Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word тӯндар meaning "uplands", "treeless mountain tract". Tundra vegetation is composed of dwarf shrubs and grasses, lichens. Scattered trees grow in some tundra regions; the ecotone between the tundra and the forest is known as timberline. There are three regions and associated types of tundra: Arctic tundra, alpine tundra, Antarctic tundra. Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt; the word "tundra" refers only to the areas where the subsoil is permafrost, or permanently frozen soil. Permafrost tundra includes vast areas of northern Canada; the polar tundra is home to several peoples who are nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area. Arctic tundra is frozen for much of the year; the soil there is frozen from 25 to 90 cm down. Instead and sometimes rocky land can only support certain kinds of Arctic vegetation, low growing plants such as moss and lichen.
There are two main seasons and summer, in the polar tundra areas. During the winter it is cold and dark, with the average temperature around −28 °C, sometimes dipping as low as −50 °C. However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south. During the summer, temperatures rise somewhat, the top layer of seasonally-frozen soil melts, leaving the ground soggy; the tundra is covered in marshes, lakes and streams during the warm months. Daytime temperatures during the summer rise to about 12 °C but can drop to 3 °C or below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national Biodiversity Action Plan. Tundra tends to be windy, with winds blowing upwards of 50–100 km/h. However, in terms of precipitation, it is desert-like, with only about 15–25 cm falling per year. Although precipitation is light, evaporation is relatively minimal. During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, so the water forms the lakes and marshes found during the summer months.
There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals that vary from 150 to 200 years, with dryer lowland areas burning more than wetter highland areas; the biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. There are a few fish species. There are few species with large populations. Notable animals in the Arctic tundra include reindeer, musk ox, Arctic hare, Arctic fox, snowy owl and polar bears near the ocean. Tundra is devoid of poikilotherms such as frogs or lizards. Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity though they are sometimes rich in natural resources such as petroleum, natural gas and uranium. In recent times this has begun to change in Alaska and some other parts of the world: for example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.
A severe threat to tundra is global warming. The melting of the permafrost in a given area on human time scales could radically change which species can survive there. Another concern is that about one third of the world's soil-bound carbon is in taiga and tundra areas; when the permafrost melts, it releases carbon in the form of carbon dioxide and methane, both of which are greenhouse gases. The effect has been observed in Alaska. In the 1970s the tundra was a carbon sink. Methane is produced when vegetation decays in wetlands; the amount of greenhouse gases which will be released under projected scenarios for global warming have not been reliably quantified by scientific studies, although a few studies were reported to be underway in 2011. It is uncertain whether the impact of increased greenhouse gases from this source will be minimal or massive. In locations where dead vegetation and peat has accumulated, there is a risk of wildfire, such as the 1,039 km2 of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.
Such events may both contribute to global warming. Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, most of the continent is covered by ice fields. However, some portions of the continent the Antarctic Peninsula, have areas of rocky soil that support plant life; the flora presently consists of around 300–400 lichens, 100 mosses, 25 liverworts, aro
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, gases from water. The goal is to produce water fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may be carried out for a variety of other purposes, including medical, pharmacological and industrial applications; the methods used include physical processes such as filtration and distillation. Water purification may reduce the concentration of particulate matter including suspended particles, bacteria, algae and fungi as well as reduce the concentration of a range of dissolved and particulate matter; the standards for drinking water quality are set by governments or by international standards. These standards include minimum and maximum concentrations of contaminants, depending on the intended use of the water. Visual inspection can not determine. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all possible contaminants that may be present in water from an unknown source.
Natural spring water – considered safe for all practical purposes in the 19th century – must now be tested before determining what kind of treatment, if any, is needed. Chemical and microbiological analysis, while expensive, are the only way to obtain the information necessary for deciding on the appropriate method of purification. According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply. The WHO estimates that 94% of these diarrheal disease cases are preventable through modifications to the environment, including access to safe water. Simple techniques for treating water at home, such as chlorination and solar disinfection, for storing it in safe containers could save a huge number of lives each year. Reducing deaths from waterborne diseases is a major public health goal in developing countries. Groundwater: The water emerging from some deep ground water may have fallen as rain many tens, hundreds, or thousands of years ago. Soil and rock layers filter the ground water to a high degree of clarity and it does not require additional treatment besides adding chlorine or chloramines as secondary disinfectants.
