document_title: Sahara

question_text: the southern border of the sahara desert is known as the

question_tokens: the southern border of the sahara desert is known as the

text: Sahara

text: Geography

text: The Sahara covers large parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, Western Sahara, Sudan and Tunisia. It covers 9 million square kilometres (3,500,000 sq mi), amounting to 31% of Africa. If all areas with a mean annual precipitation of less than 250 mm were included, the Sahara would be 11 million square kilometres (4,200,000 sq mi). It is one of three distinct physiographic provinces of the African massive physiographic division.

text: The Sahara is mainly rocky hamada (stone plateaus), Ergs (sand seas - large areas covered with sand dunes) form only a minor part, but many of the sand dunes are over 180 metres (590 ft) high.[7] Wind or rare rainfall shape the desert features: sand dunes, dune fields, sand seas, stone plateaus, gravel plains (reg), dry valleys (wadi), dry lakes (oued), and salt flats (shatt or chott).[8] Unusual landforms include the Richat Structure in Mauritania.

text: Several deeply dissected mountains, many volcanic, rise from the desert, including the Aïr Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and the Red Sea hills. The highest peak in the Sahara is Emi Koussi, a shield volcano in the Tibesti range of northern Chad.

text: The central Sahara is hyperarid, with sparse vegetation. The northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis, where moisture collects. In the central, hyperarid region, there are many subdivisions of the great desert: Tanezrouft, the Ténéré, the Libyan Desert, the Eastern Desert, the Nubian Desert and others. These extremely arid areas often receive no rain for years.

text: To the north, the Sahara skirts the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Maghreb, the Sahara borders the Mediterranean forest, woodland, and scrub eco-regions of northern Africa, all of which have a Mediterranean climate characterized by hot summers and cool and rainy winters. According to the botanical criteria of Frank White[9] and geographer Robert Capot-Rey,[10][11] the northern limit of the Sahara corresponds to the northern limit of date palm cultivation and the southern limit of the range of esparto, a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the 100 mm (3.9 in) isohyet of annual precipitation.[12]

text: To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel.[10][11] According to climatic criteria, the southern limit of the Sahara corresponds to the 150 mm (5.9 in) isohyet of annual precipitation (this is a long-term average, since precipitation varies annually).[12]

text: Important cities located in the Sahara include Nouakchott, the capital of Mauritania; Tamanrasset, Ouargla, Béchar, Hassi Messaoud, Ghardaïa, and El Oued in Algeria; Timbuktu in Mali; Agadez in Niger; Ghat in Libya; and Faya-Largeau in Chad.

text: Climate

text: The Sahara is the world's largest low-latitude hot desert. The area is located in the horse latitudes under the subtropical ridge, a significant belt of semi-permanent subtropical warm-core high pressure where the air from upper levels of the troposphere tends to sink towards the ground. This steady descending airflow causes a warming and a drying effect in the upper troposphere. The sinking air prevents evaporating water from rising and, therefore, prevents the adiabatic cooling, which makes cloud formation extremely difficult to nearly impossible.[13]

text: The permanent dissolution of clouds allows unhindered light and thermal radiation. The stability of the atmosphere above the desert prevents any convective overturning, thus making rainfall virtually non-existent. As a consequence, the weather tends to be sunny, dry and stable with a minimal risk of rainfall. Subsiding, diverging, dry air masses associated with subtropical high-pressure systems are extremely unfavorable for the development of convectional showers. The subtropical ridge is the predominant factor that explains the hot desert climate (Köppen climate classification BWh) of this vast region. The lowering of air is the strongest and the most effective over the eastern part of the Great Desert, in the Libyan Desert which is the sunniest, driest and the most nearly "rain-less" place on the planet rivaling the Atacama Desert, lying in Chile and Peru.

text: The rainfall inhibition and the dissipation of cloud cover are most accentuated over the eastern section of the Sahara rather than the western. The prevailing air mass lying above the Sahara is the continental tropical (cT) air mass, which is hot and dry. Hot, dry air masses primarily form over the North-African desert from the heating of the vast continental land area, and it affects the whole desert during most of the year. Because of this extreme heating process, a thermal low is usually noticed near the surface, and is the strongest and the most developed during the summertime. The Sahara High represents the eastern continental extension of the Azores High,[citation needed] centered over the North Atlantic Ocean. The subsidence of the Sahara High nearly reaches the ground during the coolest part of the year while it is confined to the upper troposphere during the hottest periods.

text: The effects of local surface low pressure are extremely limited because upper-level subsidence still continues to block any form of air ascent. Also, to be protected against rain-bearing weather systems by the atmospheric circulation itself, the desert is made even drier by his geographical configuration and location. Indeed, the extreme aridity of the Sahara can not be only explained by the subtropical high pressure. The Atlas Mountains, found in Algeria, Morocco and Tunisia also help to enhance the aridity of the northern part of the desert. These major mountain ranges act as a barrier causing a strong rain shadow effect on the leeward side by dropping much of the humidity brought by atmospheric disturbances along the polar front which affects the surrounding Mediterranean climates.

text: The primary source of rain in the Sahara is the Intertropical Convergence Zone, a continuous belt of low-pressure systems near the equator which bring the brief, short and irregular rainy season to the Sahel and southern Sahara. Rainfall in this giant desert has to overcome the physical and atmospheric barriers that normally prevent the production of precipitation. The harsh climate of the Sahara is characterized by: extremely low, unreliable, highly erratic rainfall; extremely high sunshine duration values; high temperatures year-round; negligible rates of relative humidity; a significant diurnal temperature variation; and extremely high levels of potential evaporation which are the highest recorded worldwide.[14]

text: Temperature

text: The sky is usually clear above the desert and the sunshine duration is extremely high everywhere in the Sahara. Most of the desert has more than 3,600 h of bright sunshine annually or over 82% of the time, and a wide area in the eastern part experiences in excess of 4,000 h of bright sunshine a year or over 91% of the time. The highest values are very close to the theoretical maximum value. A value of 4,300 h or 98% of the time would be recorded in Upper Egypt (Aswan, Luxor) and in the Nubian Desert (Wadi Halfa).[15] The annual average direct solar irradiation is around 2,800 kWh/(m2 year) in the Great Desert. The Sahara has a huge potential for solar energy production.

text: The constantly high position of the sun, the extremely low relative humidity, and the lack of vegetation and rainfall make the Great Desert the hottest continuously large area worldwide, and the hottest place on Earth during summer in some spots. The average high temperature exceeds 38 to 40 °C or 100.4 to 104.0 °F during the hottest month nearly everywhere in the desert except at very high altitudes. The highest officially recorded average high temperature[clarification needed] was 47 °C or 116.6 °F in a remote desert town in the Algerian Desert called Bou Bernous with an elevation of 378 metres (1,240 ft) meters above sea level.[15] It is the world’s highest recorded average high temperature[clarification needed] and only Death Valley, California rivals it.[16] Other hot spots in Algeria such as Adrar, Timimoun, In Salah, Ouallene, Aoulef, Reggane with an elevation between 200 and 400 metres (660 and 1,310 ft) above sea level get slightly lower summer average highs around 46 °C or 114.8 °F during the hottest months of the year. Salah, well known in Algeria for its extreme heat, has average high temperatures of 43.8 °C or 110.8 °F, 46.4 °C or 115.5 °F, 45.5 °C or 113.9 °F and 41.9 °C or 107.4 °F in June, July, August and September respectively. There are even hotter spots in the Sahara, but they are located in extremely remote areas, especially in the Azalai, lying in northern Mali. The major part of the desert experiences around three to five months when the average high strictly exceeds 40 °C or 104 °F. The southern central part of the desert experiences up to six or seven months when the average high temperature strictly exceeds 40 °C or 104 °F which shows the constancy and the length of the really hot season in the Sahara. Some examples of this are: Bilma, Niger and Faya-Largeau, Chad. The annual average daily temperature exceeds 20 °C or 68 °F everywhere and can approach 30 °C or 86 °F in the hottest regions year-round. However, most of the desert has a value in excess of 25 °C or 77 °F.

text: Sand and ground temperatures are even more extreme. During daytime, the sand temperature is extremely high as it can easily reach 80 °C or 176 °F or more.[17] A sand temperature of 83.5 °C (182.3 °F) has been recorded in Port Sudan.[17] Ground temperatures of 72 °C or 161.6 °F have been recorded in the Adrar of Mauritania and a value of 75 °C (167 °F) has been measured in Borkou, northern Chad.[17]

text: Due to lack of cloud cover and very low humidity, the desert usually features high diurnal temperature variations between days and nights. However, it is a myth that the nights are cold after extremely hot days in the Sahara. The average diurnal temperature range is typically between 13 and 20 °C or 23.4 and 36.0 °F. The lowest values are found along the coastal regions due to high humidity and are often even lower than 10 °C or 18 °F, while the highest values are found in inland desert areas where the humidity is the lowest, mainly in the southern Sahara. Still, it is true that winter nights can be cold as it can drop to the freezing point and even below, especially in high-elevation areas. The frequency of subfreezing winter nights in the Sahara is strongly influenced by the North Atlantic Oscillation (NAO), with warmer winter temperatures during negative NAO events and cooler winters with more frosts when the NAO is positive.[18] This is because the weaker clockwise flow around the eastern side of the subtropical anticyclone during negative NAO winters, although too dry to produce more than negligible precipitation, does reduce the flow of dry, cold air from higher latitudes of Eurasia into the Sahara significantly.[19]

