Antarctica
Antarctica is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest continent, being about 40% larger than Europe, and has an area of. Most of Antarctica is covered by the Antarctic ice sheet, with an average thickness of.
Antarctica is, on average, the coldest, driest, and windiest of the continents, and has the highest average elevation. It is mainly a polar desert, with annual precipitation of over along the coast and far less inland. About 70% of the world's freshwater reserves are frozen in Antarctica, which, if melted, would raise global sea levels by almost. Antarctica holds the record for the lowest measured temperature on Earth,. The coastal regions can reach temperatures over in the summer. Native species of animals include mites, nematodes, penguins, seals and tardigrades. Where vegetation occurs, it is mostly in the form of lichen or moss.
The ice shelves of Antarctica were probably first seen in 1820, during a Russian expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev. The decades that followed saw further exploration by French, American, and British expeditions. The first confirmed landing was by a Norwegian team in 1895. In the early 20th century, there were a few expeditions into the interior of the continent. British explorers Douglas Mawson, Edgeworth David, and Alistair Mackay were the first to reach the magnetic South Pole in 1909, and the geographic South Pole was first reached in 1911 by Norwegian explorer Roald Amundsen.
Antarctica is governed by about 30 countries, all of which are parties of the 1959 Antarctic Treaty System. According to the terms of the treaty, military activity, mining, nuclear explosions, and nuclear waste disposal are all prohibited in Antarctica. Tourism, fishing and research are the main human activities in and around Antarctica. During the summer months, about 5,000 people reside at research stations, a figure that drops to around 1,000 in the winter. Despite the continent's remoteness, human activity has a significant effect on it via pollution, ozone depletion, and climate change. The melting of the potentially unstable West Antarctic ice sheet causes the most uncertainty in century-scale projections of sea level rise, and the same melting also affects the Southern Ocean overturning circulation, which can eventually lead to significant impacts on the Southern Hemisphere climate and Southern Ocean productivity.
Etymology
The name given to the continent originates from the word antarctic, which comes from Middle French antartique or antarctique and, in turn, the Latin antarcticus. Antarcticus is derived from the Greek ἀντι- and ἀρκτικός. The Greek philosopher Aristotle wrote in Meteorology about an "Antarctic region" in. The Greek geographer Marinus of Tyre reportedly used the name in his world map from the second century CE, now lost. The Roman authors Gaius Julius 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, and from there the Middle English pol antartik, found first in a treatise written by the English author Geoffrey Chaucer.Belief by Europeans in the existence of a Terra Australis—a vast continent in the far south of the globe to balance the northern lands of Europe, Asia, and North Africa—had existed as an intellectual concept since classical antiquity. The belief in such a land lasted until the European discovery of Australia.
During the early 19th century, explorer Matthew Flinders doubted the existence of a detached continent south of Australia and thus advocated for the "Terra Australis" name to be used for Australia instead. In 1824, the colonial authorities in Sydney officially renamed the continent of New Holland to Australia, leaving the term "Terra Australis" unavailable as a reference to Antarctica. Over the following decades, geographers used phrases such as "the Antarctic Continent". They searched for a more poetic replacement, suggesting names such as Ultima and Antipodea. Antarctica was adopted in the 1890s, with the first use of the name being attributed to the Scottish cartographer John George Bartholomew.
Antarctica has also been known by the moniker Great White South, after which British photographer Herbert Ponting named one of his books on Antarctic photography, possibly as a counterpart to the epithet Great White North for Canada.
Geography
Positioned asymmetrically around the South Pole and largely south of the Antarctic Circle, Antarctica is surrounded by the Southern Ocean. Rivers exist in Antarctica; the longest is the Onyx. Antarctica covers more than, almost double the area of Australia, making it the fifth-largest continent, and comparable to the surface area of Pluto. Its coastline is almost long: as of 1983, of the four coastal types, 44% of the coast is floating ice in the form of an ice shelf, 38% consists of ice walls that rest on rock, 13% is ice streams or the edge of glaciers, and the remaining 5% is exposed rock.The lakes that lie at the base of the continental ice sheet occur mainly in the McMurdo Dry Valleys or various oases. Lake Vostok, discovered beneath Russia's Vostok Station, is the largest subglacial lake globally and one of the largest lakes in the world. It was once believed that the lake had been sealed off for millions of years, but scientists now estimate its water is replaced by the slow melting and freezing of ice caps every 13,000 years. During the summer, the ice at the edges of the lakes can melt, and liquid moats temporarily form. Antarctica has both saline and freshwater lakes.
