Modern humans arose in sub-Saharan Africa as early as 200,000 years ago, but our species did not venture beyond Africa until at least 80,000 years later. Just why they took so long to travel north is not clear, but many researchers have suggested that the bone-dry Sahara Desert was a major barrier to migrations from the south. Yet a new study indicates that the Sahara was crossed by wide rivers during a wet period that began about 120,000 years ago, providing a hospitable corridor for humans on the move.
The first sightings of Homo sapiens out of Africa, fossil skeletons from caves in modern-day Israel, are dated to between 120,000 and 90,000 years ago. Human evolution experts had long focused their attention on the most obvious corridor: The Nile River, whose previously disconnected segments between central Africa and the eastern Mediterranean Sea joined up beginning about 120,000 years ago. Recent research in North Africa, however, has uncovered stone tools and human fossils all along the Mediterranean coast and even in the Sahara. Some of these sites are dated to at least 90,000 years ago and possibly somewhat earlier, demonstrating that humans were able to survive in the area at about that time. In addition, a flurry of new climate studies suggests that the eastern Sahara received heavy rainfalls from Indian Ocean monsoons during this same period. Satellite radar imaging has revealed a system of more than 800 kilometers of channels, some more than 5 kilometers wide, now buried under the sands.
See the above page for more, which includes a map.
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