  The continent of Antarctica is remarkable in many ways. Unlike the northern Arctic, which is frozen ice floating on water, Antarctica is solid land that remains ice-covered year-round. It wasn't always this way ... as the continents drifted around the surface of the Earth over many millions of years, Antarctica has moved from the tropics to its current position over the South Pole. Antarctica is the coldest and windiest of the continents. It is also one of the driest ... less than 5 cm water-equivalent of snowfall per year. Yet even this tiny quantity of snowfall has accumulated into 4 km thick ice sheets over hundreds of thousands of years. The climate there is determined by a number of factors, including its extreme southern location, its high elevation, and the huge extent of sea ice that surrounds it during winter. Yet despite the inhospitable conditions, Antarctica's human population continues to grow. Conditions for living and working in Antarctica have changed greatly since the days of the first explorers. No longer must scientists leave the continent in the fall before the sea around the continent freezes ... Antarctic bases are maintained in comfort throughout the long dark winter months by air, while scientific study continues.  Antarctica's icecap contains almost 70% of the world's fresh water, and 90% of the world's ice. Huge icebergs break off each year from the ice shelves at the edge of the continent, and half of the surrounding ocean freezes over in winter, more than doubling the size of the continent.But climate change is threatening to melt the ice surrounding the continent, which has and will lead to massive regions of the coastal ice shelf breaking off and falling into the sea. It is thought that the next massive release of ice may cause ocean sea levels to rise by several feet, which would spell disaster for coastal communities and cities around the world. Studying the ice will also tell us about the past. Locked up in its 4 km thick ice sheet is a record of the Earth's climate in the past 500,000 years. Trapped bubbles in the ice contain atmospheric gases, ... evidence for levels of global pollution by industry, agriculture and atomic bombs, and for ozone depletion in the upper atmosphere. Because Antarctica sits at the South Pole, it shares one feature with the north polar regions besides cold. As the tilt of the Earth points the northern regions toward the sun for six months, giving the southern hemisphere winter, the South Pole region turns through each 24 hour day without seeing the sun at all. Winter passes in total darkness. As the Earth passes a certain point in its orbit, the northern hemisphere begins to point away from the sun, and experiences winter; in the south there is summer, and at the South Pole, the spinning Earth gives most of the continent 24 hours of sunshine every day, for 6 months. But summer at the South Pole is not like our summer. The sun may be in the sky for 24 hours, but as it moves around the horizon it never gets very high. Temperatures don't go much above freezing, so the snow and ice remain.  Cold dense air from the high centre of the continent flows outward towards the coast. The Earth's rotation causes these winds to deflect leftward, and as they encounter the steep slopes of the coast, become very strong. Sir Douglas Mawson's 1912-13 expedition, while at Cape Denison, recorded a world record yearly average wind speed of 19.4 m/s (70 km/h), and experienced gale-force winds on all but one of 203 consecutive winter days! On the coast, temperatures make it up to about the freezing mark (0°C) in the summer (December-February) months, or even slightly positive in the northern peninsula. During winter, however, temperatures average between -10°C and -30°C. Conditions in the interior, which is at a much higher altitude and farther from the ocean, are a lot colder; summer temperatures are rarely above -20°C, and in winter average -60°C. Vostok station holds the record for the lowest ever temperature recorded at the surface of the Earth ... an incredible -89.5°C.  There are now about 40 permanent scientific bases, or 'stations', in the Antarctic region The first permanently maintained base was Mawson, built by the Australians in 1954 on the coast. The United States built the first permanent inland base at the South Pole, and New Zealand built Scott Base on Ross Island, nearby.Over four thousand people work in Antarctica over the summer, but this drops to less than one thousand in winter. Many people are there to provide food, administration, communications, and training for the scientific and research personnel. The southern continents on Earth were once joined in a single supercontinent, Gondwanaland, with Antarctica in the centre. Over a period of 150 million years this supercontinent broke up and moved apart, to form the continents we know today. Buried under the ice of Antarctica is a rich collection of fossils, which will tell us much about the land as it was when it was situated farther north. Fossil finds in Antarctica have included the 1982 discovery of the first mammal remains, the 1986 discovery of the first dinosaur fossil. Such fossils have provided a nearly complete record of the breakup of the ancient supercontinent. There is much more we can learn. Less than 1% of the continent is free of ice and snow in summer, so the organisms living there are well adapted to survive the long, cold, dry winters. Physicians have made discoveries about the behavior of viruses in a cold, isolated environment. Psychological and sleep studies are frequently conducted during the winter, when Antarctica is isolated from the outside world. In the future, the sampling of a lake buried under 3.7 km of ice might reveal bacteria over half a million years old. Antarctica is a land unique on Earth, shared by the many countries which maintain bases there, including the U.S., Australia, Germany, New Zealand, England, Argentina, Russia, and many others. The Antarctic Treaty of 1961 describes how Antarctica is to be used; its objectives are:
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