Antarctica is Earth's southernmost continent, overlying the South Pole. It is situated in the southern hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. About 98% of Antarctica is covered by ice, which averages at least 1.6 kilometres (1.0 mi) in thickness. On average, Antarctica is the coldest, driest and windiest continent, and has the highest average elevation of all the continents. Since there is little precipitation, except at the coasts, the interior of the continent is technically the largest desert in the world. There are no permanent human residents. Only cold-adapted plants and animals survive there, including penguins, fur seals, mosses, lichen, and many types of algae. The continent remained largely neglected until the 20th century because of its hostile environment, lack of resources, and isolation. The Antarctic Treaty was signed in 1959 that prohibits military activities and mineral mining, supports scientific research, and protects the continent's ecozone.