1.
Antarctica
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It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 14,000,000 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, Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Antarctica is a desert, with precipitation of only 200 mm along the coast. The temperature in Antarctica has reached −89.2 °C, though the average for the quarter is −63 °C. Anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Organisms native to Antarctica include many types of algae, bacteria, fungi, plants, protista, vegetation, where it occurs, is tundra. The continent, however, remained neglected for the rest of the 19th century because of its hostile environment, lack of easily accessible resources. In 1895, the first confirmed landing was conducted by a team of Norwegians, 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, and 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, and protects the continents 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 B. C, marinus of Tyre reportedly used the name in his unpreserved world map from the 2nd century A. D. Before acquiring its present geographical connotations, the term was used for 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. Antarctica has no population and there is no evidence that it was seen by humans until the 19th century. Explorer Matthew Flinders, in particular, has credited with popularising the transfer of the name Terra Australis to Australia. Cook came within about 120 km of the Antarctic coast before retreating in the face of ice in January 1773. The first confirmed sighting of Antarctica can be narrowed down to the crews of ships captained by three individuals, according to various organisations, ships captained by three men sighted Antarctica or its ice shelf in 1820, von Bellingshausen, Edward Bransfield, and Nathaniel Palmer
2.
Transantarctic Mountains
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These mountains divide East Antarctica and West Antarctica. They include a number of named mountain groups, which are often again subdivided into smaller ranges. The range was first sighted by James Clark Ross in 1841 at what was named the Ross Ice Shelf in his honor. It was first crossed during the British National Antarctic Expedition of 1901-1904, the mountain range stretches between the Ross Sea and the Weddell Sea the entire length of Antarctica, hence the name. With a total length of about 3,500 km, the Transantarctic Mountains are one of the longest mountain ranges on Earth, the 100–300 km wide range forms the boundary between East Antarctica and West Antarctica. The summits and dry valleys of the TAM are some of the few places in Antarctica not covered by ice, the highest mountain of the TAM is 4,528 m high Mount Kirkpatrick in the Queen Alexandra Range. Isolated peaks surrounded by ice are referred to as nunataks, penguins, seals, and sea birds live along the Ross Sea coastline in Victoria Land, while life in the interior of the Transantarctic Range is limited to bacteria, lichens, algae, and fungi. Forests once covered Antarctica, including plentiful Wollemi Pine and Southern Beech, however, with the gradual cooling associated with the break-up of Gondwana, these forests gradually disappeared. It is believed that the last trees on the Antarctic continent were on Transantarctic Mountains, the Transantarctic Mountains were first seen by Captain James Ross in 1841 from the Ross Sea. The range is a barrier that must be crossed to reach the South Pole from the Ross Ice Shelf. The first crossing of the Transantarctic Mountains took place during the 1902-1904 British National Antarctic Expedition at the Ross Ice Shelf, a reconnaissance party under the command of Albert Armitage reached 2700 m altitude in 1902. The following year a party under expedition leader Robert Falcon Scott crossed into East Antarctica at a location now known as Ferrar Glacier and they explored part of Victoria Land on the Antarctic Plateau before returning via the same glacier. In 1908, Ernest Shackletons party crossed the mountains through the Beardmore Glacier, Robert Scott returned to that same glacier in 1911, while Roald Amundsen crossed the range via the Axel Heiberg Glacier. The name Transantarctic Mountains was first applied to range in a 1960 paper by geologist Warren B. It was subsequently recommended by the US-ACAN committee, a US authority for geographic names and this purely descriptive label is internationally accepted at present. The Leverett Glacier in the Queen Maud Mountains is the route through the TAM for the overland supply road between McMurdo Station and Amundsen–Scott South Pole Station. The Transantarctic Mountains are considerably older than other mountain ranges of the continent that are volcanic in origin. The range was uplifted during the opening of the West Antarctic Rift to the east, the mountains consist of sedimentary layers lying upon a basement of granites and gneisses
3.
