Shuttle images reveal Egypt's lost great lake

Desert drainage patterns point to ancient oases in Sahara

A huge lake once waxed and waned deep in the sandy heart of the Egyptian Sahara, geologists have found.



Radar images taken from the space shuttle confirm that a lake broader than Lake Erie once sprawled a few hundred kilometers west of the Nile, researchers report in the December issue of Geology. Since the lake first appeared around 250,000 years ago, it would have ballooned and shrunk until finally petering out around 80,000 years ago.
Knowing where and when such oases existed could help archaeologists understand the environment Homo sapiens traveled while migrating out of Africa for the first time, says team leader Ted Maxwell, a geologist at the Smithsonian National Air and Space Museum in Washington, D.C. Modern humans arose in Africa about 200,000 years ago.
“You realize that hey, this place was full of really large lakes when people were wandering into the rest of the world,” he says.

Since then, desert winds have eroded and sands have buried much of the region’s landscape, says Maxine Kleindienst, an anthropologist at the University of Toronto. But during next summer’s field season, she and her colleagues will be checking for ancient shorelines at the elevations suggested in the new paper.
Other studies have found evidence of mega-lakes in Chad, Libya and Sudan at various points over the past 250,000 years. The new study targeted Egypt, some 400 kilometers west of the Nile, where in the 1980s researchers reporting finding fish fossils in the desert.
That discovery, says Maxwell, triggered scientists to think about how those fish could have gotten there. In 2000, astronauts on the space shuttle Endeavour used a radar instrument to take high-resolution pictures of the area’s topography. Maxwell and his colleagues recently analyzed those pictures to deduce how water would have drained across northeastern Africa over the past few hundred thousand years, ever since the Nile was born.
In Egypt, west of the Nile Valley in a region known as Tushka, the researchers spotted a low-lying area where water would have pooled after overflowing from the river, carrying fish with it. At its maximum, this ancient lake would have stretched for 350 kilometers, down to the modern-day Sudan border.
At the time, the Tushka area had more rainfall than today and would have been covered by grasslands, says Maxwell. Heavy rain in highlands to the south, from where the Nile flows, would have caused the lake to grow; dry spells shrank it. “This lake was going up and going down in size, doing all kinds of things over multiple thousands of years,” he says.
Something similar is going on today at a smaller scale, says Mohamed Abdelsalam, a geologist at the Missouri University of Science and Technology in Rolla. Just northeast of where the huge paleolake once lay, the Nile also overflowed, starting in 1998. A series of five small “new lakes of the Sahara” was born. Deprived of water since 2003, these lakes have since almost entirely dried out, says Abdelsalam.
Today, for water, Egyptians rely almost exclusively on the Nile and its annual floods. The ancient lakes, says Maxwell, suggest that such flooding was already under way, at least to some degree, a quarter million years ago.

Visor might protect troops from blasts

Current military helmet lets explosive forces in through the face, computer simulations show

 
Adding a face shield to the standard-issue helmet worn by U.S. troops could help protect soldiers from traumatic brain injury, the signature wound of the recent wars in Iraq and Afghanistan. A new study that models how shock waves pass through the head finds that adding a face guard deflects a substantial portion of the blast that otherwise would steamroll its way through the brain.
The study, to appear in the Proceedings of the National Academy of Sciences, is part of a spate of new work tackling traumatic brain injury. An estimated 1.5 million Americans sustain mild traumatic brain injury each year, and nearly 200,000 service members have been diagnosed with it since 2000, according to the Armed Forces Health Surveillance Center in Silver Spring, Md. While direct impact, such as banging the head, clearly can injure the brain, the forces endured when explosives send shock waves crashing through the head are much more difficult to characterize.
In the new study, researchers led by Raúl Radovitzky of MIT’s Institute for Soldier Nanotechnologies created an elaborate computer model of a human head that included layers of fat and skin, the skull, and different kinds of brain tissue. The team modeled the shock wave from an explosion detonated right in front of the face under three conditions: with the head bare, protected by the currently used combat helmet and covered with the helmet plus a polycarbonate face shield.
The results showed that today’s helmet doesn’t exacerbate the damage, as some previous research had suggested. But at least in terms of blast protection, the current helmet doesn’t help much either. Addition of a face shield would improve matters, the team reports.
“The face shield contributes a lot to deflecting energy from the blast wave and not letting it directly touch the soft tissue,” says Radovitzky. “We’re not saying this is the best design for a face shield, but we’re saying we need to cover the face.”
To validate the model, researchers at MIT and elsewhere will have to conduct experiments in the real world. But the work points to an intrinsic flaw in the current helmets.
“These helmets weren’t designed to stop a pressure wave; they were designed to stop bullets,” says Albert King, director of the Bioengineering Center at Wayne State University in Detroit. “Just like a football helmet wasn’t designed to stop a concussion, but to stop skull fracture.”
Designing a blast-resistant helmet requires a better knowledge of what happens in the brain when an explosion washes over it. Soldiers experiencing explosions often describe a wind or wave that makes them see stars. “I really got my bell rung,” is a common report.
The resulting “mild” traumatic brain injury doesn’t lead to long-term loss of consciousness, and brain scans yield normal results. But labeling these injuries as mild is a misnomer, says Douglas Smith, director of the Center for Brain Injury and Repair at the University of Pennsylvania in Philadelphia.
“It is not mild; that term has led people astray,” says Smith. “It is something very serious that can lead to severe dysfunction.”
Smith and his colleagues have been working on a sensor that could be placed in a helmet or vehicle and that, like the radiation badges worn by nuclear-plant workers, would indicate exposure to blast forces likely to cause brain injury. The sensor is described in a paper to be published in NeuroImage.
While a sensor would indicate exposure to blast forces, it still isn’t clear exactly how that energy translates into brain trauma. Under everyday conditions, the brain can easily withstand a little jostling. “Plop down in your chair and your brain blobs around like Jell-O,” Smith says. But at tremendously high speeds, instead of gently stretching, brain cells can snap and break (SN: 3/13/10, p. 11) like glass.
The long-term effects of these busted brain cells are largely unknown. In addition to chronic headaches, vertigo and difficulty remembering words, research suggests that when the brain shuts down for even a few minutes, depression is more likely down the road.
Scott Matthews, a psychiatrist at the University of California, San Diego, who studies mild traumatic brain injury in returning veterans, notes that causality can’t be established. But among soldiers who were exposed to combat, he sees depression twice as often in people with traumatic brain injury.
“There’s more and more evidence that loss of consciousness changes the brain,” Matthews says.
Unraveling cause and effect and designing useful experiments to illuminate traumatic brain injury and its aftermath remains extremely challenging. And translating those scientific findings into meaningful policy can be just as difficult. Even implementing something as simple as a helmet with a face shield poses problems, says Smith.
“How do you deploy something like that?” he asks. “There are practical things like temperature issues. And then there’s wanting soldiers to be able to meet and greet in villages without looking like spacemen.”