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95-586: The Curraghs or Ballaugh Curraghs are a wetland in Ballaugh parish in the north-west of the Isle of Man . The area has a rich and varied biodiversity and is also the location of the Curraghs Wildlife Park , a zoo and nature reserve that incorporates the wetlands. During the last ice age the area was covered in sheets of ice. When this ice retreated, a depression was left at the bottom of

190-711: A sink or a source of carbon, depending on the specific wetland. If they function as a carbon sink, they can help with climate change mitigation . However, wetlands can also be a significant source of methane emissions due to anaerobic decomposition of soaked detritus , and some are also emitters of nitrous oxide . Humans are disturbing and damaging wetlands in many ways, including oil and gas extraction , building infrastructure, overgrazing of livestock , overfishing , alteration of wetlands including dredging and draining, nutrient pollution , and water pollution . Wetlands are more threatened by environmental degradation than any other ecosystem on Earth, according to

285-574: A continent as "a large space of dry land comprehending many countries all joined together, without any separation by water. Thus Europe, Asia, and Africa is one great continent, as America is another." However, the old idea of Europe, Asia and Africa as "parts" of the world ultimately persisted with these being regarded as separate continents. By convention, continents "are understood to be large, continuous, discrete masses of land, ideally separated by expanses of water". In modern schemes with five or more recognized continents, at least one pair of continents

380-520: A continent. This divides the entire land surface of Earth into continents, regions, or quasi-continents. The criterion that each continent is a discrete landmass is commonly relaxed due to historical conventions and practical use. Of the seven most globally recognized continents, only Antarctica and Australia are completely separated from other continents by the ocean. Several continents are defined not as absolutely distinct bodies but as " more or less discrete masses of land". Africa and Asia are joined by

475-615: A discrete landmass is completely disregarded if the continuous landmass of Eurasia is classified as two separate continents (Asia and Europe). Physiographically , Europe and the Indian subcontinent are large peninsulas of the Eurasian landmass. However, Europe is considered a continent with its comparatively large land area of 10,180,000 square kilometres (3,930,000 sq mi), while the Indian subcontinent, with less than half that area,

570-402: A frequency and duration to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally included swamps, marshes, bogs, and similar areas.' For each of these definitions and others, regardless of the purpose, hydrology is emphasized (shallow waters, water-logged soils). The soil characteristics and

665-425: A geological continent has been disputed by some geologists. However, a study conducted in 2021 found that part of the submerged continent is indeed Precambrian , twice as old as geologists had previously thought, which is further evidence that supports the idea of Zealandia being a geological continent. All seven geological continents are spatially isolated by geologic features. The term "continent" translates

760-550: A nearby continent to divide all the world's land into geographical regions. Under this scheme, most of the island countries and territories in the Pacific Ocean are grouped together with the continent of Australia to form the geographical region Oceania . In geology , a continent is defined as "one of Earth's major landmasses, including both dry land and continental shelves ". The geological continents correspond to seven large areas of continental crust that are found on

855-468: A part of South America. Apart from the current continents, the scope and meaning of the term continent includes past geological ones. Supercontinents , largely in evidence earlier in the geological record, are landmasses that comprise most of the world's cratons or continental cores. These have included Vaalbara , Kenorland , Columbia , Rodinia , Pannotia , and Pangaea . Over time, these supercontinents broke apart into large landmasses which formed

950-1259: A polar climate, wetland temperatures can be as low as −50 °C (−58 °F). Peatlands in arctic and subarctic regions insulate the permafrost , thus delaying or preventing its thawing during summer, as well as inducing its formation. The amount of precipitation a wetland receives varies widely according to its area. Wetlands in Wales , Scotland , and western Ireland typically receive about 1,500 mm (59 in) per year. In some places in Southeast Asia , where heavy rains occur, they can receive up to 10,000 mm (390 in). In some drier regions, wetlands exist where as little as 180 mm (7.1 in) precipitation occurs each year. Temporal variation: Surface flow may occur in some segments, with subsurface flow in other segments. Wetlands vary widely due to local and regional differences in topography , hydrology , vegetation , and other factors, including human involvement. Other important factors include fertility, natural disturbance, competition, herbivory , burial and salinity. When peat accumulates, bogs and fens arise. The most important factor producing wetlands

