Atlantis Online
November 19, 2018, 05:03:33 am
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Hunt for Lost City of Atlantis
http://news.bbc.co.uk/1/hi/world/europe/3227295.stm
 
  Home Help Arcade Gallery Links Staff List Calendar Login Register  

THE SAHARA

Pages: 1 [2] 3   Go Down
  Print  
Author Topic: THE SAHARA  (Read 3915 times)
Bianca
Superhero Member
******
Posts: 41646



« Reply #15 on: May 16, 2009, 11:02:18 pm »










There are also more local problems. According to Abdoun’s complete tree census, conducted between 1997 and 2001, the cutting of branches and roots for firewood, and the damage to trees from grazing goats are thought to be responsible for the death of eight percent of the trees first counted in 1972. What she hopes is that the tourism industry “will involve itself more in the protection of the trees and of the area in general,” she says, “for its prosperity comes from the appreciation and conservation of the region as a whole.”

She notes that Henri Lhote, who popularized the region’s prehistoric art in his 1959 book The Search for the Tassili Frescoes, wrote of having to burn newly cut cypress wood in order to cook his expedition’s dinners. “One might almost deduce from this,” she says ironically, “that it was really the tree that discovered the frescoes, and not a man.”

Surprisingly, there is also a threat to the trees from flooding. Wadis, dry most of the year, can run fast and high one minute and go back to dry the next. The cypress’s roots meander wide and shallow—the better to grab diffuse, infrequent surface moisture—but lack a firm-footed taproot. As a result, like other cypress species, the tarout often twists above and among stony streambeds, and is vulnerable to upsets in floods. Such flash floods are as common here as they are in the American Southwest: In June 2005, the popular Tuareg singer Osman Balli was killed when his Land Rover overturned in high water at a wadi crossing in the middle of Djanet, and in January 2006 the northern Tassili town of Illizi was severely damaged in a flood.

A further threat to the tarout comes from African emigrants on their way toward Europe, whose crossings on foot often take them from Djanet to the Libyan border town of Ghat. They must often burn wood to stay alive on winter nights when temperatures can drop below freezing. So many have passed this way that the direct line between the two towns is now denuded. Carpentry is a historical use of tarout wood, but is now less of a threat: An Italian–Libyan archeological expedition examined some cypress-plank doors in Ghat and determined through carbon-14 analysis that the wood was cut at least 500 years ago. Local carpenters now work with other, introduced species, such as eucalyptus.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #16 on: May 16, 2009, 11:04:02 pm »












Muhammad Beddiaf was Abdoun’s co-author on a 2002 scientific paper on the tree census, which reported that, since the early 1970’s, 10 newly germinated trees, in addition to 13 previously uncounted ones, have slightly more than made up for the 20 that had died from cutting and burning.

Beddiaf, a specialist in the area’s rock art, imagines how the trees might be somehow connected to the rock artists. “These cypresses were present at the time of the artists—perhaps not these very same trees, but ones from which these have grown. The artists were surrounded by their greenery. They no doubt relaxed under their branches. So I find it odd that the trees should not be represented in their art.” Except for a few diagrammatic renderings of gardens, dating from the most recent artistic era known as “the camel and horse period,” only hunting and war scenes are represented, in which human and animal figures seem to hang in midair.

Tuareg oral literature too seems bereft of mention of the tarout. At the campfire, Beddiaf has an extensive command of his people’s poetry and song, but when pressed for an ode to the tarout, he can muster only a tribute to other trees—as firewood!



From the fire of the acacia,

Every day it throws off sparks.

From the fire of the iseem plant,

Every day you grill two mouflon.

From the fire of the ajar tree,

Every day you shoot the arrow straight.

From the fire of the tamarisk,

Every day you eat gazelle tripe.



Tarout in Tamashek is originally a butcher’s term for the windpipe and attached lungs of a grazing animal. It is said that the tarout tree, when its slightly asymmetrical crown is in robust foliage, takes on the shape of these organs held windpipe-down, and that the term was applied to the tree because of this resemblance. But trees are often given individual names as well, referring for instance to a person who uses the tree’s limbs to hang his goods on (Tin-Ambarak or Tin-Gaded), or to a local landmark, such as a nearby mountain (Tin-Tamanzazt) or a pool of water at the tree’s roots (Tin-Balalan).

