Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use. Soil classification is a dynamic subject, from the structure of the system itself, to the definitions of classes, in the application in the field. Soil classification can be approached from the perspective of soil as a material and soil as a resource. Engineers geotechnical engineers, classify soils according to their engineering properties as they relate to use for foundation support or building material. Modern engineering classification systems are designed to allow an easy transition from field observations to basic predictions of soil engineering properties and behaviors; the most common engineering classification system for soils in North America is the Unified Soil Classification System. The USCS has three major classification groups: coarse-grained soils; the USCS further subdivides the three major soil classes for clarification.
It distinguishes sands from gravels by grain size, further classifying some as "well-graded" and the rest as "poorly-graded". Silts and clays are distinguished by the soils' Atterberg limits, separates "high-plasticity" from "low-plasticity" soils as well. Moderately organic soils are considered subdivisions of silts and clays, are distinguished from inorganic soils by changes in their plasticity properties on drying; the European soil classification system is similar, differing in coding and in adding an "intermediate-plasticity" classification for silts and clays, in minor details. Other engineering soil classification systems in the United States include the AASHTO Soil Classification System, which classifies soils and aggregates relative to their suitability for pavement construction, the Modified Burmister system, which works to the USCS, but includes more coding for various soil properties. A full geotechnical engineering soil description will include other properties of the soil including color, in-situ moisture content, in-situ strength, somewhat more detail about the material properties of the soil than is provided by the USCS code.
The USCS and additional engineering description is standardized in ASTM D 2487. For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property, behaviour, or genesis, results in classes that can be interpreted for many diverse uses. Differing concepts of pedogenesis, differences in the significance of morphological features to various land uses can affect the classification approach. Despite these differences, in a well-constructed system, classification criteria group similar concepts so that interpretations do not vary widely; this is in contrast to a technical system approach to soil classification, where soils are grouped according to their fitness for a specific use and their edaphic characteristics. Natural system approaches to soil classification, such as the French Soil Reference System are based on presumed soil genesis. Systems have developed, such as USDA soil taxonomy and the World Reference Base for Soil Resources, which use taxonomic criteria involving soil morphology and laboratory tests to inform and refine hierarchical classes.
Another approach is numerical classification called ordination, where soil individuals are grouped by multivariate statistical methods such as cluster analysis. This produces natural groupings without requiring any inference about soil genesis. In soil survey, as practiced in the United States, soil classification means criteria based on soil morphology in addition to characteristics developed during soil formation. Criteria are designed to guide choices in soil management; as indicated, this is a hierarchical system, a hybrid of both natural and objective criteria. USDA soil taxonomy provides the core criteria for differentiating soil map units; this is a substantial revision of the 1938 USDA soil taxonomy, a natural system. The USDA classification was developed by Guy Donald Smith, former director of the U. S. Department of Agriculture's soil survey investigations. Soil taxonomy based soil map units are additionally sorted into classes based on technical classification systems. Land Capability Classes, hydric soil, prime farmland are some examples.
The European Union uses the World Reference Base for Soil Resources the Update 2015 of the third edition 2014. The earlier editions of the WRB were used. According to the first edition of the WRB, the booklet "Soils of the European Union" was published by the former Institute of Environment and Sustainability. In addition to scientific soil classification systems, there are vernacular soil classification systems. Folk taxonomies have been used for millennia, while scientifically based systems are recent developments; the US Occupational Safety and Health Administration requires the classification of soils to protect workers from injury when working in excavations and trenches. OSHA uses 3 soil classifications plus one for rock, based on strength but other factors which affect the stability of cut slopes: Stable Rock: natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. Type A - cohesive, plastic soils with unconfined compressive strength greater than 1.5 ton per square foot, meeting several other
The Pampas are fertile South American lowlands that cover more than 750,000 km2 and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos and Córdoba. The vast plains are a natural region, interrupted only by the low Ventana and Tandil hills, near Bahía Blanca and Tandil, with a height of 1,300 m and 500 m, respectively; the climate is temperate, with precipitation of 600 to 1,200 mm, more or less evenly distributed through the year, making the soils appropriate for agriculture. The area is one of the distinct physiography provinces of the larger Paraná-Paraguay Plain division; the climate of the Pampas is temperate giving away to a more subtropical climate in the north and to a semiarid climate on the western fringes. Summer temperatures are more uniform than winter temperatures ranging from 28 to 33 °C during the day. However, most cities in the Pampas have high temperatures that push 38 °C, as occurs when a warm, northerly wind blows from southern Brazil. Autumn arrives in March, peaks in April and May.
