Cantabrian Mountains
The Cantabrian Mountains or Cantabrian Range are one of the main systems of mountain ranges in Spain. They stretch for over 300 km across northern Spain, from the western limit of the Pyrenees to the Galician Massif in Galicia, along the coast of the Cantabrian Sea, their easternmost end meets the Sistema Ibérico. These mountains are a distinct physiographic province of the larger Alpine System physiographic division; the Cantabrian Mountains offer a wide range of trails for hiking, as well as many challenging climbing routes. Skiing is possible in the ski resorts of Alto Campoo, Valgrande-Pajares, Fuentes de Invierno, San isidro and Manzaneda; the Cantabrian Mountains stretch east-west, nearly parallel to the sea, as far as the pass of Leitariegos extending south between León and Galicia. The range's western boundary is marked by the valley of the river Minho, by the lower Sil, which flows into the Miño, by the Cabrera River, a small tributary of the Sil. Cantabrian mountains reach its south-western limit in Portugal.
As a whole, the Cantabrian Mountains are remarkable for their intricate ramifications, but everywhere, in the east, it is possible to distinguish two principal ranges, from which the lesser ridges and mountain masses radiate. One range, or series of ranges follows the outline of the coast. In some parts the coastal range rises sheer above the sea, everywhere has so abrupt a declivity that the streams which flow seaward are all short and swift; the descent from the southern range to the high plateaux of Castile is more gradual, several large rivers, notably the Ebro, rise here and flow to the south or west. The breadth of the Cantabrian chain, with all its ramifications, increases from about 60 mi. Many peaks are over 6000 ft high, but the greatest altitudes are attained in the central ridges on the borders of León, Asturias and Cantabria. Here are the highest peak Torre de Cerredo, Peña Vieja, Peña Prieta and Espigüete. A conspicuous feature of the chain, as of the adjacent tableland, is the number of its parameras, isolated plateaus shut in by lofty mountains or by precipitous walls of rock.
The Cantabrian Mountains make a sharp divide between "Green Spain" to the north, the dry central plateau. The north facing slopes receive heavy cyclonic rainfall from the Bay of Biscay, whereas the southern slopes are in rain shadow; the Cantabrian Range has three distinct sections from west to east: The Asturian Massif and its foothills. Geologically it is an eastern prolongation of the Galician Massif with Paleozoic folds, it is cut by deep east-west oriented canyons such as the Cares River valley. Highest point Torre de Cerredo 2,648 m. Sierra de la Bobia, Pico de la Bobia 1,201 m Sierra de Tineo, Mulleiroso 1,241 m, a northern foothill located near Tineo Sierra de San Isidro, Campo de La Vaga 1,078 m Sierra de Eirelo, Pena dos Ladróis 800 m Sierra del Sueve, Picu Pienzu 1,161 m, a northern foothill west of the Sella River Sierra de Cuera, Pico Turbina 1,315 m, anorthern foothill located at the eastern end of Asturias Sierra de Quintanal, running transversally on the eastern side of the Narcea River Other ranges of the Asturian Massif are: Sierra del Aramo, Sierra de Pando, Sierra de Caniellas, Sierra de Rañadoiro, Loma de Parrondo, Sierra de San Mamés, Sierra de Serrantina, Sierra de la Zarza, Sierra de Degaña, Sierra del Acebo, Sierra de Sobia, Cordal de Lena, Sierra de Casomera, Porrones de Moneo, Cordal de Ponga The main mountains of this zone are the massive Picos de Europa.