Today, the Saharan cypress is closely studied by botanists, not only because of its rarity, but also because it is the only species in the plant kingdom known to reproduce by cloning its male genetic material through a process known as male apomixis. Female apomixis—the division of female cells inside a flower’s ovary as a means of seed formation—is common in several species, including dandelions and blackberries, but male cloning requires an additional step unique to the Saharan cypress: Pollen, carrying the male cells, enters the tree’s ovule, but instead of combining with the female cells, it divides internally to become a viable seed genetically identical to itself.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #17 on: May 16, 2009, 11:05:20 pm »










“In human terms, this is the equivalent of a mother giving birth to a baby that is genetically unrelated to her, but genetically identical to the father,” explains Richard Primack, professor of biology at Boston University.

An experiment in which pollen from the Cupressus dupreziana was dusted onto the female cones of the Mediterranean cypress, whose resulting seeds were germinated and grown for 15 years, culminated in trees physically similar and identical in their DNA to the “father” tree, but unlike the “mother.” There is no obvious evolutionary advantage to this. If other conifer species were to grow nearby—and they do not—then perhaps the pollen of the Saharan cypress could be said to profit by “borrowing” these other cones, using their ovules merely as incubators. Even so, as in all cloning, this would lead to an evolutionary dead end: genetic invariability and a species not capable of adapting to changing conditions.

Rob Nicholson, head of the Smith College Botanic Garden in Northampton, Massachusetts, collected seeds in 1985 from cypresses in the Tassili to study artificial propagation methods. One tree he germinated in the greenhouse shot up so fast it had to be cut down in order to save the roof. He has sent hundreds of cuttings from seedlings to botanic gardens in Atlanta, Pasadena, Houston and elsewhere. “To see healthy trees growing in the ground that you have started years earlier from small cuttings is almost like seeing your own child graduate from college. You feel they’ve made it!” he says.

But these New World transplants are only the latest that, since the mid-20th century, have been grown outside their home habitat. France’s oldest botanical garden, the Jardin des Plantes in Montpellier, has eight healthy specimens of Saharan cypress, while the Villa Thuret in Antibes, France, which is part of the Institut National de Recherche Agronomique, has grown trees studied closely by Christian Pichot and Muhammad el Maataoui, who first discovered its unique genetic behavior.

It was long known that only about 10 percent of seeds from both wild and cultivated Saharan cypress trees have a viable embryo, so the tree’s low fertility rate was thought to be intrinsic to the species. Pichot and el Maataoui recently determined exactly why: The tree’s meiosis—its cell division prior to reproduction—is wildly erratic. Instead of the pollen dividing neatly in half to create a pair of diploid cells, which contain two sets of chromosomes, it often creates cells containing one or four sets of chromosomes —or none. Only diploid cells can successfully germinate.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #18 on: May 16, 2009, 11:06:24 pm »











A route that takes in about half the Tassili’s 233 known trees covers territory between Wadis Tamrit, Riey, Tichouinet, InGharouhane, Amazar and Tefatast—a good walk of six days covering 160 kilometers (100 mi). Retired Algerian government forester Said Grim covered much the same ground in 1972 when he conducted the first full Saharan cypress census. Supported by a 15-donkey pack string, he traveled for three months, relying on word-of-mouth reports from Tuareg herders he met along the way to direct him to the next tree. Now living in retirement in Montreal, Grim remembers that trip as his career’s greatest challenge. “We tried to find every last tree,” he says, “and I think we were successful.”

Before that, in 1965, the trees in several wadis were photographed by a French botanical team, and many of these same trees can still be seen today—with thicker crowns, due no doubt to the relatively good rains of recent years. The physical descriptions from back then are bleaker than today’s: They speak of uncovered roots, recumbent trunks and mutilated branches. The words peu fructifié (“not thriving”) stand out. Although Beddiaf has not seen some of them since before the rains returned, he is guardedly optimistic.

“I don’t think we have a problem with drought for the moment,” he says as he surveys a large guelta, or pool of standing water. It is big enough to have been given its own name, InWatika, in memory of a man called Watika, who was buried nearby. A flock of pin-tailed sandgrouse, known here as ganga chata, rests beside the pool. Jerboa and fox tracks crisscross the bank. A curious mula-mula, or white-capped black wheatear, hops from branch to branch in an acacia. Clearly there is still life, and the potential for even more life, in this high desert.