Nematode
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The nematodes or roundworms constitute the phylum Nematoda. They are an animal phylum inhabiting a broad range of environments. Nematodes are classified along with insects and other moulting animals in the clade Ecdysozoa, Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are found in part of the earths lithosphere, even at great depths below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor, the many parasitic forms include pathogens in most plants and animals. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes, trees would still stand in ghostly rows representing our streets and highways. In 1758, Linnaeus described some nematode genera, then included in Vermes, the name of the group Nematoda, informally called nematodes, came from Nematoidea, originally defined by Karl Rudolphi, from Ancient Greek νῆμα and -eiδἠς. It was treated as family Nematodes by Burmeister, at its origin, the Nematoidea erroneously included Nematodes and Nematomorpha, attributed by von Siebold. Along with Acanthocephala, Trematoda and Cestoidea, it formed the obsolete group Entozoa and they were also classed along with Acanthocephala in the obsolete phylum Nemathelminthes by Gegenbaur. In 1861, K. M. Diesing treated the group as order Nematoda, in 1877, the taxon Nematoidea, including the family Gordiidae, was promoted to the rank of phylum by Ray Lankester. In 1919, Nathan Cobb proposed that nematodes should be recognized alone as a phylum and he argued they should be called nema in English rather than nematodes and defined the taxon Nemates, listing Nematoidea sensu restricto as a synonym. Since Cobb was the first to all but nematodes from the group, some sources consider the valid taxon name to be Nemates or Nemata. The phylogenetic relationships of the nematodes and their close relatives among the protostomian Metazoa are unresolved, traditionally, they were held to be a lineage of their own but in the 1990s, they were proposed to form the group Ecdysozoa together with moulting animals, such as arthropods. The identity of the closest living relatives of the Nematoda has always considered to be well resolved. Morphological characters and molecular phylogenies agree with placement of the roundworms as a taxon to the parasitic Nematomorpha. Together with the Scalidophora, the Nematoida form the clade Cycloneuralia, the Cycloneuralia or the Introverta—depending on the validity of the former—are often ranked as a superphylum. Due to the lack of knowledge regarding many nematodes, their systematics is contentious, an earliest and influential classification was proposed by Chitwood and Chitwood—later revised by Chitwood—who divided the phylum into two—the Aphasmidia and the Phasmidia. These were later renamed Adenophorea and Secernentea, respectively, the Secernentea share several characteristics, including the presence of phasmids, a pair of sensory organs located in the lateral posterior region, and this was used as the basis for this division
4.
Springtail
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Springtails form the largest of the three lineages of modern hexapods that are no longer considered insects. If they are considered a basal lineage of Hexapoda, they are elevated to full class status, collembolans are omnivorous, free-living organisms that prefer moist conditions. They do not directly engage in the decomposition of organic matter, but contribute to it indirectly through the fragmentation of organic matter, the Poduromorpha and Entomobryomorpha have an elongated body, while the Symphypleona and Neelipleona have a globular body. Most species have an abdominal, tail-like appendage, the furcula and it is held under tension by a small structure called the retinaculum and when released, snaps against the substrate, flinging the springtail into the air. All of this place in as little as 18 milliseconds. Springtails also possess the ability to reduce their size by as much as 30% through subsequent ecdyses if temperatures rise high enough. Since warmer conditions increase metabolic rates and energy requirements in organisms, traditionally, the springtails were divided into the orders Arthropleona, Symphypleona and occasionally also Neelipleona. The Arthropleona were divided into two superfamilies, the Entomobryoidea and the Poduroidea, but actually, these two and the Symphypleona form three lineages, each of which is equally distant from the other two. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now the Entomobryomorpha, technically, the Arthropleona are thus a partial junior synonym of the Collembola. The term Neopleona is essentially synonymous with Symphypleona + Neelipleona, the Neelipleona were originally seen as a particular advanced lineage of Symphypleona, based on the shared global body shape. But the global body of Neelipleona is realised in a different way than in Symphypleona. Subsequently, the Neelipleona were considered as being derived from the Entomobryomorpha, but analysis of 18S and 28S rRNA sequence data suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies. Springtails are attested to since the Early Devonian, the fossil from 400 million years ago, Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Given its morphology resembles extant species quite closely, the radiation of the Hexapoda can be situated in the Silurian,420 million years ago or more, instead, most are found in amber. Even these are rare and many amber deposits carry few or no collembola, the best deposits are from the early Eocene of Canada and Europe, Miocene of Central America, and the mid-Cretaceous of Burma and Canada. There are about 3,600 different species, springtails commonly consume fungal hyphae and spores, but also have been found to consume plant material and pollen, animal remains, colloidal materials, minerals and bacteria. In addition, a few species routinely climb trees and form a dominant component of canopy faunas, in temperate regions, a few species are almost exclusively arboreal. In tropical regions a single square meter of canopy habitat can support species of Collembola
5.