1045-540: A portion of the overall water cycle, which also includes atmospheric water (precipitation) and groundwater . Many wetlands are directly linked to groundwater and they can be a crucial regulator of both the quantity and quality of water found below the ground. Wetlands that have permeable substrates like limestone or occur in areas with highly variable and fluctuating water tables have especially important roles in groundwater replenishment or water recharge. Substrates that are porous allow water to filter down through

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1140-529: A protective barrier to coastal shoreline. Mangroves stabilize the coastal zone from the interior and will migrate with the shoreline to remain adjacent to the boundary of the water. The main conservation benefit these systems have against storms and storm surges is the ability to reduce the speed and height of waves and floodwaters. Continent A continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be

1235-523: A separate land. In 1507 Martin Waldseemüller published a world map, Universalis Cosmographia , which was the first to show North and South America as separate from Asia and surrounded by water. A small inset map above the main map explicitly showed for the first time the Americas being east of Asia and separated from Asia by an ocean, as opposed to just placing the Americas on the left end of

1330-738: A single landmass or a part of a very large landmass, as in the case of Asia or Europe. Due to this, the number of continents varies; up to seven or as few as four geographical regions are commonly regarded as continents. Most English-speaking countries recognize seven regions as continents. In order from largest to smallest in area, these seven regions are Asia , Africa , North America , South America , Antarctica , Europe , and Australia . Different variations with fewer continents merge some of these regions; examples of this are merging North America and South America into America , Asia and Europe into Eurasia , and Africa, Asia, and Europe into Afro-Eurasia . Oceanic islands are occasionally grouped with

1425-422: A strong influence on wetland water chemistry, particularly in coastal wetlands and in arid and semiarid regions with large precipitation deficits. Natural salinity is regulated by interactions between ground and surface water, which may be influenced by human activity. Carbon is the major nutrient cycled within wetlands. Most nutrients, such as sulfur , phosphorus , carbon , and nitrogen are found within

1520-821: A third part of the world. Division into three parts eventually came to predominate. From the Greek viewpoint, the Aegean Sea was the center of the world; Asia lay to the east, Europe to the north and west, and Africa to the south. The boundaries between the continents were not fixed. Early on, the Europe–Asia boundary was taken to run from the Black Sea along the Rioni River (known then as the Phasis ) in Georgia . Later it

1615-410: A unique kind of wetland where lush plant growth and slow decay of dead plants (under anoxic conditions) results in organic peat accumulating; bogs, fens, and mires are different names for peatlands. Variations of names for wetland systems: Some wetlands have localized names unique to a region such as the prairie potholes of North America's northern plain, pocosins , Carolina bays and baygalls of

1710-502: A very large peninsula on the fringe of a continent. Where the Americas are viewed as a single continent (America), it is divided into two subcontinents ( North America and South America ) or three ( Central America being the third). When Eurasia is regarded as a single continent, Asia and Europe are treated as subcontinents. Some areas of continental crust are largely covered by the ocean and may be considered submerged continents . Notable examples are Zealandia , emerging from

1805-515: A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding". Sometimes a precise legal definition of a wetland is required. The definition used for regulation by the United States government is: 'The term "wetlands" means those areas that are inundated or saturated by surface or ground water at

1900-422: A wetland system includes its plants ( flora ) and animals ( fauna ) and microbes (bacteria, fungi). The most important factor is the wetland's duration of flooding. Other important factors include fertility and salinity of the water or soils. The chemistry of water flowing into wetlands depends on the source of water, the geological material that it flows through and the nutrients discharged from organic matter in

1995-403: A wetland) affects hydro-periods (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland. Landscape characteristics control wetland hydrology and water chemistry. The O 2 and CO 2 concentrations of water depend upon temperature , atmospheric pressure and mixing with the air (from winds or water flows). Water chemistry within wetlands

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2090-558: A whole. To replace these wetland ecosystem services , enormous amounts of money would need to be spent on water purification plants, dams, levees, and other hard infrastructure, and many of the services are impossible to replace. Floodplains and closed-depression wetlands can provide the functions of storage reservoirs and flood protection. The wetland system of floodplains is formed from major rivers downstream from their headwaters . "The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over

2185-594: A wide area, which reduces its depth and speed. Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt so that it does not run straight off the land into water courses. This can help prevent sudden, damaging floods downstream." Notable river systems that produce wide floodplains include the Nile River , the Niger river inland delta, the Zambezi River flood plain,

