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Arable Land

Arable land

.]] In geography, arable land (from Latin arare, to plough ) is a form of agricultural land use, meaning land that can be (and is) used for growing crops. David Ricardo incorporated the idea of arable land into economic theory. Of the earth's 57 million square miles (148,000,000 km²) of land, more than 12 million square miles (31,000,000 km²) are arable. Most of the arable land on earth is around the largest rivers on earth. Some examples are: the Nile River, the Tigris and Euphrates Rivers, the Yellow River, the Amazon River, and the Rhine River. These rivers flood regularly, overspilling their banks. When the flood is over, the rivers recede, leaving behind rich silt. This silt is excellent fertilizer for crops. Even if the land is overfarmed, and all the nutrients are depleted from the soil, the land renews its fertility when the next flood comes. Rivers and streams can make desert land arable.

Unarable land

On unarable land, farming is nearly impossible unless more advanced methods of agriculture are used. Unarable land usually has no source of fresh water, and is often too hot (desert), too cold (arctic), too rocky, too mountainous, too salty, too rainy, too snowy, or too cloudy. Clouds block the sunlight plants need for photosynthesis (making sunlight into food). The plants starve without light. Starvation and nomadism often exist on unarable land. Unarable land is sometimes called 'wastes', 'badlands', 'worthless' or 'no man's land'. Sometimes, unarable land can be turned into arable land. New arable land makes more food, and can prevent starvation, saving lives. This also makes the country more self-sufficient and politically independent, because the country doesn't have to buy food from other countries. Making unarable land arable often involves digging new irrigation canals and new wells, aquaducts, desalination plants, planting trees for shade in the desert, hydroponics, fertilizer, nitrogen fertilizer, pesticides, reverse osmosis water processors, mylar insulation or other insulation against heat and cold, digging ditches and hills for protection against the wind, and greenhouses with internal light and heat for protection against the cold outside and to provide light in cloudy areas. Some examples of infertile unarable land being turned into fertile arable land are:
- Aran Island: This island off the west coast of Ireland, (not to be confused with the Isle of Arran in Scotland's Firth of Clyde), was unarable because it was too rocky. The people covered the island with a shallow layer of seaweed and sand from the ocean. This made it arable. Today, they grow crops there.
- Israel: Israel was mostly unarable desert until desalination plants were built on the coast. The plants turn salt water into fresh water for farming, drinking, and washing. They created their own large fresh water source. Some examples of fertile arable land being turned into infertile unarable land are:
- Droughts like the 'dust bowl' of the Great Depression in the U.S. turned farmland into desert.
- Rainforest Deforestation: The fertile tropical forests turn into infertile desert land.
- Romans' destruction of Carthage: At the end of the Punic Wars, the victorious Romans sowed the earth with salt, to symbolize total victory. The Roman symbol meant that Carthage would never grow back - their civilization ended. Crops won't generally grow in salty soil. This is why salt water from the ocean can't be used to water crops.
- Each year more arable land is lost to desertification and erosion from human industrial activities. Irrigation of farm land also increases the sodium, calcium, and magnesium in the soil. This process steadily concentrates salt in the ground, decreasing productivity for crops that are not salt-tolerant.
- Urban sprawl: In the United States, about 2.2 million acres (8,900 km²) of land was added to urban areas between 1992 and 2002, much of it farm land now paved.

External links

- [http://pages.prodigy.net/jhonig/bignum/qland2.html Surface Area of the Earth]
- [http://www.cnie.org/pop/conserving/landuse.htm Conserving Land: Population and Sustainable Food Production] Category:Agriculture Category:Horticulture

Geography

)]] Geography is the study of the locational and spatial variation of both natural and human phenomena on Earth. The word derives from the Greek words Ge (γη) or Gaea (γεια), both meaning "Earth", and graphein (γραφειν) meaning "to describe" and "to write". Modern geography is a diverse discipline that draws influence from almost every other arena of knowledge. Geographers engage with other disciplines according to their particular research interests and, while subjects such as biology and economics have a powerful influence, there are geographers who use concepts taken from subjects such as sociology, psychology and sports science, among many others. Within the discipline there have been many long-running tensions among those seeking to define geography - whether as a 'science' or as a 'humanity', as a 'systematic' subject or 'regional' specialism and so forth - which at various times have come close to destroying geography as an academic discipline. Whilst profound differences do exist among geographers, the dual concepts of space and place provide a commonality of interest, which gives the subject a unique identity.

Structure of geography

William Hughes - who taught the geography of the Holy Lands to divinity students at King's College London - defined geography in an address in 1863: :"Mere place names are not geography. To know by heart a whole gazeteer full of them would not, in itself, constitute anyone a geographer. Geography has higher aims than this: it seeks to classify phenomena (alike of the natural and of the political world insofar as it treats of the latter) to compare, to generalise, to ascend from effects to causes and in doing so to trace out the great laws of nature and to mark their influence upon man. In a word, geography is a science, a thing not of mere names, but of argument and reason, of cause and effect." This was a specific rejection of geography as a merely descriptive discipline and also defined it as inclusive of both the physical world and the human. Within the discipline, however, there are many areas of specialism. Modern geographers tend to specialise in one of the broad branches (or sub-branches). However, most introductory geography syllabuses seek to ensure that geographers have at least working knowledge of the main focus of each branch of the subject.

Physical geography

Physical geography (or physiogeography) focuses on geography as an Earth science. It aims to understand the physical layout of the Earth, its weather and global flora and fauna patterns. Many areas of physical geography make use of geology, particularly in the study of weathering and sediment movement. Physical Geography can be divided into the following broad categories:
- Geomorphology
- Hydrology
- Glaciology
- Biogeography
- Climatology
- Pedology (soil study)
- Coastal/Marine studies
- Geodesy
- Palaeogeography
- Environmental Geography and management
- Landscape ecology Exact lines between these different areas are often difficult to draw. Sometimes Oceanography is included as a branch within physical geography, but is now considered a separate subject in its own right. Related topics: Atmosphere - Archipelago - Continent - Desert - Island - Landform - Ocean - Sea - River - Lake - Ecology - Soil - Timeline of geography, paleontology - Geostatistics - Environmental science - Oceanography - Environmental studies

Human geography

Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various environments. It encompasses human, political, cultural, social, and economic aspects. While the major focus of human geography is not the physical landscape of the Earth (see Physical geography) it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Human geography can be divided into broad categories, such as:
- Economic geography
- Development geography
- Population geography or Demography
-
- Urban geography
- Social geography
- Behavioral geography
- Cultural geography
- Political geography, including Geopolitics
-
- Historical geography
- Regional science
- Strategic geography
- Military geography
- Feminist geography
- Distinction between these fields of study have become increasingly blurred over time and the above list should not be considered definitive. Related topics: Countries of the world - Country - Nation - State - Personal union - Province - County - City - Municipality - Central place theory - Urban morphology

Socio-environmental geography

During the time of environmental determinism, geography was defined not as the study of spatial relationships, but as the study of how humans and the natural environment interact. Though environmental determinism has died out, there remains a strong tradition of geographers addressing the relationships between people and nature. There are two main subfields of socio-environmental geography:
- cultural and political ecology (CAPE) and
- risk-hazards research.

Cultural and political ecology

Cultural ecology grew out of the work of Carl Sauer in geography and a similar school of thought in anthropology. It examined how human societies adapt themselves to the natural environment. Sustainability science has been one important outgrowth of this tradition. Political ecology arose when some geographers used aspects of critical geography to look at relations of power and how they affect people's use of the environment. For example, an influential study by Michael Watts argued that famines in the Sahel are caused by the changes in the region's political and economic system as a result of colonialism and the spread of capitalism.

