Split (1)

train · 41.2k rows

text stringlengths 151 4.06k
Although coal, hydrocarbons, iron ore, platinum, copper, chromium, nickel, gold and other minerals have been found, they have not been in large enough quantities to exploit. The 1991 Protocol on Environmental Protection to the Antarctic Treaty also restricts a struggle for resources. In 1998, a compromise agreement was reached to place an indefinite ban on mining, to be reviewed in 2048, further limiting economic development and exploitation. The primary economic activity is the capture and offshore trading of fish. Antarctic fisheries in 2000–01 reported landing 112,934 tonnes.
This large collection of meteorites allows a better understanding of the abundance of meteorite types in the solar system and how meteorites relate to asteroids and comets. New types of meteorites and rare meteorites have been found. Among these are pieces blasted off the Moon, and probably Mars, by impacts. These specimens, particularly ALH84001 discovered by ANSMET, are at the center of the controversy about possible evidence of microbial life on Mars. Because meteorites in space absorb and record cosmic radiation, the time elapsed since the meteorite hit the Earth can be determined from laboratory studies. The elapsed time since fall, or terrestrial residence age, of a meteorite represents more information that might be useful in environmental studies of Antarctic ice sheets.
In 2002 the Antarctic Peninsula's Larsen-B ice shelf collapsed. Between 28 February and 8 March 2008, about 570 km2 (220 sq mi) of ice from the Wilkins Ice Shelf on the southwest part of the peninsula collapsed, putting the remaining 15,000 km2 (5,800 sq mi) of the ice shelf at risk. The ice was being held back by a "thread" of ice about 6 km (4 mi) wide, prior to its collapse on 5 April 2009. According to NASA, the most widespread Antarctic surface melting of the past 30 years occurred in 2005, when an area of ice comparable in size to California briefly melted and refroze; this may have resulted from temperatures rising to as high as 5 °C (41 °F).
Antarctica has no indigenous population and there is no evidence that it was seen by humans until the 19th century. However, belief in the existence of a Terra Australis—a vast continent in the far south of the globe to "balance" the northern lands of Europe, Asia and North Africa—had existed since the times of Ptolemy (1st century AD), who suggested the idea to preserve the symmetry of all known landmasses in the world. Even in the late 17th century, after explorers had found that South America and Australia were not part of the fabled "Antarctica", geographers believed that the continent was much larger than its actual size.
About 98% of Antarctica is covered by the Antarctic ice sheet, a sheet of ice averaging at least 1.6 km (1.0 mi) thick. The continent has about 90% of the world's ice (and thereby about 70% of the world's fresh water). If all of this ice were melted, sea levels would rise about 60 m (200 ft). In most of the interior of the continent, precipitation is very low, down to 20 mm (0.8 in) per year; in a few "blue ice" areas precipitation is lower than mass loss by sublimation and so the local mass balance is negative. In the dry valleys, the same effect occurs over a rock base, leading to a desiccated landscape.
There is some evidence, in the form of ice cores drilled to about 400 m (1,300 ft) above the water line, that Lake Vostok's waters may contain microbial life. The frozen surface of the lake shares similarities with Jupiter's moon, Europa. If life is discovered in Lake Vostok, it would strengthen the argument for the possibility of life on Europa. On 7 February 2008, a NASA team embarked on a mission to Lake Untersee, searching for extremophiles in its highly alkaline waters. If found, these resilient creatures could further bolster the argument for extraterrestrial life in extremely cold, methane-rich environments.
Africa separated from Antarctica in the Jurassic, around 160 Ma, followed by the Indian subcontinent in the early Cretaceous (about 125 Ma). By the end of the Cretaceous, about 66 Ma, Antarctica (then connected to Australia) still had a subtropical climate and flora, complete with a marsupial fauna. In the Eocene epoch, about 40 Ma Australia-New Guinea separated from Antarctica, so that latitudinal currents could isolate Antarctica from Australia, and the first ice began to appear. During the Eocene–Oligocene extinction event about 34 million years ago, CO2 levels have been found to be about 760 ppm and had been decreasing from earlier levels in the thousands of ppm.
Antarctica is colder than the Arctic for three reasons. First, much of the continent is more than 3,000 m (9,800 ft) above sea level, and temperature decreases with elevation in the troposphere. Second, the Arctic Ocean covers the north polar zone: the ocean's relative warmth is transferred through the icepack and prevents temperatures in the Arctic regions from reaching the extremes typical of the land surface of Antarctica. Third, the Earth is at aphelion in July (i.e., the Earth is farthest from the Sun in the Antarctic winter), and the Earth is at perihelion in January (i.e., the Earth is closest to the Sun in the Antarctic summer). The orbital distance contributes to a colder Antarctic winter (and a warmer Antarctic summer) but the first two effects have more impact.
Emilio Marcos Palma was the first person born south of the 60th parallel south (the continental limit according to the Antarctic Treaty), as well as the first one born on the Antarctic mainland, in 1978 at Base Esperanza, on the tip of the Antarctic Peninsula; his parents were sent there along with seven other families by the Argentine government to determine if the continent was suitable for family life. In 1984, Juan Pablo Camacho was born at the Frei Montalva Station, becoming the first Chilean born in Antarctica. Several bases are now home to families with children attending schools at the station. As of 2009, eleven children were born in Antarctica (south of the 60th parallel south): eight at the Argentine Esperanza Base and three at the Chilean Frei Montalva Station.
About 1150 species of fungi have been recorded from Antarctica, of which about 750 are non-lichen-forming and 400 are lichen-forming. Some of these species are cryptoendoliths as a result of evolution under extreme conditions, and have significantly contributed to shaping the impressive rock formations of the McMurdo Dry Valleys and surrounding mountain ridges. The apparently simple morphology, scarcely differentiated structures, metabolic systems and enzymes still active at very low temperatures, and reduced life cycles shown by such fungi make them particularly suited to harsh environments such as the McMurdo Dry Valleys. In particular, their thick-walled and strongly melanized cells make them resistant to UV light. Those features can also be observed in algae and cyanobacteria, suggesting that these are adaptations to the conditions prevailing in Antarctica. This has led to speculation that, if life ever occurred on Mars, it might have looked similar to Antarctic fungi such as Cryomyces minteri. Some of these fungi are also apparently endemic to Antarctica. Endemic Antarctic fungi also include certain dung-inhabiting species which have had to evolve in response to the double challenge of extreme cold while growing on dung, and the need to survive passage through the gut of warm-blooded animals.
The Argentine, British and Chilean claims all overlap, and have caused friction. On 18 December 2012, the British Foreign and Commonwealth Office named a previously unnamed area Queen Elizabeth Land in tribute to Queen Elizabeth II's Diamond Jubilee. On 22 December 2012, the UK ambassador to Argentina, John Freeman, was summoned to the Argentine government as protest against the claim. Argentine–UK relations had previously been damaged throughout 2012 due to disputes over the sovereignty of the nearby Falkland Islands, and the 30th anniversary of the Falklands War.
There has been some concern over the potential adverse environmental and ecosystem effects caused by the influx of visitors. Some environmentalists and scientists have made a call for stricter regulations for ships and a tourism quota. The primary response by Antarctic Treaty Parties has been to develop, through their Committee for Environmental Protection and in partnership with IAATO, "site use guidelines" setting landing limits and closed or restricted zones on the more frequently visited sites. Antarctic sightseeing flights (which did not land) operated out of Australia and New Zealand until the fatal crash of Air New Zealand Flight 901 in 1979 on Mount Erebus, which killed all 257 aboard. Qantas resumed commercial overflights to Antarctica from Australia in the mid-1990s.
