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  • The Green Sahara:


    May 9, 2008 -- Six thousand years ago, northern Africa was a place of trees, grasslands, lakes and people. Today, it is the Sahara — a desolate area larger area than Australia.

    Lake Yoa, in northeastern Chad, has remained a lake through the millennia and is still a lake today, surrounded by hot desert. Although little rain falls, Lake Yoa's water is replenished from an underground aquifer.

    By analyzing thousands of layers of sediment in a core drilled from the bottom of this lake, an international team of scientists has reconstructed the region's climate as the savannah changed to Sahara.

    In Friday's issue of the journal Science, the researchers, led by Stefan Kröpelin, a geologist with the Institute of Prehistoric Archaeology at the University of Cologne in Germany, report that the climate transition occurred gradually. In particular, the changing types of pollen that fell on the water and drifted to the bottom tell a story of how the surrounding terrain shifted from trees to shrubs to grasses to sand — "where today you don't find a single piece of grass," Kröpelin said.

    The findings run counter to a prevailing view that the change happened abruptly, within a few centuries, about 5,500 years ago, marking the end of the "African Humid Period" when monsoon rains poured down on the region. That view arises from ocean sediment cores drilled off the coast of Africa, to the west of Mauritania. In 2000, analysis of the cores by researchers led by Peter B. deMenocal of Columbia University's Lamont-Doherty Earth Observatory showed a sudden rise in the dust blown off Africa at that time.

    Kröpelin did not dispute the ocean core data, but said it had been "overinterpreted."

    Data about what was happening on land is sparse, because sands blow around and do not preserve a clear geological record the way lake sediments do. But at Lake Yoa, the water that filled underground aquifers during the humid period, which began 14,800 years ago, is still flowing out into the 80-foot-deep lake. The groundwater is enough to offset the six meters of water that evaporates out of the lake every year, Kröpelin said. Only a few millimeters of rain fall a year.

    Kröpelin said he hoped to return to Lake Yoa next year to drill a deeper core that could trace the climate history back 12,000 years.

    DeMenocal praised Kröpelin's research. "I think it's a very good body of work," he said. "It's really the only thing of its kind from the arid interior." But he wondered, he said, whether the pollen might have come from the area just around immediately surrounding the lake and not the larger Sahara.

    "On the face of it, it's puzzling," said Jonathan Holmes, director of the Environmental Change Research Center at University College London in England. Dr. Holmes said both sets of research had been carefully done, and the challenge will be to put together a more complex history of the Sahara's climate.

    "I don't think either record is somehow wrong," said Dr. Holmes, who wrote a commentary accompanying the article in Science. "I think what they are representing are slightly different things."

    Dr. Holmes said one possibility was that the offshore dust might reflect a drop in water levels around Lake Chad, revealing more dust-producing soil, rather than a large-scale change in climate.

    However fast the drying occurred, it pushed people out of north-central Africa, DeMenocal said, and that climatically forced migrations might have led to the rise of the pharaohs and Egyptian civilization.
    Last edited by Guest 123; 18th December 2008, 02:18. Reason: Picture link fixed

  • #2

    Samedi 10 Mai 2008 -- Il a fallu des milliers d’années pour que le Sahara se transforme en désert et le changement ne s’est pas fait de manière abrupte, comme on le pensait jusqu’?* présent, ?* en croire une étude publiée, jeudi dernier, dans la revue Science. L’étude du pollen, des spores et des organismes aquatiques, retrouvés ?* l’est de N’Djamena, la capitale tchadienne, a permis de déterminer que la région était passée progressivement de l’état de savane, voici 6 000 ans, aux conditions arides qui prévalent depuis ?* peu près 2 700 ans.

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    • #3

      WASHINGTON, August 14, 2008 (Xinhua) -- The largest Stone Age graveyard found in the Sahara, which provides an unparalleled record of life when the region was green, has been discovered in Niger, an international team of archaeologists led by University of Chicago Professor Paul Sereno reported here on Thursday.

      The remarkable archaeological site, dating back 10,000 years and called Gobero after the Tuareg name for the area, was brimming with skeletons of humans and animals - including large fish and crocodiles. Gobero is hidden away within Niger's forbidding Tenere Desert.

      The discovery of the lakeside graveyard - representing two successive human populations divided by more than 1,000 years -- is reported in the September issue of National Geographic magazine and the August 14 issue of the journal PLoS ONE.

      As they explored the site, the team tiptoed among dozens of fossilized human skeletons laid bare on the surface of an ancient dune field by the hot Saharan wind. Jawbones still clenched nearly full sets of teeth; a tiny hand reached up through the sand, its finger bones intact. On the surface lay harpoon points, potsherds, beads and stone tools. The site was pristine, apparently never visited.

      "Everywhere you turned, there were bones belonging to animals that don't live in the desert," said Sereno. "I realized we were in the green Sahara."

      The excavation eventually revealed some 200 graves clearly belonging to two successive lakeside populations. The older group, determined to be Kiffian, were hunters of wild game who left evidence that they also speared huge perch with harpoons when they colonized the green Sahara during its wettest period between 10,000 and 8,000 years ago. Their tall stature, sometimes reaching well over 1.8 meters, was not immediately apparent from their tightly bound burial positions.