Risk-hazards research

Research on hazards began with the work of geographer Gilbert F. White, who sought to understand why people live in disaster-prone floodplains. Since then, the hazards field has expanded to become a multidisciplinary field examining both natural hazards (such as earthquakes) and technological hazards (such as nuclear reactor meltdowns). Geographers studying hazards are interested in both the dynamics of the hazard event and how people and societies deal with it.

Historical geography

This branch seeks to determine how cultural features of the multifarious societies across the planet evolved and came into being. Study of the landscape is one of many key foci in this field - much can be deduced about earlier societies from their impact on their local environment and surroundings. ; What's in a name? Historical geography and the Berkeley School "Historical Geography" can indeed refer to the reciprocal effects of geography and history on each other. But in the United States, it has a more specialized meaning: This is the name given by Carl Ortwin Sauer of the University of California, Berkeley to his program of reorganizing cultural geography (some say all geography) along regional lines, beginning in the first decades of the 20th Century. To Sauer, a landscape and the cultures in it could only be understood if all of its influences through history were taken into account: Physical, cultural, economic, political, environmental. Sauer stressed regional specialization as the only means of gaining expertise on regions of the world. Sauer's philosophy was the principal shaper of American geographic thought in the mid-20th century. Regional specialists remain in academic geography departments to this day. But many geographers feel that it harmed the discipline in the long run: Too much effort was spent on data collection and classification, and too little on analysis and explanation. Studies became more and more area specific as later geographers struggled to find places to make names for themselves. This probably led in turn to the 1950s crisis in Geography which nearly destroyed it as an academic discipline.

History of geography

:See main article: History of geography History of geography The Greeks are the first known culture to actively explore geography as a science and philosophy. Mapping by the Romans as they explored new lands added new techniques. During the Middle Ages, Arabs such as Idrisi, Ibn Batutta, and Ibn Khaldun maintained the Greek and Roman techniques and developed new ones. Following the journeys of Marco Polo, interest in geography spread throughout Europe. The great voyages of exploration in 16th and 17th centuries revived a desire for both accurate geographic detail, and more solid theoretical foundations. This period is also known as Great Geographical Discoveries. By the 18th century, geography had become recognized as a discrete discipline and became part of a typical university curriculum in Europe (especially Paris and Berlin). Over the past two centuries the quantity of knowledge and the number of tools has exploded. There are strong links between geography and the sciences of geology and botany, as well as economics, sociology and demographics. In the West during the 20th century, the discipline of geography went through four major phases: environmental determinism, regional geography, the quantitative revolution, and critical geography.
Geographic techniques
As spatial interrelationships are key to this synoptic science, maps are a key tool. Classical cartography has been joined by a more modern approach to geographical analysis, computer-based geographic information systems (GIS).
- Cartography studies the representation of the Earth's surface with abstract symbols (map making). Although other subdisciplines of geography rely on maps for presenting their analyses, the actual making of maps is abstract enough to be regarded separately. Cartography has grown from a collection of drafting techniques into an actual science. Cartographers must learn cognitive psychology and ergonomics to understand which symbols convey information about the Earth most effectively, and behavioral psychology to induce the readers of their maps to act on the information. They must learn geodesy and fairly advanced mathematics to understand how the shape of the Earth affects the distortion of map symbols projected onto a flat surface for viewing. It can be said, without much controversy, that cartography is the seed from which the larger field of Geography grew. Most geographers will cite a childhood fascination with maps as an early sign they would end up in the field. mathematics
- Geographic Information Systems deals with the storage of information about the Earth for automatic retrieval by a computer, in an accurate manner appropriate to the information's purpose. In addition to all of the other subdisciplines of geography, GIS specialists must understand computer science and database systems. GIS has so revolutionized the field of cartography that nearly all mapmaking is now done with the assistance of some form of GIS software.
- Geographic quantitative methods deal with numerical methods peculiar to (or at least most commonly found in) geography. In addition to spatial analyses, you are likely to find things like cluster analysis, discriminant analysis, and non-parametric statistical tests in geographic studies.
- Geographic qualitative methods, or ethnographic research techniques, are used by human geographers. In cultural geography there is a tradition of employing qualitative research techniques also used in anthropology and sociology. Participant Observation and in-depth interviews provide human geographers with qualitative data. In their study geographers use four interrelated approaches:
- Systematic - Groups geographical knowledge into categories that can be explored globally
- Regional - Examines systematic relationships between categories for a specific region or location on the planet.
- Descriptive - Simply specifies the locations of features and populations.
- Analytical - Asks why we find features and populations in a specific geographic area.
Related fields

Urban and regional planning
Urban planning and regional planning use the science of geography to assist in determining how to develop (or not develop) the land to meet particular criteria, such as safety, beauty, economic opportunities, the preservation of the built or natural heritage, etcetera. The planning of towns, cities and rural areas may be seen as applied geography although it also draws heavily upon the arts, the sciences and lessons of history. Some of the issues facing planning are considered briefly under the headings of rural exodus, urban exodus and Smart Growth.
Regional science
In the 1950s the regional science movement arose, led by Walter Isard to provide a more quantitative and analytical base to geographical questions, in contrast to the more qualitative tendencies of traditional geography programs. Regional Science comprises the body of knowledge in which the spatial dimension plays a fundamental role, such as regional economics, resource management, location theory, urban and regional planning, transport and communication, human geography, population distribution, landscape ecology, and environmental quality.
Reference

See also

- List of geography topics
- Geographical terms
- List of countries
- Geography reference tables
- Map
- Geographical renaming
- Geographic magazines
- National Geographic Society (United States)
- National Geographic Bee (United States)
- Point of Beginning
- Royal Geographical Society (United Kingdom)
External links

- [http://www.confluence.org/ Confluence.org - A work in progress, involving travelling to every point on the globe where the lines of longitude and latitude intersect and taking a photograph in each direction.]
- [http://www.aag.org/ Association of American Geographers]
- [http://www.gisuser.com/ GISuser.com, information-rich portal about GIS]
- [http://www.populationdata.net/ PopulationData.net]
- [http://www.freemaps.de/ Free Maps Germany]
- [http://www.ericdigests.org/1996-4/high.htm Using Literature To Teach Geography in High Schools. ERIC Digest.]
- [http://ericdigests.org/1992-5/geography.htm Teaching Geography at School and Home. ERIC Digest.]
- [http://ericdigests.org/1996-1/geography.htm The National Geography Content Standards. ERIC Digest.]
- [http://www.geo-guide.de Geo-Guide] extensive list of academic resources on geography and earth science
- [http://www.geopium.org Geopium: Geopolitics of Illicit Drugs in Asia]
- [http://www.nationalgeographic.com/ National Geographic Online]
- [http://www.rgs.org Royal Geographical Society]
- [http://www.rcgs.org Royal Canadian Geographical Society]
- [http://www.canadiangeographic.ca Canadian Geographic]
- [http://hypergeo.free.fr Hypergeo : Geographical Encyclopedia]
- [http://www.rare-maps.com/links.cfm Antique and Rare Maps - Art Source International] - Links to rare and antique maps and to cartography resources.
- [http://www.mapinfo.com/ MapInfo GIS Software]
- Category:School subjects als:Geografie ko:지리학 ms:Geografi ja:地理学 simple:Geography th:ภูมิศาสตร์

Plough

:For the constellation known as "The Plough" see Ursa Major. ---- Ursa Major The plough (American spelling: plow) is a tool used in farming for initial cultivation of soil in preparation for sowing seed or planting. The plough can be regarded as a development of the pick, or of the spade. Ploughs were initially pulled by humans, later by oxen, and later still in some countries, by horses. Modern ploughs are, in industrialized countries, powered by tractors. Ploughing has several beneficial effects. The major reason for ploughing is to turn over the upper layer of the soil. This may also incorporate the residue from the previous crop into the soil. Ploughing reduces the prevalence of weeds in the fields, and makes the soil more porous, easing later planting. The early German word before sound-shift is plug and in Old Prussian plugis. After the German sound shift (p = pf) it became the modern German word Pflug.

