Archaeologica.org

Six thousand years ago, northern Africa was a place of trees, grasslands, lakes and people. Today, it is the Sahara — a desolate area larger area than Australia.

Lake Yoa, in northeastern Chad, has remained a lake through the millennia and is still a lake today, surrounded by hot desert. Although little rain falls, Lake Yoa’s water is replenished from an underground aquifer.

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.