In April, highs range from 20 to 25 °C and lows from 9 to 13 °C. The first frosts arrive in mid-April in the south, in late May or early June in the north. Winters are mild, but cold waves still occur. Normal temperatures range from 12 to 19 °C during the day, from 1 to 6 °C at night. With strong northerly winds, days of over 25 °C can be recorded everywhere, during cold waves, high temperatures can be only 6 °C. Frost occurs everywhere in the Pampas, but it is much more frequent in the southwest than around the Parana and Uruguay Rivers. Temperatures under −5 °C can occur everywhere, but values of −10 °C or lower are confined to the south and west. Snow never falls in the northernmost third and is rare and light elsewhere, except for exceptional events in which depths have reached 30 cm. Springs are variable. Violent storms are more common as well as wide temperature variations: days of 35 °C can give way to nights of under 5 °C or frost, all within only a few days. Precipitation ranges from 1,200 mm in the northeast, to about 500 mm in the southern and western edges.
In the west, it is seasonal, with some places recording averages of 120 mm monthly in the summer, only 20 millimetres monthly in the winter. The eastern areas have small peaks in the fall and in the spring, with rainy summers and winters that are only drier. However, where summer rain falls as short, heavy storms, winter rain falls as cold drizzle and so the amount of rainy days is constant. Intense thunderstorms are common in the spring and summer, it has among the most frequent lightning and highest convective cloud tops in the world; the severe thunderstorms produce intense hailstorms, both floods and flash floods, as well as the most active tornado region outside the central and southeastern US. Herbivores of the pampas are the pampas deer, gray brocket, dwarf mara, plains viscacha, Brazilian guinea pig, southern mountain cavy and coypu; the biggest predator of the region is the puma followed by the maned wolf, pampas fox, geoffroy's cat, lesser grison as well as the omnivorous white-eared opossum and molinas hog-nosed skunk.
Bird species of the pampas are ruddy-headed goose, pampas meadowlark, hudsonian godwit, maguari stork, white-faced ibis, white-winged coot, southern screamer, dot-winged crake, curve-billed reedhaunter, burrowing owl and the rhea. Frequent wildfires ensure that only small plants such as grasses flourish, trees are less common; the dominant vegetation types are grassy prairie and grass steppe in which numerous species of the grass genus Stipa are conspicuous. "Pampas grass" is an iconic species of the Pampas. Vegetation includes perennial grasses and herbs. Different strata of grasses occur because of gradients of water availability; the World Wildlife Fund divides the Pampas into three distinct ecoregions. The Uruguayan Savanna lies east of the Parana River, includes all of Uruguay, most of Entre Ríos and Corrientes provinces in Argentina, the southern portion of Brazil's state of Rio Grande do Sul; the Humid Pampas include eastern Buenos Aires Province, southern Entre Ríos Province. The Semiarid Pampas includes western Buenos Aires Province and adjacent portions of Santa Fe, Córdoba, La Pampa provinces.