2280-462: Is also a subspecies of wren , possibly unique to the island. The area is also notable for its diversity of butterflies, and the Wildlife Park, whilst home to over 100 animals from around the world (including pelicans , gibbons , otters and penguins ), also features a butterfly walk, an opportunity for visitors to see the insects in an environment designed for them. One notable species is

2375-451: Is considered a subcontinent. The alternative view—in geology and geography—that Eurasia is a single continent results in a six-continent view of the world. Some view the separation of Eurasia into Asia and Europe as a residue of Eurocentrism : "In physical, cultural and historical diversity, China and India are comparable to the entire European landmass, not to a single European country. [...]." However, for historical and cultural reasons,

2470-440: Is determined by the pH , salinity , nutrients, conductivity , soil composition, hardness , and the sources of water. Water chemistry varies across landscapes and climatic regions. Wetlands are generally minerotrophic (waters contain dissolved materials from soils) with the exception of ombrotrophic bogs that are fed only by water from precipitation. Because bogs receive most of their water from precipitation and humidity from

2565-435: Is divided into several principal oceanic components by the continents and various geographic criteria. The geological definition of a continent has four criteria: high elevation relative to the ocean floor; a wide range of igneous, metamorphic and sedimentary rocks rich in silica; a crust thicker than the surrounding oceanic crust; and well-defined limits around a large enough area. The most restricted meaning of continent

2660-412: Is hydrology, or flooding . The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation . Other important factors include soil fertility, natural disturbance, competition, herbivory , burial, and salinity. When peat from dead plants accumulates, bogs and fens develop. Wetland hydrology is associated with

2755-507: Is inhabited by more numerous people and animals than our Europe, or Asia or Africa", the first known explicit identification of part of the Americas as a continent like the other three. Within a few years, the name "New World" began appearing as a name for South America on world maps, such as the Oliveriana (Pesaro) map of around 1504–1505. Maps of this time, though, still showed North America connected to Asia and showed South America as

2850-430: Is joined by land in some fashion. The criterion "large" leads to arbitrary classification: Greenland , with a surface area of 2,166,086 square kilometres (836,330 sq mi), is only considered the world's largest island, while Australia , at 7,617,930 square kilometres (2,941,300 sq mi), is deemed the smallest continent. Earth's major landmasses all have coasts on a single, continuous World Ocean , which

2945-612: Is that of a continuous area of land or mainland, with the coastline and any land boundaries forming the edge of the continent. In this sense, the term continental Europe (sometimes referred to in Britain as "the Continent") is used to refer to mainland Europe, excluding islands such as Great Britain , Iceland , Ireland , and Malta , while the term continent of Australia may refer to the mainland of Australia , excluding New Guinea , Tasmania , and other nearby islands. Similarly,

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3040-451: Is the only place in the world where both crocodiles and alligators coexist. The saltwater crocodile inhabits estuaries and mangroves. Snapping turtles also inhabit wetlands. Birds , particularly waterfowl and waders use wetlands extensively. Mammals of wetlands include numerous small and medium-sized species such as voles , bats , muskrats and platypus in addition to large herbivorous and apex predator species such as

3135-407: Is usually considered an island of Africa, but its divergent evolution has caused it to be referred to as "the eighth continent" from a biological perspective. Geologists use four key attributes to define a continent: With the addition of Zealandia in 2017, Earth currently has seven recognized geological continents: Due to a seeming lack of Precambrian cratonic rocks, Zealandia's status as

3230-545: Is usually saturated with water". More precisely, wetlands are areas where "water covers the soil , or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season". A patch of land that develops pools of water after a rain storm would not necessarily be considered a "wetland", even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other water bodies or landforms based on their water level and on

3325-458: The continental United States refers to "the 49 States (including Alaska but excluding Hawaii ) located on the continent of North America, and the District of Columbia ." From the perspective of geology or physical geography , continent may be extended beyond the confines of continuous dry land to include the shallow, submerged adjacent area (the continental shelf ) and the islands on

3420-666: The Black Sea . The names were first applied just to lands near the coast and only later extended to include the hinterlands . But the division was only carried through to the end of navigable waterways and "... beyond that point the Hellenic geographers never succeeded in laying their finger on any inland feature in the physical landscape that could offer any convincing line for partitioning an indivisible Eurasia ..." Ancient Greek thinkers subsequently debated whether Africa (then called Libya ) should be considered part of Asia or