Researchers include biologists, geologists, oceanographers, physicists, astronomers, glaciologists, and meteorologists. Geologists tend to study plate tectonics, meteorites from outer space, and resources from the breakup of the supercontinent Gondwana. Glaciologists in Antarctica are concerned with the study of the history and dynamics of floating ice, seasonal snow, glaciers, and ice sheets. Biologists, in addition to examining the wildlife, are interested in how harsh temperatures and the presence of people affect adaptation and survival strategies in a wide variety of organisms. Medical physicians have made discoveries concerning the spreading of viruses and the body's response to extreme seasonal temperatures. Astrophysicists at Amundsen–Scott South Pole Station study the celestial dome and cosmic microwave background radiation. Many astronomical observations are better made from the interior of Antarctica than from most surface locations because of the high elevation, which results in a thin atmosphere; low temperature, which minimizes the amount of water vapour in the atmosphere; and absence of light pollution, thus allowing for a view of space clearer than anywhere else on Earth. Antarctic ice serves as both the shield and the detection medium for the largest neutrino telescope in the world, built 2 km (1.2 mi) below Amundsen–Scott station.
At Buya in Eritrea, one of the oldest hominids representing a possible link between Homo erectus and an archaic Homo sapiens was found by Italian scientists. Dated to over 1 million years old, it is the oldest skeletal find of its kind and provides a link between hominids and the earliest anatomically modern humans. It is believed that the section of the Danakil Depression in Eritrea was also a major player in terms of human evolution, and may contain other traces of evolution from Homo erectus hominids to anatomically modern humans.
The Scottish traveler James Bruce reported in 1770 that Medri Bahri was a distinct political entity from Abyssinia, noting that the two territories were frequently in conflict. The Bahre-Nagassi ("Kings of the Sea") alternately fought with or against the Abyssinians and the neighbouring Muslim Adal Sultanate depending on the geopolitical circumstances. Medri Bahri was thus part of the Christian resistance against Imam Ahmad ibn Ibrahim al-Ghazi of Adal's forces, but later joined the Adalite states and the Ottoman Empire front against Abyssinia in 1572. That 16th century also marked the arrival of the Ottomans, who began making inroads in the Red Sea area.
The creation of modern-day Eritrea is a result of the incorporation of independent, distinct kingdoms and sultanates (for example, Medri Bahri and the Sultanate of Aussa) eventually resulting in the formation of Italian Eritrea. In 1947 Eritrea became part of a federation with Ethiopia, the Federation of Ethiopia and Eritrea. Subsequent annexation into Ethiopia led to the Eritrean War of Independence, ending with Eritrean independence following a referendum in April 1993. Hostilities between Eritrea and Ethiopia persisted, leading to the Eritrean–Ethiopian War of 1998–2000 and further skirmishes with both Djibouti and Ethiopia.
Excavations in and near Agordat in central Eritrea yielded the remains of an ancient pre-Aksumite civilization known as the Gash Group. Ceramics were discovered that were related to those of the C-Group (Temehu) pastoral culture, which inhabited the Nile Valley between 2500–1500 BC. Some sources dating back to 3500 BC. Shards akin to those of the Kerma culture, another community that flourished in the Nile Valley around the same period, were also found at other local archaeological sites in the Barka valley belonging to the Gash Group. According to Peter Behrens (1981) and Marianne Bechaus-Gerst (2000), linguistic evidence indicates that the C-Group and Kerma peoples spoke Afroasiatic languages of the Berber and Cushitic branches, respectively.
The Aksumites erected a number of large stelae, which served a religious purpose in pre-Christian times. One of these granite columns, the obelisk of Aksum, is the largest such structure in the world, standing at 90 feet. Under Ezana (fl. 320–360), Aksum later adopted Christianity. In the 7th century, early Muslims from Mecca also sought refuge from Quraysh persecution by travelling to the kingdom, a journey known in Islamic history as the First Hijra. It is also the alleged resting place of the Ark of the Covenant and the purported home of the Queen of Sheba.
Eritrea is a member of the United Nations, the African Union, and is an observing member of the Arab League. The nation holds a seat on the United Nations' Advisory Committee on Administrative and Budgetary Questions (ACABQ). Eritrea also holds memberships in the International Bank for Reconstruction and Development, International Finance Corporation, International Criminal Police Organization (INTERPOL), Non-Aligned Movement, Organization for the Prohibition of Chemical Weapons, Permanent Court of Arbitration, and the World Customs Organization.
The kingdom is mentioned in the Periplus of the Erythraean Sea as an important market place for ivory, which was exported throughout the ancient world. Aksum was at the time ruled by Zoskales, who also governed the port of Adulis. The Aksumite rulers facilitated trade by minting their own Aksumite currency. The state also established its hegemony over the declining Kingdom of Kush and regularly entered the politics of the kingdoms on the Arabian peninsula, eventually extending its rule over the region with the conquest of the Himyarite Kingdom.
In 1888, the Italian administration launched its first development projects in the new colony. The Eritrean Railway was completed to Saati in 1888, and reached Asmara in the highlands in 1911. The Asmara–Massawa Cableway was the longest line in the world during its time, but was later dismantled by the British in World War II. Besides major infrastructural projects, the colonial authorities invested significantly in the agricultural sector. It also oversaw the provision of urban amenities in Asmara and Massawa, and employed many Eritreans in public service, particularly in the police and public works departments. Thousands of Eritreans were concurrently enlisted in the army, serving during the Italo-Turkish War in Libya as well as the First and second Italo-Abyssinian Wars.
Following the adoption of UN Resolution 390A(V) in December 1950, Eritrea was federated with Ethiopia under the prompting of the United States. The resolution called for Eritrea and Ethiopia to be linked through a loose federal structure under the sovereignty of the Emperor. Eritrea was to have its own administrative and judicial structure, its own flag, and control over its domestic affairs, including police, local administration, and taxation. The federal government, which for all intents and purposes was the existing imperial government, was to control foreign affairs (including commerce), defense, finance, and transportation. The resolution ignored the wishes of Eritreans for independence, but guaranteed the population democratic rights and a measure of autonomy.
Additionally, the Italian Eritrea administration opened a number of new factories, which produced buttons, cooking oil, pasta, construction materials, packing meat, tobacco, hide and other household commodities. In 1939, there were around 2,198 factories and most of the employees were Eritrean citizens. The establishment of industries also made an increase in the number of both Italians and Eritreans residing in the cities. The number of Italians residing in the territory increased from 4,600 to 75,000 in five years; and with the involvement of Eritreans in the industries, trade and fruit plantation was expanded across the nation, while some of the plantations were owned by Eritreans.
Lions are said to inhabit the mountains of the Gash-Barka Region. There is also a small population of elephants that roam in some parts of the country. Dik-diks can also be found in many areas. The endangered African wild ass can be seen in Denakalia Region. Other local wildlife include bushbucks, duikers, greater kudus, klipspringers, African leopards, oryxs and crocodiles., The spotted hyena is widespread and fairly common. Between 1955 and 2001 there were no reported sightings of elephant herds, and they are thought to have fallen victim to the war of independence. In December 2001 a herd of about 30, including 10 juveniles, was observed in the vicinity of the Gash River. The elephants seemed to have formed a symbiotic relationship with olive baboons, with the baboons using the water holes dug by the elephants, while the elephants use the tree-top baboons as an early warning system.
