For thousands of years, the Nile River has fertilized valleys along its winding path through northeastern Africa, anchoring ancient civilizations and still serving as an important route of transport and irrigation today.
But the age of its venerable waters, which stretch over 4,225 miles (6,800 kilometers), has been debated, with one group of experts claiming the river was born around 6 million years ago when a drainage system changed course, while another claims the river is five times older than that.
A new study finds evidence that supports the latter theory: The Nile River may have emerged around 30 million years ago, driven by the motion of Earth’s mantle — the thick layer of rock between the Earth's core and crust, a group of researchers reported on Nov. 11 in the journal Nature Geoscience.
The Nile River is thought to have formed at the same time as the Ethiopian highlands, said lead author Claudio Faccenna, a professor at the Jackson School of Geosciences, University of Texas. The Ethiopian highlands is where one of the Nile River's major tributaries or branches, called the Blue Nile, begins.
The Blue Nile brings in the majority of the Nile River's water — and most of the sediments in it— joining with the river's other tributary (the White Nile) in Sudan, before emptying out into the Mediterranean Sea.
Faccenna and his team had previously analyzed sediments collected from the Nile Delta — land created as sediment is deposited where the river meets the Mediterranean — and compared their composition and age with ancient volcanic rock found on the Ethiopian plateau. They found that the sediments and rocks matched and were between 20 million and 30 million years old, suggesting the river formed at the same time as the plateau.
So then the researchers were interested in seeing how the river was possibly connected to Earth’s mantle, as the theory suggested, Faccenna told Live Science. In the new study, Faccenna and colleagues created a computer simulation that replayed 40 million years of Earth's plate tectonics — a theory that suggests Earth's outer shell is cut up into pieces that move around and glide over the mantle.
Their simulation showed that a hot mantle plume — an upsurge of extremely hot rock in the mantle — pushed the ground upward, creating the Ethiopian highlands and also activated a still-existing mantle "conveyor belt" that pushes upward on the Ethiopian highlands in the south and pulls the ground down in the north. This creates a northward slope, on which the Nile still runs, Faccenna said.
It's unclear if the Nile River ever changed its course throughout its life — if even slightly — and that's something that Faccenna and his team hope to figure out in the future. They also want to implement this method to analyze how the mantle might have also changed the course of other rivers around the world.
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Originally published on Live Science.