3515-613: The Isthmus of Suez , and North America and South America by the Isthmus of Panama . In both cases, there is no complete separation of these landmasses by water (disregarding the Suez Canal and the Panama Canal , which are both narrow and shallow, as well as human-made). Both of these isthmuses are very narrow compared to the bulk of the landmasses they unite. North America and South America are treated as separate continents in

3610-505: The Millennium Ecosystem Assessment from 2005. Methods exist for assessing wetland ecological health . These methods have contributed to wetland conservation by raising public awareness of the functions that wetlands can provide. Since 1971, work under an international treaty seeks to identify and protect " wetlands of international importance ." A simplified definition of wetland is "an area of land that

3705-456: The Pacific Ocean , as well as the continent of Australia . Zealandia (a submerged continent ) has been called the eighth continent. The following table provides areas given by Encyclopædia Britannica for each continent in accordance with the seven-continent model, including Australasia along with Melanesia , Micronesia , and Polynesia as parts of Oceania. It also provides populations of continents according to 2021 estimates by

3800-688: The Pantanal in South America, and the Sundarbans in the Ganges - Brahmaputra delta. Wetlands contribute many ecosystem services that benefit people. These include for example water purification , stabilization of shorelines, storm protection and flood control . In addition, wetlands also process and condense carbon (in processes called carbon fixation and sequestration ), and other nutrients and water pollutants . Wetlands can act as

3895-584: The Pleistocene ice ages , greater areas of the continental shelf were exposed as dry land, forming land bridges between Tasmania and the Australian mainland . At those times, Australia and New Guinea were a single, continuous continent known as Sahul . Likewise, Afro-Eurasia and the Americas were joined by the Bering Land Bridge . Other islands, such as Great Britain , were joined to

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3990-719: The United Nations Statistics Division based on the United Nations geoscheme , which includes all of Egypt (including the Isthmus of Suez and the Sinai Peninsula ) as a part of Africa, all of Armenia, Azerbaijan, Cyprus, Georgia, Indonesia, Kazakhstan, and Turkey (including East Thrace ) as parts of Asia, all of Russia (including Siberia ) as a part of Europe, all of Panama and the United States (including Hawaii ) as parts of North America, and all of Chile (including Easter Island ) as

4085-444: The atmosphere , their water usually has low mineral ionic composition. In contrast, wetlands fed by groundwater or tides have a higher concentration of dissolved nutrients and minerals. Fen peatlands receive water both from precipitation and ground water in varying amounts so their water chemistry ranges from acidic with low levels of dissolved minerals to alkaline with high accumulation of calcium and magnesium . Salinity has

4180-576: The beavers , coypu , swamp rabbit , Florida panther , jaguar , and moose . Wetlands attract many mammals due to abundant seeds, berries, and other vegetation as food for herbivores, as well as abundant populations of invertebrates, small reptiles and amphibians as prey for predators. Invertebrates of wetlands include aquatic insects such as dragonflies , aquatic bugs and beetles , midges, mosquitos , crustaceans such as crabs, crayfish, shrimps, microcrustaceans, mollusks like clams, mussels, snails and worms. Invertebrates comprise more than half of

4275-466: The orange tip . Ballaugh Curraghs has a persistent breeding colony of wild wallabies , said to be the largest in the British Isles, descended from two that escaped from the wildlife park some years ago. They seem to occupy a similar ecological niche to hares. The Curraghs are a tapestry of scrubland , including willow and bog myrtle scrub. Sphagnum moss , a common species, is responsible for

4370-422: The tectonic plates , but exclude small continental fragments such as Madagascar that are generally referred to as microcontinents . Continental crust is only known to exist on Earth. The idea of continental drift gained recognition in the 20th century. It postulates that the current continents formed from the breaking up of a supercontinent ( Pangaea ) that formed hundreds of millions of years ago. From

4465-791: The willow scrub habitat found in the Isle of Man . Wetland Wetlands exist on every continent , except Antarctica . The water in wetlands is either freshwater , brackish or saltwater . The main types of wetland are defined based on the dominant plants and the source of the water. For example, marshes are wetlands dominated by emergent herbaceous vegetation such as reeds , cattails and sedges . Swamps are dominated by woody vegetation such as trees and shrubs (although reed swamps in Europe are dominated by reeds, not trees). Mangrove forest are wetlands with mangroves , halophytic woody plants that have evolved to tolerate salty water . Examples of wetlands classified by