Such water may be extracted from boreholes or wells. Deep ground water is of high bacteriological quality, but the water may be rich in dissolved solids carbonates and sulfates of calcium and magnesium. Depending on the strata through which the water has flowed, other ions may be present including chloride, bicarbonate. There may be a requirement to reduce the iron or manganese content of this water to make it acceptable for drinking and laundry use. Primary disinfection may be required. Where groundwater recharge is practiced, the groundwater may require additional treatment depending on applicable state and federal regulations. Upland lakes and reservoirs: Typically located in the headwaters of river systems, upland reservoirs are sited above any human habitation and may be surrounded by a protective zone to restrict the opportunities for contamination. Bacteria and pathogen levels are low, but some bacteria, protozoa or algae will be present. Where uplands are forested or peaty, humic acids can colour the water.
Many upland sources have low pH. Rivers and low land reservoirs: Low land surface waters will have a significant bacterial load and may contain algae, suspended solids and a variety of dissolved constituents. Atmospheric water generation is a new technology that can provide high quality drinking water by extracting water from the air by cooling the air and thus condensing water vapor. Rainwater harvesting or fog collection which collect water from the atmosphere can be used in areas with significant dry seasons and in areas which experience fog when there is little rain. Desalination of seawater by distillation or reverse osmosis. Surface Water: Freshwater bodies that are open to the atmosphere and are not designated as groundwater are termed surface waters; the goals of the treatment are to remove unwanted constituents in the water and to make it safe to drink or fit for a specific purpose in industry or medical applications. Varied techniques are available to remove contaminants like fine solids, micro-organisms and some dissolved inorganic and organic materials, or environmental persistent pharmaceutical pollutants.
The choice of method will depend on the quality of the water being treated, the cost of the treatment process and the quality standards expected of the processed water. The processes below are the ones used in water purification plants; some or most may not be used depending on the scale of the quality of the raw water. Pumping and containment – The majority of water must be pumped from its source or directed into pipes or holding tanks. To avoid adding contaminants to the water, this physical infrastructure must be made from appr
A biome is a community of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. "Biome" is a broader term than "habitat". While a biome can cover large areas, a microbiome is a mix of organisms that coexist in a defined space on a much smaller scale. For example, the human microbiome is the collection of bacteria and other microorganisms that are present on or in a human body. A'biota' is the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales; the biotas of the Earth make up the biosphere. The term was suggested in 1916 by Clements as a synonym for biotic community of Möbius, it gained its current definition, based on earlier concepts of phytophysiognomy and vegetation, with the inclusion of the animal element and the exclusion of the taxonomic element of species composition.
In 1935, Tansley added the climatic and soil aspects to the idea. The International Biological Program projects popularized the concept of biome. However, in some contexts, the term biome is used in a different manner. In German literature in the Walter terminology, the term is used as biotope, while the biome definition used in this article is used as an international, non-regional, terminology - irrespectively of the continent in which an area is present, it takes the same biome name - and corresponds to his "zonobiome", "orobiome" and "pedobiome". In Brazilian literature, the term "biome" is sometimes used as synonym of "biogeographic province", an area based on species composition, or as synonym of the "morphoclimatic and phytogeographical domain" of Ab'Sáber, a geographic space with subcontinental dimensions, with the predominance of similar geomorphologic and climatic characteristics, of a certain vegetation form. Both include many biomes in fact. To divide the world in a few ecological zones is a difficult attempt, notably because of the small-scale variations that exist everywhere on earth and because of the gradual changeover from one biome to the other.
Their boundaries must therefore be drawn arbitrarily and their characterization made according to the average conditions that predominate in them. A 1978 study on North American grasslands found a positive logistic correlation between evapotranspiration in mm/yr and above-ground net primary production in g/m2/yr; the general results from the study were that precipitation and water use led to above-ground primary production, while solar irradiation and temperature lead to below-ground primary production, temperature and water lead to cool and warm season growth habit. These findings help explain the categories used in Holdridge’s bioclassification scheme, which were later simplified by Whittaker; the number of classification schemes and the variety of determinants used in those schemes, should be taken as strong indicators that biomes do not fit into the classification schemes created. Holdridge classified climates based on the biological effects of temperature and rainfall on vegetation under the assumption that these two abiotic factors are the largest determinants of the types of vegetation found in a habitat.