text: Precipitation

text: The average annual rainfall ranges from very low in the northern and southern fringes of the desert to nearly non-existent over the central and the eastern part. The thin northern fringe of the desert receives more winter cloudiness and rainfall due to the arrival of low pressure systems over the Mediterranean Sea along the polar front, although very attenuated by the rain shadow effects of the mountains and the annual average rainfall ranges from 100 millimetres (4 in) to 250 millimetres (10 in). For example, Biskra, Algeria and Ouarzazate, Morocco are found in this zone. The southern fringe of the desert along the border with the Sahel receives summer cloudiness and rainfall due to the arrival of the Intertropical Convergence Zone from the south and the annual average rainfall ranges from 100 millimetres (4 in) to 250 millimetres (10 in). For example, Timbuktu, Mali and Agadez, Niger are found in this zone. The vast central hyper-arid core of the desert is virtually never affected by northerly or southerly atmospheric disturbances and permanently remains under the influence of the strongest anticyclonic weather regime, and the annual average rainfall can drop to less than 1 millimetre (0.04 in). In fact, most of the Sahara receives less than 20 millimetres (0.8 in). Of the 9,000,000 square kilometres (3,500,000 sq mi) of desert land in the Sahara, an area of about 2,800,000 square kilometres (1,100,000 sq mi) (about 31% of the total area) receives an annual average rainfall amount of 10 millimetres (0.4 in) or less, while some 1,500,000 square kilometres (580,000 sq mi) (about 17% of the total area) receives an average of 5 millimetres (0.2 in) or less.[20] The annual average rainfall is virtually zero over a wide area of some 1,000,000 square kilometres (390,000 sq mi) in the eastern Sahara comprising deserts of: Libya, Egypt and Sudan (Tazirbu, Kufra, Dakhla, Kharga, Farafra, Siwa, Asyut, Sohag, Luxor, Aswan, Abu Simbel, Wadi Halfa) where the long-term mean approximates 0.5 millimetres (0.02 in) per year.[20] Rainfall is very unreliable and erratic in the Sahara as it may vary considerably year by year. In full contrast to the negligible annual rainfall amounts, the annual rates of potential evaporation are extraordinarily high, roughly ranging from 2,500 millimetres (100 in) per year to more than 6,000 millimetres (240 in) per year in the whole desert.[21] Nowhere else on Earth has air been found as dry and evaporative as in the Sahara region. However, at least two instances of snowfall have been recorded in Sahara, in February 1979 and December 2016, both in the town of Ain Sefra.[22]

text: Desertification and prehistoric climate

text: The climate of the Sahara has undergone enormous variations between wet and dry over the last few hundred thousand years,[23] believed to be caused by long-term changes in the North African climate cycle that alters the path of the North African Monsoon - usually southward. The cycle is caused by a 41000-year cycle in which the tilt of the earth changes between 22° and 24.5°.[20] At present (2000 AD), we are in a dry period, but it is expected that the Sahara will become green again in 15000 years (17000 AD). When the North African monsoon is at its strongest annual precipitation and subsequent vegetation in the Sahara region increase, resulting in conditions commonly referred to as the "green Sahara". For a relatively weak North African monsoon, the opposite is true, with decreased annual precipitation and less vegetation resulting in a phase of the Sahara climate cycle known as the "desert Sahara".[24]

text: The idea that changes in insolation (solar heating) caused by long-term changes in the Earth's orbit are a controlling factor for the long-term variations in the strength of monsoon patterns across the globe was first suggested by Rudolf Spitaler in the late nineteenth century,[25] The hypothesis was later formally proposed and tested by the meteorologist John Kutzbach in 1981.[26] Kutzbach's ideas about the impacts of insolation on global monsoonal patterns have become widely accepted today as the underlying driver of long term monsoonal cycles. Kutzbach never formally named his hypothesis and as such it is referred to here as the "Orbital Monsoon Hypothesis" as suggested by Ruddiman in 2001.[25]

text: During the last glacial period, the Sahara was much larger than it is today, extending south beyond its current boundaries.[27] The end of the glacial period brought more rain to the Sahara, from about 8000 BC to 6000 BC, perhaps because of low pressure areas over the collapsing ice sheets to the north.[28] Once the ice sheets were gone, the northern Sahara dried out. In the southern Sahara, the drying trend was initially counteracted by the monsoon, which brought rain further north than it does today. By around 4200 BC, however, the monsoon retreated south to approximately where it is today,[29] leading to the gradual desertification of the Sahara.[30] The Sahara is now as dry as it was about 13,000 years ago.[23]

text: The Sahara pump theory describes this cycle. During periods of a wet or "Green Sahara", the Sahara becomes a savanna grassland and various flora and fauna become more common. Following inter-pluvial arid periods, the Sahara area then reverts to desert conditions and the flora and fauna are forced to retreat northwards to the Atlas Mountains, southwards into West Africa, or eastwards into the Nile Valley. This separates populations of some of the species in areas with different climates, forcing them to adapt, possibly giving rise to allopatric speciation.

text: It is also proposed that humans accelerated the drying out period from 6,000–2,500 BC by pastoralists overgrazing available grassland.[31]

text: Evidence for cycles

text: The growth of speleothems (which requires rainwater) was detected in Hol-Zakh, Ashalim, Even-Sid, Ma'ale-ha-Meyshar, Ktora Cracks, Nagev Tzavoa Cave, and elsewhere, and has allowing tracking of prehistoric rainfall. The Red Sea coastal route was extremely arid before 140 and after 115 kya. Slightly wetter conditions appear at 90–87 kya, but it still was just one tenth the rainfall around 125 kya. In the southern Negev Desert speleothems did not grow between 185–140 kya (MIS 6), 110–90 (MIS 5.4–5.2), nor after 85 kya nor during most of the interglacial period (MIS 5.1), the glacial period and Holocene. This suggests that the southern Negev was arid to hyper-arid in these periods.[32]

text: During the Last Glacial Maximum (LGM) the Sahara desert was more extensive than it is now with the extent of the tropical forests being greatly reduced,[33] and the lower temperatures reduced the strength of the Hadley Cell. This is a climate cell which causes rising tropical air of the Inter-Tropical Convergence Zone (ITCZ) to bring rain to the tropics, while dry descending air, at about 20 degrees north, flows back to the equator and brings desert conditions to this region. It is associated with high rates of wind-blown mineral dust, and these dust levels are found as expected in marine cores from the north tropical Atlantic. But around 12,500 BC the amount of dust in the cores in the Bølling/Allerød phase suddenly plummets and shows a period of much wetter conditions in the Sahara, indicating a Dansgaard-Oeschger (DO) event (a sudden warming followed by a slower cooling of the climate). The moister Saharan conditions had begun about 12,500 BC, with the extension of the ITCZ northward in the northern hemisphere summer, bringing moist wet conditions and a savanna climate to the Sahara, which (apart from a short dry spell associated with the Younger Dryas) peaked during the Holocene thermal maximum climatic phase at 4000 BC when mid-latitude temperatures seem to have been between 2 and 3 degrees warmer than in the recent past. Analysis of Nile River deposited sediments in the delta also shows this period had a higher proportion of sediments coming from the Blue Nile, suggesting higher rainfall also in the Ethiopian Highlands. This was caused principally by a stronger monsoonal circulation throughout the sub-tropical regions, affecting India, Arabia and the Sahara.[citation needed] Lake Victoria only recently became the source of the White Nile and dried out almost completely around 15 kya.[34]

text: The sudden subsequent movement of the ITCZ southwards with a Heinrich event (a sudden cooling followed by a slower warming), linked to changes with the El Niño-Southern Oscillation cycle, led to a rapid drying out of the Saharan and Arabian regions, which quickly became desert. This is linked to a marked decline in the scale of the Nile floods between 2700 and 2100 BC.[35]

text: Ecoregions

text: The Sahara comprises several distinct ecoregions. With their variations in temperature, rainfall, elevation, and soil, these regions harbor distinct communities of plants and animals.

text: The Atlantic coastal desert is a narrow strip along the Atlantic coast where fog generated offshore by the cool Canary Current provides sufficient moisture to sustain a variety of lichens, succulents, and shrubs. It covers an area of 39,900 square kilometers (15,400 sq mi) in the south of Morocco and Mauritania.[36]

text: The North Saharan steppe and woodlands is along the northern desert, next to the Mediterranean forests, woodlands, and scrub ecoregions of the northern Maghreb and Cyrenaica. Winter rains sustain shrublands and dry woodlands that form a transition between the Mediterranean climate regions to the north and the hyper-arid Sahara proper to the south. It covers 1,675,300 square kilometers (646,840 sq mi) in Algeria, Egypt, Libya, Mauritania, Morocco, and Tunisia.[37]

text: The Sahara Desert ecoregion covers the hyper-arid central portion of the Sahara where rainfall is minimal and sporadic. Vegetation is rare, and this ecoregion consists mostly of sand dunes (erg, chech, raoui), stone plateaus (hamadas), gravel plains (reg), dry valleys (wadis), and salt flats. It covers 4,639,900 square kilometres (1,791,500 sq mi) of: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Niger, and Sudan.[8]

text: The South Saharan steppe and woodlands ecoregion is a narrow band running east and west between the hyper-arid Sahara and the Sahel savannas to the south. Movements of the equatorial Intertropical Convergence Zone (ITCZ) bring summer rains during July and August which average 100 to 200 mm (4 to 8 in) but vary greatly from year to year. These rains sustain summer pastures of grasses and herbs, with dry woodlands and shrublands along seasonal watercourses. This ecoregion covers 1,101,700 square kilometres (425,400 sq mi) in Algeria, Chad, Mali, Mauritania, and Sudan.[38]

text: In the West Saharan montane xeric woodlands, several volcanic highlands provide a cooler, moister environment that supports Saharo-Mediterranean woodlands and shrublands. The ecoregion covers 258,100 square kilometres (99,650 sq mi), mostly in the Tassili n'Ajjer of Algeria, with smaller enclaves in the Aïr of Niger, the Dhar Adrar of Mauritania, and the Adrar des Iforas of Mali and Algeria.[39]

text: The Tibesti-Jebel Uweinat montane xeric woodlands ecoregion consists of the Tibesti and Jebel Uweinat highlands. Higher and more regular rainfall and cooler temperatures support woodlands and shrublands of Date palm, acacias, myrtle, oleander, tamarix, and several rare and endemic plants. The ecoregion covers 82,200 square kilometres (31,700 sq mi) in the Tibesti of Chad and Libya, and Jebel Uweinat on the border of Egypt, Libya, and Sudan.[40]

text: The Saharan halophytics is an area of seasonally flooded saline depressions which is home to halophytic (salt-adapted) plant communities. The Saharan halophytics cover 54,000 square kilometres (21,000 sq mi) including: the Qattara and Siwa depressions in northern Egypt, the Tunisian salt lakes of central Tunisia, Chott Melghir in Algeria, and smaller areas of Algeria, Mauritania, and the southern part of Morocco.[41]

text: The Tanezrouft is one of the harshest regions on Earth as well as one of the hottest and driest parts of the Sahara, with no vegetation and very little life. It is along the borders of Algeria, Niger]] and Mali, west of the Hoggar mountains.

