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During the early part of the Mesozoic Era (which lasted from 251 million to 65 million years ago) Antarctica was a part of Pangaea, the giant supercontinent that included nearly all land on Earth. About 240 million years ago Pangaea began to split into two giant landmasses called Laurasia and Gondwanaland (also called Gondwana). Gondwanaland consisted of the present continent of Antarctica along with Australia, South America, Africa, and the Indian subcontinent. Gondwanaland itself began to break up about 185 million years ago. Antarctica gradually moved towards the South Pole. About 80 million years ago, Antarctica split from Australia and became an isolated land mass that drifted southward into its polar position. Climatic cooling began about 34 million years ago during the Oligocene Epoch. Coupled with mountain building, this cooling initiated the formation of permanent ice on land, resulting in the Antarctic ice sheet. The giant ice sheet in East Antarctica has been a stable feature for about 15 million years, beginning in the Miocene Epoch. The ice sheet on West Antarctica has collapsed and reformed a number of times during the same period.
East Antarctica makes up about two-thirds of the continent’s area. The land beneath the ice consists of a basement complex of ancient gneisses, schists, and other metamorphic rocks overlaid by sediments from the Cambrian and Permian periods. Containing evidence of tropical forests and deserts prior to the more recent glacial conditions, these layers reflect the region’s complex climatic history. Covering the land is a huge, complex ice dome rising from coastal plains to a high plateau more than 4,000 m (13,000 ft) in elevation. The Transantarctic Mountains stretch 3,500 km (2,200 mi) along the entire western flank of East Antarctica, separating it from West Antarctica. This range holds back the plateau ice of East Antarctica like a massive dam, penetrated by glaciers that flow into the Ross and Filchner-Ronne ice shelves to the west. High peaks—some rising to more than 4,300 m (14,000 ft)—poke through the ice sheet, and other portions of the range are dry valleys that are free of ice. Toward the Indian and Pacific ocean coasts lie several minor ice domes and lower plateaus, some penetrated by other mountain ranges.
The remaining third of the continent, West Antarctica, consists of a much lower, undulating ice sheet covering a complex of mountainous islands. The Antarctic Peninsula, the “tail” of land reaching toward South America, was formed by the same geologic processes that formed the Andes Mountains on that continent. Many islands, including the South Shetland Islands, lie off the Antarctic Peninsula. Deep trenches and basins beneath the ice separate the islands of West Antarctica. Vinson Massif, the highest point in Antarctica, has an elevation of 4,897 m (16,066 ft) and lies in the Sentinel Range near the Filchner-Ronne Ice Shelf. Several active volcanoes, including Mount Erebus on Ross Island, dot coastal and island areas. The multilayered land formations of West Antarctica, folded and transformed by geologic structural deformations, reveal a distinct, more turbulent geological history than that of East Antarctica. These formations consist of a Precambrian basement covered by volcanic sediments from the Carboniferous Period, Mesozoic Era, and Cenozoic Era. These volcanic sediments are in turn covered by plant-bearing Jurassic and later Cenozoic sediments.
Soils are extremely rare in Antarctica, occurring only in ice-free areas where fine rock debris can accumulate. In summer, the soils provide a damp substrate for plants such as lichens and moss, and for microorganisms. The continent’s two species of flowering plants may gain a foothold in favorable conditions found in West Antarctica. There is no Antarctic equivalent of Arctic tundra.
Unusual geological features on Antarctica include dry valleys and lakes buried deep beneath the ice sheet. Dry valleys are ice-free valleys carved by glaciers that have retreated during the past few thousand years. The valleys receive little or no snow and are mainly surfaced by rock or gravel, with summer streams and almost permanently frozen lakes. Unusual plants, animals, and microbes survive in the simple ecosystems. Much larger bodies of water called subglacial lakes have been found under the ice sheet. The largest known is Lake Vostok, which covers about 11,655 square km (5,400 square mi) in area, similar in size to Lake Ontario. Such lakes may contain interesting microbes that are unknown elsewhere, but scientists have not yet found ways of drilling down to to the lakes without severely contaminating them. A complex system of subglacial lakes may also affect how fast ice sheets and glaciers move to the coast and break up as icebergs.