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The Sahara desert contained the world's largest freshwater lake until it evaporated in just a few hundred years, a new study has found. Researchers used satellite images to map abandoned shore lines around Palaeolake Mega-Chad, and analysed sediments to calculate the age of these shore lines, producing a lake level history spanning the last 15,000 years. At its peak around 6,000 years ago, Palaeolake Mega-Chad was the largest freshwater lake on Earth, with an area of 360,000 square km.