Eritrea can be split into three ecoregions. To the east of the highlands are the hot, arid coastal plains stretching down to the southeast of the country. The cooler, more fertile highlands, reaching up to 3000m has a different habitat. Habitats here vary from the sub-tropical rainforest at Filfil Solomona to the precipitous cliffs and canyons of the southern highlands. The Afar Triangle or Danakil Depression of Eritrea is the probable location of a triple junction where three tectonic plates are pulling away from one another.The highest point of the country, Emba Soira, is located in the center of Eritrea, at 3,018 meters (9,902 ft) above sea level.
It is estimated that there are around 100 elephants left in Eritrea, the most northerly of East Africa's elephants. The endangered African wild dog (Lycaon pictus) was previously found in Eritrea, but is now deemed extirpated from the entire country. In Gash Barka, deadly snakes like saw-scaled viper are common. Puff adder and red spitting cobra are widespread and can be found even in the highlands.In the coastal areas marine species that are common include dolphin, dugong, whale shark, turtles, marlin/swordfish, and manta ray.
Eritrea is a one-party state in which national legislative elections have been repeatedly postponed. According to Human Rights Watch, the government's human rights record is considered among the worst in the world. Most Western countries have accused the Eritrean authorities of arbitrary arrest and detentions, and of detaining an unknown number of people without charge for their political activism. However, the Eritrean government has continually dismissed the accusations as politically motivated. In June 2015, a 500-page United Nations Human Rights Council report accused Eritrea's government of extrajudicial executions, torture, indefinitely prolonged national service and forced labour, and indicated that sexual harassment, rape and sexual servitude by state officials are also widespread.
In an attempt at reform, Eritrean government officials and NGO representatives have participated in numerous public meetings and dialogues. In these sessions they have answered questions as fundamental as, "What are human rights?", "Who determines what are human rights?", and "What should take precedence, human or communal rights?" In 2007, the Eritrean government also banned female genital mutilation. In Regional Assemblies and religious circles, Eritreans themselves speak out continuously against the use of female circumcision. They cite health concerns and individual freedom as being of primary concern when they say this. Furthermore, they implore rural peoples to cast away this ancient cultural practice. Additionally, a new movement called Citizens for Democratic Rights in Eritrea aimed at bringing about dialogue between the government and opposition was formed in early 2009. The group consists of ordinary citizens and some people close to the government.
In its 2014 Press Freedom Index, Reporters Without Borders ranked the media environment in Eritrea at the very bottom of a list of 178 countries, just below totalitarian North Korea. According to the BBC, "Eritrea is the only African country to have no privately owned news media", and Reporters Without Borders said of the public media, "[they] do nothing but relay the regime's belligerent and ultra-nationalist discourse. ... Not a single [foreign correspondent] now lives in Asmara." The state-owned news agency censors news about external events. Independent media have been banned since 2001. In 2015, The Guardian published an opinion piece claiming,
Even during the war, Eritrea developed its transportation infrastructure by asphalting new roads, improving its ports, and repairing war-damaged roads and bridges as a part of the Warsay Yika'alo Program. The most significant of these projects was the construction of a coastal highway of more than 500 km connecting Massawa with Asseb, as well as the rehabilitation of the Eritrean Railway. The rail line has been restored between the port of Massawa and the capital Asmara, although services are sporadic. Steam locomotives are sometimes used for groups of enthusiasts.
Eritrea is a multilingual country. The nation has no official language, as the Constitution establishes the "equality of all Eritrean languages". However, Tigrinya serves as the de facto language of national identity. With 2,540,000 total speakers of a population of 5,254,000 in 2006, Tigrinya is the most widely spoken language, particularly in the southern and central parts of Eritrea. Modern Standard Arabic and English serve as de facto working languages, with the latter used in university education and many technical fields. Italian, the former colonial language, is widely used in commerce and is taught as a second language in schools, with a few elderly monolinguals.
Eritrea has achieved significant improvements in health care and is one of the few countries to be on target to meet its Millennium Development Goal (MDG) targets in health, in particular child health. Life expectancy at birth has increased from 39.1 in 1960 to 59.5 years in 2008, maternal and child mortality rates have dropped dramatically and the health infrastructure has been expanded. Due to Eritrea's relative isolation, information and resources are extremely limited and according to the World Health Organisation (WHO) found in 2008 average life expectancy to be slightly less than 63 years. Immunisation and child nutrition has been tackled by working closely with schools in a multi-sectoral approach; the number of children vaccinated against measles almost doubled in seven years, from 40.7% to 78.5% and the underweight prevalence among children decreased by 12% in 1995–2002 (severe underweight prevalence by 28%). The National Malaria Protection Unit of the Ministry of Health has registered tremendous improvements in reducing malarial mortality by as much as 85% and the number of cases by 92% between 1998 and 2006. The Eritrean government has banned female genital mutilation (FGM), saying the practice was painful and put women at risk of life-threatening health problems.
Additionally, owing to its colonial history, cuisine in Eritrea features more Italian influences than are present in Ethiopian cooking, including more pasta and greater use of curry powders and cumin.The Italian Eritrean cuisine started to be practiced during the colonial times of the Kingdom of Italy, when a large number of Italians moved to Eritrea. They brought the use of "pasta" to Italian Eritrea, and it is one of the main food eaten in present-day Asmara. An Italian Eritrean cuisine emerged, and dishes common dishes are 'Pasta al Sugo e Berbere', which means "Pasta with tomato sauce and berbere" (spice), but there are many more like "lasagna" and "cotoletta alla milanese" (milano cutlet). Alongside sowa, people in Eritrea also tend to drink coffee. Mies is another popular local alcoholic beverage, made out of honey.
The culture of Eritrea has been largely shaped by the country's location on the Red Sea coast. One of the most recognizable parts of Eritrean culture is the coffee ceremony. Coffee (Ge'ez ቡን būn) is offered when visiting friends, during festivities, or as a daily staple of life. During the coffee ceremony, there are traditions that are upheld. The coffee is served in three rounds: the first brew or round is called awel in Tigrinya meaning first, the second round is called kalaay meaning second, and the third round is called bereka meaning "to be blessed". If coffee is politely declined, then most likely tea ("shai" ሻሂ shahee) will instead be served.
Eritrea (/ˌɛrᵻˈtreɪ.ə/ or /ˌɛrᵻˈtriːə/;, officially the State of Eritrea, is a country in East Africa. With its capital at Asmara, it is bordered by Sudan in the west, Ethiopia in the south, and Djibouti in the southeast. The northeastern and eastern parts of Eritrea have an extensive coastline along the Red Sea. The nation has a total area of approximately 117,600 km2 (45,406 sq mi), and includes the Dahlak Archipelago and several of the Hanish Islands. Its name Eritrea is based on the Greek name for the Red Sea (Ἐρυθρὰ Θάλασσα Erythra Thalassa), which was first adopted for Italian Eritrea in 1890.