text: Flora and fauna

text: The flora of the Sahara is highly diversified based on the bio-geographical characteristics of this vast desert. Floristically, the Sahara has three zones based on the amount of rainfall received – the Northern (Mediterranean), Central and Southern Zones. There are two transitional zones – the Mediterranean-Sahara transition and the Sahel transition zone.[42]

text: The Saharan flora comprises around 2800 species of vascular plants. Approximately a quarter of these are endemic. About half of these species are common to the flora of the Arabian deserts.[43]

text: The central Sahara is estimated to include five hundred species of plants, which is extremely low considering the huge extent of the area. Plants such as acacia trees, palms, succulents, spiny shrubs, and grasses have adapted to the arid conditions, by growing lower to avoid water loss by strong winds, by storing water in their thick stems to use it in dry periods, by having long roots that travel horizontally to reach the maximum area of water and to find any surface moisture, and by having small thick leaves or needles to prevent water loss by evapotranspiration. Plant leaves may dry out totally and then recover.

text: Several species of fox live in the Sahara including: the fennec fox, pale fox and Rüppell's fox. The addax, a large white antelope, can go nearly a year in the desert without drinking. The dorcas gazelle is a north African gazelle that can also go for a long time without water. Other notable gazelles include the rhim gazelle and dama gazelle.

text: The Saharan cheetah (northwest African cheetah) lives in Algeria, Togo, Niger, Mali, Benin, and Burkina Faso. There remain fewer than 250 mature cheetahs, which are very cautious, fleeing any human presence. The cheetah avoids the sun from April to October, seeking the shelter of shrubs such as balanites and acacias. They are unusually pale.[44][45] The other cheetah subspecies (northeast African cheetah) lives in Chad, Sudan and the eastern region of Niger. However, it is currently extinct in the wild in Egypt and Libya. There are approximately 2000 mature individuals left in the wild.

text: Other animals include the monitor lizards, hyrax, sand vipers, and small populations of African wild dog,[46] in perhaps only 14 countries[47] and red-necked ostrich. Other animals exist in the Sahara (birds in particular) such as African silverbill and black-faced firefinch, among others. There are also small desert crocodiles in Mauritania and the Ennedi Plateau of Chad.[48]

text: The deathstalker scorpion can be 10 cm (3.9 in) long. Its venom contains large amounts of agitoxin and scyllatoxin and is very dangerous; however, a sting from this scorpion rarely kills a healthy adult. The Saharan silver ant is unique in that due to the extreme high temperatures of their habitat, and the threat of predators, the ants are active outside their nest for only about ten minutes per day.[49]

text: Dromedary camels and goats are the domesticated animals most commonly found in the Sahara. Because of its qualities of endurance and speed, the dromedary is the favourite animal used by nomads.

text: Human activities are more likely to affect the habitat in areas of permanent water (oases) or where water comes close to the surface. Here, the local pressure on natural resources can be intense. The remaining populations of large mammals have been greatly reduced by hunting for food and recreation. In recent years development projects have started in the deserts of Algeria and Tunisia using irrigated water pumped from underground aquifers. These schemes often lead to soil degradation and salinization.

text: Researchers from Hacettepe University (Yücekutlu, N. et al., 2011) have reported that Saharan soil may have bio-available iron and also some essential macro and micro nutrient elements suitable for use as fertilizer for growing wheat.[50]

text: History

text: People lived on the edge of the desert thousands of years ago[51] since the end of the last glacial period. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles[52] survive, with half found in the Tassili n'Ajjer in southeast Algeria. Fossils of dinosaurs, including Afrovenator, Jobaria and Ouranosaurus, have also been found here. The modern Sahara, though, is not lush in vegetation, except in the Nile Valley, at a few oases, and in the northern highlands, where Mediterranean plants such as the olive tree are found to grow. It was long believed that the region had been this way since about 1600 BCE, after shifts in the Earth's axis increased temperatures and decreased precipitation, which led to the abrupt desertification of North Africa about 5,400 years ago.[29] However, this theory has recently been called into dispute, when samples taken from several 7 million year old sand deposits led scientists to reconsider the timeline for desertification.[53]

text: Kiffians

text: The Kiffian culture is a prehistoric industry, or domain, that existed between 10,000 and 8,000 years ago in the Sahara, during the Neolithic Subpluvial. Human remains from this culture were found in 2000 at a site known as Gobero, located in Niger in the Ténéré Desert.[54] The site is known as the largest and earliest grave of Stone Age people in the Sahara desert.[55] The Kiffians were skilled hunters. Bones of many large savannah animals that were discovered in the same area suggest that they lived on the shores of a lake that was present during the Holocene Wet Phase, a period when the Sahara was verdant and wet.[55] The Kiffian people were tall, standing over six feet in height.[54] Craniometric analysis indicates that this early Holocene population was closely related to the Late Pleistocene Iberomaurusians and early Holocene Capsians of the Maghreb, as well as mid-Holocene Mechta groups.[56] Traces of the Kiffian culture do not exist after 8,000 years ago, as the Sahara went through a dry period for the next thousand years.[57] After this time, the Tenerian culture colonized the area.

text: Tenerians

text: Gobero was discovered in 2000 during an archaeological expedition led by Paul Sereno, which sought dinosaur remains. Two distinct prehistoric cultures were discovered at the site: the early Holocene Kiffian culture, and the middle Holocene Tenerian culture. The Kiffians were a prehistoric people who preceded the Tenerians and vanished approximately 8000 years ago, when the desert became very dry. The desiccation lasted until around 4600 BC, when the earliest artefacts associated with the Tenerians have been dated to. Some 200 skeletons have been discovered at Gobero. The Tenerians were considerably shorter in height and less robust than the earlier Kiffians. Craniometric analysis also indicates that they were osteologically distinct. The Kiffian skulls are akin to those of the Late Pleistocene Iberomaurusians, early Holocene Capsians, and mid-Holocene Mechta groups, whereas the Tenerian crania are more like those of Mediterranean groups.[58][59] Graves show that the Tenerians observed spiritual traditions, as they were buried with artifacts such as jewelry made of hippo tusks and clay pots. The most interesting find is a triple burial, dated to 5300 years ago, of an adult female and two children, estimated through their teeth as being five and eight years old, hugging each other. Pollen residue indicates they were buried on a bed of flowers. The three are assumed to have died within 24 hours of each other, but as their skeletons hold no apparent trauma (they did not die violently) and they have been buried so elaborately - unlikely if they had died of a plague - the cause of their deaths is a mystery.

text: Tashwinat Mummy

text: Uan Muhuggiag appears to have been inhabited from at least the 6th millennium BC to about 2700 BC, although not necessarily continuously.[60] The most noteworthy find at Uan Muhuggiag is the well-preserved mummy of a young boy of approximately 2 1/2 years old. The child was in a fetal position, then embalmed, then placed in a sack made of antelope skin, which was insulated by a layer of leaves.[61] The boy's organs were removed, as evidenced by incisions in his stomach and thorax, and an organic preservative was inserted to stop his body from decomposing.[62] An ostrich eggshell necklace was also found around his neck.[60] Radiocarbon dating determined the age of the mummy to be approximately 5600 years old, which makes it about 1000 years older than the earliest previously recorded mummy in ancient Egypt.[63] In 1958-1959, an archaeological expedition led by Antonio Ascenzi conducted anthropological, radiological, histological and chemical analyses on the Uan Muhuggiag mummy. The specimen was determined to be that of a 30-month old child of uncertain sex, who possessed Negroid features. A long incision on the specimen's abdominal wall also indicated that the body had been initially mummified by evisceration and later underwent natural desiccation.[64] One other individual, an adult, was found at Uan Muhuggiag, buried in a crouched position.[60] However, the body showed no evidence of evisceration or any other method of preservation. The body was estimated to date from about 7500 BP.[65]

text: Nubians

text: During the Neolithic Era, before the onset of desertification around 9500 BCE, the central Sudan had been a rich environment supporting a large population ranging across what is now barren desert, like the Wadi el-Qa'ab. By the 5th millennium BCE, the people who inhabited what is now called Nubia, were full participants in the "agricultural revolution", living a settled lifestyle with domesticated plants and animals. Saharan rock art of cattle and herdsmen suggests the presence of a cattle cult like those found in Sudan and other pastoral societies in Africa today.[66] Megaliths found at Nabta Playa are overt examples of probably the world's first known archaeoastronomy devices, predating Stonehenge by some 2,000 years.[67] This complexity, as observed at Nabta Playa, and as expressed by different levels of authority within the society there, likely formed the basis for the structure of both the Neolithic society at Nabta and the Old Kingdom of Egypt.[68]

text: Egyptians

text: By 6000 BCE predynastic Egyptians in the southwestern corner of Egypt were herding cattle and constructing large buildings. Subsistence in organized and permanent settlements in predynastic Egypt by the middle of the 6th millennium BCE centered predominantly on cereal and animal agriculture: cattle, goats, pigs and sheep. Metal objects replaced prior ones of stone. Tanning of animal skins, pottery and weaving were commonplace in this era also. There are indications of seasonal or only temporary occupation of the Al Fayyum in the 6th millennium BCE, with food activities centering on fishing, hunting and food-gathering. Stone arrowheads, knives and scrapers from the era are commonly found.[69] Burial items included pottery, jewelry, farming and hunting equipment, and assorted foods including dried meat and fruit. Burial in desert environments appears to enhance Egyptian preservation rites, and the dead were buried facing due west.[70]

text: By 3400 BCE, the Sahara was as dry as it is today, due to reduced precipitation and higher temperatures resulting from a shift in the Earth's orbit.[29] As a result of this aridification, it became a largely impenetrable barrier to humans, with the remaining settlements mainly being concentrated around the numerous oases that dot the landscape. Little trade or commerce is known to have passed through the interior in subsequent periods, the only major exception being the Nile Valley. The Nile, however, was impassable at several cataracts, making trade and contact by boat difficult.

text: Phoenicians

text: The people of Phoenicia, who flourished from 1200–800 BCE, created a confederation of kingdoms across the entire Sahara to Egypt. They generally settled along the Mediterranean coast, as well as the Sahara, among the people of ancient Libya, who were the ancestors of people who speak Berber languages in North Africa and the Sahara today, including the Tuareg of the central Sahara.

