Antarctica is the Earth's southernmost continent, roughly centered around the South Pole. 98% of Antarctica is covered by a gigantic ice sheet, averaging 1.6 kilometers (1.0 mi) thick, which contains about 60% of the world's fresh water. The continent has the most extreme climate of any continent, experiencing the world's lowest temperatures and least rain. It is also the continent most devoid of life, with animals only living near the coasts. Antarctica has only a couple of short rivers which flow only during the summer. The continent is mainly inhabited by research scientists on temporary stays, with a population of about 4,000 during the summer and 1,000 during winter.
A long time ago, approximately 40 million years in the past, Antarctica was still connected to South America by land as well as being connected to Australia as part of a land continent called Gondwana. Gondwana has not located as close to the South Pole as Antarctica is today, and had a tropical and sub-tropical climate, complete with dense forests and marsupial fauna. Then, approximately 40 million years ago, Australia broke away from Antarctica, beginning to isolate it. Around this time, an Ice Age on Earth began, and Antarctica cooled down, becoming more of a tundra climate.
23 million years ago, Antarctica finally broke from South America, and the Drake Passage opened, allowing a freezing circumpolar current to circulate Antarctica. The Ice Age was in full swing, and snow hitting the ground in Antarctica stopped melting, even during the summer, and continental ice sheets began to form. By about 15 million years ago, most of the continent was covered in ice.
Antarctica was not discovered by humans until 27 January 1820, when Russian Imperial Navy captain Von Bellingshausen sighted the Antarctic mainland from his ship. For millennia previous, geographers had suspected the existence of a vast, far south land — which they called "Terra Australis" — to "balance" out the land masses of the north. The reasoning is not especially sound, but these geographers ended up being right.
Today, Antarctica is home to just over a dozen research bases, manned by scientific researchers from over a dozen countries. Even a few families live in Antarctica on a temporary basis, as their relatives work in the facilities there. There is even an Antarctic base at the South Pole itself.