Eritrea's ethnic groups each have their own styles of music and accompanying dances. Amongst the Tigrinya, the best known traditional musical genre is the guaila. Traditional instruments of Eritrean folk music include the stringed krar, kebero, begena, masenqo and the wata (a distant/rudimentary cousin of the violin). The most popular Eritrean artist is the Tigrinya singer Helen Meles, who is noted for her powerful voice and wide singing range. Other prominent local musicians include the Kunama singer Dehab Faytinga, Ruth Abraha, Bereket Mengisteab, Yemane Baria, and the late Abraham Afewerki.
During the Middle Ages, the Eritrea region was known as Medri Bahri ("sea-land"). The name Eritrea is derived from the ancient Greek name for Red Sea (Ἐρυθρὰ Θάλασσα Erythra Thalassa, based on the adjective ἐρυθρός erythros "red"). It was first formally adopted in 1890, with the formation of Italian Eritrea (Colonia Eritrea). The territory became the Eritrea Governorate within Italian East Africa in 1936. Eritrea was annexed by Ethiopia in 1953 (nominally within a federation until 1962) and an Eritrean Liberation Front formed in 1960. Eritrea gained independence following the 1993 referendum, and the name of the new state was defined as State of Eritrea in the 1997 constitution.[citation needed]
In 2010, a genetic study was conducted on the mummified remains of baboons that were brought back as gifts from Punt by the ancient Egyptians. Led by a research team from the Egyptian Museum and the University of California, the scientists used oxygen isotope analysis to examine hairs from two baboon mummies that had been preserved in the British Museum. One of the baboons had distorted isotopic data, so the other's oxygen isotope values were compared to those of present-day baboon specimens from regions of interest. The researchers found that the mummies most closely matched modern baboon specimens in Eritrea and Ethiopia, which they suggested implied that Punt was likely a narrow region that included eastern Ethiopia and all of Eritrea.
After the decline of Aksum, the Eritrean highlands were under the domain of Bahr Negash ruled by the Bahr Negus. The area was then known as Ma'ikele Bahr ("between the seas/rivers," i.e. the land between the Red Sea and the Mereb river). It was later renamed under Emperor Zara Yaqob as the domain of the Bahr Negash, the Medri Bahri ("Sea land" in Tingrinya, although it included some areas like Shire on the other side of the Mereb, today in Ethiopia). With its capital at Debarwa, the state's main provinces were Hamasien, Serae and Akele Guzai.
In 1922, Benito Mussolini's rise to power in Italy brought profound changes to the colonial government in Italian Eritrea. After il Duce declared the birth of the Italian Empire in May 1936, Italian Eritrea (enlarged with northern Ethiopia's regions) and Italian Somaliland were merged with the just conquered Ethiopia in the new Italian East Africa (Africa Orientale Italiana) administrative territory. This Fascist period was characterized by imperial expansion in the name of a "new Roman Empire". Eritrea was chosen by the Italian government to be the industrial center of Italian East Africa.
When Emperor Haile Selassie unilaterally dissolved the Eritrean parliament and annexed the country in 1962, the Eritrean Liberation Front (ELF) waged an armed struggle for independence. The ensuing Eritrean War for Independence went on for 30 years against successive Ethiopian governments until 1991, when the Eritrean People's Liberation Front (EPLF), a successor of the ELF, defeated the Ethiopian forces in Eritrea and helped a coalition of Ethiopian rebel forces take control of the Ethiopian Capital Addis Ababa.
Disagreements following the war have resulted in stalemate punctuated by periods of elevated tension and renewed threats of war. The stalemate led the President of Eritrea to urge the UN to take action on Ethiopia with the Eleven Letters penned by the President to the United Nations Security Council. The situation has been further escalated by the continued efforts of the Eritrean and Ethiopian leaders in supporting opposition in one another's countries.[citation needed] In 2011, Ethiopia accused Eritrea of planting bombs at an African Union summit in Addis Ababa, which was later supported by a UN report. Eritrea denied the claims.
However, Eritrea still faces many challenges. Despite number of physicians increasing from only 0.2 in 1993 to 0.5 in 2004 per 1000 population, this is still very low. Malaria and tuberculosis are common in Eritrea. HIV prevalence among the 15–49 group exceeds 2%. The fertility rate is at about 5 births per woman. Maternal mortality dropped by more than half from 1995 to 2002, although the figure is still high. Similarly, between 1995 and 2002, the number of births attended by skilled health personnel has doubled but still is only 28.3%. A major cause of death in neonates is by severe infection. Per capita expenditure on health is low in Eritrea.
Traditional Eritrean attire is quite varied among the ethnic groups of Eritrea. In the larger cities, most people dress in Western casual dress such as jeans and shirts. In offices, both men and women often dress in suits. Traditional clothing for Christian Tigrinya-speaking highlanders consists of bright white gowns called zurias for the women, and long white shirts accompanied by white pants for the men. In Muslim communities in the Eritrean lowland, the women traditionally dress in brightly colored clothes. Only Rashaida women maintain a tradition of covering half of their faces, though they do not cover their hair.
Football and cycling are the most popular sports in Eritrea. In recent years, Eritrean athletes have also seen increasing success in the international arena. Zersenay Tadese, an Eritrean athlete, currently holds the world record in half marathon distance running. The Tour of Eritrea, a multi-stage international cycling event, is held annually throughout the country. The Eritrea national cycling team has experienced a lot of success, winning the continental cycling championship several years in a row. Six Eritrean riders have been signed to international cycling teams, including Natnael Berhane and Daniel Teklehaimanot. Berhane was named African Sportsman of the Year in 2013, ahead of footballers Yaya Touré and Didier Drogba, while Teklehaimanot became the first Eritrean to ride the Vuelta a España in 2012. In 2015 Teklehaimanot won the King of the Mountains classification in the Critérium du Dauphine. Teklehaimanot and fellow Eritrean Merhawi Kudus became the first black African riders to compete in the Tour de France when they were selected by the MTN–Qhubeka team for the 2015 edition of the race, where, on 9 July, Teklehaimanot became the first African rider to wear the polkadot jersey.
During the last interglacial period, the Red Sea coast of Eritrea was occupied by early anatomically modern humans. It is believed that the area was on the route out of Africa that some scholars suggest was used by early humans to colonize the rest of the Old World. In 1999, the Eritrean Research Project Team composed of Eritrean, Canadian, American, Dutch and French scientists discovered a Paleolithic site with stone and obsidian tools dated to over 125,000 years old near the Bay of Zula south of Massawa, along the Red Sea littoral. The tools are believed to have been used by early humans to harvest marine resources like clams and oysters.
At the end of the 16th century, the Aussa Sultanate was established in the Denkel lowlands of Eritrea. The polity had come into existence in 1577, when Muhammed Jasa moved his capital from Harar to Aussa (Asaita) with the split of the Adal Sultanate into Aussa and the Sultanate of Harar. At some point after 1672, Aussa declined in conjunction with Imam Umar Din bin Adam's recorded ascension to the throne. In 1734, the Afar leader Kedafu, head of the Mudaito clan, seized power and established the Mudaito Dynasty. This marked the start of a new and more sophisticated polity that would last into the colonial period.
