Sahara's lost rivers reveal man at work

The Sahara may be a by-word in deserts nowadays, but half a million years ago prehistoric humans lived and made tools there amongst plentiful rivers.

Radar observations carried out by the Space Shuttle in 1981 pointed towards the existence below the Saharan surface of dried-up ancient riverbeds which, when they flowed, would have made ideal sites for early humans to build villages.

New, unpublished research by Professor Vance Haynes at the University of Arizona, suggests that the rivers were flowing about 400,000 years ago, and that those early humans made tools such as hand axes and even meat cleavers. The findings, from digging by a team of archaeologists from the university, indicates that what is now wasteland was once a fertile area. During previous ice ages - the last of which was only 10,000 years ago - it may have been a temperate, fertile region, compared with chillier areas further north.

Today it is one of the most inhospitable places on the planet, devoid of vegetation, less than a millimetre of rain annually, and with baking temperatures.

Present theories suggest that humans originated in the Great Rift Valley area of central Africa, where fossils of hominids from up to 3 million years ago have been found. But palaeontologists have wondered about how widely early humans were spread across the continent, and how they would have migrated to other countries. If they were well-established in northern Africa, using the fertile Sahara as a base, then they might have arrived in Europe and Asia far earlier than if they were mainly based in mid- Africa and migrated north.

Early results of the work were announced last January. Previously, imaging radar deployed from the Space Shuttle has been used to uncover buried parts of the Great Wall of China, providing precise indicators to archaeologists of where to begin digging. The same radar has also been used to indicate the areas of northern Africa where the present-day continents collided 650 million years ago.

"These data reveal geologic structures buried beneath the thin skin of desert sands, like an X-ray's ability to study the inside of a human body," said Robert Stern, of the University of Texas at Dallas, who helped set up the radar system. "If you're standing on the surface there is little to be seen. The geologic structures we are seeing are obscured by a few inches to a few feet of sand."

According to fossils found in 1995 in Kenya, the first hominids may have evolved about 4.2 million years ago, much earlier than "Lucy", who first walked upright 3.2 million years ago in Olduvai Gorge, Tanzania.