The Dry Sahara (broadcast Friday, May 9th, 2008)

Lake Yoa, Ounianga Kebir, Northeast Chad. The Sahara's largest lake is wholly sustained by fossil groundwater dating from the humid past. Its bottom deposits provide the only continuous high-resolution climate archive of the world's major desert. Image courtesy of S. Kröpelin / University of Cologne

What made the Sahara Desert go dry -- and is there any water there left to be found? Writing in the journal Science, a team of researchers reports this week that they believe that the drying of the Sahara was not a sudden event, but rather took place over some 6000 years. The researchers looked at sediment samples taken from cores drilled in the bottom of Lake Yoa, one of the Sahara's few remaining lakes. The sediment layers at the bottom of the lake show a gradual change, the researchers say, involving a gradual reduction in the abundance of tropical vegetation, followed by the loss of grass cover, and the eventual establishment of the modern desert plant community. Arid conditions similar to those today were in place as much as 2700 years ago, the team found. We'll talk with one of the authors of the controversial study, which counters several previous findings indicating a more sudden change in conditions in the Sahara. We'll also talk about whether the ancient waters of the Sahara remain hidden under the desert -- and, if so, what can be done to locate them. Teachers, find more information about using Science Friday as a classroom resource in the Kids' Connection.

Guests

Stefan Kropelin
Geo-archaeologist
Senior Research Scientist, Africa Research Unit, Institute of Prehistoric Archaeology
University of Cologne
Koeln, Germany