Geologists have found that a huge lake waxed and waned deep in the sandy heart of the Egyptian Sahara.
Tushka region of Egypt is covered by a huge sand sheet today, but years ago, it was home to a lake as big as one of the Great Lakes, said T Maxwell, a geologist at the Smithsonian National Air and Space Museum in Washington.
Radar images taken from the space shuttle have confirmed that a lake broader than Lake Erie once sprawled a few hundred kilometres west of the Nile, reports Science News.
Knowing where and when such oases existed could help archaeologists understand the environment Homo sapiens travelled while migrating out of Africa for the first time, said team leader Maxwell.
"You realise that, hey, this place was full of really large lakes when people were wandering into the rest of the world," he said.
At perhaps its greatest extent, the Tushka Lake would have covered more than 68,000 square kilometres. At other times less water would have flown into the low-lying basin from the Nile.
Since then, desert winds have eroded and sands have buried much of the region's landscape, said Maxine Kleindienst, an anthropologist at the University of Toronto.
Other studies have found evidence of mega-lakes in Chad, Libya and Sudan at various points over the past 250,000 years.
The findings were reported in the journal Geology.