text: The Phoenician alphabet seems to have been adopted by the ancient Libyans of north Africa, and Tifinagh is still used today by Berber-speaking Tuareg camel herders of the central Sahara.

text: Sometime between 633 BCE and 530 BCE, Hanno the Navigator either established or reinforced Phoenician colonies in Western Sahara, but all ancient remains have vanished with virtually no trace.

text: Greeks

text: By 500 BCE, Greeks arrived in the desert. Greek traders spread along the eastern coast of the desert, establishing trading colonies along the Red Sea. The Carthaginians explored the Atlantic coast of the desert, but the turbulence of the waters and the lack of markets caused a lack of presence further south than modern Morocco. Centralized states thus surrounded the desert on the north and east; it remained outside the control of these states. Raids from the nomadic Berber people of the desert were of constant concern to those living on the edge of the desert.

text: Urban civilization

text: An urban civilization, the Garamantes, arose around 500 BCE in the heart of the Sahara, in a valley that is now called the Wadi al-Ajal in Fezzan, Libya.[23] The Garamantes achieved this development by digging tunnels far into the mountains flanking the valley to tap fossil water and bring it to their fields. The Garamantes grew populous and strong, conquering their neighbors and capturing many slaves (who were put to work extending the tunnels). The ancient Greeks and the Romans knew of the Garamantes and regarded them as uncivilized nomads. However, they traded with them, and a Roman bath has been found in the Garamantes' capital of Garama. Archaeologists have found eight major towns and many other important settlements in the Garamantes' territory. The Garamantes' civilization eventually collapsed after they had depleted available water in the aquifers and could no longer sustain the effort to extend the tunnels further into the mountains.[71]

text: Berbers

text: The Berber people occupied (and still occupy) much of the Sahara. The Garamantes Berbers built a prosperous empire in the heart of the desert.[72] The Tuareg nomads continue to inhabit and move across wide Sahara surfaces to the present day.

text: Islamic expansion

text: The Byzantine Empire ruled the northern shores of the Sahara from the 5th to the 7th centuries. After the Muslim conquest of Arabia, specifically the Arabian peninsula, the Muslim conquest of North Africa began in the mid-7th to early 8th centuries and Islamic influence expanded rapidly on the Sahara. By the end of 641 all of Egypt was in Muslim hands. Trade across the desert intensified, and a significant slave trade crossed the desert. It has been estimated that from the 10th to 19th centuries some 6,000 to 7,000 slaves were transported north each year.[73]

text: Ottoman Turkish era

text: In the 16th century the northern fringe of the Sahara, such as coastal regencies in present-day Algeria and Tunisia, as well as some parts of present-day Libya, together with the semi-autonomous kingdom of Egypt, were occupied by the Ottoman Empire. From 1517 Egypt was a valued part of the Ottoman Empire, ownership of which provided the Ottomans with control over the Nile Valley, the east Mediterranean and North Africa. The benefit of the Ottoman Empire was the freedom of movement for citizens and goods. Traders exploited the Ottoman land routes to handle the spices, gold and silk from the East, manufactured goods from Europe, and the slave and gold traffic from Africa. Arabic continued as the local language and Islamic culture was much reinforced. The Sahel and southern Sahara regions were home to several independent states or to roaming Tuareg clans.

text: European colonialism

text: European colonialism in the Sahara began in the 19th century. France conquered the regency of Algiers from the Ottomans in 1830, and French rule spread south from Algeria and eastwards from Senegal into the upper Niger to include present-day Algeria, Chad, Mali then French Sudan including Timbuktu, Mauritania, Morocco (1912), Niger, and Tunisia (1881). By the beginning of the 20th century, the trans-Saharan trade had clearly declined because goods were moved through more modern and efficient means, such as airplanes, rather than across the desert.[74]

text: The French Colonial Empire was the dominant presence in the Sahara. It established regular air links from Toulouse (HQ of famed Aéropostale), to Oran and over the Hoggar to Timbuktu and West to Bamako and Dakar, as well as trans-Sahara bus services run by La Companie Transsaharienne (est. 1927).[75] A remarkable film shot by famous aviator Captain René Wauthier documents the first crossing by a large truck convoy from Algiers to Tchad, across the Sahara.[76]

text: Egypt, under Muhammad Ali and his successors, conquered Nubia in 1820–22, founded Khartoum in 1823, and conquered Darfur in 1874. Egypt, including the Sudan, became a British protectorate in 1882. Egypt and Britain lost control of the Sudan from 1882 to 1898 as a result of the Mahdist War. After its capture by British troops in 1898, the Sudan became an Anglo-Egyptian condominium.

text: Spain captured present-day Western Sahara after 1874, although Rio del Oro remained largely under Sahrawi influence. In 1912, Italy captured parts of what was to be named Libya from the Ottomans. To promote the Roman Catholic religion in the desert, Pope Pius IX appointed a delegate Apostolic of the Sahara and the Sudan in 1868; later in the 19th century his jurisdiction was reorganized into the Vicariate Apostolic of Sahara.

text: Breakup of the empires and afterwards

text: Egypt became independent of Britain in 1936, although the Anglo-Egyptian treaty of 1936 allowed Britain to keep troops in Egypt and to maintain the British-Egyptian condominium in the Sudan. British military forces were withdrawn in 1954.

text: Most of the Saharan states achieved independence after World War II: Libya in 1951; Morocco, Sudan, and Tunisia in 1956; Chad, Mali, Mauritania, and Niger in 1960; and Algeria in 1962. Spain withdrew from Western Sahara in 1975, and it was partitioned between Mauritania and Morocco. Mauritania withdrew in 1979; Morocco continues to hold the territory.

text: In the post-World War II era, several mines and communities have developed to utilize the desert's natural resources. These include large deposits of oil and natural gas in Algeria and Libya, and large deposits of phosphates in Morocco and Western Sahara.

text: A number of Trans-African highways have been proposed across the Sahara, including the Cairo–Dakar Highway along the Atlantic coast, the Trans-Sahara Highway from Algiers on the Mediterranean to Kano in Nigeria, the Tripoli – Cape Town Highway from Tripoli in Libya to N'Djamena in Chad, and the Cairo – Cape Town Highway which follows the Nile. Each of these highways is partially complete, with significant gaps and unpaved sections.

text: People and languages

text: The people of the Sahara are of various origins. Among them the Amaziɣ including the Turūq, various Arabized Amaziɣ groups such as the Hassaniya-speaking Sahrawis, whose populations include the Znaga, a tribe whose name is a remnant of the pre-historic Zenaga language. Other major groups of people include the: Toubou, Nubians, Zaghawa, Kanuri, Hausa, Songhai, Beja, and Fula/Fulani (French: Peul; Fula: Fulɓe).

text: Arabic dialects are the most widely spoken languages in the Sahara. Arabic, Berber and its variants now regrouped under the term Amazigh (which includes the Guanche language spoken by the original Berber inhabitants of the Canary Islands) and Beja languages are part of the Afro-Asiatic or Hamito-Semitic family.[citation needed] Unlike neighboring West Africa and the central governments of the states that comprise the Sahara, the French language bears little relevance to inter-personal discourse and commerce within the region, its people retaining staunch ethnic and political affiliations with Tuareg and Berber leaders and culture.[77] The legacy of the French colonial era administration is primarily manifested in the territorial reorganization enacted by the Third and Fourth republics, which engendered artificial political divisions within a hitherto isolated and porous region.[78] Diplomacy with local clients was conducted primarily in Arabic, which was the traditional language of bureaucratic affairs. Mediation of disputes and inter-agency communication was served by interpreters contracted by the French government, who, according to Keenan, "documented a space of intercultural mediation," contributing much to preserving the indigenous cultural identities in the region.[79]


document_title: Office of Professional Responsibility

question_text: who is the head of the office of professional responsibility

root

text: Office of Professional Responsibility

text: The Office of Professional Responsibility (OPR) is part of the United States Department of Justice (DOJ) responsible for investigating attorneys employed by the DOJ who have been accused of misconduct or crimes in their professional functions. The OPR promulgates independent standards of ethical and criminal conduct for DOJ attorneys, while the DOJ's Office of the Inspector General (OIG) has jurisdiction of non-attorney DOJ employees. Mary Patrice Brown was named acting head of the office in April 2009.[1] Robin Ashton became the head of the office in 2011[2]

tag: p

text: The OPR receives reports of allegations of misconduct made against DOJ attorneys from many sources. Nearly half of all such allegations are reported to OPR by DOJ sources, such as the attorney involved.[3] The remaining complaints come from a variety of sources, including private attorneys, defendants and civil litigants, other federal agencies, state or local government officials, judicial and congressional referrals, and media reports. OPR gives expedited attention to judicial findings of misconduct.

text: The OPR reviews each allegation and determines whether further investigation is warranted. The determination is a matter of investigative judgment that weighs many factors, including the nature of the allegation, its apparent credibility, its specificity, its susceptibility to verification, and the source of the allegation. A decision to open a matter does not give rise to a presumption of misconduct, nor shift the burden of proof to the accused person. The OPR's investigations involve a wide range of allegations, and the investigative methods used vary accordingly.

text: In many cases, the OPR notifies the accused attorney and requests a written response. Sometimes, the OPR also makes on-site investigations. The OPR reports the results of the investigation to the component head concerned and to the Office of the Deputy Attorney General. The OPR also advises the complainant and the accused attorney of its conclusion.

text: OPR has a policy of not reporting or investigating complaints for violation of duty of candor towards the tribunal that may be resolved in court. It does not publish this policy in the Federal Register. OPR does not publish agendas of its meetings or keep minutes of its meetings.[4][5][6]


document_title: Reko Diq

question_text: reko diq is a mining project in pakistan for

text: Reko Diq

text:
Reko Diq

Town

Reko Diq

Reko Diq

Show map of Balochistan, PakistanShow map of PakistanShow all

Coordinates: 29°06′3.02″N 62°06′20.10″E / 29.1008389°N 62.1055833°E / 29.1008389; 62.1055833Coordinates: 29°06′3.02″N 62°06′20.10″E / 29.1008389°N 62.1055833°E / 29.1008389; 62.1055833