The Pampas are bounded by the drier Argentine espinal grasslands, which form a semicircle around the north and south of the Humid Pampas. Winters are cool to mild and summers are warm and humid. Rainfall is uniform throughout the year, but is a little heavier during the summer. Annual rainfall is heaviest near the coast and decreases further inland. Rain during the late spring and summer arrives in the form of brief heavy showers and thunderstorms. More general rainfall occurs the remainder of the year as cold fronts and storm systems move through. Although cold spells during the winter send nighttime temperatures below freezing, snow is quite rare. In most winters, a few light snowfalls occur over inland areas. Central Argentina boasts a successful agricultural business, with crops grown on the Pampas south and west of Buenos Aires. Much of the area is used for
Humid continental climate
A humid continental climate is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by large seasonal temperature differences, with warm to hot summers and cold winters. Precipitation is distributed throughout the year; the definition of this climate regarding temperature is as follows: the mean temperature of the coldest month must be below −3 °C and there must be at least four months whose mean temperatures are at or above 10 °C. In addition, the location in question must not be arid; the Dfb and Dsb subtypes are known as hemiboreal. Humid continental climates are found between latitudes 40° N and 60° N, within the central and northeastern portions of North America and Asia, they are much less found in the Southern Hemisphere due to the larger ocean area at that latitude and the consequent greater maritime moderation. In the Northern Hemisphere some of the humid continental climates in Scandinavia, Nova Scotia, Newfoundland are maritime-influenced, with cool summers and winters being just below the freezing mark.
More extreme humid continental climates found in northeast China, southern Siberia, the Canadian Prairies, the Great Lakes region of the American Midwest and Central Canada combine hotter summer maxima and colder winters than the marine-based variety. Using the Köppen climate classification, a climate is classified as humid continental when the temperature of the coldest month is below −3 °C and there must be at least four months whose mean temperatures are at or above 10 °C; these temperatures were not arbitrary. In Europe, the −3 °C average temperature isotherm was near the southern extent of winter snowpack; the 10 °C average temperature was found to be the minimum temperature necessary for tree growth. Wide temperature ranges are common within this climate zone. Second letter in the classification symbol defines seasonal rainfall as follows: s: A dry summer—the driest summer month has less than 40 millimetres of rainfall and has less than 1⁄3 the precipitation of the wettest winter month, w: A dry winter—the driest winter month has less than one‑tenth of the precipitation found in the wettest summer month, f: Without dry season—does not meet either of the alternative specifications.while the third letter denotes the extent of summer heat: a: Hot summer, warmest month averages at least 22 °C, b: Warm summer, warmest month averages below 22 °C and at least four months averages above 10 °C.
Within North America, moisture within this climate regime is supplied by the Gulf of Mexico and adjacent western subtropical Atlantic. Precipitation is well distributed year-round in many areas with this climate, while others may see a marked reduction in wintry precipitation, which increases the chances of a wintertime drought. Snowfall occurs in all areas with a humid continental climate and in many such places is more common than rain during the height of winter. In places with sufficient wintertime precipitation, the snow cover is deep. Most summer rainfall occurs during thunderstorms, in North America and Asia an tropical system. Though humidity levels are high in locations with humid continental climates, the "humid" designation means that the climate is not dry enough to be classified as semi-arid or arid. By definition, forests thrive within this climate. Biomes within this climate regime include temperate woodlands, temperate grasslands, temperate deciduous, temperate evergreen forests, coniferous forests.
Within wetter areas, spruce, pine and oak can be found. Fall foliage is noted during the autumn. A hot summer version of a continental climate features an average temperature of at least 22 °C in its warmest month. Since these regimes are limited to the Northern Hemisphere, the warmest month is July or August. For example, Chicago has average July afternoon temperatures near 29 °C, while average January afternoon temperature are near −1 °C. Frost free periods last 4–6 months within this climate regime. Within North America, this climate includes small areas of central and southeast Canada, portions of the central and eastern United States from the 100th meridian eastward to the Atlantic. Precipitation is less seasonally uniform in the west; the western states of the central United States have thermal regimes which fit the Dfa climate type, but are quite dry, are grouped with the steppe climates. In the Eastern Hemisphere, this climate regime is found within interior Eurasia, east-central Asia, parts of India.
