The new research indicates that a series of long-buried river channels may have provided alternative routes through the arid terrain of modern-day Chad and Libya.

Using radar imagery, a team of scientists led by Anne Osborne, a geochemist at the University of Bristol, discovered fossilised river channels weaving north from the central Saharan watershed into the Mediterranean. These indicate that a known period of wet weather, which affected southern parts of the Sahara during the interglacial period (130–117,000 years ago), spread further north than previously thought, providing a web of wet corridors through the inhospitable Saharan environment for early humans to follow. Subsequent analysis of fossilised snail shells extracted from the channels proved that these rivers were in flow during the period when Homo sapiens is thought to have migrated.

‘The study shows, for the first time, that monsoon rains fed rivers that extended from the Saharan watershed, across the northern Sahara, to the Mediterranean Sea,’ said Dr Derek Vance, one of the paper’s senior authors.

‘These corridors rivalled the Nile Valley as potential routes for early modern human migrations to the Mediterranean shores.’

January 2009