A recent study by Abdoun has shown that young cypress trees can take quick advantage of even extremely brief wet cycles—even winter hoarfrost and summer morning dew—sometimes adding more than one ring per year and adding radial growth at a rate up to 10 times faster than older trees. She also found that, in some cases, trees temporarily stop growing annual rings altogether, which is perhaps a genetic adaptation to periods of severe drought.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #19 on: May 16, 2009, 11:07:41 pm »











And old trees, just like old humans, slow down considerably: Abdoun’s carbon-14 analysis showed that a tree in Wadi Tichouinet estimated to be 2200 years old, with a trunk radius of 63 centimeters (25"), has taken three-quarters of its life just to grow the last one-third of its width. A tree in Wadi InGharouhane is thought to have taken 1130 years to add just 25 centimeters (10") to its radius. These widely varied growth patterns, dependent upon microhabitat fluctuations, make it difficult to correlate rings in different trees to specific years. One tree may benefit from rain runoff coursing through the sandy soil it is rooted in, while a tree very nearby may miss even a quick sip.

Ahmad Hadrawi is a former park warden who now sells blankets in the Djanet marketplace. He retired in 2004 after spending 33 years in the field, much of it in tree protection. Over that time, he cared for his charges by reburying roots exposed by flooding, searching for new growth and collecting seeds for the National Forestry Research Center in Algiers. He got to know the trees almost as people.

“These trees need experts to help keep them alive,” he says. “They need people like me. Some are like babies, some are like old men, and some are still strong and can live by themselves.”

Hadrawi is correct to say that the trees need people—if only to protect them from tour groups scrounging for campfire wood. “The one we call Tin-Balalan,” he says, referring to the tarout with a 12-meter (48') girth in Wadi Amazar, “is, you know, the biggest in the world. It will not die anytime soon.” He is also correct about this, if we can assume that girth is relative to age. When last seen in February 2006, Tin-Balalan had a healthy crown and was drinking from a standing pool of water near its roots.






 Louis Werner

is a free-lance writer and filmmaker living in New York. He can be reached at wernerworks@msn.com



 Kevin Bubriski

(www.kevinbubriski.com) is a documentary photographer who lives in southern Vermont.
His solo exhibition “Nepal Photographs: 1975–2005” is on view at the Visual Arts Center
of Union College in Schenectady, New York.




This article appeared on pages 32-39 of the September/October 2007 print edition of Saudi Aramco World.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #20 on: May 17, 2009, 08:45:22 am »












Written by
Graham Chandler
Saudiaramcoworld.com


Three reddish-brown giraffe images watch over Nick Brooks as he struggles, hunched over, to shovel sand from the rock shelter’s floor. Some 150 meters (500') above a sweeping, flat and desolate Western Sahara landscape, the burly environmental scientist is hoping these cliffs of Bou Dheir will reveal just when those animals roamed the plains. Three thousand years ago? Four thousand? Five thousand?

 
Today, only traces remain of the seasonal watercourse that until 5500 to 6000 years ago supported a landscape whose rich hunting we deduce from the abundance of animals in the area’s rock art.


Pinning down dates like these is essential to the study of human response to drastic alterations in climate. While many scientists believe climate change was responsible for the decline of such civilizations as the Mayan, a growing number, including Brooks, believes there’s also evidence that earlier global climate shifts actually spurred the beginnings of the world’s first civilizations.

For all of Earth’s history, the only constant about global climate has been its changes. For those climate-change episodes severe enough (and recent enough) to affect human survival, the response, in most cases, must have been to migrate and continue life in a new place, to adapt to new resources—or perish.

But one climatic episode in particular, a massive change during the fourth and early third millennium BC, shifted global rainfall patterns in many subtropical and temperate northern-hemisphere regions and caused severe desertification. Only that change—not any of the earlier ones—was immediately followed by the new human social arrangement we call “civilization.” Was that because the affected humans were larger groups that were forced to share limited resources, since they were boxed into refuges with no other place to go?
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #21 on: May 17, 2009, 08:51:34 am »











“If we define civilization as the emergence of large urban centers, labor specialization, bureaucracy, a high degree of social stratification with centralized authority, monumental architecture and writing —all these emerged as the result of increased competition for resources,” Brooks told me earlier. “What happens is increased territoriality, increased social pressures, technological innovations like irrigation, farming and herding, and concentration of political power.”