Holdridge uses the four axes to define 30 so-called "humidity provinces", which are visible in his diagram. While this scheme ignores soil and sun exposure, Holdridge acknowledged that these were important; the principal biome-types by Allee: Tundra Taiga Deciduous forest Grasslands Desert High plateaus Tropical forest Minor terrestrial biomes The principal biomes of the world by Kendeigh: Terrestrial Temperate deciduous forest Coniferous forest Woodland Chaparral Tundra Grassland Desert Tropical savanna Tropical forest Marine Oceanic plankton and nekton Balanoid-gastropod-thallophyte Pelecypod-annelid Coral reef Whittaker classified biomes using two abiotic factors: precipitation and temperature. His scheme can be seen as a simplification of Holdridge's. Whittaker based his approach on empirical sampling, he was in a unique position to make such a holistic assertion because he had compiled a review of biome classifications. Physiognomy: the apparent characteristics, outward features, or appearance of ecological communities or species.
Biome: a grouping of terrestrial ecosystems on a given continent, similar in vegetation structure, features of the environment and characteristics of their animal communities. Formation: a major kind of community of plants on a given continent. Biome-type: grouping of convergent biomes or formations of different continents, defined by physiognomy. Formation-type: a grouping of convergent formations. Whittaker's distinction between biome and formation can be simplified: formation is used when applied to plant communities only, while biome is used when concerned with both plants and animals. Whittaker's convention of biome-type or formation-type is a broader method to categorize similar communities. Whittaker, seeing the need for a simpler way to express the relationship of community structure to the environment, used what he called "gradient analysis" of ecocline patterns to relate communities to climate on a worldwide scale. Whittaker
Pesticides are substances that are meant to control pests, including weeds. The term pesticide includes all of the following: herbicide, insecticides nematicide, piscicide, rodenticide, insect repellent, animal repellent and fungicide; the most common of these are herbicides which account for 80% of all pesticide use. Most pesticides are intended to serve as plant protection products, which in general, protect plants from weeds, fungi, or insects. In general, a pesticide is a chemical or biological agent that deters, kills, or otherwise discourages pests. Target pests can include insects, plant pathogens, molluscs, mammals, fish and microbes that destroy property, cause nuisance, or spread disease, or are disease vectors. Along with these benefits, pesticides have drawbacks, such as potential toxicity to humans and other species; the Food and Agriculture Organization has defined pesticide as: any substance or mixture of substances intended for preventing, destroying, or controlling any pest, including vectors of human or animal disease, unwanted species of plants or animals, causing harm during or otherwise interfering with the production, storage, transport, or marketing of food, agricultural commodities and wood products or animal feedstuffs, or substances that may be administered to animals for the control of insects, arachnids, or other pests in or on their bodies.
The term includes substances intended for use as a plant growth regulator, desiccant, or agent for thinning fruit or preventing the premature fall of fruit. Used as substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. Pesticides can be classified by target organism, chemical structure, physical state. Biopesticides include biochemical pesticides. Plant-derived pesticides, or "botanicals", have been developing quickly; these include the pyrethroids, nicotinoids, a fourth group that includes strychnine and scilliroside. Many pesticides can be grouped into chemical families. Prominent insecticide families include organochlorines and carbamates. Organochlorine hydrocarbons could be separated into dichlorodiphenylethanes, cyclodiene compounds, other related compounds, they operate by disrupting the sodium/potassium balance of the nerve fiber, forcing the nerve to transmit continuously. Their toxicities vary but they have been phased out because of their persistence and potential to bioaccumulate.
Organophosphate and carbamates replaced organochlorines. Both operate through inhibiting the enzyme acetylcholinesterase, allowing acetylcholine to transfer nerve impulses indefinitely and causing a variety of symptoms such as weakness or paralysis. Organophosphates are quite toxic to vertebrates and have in some cases been replaced by less toxic carbamates. Thiocarbamate and dithiocarbamates are subclasses of carbamates. Prominent families of herbicides include phenoxy and benzoic acid herbicides, triazines and Chloroacetanilides. Phenoxy compounds tend to selectively kill broad-leaf weeds rather than grasses; the phenoxy and benzoic acid herbicides function similar to plant growth hormones, grow cells without normal cell division, crushing the plant's nutrient transport system. Triazines interfere with photosynthesis. Many used pesticides are not included in these families, including glyphosate; the application of pest control agents is carried out by dispersing the chemical in a solvent-surfactant system to give a homogeneous preparation.
