Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic 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 29 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 or () and the Latin (). is derived from the Greek () and (, ). 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 in the second century AD. The Roman authors Gaius Julius Hyginus and Apuleius used for the South Pole the romanised Greek name , from which derived the Old French (modern ) attested in 1270, and from there the Middle English , found first in a treatise written by the English author Geoffrey Chaucer.
European ideas regarding the existence of a —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. Terra Australis was therefore the name used to refer to all hypothetical landmasses proposed to be where Antarctica is now known to exist. Assertion of the presence of such a land lasted until the European discovery of Australia.
In the early 19th century, explorer Matthew Flinders doubted the existence of a detached continent south of Australia, then called New Holland, and advocated for the "Terra Australis" name to be used for Australia instead. In 1824, the colonial authorities in Sydney 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.
Geography
Positioned asymmetrically around the South Pole and largely south of the Antarctic Circle (one of the five major circles of latitude that mark maps of the world), 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. , 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. 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 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. The Neoproterozoic fusion of Antarctica into Gondwana likely resulted in extensive mountain formation. Modern Antarctica was formed as Gondwana gradually broke apart beginning in the Early Jurassic, around 183 Ma. For a large proportion of the Phanerozoic, Antarctica had a relatively temperate climate, and it was covered in forests, despite being at high latitude for most of the last 400 million years.
Paleozoic era (539–252 Ma)
During the Cambrian period, Gondwana had a mild climate. Mountainous areas of Antarctica may have undergone extensive erosion during the early Palaeozoic. From the Cambrian to the Devonian, Antarctica drifted to from being situated in the tropics to being situated at high temperate latitudes, and partly within the Antarctic Circle by the end of the Devonian. The Mid-Late Devonian Aztec Siltstone in Victoria Land has yielded an important fauna of early jawed fish, and also (along with the underlying Beacon Heights Orthoquartzite) indicates that Antarctica had by this time been colonised by vegetation, including lycopods. Pollen records indicate that during the Late Devonian, Antarctica was colonised by the progymnosperm Archaeopteris, one of the first large woody trees.
Antarctica became glaciated during the Late Paleozoic icehouse beginning at the end of the Devonian period (360 Ma), 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 (an extinct group of seed plants with no close living relatives), 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 (terrestrial vertebrates) 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 (pteridosperms) 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. Animals known from this formation include therapsids, including cynodonts, therocephalians, and dicynodonts (notably Lystrosaurus), temnospondyl amphibians, as well as procolophonid and archosauromorph reptiles, who likely lived in a subarctic to temperate climate.
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 (about 125 Ma). 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. Across Antarctica, coniferous forests, predominantly composed of podocarps and araucarian conifers, dominated throughout the Cretaceous period (143–66 Ma), though southern beech trees (Nothofagus) 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 (Cryolophosaurus and Glacialisaurus, from the Early Jurassic Hanson Formation of the Transantarctic Mountains, and Antarctopelta, Trinisaura, Morrosaurus and Imperobator from Late Cretaceous of the Antarctic Peninsula) have been described.
Cenozoic era before present (66–10 Ma)