Country
 Pakistan

Province
Balochistan

Tehsil
Chagai

Government

 • Type
Town

Time zone
PST (UTC+5)

tag: table

text: Reko Diq is a small town in Chagai District, Balochistan, Pakistan. It is located in a desert area, 70 kilometres north-west of Naukundi, close to Pakistan's border with Iran and Afghanistan. The area is located in Tethyan belt that stretches all the way from Turkey and Iran into Pakistan.

text: Reko Diq is a remote location in the North-West of Chagai district. Chagai is a sparsely populated western desert district of Balochistan. It is mostly low relief and thinly populated desert. The weather of Chagai ranges from very hot summers of 40-50 °C to very cool winters of up to -10 °C with less than 40 mm precipitation (winter rain and minor snow). It also exhibits periods of high wind and dust/sand storms which have a demobilizing impact on the local activities and trade. Access to the Chagai district is via the Zahidan - Quetta highway also known as the London Road.

text: According to the 1998 census the population of Chagai District was 202,562, along with approximately 53,000 Afghan refugees. The population of Chagai District was estimated to be over 250,000 in 2005. Over 50% of the people of the area are Muslims. According to Dr. Samar Mubarakmand (Member Science & Technology, Planning Commission of Pakistan) Geological Survey of Pakistan had discovered the Reko Diq reserves way back in 1978.[1]

text: Reko Diq, which means sandy peak in Baluchi language, is also the name of an ancient volcano.

text: Reko Diq Mine is famous because of its vast Gold and Copper Reserves and its believed to have the world 5th largest gold deposit.[2]


document_title: When Calls the Heart

question_text: who played cody on when calls the heart

question_tokens: who played cody on when calls the heart

text: When Calls the Heart

text: Plot[edit]

text: When Calls the Heart tells the story of Elizabeth Thatcher (Erin Krakow), a young teacher accustomed to her high-society life. She receives her first classroom assignment in Coal Valley, a small coal-mining town in Western Canada which is located just south of Robb, Alberta. There, life is simple—but often fraught with challenges. Elizabeth charms most everyone in Coal Valley, except Royal North West Mounted Police Constable Jack Thornton (Daniel Lissing). He believes Thatcher's wealthy father has doomed the lawman's career by insisting he be assigned in town to protect the shipping magnate's daughter. The town of Coal Valley was renamed Hope Valley in Episode 1, Season 2 after the coal mine was closed.

text: Living in this 1910 coal town, Elizabeth must learn the ways of the Canadian frontier movement if she wishes to thrive in the rural west on her own. Lori Loughlin portrays Abigail Stanton, whose husband, the foreman of the mine, and her only son—along with 45 other miners—have recently been killed in an explosion, which turns out to have been a tragic accident waiting to happen—a result of the mining-company site manager's irresponsible management and lack of due care in his management of the mine. The newly widowed women find their faith tested when they must go to work in the mine to keep a roof over their heads, food on the table, and compile a wage for the town's teacher.[10]

text: Episodes[edit]

text: SeasonEpisodesOriginally airedFirst airedLast aired112January 11, 2014 (2014-01-11)March 29, 2014 (2014-03-29)27April 25, 2015 (2015-04-25)June 13, 2015 (2015-06-13)New Year's WishDecember 26, 2015 (2015-12-26)38February 21, 2016 (2016-02-21)April 10, 2016 (2016-04-10)ChristmasDecember 25, 2016 (2016-12-25)410February 19, 2017 (2017-02-19)April 23, 2017 (2017-04-23)The Christmas Wishing TreeDecember 25, 2017 (2017-12-25)510February 18, 2018 (2018-02-18)April 22, 2018 (2018-04-22)

text: Cast[edit]

text: Main[edit]

text:
Erin Krakow as Elizabeth Thatcher Thornton
Daniel Lissing as Jack Thornton (Seasons 1–5)
Lori Loughlin as Abigail Stanton
Jack Wagner as Bill Avery
Martin Cummins as Henry Gowen
Pascale Hutton as Rosemary LeVeaux Coulter
Kavan Smith as Leland Coulter

tag: ul

text: Recurring[edit]

text:
Paul Greene as Carson Shepherd
Clayton Chitty as Kevin Townsend
Andrea Brooks as Faith Carter
Eva Bourne as Clara Weller Stanton
Aren Buchholz as Jesse Flynn
Carter Ryan Evancic as Cody Hastings
Loretta Walsh as Florence Blakeley
Erica Carroll as Dottie Ramsey
Johannah Newmarch as Molly Sullivan
Mark Humphrey as Frank Hogan
Chelah Horsdal as Cat Montgomery
Mitchell Kummen as Gabe Montgomery
Gracyn Shinyei as Emily Montgomery
Logan Williams as Miles Montgomery
Ben Rosenbaum as Mike Hickam
Ava Grace Cooper as Opal
Charlotte Hegele as Julie Thatcher
Max Lloyd-Jones as Tom Thornton
Brooke Shields as Charlotte Thornton
Ali Skovbye as Becky Hastings
Garwin Sanford as William Thatcher
Lynda Boyd as Grace Thatcher
Devon Weigel as Viola Thatcher
Marcus Rosner as Charles Kensington
Josie Bissett as AJ Foster
Steve Bacic as Charles Spurlock
Kristina Wagner as Nora Avery
Mamie Laverock as Rosaleen Sullivan
Adrian Hough as Reverend Anderson
Will Verchere-Gopaulsingh as Caleb Dunbar
Laura Bertram as Mary Dunbar
Derek Hamilton as Dewitt Graves
Niall Matter as Shane Cantrell (season 4)
Spencer Drever as Cyrus Rivera (season 4)

text: Characters[edit]

text: This section may contain an excessive amount of intricate detail that may interest only a particular audience. Please help by spinning off or relocating any relevant information, and removing excessive detail that may be against Wikipedia's inclusion policy. (October 2018) (Learn how and when to remove this template message)

text: Elizabeth Thatcher Thornton is an independent, strong-minded, passionate and dedicated young teacher from the city. The middle daughter of William and Grace Thatcher, Elizabeth has two sisters, older sister Viola and younger sister Julie.  Elizabeth was in her mid-20's when she found herself in Coal Valley, a small community on the Canadian frontier in need of a teacher, and quickly discovers it is not an easy place to live, lacking the creature comforts and luxuries of her privileged life with her family. She soon meets the newly appointed and charismatic Mountie Jack Thornton and develops an immediate dislike for him. However, over time they become good friends, and develop an obvious attraction to one another. In the season 1 finale, "Prelude to a Kiss" (also titled as "Final Adieu"), after overcoming many obstacles throughout the season, Jack tells Elizabeth "You're the one, you're the only one" and they share a kiss. Throughout season 2, Elizabeth's feelings for Jack are high at times as well as low. Finally, in the season 2 finale, she admits that his job as a Mountie scares her. After being comforted both admitting that they love each other, Jack and Elizabeth kiss. Season 3 continues the love story of Jack and Elizabeth, all leading up to Jack's marriage proposal in season 4 "My Heart Will Go On." The two wed in season 5's "My Heart Is Yours." Just days into their marriage, Jack is given a new assignment and leaves. He is killed (offscreen) in season 5's "In My Dreams." In the season 5 finale, "Close to My Heart," Elizabeth finds out she is pregnant with Jack's baby.

text: Jack Thornton is a laid back country boy. Jack is the son of Mountie Thomas Thornton and his wife Charlotte Thornton. Jack has a younger brother, Tom (named after his father). As a Mountie and a man of stout character and integrity, he often finds himself protecting and saving people. In season 1's "A Telling Silence," Jack finds a basset hound whom he names Rip (after Rip Van Winkle) and takes home with him. A source of comfort and companion in the small town, Jack often goes to Rip when times in his life are difficult. In season 2's "With All My Heart," Rip, who's afraid of thunder, hides in the mine shafts during a storm. Jack and Elizabeth search for him; in their search, their relationship grows stronger. Upon his first meeting of Elizabeth, Jack developed an instant dislike and it appeared she irritated him. However, he grew to like and then fall madly and completely in love with her over time. In "Rules of Engagement" (S.1), it is revealed that Jack was briefly engaged to Rosemary LeVeaux when she comes looking for him. However, they have both changed and realize that they cannot have a relationship as they once did ever again. In "Prelude to a Kiss" (S.1), Jack found out that Elizabeth may be leaving Coal Valley. Taking her on a walk and giving her a framed picture of them that he had sketched, he asks her not to leave Coal Valley and tells her, "You're the one, you're the only one." She replied that she was "not going anywhere", Coal Valley was where she belonged before they share a kiss. In season 2, Elizabeth and Jack share a hot-and-cold relationship until the finale, "With All My Heart." They both admit that they love each other and share another kiss. Jack's brother, Tom, is introduced season 2's "Trials of the Heart," and their rocky relationship continues until "Coming Together, Coming Apart." Jack gently reminds his younger brother how their father was so proud of him, but he wouldn't be proud of the way he was currently living. Both in tears, Jack tells his younger brother that he believes in him and that he can turn his life around. More recently, Jack has become good friends with the sawmill operator, Lee Coulter. In season 3, Jack begins the new year knowing that Elizabeth only has eyes for him and that her relationship with Charles is over for good. In "Hearts In Question," Jack's mother Charlotte shows up unexpectedly. She meets Elizabeth and is suspicious of her, but through staying her sees Elizabeth for who she really is: a trustworthy, dedicated teacher. In the season finale, "Prayers From The Heart," Jack is injured in a flood. But he miraculously recovers in time to serve as Lee's best man at his wedding. Jack proposes to Elizabeth in season 4's "My Heart Will Go On," the night before he leaves for a new Mountie assignment. In season 5's "My Heart Is Yours," Jack and Elizabeth finally wed. Days into their new marriage, Jack receives a new assignment and leaves. He is killed (offscreen) in season 5's "In My Dreams," but his legacy will live on in his wife and their unborn child.