History of the plough

Old Prussian When agriculture was first developed, simple hand held digging sticks or hoes would have been used in highly fertile areas, such as the banks of the Nile where the annual flood rejuvenates the soil, to create furrows wherein seeds could be sown. In order to regularly grow crops in less fertile areas, the soil must be turned to bring nutrients to the surface. The domestication of oxen in Mesopotamia, perhaps as early as the 6th millennium BC, provided mankind with the pulling power necessary to develop the plough. The very earliest ploughs were simple scratch-ploughs and consisted of a frame holding a vertical wooden stick that was dragged through the topsoil. These were much later developed into mouldboard ploughs (American spelling: moldboard) that turned the soil in one run across the field, depositing the weeds and undecomposed remains of the previous crop under the soil and raising the rain-percolated nutrients back to the surface. This plough also allowed for ploughing while the ground was wet. The water was drained due to channels formed under the overturned earth. This important innovation, introduced into Europe around 600AD, allowed the heavy northern soils to be worked. The mouldboard, carried below the frame, is tipped with a share, an asymmetric arrow-shaped device designed to slice through the ground horizontally as it moves forward. It also has a coulter, a sharpened blade or disc, attached to the frame of the plough to cut down through the ground, ahead of the share, and also to cut deepset and tough roots. A runner extending from behind the share to the rear of the plough controls the direction of the plough, because it is held against the bottom land-side corner of the new furrow being formed. The holding force is the weight of the sod, as it is raised and rotated, on the curved surface of the moldboard. Because of this runner, the mouldboard plough is harder to turn around than the scratch plough, and its introduction brought about a change in the shape of fields -- from mostly square fields into longer rectangular "strips" (hence the introduction of the furlong). The first commercially successful iron plough was the Rotherham plough, developed by Joseph Foljambe in Rotherham, England, in 1730. It was durable and light, and was engineered after the mathematical principles of James Small, who designed a mouldboard that would cut, lift and turn over the strip of earth. (It should be noted that all the major components of the Rotherham plough had been well known in China for millennia, and diffusion of technology from China, probably by the Dutch, is highly likely). Steel ploughs were developed during the Industrial Revolution and were lighter and more durable than ploughs made of iron or wood. The cast-steel plow was developed by U.S. blacksmith John Deere in the 1830s. By this time the hitch, to the draught animals, was adjustable so that the wheel at the front was held onto the ground. The first steel ploughs were walking ploughs, having two handles held by the ploughman to provide a degree of control over the depth and location of the furrow behind the draughting force. The ploughman often was also controlling the draught animal(s). Riding ploughs with wheels and a seat for the operator came later, and often had more than one share. A single draught horse can normally pull a single-furrow plough in clean, light, soil but in heavier soils two animals are needed, one walking on the land and one in the furrow. For ploughs with two or more furrows, one or more horses have to walk on the loose, ploughed, sod -- and that makes hard going for them. It is usual to rest such animals every half hour for about ten minutes. The Stump-Jump plough is an Australian invention of the 1870s, designed to cope with the breaking up of new farming land, that contains many tree stumps and rocks that would be very expensive to remove from paddocks. The plough uses a moveable weight to hold the ploughshare in position. When a tree stump or other obstruction such as a rock is encountered, the ploughshare is thrown upwards, clear of the obstacle, to avoid breaking the harness or linkage of the whole plough; ploughing can be continued when the weight is returned to the earth after the obstacle is passed. A simpler system, developed later, uses a concave disk (or a pair of them) set at a large angle to the direction of progress, that uses the concave shape to hold the disk into the soil -- unless something hard strikes the circumference of the disk, causing it to roll up and over the obstruction. As the arrangement is dragged forward, the sharp edge of the disk cuts the soil, and the concave surface of the rotating disk lifts and throws the soil to the side. It doesn't make as good a job as the mouldboard plough (but this is not considered a disadvantage, because it helps fight the wind erosion), but it does lift and break up the soil.

The modern plough

Traditional ploughs can only turn the soil over in one direction, as dictated by the shape of the mouldboard. The resulting method of traversing an entire field leads to the ridge and furrow effect seen in some ancient fields. Modern ploughs are reversible, having 2 sets of mouldboards: while one is working the land, the other is carried upside-down in the air. During the cultivation process, hydraulics are used to turn over the entire implement at each end of the field so that the second set of moulboards can be used. The field can then be traversed in such a way as to keep the land level, avoiding ridges and furrows. The modern reversible plough is mounted on a tractor via a three-point hitch. These commonly have sets of 2 up to 5 mouldboards, but semi-mounted ploughs, the lifting of which are supplemented by a wheel about half-way along its length, can have as many as 18. The hydraulic system of the tractor is used to lift and reverse the implement, as well as adjust furrow width and depth. The ploughman still has to set the draughting linkage from the tractor so that the plough is carried at the proper angle in the soil. This angle and depth can be controlled automatically by modern tractors.

Plough parts

- Frame
- Frog
- Share
- Mouldboard
- Runner
- Landside
- Shin
- Trashboard
- Handles
- Hitch
- Knife or coulter On modern ploughs and some older ploughs, the mouldboard is separate from the share and runner, allowing these parts to be replaced without replacing the mouldboard. Abrasion eventually destroys all parts of a plough that contact the soil.

Other uses

On a vehicle such as a tram, a plough is also the name commonly given to the pair of shoes, one pick-up and one return, both attached to a busbar, that draw power from a pair of live rails underneath the road.h

Land use

Land use is the pattern of construction and activity land is used for. Patterns of land use arise naturally in a culture though customs and practices, but land use may also be formally regulated by Zoning, other laws or private agreements such as restrictive covenants. For example, the setting aside of wilderness either publicly as a Wilderness Area or privately as a conservation easement.

Agriculture

working the land in the traditional way, with horse and plough]] Agriculture is the process of producing food, feed, fiber and other desired products by the cultivation of certain plants and the raising of domesticated animals (livestock). The practice of agriculture is also known as "farming", while scientists, inventors and others devoted to improving farming methods and implements are also said to be engaged in agriculture. More people in the world are involved in agriculture as their primary economic activity than in any other, yet it only accounts for four percent of the world's GDP.