Mite
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Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology, in soil ecosystems, mites are favored by high organic matter content and by moist conditions, wherein they actively engage in the fragmentation and mixing of organic matter. Mites are among the most diverse and successful of all the invertebrate groups and they have exploited an incredible array of habitats, and because of their small size, go largely unnoticed. Many live freely in the soil or water, but there are also a number of species that live as parasites on plants, animals. It is estimated that 48,200 species of mites have been described, mites occupy a wide range of ecological niches. For example, Oribatida mites are important decomposers and occur in many habitats and they eat a wide variety of material including living and dead plant and fungal material, lichens and carrion, some are even predatory, though no species of Oribatida mite are parasites. Many mites which have well studied are parasitic on plants. One family of mites Pyroglyphidae, or nest mites, live primarily in the nests of birds and these mites are largely parasitic and consume blood, skin and keratin. Dust mites, which feed mostly on dead skin and hair shed from humans instead of consuming them from the organism directly, insects may also be infested by parasitic mites. Examples are Varroa destructor, which attaches to the body of the bee, and Acarapis woodi. There are hundreds of species of associated with other bee species. They attach to the bees in a variety of ways, for example, Trigona corvina workers have been found with mites attached to the outer face of their hind tibiae. Some are thought to be parasites, while others are beneficial symbionts, mites also parasitize some ant species, such as Eciton burchellii. Some of the plant pests include the spider mites, thread-footed mites. Among the species that attack animals are members of the sarcoptic mange mites, demodex mites are parasites that live in or near the hair follicles of mammals, including humans. Acari are mites, except for the three families of ticks, mites also hold the record speed, for its length, Paratarsotomus macropalpis is the fastest animal on Earth. The majority of species are harmless to humans, but a few species of mites can colonize humans directly, act as vectors for disease transmission. Mites which colonize human skin are the cause of several types of skin rashes, such as grain itch, grocers itch
6.
Leopard seal
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The leopard seal, also referred to as the sea leopard, is the second largest species of seal in the Antarctic. Along with all of the earless seals, it belongs to the family Phocidae. The name hydrurga means water worker and leptonyx is the Greek for small clawed, the leopard seal is large and muscular, with a dark grey back and light grey on its stomach. Its throat is whitish with the spots that give the seal its common name. Females are slightly larger than the males, the overall length of this seal is 2. 4–3.5 m and weight is from 200 to 600 kilograms. They are about the length as the northern walrus. Its front teeth are sharp like those of other carnivores, but its molars lock together in a way allows them to sieve krill from the water. The leopard seal lives in the waters surrounding the Antarctic continent. Where most seals remain restricted within the ice throughout the year, some move further north in the austral winter to subantarctic islands. This trait of vocalizing underwater for long periods however has made available to acoustic surveys. Leopard seals are solitary and widely distributed throughout the pack ice, higher densities of leopard seals are seen in the Western Antarctic than in other regions. Leopard seals are very vocal underwater during the austral summer, the male seals produce loud calls for many hours each day. While singing the seal hangs upside down and rocks from side to side under the water and their back is bent, the neck and cranial thoracic region is inflated and as they call their chest pulses. Adult male leopard seals have only a few stylized calls, some are like bird or cricket-like trills yet others are low haunting moans, the leopard seals have age-related differences in their calling patterns, just like birds. Where the younger male seals have many different types of variable calls - the adult male seals have only a few, each male seal produces individually distinctive songs. They arrange their few call types into individually distinctive sequences, the acoustic behavior of the leopard seal is believed to be linked to their breeding behaviour. The females give birth to a single pup during the summer on the floating ice floes of the Antarctic pack ice. She protects her pup until it is able to fend for itself, the leopard seal is bold, powerful and curious
7.
Weddell seal
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The Weddell seal, Leptonychotes weddellii, is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. Weddell seals have the most southerly distribution of any mammal, with a habitat that extends as far south as McMurdo Sound. It is the species in the genus Leptonychotes, and the only member of the Antarctic tribe of lobodontine seals to prefer in-shore habitats on shore-fast ice over free-floating pack ice. Genetic evidence suggests that Weddell seal population numbers may have increased during the Pleistocene, because of its abundance, relative accessibility, and ease of approach by humans, it is the best-studied of the Antarctic seals. An estimated 800,000 individuals remain today, Weddell seal pups leave their mothers at a few months of age. In those months, they are fed by their mothers warming and they leave when they are ready to hunt and are fat enough to survive in the harsh weather. The Weddell seal was discovered and named in the 1820s during expeditions led by James Weddell, however, it is found in relatively uniform densities around the entire Antarctic continent. The Weddell seal shares a recent ancestor with the other Antarctic seals. These include the seal, the Ross seal, and the leopard seal. These species share teeth adaptations including lobes and cusps useful for straining smaller prey items out of the water, Weddell seals measure about 2. 5-3.5 m long and weigh 400–600 kg. Males weigh less than females, usually about 500 kg or less, male and female Weddell seals are generally about the same length, though females can be slightly larger. However, the male tends to have a thicker neck. A molecular genetic based technique has been established to confirm the sex of individuals in the laboratory, the Weddell seal face has been compared to that of a cat due to a short mouth line and similarities in the structure of the nose and whiskers. Their upturned mouths give them the appearance of smiling, the Weddell seal grows a thin fur coat around its whole body except for small areas around the flippers. The colour and pattern of the varies, often fading to a duller colour as the seal ages. This coat moults around the beginning of summer, adults are generally brown, with lighter ventral pelage. They are mottled with darker and lighter patches, those on the belly being silvery white. Adult males usually bear scars, most of them around the genital region, young Weddell seals have gray pelage for the first 3 to 4 weeks, later, they turn a darker color
8.