text: Abigail Stanton is a Coal Valley woman whose husband and son died in the mining accident. Abigail is a very kind woman, and she stands strongly for the things she believes in. She is one of the first women to welcome Elizabeth and the two women quickly become friends.  When Elizabeth accidentally burns down the little teacherage, Abigail gladly welcomes her into her home to live. After being complimented on her cooking, Abigail decides to open a cafe in Coal Valley. Together, Abigail and Elizabeth move into the rooms above the cafe. At the end of season 1, Abigail enjoys the company of Bill Avery, a Mountie, serving as a Forensic Investigator and friend of Jack Thornton's. In season 2, Abigail takes in her daughter-in-law, Clara, the wife of her late son Peter whom Abigail sees as the daughter she never had. With Bill's past being revealed, Abigail ends their friendship and spends more time with the new pastor, Frank Hogan.  Also, she is a strong independent woman that is set on doing the things that are right and tries to help Elizabeth. In season 3, Abigail takes in two orphans, Becky Hastings, and her younger brother Cody. In season 4's "Heart of A Fighter," Abigail legally adopts Becky and Cody. Abigail serves as one of Elizabeth's matrons of honor in season 5's "My Heart Is Yours."

text: Bill Avery is a mysterious, quiet man. He first appears in season 1's "Rules of Engagement," in order to help Jack expose Mr. Gowen's wrongdoings. Bill is immediately attracted to widow Abigail Stanton. Things are going well until Abigail discovers a picture of Bill's family and his wedding ring. He later tells her that his son died, as well as his wife. However, his wife, Nora, comes to confront him in season 2's "Heart's Desire."

text: Henry Gowen is a cold, cynical man who formerly owned the coal mine. After the mine was shut down, Henry became the mayor of Hope Valley and still creates a cold, cynical presence whenever people are around him. Henry is highly disliked and feared in the town. He frequently uses bribery to get what he wants, which is never for the good of the town. In season 5, however, Henry seems to be turning into a new man, coming to the aid of the town often and actually helping Bill catch a criminal red-handed in season 5's "In My Dreams."

text: Rosemary "Rosie" LeVeaux Coulter is a flamboyant, enthusiastic actress from New York. She was briefly engaged to Jack Thornton, but they both realized that it wouldn't work out. Rosie immediately disliked Elizabeth and viewed her as "the competition," but eventually came to really care about Elizabeth, even if she has a hard time showing it. At the beginning of season 2, Rosemary began working at the cafe with Abigail and the two quickly became friends. Spending time with Abigail helped tone down some of Rosemary's enthusiasm and made her a more likable person. Rosemary even came to like Elizabeth, even if only on an acquaintance level. Truthfully, she cares about everyone in Hope Valley, especially Lee, with whom she shares an mutual attraction. When Rosie is not spending time with Lee, talking to Abigail, or dreaming about the glamorous life of an actress, she can often be found somewhere writing her weekly advice column for Hope Valley's newspaper! In season 3, Rosemary's friendship with Elizabeth deepened. Instead of viewing her as an adversary, she finds a friend in Elizabeth. Throughout season 3, Rosemary's relationship with Lee becomes more romantic. In "Heart Of A Hero," seeing that Lee needs to spend more time at the sawmill to help the new settlers find jobs, Rosemary tells Lee that the theater doesn't have to be built. He insists, but she says how important his job is. He smiles and tells her he will one day build her theatre, telling her that she is "the best part of his life." The couple shares in their first kiss. In "A Gentle Heart," Lee is injured. Thinking he is asleep, Rosemary pours out her heart to him, telling how much she loves him. In "Heartbreak," Rosemary is offered a job in Hollywood filming. This has always been Rosemary's dream, to be an actress. Lee unselfishly tells her to do whatever she feels best, but the thought of her leaving Hope Valley hurts him. Rosemary considers her options and realizes that her place is in Hope Valley, with Lee. Lee then tells her that he has another "role" that he thinks would be perfect for her and proposes marriage. She happily accepts. In "Hearts In Question," Rosemary enthusiastically plans for their wedding. The couple weds in the season 3 finale "Prayers From The Heart," with Elizabeth and Abigail as her maids of honor. Rosemary is one of Elizabeth's matrons of honor in season 5's "My Heart Is Yours."

text: Lee Coulter is a kind, laid-back, patient man who opens a sawmill in Hope Valley. When timber becomes Coal Valley's major source of natural resources, the town is renamed Hope Valley.  He shares a mutual attraction to Rosemary and proves to be one of the few people who can outwit her.  When she declines his romantic intentions, Lee recruits his friend, Molly Sullivan, to make Rosemary jealous; the ploy succeeds and Rosemary accepts his suit, appreciating Lee's good qualities.  Despite her dramatic and occasionally prickly personality, Lee's compassion and patience never fails with her.  With Rosemary's help, Lee beat Mr. Gowen at his own game in "Heart and Home."  When not at work, Lee enjoys being with friends, including Jack Thornton, who shares Lee's simple and laid back outlook, allowing the men to discuss their lives and exchange romantic advice. In season 3, Lee's mill is unfortunately sabotaged by a man inside. Through Bill and Jack's investigation, they find the culprit. In season 3's "Heart Of A Hero," Rosemary unselfishly gives up the theater that Lee promised to build her. Lee promises that one day, he will build her the theater at a time when he isn't so involved with the sawmill and finding people jobs. In "A Gentle Heart," Lee is injured. Thinking Lee is asleep, Rosemary pours out her heart to Lee, telling him how afraid she was when she heard he had been injured. He however hears each and every word. She told him how much she loves him and to never leave her. In the episode "Heartbreak," Lee thinks Rosemary may leave Hope Valley when she is offered a movie job in Hollywood. When she gives up the movie, seeing her future in Hope Valley with him, he asks her to marry him. The couple weds in the season 3 finale, "Prayers From The Heart." Jack serves the role of Lee's best man. Lee returns the honor for Jack in season 5's "My Heart Is Yours." In season 4's "Heart of A Fighter," we learn that Lee lost his brother Patrick at a young age.

text: Julie Thatcher is Elizabeth's hopeless romantic younger sister. She often gets herself into sticky situations by falling head over heels for men who aren't quite what they seem. In season 2 she gets involved with Jack's brother Tom, which causes trouble with her family and for Jack and Elizabeth's relationship.

text: Cat Montgomery is a kind, encouraging woman in Coal Valley. She is a widow and mother of three: Gabe, Miles, and Emily. Cat was one of the first mothers to show kindness to Elizabeth when she first came. She desperately wants her children to remember the good memories of their father as seen by her self-sacrificing acts in "Secrets and Lies."  Possessing a great sense of teamwork and encouragement, Cat supports the women of Coal Valley while working in the mines in "Cease and Desist." She is good friends with Elizabeth and Abigail. In "These Games," she also helps Jack catch a thief.

text: Florence Blakeley is a feisty gossip in Hope Valley. She often has a pessimistic perspective and always seems to find the negative, even in a very positive situation. In "Heart and Home," Abigail told Florence what she really thought about her, which causes Florence to rein in her negativity somewhat, though she remains fairly outspoken.  While not always likable, Florence adds spice to life in Hope Valley.

text: Molly Sullivan is a friend of Lee Coulter and Elizabeth Thatcher. Molly's husband was killed in the mine disaster. She has a daughter Rosaleen. In season 1's "A Telling Silence," Rosaleen has trouble in school because she misses her father so much. When she runs away, Elizabeth finds her in the mine, feeling guilty that she didn't bring her father his lunch the day of the disaster because she wanted to play with a friend instead. She fears her mother will blame her, but Elizabeth convinces her that Molly will "say that she loves her more than life itself." Molly is reunited with her daughter, to the joy of the town's people. In season 2's "With All My Heart," Lee feels it's time to "play hard to get" with Rosemary, so he enlists help from Molly. She pretends to be interested in him romantically. This ploy works and Rosemary admits that she does in fact like him. Molly is a kind woman and was among the first to welcome Elizabeth to town.

text: Clara Stanton is the wife of Abigail's late son Peter, and is a sweet, quiet, and sensitive young woman.  Abigail never knew she had a daughter-in-law until season 2's "Trials of the Heart;" with Peter having married Clara only three days before he was killed. In "Heart's Desire," Abigail invites Clara to come live with her in Hope Valley, an offer that Clara accepts.

text: Charles Kensington III is an old friend of Elizabeth with whom she reconnects while in Hamilton. He is interested in her, though her feelings for Jack get in the way of their relationship.

text: Production[edit]

text: The series, originally planned to be filmed in Colorado, is filmed south of Vancouver, British Columbia, on a farm surrounded by vineyards. The fictional frontier town of Coal Valley was erected in late 2013. Some of the set trimmings and a stage coach came from the Hell on Wheels set.[11] The Thatcher home is the University Women's Club of Vancouver.[12]

text: The series was renewed for a second season,[13] which aired from April 25 to June 13, 2015. Hallmark Channel announced in July 2015 that the series had been renewed for a third season, which aired from February 21 to April 10, 2016,[14] with a sneak peek airing during the 2015 Christmas season.[15]

text: In mid-2016, it was announced that Season 4 would premiere on the Hallmark Channel Christmas Day with a two-hour special. On April 11, 2016, Lissing and Krakow announced via the series' Facebook page that Hallmark Channel had renewed the series for a fourth season, which aired from February 19 to April 23, 2017.[16][17]

text: Filming for season five began in Vancouver on August 22, 2017, and ended on December 21, 2017.[18][19]

text: Broadcast[edit]

text: The first season of the series was subsequently picked up by CBC Television for rebroadcast as a summer series in 2015.[20] The network has since aired all five seasons.[21][22] The series became available internationally on Netflix in August 2017.