A virus lethality study performed in 1977 demonstrated that a particular pesticide did not increase the lethality of the virus, however combinations which included some surfactants and the solvent showed that pretreatment with them markedly increased the viral lethality in the test mice. Pesticides can be classified based upon their biological mechanism application method. Most pesticides work by poisoning pests. A systemic pesticide moves inside a plant following absorption by the plant. With insecticides and most fungicides, this movement is upward and outward. Increased efficiency may be a result. Systemic insecticides, which poison pollen and nectar in the flowers, may kill bees and other needed pollinators. In 2010, the development of a new class of fungicides called; these work by taking advantage of natural defense chemicals released by plants called phytoalexins, which fungi detoxify using enzymes. The paldoxins inhibit the fungi's detoxification enzymes, they are believed to be greener.
Since before 2000 BC, humans have utilized pesticides to protect their crops. The first known pesticide was elemental sulfur dusting used in ancient Sumer about 4,500 years ago in ancient Mesopotamia; the Rig Veda, about 4,000 years old, mentions the use of poisonous plants for pest control. By the 15th century, toxic chemicals such as arsenic and lead were being applied to crops to kill pests. In the 17th century, nicotine sulfate was extracted from tobacco leaves for use as an insecticide; the 19th century saw the introduction of two more natural pesticides, derived fr
An ocean is a body of water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean; these are, in descending order by area, the Pacific, Indian and Arctic Oceans. The word "ocean" is used interchangeably with "sea" in American English. Speaking, a sea is a body of water or enclosed by land, though "the sea" refers to the oceans. Saline water covers 361,000,000 km2 and is customarily divided into several principal oceans and smaller seas, with the ocean covering 71% of Earth's surface and 90% of the Earth's biosphere; the ocean contains 97% of Earth's water, oceanographers have stated that less than 5% of the World Ocean has been explored. The total volume is 1.35 billion cubic kilometers with an average depth of nearly 3,700 meters. As the world ocean is the principal component of Earth's hydrosphere, it is integral to life, forms part of the carbon cycle, influences climate and weather patterns; the World Ocean is the habitat of 230,000 known species, but because much of it is unexplored, the number of species that exist in the ocean is much larger over two million.
The origin of Earth's oceans is unknown. Extraterrestrial oceans may be composed of water or other compounds; the only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories and Venus are theorized to have had large water oceans; the Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of natural satellites; the Solar System's giant planets are thought to have liquid atmospheric layers of yet to be confirmed compositions. Oceans may exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone.
Ocean planets are a hypothetical type of planet with a surface covered with liquid. The word ocean comes from the figure in classical antiquity, the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world; the concept of Ōkeanós has an Indo-European connection. Greek Ōkeanós has been compared to the Vedic epithet ā-śáyāna-, predicated of the dragon Vṛtra-, who captured the cows/rivers. Related to this notion, the Okeanos is represented with a dragon-tail on some early Greek vases. Though described as several separate oceans, the global, interconnected body of salt water is sometimes referred to as the World Ocean or global ocean; the concept of a continuous body of water with free interchange among its parts is of fundamental importance to oceanography. The major oceanic divisions – listed below in descending order of area and volume – are defined in part by the continents, various archipelagos, other criteria.
Oceans are fringed by smaller, adjoining bodies of water such as seas, bays and straits. The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system, part of every ocean and the longest mountain range in the world; the continuous mountain range is 65,000 km long. The total mass of the hydrosphere is about 1.4 quintillion metric tons, about 0.023% of Earth's total mass. Less than 3% is freshwater; the area of the World Ocean is about 361.9 million square kilometers, which covers about 70.9% of Earth's surface, its volume is 1.335 billion cubic kilometers. This can be thought of as a cube of water with an edge length of 1,101 kilometers, its average depth is about 3,688 meters, its maximum depth is 10,994 meters at the Mariana Trench. Nearly half of the world's marine waters are over 3,000 meters deep; the vast expanses of deep ocean cover about 66% of Earth's surface. This does not include seas not connected to the World Ocean, such as the Caspian Sea; the bluish ocean color is a composite of several contributing agents.
