Once Lush Sahara Dried Up Over Millennia, Study Says

The grassy prehistoric Sahara turned into Earth's largest hot desert more slowly than previously thought, a new report says—and some say global warming may turn the desert green once again.

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

Lake Yoa, sustained by prehistoric groundwater, has survived for millennia despite constant drought and searing heat.