Beginning around 5500 years ago, Brooks says, humans developed civilizations in Egypt, Mesopotamia, the Indus Valley, north-central China and northern coastal Peru.

Like most other scientists, he shuns the idea of “climatic determinism,” but Brooks says the term illustrates that climatic and environmental change of the kind usually associated with the collapse
of civilizations also appears to have played a significant role in their emergence.

A research fellow at the Tyndall Centre for Climate Change in Norwich, England, Brooks directs the Western Sahara Project, and he is a special consultant on climate change adaptation for the United Nations Development Program.

He has spent considerable time on the topic in Libya, including investigating the role climate change played in the 2500-year-old Garamantes civilization of southwestern Libya, a region known as the Fezzan.

At the Sahara’s eastern end, other research is showing how desertification contributed to the emergence of the dynastic civilization of the Nile Valley in present-day Egypt and Sudan.

So, five years ago Brooks undertook study of the Sahara’s western end, long neglected in part because of politics and funding difficulties.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #22 on: May 17, 2009, 08:52:56 am »



Standing Stones On Wadi Tifariti








Along the edges of Wadi Tifariti, archeologists have found evidence of a knapper’s site, where small blades and arrowheads were made.


“The area was pretty much unknown,” says Brooks. “Today the western Sahara is much more vegetated than the same latitudes further east. Certainly there is abundant evidence of water in the past, and, as in the rest of the Sahara, there are plenty of petroglyphs of large, humid-climate fauna.” He says the timing and speed of the Sahara desertification varied from place to place by as much as 1500 years, mediated by geography, topography, hydrogeology and the complexity of regional climatic systems. But most of the process, he says, was essentially complete by or soon after 3000 BC.

In the western Sahara, Brooks has found scads of evidence of human habitation—rock art, burial tumuli, enigmatic stone monuments and thousands of stone tools—but, unlike in the eastern Sahara, there are as yet no findings of civilizations here.

The plethora of cultural artifacts spurred Brooks to bring along this year archeologist Anne Pirie of the University of Reading. Focusing on the stone artifacts, she has identified small arrow or spear points similar to some found along the southern edge of the west and central Sahara that have been dated to between 6800 and 6500 BC, as well as much earlier Middle Paleolithic Levallois points that generally date to some 150,000 years ago.

There’s much more work to be done, but an exceedingly long human occupation is evident.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #23 on: May 17, 2009, 08:54:36 am »










The noonday sun turns the desert sprawl below us into a shimmer, and the tender breeze at this relaxing spot tempts us to imagine prehistoric hunters whiling away their hours painting scenes on rock walls as they keep watch for prey in grassy savannah below.

On the walls, dramatic scenes of hunters armed with spears, aggressively moving in on herds, excite team member Maria Gaugnin, who’s here researching Saharan rock art for her doctoral degree at the University of Edinburgh.

Earlier, while researching in the Fezzan, “we found depictions of hippo and water buffalo,” she says—which could mean the climate was a lot wetter when they were painted. If similar animal images are here, and the art can be dated, she figures it would go a long way toward defining the time of the last wet period. “No one has seriously attempted to match the animals with their environments here in the Sahara,” she says.



Geological dating of the end of the last wet period here falls to another team member, Ann Mather, an earth scientist from the University of Plymouth who specializes in geomorphology and sedimentology. She avidly watches Brooks shoveling out the rock shelter, hoping she’ll be able to sample its lowest layer.

All the sand buildup that has reduced the shelter to a crawlspace would have occurred after the dry period began, and so, she reasons, if the lowest layers could be dated, it would help pin down when that drifting started—essentially, when the first wisps of sand blew in.

The team members, myself and three volunteers all arrived in the desert a week earlier on a night flight from Algiers to Tindouf, in southwestern Algeria, where we met with our guides and drivers, Osman and Sidi Ahmed.




They are Sahrawi (Tuaregs): indigenous Bedouins of Western Sahara.


