC guidelines, the -oic acid nomenclature detail is based on the name of the previously-known chemical benzoic acid. Alternately, it can be named as a carboxy or carboxylic acid substituent on another parent structure, for example, 2-carboxyfuran. The carboxylate anion of an acid is usually named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a conjugate acid and its conjugate base. For example, the base of acetic acid is acetate. The radical •COOH has only a fleeting existence. The acid dissociation constant of •COOH has been measured using electron paramagnetic resonance spectroscopy, the carboxyl group tends to dimerise to form oxalic acid. Because they are both hydrogen-bond acceptors and hydrogen-bond donors, they participate in hydrogen bonding. Together the hydroxyl and carbonyl group forms the functional group carboxyl, carboxylic acids usually exist as dimeric pairs in nonpolar media due to their tendency to self-associate. Smaller carboxylic acids are soluble in water, whereas higher carboxylic acids are less due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers. Carboxylic acids tend to have higher boiling points than water, not only because of their surface area. Carboxylic acids tend to evaporate or boil as these dimers, for boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, both of which increase the enthalpy of vaporization requirements significantly
42.
Hydrocarbon
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In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon, and thus are group 14 hydrides. Hydrocarbons from which one atom has been removed are functional groups. Aromatic hydrocarbons, alkanes, alkenes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons, the classifications for hydrocarbons, defined by IUPAC nomenclature of organic chemistry are as follows, Saturated hydrocarbons are the simplest of the hydrocarbon species. They are composed entirely of single bonds and are saturated with hydrogen, the formula for acyclic saturated hydrocarbons is CnH2n+2. The most general form of saturated hydrocarbons is CnH2n+2, where r is the number of rings and those with exactly one ring are the cycloalkanes. Saturated hydrocarbons are the basis of petroleum fuels and are found as linear or branched species. Substitution reaction is their characteristics property, hydrocarbons with the same molecular formula but different structural formulae are called structural isomers. As given in the example of 3-methylhexane and its higher homologues, chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol. Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms and those with double bond are called alkenes. Those with one double bond have the formula CnH2n and those containing triple bonds are called alkyne. Those with one triple bond have the formula CnH2n−2, aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring. Hydrocarbons can be gases, liquids, waxes or low melting solids or polymers, in terms of shells, carbon consists of an incomplete outer shell, which comprises 4 electrons, and thus has 4 electrons available for covalent or dative bonding. Some hydrocarbons also are abundant in the solar system, lakes of liquid methane and ethane have been found on Titan, Saturns largest moon, confirmed by the Cassini-Huygens Mission. Hydrocarbons are also abundant in nebulae forming polycyclic aromatic hydrocarbon compounds, hydrocarbons are a primary energy source for current civilizations. The predominant use of hydrocarbons is as a fuel source. In their solid form, hydrocarbons take the form of asphalt, mixtures of volatile hydrocarbons are now used in preference to the chlorofluorocarbons as a propellant for aerosol sprays, due to chlorofluorocarbons impact on the ozone layer. Methane and ethane are gaseous at ambient temperatures and cannot be liquefied by pressure alone. Propane is however easily liquefied, and exists in propane bottles mostly as a liquid, butane is so easily liquefied that it provides a safe, volatile fuel for small pocket lighters
43.
Fullerene
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A fullerene is a molecule of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes, also referred to as Buckminsterfullerenes, resemble the balls used in football, cylindrical fullerenes are also called carbon nanotubes. Fullerenes are similar in structure to graphite, which is composed of stacked sheets of linked hexagonal rings. The name was an homage to Buckminster Fuller, whose geodesic domes it resembles, the structure was also identified some five years earlier by Sumio Iijima, from an electron microscope image, where it formed the core of a bucky onion. Fullerenes have since found to occur in nature. More recently, fullerenes have been detected in outer space, according to astronomer Letizia Stanghellini, It’s possible that buckyballs from outer space provided seeds for life on Earth. The discovery of fullerenes greatly expanded the number of carbon allotropes, which until recently were limited to graphite, graphene, diamond. The icosahedral C60H60 cage was mentioned in 1965 as a topological structure. Eiji Osawa of Toyohashi University of Technology predicted the existence of C60 in 1970 and he noticed that the structure of a corannulene molecule was a subset of an Association football shape, and he hypothesised that a full ball shape could also exist. Japanese scientific journals reported his idea, but neither it nor any translations of it reached Europe or the Americas, also in 1970, R. W. Henson proposed the structure and made a model of C60. Unfortunately, the evidence for new form of carbon was very weak and was not accepted. The results were never published but were acknowledged in Carbon in 1999, in 1973 independently from Henson, a group of scientists from the USSR, directed by Prof. Bochvar, made a quantum-chemical analysis of the stability of C60 and calculated its electronic structure. As in the cases, the scientific community did not accept the theoretical prediction. The paper was published in 1973 in Proceedings of the USSR Academy of Sciences, in mass spectrometry discrete peaks appeared corresponding to molecules with the exact mass of sixty or seventy or more carbon atoms. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of molecules, C60 and other fullerenes were later noticed occurring outside the laboratory. By 1990 it was easy to produce gram-sized samples of fullerene powder using the techniques of Donald Huffman, Wolfgang Krätschmer, Lowell D. Lamb. Fullerene purification remains a challenge to chemists and to a large extent determines fullerene prices, so-called endohedral fullerenes have ions or small molecules incorporated inside the cage atoms. Fullerene is a reactant in many organic reactions such as the Bingel reaction discovered in 1993
44.