In the vacuum that followed the 1889 death of Emperor Yohannes II, Gen. Oreste Baratieri occupied the highlands along the Eritrean coast and Italy proclaimed the establishment of the new colony of Italian Eritrea, a colony of the Kingdom of Italy. In the Treaty of Wuchale (It. Uccialli) signed the same year, King Menelik of Shewa, a southern Ethiopian kingdom, recognized the Italian occupation of his rivals' lands of Bogos, Hamasien, Akkele Guzay, and Serae in exchange for guarantees of financial assistance and continuing access to European arms and ammunition. His subsequent victory over his rival kings and enthronement as Emperor Menelek II (r. 1889–1913) made the treaty formally binding upon the entire territory.
In the 1950s, the Ethiopian feudal administration under Emperor Haile Selassie sought to annex Eritrea and Italian Somaliland. He laid claim to both territories in a letter to Franklin D. Roosevelt at the Paris Peace Conference and at the First Session of the United Nations. In the United Nations, the debate over the fate of the former Italian colonies continued. The British and Americans preferred to cede all of Eritrea except the Western province to the Ethiopians as a reward for their support during World War II. The Independence Bloc of Eritrean parties consistently requested from the UN General Assembly that a referendum be held immediately to settle the Eritrean question of sovereignty.
The Eritrean highway system is named according to the road classification. The three levels of classification are: primary (P), secondary (S), and tertiary (T). The lowest level road is tertiary and serves local interests. Typically they are improved earth roads which are occasionally paved. During the wet seasons these roads typically become impassable. The next higher level road is a secondary road and typically is a single-layered asphalt road that connects district capitals together and those to the regional capitals. Roads that are considered primary roads are those that are fully asphalted (throughout their entire length) and in general they carry traffic between all the major towns in Eritrea.
According to recent estimates, 50% of the population adheres to Christianity, Islam 48%, while 2% of the population follows other religions including traditional African religion and animism. According to a study made by Pew Research Center, 63% adheres to Christianity and 36% adheres to Islam. Since May 2002, the government of Eritrea has officially recognized the Eritrean Orthodox Tewahedo Church (Oriental Orthodox), Sunni Islam, the Eritrean Catholic Church (a Metropolitanate sui juris) and the Evangelical Lutheran church. All other faiths and denominations are required to undergo a registration process. Among other things, the government's registration system requires religious groups to submit personal information on their membership to be allowed to worship.
Education in Eritrea is officially compulsory between seven and 13 years of age. However, the education infrastructure is inadequate to meet current needs. Statistics vary at the elementary level, suggesting that between 65 and 70% of school-aged children attend primary school; Approximately 61% attend secondary school. Student-teacher ratios are high: 45 to 1 at the elementary level and 54 to 1 at the secondary level. There are an average 63 students per classroom at the elementary level and 97 per classroom at the secondary level. Learning hours at school are often less than six hours per day. Skill shortages are present at all levels of the education system, and funding for and access to education vary significantly by gender and location. Illiteracy estimates for Eritrea range from around 40% to as high as 70%.
A typical traditional Eritrean dish consists of injera accompanied by a spicy stew, which frequently includes beef, kid, lamb or fish. Overall, Eritrean cuisine strongly resembles those of neighboring Ethiopia, Eritrean cooking tend to feature more seafood than Ethiopian cuisine on account of their coastal location. Eritrean dishes are also frequently "lighter" in texture than Ethiopian meals. They likewise tend to employ less seasoned butter and spices and more tomatoes, as in the tsebhi dorho delicacy.
Depleted uranium is also used as a shielding material in some containers used to store and transport radioactive materials. While the metal itself is radioactive, its high density makes it more effective than lead in halting radiation from strong sources such as radium. Other uses of depleted uranium include counterweights for aircraft control surfaces, as ballast for missile re-entry vehicles and as a shielding material. Due to its high density, this material is found in inertial guidance systems and in gyroscopic compasses. Depleted uranium is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost. The main risk of exposure to depleted uranium is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak alpha emitter).
The discovery and isolation of radium in uranium ore (pitchblende) by Marie Curie sparked the development of uranium mining to extract the radium, which was used to make glow-in-the-dark paints for clock and aircraft dials. This left a prodigious quantity of uranium as a waste product, since it takes three tonnes of uranium to extract one gram of radium. This waste product was diverted to the glazing industry, making uranium glazes very inexpensive and abundant. Besides the pottery glazes, uranium tile glazes accounted for the bulk of the use, including common bathroom and kitchen tiles which can be produced in green, yellow, mauve, black, blue, red and other colors.
The X-10 Graphite Reactor at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor (after Enrico Fermi's Chicago Pile) and was the first reactor designed and built for continuous operation. Argonne National Laboratory's Experimental Breeder Reactor I, located at the Atomic Energy Commission's National Reactor Testing Station near Arco, Idaho, became the first nuclear reactor to create electricity on 20 December 1951. Initially, four 150-watt light bulbs were lit by the reactor, but improvements eventually enabled it to power the whole facility (later, the town of Arco became the first in the world to have all its electricity come from nuclear power generated by BORAX-III, another reactor designed and operated by Argonne National Laboratory). The world's first commercial scale nuclear power station, Obninsk in the Soviet Union, began generation with its reactor AM-1 on 27 June 1954. Other early nuclear power plants were Calder Hall in England, which began generation on 17 October 1956, and the Shippingport Atomic Power Station in Pennsylvania, which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a submarine, the USS Nautilus, in 1954.
Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. Uranium is the 51st element in order of abundance in the Earth's crust. Uranium is also the highest-numbered element to be found naturally in significant quantities on Earth and is almost always found combined with other elements. Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernovae. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics.
Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor control rods (see nuclear reactor physics for a description of this process of reactor control).
In nature, uranium(VI) forms highly soluble carbonate complexes at alkaline pH. This leads to an increase in mobility and availability of uranium to groundwater and soil from nuclear wastes which leads to health hazards. However, it is difficult to precipitate uranium as phosphate in the presence of excess carbonate at alkaline pH. A Sphingomonas sp. strain BSAR-1 has been found to express a high activity alkaline phosphatase (PhoK) that has been applied for bioprecipitation of uranium as uranyl phosphate species from alkaline solutions. The precipitation ability was enhanced by overexpressing PhoK protein in E. coli.
It is estimated that 5.5 million tonnes of uranium exists in ore reserves that are economically viable at US$59 per lb of uranium, while 35 million tonnes are classed as mineral resources (reasonable prospects for eventual economic extraction). Prices went from about $10/lb in May 2003 to $138/lb in July 2007. This has caused a big increase in spending on exploration, with US$200 million being spent worldwide in 2005, a 54% increase on the previous year. This trend continued through 2006, when expenditure on exploration rocketed to over $774 million, an increase of over 250% compared to 2004. The OECD Nuclear Energy Agency said exploration figures for 2007 would likely match those for 2006.
A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays (electrons or positrons from the elements produced; see beta particle). The fission products were at first mistaken for new elements of atomic numbers 93 and 94, which the Dean of the Faculty of Rome, Orso Mario Corbino, christened ausonium and hesperium, respectively. The experiments leading to the discovery of uranium's ability to fission (break apart) into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann in Hahn's laboratory in Berlin. Lise Meitner and her nephew, the physicist Otto Robert Frisch, published the physical explanation in February 1939 and named the process "nuclear fission". Soon after, Fermi hypothesized that the fission of uranium might release enough neutrons to sustain a fission reaction. Confirmation of this hypothesis came in 1939, and later work found that on average about 2.5 neutrons are released by each fission of the rare uranium isotope uranium-235. Further work found that the far more common uranium-238 isotope can be transmuted into plutonium, which, like uranium-235, is also fissile by thermal neutrons. These discoveries led numerous countries to begin working on the development of nuclear weapons and nuclear power.