They are composed of Carboniferous marl. The Paramo de Masa and La Lora grasslands are located in the south crossed by the Rudrón Valley. Sierra de Covadonga, west of the Picos de Europa Sierra de Dobros, north of the Picos de Europa The Picos de Europa are divided into three sectors or massifs: Cornión Massif in the west, Torre Santa 2,596 m Urrieles Massif in the center, Torrecerredo 2,650 m Ándara Massif in the east, Morra de Lechugales 2,444 m Sierra de Liencres, a coastal range, another northern foothill Sierra Nedrina Mountain ranges in Cantabria, located further east: Fuentes Carrionas Massif, Peña Prieta 2,536 m, close to the eastern end of the Picos de Europa Sierra Cocón above Tresviso Sierra del Escudo de Cabuérniga, a northern foothill of the system, located between the main ridges and the sea Sierra de la Gándara, Peña Cabarga 537 m, a lower northern foothill located further east Montes de Ucieda Alto del Gueto Sierra de la Matanza Sierra de Peña Sagra, Peña Sagra 2,046 m Sierra de Peña Labra, Pico Tres Mares 2,175 m and Peña Labra 2,006 m Sierra del Cordel in the Saja and Nansa Comarca Sierra del Escudo, between Campoo de Yuso and Luena Sierra de Híjar, foothills located in the high plateau at the southeastern end of the central zone Valdecebollas Sierra del Hornijo, Mortillano 1,410 Sierra de Breñas, foothill running perpendicular to the coast Montes de Pas, Castro Valnera 1,707 m in the transition area to the Basque Mountains The Basque Mountains at the eastern end of the system, with eroded Mesozoic folds and ranges of moderate height: Inner ranges: Sierra Salbada Mounts of Gasteiz, Kapildui 1,177 m Izki Urbasa, Baiza 1,183 m Andía, with the impressive Beriain 1,493 m Coastal ranges: Gorbea 1,481 m Urkiola, A
American Museum of Natural History
The American Museum of Natural History, located on the Upper West Side of Manhattan, New York City, is one of the largest natural history museums in the world. Located in Theodore Roosevelt Park across the street from Central Park, the museum complex comprises 28 interconnected buildings housing 45 permanent exhibition halls, in addition to a planetarium and a library; the museum collections contain over 33 million specimens of plants, fossils, rocks, human remains, human cultural artifacts, of which only a small fraction can be displayed at any given time, occupies more than 2 million square feet. The museum has a full-time scientific staff of 225, sponsors over 120 special field expeditions each year, averages about five million visits annually; the one mission statement of the American Museum of Natural History is: "To discover and disseminate—through scientific research and education—knowledge about human cultures, the natural world, the universe." Before construction of the present complex, the museum was housed in the Arsenal building in Central Park.
Theodore Roosevelt, Sr. the father of the 26th U. S. President, was one of the founders along with John David Wolfe, William T. Blodgett, Robert L. Stuart, Andrew H. Green, Robert Colgate, Morris K. Jesup, Benjamin H. Field, D. Jackson Steward, Richard M. Blatchford, J. P. Morgan, Adrian Iselin, Moses H. Grinnell, Benjamin B. Sherman, A. G. Phelps Dodge, William A. Haines, Charles A. Dana, Joseph H. Choate, Henry G. Stebbins, Henry Parish, Howard Potter; the founding of the museum realized the dream of naturalist Dr. Albert S. Bickmore. Bickmore, a one-time student of zoologist Louis Agassiz, lobbied tirelessly for years for the establishment of a natural history museum in New York, his proposal, backed by his powerful sponsors, won the support of the Governor of New York, John Thompson Hoffman, who signed a bill creating the American Museum of Natural History on April 6, 1869. In 1874, the cornerstone was laid for the museum's first building, now hidden from view by the many buildings in the complex that today occupy most of Manhattan Square.
The original Victorian Gothic building, opened in 1877, was designed by Calvert Vaux and J. Wrey Mould, both closely identified with the architecture of Central Park; the original building was soon eclipsed by the south range of the museum, designed by J. Cleaveland Cady, an exercise in rusticated brownstone neo-Romanesque, influenced by H. H. Richardson, it extends 700 feet with corner towers 150 feet tall. Its pink brownstone and granite, similar to that found at Grindstone Island in the St. Lawrence River, came from quarries at Picton Island, New York; the entrance on Central Park West, the New York State Memorial to Theodore Roosevelt, completed by John Russell Pope in 1936, is an overscaled Beaux-Arts monument. It leads to a vast Roman basilica, where visitors are greeted with a cast of a skeleton of a rearing Barosaurus defending her young from an Allosaurus; the museum is accessible through its 77th street foyer, renamed the "Grand Gallery" and featuring a suspended Haida canoe. The hall leads into the oldest extant exhibit in the hall of Northwest Coast Indians.