Heterocyclic compound
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A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring. Heterocyclic chemistry is the branch of chemistry dealing with the synthesis, properties. Examples of heterocyclic compounds include all of the acids, the majority of drugs, most biomass. Although heterocyclic compounds may be inorganic, most contain at least one carbon, while atoms that are neither carbon nor hydrogen are normally referred to in organic chemistry as heteroatoms, this is usually in comparison to the all-carbon backbone. But this does not prevent a compound such as borazine from being labelled heterocyclic, IUPAC recommends the Hantzsch-Widman nomenclature for naming heterocyclic compounds. Heterocyclic compounds can be classified based on their electronic structure. The saturated heterocycles behave like the acyclic derivatives, thus, piperidine and tetrahydrofuran are conventional amines and ethers, with modified steric profiles. Therefore, the study of heterocyclic chemistry focuses especially on unsaturated derivatives, included are pyridine, thiophene, pyrrole, and furan. Another large class of heterocycles are fused to rings, which for pyridine, thiophene, pyrrole, and furan are quinoline, benzothiophene, indole. Fusion of two benzene rings gives rise to a large family of compounds, respectively the acridine, dibenzothiophene, carbazole. The unsaturated rings can be classified according to the participation of the heteroatom in the pi system, heterocycles with three atoms in the ring are more reactive because of ring strain. Those containing one heteroatom are, in general, stable and those with two heteroatoms are more likely to occur as reactive intermediates. Five-membered rings with one heteroatom, The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are called the azoles. Thiazoles and isothiazoles contain a sulfur and an atom in the ring. A large group of 5-membered ring compounds with three heteroatoms also exists, one example is dithiazoles that contain two sulfur and a nitrogen atom. Five-member ring compounds with four heteroatoms, With 5-heteroatoms, the compound may be considered rather than heterocyclic. With 7-membered rings, the heteroatom must be able to provide an empty pi orbital for normal aromatic stabilization to be available, otherwise, for example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is quinoline or isoquinoline, for azepine, benzazepine is the preferred name
45.
Carbonyl group
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In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom, C=O. It is common to several classes of compounds, as part of many larger functional groups. A compound containing a group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex, the remainder of this article concerns itself with the organic chemistry definition of carbonyl, where carbon and oxygen share a double bond. A carbonyl group characterizes the types of compounds, Note that the most specific labels are usually employed. For example, ROR structures are known as acid anhydride rather than the more generic ester, other organic carbonyls are urea and the carbamates, the derivatives of acyl chlorides chloroformates and phosgene, carbonate esters, thioesters, lactones, lactams, hydroxamates, and isocyanates. Examples of inorganic compounds are carbon dioxide and carbonyl sulfide. A special group of compounds are 1, 3-dicarbonyl compounds that have acidic protons in the central methylene unit. Examples are Meldrums acid, diethyl malonate and acetylacetone, because oxygen is more electronegative than carbon, carbonyl compounds often have resonance structures which affect their reactivity. This relative electronegativity draws electron density away from carbon, increasing the bonds polarity, carbon can then be attacked by nucleophiles or a negatively charged part of another molecule. During the reaction, the double bond is broken. This reaction is known as addition-elimination or condensation, the electronegative oxygen also can react with an electrophile, for example a proton in an acidic solution or with Lewis acids to form an oxocarbenium ion. The polarity of oxygen also makes the alpha hydrogens of carbonyl compounds much more acidic than typical sp3 C-H bonds, for example, the pKa values of acetaldehyde and acetone are 16.7 and 19 respectively, while the pKa value of methane is extrapolated to be approximately 50. This is because a carbonyl is in resonance with an enol. The deprotonation of the enol with a base produces an enolate. Amides are the most stable of the carbonyl couplings due to their high resonance stabilization between the nitrogen-carbon and carbon-oxygen bonds, carbonyl groups can be reduced by reaction with hydride reagents such as NaBH4 and LiAlH4, with bakers yeast, or by catalytic hydrogenation. Ketones give secondary alcohols while aldehydes, esters and carboxylic acids give primary alcohols, carbonyls can be alkylated in nucleophilic addition reactions using organometallic compounds such as organolithium reagents, Grignard reagents, or acetylides. Carbonyls also may be alkylated by enolates as in aldol reactions, carbonyls are also the prototypical groups with vinylogous reactivity
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. PMID 11226205.
