When was sahara desert formed

The Sahara is the world's largest and most legendary subtropical desert, but knowledge about it is surprisingly limited. Even estimates of when it formed vary widely, from more than five million years ago to mere thousands. Now, however, geologists studying wind-carried Saharan dust on the Canary Islands have come closer to pinning this down: it is, they report, close to five million years old.

One reason for the uncertainty over the Sahara's age is that researchers use such different methods to estimate it; these include studying desert dust found in sediment under the Atlantic Ocean, analyzing sandstone and modeling the ancient climate. To help settle things, geomorphologist Daniel Muhs of the U. Geological Survey lead author on the new research and his colleagues looked at sediment on Spain's Fuerteventura and Gran Canaria islands, where they found evidence of Saharan dust.

The dust appeared in ancient soil layers, whose age they assessed on the basis of fossils found in the same layers—and that age agreed with earlier marine sediment studies. Note: Content may be edited for style and length. Science News. Journal Reference : William R. Boos, Robert L. Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall.

Nature Geoscience , ; 9 12 : DOI: ScienceDaily, 30 November It was as if, every time humans and their goats and cattle hopscotched across the grasslands, they had turned everything to scrub and desert in their wake. Wright thinks this is exactly what happened. He suggests this may have triggered the end of the humid period more abruptly than can be explained by the orbital changes. These nomadic humans also may have used fire as a land management tool, which would have exacerbated the speed at which the desert took hold.

Instead, the culprits might be regular old vegetation feedbacks and changes in the amount of dust. And then at some point you pass the tipping point where change accelerates. During the last humid period, the Sahara was filled with hunter-gatherers. That said, there's geologic evidence from ocean sediments that these orbitally-paced Green Sahara events occur as far back as the Miocene epoch 23 million to 5 million years ago , including during periods when atmospheric carbon dioxide was similar to, and possibly higher, than today's levels.

So, a future Green Sahara event is still highly likely in the distant future. Today's rising greenhouse gases could even have their own greening effect on the Sahara, though not to the degree of the orbital-forced changes, according to a March review published in the journal One Earth. But this idea is far from certain, due to climate model limitations. Meanwhile, there is another way to turn parts of the Sahara into a green landscape; if massive solar and wind farms were installed there, rainfall could increase in the Sahara and its southern neighbor, the semiarid Sahel, according to a study published in the journal Science.

Wind and solar farms can increase heat and humidity in the areas around them, Live Science previously reported. An increase in precipitation, in turn, could lead vegetation growth, creating a positive feedback loop, the researchers of that study said.

However, this huge undertaking has yet to be tested in the Sahara Desert, so until such a project gets funding, humans might have to wait until the year or longer to see whether the Sahara will turn green again.

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