4560-492: The "subcontinents" concerned are on different tectonic plates from the rest of the continent, providing a geological justification for the terminology. Greenland , generally considered the world's largest island on the northeastern periphery of the North American Plate , is sometimes referred to as a subcontinent. This is a significant departure from the more conventional view of a subcontinent as comprising

4655-588: The 16th century the English noun continent was derived from the term continent land , meaning continuous or connected land and translated from the Latin terra continens . The noun was used to mean "a connected or continuous tract of land" or mainland . It was not applied only to very large areas of land—in the 17th century, references were made to the continents (or mainlands) of the Isle of Man , Ireland and Wales and in 1745 to Sumatra . The word continent

4750-533: The Americas, Columbus never believed he had reached a new continent—he always thought it was part of Asia. In 1501, Amerigo Vespucci and Gonçalo Coelho attempted to sail around what they considered the southern end of the Asian mainland into the Indian Ocean , passing through Fernando de Noronha . After reaching the coast of Brazil , they sailed along the coast of South America much farther south than Asia

4845-697: The Black Sea and the Caspian Sea , and the border between Asia and Africa at the isthmus between the Red Sea and the mouth of Lake Bardawil on the Mediterranean Sea . The Roman author Pliny the Elder , writing in the 1st century CE, stated that "The whole globe is divided into three parts, Europe, Asia, and Africa", adding: I shall first then speak of Europe, the foster-mother of that people which has conquered all other nations, and itself by far

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4940-691: The Catholic church, began to associate itself with the concept of Europe. Through the Roman period and the Middle Ages , a few writers took the Isthmus of Suez as the boundary between Asia and Africa, but most writers continued to consider it the Nile or the western border of Egypt (Gibbon). In the Middle Ages, the world was usually portrayed on T and O maps , with the T representing the waters dividing

5035-544: The Curragh became a designated Ramsar site . This refers to an organisation devoted to conserving important areas of wetland worldwide. The area is deemed important as it is inhabited by the second-largest roost of hen harriers in Europe ; a bird that descends on the area during the winter months. Other birds include peregrine falcons , merlins , robins , willow warblers , song thrushes and dunnocks among others. There

5130-591: The Curraghs, so that the area could be extensively farmed. However, with the land 15 m above sea level, it was decided that it was not economically viable to drain the wetlands. In 1963, much of the area came under the control of the Manx government , and two years later the 26-acre (11 ha) Curraghs Wildlife Park was opened. In 1990, protection of the government-controlled area was transferred to Manx National Heritage ; and in 2006 about 477 acres, or 193 hectares, of

5225-498: The Earth, the text claims that the Earth has seven continents and Lord Vishnu Measured the entire universe from his first foot from the land of Earth which has 7 continents. ato devā avantu no yato viṣṇurvicakrame | pṛthivyāḥ saptadhāmabhiḥ || idaṃ viṣṇurvi cakrame tredhā ni dadhe padam | samūḷhamasya pāṃsure || trīṇi padā vi cakrame viṣṇurghopā adābhyaḥ | ato dharmāṇi dhārayan || The Gods be gracious unto us even from

5320-619: The Greek word ἤπειρος , meaning "landmass, terra firma", the proper name of Epirus and later especially used for Asia (i.e. Asia Minor ). The first distinction between continents was made by ancient Greek mariners who gave the names Europe and Asia to the lands on either side of the waterways of the Aegean Sea , the Dardanelles strait, the Sea of Marmara , the Bosporus strait and

5415-639: The Okavango River inland delta, the Kafue River flood plain, the Lake Bangweulu flood plain (Africa), Mississippi River (US), Amazon River (South America), Yangtze River (China), Danube River (Central Europe) and Murray-Darling River (Australia). Groundwater replenishment can be achieved for example by marsh , swamp , and subterranean karst and cave hydrological systems. The surface water visibly seen in wetlands only represents

5510-522: The Southeastern US, mallines of Argentina, Mediterranean seasonal ponds of Europe and California, turloughs of Ireland, billabongs of Australia, among many others. Wetlands are found throughout the world in different climates. Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in the temperate zones , midway between the North or South Poles and

