Antarctica is the world's most southern continent. It is located in the Southern Hemisphere's Antarctic zone, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. It is the fifth-largest continent, covering 14,200,000 square kilometers, and is nearly twice the size of Australia. With just 5,000 inhabitants in the summer and 1,000 in the winter, it is by far the least populated continent. With the exception of the McMurdo Dry Valleys and the northernmost ranges of the Antarctic Peninsula, 98% of Antarctica is covered by ice with an average thickness of 1.9 km. Antarctica is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Despite the fact that much of Antarctica is a polar desert, with annual precipitation of just 200 mm along the coast and much less inland, the continent holds 80% of the world's freshwater reserves, enough to lift global sea levels by around 60 meters if it all melted. The temperature in Antarctica has fallen to 89.2 degrees Celsius, despite the fact that the average for the third quarter is 63 degrees Celsius. Many forms of algae, bacteria, fungi, plants, protista, and animals native to Antarctica include mites, nematodes, penguins, seals, and tardigrades. Tundra vegetation is found where it grows. Antarctica was the last continent to be discovered, with the Fimbul ice shelf being discovered in 1820 by the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on the Vostok and Mirny. Because of its harsh climate, lack of easily available resources, and isolation, the continent was largely ignored for the rest of the nineteenth century. The United States Exploring Expedition, led by Lieut. Robert F. Scott, explored land in Antarctica for the first time in January 1840, almost simultaneously. A separate French expedition led by Jules Dumont d'Urville joined Charles Wilkes. The latter made a temporary landing, while the Wilkes expedition stayed in the area long enough to survey and chart some 800 miles of the continent, despite not landing. In 1895, a group of Norwegians made the first confirmed landing. Parties to the Antarctic Treaty System control Antarctica. The Antarctic Treaty was signed by twelve countries in 1959, and thirty-eight countries have since signed it. Military operations, mineral extraction, nuclear accidents, and nuclear waste disposal are all prohibited by the treaty. It promotes scientific study while also safeguarding the continent's biodiversity. At research stations strewn throughout the continent, between 1,000 and 5,000 people from various countries live.