A 3,200-year interlude of tropical rains once transformed the eastern Sahara into a verdant savanna where seminomadic people thrived amid elephants, cattle and more than 30 species of fish, according to German researchers.
After collecting more than 500 radiocarbon dates at 150 sites in an area larger than Western Europe, University of Cologne researchers found that the sudden climate change 10,500 years ago coaxed thousands of people to move into the now desolate expanse.
The researchers based their dates on bone, charcoal and human artifacts found in the area.
The prehistoric settlements show evidence of the first attempts in Africa at raising cattle and fashioning ceramic pottery, said geo-archeologist Stefan Kroepelin, one of the authors of the paper, published Friday in the journal Science.
The ancient people of the Sahara also left artwork behind, including a depiction of swimmers on a cave wall in Gilf Kebir, an area that is only sand today.
The greening of the eastern Sahara was part of a broad climatic change that, in part, occurred when Earth drew slightly closer to the sun, Kroepelin said.
Around 8500 BC, wild grains grew over dunes and the area came to resemble the present-day Serengeti National Park in Kenya, he said. The areas around the Nile River that had been settled by humans turned into uninhabitable marshland.
The researchers believe that the eastern Sahara, which includes parts of Egypt, Sudan, Libya and Chad, began to dry out around 5300 BC, and that most of the tribes had retreated eastward to the Nile or southward to northern Sudan by 3500 BC.
Kroepelin said current global warming could one day make the Sahara habitable again.
"The Sahara is a past and future place to live for mankind," he said.