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The Sahara Desert Is Twice as Old as Previously Thought

Once upon a time, North Africa was a lush, vegetated landscape.
Image: Hans Kylberg/Flickr

The world's largest hot desert wasn't always so. Once upon a time, North Africa was a lush, vegetated landscape; now it's the Sahara. Scientists have been working to figure out what exactly happened to force such a transition and also when.

We already knew that the Sahara wasn't always like it is today. There are populations of crocodiles found living in Mauritania, in temporary wetlands that form after rain, that are surrounded by sand dunes and rocks for miles around. Researchers think these crocs date back to a lusher, greener Sahara of 8,000 to 10,000 years ago.

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Scientists have also found that the Sahara desert is actually sensitive small changes in Earth's orbit, and Earth's tilt has changed ever so slightly—from 24.14 degrees 9,000 years ago, to its current 23.45 degrees. They date the Sahara's current arid state to around 5,440 years ago, give or take 30 years or so, when summer temperatures increased sharply, and precipitation decreased.

But a paper just published in the journal Nature has worked out what made North Africa so sensitive to changes in the Earth's orbit in the first place: the death of an ancient giant ocean, the Tethys, some seven to 11 million years ago.

Using "snapshot simulations," the team behind the current paper found that, as the tectonic plates shifted and the Tethys ocean became the Mediterranean, Black, and Caspian Seas (at around :36 above), the African monsoon was weakened. Consequently, the Sahara's climate destabilized and became subject to the whims of Earth's orbit—a boom and bust between being humid and being a desert.

The researchers also note that, "interestingly, these major changes in North African climate and environment are coincident with an important time period for the emergence of early hominids." I for one would be ready to walk upright out of anywhere that's alternating between those climates.