The interactions of carbonate anions with uranium(VI) cause the Pourbaix diagram to change greatly when the medium is changed from water to a carbonate containing solution. While the vast majority of carbonates are insoluble in water (students are often taught that all carbonates other than those of alkali metals are insoluble in water), uranium carbonates are often soluble in water. This is because a U(VI) cation is able to bind two terminal oxides and three or more carbonates to form anionic complexes.
Uranium is more plentiful than antimony, tin, cadmium, mercury, or silver, and it is about as abundant as arsenic or molybdenum. Uranium is found in hundreds of minerals, including uraninite (the most common uranium ore), carnotite, autunite, uranophane, torbernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from sources with as little as 0.1% uranium).
Natural uranium consists of three major isotopes: uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three are radioactive, emitting alpha particles, with the exception that all three of these isotopes have small probabilities of undergoing spontaneous fission, rather than alpha emission. There are also five other trace isotopes: uranium-239, which is formed when 238U undergoes spontaneous fission, releasing neutrons that are captured by another 238U atom; uranium-237, which is formed when 238U captures a neutron but emits two more, which then decays to neptunium-237; uranium-233, which is formed in the decay chain of that neptunium-237; and finally, uranium-236 and -240, which appear in the decay chain of primordial plutonium-244. It is also expected that thorium-232 should be able to undergo double beta decay, which would produce uranium-232, but this has not yet been observed experimentally.
An additional 4.6 billion tonnes of uranium are estimated to be in sea water (Japanese scientists in the 1980s showed that extraction of uranium from sea water using ion exchangers was technically feasible). There have been experiments to extract uranium from sea water, but the yield has been low due to the carbonate present in the water. In 2012, ORNL researchers announced the successful development of a new absorbent material dubbed HiCap which performs surface retention of solid or gas molecules, atoms or ions and also effectively removes toxic metals from water, according to results verified by researchers at Pacific Northwest National Laboratory.
Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 has the distinction of being the only naturally occurring fissile isotope. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. While uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons, uranium-235 and to a lesser degree uranium-233 have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons. Depleted uranium (238U) is used in kinetic energy penetrators and armor plating.
A person can be exposed to uranium (or its radioactive daughters, such as radon) by inhaling dust in air or by ingesting contaminated water and food. The amount of uranium in air is usually very small; however, people who work in factories that process phosphate fertilizers, live near government facilities that made or tested nuclear weapons, live or work near a modern battlefield where depleted uranium weapons have been used, or live or work near a coal-fired power plant, facilities that mine or process uranium ore, or enrich uranium for reactor fuel, may have increased exposure to uranium. Houses or structures that are over uranium deposits (either natural or man-made slag deposits) may have an increased incidence of exposure to radon gas. The Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit for uranium exposure in the workplace as 0.25 mg/m3 over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.2 mg/m3 over an 8-hour workday and a short-term limit of 0.6 mg/m3. At levels of 10 mg/m3, uranium is immediately dangerous to life and health.
The most common forms of uranium oxide are triuranium octoxide (U 3O 8) and UO 2. Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel. At ambient temperatures, UO 2 will gradually convert to U 3O 8. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.
The use of uranium in its natural oxide form dates back to at least the year 79 CE, when it was used to add a yellow color to ceramic glazes. Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy, by R. T. Gunther of the University of Oxford in 1912. Starting in the late Middle Ages, pitchblende was extracted from the Habsburg silver mines in Joachimsthal, Bohemia (now Jáchymov in the Czech Republic), and was used as a coloring agent in the local glassmaking industry. In the early 19th century, the world's only known sources of uranium ore were these mines.
On 2 December 1942, as part of the Manhattan Project, another team led by Enrico Fermi was able to initiate the first artificial self-sustained nuclear chain reaction, Chicago Pile-1. Working in a lab below the stands of Stagg Field at the University of Chicago, the team created the conditions needed for such a reaction by piling together 400 short tons (360 metric tons) of graphite, 58 short tons (53 metric tons) of uranium oxide, and six short tons (5.5 metric tons) of uranium metal, a majority of which was supplied by Westinghouse Lamp Plant in a makeshift production process.
Uranium is used as a colorant in uranium glass producing orange-red to lemon yellow hues. It was also used for tinting and shading in early photography. The 1789 discovery of uranium in the mineral pitchblende is credited to Martin Heinrich Klaproth, who named the new element after the planet Uranus. Eugène-Melchior Péligot was the first person to isolate the metal and its radioactive properties were discovered in 1896 by Henri Becquerel. Research by Otto Hahn, Lise Meitner, Enrico Fermi and others, such as J. Robert Oppenheimer starting in 1934 led to its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for public health and safety. See Nuclear proliferation.
In nature, uranium is found as uranium-238 (99.2742%) and uranium-235 (0.7204%). Isotope separation concentrates (enriches) the fissionable uranium-235 for nuclear weapons and most nuclear power plants, except for gas cooled reactors and pressurised heavy water reactors. Most neutrons released by a fissioning atom of uranium-235 must impact other uranium-235 atoms to sustain the nuclear chain reaction. The concentration and amount of uranium-235 needed to achieve this is called a 'critical mass'.
The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of depleted uranium (DU) alloyed with 1–2% other elements, such as titanium or molybdenum. At high impact speed, the density, hardness, and pyrophoricity of the projectile enable the destruction of heavily armored targets. Tank armor and other removable vehicle armor can also be hardened with depleted uranium plates. The use of depleted uranium became politically and environmentally contentious after the use of such munitions by the US, UK and other countries during wars in the Persian Gulf and the Balkans raised questions concerning uranium compounds left in the soil (see Gulf War Syndrome).
The discovery of the element is credited to the German chemist Martin Heinrich Klaproth. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide. Klaproth assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder, which he thought was the newly discovered metal itself (in fact, that powder was an oxide of uranium). He named the newly discovered element after the planet Uranus, (named after the primordial Greek god of the sky), which had been discovered eight years earlier by William Herschel.
Uranium ore is mined in several ways: by open pit, underground, in-situ leaching, and borehole mining (see uranium mining). Low-grade uranium ore mined typically contains 0.01 to 0.25% uranium oxides. Extensive measures must be employed to extract the metal from its ore. High-grade ores found in Athabasca Basin deposits in Saskatchewan, Canada can contain up to 23% uranium oxides on average. Uranium ore is crushed and rendered into a fine powder and then leached with either an acid or alkali. The leachate is subjected to one of several sequences of precipitation, solvent extraction, and ion exchange. The resulting mixture, called yellowcake, contains at least 75% uranium oxides U3O8. Yellowcake is then calcined to remove impurities from the milling process before refining and conversion.
Two major types of atomic bombs were developed by the United States during World War II: a uranium-based device (codenamed "Little Boy") whose fissile material was highly enriched uranium, and a plutonium-based device (see Trinity test and "Fat Man") whose plutonium was derived from uranium-238. The uranium-based Little Boy device became the first nuclear weapon used in war when it was detonated over the Japanese city of Hiroshima on 6 August 1945. Exploding with a yield equivalent to 12,500 tonnes of TNT, the blast and thermal wave of the bomb destroyed nearly 50,000 buildings and killed approximately 75,000 people (see Atomic bombings of Hiroshima and Nagasaki). Initially it was believed that uranium was relatively rare, and that nuclear proliferation could be avoided by simply buying up all known uranium stocks, but within a decade large deposits of it were discovered in many places around the world.
