Three river systems that once flowed over 100,000 years ago have been identified in the Sahara Desert of North Africa.  Satellite images from 30 years ago suggested they may be there, buried under the sands of Libya, Algeria and Tunisia. But new research by Dr. Michael Rogerson, a Senior Lecturer in Paleoclimatology at the University of Hull in England, has helped confirm their existence. Climate models from that era, together with the topography of the region, suggest that monsoons produced enough rainfall to form rivers that would have to have flowed south to north.  One of the rivers carried enough water to flow through Libya to the Mediterranean, possibly providing a green corridor for early human migration out of Africa.