Buried Saharan rivers might have been early expressways
Humans might have migrated across the arid region along three once-lush waterways
Web edition: September 12, 2013
Three rivers now interred beneath heaps of sand in the Sahara Desert might have been the superhighways of the Stone Age.
Simulations reveal that the rivers, each about as big as the Missouri
or Rhine River, meandered across the Sahara 125,000 years ago. Early
humans probably followed the lush corridors as migration routes across
North Africa, scientists propose September 11 in PLOS ONE.
Satellite data and other geologic evidence had previously suggested
that now-extinct rivers once snaked across the Sahara. But the records
couldn’t say when and how much water flowed, says Jennifer Smith, a
geologist at Washington University in St. Louis. The simulation, she
says, “gives us a much clearer picture of these landscapes.”
The ancient rivers existed when the winds of the African monsoon were
up to 1,000 kilometers farther north than today and brought seasonal
rain to mountains in the central Sahara. The rain ran down the peaks and
flowed north toward the Mediterranean Sea.
Although the Sahara was wetter, much of it was still semiarid, says
study coauthor Tom Coulthard, a hydrologist at the University of Hull in
England. “We were quite pessimistic about whether there was enough
water to make it across the desert.”
But that’s just what Coulthard and colleagues found. The team
simulated how much rain fell on mountains in southern Algeria, southern
Libya and northern Chad over a 25-year period roughly 125,000 years ago.
They then used topographic maps to see how rainwater flowed across 12
million square kilometers of North Africa.
Their findings indicate that two rivers were perennially present in
parts of eastern Libya, northern Chad and western Egypt while a third,
seasonal river was 2,000 kilometers to the west in Algeria. In addition,
more than 70,000 square kilometers of lagoons and wetlands covered
northeastern Libya. The team didn’t simulate runoff to the Nile, but
that river probably would have been around too, Coulthard says.
Plants and animals living around the rivers probably drew early
humans to these waterways. The western river may have been a preferred
route, the researchers speculate. The river connected a humid,
mountainous area in the south with a wet, temperate region along the
Mediterranean coast. Dozens of archaeological sites dating to around
this time pepper the western region; only a few have been found near the
eastern rivers.
The lack of archaeological sites in the east may simply reflect a
preservation bias or a preference in where researchers have looked, says
Michael Petraglia, an archaeologist at Oxford who wasn’t part of the
study.
Chris Stringer, an anthropologist at the Natural History Museum in
London, suggests a similar simulation of African rivers 100,000 years
ago could help researchers understand how unique human behaviors, such
as bead-making and pigment use, spread across Africa around this time.
Humans might have migrated across the arid region along three once-lush waterways
Web edition: September 12, 2013
Three rivers now interred beneath heaps of sand in the Sahara Desert might have been the superhighways of the Stone Age.
Simulations reveal that the rivers, each about as big as the Missouri
or Rhine River, meandered across the Sahara 125,000 years ago. Early
humans probably followed the lush corridors as migration routes across
North Africa, scientists propose September 11 in PLOS ONE.
Satellite data and other geologic evidence had previously suggested
that now-extinct rivers once snaked across the Sahara. But the records
couldn’t say when and how much water flowed, says Jennifer Smith, a
geologist at Washington University in St. Louis. The simulation, she
says, “gives us a much clearer picture of these landscapes.”
The ancient rivers existed when the winds of the African monsoon were
up to 1,000 kilometers farther north than today and brought seasonal
rain to mountains in the central Sahara. The rain ran down the peaks and
flowed north toward the Mediterranean Sea.
Although the Sahara was wetter, much of it was still semiarid, says
study coauthor Tom Coulthard, a hydrologist at the University of Hull in
England. “We were quite pessimistic about whether there was enough
water to make it across the desert.”
But that’s just what Coulthard and colleagues found. The team
simulated how much rain fell on mountains in southern Algeria, southern
Libya and northern Chad over a 25-year period roughly 125,000 years ago.
They then used topographic maps to see how rainwater flowed across 12
million square kilometers of North Africa.
Their findings indicate that two rivers were perennially present in
parts of eastern Libya, northern Chad and western Egypt while a third,
seasonal river was 2,000 kilometers to the west in Algeria. In addition,
more than 70,000 square kilometers of lagoons and wetlands covered
northeastern Libya. The team didn’t simulate runoff to the Nile, but
that river probably would have been around too, Coulthard says.
Plants and animals living around the rivers probably drew early
humans to these waterways. The western river may have been a preferred
route, the researchers speculate. The river connected a humid,
mountainous area in the south with a wet, temperate region along the
Mediterranean coast. Dozens of archaeological sites dating to around
this time pepper the western region; only a few have been found near the
eastern rivers.
The lack of archaeological sites in the east may simply reflect a
preservation bias or a preference in where researchers have looked, says
Michael Petraglia, an archaeologist at Oxford who wasn’t part of the
study.
Chris Stringer, an anthropologist at the Natural History Museum in
London, suggests a similar simulation of African rivers 100,000 years
ago could help researchers understand how unique human behaviors, such
as bead-making and pigment use, spread across Africa around this time.
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