The Antarctic region is defined by the Antarctic Treaty as the land and ice shelves south of 60° S. Antarctica is the 5th largest continent and is primarily covered in thick ice. There are no permanent residents in Antarctica, but depending on the time of year, there can be anywhere from 1000 to 5000 people stationed at various research stations. These stations include U.S. stations McMurdo Station on Ross Island, and the Amundsen-Scott South Pole Station at the geographic South Pole.