Prominent contributors include dissolved organic chlorophyll. Mariners and other seafarers have reported that the ocean emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow, it is most caused by bioluminescence. Oceanographers divide the ocean into different vertical zones defined by physical and biological conditions; the pelagic zone includes all open ocean regions, can be divided into further regions categorized by depth and light abundance. The photic zone includes the oceans from the surface to a depth of
Antarctica is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere entirely south of the Antarctic Circle, is surrounded by the Southern Ocean. At 14,200,000 square kilometres, it is the fifth-largest continent. For comparison, Antarctica is nearly twice the size of Australia. About 98% of Antarctica is covered by ice that averages 1.9 km in thickness, which extends to all but the northernmost reaches of the Antarctic Peninsula. Antarctica, on average, is the coldest and windiest continent, has the highest average elevation of all the continents. Most of Antarctica is a polar desert, with annual precipitation of only 200 mm along the coast and far less inland; the temperature in Antarctica has reached −89.2 °C, though the average for the third quarter is −63 °C. Anywhere from 1,000 to 5,000 people reside throughout the year at research stations scattered across the continent. Organisms native to Antarctica include many types of algae, fungi, plants and certain animals, such as mites, penguins and tardigrades.
Vegetation, where it occurs, is tundra. Antarctica is noted as the last region on Earth in recorded history to be discovered, unseen until 1820 when the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on Vostok and Mirny sighted the Fimbul ice shelf; the continent, remained neglected for the rest of the 19th century because of its hostile environment, lack of accessible resources, isolation. In 1895, the first confirmed. Antarctica is a de facto condominium, governed by parties to the Antarctic Treaty System that have consulting status. Twelve countries signed the Antarctic Treaty in 1959, thirty-eight have signed it since then; the treaty prohibits military activities and mineral mining, prohibits nuclear explosions and nuclear waste disposal, supports scientific research, protects the continent's ecozone. Ongoing experiments are conducted by more than 4,000 scientists from many nations; the name Antarctica is the romanised version of the Greek compound word ἀνταρκτική, feminine of ἀνταρκτικός, meaning "opposite to the Arctic", "opposite to the north".
Aristotle wrote in his book Meteorology about an Antarctic region in c. 350 BC Marinus of Tyre used the name in his unpreserved world map from the 2nd century CE. The Roman authors Hyginus and Apuleius used for the South Pole the romanised Greek name polus antarcticus, from which derived the Old French pole antartike attested in 1270, from there the Middle English pol antartik in a 1391 technical treatise by Geoffrey Chaucer. Before acquiring its present geographical connotations, the term was used for other locations that could be defined as "opposite to the north". For example, the short-lived French colony established in Brazil in the 16th century was called "France Antarctique"; the first formal use of the name "Antarctica" as a continental name in the 1890s is attributed to the Scottish cartographer John George Bartholomew. The long-imagined south polar continent was called Terra Australis, sometimes shortened to'Australia' as seen in a woodcut illustration titled Sphere of the winds, contained in an astrological textbook published in Frankfurt in 1545.
Although the longer Latin phrase was better known, the shortened name Australia was used in Europe's scholarly circles. In the nineteenth century, the colonial authorities in Sydney removed the Dutch name from New Holland. Instead of inventing a new name to replace it, they took the name Australia from the south polar continent, leaving it nameless for some eighty years. During that period, geographers had to make do with clumsy phrases such as "the Antarctic Continent", they searched for a more poetic replacement, suggesting various names such as Antipodea. Antarctica was adopted in the 1890s. Antarctica has no indigenous population, there is no evidence that it was seen by humans until the 19th century. However, in February 1775, during his second voyage, Captain Cook called the existence of such a polar continent "probable" and in another copy of his journal he wrote:" believe it and it's more than probable that we have seen a part of it". However, belief in the existence of a Terra Australis—a vast continent in the far south of the globe to "balance" the northern lands of Europe and North Africa—had prevailed since the times of Ptolemy in the 1st century AD.
In the late 17th century, after explorers had found that South America and Australia were not part of the fabled "Antarctica", geographers believed that the continent was much larger than its actual size. Integral to the story of the origin of Antarctica's name is that it was not named Terra Australis—this name was given to Australia instead, because of the misconception that no significant landmass could exist further south. Explorer Matthew Flinders, in particular, has been credited with popularising the transfer of the name Terra Australis to Australia, he justified the titling of his book A Voyage to Terra Australis by writing in the introduction: There is no probability, that any other detached body of land, of nearly equal extent, will be found in a more southern latitude.