A continent centred on the South Pole, situated mainly within the Antarctic Circle and almost entirely covered by an ice sheet. Exploration at first concentrated on establishing the existence of a continent. Bransfield, Biscoe, Foster, Wilkes, Ross, and Dumont D’Urville all explored the coastline of Antarctica between 1820 and 1840. Later explorers concentrated on reaching the South Pole. Scott pioneered the way in 1902, followed by Shackleton in 1908; in 1911 Amundsen was the first to reach the Pole, and Scott reached it a month later. The American aviator Richard Byrd flew over the South Pole in 1929. Although there is no permanent human habitation, Norway, Australia, France, New Zealand, and the UK claim sectors of the continent (Argentina and Chile claim parts of the British sector); its exploration and exploitation are governed by an international treaty (Antarctic Treaty) of 1959 renewed in 1991.