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News: Remains of ancient civilisation discovered on the bottom of a lake
http://en.rian.ru/analysis/20071227/94372640.html
 
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THE SAHARA

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Author Topic: THE SAHARA  (Read 3892 times)
Bianca
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« Reply #30 on: May 17, 2009, 09:02:26 am »








We all pitch in, searching more walls for pictographs.

Excitement abounds when new images are spotted.

“Maria, I have what might be a hippo here,” Brooks calls out. “Not much of its head, but the body....”

Gaugnin extricates herself from a tight cave corner and bounds over. “No, the legs are far too long,”
she sighs. “It looks more like a gazelle with a fat rump.”



 
Ostriches  near Wadi Ternit  may have appeared 5500 to 6000 years ago, and are also among the
fauna that is depicted in the area’s rock art. 


Next to the shelter with the white rhino image, Gaugnin has spotted a collapsed rock shelter with more rock paintings.

That gives her an idea: If the approximate date of the collapse could be determined, it would provide at least an end date—a date after which the painting must have been made.

Mather concurs.

“Let’s take a sample from the broken edge,” she says. “Here, this one follows the bedding plane.”

Clink, clink goes the hammer as a fist-sized chunk of sandstone and pyroxene falls loose. “We’ll use cosmogenic dating on this one,” she says, marking today’s date and GPS coordinates on the sample
with a felt pen.

Such are the trials and perils of dating western Saharan climate change.

It’s not as easy as picking up soil or rock samples and sending them off to the lab and waiting for the answer. It’s fraught with approximations, relative dates, post hoc dates, cross-checks and correlations.
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Bianca
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« Reply #31 on: May 17, 2009, 09:05:49 am »










Like the alluvial fans and lake bottoms, the Bou Dheir cave bottom doesn’t yield a good, datable sample either. But on the way back to Rabuni, Mather spots something on the roadside she hadn’t expected: a tufa, or carbonate, outcropping.

That usually indicates the remains of a freshwater lake.

She motions to driver Sidi Ahmed to stop, bounds out of the Toyota with her geologist’s hammer and pecks away at the chalk-like protrusion. She points to one good sign. “It’s quite filamentous,” she says, “so it’s likely not just formed by groundwater.” She takes a sample for dating, probably by way
of the uranium-thorium method—similar in principle to carbon-14 dating.

 
The valley of Lajuad has been dry year-round since desertification began. How did the people who

once made their livelihoods here respond when the rains no longer came?


Samples packed away, we bounce back across the arid result of Earth’s last great climate change.

What might happen this time around? The 130-country Intergovernmental Panel on Climate Change—co-winner of the Nobel Peace Prize—has mentioned that future responses to global warming could include the “migration of hundreds of millions of people from equatorial regions.”

Brooks isn’t surprised.

Our desert trip done, freshly shaved and sipping a café au lait in a splash of morning sun on the hotel patio in Algiers, he voices his hope that the latest climate change might be the dawn of a new, more responsible model of civilization.

Speaking of the old model, he says, “We’ve done our early development period, and our period of adolescent rebellion and irresponsibility. We’re now into post-adolescence.”




 Free-lance writer Graham Chandler (www.grahamchandler.ca)

received his doctorate in archeology from the University of London,
and he lives in Calgary, Alberta.
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Qoais
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« Reply #32 on: December 17, 2009, 09:52:12 pm »

EMI KOUSSI - HIGHEST PEAK IN SAHARA

Emi Koussi is a high pyroclastic shield volcano that lies at the south end of the Tibesti Mountains in the central Sahara of northern Chad. It is the highest mountain in Chad, and the highest in the Sahara. The volcano is one of several in the Tibesti massif, and reaches 3445 m in altitude, rising 2.3 km above the surrounding sandstone plains. The volcano is 60 by 80 km wide.
Two nested calderas cap the volcano, the outer one being about 12 by 15 km in size. Within it on the southeast side is a smaller caldera, about 2-3 km wide and 350 m deep. Numerous lava domes, cinder cones, maars, and lava flows are found both within the calderas and along the outer flanks of the shield.
Emi Koussi has been used as a close analog to the famous Martian volcano Elysium Mons. One of the most important morphological differences between volcanoes on Mars and Earth is the widespread furrowing of the surface due to flowing water on terrestrial volcanoes. The furrows are shallow valleys. Larger channels have a different origin. Major channels can be seen on volcanoes on both planets and indicate low points in caldera rims where lava spilled out of pre-collapse craters.
http://en.wikipedia.org/wiki/Emi_Koussi

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An open-minded view of the past allows for an unprejudiced glimpse into the future.

Logic rules.

"Intellectual brilliance is no guarantee against being dead wrong."
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