Since 1930, little has been added to the exterior of the original building. The architect Kevin Roche and his firm Roche-Dinkeloo have been responsible for the master planning of the museum since the 1990s. Various renovations to both the interior and exterior have been carried out. Renovations to the Dinosaur Hall were undertaken starting in 1991, the museum restored the mural in Roosevelt Memorial Hall in 2010. In 1992 the Roche-Dinkeloo firm designed the eight-story AMNH Library. However, the entirety of the master plan was not realized, by 2015, the museum consisted of 25 separate buildings that were poorly connected; the museum's south façade, spanning 77th Street from Central Park West to Columbus Avenue was cleaned, repaired and re-emerged in 2009. Steven Reichl, a spokesman for the museum, said that work would include restoring 650 black-cherry window frames and stone repairs; the museum's consultant on the latest renovation is Wiss, Elstner Associates, Inc. an architectural and engineering firm with headquarters in Northbrook, Illinois.
In 2014, the museum published plans for a $325 million, 195,000-square-foot annex, the Richard Gilder Center for Science and Innovation, on the Columbus Avenue side. Designed by Studio Gang, Higgins Quasebarth & Partners and landscape architects Reed Hilderbrand, the new building's pink Milford granite facade will have a textural, curvilinear design inspired by natural topographical elements showcased in the museum, including "geological strata, glacier-gouged caves, curving canyons, blocks of glacial ice," as a striking contrast to the museum's predominance of High Victorian Gothic, Richardson Romanesque and Beaux Arts architectural styles; the interior itself would contain a new entrance from Columbus Avenue north of 79th Street. This expansion was supposed to be located to the south of the existing museum, occupying parts of Theodore Roosevelt Park; the expansion was relocated to the west side of the existing museum, its footprint was reduced in size, due to opposition to construction in the park.
The annex would instead replace three existing buildings along Columbus Avenue's east side, with more than 30 connections to the existing museum, it would be six stories high, the same height as the existing buildings. The plans for the expansion wer
Calibration of radiocarbon dates
Radiocarbon dating measurements produce ages in "radiocarbon years", which must be converted to calendar ages by a process called calibration. Calibration is needed because the atmospheric 14C/12C ratio, a key element in calculating radiocarbon ages, has not been constant historically. Although Willard Libby, the inventor of radiocarbon dating, had pointed out as early as 1955 the possibility that the 14C/12C ratio might have varied over time, it was not until discrepancies began to accumulate between measured ages and known historical dates for artefacts that it became clear that a correction would need to be applied to radiocarbon ages to obtain calendar dates. A general abbreviation, ambiguous if not understood from context, used for reporting dates obtained with any method is Before Present, where "present" is 1950. Radiocarbon years ago may be abbreviated "14Cya" or "uncal BP" and calibrated dates as "cal BP". To produce a curve that can be used to relate calendar years to radiocarbon years, a sequence of securely dated samples is needed which can be tested to determine their radiocarbon age.
Dendrochronology or the study of tree rings led to the first such sequence: tree rings from individual pieces of wood show characteristic sequences of rings that vary in thickness because of environmental factors such as the amount of rainfall in a given year. These factors affect all trees in an area, so examining tree-ring sequences from old wood allows the identification of overlapping sequences. In this way, an uninterrupted sequence of tree rings can be extended far into the past; the first such published sequence, based on bristlecone pine tree rings, was created in the 1960s by Wesley Ferguson. Hans Suess used this data to publish the first calibration curve for radiocarbon dating in 1967; the curve showed two types of variation from the straight line: a long term fluctuation with a period of about 9,000 years, a shorter term variation referred to as "wiggles", with a period of decades. Suess said, it was unclear for some time whether the wiggles were real or not, but they are now well-established.
The calibration method assumes that the temporal variation in 14C level is global, such that a small number of samples from a specific year are sufficient for calibration. This was experimentally verified in the 1980s. Over the next thirty years many calibration curves were published using a variety of methods and statistical approaches; these were superseded by the INTCAL series of curves, beginning with INTCAL98, published in 1998, updated in 2004, 2009, most 2013. The improvements to these curves are based on new data gathered from tree rings, varves and other studies. Significant additions to the datasets used for INTCAL13 include non-varved marine foraminifera data, U-Th dated speleothems; the INTCAL13 data includes separate curves for the northern and southern hemispheres, as they differ systematically because of the hemisphere effect. Once testing has produced a sample age in radiocarbon years, with an associated error range of plus or minus one standard deviation, the calibration curve can be used to derive a range of calendar ages for the sample.