5605-502: The US, the best known classifications are the Cowardin classification system and the hydrogeomorphic (HGM) classification system. The Cowardin system includes five main types of wetlands: marine (ocean-associated), estuarine (mixed ocean- and river-associated), riverine (within river channels), lacustrine (lake-associated) and palustrine (inland nontidal habitats). Peatlands are

5700-610: The United States' commercial fish and shellfish stocks depend solely on estuaries to survive. Amphibians such as frogs and salamanders need both terrestrial and aquatic habitats in which to reproduce and feed. Because amphibians often inhabit depressional wetlands like prairie potholes and Carolina bays, the connectivity among these isolated wetlands is an important control of regional populations. While tadpoles feed on algae, adult frogs forage on insects. Frogs are sometimes used as an indicator of ecosystem health because their thin skin permits absorption of nutrients and toxins from

5795-477: The concept of a continent may go beyond the continental shelf to include oceanic islands and continental fragments. In this way, Iceland is considered a part of Europe, and Madagascar a part of Africa. Extrapolating the concept to its extreme, some geographers group the Australian continental landmass with other islands in the Pacific Ocean into Oceania , which is usually considered a region rather than

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5890-405: The division into three of what is really a single landmass, a debate that continues nearly two and a half millennia later. Herodotus believed Europe to be larger (at least in width) than the other two continents: I wonder, then, at those who have mapped out and divided the world into Libya, Asia, and Europe; for the difference between them is great, seeing that in length Europe stretches along both

5985-634: The equator. In these zones, summers are warm and winters are cold, but temperatures are not extreme. In subtropical zone wetlands, such as along the Gulf of Mexico , average temperatures might be 11 °C (52 °F). Wetlands in the tropics are subjected to much higher temperatures for a large portion of the year. Temperatures for wetlands on the Arabian Peninsula can exceed 50 °C (122 °F) and these habitats would therefore be subject to rapid evaporation. In northeastern Siberia , which has

6080-504: The following areas: According to the Ramsar Convention: The economic worth of the ecosystem services provided to society by intact, naturally functioning wetlands is frequently much greater than the perceived benefits of converting them to 'more valuable' intensive land use – particularly as the profits from unsustainable use often go to relatively few individuals or corporations, rather than being shared by society as

6175-415: The high levels of peat in the area. The peat and wetland topography of the area combine to create a series of bogs . The abundance of peat has had a direct effect on the island's human inhabitants over the years, with the peat being used as fuel in people's homes. The Curraghs are also home to six different species of orchid , including the heath spotted orchid . In Manx Gaelic , a curragh refers to

6270-468: The interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both." In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. Under the Ramsar international wetland conservation treaty , wetlands are defined as follows: An ecological definition of

6365-462: The known animal species in wetlands, and are considered the primary food web link between plants and higher animals (such as fish and birds). Depending on a wetland's geographic and topographic location, the functions it performs can support multiple ecosystem services , values, or benefits. United Nations Millennium Ecosystem Assessment and Ramsar Convention described wetlands as a whole to be of biosphere significance and societal importance in

6460-490: The mainlands of their continents. At that time, there were just three discrete landmasses in the world: Africa - Eurasia - America , Antarctica , and Australia - New Guinea ( Sahul ). There are several ways of distinguishing the continents: In the English-speaking countries, geographers often use the term Oceania to denote a geographical region which includes most of the island countries and territories in

6555-429: The map and Asia on the right end. In the accompanying book Cosmographiae Introductio , Waldseemüller noted that the earth is divided into four parts, Europe, Asia, Africa, and the fourth part, which he named "America" after Amerigo Vespucci's first name. On the map, the word "America" was placed on part of South America. The Sanskrit text Rig Veda often dated 1500 BCE has the earliest mention of seven continents in

6650-549: The mid-17th century, Peter Heylin wrote in his Cosmographie that "A Continent is a great quantity of Land, not separated by any Sea from the rest of the World, as the whole Continent of Europe, Asia, Africa." In 1727, Ephraim Chambers wrote in his Cyclopædia, "The world is ordinarily divided into two grand continents: the Old and the New ." And in his 1752 atlas, Emanuel Bowen defined

6745-543: The most beauteous portion of the earth. Indeed, many persons have, not without reason, considered it, not as a third part only of the earth, but as equal to all the rest, looking upon the whole of our globe as divided into two parts only, by a line drawn from the river Tanais to the Straits of Gades. Following the fall of the Western Roman Empire , the culture that developed in its place , linked to Latin and

