An ancient lake bed 350 kilometers long has been discovered beneath the sands of Egypt's vast Sahara desert. Geologist Ted Maxwell at the Smithsonian National Air and Space Museum in Washington DC, and colleagues examined high resolution pictures. The lake appeared around 250,000 years ago - during a period of wet climate when the region would have been covered in grasslands - and dried up 80,000 years ago, covering an area of 68,200 square kilometers at its peak.