Overview

GDP, Indonesia]] Agriculture can refer to subsistence agriculture, the production of enough food to meet just the needs of the farmer/agriculturalist and his/her family. It may also refer to industrial agriculture, (often referred to as factory farming) long prevalent in "developed" nations and increasingly so elsewhere, which consists of obtaining financial income from the cultivation of land to yield produce, the commercial raising of animals (animal husbandry), or both. Agriculture is also short for the study of the practice of agriculture—more formally known as agricultural science. Agricultural students are known (sometimes derisively) as "Aggies". Increasingly, in addition to food for humans and animal feeds, agriculture produces goods such as cut flowers, ornamental and nursery plants, timber or lumber, fertilizers, animal hides, leather, industrial chemicals (starch, sugar, ethanol, alcohols and plastics), fibers (cotton, wool, hemp, and flax), fuels (methane from biomass, biodiesel) and both legal and illegal drugs (biopharmaceuticals, tobacco, marijuana, opium, cocaine). Genetically engineered plants and animals produce specialty drugs. In the Western world, the use of gene manipulation, better management of soil nutrients, and improved weed control have greatly increased yields per unit area. At the same time, the use of mechanization has decreased labour requirements. The developing world generally produces lower yields, having less of the latest science, capital, and technology base. Modern agriculture depends heavily on engineering and technology and on the biological and physical sciences. Irrigation, drainage, conservation and sanitary engineering, each of which is important in successful farming, are some of the fields requiring the specialized knowledge of agricultural engineers. Agricultural chemistry deals with other vital farming concerns, such as the application of fertilizer, insecticides (see Pest control), and fungicides, soil makeup, analysis of agricultural products, and nutritional needs of farm animals.Plant breeding and genetics contribute additionally to farm productivity. Advanced seed engineering has allowed strains of seed to become perfect in every farming situation. Seeds can now germinate faster and adapt to shorter growing seasons in different climates. Present-day seed can resist the spraying of pesticides that kill all green-leaf plants. Hydroponics, a method of soilless gardening in which plants are grown in chemical nutrient solutions, may help meet the need for greater food production as the world's population increases. The packing, processing, and marketing of agricultural products are closely related activities also influenced by science. Methods of quick-freezing and dehydration have increased the markets for farm products (see Food preservation; Meat packing industry). Mechanization, the outstanding characteristic of late 19th and 20th century agricultural evolution, has eased much of the backbreaking toil of the farmer. More significantly, mechanization has enormously increased farm efficiency and productivity (see Agricultural machinery). Animals, including horses, mules, oxen, camels, llamas, alpacas, and dogs; however, are still used to cultivate fields, harvest crops and transport farm products to markets in many parts of the world. Airplanes, helicopters, trucks and tractors are used in agriculture for seeding, spraying operations for insect and disease control, Aerial topdressing, transporting perishable products, and fighting forest fires. Radio and television disseminate vital weather reports and other information such as market reports that concern farmers. Computers have become an essential tool for farm management. Aerial topdressing] According to the National Academy of Engineering in the US, agricultural mechanization is one of the 20 greatest engineering achievements of the 20th century. Early in the century, it took one American farmer to produce food for 2.5 people, where today, due to engineering technology (also, plant breeding and agrichemicals), a single farmer can feed over 130 people [http://www.greatachievements.org/greatachievements/ga_7_2.html]. This comes at a cost, however, of large amounts of energy input, from unsustainable, mostly fossil fuel, sources. Animal husbandry means breeding and raising animals for meat or to harvest animal products (like milk, eggs, or wool) on a continual basis. In recent years some aspects of industrial intensive agriculture have been the subject of increasing discussion. The widening sphere of influence held by large seed and chemical companies, meat packers and food processors has been a source of concern both within the farming community and for the general public. There has been increased activity of some people against some farming practices, raising chickens for food being one example. Another issue is the type of feedgiven to some animals that can cause Bovine Spongiform Encephalopathy in cattle. There has also been concern because of the disastrous effect that intensive agriculture has on the environment. In the US, for example, fertilizer has been running off into the Mississippi for years and has caused a dead spot in the Gulf of Mexico, where the Mississippi empties. Intensive agriculture also depletes the fertility of the land over time and the end effect is that which happened in the Middle East, were some of the most fertile farmland in the world was turned into a desert by intensive agriculture. The patent protection given to companies that develop new types of seed using genetic engineering has allowed seed to be licensed to farmers in much the same way that computer software is licensed to users. This has changed the balance of power in favor of the seed companies, allowing them to dictate terms and conditions previously unheard of. Some argue these companies are guilty of biopiracy. Soil conservation and nutrient management have been important concerns since the 1950s, with the best farmers taking a stewardship role with the land they operate. However, increasing contamination of waterways and wetlands by nutrients like nitrogen and phosphorus are of concern in many countries. Increasing consumer awareness of agricultural issues has led to the rise of community-supported agriculture, local food movement, slow food, and commercial organic farming, though these yet remain fledgling industries.

History

organic farming Archaeobotanists have traced the selection and cultivation of specific food plant characteristics, such as a semi-tough rachis and larger seeds, to just after the Younger Dryas (about 9,500 BC) in the early Holocene in the Levant region of the Fertile Crescent. Limited anthropological and archaeological evidence both indicate a grain-grinding culture farming along the Nile in the 10th millennium BC using the world's earliest known type of sickle blades. There is even earlier evidence for conscious cultivation and seasonal harvest: grains of rye with domestic traits have been recovered from Epi-Palaeolithic (10,000+ BC) contexts at Abu Hureyra in Syria, but this appears to be a localised phenomenon resulting from cultivation of stands of wild rye, rather than a definitive step towards domestication. It is not until ca. 8,500 BC, in middle-Eastern cultures referred to as Pre-Pottery Neolithic B (PPNB), where there is the first definite evidence for the emergence of a widespread subsistence economy that was dependent on domesticated plants and animals. In these contexts lie the origins of the eight so-called founder crops of agriculture: firstly emmer wheat, einkorn wheat, then hulled barley, pea, lentil, bitter vetch, chick pea and flax. These eight crops occur more or less simultaneously on PPNB sites in this region, although the consensus is that wheat was the first to be sown and harvested on a significant scale. There are many sites that date to between ca. 8,500 BC and 7,500 BC where the systematic farming of these crops contributed the major part of the inhabitants' diet. From the Fertile Crescent agriculture spread eastwards to Central Asia and westwards into Cyprus, Anatolia and, by 7,000 BC, Greece. Farming, principally of emmer and einkorn, reached northwestern Europe via southeastern and central Europe by ca. 4,800 BC (see, among others, Price, D. [ed.] 2000. Europe's First Farmers. Cambridge University Press; Harris, D. [ed.] 1996 The Origins and Spread of Agriculture in Eurasia. UCL Press). Europeing an alfalfa field]] The reasons for the earliest introduction of farming may have included climate change, but possibly there were also social reasons (e.g. accumulation of food surplus for competitive gift-giving). Most certainly there was a gradual transition from hunter-gatherer to agricultural economies after a lengthy period when some crops were deliberately planted and other foods were gathered from the wild. Although localised climate change is the favoured explanation for the origins of agriculture in the Levant, the fact that farming was 'invented' at least three times, possibly more, suggests that social reasons may have been instrumental. In addition to emergence of farming in the Fertile Crescent, agriculture appeared by at least 6,800 BC in East Asia (rice) and, later, in Central and South America (maize, squash). Small scale agriculture also likely arose independently in early Neolithic contexts in India (rice) and Southeast Asia (taro). Southeast Asia. Baked clay. Field Museum]] Full dependency on domestic crops and animals (i.e. when wild resources contributed a nutritionally insignificant component to the diet) was not until the Bronze Age. If the operative definition of agriculture includes large scale intensive cultivation of land, mono-cropping, organised irrigation, and use of a specialized labour force, the title "inventors of agriculture" would fall to the Sumerians, starting ca. 5,500 BC. Intensive farming allows a much greater density of population than can be supported by hunting and gathering and allows for the accumulation of excess product to keep for winter use or to sell for profit. The ability of farmers to feed large numbers of people whose activities have nothing to do with material production was the crucial factor in the rise of standing armies. The agriculturalism of the Sumerians allowed them to embark on an unprecedented territorial expansion, making them the first empire builders. Not long after, the Egyptians, powered by effective farming of the Nile valley, achieved a population density from which enough warriors could be drawn for a territorial expansion more than tripling the Sumerian empire in area. The invention of a three field system of crop rotation during the Middle Ages vastly improved agricultural efficiency. After 1492 the world's agricultural patterns were shuffled in the widespread exchange of plants and animals known as the Columbian Exchange. Crops and animals that were previously only known in the Old World were now transplanted to the New and vice versa. Perhaps most notably, the tomato became a favorite in European cuisine, while certain wheat strains quickly took to western hemisphere soils and became a dietary staple even for native North, Central and South Americans. By the early 1800s agricultural practices, particularly careful selection of hardy strains and cultivars, had so improved that yield per land unit was many times that seen in the Middle Ages and before, especially in the largely virgin lands of North and South America. With the rapid rise of mechanization in the 20th century, especially in the form of the tractor, the demanding tasks of sowing, harvesting and threshing could be performed with a speed and on a scale barely imaginable before. These advances have led to efficiencies enabling certain modern farms in the United States, Argentina, Israel, Germany and a few other nations to output volumes of high quality produce per land unit at what may be the practical limit.