document_title: Polyphony

question_text: which person or group brought polyphonic music into the christian church

text: Polyphony

text: Origins[edit]

text: Traditional (non-professional) polyphony has a wide, if uneven, distribution among the peoples of the world[citation needed]. Most polyphonic regions of the world are in sub-Saharan Africa, Europe and Oceania. It is believed that the origins of polyphony in traditional music vastly predate the emergence of polyphony in European professional music. Currently there are two contradictory approaches to the problem of the origins of vocal polyphony: the Cultural Model, and the Evolutionary Model.[4] According to the Cultural Model, the origins of polyphony are connected to the development of human musical culture; polyphony came as the natural development of the primordial monophonic singing; therefore polyphonic traditions are bound to gradually replace monophonic traditions.[5] According to the Evolutionary Model, the origins of polyphonic singing are much deeper, and are connected to the earlier stages of human evolution; polyphony was an important part of a defence system of the hominids, and traditions of polyphony are gradually disappearing all over the world.[6]:198–210

text: Although the exact origins of polyphony in the Western church traditions are unknown, the treatises Musica enchiriadis and Scolica enchiriadis, both dating from c. 900, are usually considered the oldest extant written examples of polyphony. These treatises provided examples of two-voice note-against-note embellishments of chants using parallel octaves, fifths, and fourths. Rather than being fixed works, they indicated ways of improvising polyphony during performance. The Winchester Troper, from c. 1000, is the oldest extant example of notated polyphony for chant performance, although the notation does not indicate precise pitch levels or durations.[7]

text: European polyphony[edit]

text: Historical context[edit]

text: European polyphony rose out of melismatic organum, the earliest harmonization of the chant. Twelfth-century composers, such as Léonin and Pérotin developed the organum that was introduced centuries earlier, and also added a third and fourth voice to the now homophonic chant. In the thirteenth century, the chant-based tenor was becoming altered, fragmented, and hidden beneath secular tunes, obscuring the sacred texts as composers continued to play with this new invention called polyphony. The lyrics of love poems might be sung above sacred texts in the form of a trope, or the sacred text might be placed within a familiar secular melody. The oldest surviving piece of six-part music is the English rota Sumer is icumen in (c. 1240).[8]

text: These musical innovations appeared in a greater context of societal change. After the first millennium, European monks decided to start translating the works of Greek philosophers into the vernacular. Western Europeans were aware of Plato, Socrates, and Hippocrates during the Middle Ages. However they had largely lost touch with the content of their surviving works because the use of Greek as a living language was restricted to the lands of the Eastern Roman Empire (Byzantium). Once these ancient works started being translated thus becoming accessible, the philosophies had a great impact on the mind of Western Europe. This sparked a number of innovations in medicine, science, art, and music.

text: Western Europe and Roman Catholicism[edit]

text: European polyphony rose prior to, and during the period of the Western Schism. Avignon, the seat of the antipopes, was a vigorous center of secular music-making, much of which influenced sacred polyphony.[9]

text: It was not merely polyphony that offended the medieval ears, but the notion of secular music merging with the sacred and making its way into the papal court. It gave church music more of a jocular performance quality removing the solemn worship they were accustomed to. The use of and attitude toward polyphony varied widely in the Avignon court from the beginning to the end of its religious importance in the fourteenth century. Harmony was not only considered frivolous, impious, and lascivious, but an obstruction to the audibility of the words. Instruments, as well as certain modes, were actually forbidden in the church because of their association with secular music and pagan rites. Dissonant clashes of notes give a creepy feeling that was labeled as evil, fueling their argument against polyphony as being the devil’s music. After banishing polyphony from the Liturgy in 1322, Pope John XXII spoke in his 1324 bull Docta Sanctorum Patrum warning against the unbecoming elements of this musical innovation.[10] Pope Clement VI, however, indulged in it.

text: The oldest extant polyphonic setting of the mass attributable to one composer is Guillaume de Machaut's Messe de Nostre Dame, dated to 1364, during the pontificate of Pope Urban V.

text: More recently, the Second Vatican Council (1962–1965) stated: "Gregorian chant, other things being equal, should be given pride of place in liturgical services. But other kinds of sacred music, especially polyphony, are by no means excluded.... Religious singing by the people is to be skillfully fostered, so that in devotions and sacred exercises, as also during liturgical services, the voices of the faithful may ring out”.[11]

text: Notable works and artists[edit]

text:
Tomás Luis de Victoria
William Byrd, Mass for Five Voices
Thomas Tallis
Orlandus Lassus, Missa super Bella'Amfitrit'altera
Guillaume de Machaut, Messe de Nostre Dame
Jacob Obrecht
Palestrina, Missa Papae Marcelli
Josquin des Prez, Missa Pange Lingua
Gregorio Allegri, Miserere

text: Protestant Britain and the United States[edit]

text: English Protestant west gallery music included polyphonic multi-melodic harmony, including fuguing tunes, by the mid-18th century. This tradition passed with emigrants to North America, where it was proliferated in tunebooks, including shape-note books like The Southern Harmony and The Sacred Harp. While this style of singing has largely disappeared from British and North American sacred music, it survived in the rural Southern United States, until it again began to grow a following throughout the United States and even in places such as Ireland, the United Kingdom, Poland, Australia and New Zealand, among others.[citation needed]

text: Balkan region[edit]

text: Polyphonic singing in the Balkans is traditional folk singing of this part of southern Europe. It is also called ancient, archaic or old-style singing.[12][13]

text:
Byzantine chant
Ojkanje singing, in Croatia
Ganga singing, in Croatia, Montenegro and Bosnia and Herzegovina
Epirote singing, in northern Greece and southern Albania (see below)
Iso-polyphony in southern Albania (see below)
Gusle singing, in Serbia, Montenegro, Bosnia and Herzegovina, Croatia and Albania
Izvika singing, in Serbia
Woman choirs of Shopi (Bistritsa Babi) and Pirin, in Bulgaria

text: Incipient polyphony (previously primitive polyphony) includes antiphony and call and response, drones, and parallel intervals.

text: Balkan drone music is described as polyphonic due to Balkan musicians using a literal translation of the Greek polyphōnos ('many voices'). In terms of Western classical music, it is not strictly polyphonic, due to the drone parts having no melodic role, and can better be described as multipart.[14]

text: The polyphonic singing tradition of Epirus is a form of traditional folk polyphony practiced among Aromanians, Albanians, Greeks, and Macedonian Slavs in southern Albania and northwestern Greece.[15][16] This type of folk vocal tradition is also found in the Republic of Macedonia and Bulgaria. Albanian polyphonic singing can be divided into two major stylistic groups as performed by the Tosks and Labs of southern Albania. The drone is performed in two ways: among the Tosks, it is always continuous and sung on the syllable ‘e’, using staggered breathing; while among the Labs, the drone is sometimes sung as a rhythmic tone, performed to the text of the song. It can be differentiated between two-, three- and four-voice polyphony.

text: The phenomenon of Albanian folk iso-polyphony (Albanian iso-polyphony) has been proclaimed by UNESCO a "Masterpiece of the Oral and Intangible Heritage of Humanity". The term iso refers to the drone, which accompanies the iso-polyphonic singing and is related to the ison of Byzantine church music, where the drone group accompanies the song.[17][18]

text: Caucasus region[edit]

text: Georgia[edit]

text: Polyphony in the Republic of Georgia is arguably the oldest polyphony in the Christian world. Georgian polyphony is traditionally sung in three parts with strong dissonances, parallel fifths, and a unique tuning system based on perfect fifths. Georgian polyphonic singing has been proclaimed by UNESCO an Intangible Cultural Heritage of Humanity.[19] Polyphony plays a crucial role in Abkhazian traditional music. Polyphony is present in all genres where the social environment provides more than one singer to support the melodic line. Readers might remember (from the very beginning of this book) the recollection of I. Zemtsovsky, when a dozing Abkhazian started singing a drone to support a singer unknown to him. Abkhazian two and three-part polyphony is based on a drone (sometimes a double drone). Two part drone songs are considered by Abkhazian and Georgian scholars the most important indigenous style of Abkhazian polyphony. Two-part drone songs are dominating in Gudauta district, the core region of ethnic Abkhazians. Millennia of cultural, social and economic interactions between Abkhazians and Georgians on this territory resulted in reciprocal influences, and in particular, creation of a new, so-called “Georgian style” of three-part singing in Abkhazia, unknown among Adighis. This style is based on two leading melodic lines (performed by soloists - akhkizkhuo) singing together with the drone or ostinato base (argizra). Indigenous Abkhazian style of three-part polyphony uses double drones (in fourths, fifths, or octaves) and one leading melodic line at one time. Abkhazians use a very specific cadence: tetrachordal downward movement, ending on the interval fourth.[6]:55

text: Chechens and Ingushes[edit]

text: Both Chechen and Ingush traditional music could be very much defined by their tradition of vocal polyphony. As in other North Caucasian musical cultures, Chechen and Ingush polyphony is based on a drone. Unlike most of the other North Caucasian polyphonic traditions (where two-part polyphony is the leading type), Chechen and Ingush polyphony is mostly three-part. Middle part, the carrier of the main melody of songs, is accompanied by the double drone, holding the interval of the fifth “around” the main melody. Intervals and chords, used in Chechen and Ingush polyphony, are often dissonances (sevenths, seconds, fourths). This is quite usual in all North Caucasian traditions of polyphony as well, but in Chechen and Ingush traditional songs more sharp dissonances are used. In particular, a specific cadence, where the final chord is a dissonant three-part chord, consisting of fourth and the second on top (c-f-g), is quite unique for North Caucasia. Only on the other side of Caucasian mountains, in western Georgia, there are only few songs that finish on the same dissonant chord (c-f-g).[6]:60–61


document_title: World energy resources

question_text: where does the world get most of its energy

text: World energy resources

text: Fossil fuel[edit]

text: Remaining reserves of fossil fuel are estimated as:[3]

text:
Fuel
Proven energy reserves in ZJ (end of 2009)

Coal
19.8

Gas
  36.4

Oil
  8.1

text: These are the proven energy reserves; real reserves may be up to a factor 4 larger. Significant uncertainty exists for these numbers. Estimating the remaining fossil fuels on the planet depends on a detailed understanding of the Earth's crust. While modern drilling technology makes it possible to drill wells in up to 3 km of water to verify the exact composition of the geology, one half of the ocean is deeper than 3 km, leaving about a third of the planet beyond the reach of detailed analysis.

text: In addition to uncertainty in real reserves, there is significant uncertainty in technological and economical factors that impact what percentage of reserves can be recovered gainfully. In general the easiest to reach deposits are the first extracted. Factors affecting the cost of exploiting the remaining reserves include the accessibility of fossil deposits, the level of sulfur and other pollutants in the oil and the coal, transportation costs, and societal instability in producing regions.

