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| More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time, Gondwana gradually broke apart and Antarctica as we know it today was formed around 25 million years ago. Antarctica was not always cold, dry, and covered in ice sheets. At a number of points in its long history, it was farther north, experienced a tropical or temperate climate, was covered in forests, and inhabited by various ancient life forms. | | More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time, Gondwana gradually broke apart and Antarctica as we know it today was formed around 25 million years ago. Antarctica was not always cold, dry, and covered in ice sheets. At a number of points in its long history, it was farther north, experienced a tropical or temperate climate, was covered in forests, and inhabited by various ancient life forms. |
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| ===Palaeozoic era (540–250 Ma)===
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| During the Cambrian period, Gondwana had a mild climate. West Antarctica was partially in the Northern Hemisphere, and during this period large amounts of sandstones, limestones and shales were deposited. East Antarctica was at the equator, where sea floor invertebrates and trilobites flourished in the tropical seas. By the start of the Devonian period (416 Ma), Gondwana was in more southern latitudes and the climate was cooler, though fossils of land plants are known from this time. Sand and silts were laid down in what is now the Ellsworth, [[Horlick Mountains|Horlick]] and Pensacola Mountains. Glaciation began at the end of the Devonian period (360 Ma), as Gondwana became centred on the South Pole and the climate cooled, though flora remained. During the Permian period, the land became dominated by seed plants such as Glossopteris, a pteridosperm which grew in swamps. Over time these swamps became deposits of coal in the [[Transantarctic Mountains]]. Towards the end of the Permian period, continued warming led to a dry, hot climate over much of Gondwana.
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| ===Mesozoic era (250–66 Ma)===
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| As a result of continued warming, the polar ice caps melted and much of Gondwana became a desert. In [[Eastern Antarctica]], seed ferns or pteridosperms became abundant and large amounts of sandstone and shale were laid down at this time. ''Synapsids'', commonly known as "mammal-like reptiles", were common in Antarctica during the Early Triassic and included forms such as Lystrosaurus. The Antarctic Peninsula began to form during the Jurassic period (206–146 Ma), and islands gradually rose out of the ocean. Ginkgo trees, conifers, bennettites, horsetails, ferns and cycads were plentiful during this period. In West Antarctica, coniferous forests dominated through the entire Cretaceous period (146–66 Ma), though southern beech became more prominent towards the end of this period. Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only three Antarctic dinosaur genera (''Cryolophosaurus'' and ''Glacialisaurus'', from the Hanson Formation, and ''Antarctopelta'') have been described to date. It was during this era that Gondwana began to break up.
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| However, there is some evidence of antarctic marine glaciation during the Cretaceous period.
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| ===Gondwana breakup (160–23 Ma)===
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| The cooling of Antarctica occurred stepwise, as the continental spread changed the oceanic currents from longitudinal equator-to-pole temperature-equalising currents to latitudinal currents that preserved and accentuated latitude temperature differences.
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| Africa separated from Antarctica in the Jurassic, around 160 Ma, followed by the Indian subcontinent in the early Cretaceous (about 125 Ma). By the end of the Cretaceous, about 66 Ma, Antarctica (then connected to Australia) still had a subtropical climate and flora, complete with a marsupial fauna. In the Eocene epoch, about 40 Ma Australia-New Guinea separated from Antarctica, so that latitudinal currents could isolate Antarctica from Australia, and the first ice began to appear. During the Eocene–Oligocene extinction event about 34 million years ago, CO2 levels have been found to be about 760 ppm and had been decreasing from earlier levels in the thousands of ppm.
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| Around 23 Ma, the Drake Passage opened between Antarctica and South America, resulting in the Antarctic Circumpolar Current that completely isolated the continent. Models of the changes suggest that declining CO2 levels became more important. The ice began to spread, replacing the forests that then covered the continent.
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| ===Neogene Period (23–0.05 Ma)===
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| Since about 15 Ma, the continent has been mostly covered with ice.
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| Meyer Desert Formation biota
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| Main article: Meyer Desert Formation biota
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| Fossil Nothofagus leaves in the Meyer Desert Formation of the Sirius Group show that intermittent warm periods allowed Nothofagus shrubs to cling to the Dominion Range as late as 3–4 Ma (mid-late Pliocene). After that, the Pleistocene ice age covered the whole continent and destroyed all major plant life on it.
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| ===Present-day===
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| The geological study of Antarctica has been greatly hindered by nearly all of the continent being permanently covered with a thick layer of [[ice]]. However, new techniques such as remote sensing, ground-penetrating radar and satellite imagery have begun to reveal the structures beneath the ice. | | The geological study of Antarctica has been greatly hindered by nearly all of the continent being permanently covered with a thick layer of [[ice]]. However, new techniques such as remote sensing, ground-penetrating radar and satellite imagery have begun to reveal the structures beneath the ice. |
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