They loaded us into two Toyota Land Cruisers and drove us to the white-walled Rabuni camp, where
we provisioned for our two-week foray. Rounding out the local team is our Sahrawi archeologist Hussein Mohammed Ali.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #24 on: May 17, 2009, 08:55:58 am »



SLUGIULLA ROCK ART

Giraffe









The early morning started us bouncing over desert roads and tracks, using the occasional shortcut across hard-packed sand, all to the lively strings of the Sahrawi tidinit playing on the stereo.

First stop was the site of Sluguilla, a previously discovered 26-kilometer (16-mi) stretch of rock engravings on flat stones.

Animal images range from giraffes to elephants and rhinos. “This is a place where people would have gathered in the past, exchanged stories, renewed old acquaintances, where the young would meet marriage partners, and so on,” says Brooks. 


Sluguilla hasn’t been dated. But clearly this entire area has been tramped by human feet for hundreds

of millennia.


Stone Age artifacts ranging from Acheulian hand axes—these can go back more than half a million years—to more recent tanged points of chert, the color of dark chocolate, lie scattered wherever we walk.

That evening, after a camel stew simmered on an acacia-wood campfire, Brooks relaxes over sweet green tea and tells us about his recent presentation on climate change, the Sahara and the origins of the earliest civilizations at the British Association Festival of Science.

“The Independent, Times, Telegraph, Scotsman and Irish Times were all very keen and prepared
articles on it,” he says.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #25 on: May 17, 2009, 08:57:17 am »



WESTERN SAHARA PROJECT MAP








That media interest grew because the idea that climate change could have led to the world’s first civilizations
has only recently been considered seriously by academics.

The Western Sahara Project members aren’t the only ones.

Daniel Sandweiss, professor of anthropology and quaternary and climate studies at the University of Maine, has
long been studying the cultural effects of climate changes along the northwestern coast
of South America. He too shuns use of the term “environmental determinism,” but he says there is a connection.

“Although environmental factors can move people in particular directions or force people to change in some way, you can’t absolutely predict direct causative links between environmental change and particular human outcomes,” Sandweiss tells me in a later interview. “But you can say that in periods
of particularly stressful change, people respond in some way. And archeologically we can look at the outcomes
and suggest that, in some cases, there is a link.”

Maybe behavior wasn’t determined by the climatic event, since there were many different choices how people
might deal with environmental change. “But it appears that part of the response to the changes in the climate
is what we see in the culture.”

Clearly not all climate change results in the rise of civilizations, he adds.

Conditions have to be right.

“If mobile hunter-gatherers living in a region where population density is low have a downturn in their particular territory, they could move somewhere else and continue the same lifestyle. Maybe you exploit different plants
and animals in the new location, but you’re still a hunter-gatherer or fisher. And you might some day come back
to your original area—you can move around.”
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #26 on: May 17, 2009, 08:58:13 am »










And here is where the difference lies.

Sandweiss says that if the new landscape fills up with too many people, the population becomes tied
to productive systems—such as irrigation agriculture—that require particular locales and infrastructure investments. “It becomes difficult for people to move around any more,” he says. “At some point there are simply too many people in the group, and too much population surrounding them, to allow them to move, and not enough new places to go.”

Sandweiss has found links with past El Niños (southward currents in the equatorial Pacific Ocean that influence weather and ecology) on the northwestern Peruvian coast. “El Niños may well have been as frequent 9000 years ago as now, but you didn’t get civilization then—because you’re talking about low population densities, hunter-gatherers, fishers who are extremely mobile. The landscape wasn’t filled
up, so they moved around.”

But he’s found that after a shift in the El Niño system about 5800 years ago that reduced natural sustenance at a time of higher population densities, traces of civilization first appeared. “We’re getting many of the things that most people consider part of civilization,” he says.

“Monumental construction, some early evidence for irrigation agriculture, apparently a social hierarchy in which a small number of people had more power and better living conditions than the majority of the people, and they were mobilizing labor to build those mounds.

So there’s a significant amount going on, arts of various kinds, and textiles. We’re beginning to get specialization of labor. So many of the things that we see in the standard definition of civilization are coalescing at this time.” 
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #27 on: May 17, 2009, 08:59:07 am »









It happened elsewhere, too, around the same time—about 5800 years ago.

When the rains failed decade after decade in Mesopotamia, small farming villages were devastated. Dense populations in a landscape with minimal carrying capacity forced the intensification of cropping and food storage—and the first appearance of bureaucracies to enforce equal distribution and protection.