The calibration curve itself has an associated error term, which can be seen on the graph labelled "Calibration error and measurement error". This graph shows INTCAL13 data for the calendar years 3100 BP to 3500 BP; the solid line is the INTCAL13 calibration curve, the dotted lines show the standard error range—as with the sample error, this is one standard deviation. Reading off the range of radiocarbon years against the dotted lines, as is shown for sample t2, in red, gives too large a range of calendar years; the error term should be the root of the sum of the squares of the two errors: σ t o t a l = 1 2 Example t1, in green on the graph, shows this procedure—the resulting error term, σtotal, is used for the range, this range is used to read the result directly from the graph itself, without reference to the lines showing the calibration error. Variations in the calibration curve can lead to different resulting calendar year ranges for samples with different radiocarbon ages; the graph to the right shows the part of the INTCAL13 calibration curve from 1000 BP to 1400 BP, a range in which there are significant departures from a linear relationship between radiocarbon age and calendar age.
In places where the calibration curve is steep, does not change direction, as in example t1 in blue on the graph to the right, the resulting calendar year range is quite narrow. Where the curve varies both up and down, a single radiocarbon date range may produce two or more separate calendar year ranges. Example t2, in red on the graph, shows this situation: a radiocarbon age range of about 1260 BP to 1280 BP converts to three separate ranges between about 1190 BP and 1260 BP. A third possibility is; the me
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between Spain and France. Reaching a height of 3,404 metres altitude at the peak of Aneto, the range separates the Iberian Peninsula from the rest of continental Europe, extends for about 491 km from the Bay of Biscay to the Mediterranean Sea. For the most part, the main crest forms a divide between Spain and France, with the microstate of Andorra sandwiched in between; the Principality of Catalonia alongside with the Kingdom of Aragon in the Crown of Aragon and the Kingdom of Navarre have extended on both sides of the mountain range, with smaller northern portions now in France and larger southern parts now in Spain. In Greek mythology, Pyrene is a princess; the Greek historian Herodotus says. According to Silius Italicus, she was the virgin daughter of Bebryx, a king in Mediterranean Gaul by whom the hero Hercules was given hospitality during his quest to steal the cattle of Geryon during his famous Labours.
Hercules, characteristically drunk and lustful, violates the sacred code of hospitality and rapes his host's daughter. Pyrene runs away to the woods, afraid that her father will be angry. Alone, she pours out her story to the trees, attracting the attention of wild beasts who tear her to pieces. After his victory over Geryon, Hercules passes through the kingdom of Bebryx again, finding the girl's lacerated remains; as is the case in stories of this hero, the sober Hercules responds with heartbroken grief and remorse at the actions of his darker self, lays Pyrene to rest tenderly, demanding that the surrounding geography join in mourning and preserve her name: "struck by Herculean voice, the mountaintops shudder at the ridges. … The mountains hold on to the wept-over name through the ages." Pliny the Elder connects the story of Hercules and Pyrene to Lusitania, but rejects it as fabulosa fictional. Other classical sources derived the name from the Greek word for fire, Ancient Greek: πῦρ. According to Greek historian Diodorus Siculus "..in ancient times, we are told, certain herdsmen left a fire and the whole area of the mountains was consumed.
The Spanish Pyrenees are part of the following provinces, from east to west: Girona, Lleida, Huesca and Gipuzkoa. The French Pyrenees are part of the following départements, from east to west: Pyrénées-Orientales, Ariège, Haute-Garonne, Hautes-Pyrénées, Pyrénées-Atlantiques; the independent principality of Andorra is sandwiched in the eastern portion of the mountain range between the Spanish Pyrenees and French Pyrenees. Physiographically, the Pyrenees may be divided into three sections: the Atlantic, the Central, the Eastern Pyrenees. Together, they form a distinct physiographic province of the larger Alpine System division. In the Western Pyrenees, from the Basque mountains near the Bay of Biscay of the Atlantic Ocean, the average elevation increases from west to east; the Central Pyrenees extend eastward from the Somport pass to the Aran Valley, they include the highest summits of this range: Pico d'Aneto 3,404 metres in the Maladeta ridge, Pico Posets 3,375 metres, Monte Perdido 3,355 metres.