Within Europe, the Dfa climate type is present near the Black Sea in southern Ukraine, the Southern Federal District of Russia, southern Moldova, parts of southern Romania, Bulgaria, but tends to be drier and can be semi-arid in these places. In East Asia, this climate exhibits a monsoonal tendency with much higher precipitation in summer than in winter, due the effects of the strong Siberian High much colder winter temperatures than similar latitudes around the world, however with lower snowfall, the exception being western Japan with its heavy snowfall. Tōhoku, between Tokyo and Hokkaidō and Wester
Chernozem is a black-colored soil containing a high percentage of humus and high percentages of phosphoric acids and ammonia. Chernozem is fertile and can produce high agricultural yields with its high moisture storage capacity. Chernozems are a Reference Soil Group of the World Reference Base for Soil Resources; the name comes from the Russian terms for soil, earth or land. The soil, rich in organic matter presenting a black color, was first identified by Russian geologist Vasily Dokuchaev in 1883 in the tallgrass steppe or prairie of European Russia. Chernozems cover about 230 million hectares of land. There are two "chernozem belts" in the world. One is the Eurasian steppe which extends from eastern Croatia, along the Danube to northeast Ukraine across the Central Black Earth Region of Central Russia, southern Russia into Siberia; the other stretches from the Canadian Prairies in Manitoba through the Great Plains of the US as far south as Kansas. Similar soil types occur in Hungary. Chernozem layer thickness may vary from several centimetres up to 1.5 metres in Ukraine, as well as the Red River Valley region in the Northern US and Canada.
The terrain can be found in small quantities elsewhere. It exists in Northeast China, near Harbin; the only true Chernozem in Australia is located around Nimmitabel, with some of the richest soils in the nation. There is a large black market for the soil in Ukraine; the sale of agricultural land has been illegal in Ukraine since 1992, but the soil, transported by truck, has US$900 million annually in black market sales. Chernozemic soils are a soil type in the Canadian system of soil classification and the World Reference Base for Soil Resources. Theories of Chernozem origin: 1761 — Johan Gottschalk Wallerius 1763 — Mikhail Lomonosov 1799 — Peter Simon Pallas 1835 — Charles Lyell 1840 — Sir Roderick Murchison 1850 — Karl Eichwald 1851 — А. Petzgold 1852 — Nikifor Borisyak 1853 — Vangengeim von Qualen 1862 — Rudolf Ludwig 1866 — Franz Josef Ruprecht 1879 — First chernozem papers translated from Russian 1883 — Vasily Dokuchaev published his book Russian Chernozem with a complete study of this soil in European Russia.
1929 — Otto Schlüter 1999 — Michael W. I Schmidt Dark earth Terra preta profile photos WRB homepage profile photos IUSS World of Soils IUSS Working Group WRB: World Reference Base for Soil Resources 2014, Update 2015. World Soil Resources Reports 106, FAO, Rome 2015. ISBN 978-92-5-108369-7; the dictionary definition of chernozem at Wiktionary
The Paraná River is a river in south Central South America, running through Brazil and Argentina for some 4,880 kilometres. It is second in length only to the Amazon River among South American rivers; the name Paraná is an abbreviation of the phrase "para rehe onáva", which comes from the Tupi language and means "like the sea". It merges first with the Paraguay River and farther downstream with the Uruguay River to form the Río de la Plata and empties into the Atlantic Ocean; the first European to go up the Paraná River was the Venetian explorer Sebastian Cabot, in 1526, while working for Spain. The course is formed at the confluence of the Rio Grande rivers in southern Brazil. From the confluence the river flows in a southwestern direction for about 619 km before encountering the city of Saltos del Guaira, Paraguay; this was once the location of the Guaíra Falls (Sete Quedas waterfalls, where the Paraná fell over a series of seven cascades. This natural feature was said to rival the world-famous Iguazu Falls to the south.
