The rains stopped coming, the temperature rose, and the great grasslands of North Africa turned to desert thousands of years ago. These changes may have helped develop the foundations of civilization in the Nile Valley.
The transition to today's arid climate was not gradual, but took place over two episodes. The first is from 6700 to 5500 years ago and the second is from 4000 to 3600 years ago, according to an article published in the journal Geophysical Research Letters.
“The last period was very difficult, it destroyed ancient civilizations and socio-economic systems,” the researchers write.
A team of researchers led by Martin Klassen from the Potsdam Institute for the Study of Climate Change in Germany analyzed computer climate models over the past several thousand years.
They concluded that the current desert climate in the Sahara was caused by changes in the Earth's orbit and the tilt of the Earth's axis. While the changes in the Earth's orbit were gradual, the transformations in the climate and flora of North Africa were dramatic.
Dramatic changes in the climate and vegetation of the Sahara have occurred over hundreds of years, scientists said. There were no more grass and other plants collecting water and giving it back to the atmosphere; hot sand and strong sun now dominate the region, and rivers and streams have dried up.
This event devastated the ancient civilizations in the area, now only rock carvings remind of them. The changes may have stimulated them to move to the Nile Valley and other river valleys, where great civilizations developed.
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"But the migration of people from the Sahara to the Nile is a hypothesis," said Klassen. "Whether migration really was an incentive for advanced civilizations is not yet known exactly … It seems plausible to me,"
Classen and his team used computer climate models to calculate the effects of weather, oceans, and vegetation separately and in various combinations. They concluded that the oceans play only a minor role in the desertification of the Sahara.
The study also suggested that the ways and techniques of land use of the people of the Sahara were not significant causes of desertification.
Klassen noted that changes in the Earth's orbit and the tilt of its axis will occur in the future.