In the Eastern Pyrenees, with the exception of one break at the eastern extremity of the Pyrénées Ariègeoises in the Ariège area, the mean elevation is remarkably uniform until a sudden decline occurs in the easternmost portion of the chain known as the Albères. Most foothills of the Pyrenees are on the Spanish side, where there is a large and complex system of ranges stretching from Spanish Navarre, across northern Aragon and into Catalonia reaching the Mediterranean coast with summits reaching 2,600 m. At the eastern end on the southern side lies a distinct area known as the Sub-Pyrenees. On the French side the slopes of the main range descend abruptly and there are no foothills except in the Corbières Massif in the northeastern corner of the mountain system; the Pyrenees are older than the Alps: their sediments were first deposited in coastal basins during the Paleozoic and Mesozoic eras. Between 100 and 150 million years ago, during the Lower Cretaceous Period, the Bay of Biscay fanned out, pushing present-day Spain against France and applying intense compressional pressure to large layers of sedimentary rock.
The intense pressure and uplifting of the Earth's crust first affected the eastern part and moved progressively to the entire chain, culminating in the Eocene Epoch. The eastern part of the Pyrenees consists of granite and gneissose rocks, while in the western part the granite peaks are flanked by layers of limestone; the massive and unworn character of the chain comes from its abundance of granite, resistant to erosion, as well as weak glacial development. The upper parts of the Pyrenees contain low-relief surfaces forming a peneplain; this peneplain originated no earlier than in Late Miocene times. It formed at height as extensive sedimentation raised the local base
Oban
Oban is a resort town within the Argyll and Bute council area of Scotland. Despite its small size, it is the largest town between Fort William. During the tourist season, the town can play host to up to 25,000 people. Oban occupies a setting in the Firth of Lorn; the bay is a near perfect horseshoe, protected by the island of Kerrera. To the north, is the long low island of Lismore, the mountains of Morvern and Ardgour; the site where Oban now stands has been used by humans since at least mesolithic times, as evidenced by archaeological remains of cave dwellers found in the town. Just outside the town stands Dunollie Castle, on a site that overlooks the main entrance to the bay and has been fortified since the Bronze age. Prior to the 19th century, the town itself supported few households, sustaining only minor fishing, trading and quarrying industries, a few hardy tourists; the Renfrew trading company established a storehouse there in about 1714 as a local outlet for its merchandise, but a Custom-house was not deemed necessary until 1736 when "Oban being reckoned a proper place for clearing out vessels for the herring fishery".
The modern town of Oban grew up around the distillery, founded there in 1794. The town was raised to a burgh of barony in 1811 by royal charter. Sir Walter Scott visited the area in 1814, the year in which he published his poem The Lord of the Isles; the town was made a Parliamentary Burgh in 1833. A rail link - the Callander and Oban Railway - was authorised in 1864 but took years to reach the town; the final stretch of track to Oban opened on 30 June 1880. This brought further prosperity, giving new energy to tourism. At this time work on the ill-fated Oban Hydro was commenced but abandoned, left to fall into disrepair, after 1882 when Dr Orr, the schemes originator, realised he had grossly underestimated its cost. Work on McCaig's Tower, a prominent local landmark, started in 1895, it was paid for by John Stewart McCaig and was constructed, in hard times, to give work for local stone masons. However, its construction ceased in 1902 on the death of its benefactor. During World War II, Oban was used by Merchant and Royal Navy ships and was an important base in the Battle of the Atlantic.
The Royal Navy had a signal station near Ganavan, an anti-submarine indicator loop station, which detected any surface or submarine vessels between Oban and Lismore. There was a controlled minefield in the Sound of Kerrera, operated from a building near the caravan site at Gallanach. There was a Royal Air Force flying boat base at Ganavan and on Kerrera, an airfield at North Connel built by the Royal Air Force. A Sector Operations Room was built near the airfield. Oban was important during the Cold War because the first Transatlantic Telephone Cable came ashore at Gallanach Bay; this carried the Hot Line between the USSR presidents. At North Connel, next to the airfield/airport was the NRC of the Royal Observer Corps. Since the 1950s, the principal industry has remained tourism, though the town is an important ferry port, acting as the hub for Caledonian MacBrayne ferries to many of the islands of the Inner and Outer Hebrides; as with the rest of the British Isles, Oban experiences a maritime climate with cool summers and mild winters.