text: Coal[edit]

text: Coal is the most abundant and burned fossil fuel. This was the fuel that launched the industrial revolution and has continued to grow in use; China, which already has many of the world's most polluted cities,[4] was in 2007 building about two coal-fired power plants every week.[5][6] Coal is the fastest growing fossil fuel and its large reserves would make it a popular candidate to meet the energy demand of the global community, short of global warming concerns and other pollutants.[7] According to the International Energy Agency the proven reserves of coal are around 909 billion tonnes, which could sustain the current production rate for 155 years,[8] although at a 5% growth per annum this would be reduced to 45 years, or until 2051. With the Fischer- Tropsch process it is possible to make liquid fuels such as diesel and jet fuel from coal. In the United States, 49% of electricity generation comes from burning coal.[9]

text: Natural Gas[edit]

text: Natural gas is a widely available fossil fuel with estimated 850 000 km³ in recoverable reserves and at least that much more using enhanced methods to release shale gas. Improvements in technology and wide exploration led to a major increase in recoverable natural gas reserves as shale fracking methods were developed. At present usage rates, natural gas could supply most of the world's energy needs for between 100 and 250 years, depending on increase in consumption over time.

text: Oil[edit]

text: It is estimated that there may be 57 ZJ of oil reserves on Earth (although estimates vary from a low of 8 ZJ,[10] consisting of currently proven and recoverable reserves, to a maximum of 110 ZJ[11]) consisting of available, but not necessarily recoverable reserves, and including optimistic estimates for unconventional sources such as tar sands and oil shale. Current consensus among the 18 recognized estimates of supply profiles is that the peak of extraction will occur in 2020 at the rate of 93-million barrels per day (mbd). Current oil consumption is at the rate of 0.18 ZJ per year (31.1 billion barrels) or 85-mbd.

text: There is growing concern that peak oil production may be reached in the near future, resulting in severe oil price increases.[12] A 2005 French Economics, Industry and Finance Ministry report suggested a worst-case scenario that could occur as early as 2013.[13] There are also theories that peak of the global oil production may occur in as little as 2–3 years. The ASPO predicts peak year to be in 2010. Some other theories present the view that it has already taken place in 2005. World crude oil production (including lease condensates) according to US EIA data decreased from a peak of 73.720 mbd in 2005 to 73.437 in 2006, 72.981 in 2007, and 73.697 in 2008.[14] According to peak oil theory, increasing production will lead to a more rapid collapse of production in the future, while decreasing production will lead to a slower decrease, as the bell-shaped curve will be spread out over more years.

text: In a stated goal of increasing oil prices to $75/barrel, which had fallen from a high of $147 to a low of $40, OPEC announced decreasing production by 2.2 mbd beginning 1 January 2009.[15]

text: Sustainability[edit]

text: Political considerations over the security of supplies, environmental concerns related to global warming and sustainability are expected to move the world's energy consumption away from fossil fuels. The concept of peak oil shows that about half of the available petroleum resources have been produced, and predicts a decrease of production.

text: A government move away from fossil fuels would most likely create economic pressure through carbon emissions and green taxation. Some countries are taking action as a result of the Kyoto Protocol, and further steps in this direction are proposed. For example, the European Commission has proposed that the energy policy of the European Union should set a binding target of increasing the level of renewable energy in the EU's overall mix from less than 7% in 2007 to 20% by 2020.[16]

text: The antithesis of sustainability is a disregard for limits, commonly referred to as the Easter Island Effect, which is the concept of being unable to develop sustainability, resulting in the depletion of natural resources.[17] Some estimate, assuming current consumption rates, current oil reserves could be completely depleted by the year 2050.[18]

text: Nuclear fuel[edit]

text: Nuclear energy[edit]

text: The International Atomic Energy Agency estimates the remaining uranium resources to be equal to 2500 ZJ.[19] This assumes the use of breeder reactors, which are able to create more fissile material than they consume. IPCC estimated currently proved economically recoverable uranium deposits for once-through fuel cycles reactors to be only 2 ZJ. The ultimately recoverable uranium is estimated to be 17 ZJ for once-through reactors and 1000 ZJ with reprocessing and fast breeder reactors.[20]

text: Resources and technology do not constrain the capacity of nuclear power to contribute to meeting the energy demand for the 21st century. However, political and environmental concerns about nuclear safety and radioactive waste started to limit the growth of this energy supply at the end of last century, particularly due to a number of nuclear accidents. Concerns about nuclear proliferation (especially with plutonium produced by breeder reactors) mean that the development of nuclear power by countries such as Iran and Syria is being actively discouraged by the international community.[21]

text: Although at the beginning of the 21st century uranium is the primary nuclear fuel worldwide, others such as thorium and hydrogen had been under investigation since the middle of the 20th century.

text: Thorium reserves significantly exceed those of uranium, and of course hydrogen is abundant. It is also considered by many to be easier to obtain than uranium. While uranium mines are enclosed underground and thus very dangerous for the miners, thorium is taken from open pits, and is estimated to be roughly three times as abundant as uranium in the Earth's crust.[22]

text: Since the 1960s, numerous facilities throughout the world have burned Thorium.

text: Nuclear fusion[edit]

text: Alternatives for energy production through fusion of hydrogen has been under investigation since the 1950s. No materials can withstand the temperatures required to ignite the fuel, so it must be confined by methods which use no materials. Magnetic and inertial confinement are the main alternatives (Cadarache, Inertial confinement fusion) both of which are hot research topics in the early years of the 21st century.

text: Fusion power is the process driving the sun and other stars. It generates large quantities of heat by fusing the nuclei of hydrogen or helium isotopes, which may be derived from seawater. The heat can theoretically be harnessed to generate electricity. The temperatures and pressures needed to sustain fusion make it a very difficult process to control. Fusion is theoretically able to supply vast quantities of energy, with relatively little pollution.[23] Although both the United States and the European Union, along with other countries, are supporting fusion research (such as investing in the ITER facility), according to one report, inadequate research has stalled progress in fusion research for the past 20 years.[24]

text: Renewable resources[edit]

text: Renewable resources are available each year, unlike non-renewable resources, which are eventually depleted. A simple comparison is a coal mine and a forest. While the forest could be depleted, if it is managed it represents a continuous supply of energy, vs. the coal mine, which once has been exhausted is gone. Most of earth's available energy resources are renewable resources. Renewable resources account for more than 93 percent of total U.S. energy reserves. Annual renewable resources were multiplied times thirty years for comparison with non-renewable resources. In other words, if all non-renewable resources were uniformly exhausted in 30 years, they would only account for 7 percent of available resources each year, if all available renewable resources were developed.[25]

text: Solar energy[edit]

text: Renewable energy sources are even larger than the traditional fossil fuels and in theory can easily supply the world's energy needs. 89 PW[26] of solar power falls on the planet's surface. While it is not possible to capture all, or even most, of this energy, capturing less than 0.02% would be enough to meet the current energy needs. Barriers to further solar generation include the high price of making solar cells and reliance on weather patterns to generate electricity. Also, current solar generation does not produce electricity at night, which is a particular problem in high northern and southern latitude countries; energy demand is highest in winter, while availability of solar energy is lowest. This could be overcome by buying power from countries closer to the equator during winter months, and may also be addressed with technological developments such as the development of inexpensive energy storage. Globally, solar generation is the fastest growing source of energy, seeing an annual average growth of 35% over the past few years. Japan, Europe, China, U.S. and India are the major growing investors in solar energy. Solar power's share of worldwide electricity usage at the end of 2014 was 1%.[27]

text: Wind power[edit]

text: The available wind energy estimates range from 300 TW to 870 TW.[26][28] Using the lower estimate, just 5% of the available wind energy would supply the current worldwide energy needs. Most of this wind energy is available over the open ocean. The oceans cover 71% of the planet and wind tends to blow more strongly over open water because there are fewer obstructions.

text: Wave and tidal power[edit]

text: At the end of 2005, 0.3 GW of electricity was produced by tidal power.[29] Due to the tidal forces created by the Moon (68%) and the Sun (32%), and the Earth's relative rotation with respect to Moon and Sun, there are fluctuating tides. These tidal fluctuations result in dissipation at an average rate of about 3.7 TW.[30]

text: Another physical limitation is the energy available in the tidal fluctuations of the oceans, which is about 0.6 EJ (exajoule).[31] Note this is only a tiny fraction of the total rotational energy of the Earth. Without forcing, this energy would be dissipated (at a dissipation rate of 3.7 TW) in about four semi-diurnal tide periods. So, dissipation plays a significant role in the tidal dynamics of the oceans. Therefore, this limits the available tidal energy to around 0.8 TW (20% of the dissipation rate) in order not to disturb the tidal dynamics too much.[citation needed]

text: Waves are derived from wind, which is in turn derived from solar energy, and at each conversion there is a drop of about two orders of magnitude in available energy. The total power of waves that wash against our shores add up to 3 TW.[32]

text: Geothermal[edit]

text: Estimates of exploitable worldwide geothermal energy resources vary considerably, depending on assumed investments in technology and exploration and guesses about geological formations. According to a 1999 study, it was thought that this might amount to between 65 and 138 GW of electrical generation capacity 'using enhanced technology'.[33] Other estimates range from 35 to 2000 GW of electrical generation capacity, with a further potential for 140 EJ/year of direct use.[34]

text: A 2006 report by MIT that took into account the use of Enhanced Geothermal Systems (EGS) concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050, just in the United States, for a maximum investment of 1 billion US dollars in research and development over 15 years.[35] The MIT report calculated the world's total EGS resources to be over 13 YJ, of which over 200 ZJ would be extractable, with the potential to increase this to over 2 YJ with technology improvements - sufficient to provide all the world's energy needs for several millennia.[35] The total heat content of the Earth is 13,000,000 YJ.[34]

text: Biomass[edit]

text: Production of biomass and biofuels are growing industries as interest in sustainable fuel sources is growing. Utilizing waste products avoids a food vs fuel trade-off, and burning methane gas reduces greenhouse gas emissions, because even though it releases carbon dioxide, carbon dioxide is 23 times less of a greenhouse gas than is methane. Biofuels represent a sustainable partial replacement for fossil fuels, but their net impact on greenhouse gas emissions depends on the agricultural practices used to grow the plants used as feedstock to create the fuels. While it is widely believed that biofuels can be carbon-neutral, there is evidence that biofuels produced by current farming methods are substantial net carbon emitters.[36][37][38] Geothermal and biomass are the only two renewable energy sources that require careful management to avoid local depletion.[39]

text: Hydropower[edit]

text: In 2005, hydroelectric power supplied 16.4% of world electricity, down from 21.0% in 1973, but only 2.2% of the world's energy.[40]