| Summary: | Antarctica consists of two geologically distinct provinces, a Precambrian craton in the eastern hemisphere, and a younger series of mobile belts south of the Pacific Ocean. Unlike its land-based counterpart covering the East Antarctic craton, the base of the West Antarctic ice sheet (WAIS) is largely below sea level in the Ross and Weddell embayments. The East Antarctic craton separated from the other southern continents during the Mesozoic fragmentation of the Gondwanaland supercontinent. Since separation, East Antarctica has been near the South Pole and during the immediate past-40 million year history of Cenozoic continental glaciation, Antarctica has remained close to its present position. During the breakup of Gondwanaland, the four major crustal units that comprise the exposed rocks of West Antarctica-the Antarctic Peninsula, Thurston Island, the Ellsworth-Whitmore mountains, and Marie Byrd Land rotated outward from the convergent Pacific margin of the East Antarctic craton as rigid blocks. The driving forces for this relative motion appear to have been a major mantle plume in the case of the Antarctic Peninsula, Ellsworth-Whitmore
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