May 10, 2008

Sahara desert formed slowly

A new research is based on deposits from a unique desert lake in remote northern Chad suggests that Sahara, the biggests desert in the World, gradually transformed into desert from a green savannah. This study contradicts past research that suggested the region dried up within a few hundred years.

Lake Yoa, sustained by prehistoric groundwater, has survived for millennia despite constant drought and searing heat. The body of water contains an unbroken climate record going back at least 6,000 years, said study lead author Stefan Kröpelin of the Institute of Prehistoric Archaeology at the University of Cologne in Germany. Ancient pollen, insects, algae, and other fossil clues preserved in the lake's sediments point to a gradual transformation to a desert environment.

The pollen samples revealed that the decrease in tropical trees accelerated after 4,800 years ago, while desert plants took root between 3,900 and 3,100 years ago. The study supports previous archaeological findings that human populations in the Sahara moved south over several millennia, following the monsoon rains.


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