6840-424: The northern hills and the wetlands were formed in this basin. Over the years the land has been used to graze animals and grow hay , one of the few exploitable crops suited to the conditions of the wetlands. The Curraghs has also been a valuable resource for humans, as well as providing aesthetic appeal; the area is rich in peat , which was used as a fuel in the island's homes. The nearby village of Kirk Michael

6935-475: The ocean primarily in New Zealand and New Caledonia , and the almost completely submerged Kerguelen Plateau in the southern Indian Ocean . Some islands lie on sections of continental crust that have rifted and drifted apart from a main continental landmass. While not considered continents because of their relatively small size, they may be considered microcontinents . Madagascar, the largest example,

7030-455: The others together, and it appears to me to be wider beyond all comparison. Eratosthenes , in the 3rd century BCE, noted that some geographers divided the continents by rivers (the Nile and the Don), thus considering them "islands". Others divided the continents by isthmuses , calling the continents "peninsulas". These latter geographers set the border between Europe and Asia at the isthmus between

7125-479: The place whence Vishnu strode Through the seven regions of the earth! Through all this world strode Vishnu; thrice his foot he planted, and the whole Was gathered in his footstep's dust. Vishnu, the Guardian, he whom none deceiveth , made three steps; thenceforth Establishing his high decrees. In regard to the above-quoted verses, it is commonly accepted that there are Seven Continents or 'regions of

7220-837: The plants and animals controlled by the wetland hydrology are often additional components of the definitions. Wetlands can be tidal (inundated by tides) or non-tidal. The water in wetlands is either freshwater , brackish , saline , or alkaline . There are four main kinds of wetlands – marsh , swamp , bog , and fen (bogs and fens being types of peatlands or mires ). Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types. Sub-types include mangrove forests , carrs , pocosins , floodplains , peatlands, vernal pools , sinks , and many others. The following three groups are used within Australia to classify wetland by type: Marine and coastal zone wetlands, inland wetlands and human-made wetlands. In

7315-558: The present continents. Certain parts of continents are recognized as subcontinents, especially the large peninsulas separated from the main continental landmass by geographical features. The most widely recognized example is the Indian subcontinent . The Arabian Peninsula , Southern Africa , the Southern Cone of South America, and Alaska in North America might be considered further examples. In many of these cases,

7410-552: The seven-continent model. However, they may also be viewed as a single continent known as America . This viewpoint was common in the United States until World War II , and remains prevalent in some Asian six-continent models. The single American continent model remains a common view in European countries like France, Greece, Hungary, Italy, Malta, Portugal, Spain, Latin American countries and some Asian countries. The criterion of

7505-415: The shelf ( continental islands ), as they are structurally part of the continent. From this perspective, the edge of the continental shelf is the true edge of the continent, as shorelines vary with changes in sea level. In this sense the islands of Great Britain and Ireland are part of Europe, while Australia and the island of New Guinea together form a continent. Taken to its limit, this view could support

7600-429: The soil and underlying rock into aquifers which are the source of much of the world's drinking water . Wetlands can also act as recharge areas when the surrounding water table is low and as a discharge zone when it is high. Mangroves , coral reefs , salt marsh can help with shoreline stabilization and storm protection. Tidal and inter-tidal wetland systems protect and stabilize coastal zones. Coral reefs provide

7695-537: The soil of wetlands. Anaerobic and aerobic respiration in the soil influences the nutrient cycling of carbon, hydrogen, oxygen, and nitrogen, and the solubility of phosphorus thus contributing to the chemical variations in its water. Wetlands with low pH and saline conductivity may reflect the presence of acid sulfates and wetlands with average salinity levels can be heavily influenced by calcium or magnesium. Biogeochemical processes in wetlands are determined by soils with low redox potential. The life forms of

7790-412: The soils and plants at higher elevations. Plants and animals may vary within a wetland seasonally or in response to flood regimes. There are four main groups of hydrophytes that are found in wetland systems throughout the world. Submerged wetland vegetation can grow in saline and fresh-water conditions. Some species have underwater flowers, while others have long stems to allow the flowers to reach

7885-530: The sources of water include tidal wetlands , where the water source is ocean tides ); estuaries , water source is mixed tidal and river waters; floodplains , water source is excess water from overflowed rivers or lakes; and bogs and vernal ponds , water source is rainfall or meltwater . The world's largest wetlands include the Amazon River basin , the West Siberian Plain ,