Crops

Seed Testing

Seeds are tested for various qualities to ensure a high quality harvest, and to limit or prevent the spread of undesirable and invasive species. Seed test types Descriptions of various tests done on seed Seed related databases ISTA, the International Seed Testing Association, maintains a list of links to Seed Organizations worldwide:
- http://www.seedtest.org/en/content---1--1014--329.html

World production of major crops in 2004

In millions of metric tons, based on FAO estimates[http://faostat.fao.org/faostat/form?collection=Production.Crops.Primary&Domain=Production&servlet=1&hasbulk=0&version=ext&language=EN]: By crop types :Cereals 2,264 :Vegetables and melons 866 :Roots and Tubers 715 :Milk 619 :Fruit 503 :Meat 259 :Oilcrops 133 :Fish 130 (2001 estimate) :Eggs 63 :Pulses 60 :Vegetable Fiber 30 By individual crops :Sugar Cane 1,324 :Maize 721 :Wheat 627 :Rice 605 :Potatoes 328 :Sugar Beet 249 :Soybean 204 :Oil Palm Fruit 162 :Barley 154 :Tomato 120

Crop improvement

Tomato Tomato
- See main article on Plant breeding Domestication of plants is done in order to increase yield, improve disease resistance and drought tolerance, ease harvest and to improve the taste and nutritional value and many other characteristics. Centuries of careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant breeders use greenhouses and other techniques to get as many as three generations of plants per year so that they can make improvements all the more quickly. Plant selection and breeding in the 1920s and '30s improved pasture (grasses and clover) in New Zealand. Extensive radiation mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn and barley. For example, average yields of corn (maize) in the USA have increased from around 2.5 tons per hectare (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001, primarily due to improvements in genetics. Similarly, worldwide average wheat yields have increased from less than 1 t/ha in 1900 to more than 2.5 t/ha in 1990. South American average wheat yields are around 2 t/ha, African under 1 t/ha, Egypt and Arabia up to 3.5 to 4 t/ha with irrigation. In contrast, the average wheat yield in countries such as France is over 8 t/ha. Higher yields are due to improvements in genetics, as well as use of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging). [Conversion note: 1 bushel of wheat = 60 pounds (lb) ≈ 27.215 kg. 1 bushel of corn = 56 pounds ≈ 25.401 kg] In industrialized agriculture, crop "improvement" has often reduced nutritional and other qualities of food plants to serve the interests of producers. After mechanical tomato-harvesters were developed in the early 1960s, agricultural scientists bred tomatoes that were harder and less nutritious (Friedland and Barton 1975). In fact, a major longitudinal study of nutrient levels in numerous vegetables showed significant declines in the last 50 years; garden vegetables in the U.S. today contain on average 38 percent less vitamin B2 and 15 percent less vitamin C (Davis and Riordan 2004). Very recently, genetic engineering has begun to be employed in some parts of the world to speed up the selection and breeding process. The most widely used modification is a herbicide resistance gene that allows plants to tolerate exposure to glyphosate, which is used to control weeds in the crop. A less frequently used but more controversial modification causes the plant to produce a toxin to reduce damage from insects (c.f. Starlink). There are specialty producers who raise less common types of livestock or plants. Aquaculture, the farming of fish, shrimp, and algae, is closely associated with agriculture. Apiculture, the culture of bees, traditionally for honey—increasingly for crop pollination. See also : botany, List of domesticated plants, List of vegetables, List of herbs, List of fruit

Environmental problems

Agriculture may often cause environmental problems because it changes natural environments and produces harmful by-products. Some of the negative effects are:
- Nitrogen and phosphorus surplus in rivers and lakes.
- Detrimental effects of herbicides, fungicides, insecticides, and other biocides.
- Conversion of natural ecosystems of all types into arable land.
- Consolidation of diverse biomass into a few species.
- Erosion
- Depletion of minerals in the soil
- Particulate matter, including ammonia and ammonium off-gasing from animal waste contributing to air pollution
- Weeds - feral plants and animals
- Odor from agricultural waste
- Soil salination in dry areas.

Policy

Agricultural policy focuses on the goals and methods of agricultural production. At the policy level, common goals of agriculture include:
- Food safety: Ensuring that the food supply is free of contamination.
- Food security: Ensuring that the food supply meets the population's needs.
- Food quality: Ensuring that the food supply is of a consistent and known quality.
- Conservation
- Environmental impact
- Economic stability

Methods

There are various methods of agricultural production:
- aeroponics
- aerial topdressing
- agricultural machinery
- animal husbandry
- aquaculture
- beekeeping
- crop rotation
- Concentrated Animal Feeding Operation (CAFO, factory farming)
- composting
- dairy farming
- detasseling
- domestication
- fencing
- fertilizers
- greenhouse
- harvest
- heliciculture
- hybrid seed
- hydroponics
- Integrated Pest Management (IPM)
- irrigation
- livestock
- market gardening
- monoculture
- no-till farming
- organic farming
- plant breeding
- pollination management
- precision farming
- ranching
- season extension
- seed saving
- shepherding
- subsistence farming
- succession planting
- sustainable agriculture
- terracing
- vegetable farming
- tillage
- weed control

References

- Wells, Spencer: The Journey of Man : A Genetic Odyssey. Princeton University Press, 2003. ISBN: 069111532X
- Crosby, Alfred W.: The Columbian Exchange : Biological and Cultural Consequences of 1492. Praeger Publishers, 2003 (30th Anniversary Edition). ISBN: 0275980731
- Collinson, M. (editor): A History of Farming Systems Research. CABI Publishing, 2000. ISBN: 0851994059
- Davis, Donald R., and Hugh D. Riordan (2004) Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999. Journal of the American College of Nutrition, Vol. 23, No. 6, 669-682.
- Friedland, William H. and Amy Barton (1975) Destalking the Wily Tomato: A Case Study of Social Consequences in California Agricultural Research. Univ. California at Sta. Cruz, Research Monograph 15.·

External links

- [http://www.fao.org www.fao.org] — Food and Agriculture Organization of the United Nations World Agricultural Information Centre
- [http://www.fao.org/waicent/portal/statistics_en.asp www.fao.org] — The UN Statistical Databases
- [http://www.fao.org/ag/ FAO Agriculture Department] and its [http://www.fao.org/docrep/006/y5160e/y5160e00.HTM State of Food and Agriculture 2003-2004] with a focus on the impact of biotechnology
- [http://www.greenfacts.org/gmo/index.htm GM Crops in Agriculture] – A summary for non-specialists of the above FAO report by GreenFacts.
-
- [http://imperium.lenin.ru/~kaledin/tmp/agricltr.txt Agriculture: Demon Engine of Civilization] by John Zerzan
- [http://www.livinghistoryfarm.org/index.html History of farming in Nebraska, USA]

Specific countries

- [http://www.agr.gc.ca/ www.agr.gc.ca] — Agriculture & Agri-Food Canada
- [http://www.nationalpak.com www.nationalpak.com] — Agriculture of Pakistan
- [http://www.nationalacademies.org/agriculture/ www.nationalacademies.org] — Agriculture at the United States National Academies
- [http://www.usda.gov/ www.usda.gov] — United States Department of Agriculture
- [http://www.fas.usda.gov/currwmt.html Current World Production, Market and Trade Reports] from the Foreign Agricultural Service
- [http://www.ers.usda.gov/ USDA's main source of economic information and research] from the Economic Research Service
- [http://www.ars.usda.gov/ In-house Research Arm] from the Agricultural Research Service
- [http://www.nal.usda.gov/ National Agricultural Library]
- [http://www.trader-china.com/Agriculture/index.html Agriculture Directory] ko:농업 ja:農業 nb:Landbruk simple:Agriculture

Theory

Theory has a number of distinct meanings in different fields of knowledge, depending on the context and their methodologies.

