Dust reveals age of the Sahara

One of the great mysteries is the moment when the Sahara came into being. Wild guesses range between 2.6 and 7.0 million years ago. Others still think that the desert was wet and green around 5,000 years ago, covered in swamps and lakes.

Now, new research indicates that the desert is around 4.6 million years old[1]. The conclusion was reached after analyzing ancient Saharan dust that had blown over to the Spanish Canary Islands—which lie off the coast of northwestern Africa in the Atlantic Ocean.

The Canary Islands are affected by a weather phenomenon known locally as the 'Calima' which occurs every year and drags vast quantities of dust from the Sahara across the Atlantic Ocean. On two of the islands - Fuerteventura and Gran Canaria - the scientists investigated sediments to identify and date of this ancient dust in so-called paleosols; buried, ancient soils.

When the Sahara was still lush and moist no (or hardly any) dust would have been able to reach the Canary Islands. So, what the scientists needed to find was the first level of dust and hopefully date this dust via known and dated basalt from volcanic eruptions.

"One thick buried layer of sand on Gran Canaria is found between lava flows that are both about three million years old. On Fuerteventura, there is a series of six buried levels of dust between dune sands," lead scientist Daniel Muhs said. "Below the oldest dune sand is a lava dated to about 4.8 million years old and the youngest (uppermost) one is dated to about 2.8 million years. So, all six of these buried soils are between 2.8 million years and 4.8 million years old."

These results agree with data collected from deep-sea sediments that indicate increases in Saharan dust being blown over the Atlantic at least 4.6 million years ago[2].

Combining both results indicate an age for the Sahara of between 3.0 and 4.8 million years.

[1] Muhs et al: The Antiquity Of The Sahara Desert: New Evidence From The Mineralogy And Geochemistry Of Pliocene Paleosols On The Canary Islands, Spain in GSA Annual Meeting in Phoenix, Arizona, USA – 2019
[2] Tiedeman et al: Climatic Changes in the Western Sahara: Aeolo-Marine Sediment Record of the Last 8 Million Years (Sites 657-661) in Proceedings of the Ocean Drilling Program: Scientific Results – 1989. See here.