The nearest official Met Office weather station for which online records are available is at Dunstaffnage, about 2.7 miles north-north-east of Oban town centre. Rainfall is high, but thanks to the Gulf Stream, the temperature falls below 0 °C; the local culture is Gaelic. In 2011, 8.2% of the town's population over age 3 could speak Gaelic and 11.3% had some facility in the language. Oban is considered the home of the Royal National Mòd, since it was first held there in 1892, with ten competitors on a Saturday afternoon; the town hosted the centenary Mod in 1992 and in 2003 the 100th Mod, the two events attracting thousands of competitors and visitors. The Mod is held in Oban every 6–8 years, has last been held in October 2015. An annual Highland Games, known as the Argyllshire Gathering, is held in the town; the Corran Halls theatre acts as a venue for community events and touring entertainers, touring companies such as Scottish Opera. The town has a two-screen cinema, which closed in early 2010.
Thanks to a local community initiative supported by a number of famous names, it reopened in August 2012 as the Phoenix Cinema. Oban has itself been used as a backdrop to several films, including Ring of Bright Water and Morvern Callar; the Oban War and Peace Museum advances the education of present and future generations by collecting, maintaining and exhibiting items of historical and cultural interest relating to the Oban area in peacetime and during the war years. A museum operates within Oban Distillery, just behind the main seafront; the distillation of whisky in Oban predates the town: whisky has been produced on the site since 1794. The Hope MacDougall collection is a unique record of the working and domestic lives of people in Scotland. Music is central to Gaelic culture, there is lively interest in the town. In the 2010 pipe band season, the local Oban High School Pipe Band, led by Angus MacColl, was successful in winning the World Pipe Band Championships in Glasgow, the Cowal Games competition, an
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxyhydroxides. Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, are used by humans, e.g. as iron ores, catalysts, in thermite and hemoglobin. Common rust is a form of iron oxide. Iron oxides are used as inexpensive, durable pigments in paints and colored concretes. Colors available are in the "earthy" end of the yellow/orange/red/brown/black range; when used as a food coloring, it has E number E172. Oxide of FeIIFeO: iron oxide, wüstite FeO2: iron dioxide Mixed oxides of FeII and FeIIIFe3O4: Iron oxide, magnetite Fe4O5 Fe5O6 Fe5O7 Fe25O32 Fe13O19 Oxide of FeIIIFe2O3: iron oxide α-Fe2O3: alpha phase, hematite β-Fe2O3: beta phase γ-Fe2O3: gamma phase, maghemite ε-Fe2O3: epsilon phase iron hydroxide iron hydroxide, akaganéite, feroxyhyte, ferrihydrite, or 5 Fe 2 O 3 ⋅ 9 H 2 O, better recast as FeOOH ⋅ 0.4 H 2 O high-pressure FeOOH schwertmannite green rust Several species of bacteria, including Shewanella oneidensis, Geobacter sulfurreducens and Geobacter metallireducens, metabolically utilize solid iron oxides as a terminal electron acceptor, reducing Fe oxides to Fe containing oxides.
Under conditions favoring iron reduction, the process of iron oxide reduction can replace at least 80% of methane production occurring by methanogenesis. This phenomenon occurs in a nitrogen-containing environment with low sulfate concentrations. Methanogenesis, an Archaean driven process, is the predominate form of carbon mineralization in sediments at the bottom of the ocean. Methanogenesis completes the decomposition of organic matter to methane; the specific electron donor for iron oxide reduction in this situation is still under debate, but the two potential candidates include either Titanium or compounds present in yeast. The predicted reactions with Titanium serving as the electron donor and phenazine-1-carboxylate serving as an electron shuttle is as follows: Ti-cit + CO2 + 8H+ → CH4 + 2H2O + Ti + cit ΔE = –240 + 300 mV Ti-cit + PCA → PCA + Ti + cit ΔE = –116 + 300 mV PCA + Fe3 → Fe2+ + PCA ΔE = –50 + 116 mV Note: cit = citrate. Titanium is oxidized to Titanium; the reduced form of PCA can reduce the iron hydroxide.
