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Scientists have shed new light on the age of the Sahara, the world's largest hot desert, which covers a vast expanse of the African continent.
The age of the desert has been the subject of controversy for decades, with various groups of researchers offering different estimates.
"People have been trying to understand this for several decades," said Daniel Muhs, a geologist at the US Geological Survey in Denver, Colorado, in a statement. "More recent studies say that it was the beginning of the Pleistocene [about 2.6 million years ago.]"
Others suggest that the desert could have formed even further – about seven million years ago. In addition, other researchers still claim that the desert was wet and green about 5,000 years ago, covered with swamps and lakes
Now, research by Muhs and his colleagues indicates that the desert is at least 4.6 million years old, bringing new evidence to the long-standing debate that has emerged.
Muhs drew his conclusions after analyzing the ancient Saharan dust that had invaded the Spanish Canary Islands, located off the northwestern coast of Africa.
The Canaries are affected by a meteorological phenomenon known locally as "Calima" that occurs every year and causes large amounts of dust from the Sahara to the Atlantic Ocean.
On two of the islands – Fuerteventura and Gran Canaria – scientists have been investigating sediments to identify and date any of these ancient dusts in so-called paleosols – buried ancient soils.
"With Spanish geologist colleagues from the University of Las Palmas, we searched for buried soils, sandwiched between layers of dated volcanic rocks (basalts)," Muhs told Newsweek. "There are places both on the island of Gran Canaria and on the island of Fuerteventura where buried soils like this occur, sometimes between volcanic eruptions."
"A thick soil buried on Gran Canaria lies between lava flows that are about 3 million years old, and in Fuerteventura there is a series of six soils buried between dune sands." -he declares. "Below the oldest sand dune is a lava dating back about 4.8 million years ago and the youngest (highest) date of about 2.8 million years ago. Therefore, all 6 of these buried soils are between 4.8 and 2.8 million years old. "
The team sampled the soils of both islands, studied them in laboratories of the United States Geological Survey and found that they all contained quartz and mica. These are abundant in African dust but rare in the volcanic rocks that dominate the Canaries.
"It tells us that these minerals are exotic, and the easiest way to get them to the Canary Islands is to move them by the wind, in dust storms, from the neighboring Sahara," said Muhs. "Part of the dust continues to move west, but some of the dust is trapped by the vegetation of the Canary Islands and is added to the soil."
The researchers were able to date approximately the date that this dust could have dissipated using layers of volcanic rock containing minerals acting as geological clocks, thus allowing geologists to determine when the lava was cooling down and solidified.
The findings of the team indicate that even the oldest buried soil, perhaps a little less than 4.8 million years ago, contains Saharan minerals.
"This tells us that the Sahara is at least several million years old and that it probably fertilizes the leeward soils, like the Canary Islands, for much longer than we thought," said Muhs. "This could even include adding nutrients to the nutrient-poor soils of the Amazon rainforest, as the Saharan dust travels almost every year now."
"The same process of fertilizing Saharan dust in the Amazonian forest could therefore last for several million years," he said.
These results are consistent with data collected in deepwater sediments that indicate an increase in Saharan dust blown on the Atlantic at least 4.6 million years ago. Although this suggests that the desert is at least as old, the results do not rule out the possibility that it was formed sooner.
If the team were able to find older paleosols containing Saharan dust, it would be possible to conclude that the desert is even older.
Mathieu Schuster, a scientist from the University of Strasbourg, who did not participate in the research, said the latest work brings "a new type of evidence for the antiquity of the Sahara desert" . Previously, he was involved in research that the desert was about 7 million years old.
"The result obtained by Professor Muhs and his team is in keeping with the existing knowledge based on the isolated wind dust found in the marine register, as well as on the Chadian in situ wind dune deposits of the Chad Basin that my colleagues and I have published. a few years ago. "
Schuster said that in recent decades, the origin of the Sahara was considered relatively new and related to the Quaternary Ice Age, which began about 2.58 million years ago. ; years.
"It was then quite controversial for us to propose that the Sahara desert be 7 million years old," he said. "I am therefore very happy to read about the work and results of Prof. Muhs This work is important because we now have a decent set of independent results strongly suggesting the antiquity of the Sahara desert."
This article has been updated to include additional comments by Daniel Muhs and Mathieu Schuster.
Daniel Muhs
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