7980-406: The spatial and temporal dispersion, flow, and physio-chemical attributes of surface and ground waters. Sources of hydrological flows into wetlands are predominantly precipitation , surface water (saltwater or freshwater), and groundwater. Water flows out of wetlands by evapotranspiration , surface flows and tides , and subsurface water outflow. Hydrodynamics (the movement of water through and from

8075-719: The surface of the water. When trees and shrubs comprise much of the plant cover in saturated soils, those areas in most cases are called swamps . The upland boundary of swamps is determined partly by water levels. This can be affected by dams Some swamps can be dominated by a single species, such as silver maple swamps around the Great Lakes . Others, like those of the Amazon basin , have large numbers of different tree species. Other examples include cypress ( Taxodium ) and mangrove swamps. Many species of fish are highly dependent on wetland ecosystems. Seventy-five percent of

8170-496: The surface. Submerged species provide a food source for native fauna, habitat for invertebrates, and also possess filtration capabilities. Examples include seagrasses and eelgrass . Floating water plants or floating vegetation are usually small, like those in the Lemnoideae subfamily (duckweeds). Emergent vegetation like the cattails ( Typha spp.), sedges ( Carex spp.) and arrow arum ( Peltandra virginica ) rise above

8265-464: The surrounding environment resulting in increased extinction rates in unfavorable and polluted environmental conditions. Reptiles such as snakes , lizards , turtles , alligators and crocodiles are common in wetlands of some regions. In freshwater wetlands of the Southeastern US, alligators are common and a freshwater species of crocodile occurs in South Florida. The Florida Everglades

8360-651: The three continents. By the middle of the 18th century, "the fashion of dividing Asia and Africa at the Nile, or at the Great Catabathmus [the boundary between Egypt and Libya ] farther west, had even then scarcely passed away". Christopher Columbus sailed across the Atlantic Ocean to the Caribbean in 1492, sparking a period of European exploration of the Americas . But despite four voyages to

8455-440: The types of plants that live within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants . A more concise definition is a community composed of hydric soil and hydrophytes . Wetlands have also been described as ecotones , providing a transition between dry land and water bodies. Wetlands exist "...at

8550-479: The view of Europe as a separate continent continues in almost all categorizations. If continents are defined strictly as discrete landmasses, embracing all the contiguous land of a body, then Africa, Asia, and Europe form a single continent which may be referred to as Afro-Eurasia . Combined with the consolidation of the Americas, this would produce a four-continent model consisting of Afro-Eurasia, America, Antarctica, and Australia. When sea levels were lower during

8645-471: The view that there are only three continents: Antarctica, Australia-New Guinea, and a single mega-continent which joins Afro-Eurasia and America via the contiguous continental shelf in and around the Bering Sea. The vast size of the latter compared to the first two might even lead some to say it is the only continent, the others being more comparable to Greenland or New Zealand. As a cultural construct ,

8740-502: Was a great consumer of the peat in the Curraghs. It was the exploitation of peat that made the land slightly drier than it is today. When the practice of peat cutting was discontinued, the ditches in the area filled with water and bogs were formed. In the 1930s, the Manx government intended to make a profit by growing New Zealand flax on the Curraghs. This plan failed, but in the 1950s the government pressed ahead with another plan to drain

8835-438: Was known to extend, confirming that this was a land of continental proportions. On return to Europe, an account of the voyage, called Mundus Novus ("New World"), was published under Vespucci's name in 1502 or 1503, although it seems that it had additions or alterations by another writer. Regardless of who penned the words, Mundus Novus credited Vespucci with saying, "I have discovered a continent in those southern regions that

8930-417: Was used in translating Greek and Latin writings about the three "parts" of the world, although in the original languages no word of exactly the same meaning as continent was used. While continent was used on the one hand for relatively small areas of continuous land, on the other hand geographers again raised Herodotus's query about why a single large landmass should be divided into separate continents. In

9025-685: Was viewed as running from the Black Sea through Kerch Strait , the Sea of Azov and along the Don River (known then as the Tanais ) in Russia . The boundary between Asia and Africa was generally taken to be the Nile River. Herodotus in the 5th century BCE objected to the whole of Egypt being split between Asia and Africa ("Libya") and took the boundary to lie along the western border of Egypt, regarding Egypt as part of Asia. He also questioned

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