Elephant seal
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Elephant seals are large, oceangoing earless seals in the genus Mirounga. The two species, the elephant seal and the southern elephant seal, were both hunted to the brink of extinction by the end of the 19th century, but the numbers have since recovered. The northern elephant seal, somewhat smaller than its southern relative, the most northerly breeding location on the Pacific Coast is at Race Rocks, at the southern tip of Vancouver Island in the Strait of Juan de Fuca. In southern Chile, there is a colony of 120 animals at Jackson Bay, Admiralty Sound. The oldest known unambiguous elephant seal fossils are fossils of an unnamed member of the tribe Miroungini described from the late Pliocene Petane Formation of New Zealand. Elephant seals breed annually and are faithful to colonies that have established breeding areas. Elephant seals take their name from the proboscis of the adult male. The bulls proboscis is used in producing extraordinarily loud roaring noises, more importantly, however, the nose acts as a sort of rebreather, filled with cavities designed to reabsorb moisture from the animals exhalations. This is important during the season when the seals do not leave the beach to feed. Northern elephant seal bulls reach a length of 4.3 to 4.8 m, elephant seals spend upwards of 80% of their lives in the ocean. They can hold their breath for more than 100 minutes – longer than any other noncetacean mammal, elephant seals dive to 1,550 m beneath the oceans surface. Their stomachs also often contain gastroliths, while excellent swimmers, they are also capable of rapid movement on land. Elephant seals are shielded from cold by their blubber, more so than by fur. The animals hair and outer layers of skin molt in large patches, the skin has to be regrown by blood vessels reaching through the blubber. When molting occurs, the seal is susceptible to the cold, northern males and young adults haul out during June to July to molt, northern females and immature seals during April to May. Elephant seals have a large volume of blood, allowing them to hold a large amount of oxygen for use when diving. They have large sinuses in their abdomens to hold blood and can store oxygen in their muscles with increased myoglobin concentrations in muscle. In addition, they have a proportion of oxygen-carrying red blood cells
9.
Crabeater seal
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The crabeater seal is a true seal with a circumpolar distribution around the coast of Antarctica. They are by far the most abundant seal species in the world, while population estimates are uncertain, there are at least 7 million and possibly as many as 75 million individuals. This success of species is due to its specialized predation on the abundant Antarctic krill of the Southern Ocean, for which it has uniquely adapted. Indeed, its name, translated as lobe-toothed crab eater. Despite its name, crabeater seals do not eat crabs, as well as being an important krill predator, the crabeater seal is an important component of the diet of leopard seals, which consume about 80% of all crabeater pups. The crabeater seal shares a recent ancestor with the other Antarctic seals. These include the Ross seal, leopard seal and Weddell seal and these species, collectively belonging to the Lobodontini tribe of seals, share teeth adaptations including lobes and cusps useful for straining smaller prey items out of the water column. Adult seals grow to a length of 230 cm and an average weight of around 200 kg. A molecular genetic based technique has been established to confirm the sex of individuals in the laboratory, large crabeater seals can weigh up to 300 kg. Pups are about 120 cm in length and 20 to 30 kg at birth. While nursing, pups grow at a rate of about 4.2 kg a day, pups are born with a light brown, downy pelage, until the first molt at weaning. After molting, their fur is a darker brown fading to blonde on their bellies, the fur lightens throughout the year, becoming completely blonde in summer. Older animals become progressively paler, even when freshly molted, crabeaters have relatively slender bodies and long skulls and snouts compared to other phocids. Perhaps their most distinctive adaptation is the unique dentition that enables this species to sieve Antarctic krill, the postcanine teeth are finely divided with multiple cusps. Together with the fit of the upper and lower jaw. They spend the year on the pack ice zone as it advances. They colonized Antarctica during the late Miocene or early Pliocene, at a time when the region was warmer than today. The population is connected and fairly well mixed, and genetic evidence does not suggest any subspecies separations, currently, no reliable estimates of the total crabeater seal population are available
10.