The falls were flooded, however, by the construction of the Itaipu Dam, which began operating in 1984. For the next 200 km the Paraná flows southward and forms a natural boundary between Paraguay and Brazil until the confluence with the Iguazu River. Shortly upstream from this confluence, the river is dammed by the Itaipu Dam, the second largest hydroelectric power plant in the world, creating a massive, shallow reservoir behind it. After merging with the Iguazu, the Paraná becomes the natural border between Paraguay and Argentina. Overlooking the Paraná River from Encarnación, across the river, is downtown Posadas, Argentina; the river continues its general southward course for about 468 km before making a gradual turn to the west for another 820 km, encounters the Paraguay River, the largest tributary along the course of the river. Before this confluence the river passes through a second major hydroelectric project, the Yaciretá Dam, a joint project between Paraguay and Argentina; the massive reservoir formed by the project has been the source of a number of problems for people living along the river, most notably the poorer merchants and residents in the low-lying areas of Encarnación, a major city on the southern border of Paraguay.
River levels rose upon completion of the dam, flooding out large sections of the city's lower areas. From the confluence with the Paraguay River, the Paraná again turns to the south for another 820 km through Argentina, making a slow turn back to the east near the city of Rosario for the final stretch of less than 500 km before merging with the Uruguay River to form the Río de la Plata; this flows into the Atlantic Ocean. During the part of its course downstream from the city of Diamante, Entre Ríos, it splits into several arms and it forms the Paraná Delta. Together with its tributaries, the Rio Paraná forms a massive drainage basin that encompasses much of the southcentral part of South America including all of Paraguay, much of southern Brazil, northern Argentina, the southeastern part of Bolivia. If the Uruguay River is counted as a tributary to the Paraná, this watershed extends to cover most of Uruguay as well; the volume of water flowing into the Atlantic Ocean through the Río de la Plata equals the volume at the Mississippi River delta.
This watershed contains a number of large cities, including São Paulo, Buenos Aires, Asunción, Brasília, La Plata. The Paraná and its tributaries provide a source of income and of daily sustenance for fishermen who live along its banks; some of the species of fish are commercially important, they are exploited for heavy internal consumption or for export. The Parana River delta ranks as one of the world's greatest bird-watching destinations. Much of the length of the Paraná is navigable, the river serves as an important waterway linking inland cities in Argentina and Paraguay with the ocean, providing deepwater ports in some of these cities; the construction of enormous hydroelectric dams along the river's length has blocked its use as a shipping corridor to cities further upstream, but the economic impact of those dams offsets this. The Yacyretá Dam and the Itaipu Dam on the Paraguay border have made the small undeveloped nation of Paraguay the world's largest exporter of hydroelectric power.
Due to its use for oceangoing ships, measurements of the water tables extend back to 1904. The data correlates with the solar cycle; the course of the Paraná is crossed by the following bridges, beginning upstream: Tributaries of the Río de la Plata Paraná River steamers Information and a map of the Paraná's watershed "Paraná". New International Encyclopedia. 1905
Brazil the Federative Republic of Brazil, is the largest country in both South America and Latin America. At 8.5 million square kilometers and with over 208 million people, Brazil is the world's fifth-largest country by area and the fifth most populous. Its capital is Brasília, its most populated city is São Paulo; the federation is composed of the union of the 26 states, the Federal District, the 5,570 municipalities. It is the largest country to have Portuguese as an official language and the only one in the Americas. Bounded by the Atlantic Ocean on the east, Brazil has a coastline of 7,491 kilometers, it borders all other South American countries except Ecuador and Chile and covers 47.3% of the continent's land area. Its Amazon River basin includes a vast tropical forest, home to diverse wildlife, a variety of ecological systems, extensive natural resources spanning numerous protected habitats; this unique environmental heritage makes Brazil one of 17 megadiverse countries, is the subject of significant global interest and debate regarding deforestation and environmental protection.