In 2005, seventeen countries produced concentrated uranium oxides, with Canada (27.9% of world production) and Australia (22.8%) being the largest producers and Kazakhstan (10.5%), Russia (8.0%), Namibia (7.5%), Niger (7.4%), Uzbekistan (5.5%), the United States (2.5%), Argentina (2.1%), Ukraine (1.9%) and China (1.7%) also producing significant amounts. Kazakhstan continues to increase production and may have become the world's largest producer of uranium by 2009 with an expected production of 12,826 tonnes, compared to Canada with 11,100 t and Australia with 9,430 t. In the late 1960s, UN geologists also discovered major uranium deposits and other rare mineral reserves in Somalia. The find was the largest of its kind, with industry experts estimating the deposits at over 25% of the world's then known uranium reserves of 800,000 tons.
During the Cold War between the Soviet Union and the United States, huge stockpiles of uranium were amassed and tens of thousands of nuclear weapons were created using enriched uranium and plutonium made from uranium. Since the break-up of the Soviet Union in 1991, an estimated 600 short tons (540 metric tons) of highly enriched weapons grade uranium (enough to make 40,000 nuclear warheads) have been stored in often inadequately guarded facilities in the Russian Federation and several other former Soviet states. Police in Asia, Europe, and South America on at least 16 occasions from 1993 to 2005 have intercepted shipments of smuggled bomb-grade uranium or plutonium, most of which was from ex-Soviet sources. From 1993 to 2005 the Material Protection, Control, and Accounting Program, operated by the federal government of the United States, spent approximately US $550 million to help safeguard uranium and plutonium stockpiles in Russia. This money was used for improvements and security enhancements at research and storage facilities. Scientific American reported in February 2006 that in some of the facilities security consisted of chain link fences which were in severe states of disrepair. According to an interview from the article, one facility had been storing samples of enriched (weapons grade) uranium in a broom closet before the improvement project; another had been keeping track of its stock of nuclear warheads using index cards kept in a shoe box.
Salts of many oxidation states of uranium are water-soluble and may be studied in aqueous solutions. The most common ionic forms are U3+ (brown-red), U4+ (green), UO+ 2 (unstable), and UO2+ 2 (yellow), for U(III), U(IV), U(V), and U(VI), respectively. A few solid and semi-metallic compounds such as UO and US exist for the formal oxidation state uranium(II), but no simple ions are known to exist in solution for that state. Ions of U3+ liberate hydrogen from water and are therefore considered to be highly unstable. The UO2+ 2 ion represents the uranium(VI) state and is known to form compounds such as uranyl carbonate, uranyl chloride and uranyl sulfate. UO2+ 2 also forms complexes with various organic chelating agents, the most commonly encountered of which is uranyl acetate.
Some organisms, such as the lichen Trapelia involuta or microorganisms such as the bacterium Citrobacter, can absorb concentrations of uranium that are up to 300 times the level of their environment. Citrobacter species absorb uranyl ions when given glycerol phosphate (or other similar organic phosphates). After one day, one gram of bacteria can encrust themselves with nine grams of uranyl phosphate crystals; this creates the possibility that these organisms could be used in bioremediation to decontaminate uranium-polluted water. The proteobacterium Geobacter has also been shown to bioremediate uranium in ground water. The mycorrhizal fungus Glomus intraradices increases uranium content in the roots of its symbiotic plant.
Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds. Two crystal modifications of uranium hydride exist: an α form that is obtained at low temperatures and a β form that is created when the formation temperature is above 250 °C.
Uranium carbides and uranium nitrides are both relatively inert semimetallic compounds that are minimally soluble in acids, react with water, and can ignite in air to form U 3O 8. Carbides of uranium include uranium monocarbide (UC), uranium dicarbide (UC 2), and diuranium tricarbide (U 2C 3). Both UC and UC 2 are formed by adding carbon to molten uranium or by exposing the metal to carbon monoxide at high temperatures. Stable below 1800 °C, U 2C 3 is prepared by subjecting a heated mixture of UC and UC 2 to mechanical stress. Uranium nitrides obtained by direct exposure of the metal to nitrogen include uranium mononitride (UN), uranium dinitride (UN 2), and diuranium trinitride (U 2N 3).
To be considered 'enriched', the uranium-235 fraction should be between 3% and 5%. This process produces huge quantities of uranium that is depleted of uranium-235 and with a correspondingly increased fraction of uranium-238, called depleted uranium or 'DU'. To be considered 'depleted', the uranium-235 isotope concentration should be no more than 0.3%. The price of uranium has risen since 2001, so enrichment tailings containing more than 0.35% uranium-235 are being considered for re-enrichment, driving the price of depleted uranium hexafluoride above $130 per kilogram in July 2007 from $5 in 2001.
Normal functioning of the kidney, brain, liver, heart, and other systems can be affected by uranium exposure, because, besides being weakly radioactive, uranium is a toxic metal. Uranium is also a reproductive toxicant. Radiological effects are generally local because alpha radiation, the primary form of 238U decay, has a very short range, and will not penetrate skin. Uranyl (UO2+ 2) ions, such as from uranium trioxide or uranyl nitrate and other hexavalent uranium compounds, have been shown to cause birth defects and immune system damage in laboratory animals. While the CDC has published one study that no human cancer has been seen as a result of exposure to natural or depleted uranium, exposure to uranium and its decay products, especially radon, are widely known and significant health threats. Exposure to strontium-90, iodine-131, and other fission products is unrelated to uranium exposure, but may result from medical procedures or exposure to spent reactor fuel or fallout from nuclear weapons. Although accidental inhalation exposure to a high concentration of uranium hexafluoride has resulted in human fatalities, those deaths were associated with the generation of highly toxic hydrofluoric acid and uranyl fluoride rather than with uranium itself. Finely divided uranium metal presents a fire hazard because uranium is pyrophoric; small grains will ignite spontaneously in air at room temperature.
The gas centrifuge process, where gaseous uranium hexafluoride (UF 6) is separated by the difference in molecular weight between 235UF6 and 238UF6 using high-speed centrifuges, is the cheapest and leading enrichment process. The gaseous diffusion process had been the leading method for enrichment and was used in the Manhattan Project. In this process, uranium hexafluoride is repeatedly diffused through a silver-zinc membrane, and the different isotopes of uranium are separated by diffusion rate (since uranium 238 is heavier it diffuses slightly slower than uranium-235). The molecular laser isotope separation method employs a laser beam of precise energy to sever the bond between uranium-235 and fluorine. This leaves uranium-238 bonded to fluorine and allows uranium-235 metal to precipitate from the solution. An alternative laser method of enrichment is known as atomic vapor laser isotope separation (AVLIS) and employs visible tunable lasers such as dye lasers. Another method used is liquid thermal diffusion.