Antarctica is divided into West Antarctica and East Antarctica by the Transantarctic Mountains, which stretch from Victoria Land to the Ross Sea. The vast majority of Antarctica is covered by the Antarctic ice sheet, which averages in thickness. The ice sheet extends to all but a few oases, which, with the exception of the McMurdo Dry Valleys, are located in coastal areas. Several Antarctic ice streams flow to one of the many Antarctic ice shelves, a process described by ice-sheet dynamics.
East Antarctica comprises Coats Land, Queen Maud Land, Enderby Land, Mac. Robertson Land, Wilkes Land, and Victoria Land. All but a small portion of the region lies within the Eastern Hemisphere. East Antarctica is largely covered by the East Antarctic Ice Sheet. There are numerous islands surrounding Antarctica, most of which are volcanic and very young by geological standards. The most prominent exceptions to this are the islands of the Kerguelen Plateau, the earliest of which formed around 40 Ma.
Vinson Massif, in the Ellsworth Mountains, is the highest peak in Antarctica at. Mount Erebus on Ross Island is the world's southernmost active volcano and erupts around 10 times each day. Ash from eruptions has been found from the volcanic crater. There is evidence of a large number of volcanoes under the ice, which could pose a risk to the ice sheet if activity levels were to rise. The ice dome known as Dome Argus in East Antarctica is the highest Antarctic ice feature, at. It is one of the world's coldest and driest places—temperatures there may reach as low as, and the annual precipitation is.
Geologic history
From the end of the Neoproterozoic era to the Cretaceous, Antarctica was part of the supercontinent Gondwana. Modern Antarctica was formed as Gondwana gradually broke apart beginning around 183 Ma. For a large proportion of the Phanerozoic, Antarctica had a tropical or temperate climate, and it was covered in forests.Paleozoic era (539–252 Ma)
During the Cambrian period, Gondwana had a mild climate. West Antarctica was partially in the Northern Hemisphere, and during the time, large amounts of sandstones, limestones, and shales were deposited. East Antarctica was at the equator, where seafloor invertebrates and trilobites flourished in the tropical seas. By the start of the Devonian period, Gondwana was in more southern latitudes, and the climate was cooler, though fossils of land plants are known from then. Sand and silts were laid down in what is now the Ellsworth, Horlick, and Pensacola Mountains.Antarctica became glaciated during the Late Paleozoic icehouse beginning at the end of the Devonian period, though glaciation would substantially increase during the late Carboniferous. It drifted closer to the South Pole, and the climate cooled, though flora remained. After deglaciation during the latter half of the Early Permian, the land became dominated by glossopterids, most prominently Glossopteris, a tree interpreted as growing in waterlogged soils, which formed extensive coal deposits. Other plants found in Antarctica during the Permian include Cordaitales, sphenopsids, ferns, and lycophytes. At the end of the Permian, the climate became drier and hotter over much of Gondwana, and the glossopterid forest ecosystems collapsed, as part of the Permian–Triassic extinction event. There is no evidence of any tetrapods having lived in Antarctica during the Paleozoic.
Mesozoic era (252–66 Ma)
The continued warming dried out much of Gondwana. During the Triassic period, Antarctica was dominated by seed ferns belonging to the genus Dicroidium, which grew as trees. Other associated Triassic flora included ginkgophytes, cycadophytes, conifers, and sphenopsids. Tetrapods first appeared in Antarctica during the Early Triassic epoch, with the earliest known fossils found in the Fremouw Formation of the Transantarctic Mountains. Synapsids included species such as Lystrosaurus, and were common during the Early Triassic.The Antarctic Peninsula began to form during the Jurassic period. Africa separated from Antarctica in the Jurassic around 160 Ma, followed by the Indian subcontinent in the early Cretaceous. Ginkgo trees, conifers, Bennettitales, horsetails, ferns and cycads were plentiful during the time. About 80 million years ago, flowering plants became the most diverse groups of plants on the continent. In West Antarctica, coniferous forests dominated throughout the Cretaceous period, though southern beech trees became prominent towards the end of the Cretaceous. Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only a few Antarctic dinosaur genera have been described.