Etymology

The word ‘theory’ derives from the Greek ‘theorein’, which means ‘to look at’. According to some sources, it was used frequently in terms of ‘looking at’ a theatre stage, which may explain why sometimes the word ‘theory’ is used as something provisional or not completely resembling real. The term ‘theoria’ (a noun) was already used by the scholars of ancient Greeks.

Science

In scientific usage, a theory does not mean an unsubstantiated guess or hunch, as it does in other contexts. Neither is a scientific theory a fact. Scientific theories are never proven to be true, but can be disproven. All scientific understanding takes the form of hypotheses, theories, or laws. Theories are typically ways of explaining why things happen, often, but not always after the fact that they happen is no longer in scientific dispute. In referring to the "theory of global warming" for example, the worldwide temperatures have been measured and seem to be increasing. The "theory of global warming" refers instead to scientific work that attempts to explain how and why this could be happening. In various sciences, a theory is a logically self-consistent model or framework for describing the behavior of a certain natural or social phenomenon, thus either originating from or supported by experimental evidence (see scientific method). In this sense, a theory is a systematic and formalized expression of all previous observations made that is predictive, logical, testable, and has never been falsified. In physics, the term theory is generally used for a mathematical framework derived from a small set of basic principles, capable of producing experimental predictions for a given category of physical systems. A good example is electromagnetic theory, which encompasses the results that can be derived from Maxwell's equations. This theory is usually taken to be synonymous with classical electromagnetism. The term theoretical is used in science to describe a result that is predicted by theory but has not yet been observed. For example, until recently, black holes were considered theoretical. It is not uncommon in the history of physics for theory to produce predictions that are later confirmed by experiment; failed predictions, however, also occur, and sometimes work to falsify a theory. Conversely, at any time in the study of physics there can also be confirmed experimental results that are not yet explained by theory. For a given body of theory to be considered part of established scientific knowledge, it is usually necessary for it to characterize a critical experiment, namely an experimental result not predicted by any existing established theory. Unfortunately, usage of the term theory is muddled by scientists in such examples as string theory and various theories of everything, which are more correctly characterized at present as a bundle of competing hypotheses or a protoscience. A hypothesis, however, is still vastly more reliable than a conjecture, which is at best an untested guess consistent with selected data and often simply a belief based on non-repeatable experiments, anecdotes, popular opinion, "wisdom of the ancients," commercial motivation, or mysticism. Even worse, theory has almost the opposite meaning in common use than its definition in the sciences, and this change can be seen in modern dictionaries which now list theory as a "guess or hunch" in preference to the former scientific definition that used to be the dominant one. In everyday language, a theory is (Morrison, 2005, p. 39): :...a hunch that a detective comes up with in a murder mystery. It is one of several competing ideas, none of them proved. Fringe theories and conspiracy theories are crazy ideas that are out of the mainstream. New medicines or changes in the tax laws may be good in theory but don't work in practice. Among some scientists, theorists are thought to lack solid grounding in the facts... Even scientists tend to use the now common definition in everyday speech and writing, being more careful in published material. Yet a California Academy of Sciences exhibit on fossils included this line: "Scientists have a number of theories about why ammonites develop spines on their shells" (emphasis added; from Morrison, 2005).

Models

Humans construct theories in order to explain, predict and master phenomena (e.g. inanimate things, events, or the behaviour of animals). In many instances, this is seen to be the construction of models of reality. A theory makes generalizations about observations and consists of an interrelated, coherent set of ideas and models. According to Stephen Hawking in A Brief History of Time, "a theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations." He goes on to state, "any physical theory is always provisional, in the sense that it is only a hypothesis; you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory." This is borne out by what Isaac Asimov said in "Understanding Physics". He spoke of theories as "arguments" where one deduces a "scheme" or model. Arguments or theories always begin with Hawking's "arbitrary elements" which are here described as "assumptions". An assumption according to Asimov is "something accepted without proof, and it is incorrect to speak of an assumption as either true or false, since there is no way of proving it to be either. (If there were, it would no longer be an assumption.) It is better to consider assumptions as either useful or useless, depending on whether deductions made from them corresponded to reality. .. On the other hand, it seems obvious that assumptions are the weak points in any argument, as they have to be accepted on faith in a philosophy of science that prides itself on its rationalsim. Since we must start somewhere, we must have assumptions, but at least let us have as few assumptions as possible." (See Ockham's razor) An example of using assumptions to formulate a theory is when Albert Einstein put forth his Special Theory of Relativity. He took two phenomena that had been observed i.e. that the "addition of velocities" is valid (Galilean transformation) and that light did not appear to have an "addition of velocities" (Michelson-Morley experiment). He assumed that both of these were correct and formulated his theory based on these assumptions by simply altering the Galilean transformation to accommodate the lack of addition of velocities with regard to the speed of light. Therefore, the model created in his theory is based on the assumption that light maintains a constant velocity (or more precisely the speed of light is a constant). An example of how theories are models can be seen from theories on the planetary system. The Greeks formulated theories that were recorded by the astronomer Ptolemy. In Ptolemy's planetary model, the earth was at the center, the planets and the sun made circular orbits around the earth, and the stars were on a sphere outside of the orbits of the planet and the earth. Retrograde motion of the planets was explained by smaller circular orbits of individual planets. This could actually be built into a literal model and illustrated as a model. Mathematical calculations could be made for the prediction of where the planets would be to a great degree of accuracy, so that this model of the planetary system survived over 1500 years until the time of Copernicus. So one can see how a theory is a model of reality that explains certain scientific facts yet may not be a true picture of reality and another more accurate theory can later replace the previous model.

Types of theories

There are two uses of the word theory; a supposition which is not backed by observation is known as a conjecture, and if backed by observation it is a hypothesis. Most theory evolves from hypotheses, but the reverse is not true: many hypotheses turn out to be false and so do not evolve into theory. A theory is different from a theorem. The former is a model of physical events and cannot be proved from basic axioms. The latter is a statement of mathematical fact which logically follows from a set of axioms. A theory is also different from a physical law in that the former is a model of reality whereas the latter is a statement of what has been observed. Theories can become accepted if they are able to make correct predictions and avoid incorrect ones. Theories which are simpler, and more mathematically elegant, tend to be accepted over theories which are complex. Theories are more likely to be accepted if they connect a wide range of phenomena. The process of accepting theories, or of extending existing theory, is part of the scientific method.