Brazil was inhabited by numerous tribal nations prior to the landing in 1500 of explorer Pedro Álvares Cabral, who claimed the area for the Portuguese Empire. Brazil remained a Portuguese colony until 1808, when the capital of the empire was transferred from Lisbon to Rio de Janeiro. In 1815, the colony was elevated to the rank of kingdom upon the formation of the United Kingdom of Portugal and the Algarves. Independence was achieved in 1822 with the creation of the Empire of Brazil, a unitary state governed under a constitutional monarchy and a parliamentary system; the ratification of the first constitution in 1824 led to the formation of a bicameral legislature, now called the National Congress. The country became a presidential republic in 1889 following a military coup d'état. An authoritarian military junta came to power in 1964 and ruled until 1985, after which civilian governance resumed. Brazil's current constitution, formulated in 1988, defines it as a democratic federal republic. Due to its rich culture and history, the country ranks thirteenth in the world by number of UNESCO World Heritage Sites.
Brazil is considered an advanced emerging economy. It has the ninth largest GDP in the world by nominal, eight and PPP measures, it is one of the world's major breadbaskets, being the largest producer of coffee for the last 150 years. It is classified as an upper-middle income economy by the World Bank and a newly industrialized country, with the largest share of global wealth in Latin America. Brazil is a regional power and sometimes considered a great or a middle power in international affairs. On account of its international recognition and influence, the country is subsequently classified as an emerging power and a potential superpower by several analysts. Brazil is a founding member of the United Nations, the G20, BRICS, Union of South American Nations, Organization of American States, Organization of Ibero-American States and the Community of Portuguese Language Countries, it is that the word "Brazil" comes from the Portuguese word for brazilwood, a tree that once grew plentifully along the Brazilian coast.
In Portuguese, brazilwood is called pau-brasil, with the word brasil given the etymology "red like an ember", formed from brasa and the suffix -il. As brazilwood produces a deep red dye, it was valued by the European textile industry and was the earliest commercially exploited product from Brazil. Throughout the 16th century, massive amounts of brazilwood were harvested by indigenous peoples along the Brazilian coast, who sold the timber to European traders in return for assorted European consumer goods; the official Portuguese name of the land, in original Portuguese records, was the "Land of the Holy Cross", but European sailors and merchants called it the "Land of Brazil" because of the brazilwood trade. The popular appellation eclipsed and supplanted the official Portuguese name; some early sailors called it the "Land of Parrots". In the Guarani language, an official language of Paraguay, Brazil is called "Pindorama"; this was the name the indigenous population gave to the region, meaning "land of the palm trees".
Some of the earliest human remains found in the Americas, Luzia Woman, were found in the area of Pedro Leopoldo, Minas Gerais and provide evidence of human habitation going back at least 11,000 years. The earliest pottery found in the Western Hemisphere was excavated in the Amazon basin of Brazil and radiocarbon dated to 8,000 years ago; the pottery was found near Santarém and provides evidence that the tropical forest region supported a complex prehistoric culture. The Marajoara culture flourished on Marajó in the Amazon delta from 800 CE to 1400 CE, developing sophisticated pottery, social stratification, large populations, mound building, complex social formations such as chiefdoms. Around the time of the Portuguese arrival, the territory of current day Brazil had an estimated indigenous population of 7 million people semi-nomadic who subsisted on hunting, fishing and migrant agriculture; the indigenous population of Brazil comprised several large indigenous ethnic groups. The Tupí people were subdivided into the Tupiniquins and Tupinambás, there were many subdivisions of the other gro
Asia is Earth's largest and most populous continent, located in the Eastern and Northern Hemispheres. It shares the continental landmass of Eurasia with the continent of Europe and the continental landmass of Afro-Eurasia with both Europe and Africa. Asia covers an area of 44,579,000 square kilometres, about 30% of Earth's total land area and 8.7% of the Earth's total surface area. The continent, which has long been home to the majority of the human population, was the site of many of the first civilizations. Asia is notable for not only its overall large size and population, but dense and large settlements, as well as vast populated regions, its 4.5 billion people constitute 60% of the world's population. In general terms, Asia is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean, on the north by the Arctic Ocean; the border of Asia with Europe is a historical and cultural construct, as there is no clear physical and geographical separation between them. It has moved since its first conception in classical antiquity.
