ÂÒÂ×Ðã in the News: Shift From Savannah to Sahara Was Gradual
9 May 2008
Kenneth Chang, 'New York Times'Ìý Six thousand years ago, northern Africa was a place of trees, grasslands, lakes and people.
Lake Yoa, in northeastern Chad, has remained a lake through the millennia and is still a lake today, surrounded by hot desert. …
By analyzing thousands of layers sediment in a core drilled from the bottom of this lake, an international team of scientists has reconstructed the region's climate as the savannah changed to Sahara. …
In Friday's issue of the journal Science, the researchers, led by Stefan Kröpelin, a geologist with the Institute of Prehistoric Archaeology at the University of Cologne in Germany, report that the climate transition occurred gradually. …
The findings run counter to a prevailing view that the change happened abruptly, within a few centuries, about 5,500 years ago. …
That view arises from ocean sediment cores drilled off the coast of Africa, to the west of Mauritania. …
"On the face of it, it's puzzling," said Jonathan A. Holmes, director of the ÂÒÂ×Ðã Environmental Change Research Center. Dr. Holmes said both sets of research had been carefully done, and the challenge will be to put together a more complex history of the Sahara's climate. …
Dr. Holmes said one possibility was that the offshore dust might reflect a drop in water levels around Lake Chad, revealing more dust-producing soil, rather than a large-scale change in climate. …