Further explanation of a scientific theory

As noted above, in common usage a theory is defined as little more than a guess or a hypothesis. But in science and generally in academic usage, a theory is much more than that. A theory is an established paradigm that explains all or much of the data we have and offers valid predictions that can be tested. In science, a theory is not considered fact or infallible, because we can never assume we know all there is to know. Instead, theories remain standing until they are disproved, at which point they are thrown out altogether or modified to fit the additional data. Theories start out with empirical observations such as "sometimes water turns into ice." At some point, there is a need or curiosity to find out why this is, which leads to a theoretical/scientific phase. In scientific theories, this then leads to research, in combination with auxiliary and other hypotheses (see scientific method), which may then eventually lead to a theory. Some scientific theories (such as the theory of gravity) are so widely accepted that they are often seen as laws. This, however, rests on a mistaken assumption of what theories and laws are. Theories and laws are not rungs in a ladder of truth, but different sets of data. A law is a general statement based on observations. A canonical example of a disproved theory is the geocentric model of the universe proposed by Ptolemy. Evidence, in the form of Galileo's observation of the phases of Venus in 1610, was produced which was completely incompatible with the predictions set forth by the theory. This falsification, though, did not necessarily mean that only one alternative theory was necessarily the "correct" replacement — both the Copernican system and the Tychonian system predicted the phases of Venus.

Characteristics

In science, a body of descriptions of knowledge is usually only called a theory once it has a firm empirical basis, i.e., it # is consistent with pre-existing theory to the extent that the pre-existing theory was experimentally verified, though it will often show pre-existing theory to be wrong in an exact sense, # is supported by many strands of evidence rather than a single foundation, ensuring that it probably is a good approximation if not totally correct, # makes predictions that might someday be used to disprove the theory, # is tentative, correctable and dynamic, in allowing for changes to be made as new data is discovered, rather than asserting certainty, and # is the most parsimonious explanation, sparing in proposed entities or explanations, commonly referred to as passing Occam's Razor. This is true of such established theories as special and general relativity, quantum mechanics, plate tectonics, evolution, etc. Theories considered scientific meet at least most, but ideally all, of the above criteria. The fewer which are matched, the less scientific it is; those that meet only several or none at all, cannot be said to be scientific in any meaningful sense of the word. Karl Popper described the characteristics of a scientific theory as: 1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations. 2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory. 3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is. 4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice. 5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks. 6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory. (I now speak in such cases of "corroborating evidence.") 7. Some genuinely testable theories, when found to be false, are still upheld by their admirers — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status. (I later described such a rescuing operation as a "conventionalist twist" or a "conventionalist stratagem.") One can sum up all this by saying that the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability."--end quote

Mathematics

In mathematics, the word theory is used informally to refer to certain distinct bodies of knowledge about mathematics. This knowledge consists of axioms, definitions, theorems and computational techniques, all related in some way by tradition or practice. Examples include group theory, set theory, Lebesgue integration theory and field theory. The term "theory" also has a formal usage in mathematics, particularly in mathematical logic and model theory. A theory in this sense is a set of statements closed under certain rules of inference. A typical theory will present certain axioms and rules, corresponding to a useful or interesting abstraction, and then derive non-obvious theorems from those axioms. The resulting theorems often provide solutions to real-world problems which correspond to the original abstraction. Obvious examples include arithmetic (abstracting the concept of number), geometry (the concept of space), and probability (the concept of randomness). However, Gödel's incompleteness theorem shows that no consistent theory capable of defining the concept of natural numbers can derive all true statements about those numbers. This sets a fundamental limit to the applicability of any mathematical system.

Other fields

Theories exist not only in the so-called hard sciences; but in all fields of academic study, from philosophy to music to literature. In the humanities, theory is often used as an abbreviation for critical theory or literary theory, referring to continental philosophy's aesthetics or its attempts to understand the structure of society and to conceptualize alternatives. In philosophy, theoreticism refers to the overuse of theory.

List of famous theories

- Mathematics: Axiomatic set theory - Chaos theory - Graph theory - Number theory - Probability theory
- Statistics : Extreme value theory
- Physics: Theory of relativity - Special relativity - General relativity - Quantum field theory - Acoustic theory - Antenna theory
- Planetary science: Giant impact theory
- Biology: Evolution by natural selection - Cell theory
- Chemistry: Atomic theory - Kinetic theory of gases
- Geology: Continental drift - Plate tectonics
- Climatology: Global warming
- Humanities: Critical theory
- Sociology: Social Theory - Critical social theory - Value theory
- Philosophy: Speculative reason
- Literature: Literary theory
- Music: Music theory
- Computer science: Algorithmic information theory - Computation theory
- Games: Rational choice theory - Game theory
- Other: Obsolete scientific theories - Phlogiston theory

Reference

- Morrison, David. 2005. "Only a theory? Framing the evolution/creation issue". Skeptical Inquirer, 29 (6): 37-41.
- Karl Popper, Conjectures and Refutations, London: Routledge and Keagan Paul, 1963, pp. 33-39; from Theodore Schick, ed., Readings in the Philosophy of Science, Mountain View, CA: Mayfield Publishing Company, 2000, pp. 9-13. Theories Category:Scientific method Category:Mathematical terminology Category:Philosophy of science ja:理論

Nile

:For alternative meanings of "Nile", see Nile (disambiguation) The Nile (Arabic: النيل an-nīl), in Africa, is one of the two longest rivers on Earth.

Terminology of the Nile

The word "Nile" comes from the word Neilos (Νειλος), a Greek name for the Nile. Another Greek name for the Nile was Aigyptos (Αιγυπτος), which itself is the source of the name "Egypt".

Longest river

The Nile is usually considered the longest river in the world, but whether the Nile is actually longer than South America's Amazon still remains the subject of much debate. This is, for the most part, due to two reasons: first, the lengths of rivers vary over time and, second, the point from which the length of a river is measured is not always agreed upon. The Nile also carries far less water than the Amazon.

Branches

Amazon There are two great branches of the Nile: the White Nile, from equatorial East Africa, and the Blue Nile, from Ethiopia. Both branches formed on the western flanks of the East African Rift, which is the southern African part of the Great Rift Valley.

White Nile

Lake Victoria, which lies between Uganda, Kenya and Tanzania is considered to be the source of the Nile, although the lake itself has feeder rivers of considerable size from the other Great Lakes of Africa. In particular, the farthest headstream of the Nile is the Ruvyironza River in Burundi, which is an upper branch of the Kagera River. The Kagera flows for 690 km (429 miles) before reaching Lake Victoria. Leaving Lake Victoria, the river is known as the Victoria Nile. It flows further for approximately 500 km (300 miles), through Lake Kyoga, until it reaches Lake Albert. After leaving Lake Albert, the river is known as the Albert Nile. It then flows into Sudan, where it becomes known as the Bahr al Jebel. At the confluence of the Bahr al Jebel with the Bahr el Ghazal, itself 720 km (445 miles) long, the river beomes known as the Bahr al Abyad, or the White Nile, from the clay suspended in its waters. From there, the river flows to Khartoum.