The division of Eurasia into two continents reflects East–West cultural and ethnic differences, some of which vary on a spectrum rather than with a sharp dividing line. The most accepted boundaries place Asia to the east of the Suez Canal separating it from Africa. China and India alternated in being the largest economies in the world from 1 to 1800 CE. China was a major economic power and attracted many to the east, for many the legendary wealth and prosperity of the ancient culture of India personified Asia, attracting European commerce and colonialism; the accidental discovery of a trans-Atlantic route from Europe to America by Columbus while in search for a route to India demonstrates this deep fascination. The Silk Road became the main east–west trading route in the Asian hinterlands while the Straits of Malacca stood as a major sea route. Asia has exhibited economic dynamism as well as robust population growth during the 20th century, but overall population growth has since fallen. Asia was the birthplace of most of the world's mainstream religions including Hinduism, Judaism, Buddhism, Taoism, Islam, Sikhism, as well as many other religions.
Given its size and diversity, the concept of Asia—a name dating back to classical antiquity—may have more to do with human geography than physical geography. Asia varies across and within its regions with regard to ethnic groups, environments, historical ties and government systems, it has a mix of many different climates ranging from the equatorial south via the hot desert in the Middle East, temperate areas in the east and the continental centre to vast subarctic and polar areas in Siberia. The boundary between Asia and Africa is the Red Sea, the Gulf of Suez, the Suez Canal; this makes Egypt a transcontinental country, with the Sinai peninsula in Asia and the remainder of the country in Africa. The border between Asia and Europe was defined by European academics; the Don River became unsatisfactory to northern Europeans when Peter the Great, king of the Tsardom of Russia, defeating rival claims of Sweden and the Ottoman Empire to the eastern lands, armed resistance by the tribes of Siberia, synthesized a new Russian Empire extending to the Ural Mountains and beyond, founded in 1721.
The major geographical theorist of the empire was a former Swedish prisoner-of-war, taken at the Battle of Poltava in 1709 and assigned to Tobolsk, where he associated with Peter's Siberian official, Vasily Tatishchev, was allowed freedom to conduct geographical and anthropological studies in preparation for a future book. In Sweden, five years after Peter's death, in 1730 Philip Johan von Strahlenberg published a new atlas proposing the Urals as the border of Asia. Tatishchev announced; the latter had suggested the Emba River as the lower boundary. Over the next century various proposals were made until the Ural River prevailed in the mid-19th century; the border had been moved perforce from the Black Sea to the Caspian Sea into which the Ural River projects. The border between the Black Sea and the Caspian is placed along the crest of the Caucasus Mountains, although it is sometimes placed further north; the border between Asia and the region of Oceania is placed somewhere in the Malay Archipelago.
The Maluku Islands in Indonesia are considered to lie on the border of southeast Asia, with New Guinea, to the east of the islands, being wholly part of Oceania. The terms Southeast Asia and Oceania, devised in the 19th century, have had several vastly different geographic meanings since their inception; the chief factor in determining which islands of the Malay Archipelago are Asian has been the location of the colonial possessions of the various empires there. Lewis and Wigen assert, "The narrowing of'Southeast Asia' to its present boundaries was thus a gradual process." Geographical Asia is a cultural artifact of European conceptions of the world, beginning with the Ancient Greeks, being imposed onto other cultures, an imprecise concept causing endemic contention about what it means. Asia does not correspond to the cultural borders of its various types of constituents. From the time of Herodotus a minority of geographers have rejected the three-continent system on the grounds that there is no substantial physical separation between