Queen Maud Land
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Queen Maud Land is a c.2.7 million-square-kilometre region of Antarctica claimed as a dependent territory by Norway. The territory lies between 20° west and 45° east, between the British Antarctic Territory to the west and the Australian Antarctic Territory to the east. On most maps there had been an area between Queen Maud Lands borders of 1939 and the South Pole until June 12,2015 when Norway formally annexed that area. Positioned in East Antarctica, the territory comprises about one-fifth of the area of Antarctica. The claim is named after the Norwegian queen Maud of Wales, Norwegian Hjalmar Riiser-Larsen was the first person known to have set foot in the territory, in 1930. On 14 January 1939, the territory was claimed by Norway, from 1939 until 1945, Nazi Germany claimed New Swabia, which consisted of part of Queen Maud Land. On 23 June 1961, Queen Maud Land became part of the Antarctic Treaty System and it is one of two Antarctic claims made by Norway, the other being Peter I Island. They are administrated by the Polar Affairs Department of the Norwegian Ministry of Justice, most of the territory is covered by the Antarctic ice sheet, and a tall ice wall stretches throughout its coast. In some areas further within the ice sheet, mountain ranges breach through the ice, allowing for birds to breed, the region is divided into the Princess Martha Coast, Princess Astrid Coast, Princess Ragnhild Coast, Prince Harald Coast and Prince Olav Coast. The waters off the coast are called the King Haakon VII Sea, there is no permanent population, although there are 12 active research stations housing a maximum average of 40 scientists, the numbers fluctuating depending on the season. Six are occupied year-round, while the remainder are seasonal summer stations, the territory is estimated to cover around 2,700,000 square kilometres. The limits of the claim, put forth in 1939, did not fix the northern and southern limits other than as the beach in Antarctica. With the land lies beyond this beach and the sea beyond. The sea that extends off the coast between the limits of Queen Maud Land is generally called King Haakon VII Sea. There is no land at the coast, the coast consists of a 20-to-30-metre high wall of ice throughout almost the entire territory. It is thus possible to disembark from a ship in a few places. The other major mountain ranges are the Heimefront Range, Orvin Mountains, Wohlthat Mountains, geologically, the ground of Queen Maud Land is dominated by Precambrian gneiss, formed c.1 to 1.2 Ga, before the creation of the supercontinent Gondwana. The mountains consist mostly of crystalline and granitic rocks, formed c.500 to 600 Ma in the Pan-African orogeny during the assembly of Gondwana, in the farthest western parts of the territory, there are younger sedimentary and volcanic rocks
11.
United States
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
12.
Earth
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Earth, otherwise known as the World, or the Globe, is the third planet from the Sun and the only object in the Universe known to harbor life. It is the densest planet in the Solar System and the largest of the four terrestrial planets, according to radiometric dating and other sources of evidence, Earth formed about 4.54 billion years ago. Earths gravity interacts with objects in space, especially the Sun. During one orbit around the Sun, Earth rotates about its axis over 365 times, thus, Earths axis of rotation is tilted, producing seasonal variations on the planets surface. The gravitational interaction between the Earth and Moon causes ocean tides, stabilizes the Earths orientation on its axis, Earths lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earths surface is covered with water, mostly by its oceans, the remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earths polar regions are covered in ice, including the Antarctic ice sheet, Earths interior remains active with a solid iron inner core, a liquid outer core that generates the Earths magnetic field, and a convecting mantle that drives plate tectonics. Within the first billion years of Earths history, life appeared in the oceans and began to affect the Earths atmosphere and surface, some geological evidence indicates that life may have arisen as much as 4.1 billion years ago. Since then, the combination of Earths distance from the Sun, physical properties, in the history of the Earth, biodiversity has gone through long periods of expansion, occasionally 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 7.4 billion humans live on Earth and depend on its biosphere and minerals for their survival. Humans have developed diverse societies and cultures, politically, the world has about 200 sovereign states, the modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe. It has cognates in every Germanic language, and their proto-Germanic root has been reconstructed as *erþō, originally, earth was written in lowercase, and from early Middle English, its definite sense as the globe was expressed as the earth. By early Modern English, many nouns were capitalized, and the became the Earth. More recently, the name is simply given as Earth. House styles now vary, Oxford spelling recognizes the lowercase form as the most common, another convention capitalizes Earth when appearing as a name but writes it in lowercase when preceded by the. It almost 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 Gya the primordial Earth had formed, the formation and evolution of Solar System bodies occurred along with the Sun
This article incorporates public domain material from the United States Geological Survey document "East Antarctica" (content from the Geographic Names Information System).
