Once Green Sahara Dried Up Slower Than Previously Thought, Study Says

Washington D.C. (AHN) - The Sahara turned into Earth's largest hot desert 2,700 years ago much slower than previously believed, a new study says. The report clashes with an earlier theory that desertification of the area came abruptly.

The new research is based on deposits from a unique desert lake in remote northern Chad.

Despite constant drought and searing heat, Lake Yoa, sustained by prehistoric groundwater, has survived for several thousand years. The lake contains an unbroken climate record going back at least 6,000 years.

Lead study author Stefan Kröpelin of the Institute of Prehistoric Archaeology at the University of Cologne in Germany says that many fossil clues preserved in the lake's sediments suggest that a gradual transformation to a desert environment.

The region also was inhabited, according to the European-U.S.-Canadian team of scientists behind a study in Science magazine dated May 9. Those findings contradict previous theories that there was a rapid collapse of vegetation in the region in a sudden end to the African Humid Period, about 5,500 years ago.

The new study says the transition of Sahara to desert took its time and scientists found evidence for a slow decline in tropical plants, followed by the gradual loss of savannah-type grasslands, and then the eventual spread of desert species, National Geographic reported.

The decrease in tropical trees accelerated 4,800 years ago, while desert plants took root between 3,900 and 3,100 years ago, pollen samples reveal.

The only rapid change noted was in the lake itself, which switched from a freshwater to a salt lake between 4,200 and 3,900 years ago. Further research at Lake Yoa should provide clues to a potential regreening of the Sahara, scientists say, adding that it could be triggered by the current trend of global warming.