Blue Nile

Meanwhile, the Blue Nile (or Bahr al Azraq to Sudanese; Abbay to Ethiopians) springs from Lake Tana in the Ethiopian Highlands. The Blue Nile flows about 1,400 km (850 miles) to Khartoum, where the Blue Nile and White Nile join to form "the Nile." Most of the water carried by the Nile (about 85%) originates from Ethiopia, but this runoff only happens in summer, when the great rains fall on the Ethiopian Plateau; the rest of the year the great rivers draining Ethiopia to the Nile (Sobat, Blue Nile, and Atbara) flow weakly or are dry. Khartoum)]]

The Nile

After the Blue and White Niles merge, the only remaining major tributary is the Atbara River, which originates in Ethiopia north of Lake Tana, and is approximately 800 km (500 miles) long. It joins the Nile approximately 300 km (200 miles) past Khartoum. The Nile is also unusual in that its last tributary (the Atbara) joins it approximately halfway to the sea. From that point north, the Nile diminishes because of evaporation. The Nile in Sudan is distinctive for two reasons: 1) it flows over 6 groups of cataracts, from the first at Aswan to the sixth at Sabaloka (just north of Khartoum); and 2) it reverses course for much of its course, flowing back to the SW before returning to flow north again to the sea. This is the "Great Bend of the Nile". 6 groups of cataracts The Nile then reaches the man-made Lake Nasser, impounded behind the Aswan High Dam 270 km (170 miles) into Egypt from the Sudanese border. Since 1998 some of Lake Nasser's waters have spilt westward to form the Toshka Lakes. From Lake Nasser the main channel flows north through Egypt and into the Mediterranean Sea; a side channel, the Bahr Yussef, splits from the main channel downriver from the city of Asyut, and empties into the Fayum. Where the Nile meets the Mediterranean, the Nile Delta, is the eponym of all river deltas worldwide. Enrichment from Nile sediments carried eastward by currents nurture the fishing industries of the Eastern Mediterranean, or used to before the Aswan High Dam was built.

History of the Nile

The Nile (iteru in Ancient Egyptian) was the lifeline of the ancient Egyptian civilization, with most of the population and all of the cities of Egypt resting along those parts of the Nile valley lying north of Aswan. The Nile has been the lifeline for Egyptian culture since the Stone Age. Climate change — or perhaps overgrazing — about 8000 BC desiccated the pastoral lands of Egypt to form the Sahara and the tribes naturally migrated to the river, where they developed a settled agricultural economy and more centralized society. Despite the attempts of the Greeks and Romans (who were unable to penetrate the Sudd), the source of the Nile was unknown until the 19th century, when John Hanning Speke was the first to identify it as Lake Victoria. Various earlier expeditions since ancient times had failed to determine the river's source, thus yielding classical Hellenistic and Roman representations of the river as a male god with his face and head obscured in drapery. Speke was part of a 1856–1858 expedition led by Richard Francis Burton to search for the source of the Nile by entering Africa from Dar-Es-Salam (modern Tanzania). Burton was convinced that Lake Tanganyika was the source, but it was Speke who, leaving a sick Burton behind, found the large body of water now known as Lake Victoria and convinced himself that this was the Nile's true source. Speke returned with James Augustus Grant in 1860-1863 for further explorations around Lake Victoria and traced the Nile northwards to Gondokoro, on the southern boundary of the Sudd. The White Nile Expedition, led by South African national Hendri Coetzee, was to become the first to navigate the Nile in its entire length. The expedition took off from The Source of the Nile in Uganda on January 17, 2004 and arrived safely at the Mediterranean in Rosetta, Egypt, 4 months and 2 weeks later. National Geographic are releasing a feature film about the expedition in towards the end of 2005, to be entitled The Longest River. On April 28, 2004, geologist Pasquale Scaturro and his partner, kayaker and documentary filmmaker Gordon Brown became the first people to navigate the Blue Nile, from Lake Tana in Ethiopia to the beaches of Alexandria on the Mediterranean. Though their expedition included a number of others, Brown and Scaturro were the only ones to remain on the expedition for the entire journey. They chronicled their adventure with an IMAX camera and two handheld video cams, sharing their story in the IMAX film "Mystery of the Nile," and in a book of the same title. Despite this attempt, the team was forced to use outboard motors for most of their journey and it was not until January 29, 2005 when Canadian Les Jickling and New Zealander Mark Tanner reached the Mediterranean Sea that the river had been paddled for the first time under human power. The Nile still supports much of the population of Africans living along its banks, as well as Egyptians; the latter living between otherwise inhospitable regions of the Sahara Desert. The river flooded every summer, depositing fertile soil on the fields. The flow of the river is disturbed at several points by cataracts, which are sections of faster flowing water with many small islands, shallow water, and rocks, forming an obstacle to navigation by boats. The sudd in the Sudan also forms a formidable obstacle for navigation and flow of water, to the extent that Egypt had once attempted to dig a canal (the Jongeli Cananl) to improve the flow of this stagnant mass of water (also known as Lake No). boat The Nile was, and still is, used to transport goods to different places along its long path; especially since winter winds in this area blow up river, the ships could travel up with no work by using the sail, and down using the flow of the river. While most Egyptians still live in the Nile valley, the construction of the Aswan High Dam (finished in 1970) to provide hydroelectricity ended the summer floods and their renewal of the fertile soil. Cities on the Nile include Khartoum, Aswan, Luxor (Thebes), and the Giza–Cairo conurbation. The first cataract, the closest to the mouth of the river, is at Aswan to the north of the Aswan Dams. The Nile north of Aswan is a regular tourist route, with cruise ships and traditional wooden sailing boats known as feluccas. In addition, many "floating hotel" cruise boats ply the route between Luxor and Aswan, stopping in at Edfu and Kom Ombo along the way. It used to be possible to sail on these boats all the way from Cairo to Aswan, but security concerns have shut down the northernmost portion for many years.

Flooding of the Nile

The annual cycles of the Nile were very important to the lives of ancient Egyptians. The Nile 'mysteriously' but predictably rose each summer to flood and fertilize the land, without rain and in the hottest time of the year. A good flood and Egypt's wealth was assured; a poor flood or too great of a flood and Egypt would suffer. The cyclic mystery created awe and stimulated worship, and the job of recording the history of Nile flooding, when the Nile was expected to flood, and the locations of farmers' plots after the floodwaters receded stimulated creation of the first scientific instrument (the Nilometer), astronomy, and surveying. The concerns of ancient Egyptians for a good flood were justified. The failure of the Nile floods and the generally low level of the river is thought to have been responsible for the collapse of the Old Kingdom about 4200 years ago. These concerns are captured in the Bible, where Joseph correctly interpreted Pharoah's dreams of 7 years of abundance and 7 years of poverty in Egypt to relate to good and then bad Nile floods. Ledyard, in his Travels, speaks contemptuously of this celebrated wonder:—"This is the mighty, the sovereign of rivers—the vast Nile that has been metamorphosed into one of the wonders of the world! Let me be careful how I read, and, above all, how I read ancient history. You have heard, and read too, much of its inundations. If the thousands of large and small canals from it, and the thousands of men and machines employed to transfer, by artificial means, the water of the Nile to the meadows on its banks—if this be the inundation that is meant, it is true; any other is false; it is not an inundating river." More recently, drought during the 1980s led to widespread starvation in Ethiopia and Sudan but Egypt was protected from drought by water impounded in Lake Nasser.

The Eonile

The present Nile is at least the fifth river that has flowed north from the Ethiopian Highands. Satellite imagery was used to identify dry watercourses in the desert to the west of the Nile. An Eonile canyon, now filled by surface drift, represents an ancestral Nile called the Eonile that flowed during the later Miocene. The Eonile transported clastic sediments to the Mediterranean, where several gas fields have been discovered within these sediments. South of Cairo, the sand-filled canyon can reach a depth of up to 1400 meters. During the late Miocene Messinian Salinity Crisis, when the Mediterranean Sea was a closed basin and sealevel in the sea dropped approximately 1500 m, the Nile cut its course down to the new base level until it was several hundred feet below world ocean level at Aswan. This huge canyon is now full of later sediment. Formerly Lake Tanganyika drained northwards into the Nile, until the Virunga Volcanoes blocked its course in Rwanda. That would have made the Nile much longer, with its longest headwaters in northern Zambia.