On the other hand when airborne, iron oxides have been shown to harm the lung tissues of living organisms by the formation of hydroxyl radicals, leading to the creation of alkyl radicals. The following reactions occur when Fe2O3 and FeO, hereafter represented as Fe3+ and Fe2+ iron oxide particulates accumulate in the lungs. O2 + e− → O2• –The formation of the superoxide anion is catalyzed by a transmembrane enzyme called NADPH oxidase; the enzyme facilitates the transport of an electron across the plasma membrane from cytosolic NADPH to extracellular oxygen to produce O2• –. NADPH and FAD are bound to cytoplasmic binding sites on the enzyme. Two electrons from NADPH are transported to FAD which reduces it to FADH2. One electron moves to one of two heme groups in the enzyme within the plane of the membrane; the second electron pushes the first electron to the second heme group so that it can associate with the first heme group. For the transfer to occur, the second heme must be bound to extracellular oxygen, the acceptor of the electron.
This enzyme can be located within the membranes of intracellular organelles allowing the formation of O2• – to occur within organelles. 2O2• – + 2 H+ → H2O2 + O2 The formation of hydrogen peroxide can occur spontaneously when the environment has a lower pH at pH 7.4. The enzyme superoxide dismutase can catalyze this reaction. Once H2O2 has been synthesized, it can diffuse thro
Radiocarbon dating
Radiocarbon dating is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960, it is based on the fact that radiocarbon is being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting 14C combines with atmospheric oxygen to form radioactive carbon dioxide, incorporated into plants by photosynthesis; when the animal or plant dies, it stops exchanging carbon with its environment, from that point onwards the amount of 14C it contains begins to decrease as the 14C undergoes radioactive decay. Measuring the amount of 14C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died; the older a sample is, the less 14C there is to be detected, because the half-life of 14C is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods permit accurate analysis of older samples.
Research has been ongoing since the 1960s to determine what the proportion of 14C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of 14C in different types of organisms, the varying levels of 14C throughout the biosphere. Additional complications come from the burning of fossil fuels such as coal and oil, from the above-ground nuclear tests done in the 1950s and 1960s; because the time it takes to convert biological materials to fossil fuels is longer than the time it takes for its 14C to decay below detectable levels, fossil fuels contain no 14C, as a result there was a noticeable drop in the proportion of 14C in the atmosphere beginning in the late 19th century. Conversely, nuclear testing increased the amount of 14C in the atmosphere, which attained a maximum in about 1965 of twice what it had been before the testing began.
Measurement of radiocarbon was done by beta-counting devices, which counted the amount of beta radiation emitted by decaying 14C atoms in a sample. More accelerator mass spectrometry has become the method of choice; the development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances. Histories of archaeology refer to its impact as the "radiocarbon revolution". Radiocarbon dating has allowed key transitions in prehistory to be dated, such as the end of the last ice age, the beginning of the Neolithic and Bronze Age in different regions. In 1939, Martin Kamen and Samuel Ruben of the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research, they synthesized 14C using the laboratory's cyclotron accelerator and soon discovered that the atom's half-life was far longer than had been thought.
This was followed by a prediction by Serge A. Korff employed at the Franklin Institute in Philadelphia, that the interaction of thermal neutrons with 14N in the upper atmosphere would create 14C, it had been thought that 14C would be more to be created by deuterons interacting with 13C. At some time during World War II, Willard Libby, at Berkeley, learned of Korff's research and conceived the idea that it might be possible to use radiocarbon for dating. In 1945, Libby moved to the University of Chicago, he published a paper in 1946 in which he proposed that the carbon in living matter might include 14C as well as non-radioactive carbon. Libby and several collaborators proceeded to experiment with methane collected from sewage works in Baltimore, after isotopically enriching their samples they were able to demonstrate that they contained 14C. By contrast, methane created from petroleum showed no radiocarbon activity because of its age; the results were summarized in a paper in Science in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin.
Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years; these results were published in Science in 1949. Within 11 years of their announcement, more than 20 radiocarbon dating laboratories had been set up worldwide. In 1960, Libby was awarded the Nobel Prize in Chemistry for this work. In nature, carbon exists as two stable, nonradioactive isotopes: carbon-12, carbon-13, a radioactive isotope, carbon-14 known as "radiocarbon"; the half-life
.jpg)