Temples, city walls and other public works followed.

“The villages had coalesced into cities,” writes Brian Fagan, emeritus professor of anthropology at the University of California and one of the world’s leading archeological writers. “By 3100 BC, the southern cities had become the world’s first civilization. Ur became the hallmark of Mesopotamian civilization.”

In his recent book 'The Long Summer: How Climate Changed Civilization', he tells the story of human adaptation to the demands and challenges of ever-changing climate.

“Fagan might be more positive than I am about this innovation, casting it as a creative response to crisis,” says Brooks. “I see it more as a last resort, something that people found themselves doing without ever intending to—not that Fagan would argue that people ever planned to become civilized.”

Brooks says in Western Sahara there isn’t yet enough information to develop a narrative equivalent to that of Mesopotamia, but he wants to test the hypothesis that the social changes indicated by the arrival of cattle herding and the building of monuments paralleled, and were in large part a response to, changes in climate, especially desertification.

“In particular, we want to know whether these developments postdated those in the rest of the Sahara,” he says. “And if so, whether there is any evidence that western Sahara acted as a refuge
for those feeling aridity in parts of the Sahara to the east, where desertification was more advanced.”
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #28 on: May 17, 2009, 09:00:18 am »



WADI ERNI
Rock Art






The flats of Wadi Erni may have offered good fishing in the broad shallows, where rock art indicates humans may have been joined in the water by hippo.


After a night under a canopy of a million stars, we break camp and split into two groups—one will look for archeological sites and the other, with Mather, for alluvial fans and other datable geological formations.

To most reliably date events like ancient climate change, several indicators are best, to cross-check one against another.

Mather’s passion is the alluvial fans, which happen when water flows erode hillsides into flat valleys and the transported sediment forms large, delta-like structures. If these can be dated, they could indicate when the region last experienced regular heavy rainfalls. Before coming here, she pored over satellite photos to pinpoint fans that looked promising.

We bounce over rocks and soft sand with our GPS units at arm’s length out the window, looking for Mather’s fans. She looks at escarpment after escarpment. “Don’t know if these are alluvial,” she says. “They all look colluvial to me.” (Colluvial means they were built up through rockfall.) “We really need a place where there is some catchment area.”

When she finds the right one, it will be a prize.

“The newest sediments end up on the bottom of the fan and the oldest near the top,” she says. She wants to date the newest, because that’s the last time great volumes of water flowed here.

But she says she needs fans with well-defined layers deep enough to yield a sample that she could
date by optically-stimulated luminescence (OSL).

OSL is expensive—around a thousand dollars per sample—but it provides a pretty accurate measure of when the soil was last exposed to sunlight.
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Bianca
Superhero Member
******
Posts: 41646



« Reply #29 on: May 17, 2009, 09:01:22 am »










Alas, things often look different from a satellite.

None of the fans proves datable, so Mather turns to Plan B.

She says she can also date the end of the last wet period using sediments from a massive, dried-up lake bottom she spotted on her satellite map.

Off we bound, crossing the lake’s ancient shoreline, zigging and zagging over the cracked mud surface.

 We pass two parallel rows of stones, but they are not ancient: They are used for camel racing. At the old lake’s center, Mather declares, “Let’s dig a hole and see what’s under here.” We dig down about half a meter. “I would love to have a [natural] channel here,” says Mather, “so I could see the layers and tell how far we have to go down.” But we find no layers; neither the fans nor the lakes pan out.

In the late afternoon we rejoin the others, who have been exploring rock shelters eroded over thousands of millennia out of sandstone and mudstone seafloors.

Many are rich with rock art.

Gaugnin has found some indications of climate characteristics: white rhino images.

She points to one, explaining, “See here? It has a longer head and a slight hump on the shoulder and a wider mouth.” It’s the wide mouth that’s the clue: It means it’s more of a grazing animal than the black rhino, and grazing means it lived in a wetter climate than the black rhino likes.

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.”
Report Spam   Logged

Your mind understands what you have been taught; your heart what is true.
Pages: 1 [2] 3   Go Up
  Print  
 
Jump to:  

Powered by EzPortal
Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum | Buy traffic for your forum/website
Powered by SMF | SMF © 2016, Simple Machines
Privacy Policy