Uranium is a chemical element with symbol U and atomic number 92. It is a silvery-white metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly radioactive because all its isotopes are unstable (with half-lives of the six naturally known isotopes, uranium-233 to uranium-238, varying between 69 years and 4.5 billion years). The most common isotopes of uranium are uranium-238 (which has 146 neutrons and accounts for almost 99.3% of the uranium found in nature) and uranium-235 (which has 143 neutrons, accounting for 0.7% of the element found naturally). Uranium has the second highest atomic weight of the primordially occurring elements, lighter only than plutonium. Its density is about 70% higher than that of lead, but slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.
Uranium metal reacts with almost all non-metal elements (with an exception of the noble gases) and their compounds, with reactivity increasing with temperature. Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly. When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide. Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry.
During the later stages of World War II, the entire Cold War, and to a lesser extent afterwards, uranium-235 has been used as the fissile explosive material to produce nuclear weapons. Initially, two major types of fission bombs were built: a relatively simple device that uses uranium-235 and a more complicated mechanism that uses plutonium-239 derived from uranium-238. Later, a much more complicated and far more powerful type of fission/fusion bomb (thermonuclear weapon) was built, that uses a plutonium-based device to cause a mixture of tritium and deuterium to undergo nuclear fusion. Such bombs are jacketed in a non-fissile (unenriched) uranium case, and they derive more than half their power from the fission of this material by fast neutrons from the nuclear fusion process.
Uranium was also used in photographic chemicals (especially uranium nitrate as a toner), in lamp filaments for stage lighting bulbs, to improve the appearance of dentures, and in the leather and wood industries for stains and dyes. Uranium salts are mordants of silk or wool. Uranyl acetate and uranyl formate are used as electron-dense "stains" in transmission electron microscopy, to increase the contrast of biological specimens in ultrathin sections and in negative staining of viruses, isolated cell organelles and macromolecules.
In 1972, the French physicist Francis Perrin discovered fifteen ancient and no longer active natural nuclear fission reactors in three separate ore deposits at the Oklo mine in Gabon, West Africa, collectively known as the Oklo Fossil Reactors. The ore deposit is 1.7 billion years old; then, uranium-235 constituted about 3% of the total uranium on Earth. This is high enough to permit a sustained nuclear fission chain reaction to occur, provided other supporting conditions exist. The capacity of the surrounding sediment to contain the nuclear waste products has been cited by the U.S. federal government as supporting evidence for the feasibility to store spent nuclear fuel at the Yucca Mountain nuclear waste repository.
Uranium's average concentration in the Earth's crust is (depending on the reference) 2 to 4 parts per million, or about 40 times as abundant as silver. The Earth's crust from the surface to 25 km (15 mi) down is calculated to contain 1017 kg (2×1017 lb) of uranium while the oceans may contain 1013 kg (2×1013 lb). The concentration of uranium in soil ranges from 0.7 to 11 parts per million (up to 15 parts per million in farmland soil due to use of phosphate fertilizers), and its concentration in sea water is 3 parts per billion.
Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468×109 years, roughly the age of the Earth. Uranium-235 has a half-life of about 7.13×108 years, and uranium-234 has a half-life of about 2.48×105 years. For natural uranium, about 49% of its alpha rays are emitted by each of 238U atom, and also 49% by 234U (since the latter is formed from the former) and about 2.0% of them by the 235U. When the Earth was young, probably about one-fifth of its uranium was uranium-235, but the percentage of 234U was probably much lower than this.
Most ingested uranium is excreted during digestion. Only 0.5% is absorbed when insoluble forms of uranium, such as its oxide, are ingested, whereas absorption of the more soluble uranyl ion can be up to 5%. However, soluble uranium compounds tend to quickly pass through the body, whereas insoluble uranium compounds, especially when inhaled by way of dust into the lungs, pose a more serious exposure hazard. After entering the bloodstream, the absorbed uranium tends to bioaccumulate and stay for many years in bone tissue because of uranium's affinity for phosphates. Uranium is not absorbed through the skin, and alpha particles released by uranium cannot penetrate the skin.
Calcined uranium yellowcake, as produced in many large mills, contains a distribution of uranium oxidation species in various forms ranging from most oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than those with long retention times or particles recovered in the stack scrubber. Uranium content is usually referenced to U 3O 8, which dates to the days of the Manhattan project when U 3O 8 was used as an analytical chemistry reporting standard.
Appointments to the Order of the British Empire were at first made on the nomination of the self-governing Dominions of the Empire, the Viceroy of India, and the colonial governors, as well as on nominations from within the United Kingdom. As the Empire evolved into the Commonwealth, nominations continued to come from the Commonwealth realms, in which the monarch remained head of state. These overseas nominations have been discontinued in realms that have established their own Orders—such as the Order of Australia, the Order of Canada, and the New Zealand Order of Merit—but members of the Order are still appointed in the British Overseas Territories.
Any individual made a member of the Order for gallantry could wear an emblem of two crossed silver oak leaves on the same riband, ribbon or bow as the badge. It could not be awarded posthumously and was effectively replaced in 1974 with the Queen's Gallantry Medal. If recipients of the Order of the British Empire for Gallantry received promotion within the Order, whether for gallantry or otherwise, they continued to wear also the insignia of the lower grade with the oak leaves. However, they only used the post-nominal letters of the higher grade.
Honorary knighthoods are appointed to citizens of nations where Queen Elizabeth II is not Head of State, and may permit use of post-nominal letters but not the title of Sir or Dame. Occasionally honorary appointees are, incorrectly, referred to as Sir or Dame - Bill Gates or Bob Geldof, for example. Honorary appointees who later become a citizen of a Commonwealth realm can convert their appointment from honorary to substantive, then enjoy all privileges of membership of the order including use of the title of Sir and Dame for the senior two ranks of the Order. An example is Irish broadcaster Terry Wogan, who was appointed an honorary Knight Commander of the Order in 2005 and on successful application for dual British and Irish citizenship was made a substantive member and subsequently styled as "Sir Terry Wogan KBE".
The Order has six officials: the Prelate; the Dean; the Secretary; the Registrar; the King of Arms; and the Usher. The Bishop of London, a senior bishop in the Church of England, serves as the Order's Prelate. The Dean of St Paul's is ex officio the Dean of the Order. The Order's King of Arms is not a member of the College of Arms, as are many other heraldic officers. The Usher of the Order is known as the Gentleman Usher of the Purple Rod; he does not – unlike his Order of the Garter equivalent, the Gentleman Usher of the Black Rod – perform any duties related to the House of Lords.
Appointments to the Order of the British Empire were discontinued in those Commonwealth realms that established a national system of honours and awards such as the Order of Australia, the Order of Canada, and the New Zealand Order of Merit. In many of these systems, the different levels of award and honour reflect the Imperial system they replaced. Canada, Australia, and New Zealand all have (in increasing level of precedence) Members of, Officers of, and Companions to (rather than Commanders of) their respective orders, with both Australia and New Zealand having Knights and Dames as their highest classes.
The members of The Beatles were made MBEs in 1965. John Lennon justified the comparative merits of his investiture by comparing military membership in the Order: "Lots of people who complained about us receiving the MBE [status] received theirs for heroism in the war – for killing people… We received ours for entertaining other people. I'd say we deserve ours more." Lennon later returned his MBE insignia on 25 November 1969 as part of his ongoing peace protests. Other criticism centres on the claim that many recipients of the Order are being rewarded with honours for simply doing their jobs; critics claim that the civil service and judiciary receive far more orders and honours than leaders of other professions.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.