      The more recent population was the Tenerian, a more lightly built people who appeared to have had a diverse economy of hunting, fishing and cattle herding. They lived during the latter part of the green Sahara, about 7,000 to 4,500 years ago. Their one-of-a-kind burials often included jewelry or ritual poses - a girl wearing an upper-arm bracelet carved from a hippo tusk, for example, and a stunning triple burial containing a woman and two children in a poignant embrace.

      Although the Sahara has long been the world's largest desert, a faint wobble in Earth's orbit and other factors occurring some 12,000 years ago caused Africa's seasonal monsoons to shift slightly north, bringing new rains to the Sahara. From Egypt in the east to Mauritania in the west, lakes with lush margins dotted the formerly parched landscape, drawing animals, fish and eventually people. Separating these two populations was an arid interval perhaps as long as a millennium that began about 8,000 years ago, when the lake disappeared and the site was abandoned, said the archaeologists.

      The team is continuing to analyze Gobero bones for more clues to the people's health and diet. A large-scale return expedition is planned to the site to further explore the two populations that coped with extreme climate change.

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      • #4

        August 15, 2008 -- A tiny woman and two children were laid to rest on a bed of flowers 5,000 years ago in what is now the barren Sahara Desert.

        Researchers discovered the slender arms of the youngsters still extended to the woman in a perpetual embrace.

        The remarkable cemetery is providing clues to two civilisations who lived there, a thousand years apart, when the region was moist and green.

        Paul Sereno of the University of Chicago and colleagues were searching for the remains of dinosaurs in the African country of Niger when they came across the startling find.

        Some 200 graves of humans were found during fieldwork at the site in 2005 and 2006, as well as remains of animals, large fish and crocodiles.

        'Everywhere you turned, there were bones belonging to animals that don't live in the desert,' said Sereno.

        'I realized we were in the green Sahara.'

        The graveyard, uncovered by hot desert winds, is near what would have been a lake at the time people lived there. It's in a region called Gobero, hidden away in Niger's forbidding Tenere Desert, known to Tuareg nomads as a 'desert within a desert.'

        The human remains dated from two distinct populations that lived there during wet times, with a dry period in between.

        The first group, known as the Kiffian, hunted wild animals and speared huge perch with harpoons. They colonised the region when the Sahara was at its wettest, between 10,000 and 8,000 years ago.

        The researchers said the Kiffians were tall, sometimes reaching well over 6ft.

        The second group lived in the region between 7,000 and 4,500 years ago. The Tenerians were smaller and had a mixed economy of hunting, fishing and cattle herding.

        Their burials often included jewellery or ritual poses. For example, one girl had an upper-arm bracelet carved from a hippo tusk. An adult Tenerian male was buried with his skull resting on part of a clay vessel; another adult male was interred seated on the shell of a mud turtle.

        Pollen remains show the woman and two children were buried on a bed of flowers.

        The researchers preserved the group just as they had been for thousands of years.

        'At first glance, it's hard to imagine two more biologically distinct groups of people burying their dead in the same place,' said team member Chris Stojanowski, a bioarchaeologist from Arizona State University.

        Stojanowski said ridges on the thigh bone of one Kiffian man show he had huge leg muscles, 'which suggests he was eating a lot of protein and had an active, strenuous lifestyle. The Kiffian appear to have been fairly healthy - it would be difficult to grow a body that tall and muscular without sufficient nutrition.'

        On the other hand, ridges on a Tenerian male were barely visible.

        'This man's life was less rigorous, perhaps taking smaller fish and game with more advanced hunting technologies,' Stojanowski said.

        Helene Jousse, a zooarchaeologist from the Museum of Natural History in Vienna, Austria, reported that animal bones found in the area were from types common today in the Serengeti in Kenya, such as elephants, giraffes, hartebeests and warthogs.

        The finds are detailed in the journal PLoS One and the September issue of National Geographic Magazine.

        While the Sahara is desert today, a small difference in Earth's orbit once brought seasonal monsoons farther north, wetting the landscape with lakes with lush margins and drawing animals and people.

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        • #5

          December 17, 2008 -- A prehistoric 'river of the giants' that was once home to gigantic fish, towering dinosaurs and 60 foot long crocodiles has been unearthed by British fossil hunters. The river - as wide as the Danube - flowed across the Sahara desert 100 million years ago, surrounded by lush forests, waterways and lakes.

          The site has yielded some of the most exciting African prehistoric finds in years - including the tip of a giant flying reptile's beak and a limb bone from a 65 foot long plant-eating dinosaur. Both are thought to be new species. Other finds include the remains of a crocodile the length of two double deckers, two inch long scales shed by an freshwater predatory fish, and teeth from a massive sawfish.


          One of the scientists, Dr David Martill, from the University of Portsmouth, said: 'This river system was stuffed full of gigantic fishes, each 2 to 4 metres long.

          'Everything there was of a huge size. You could call it the ancient river of the giants.'

          The 16 inch long beak tip belonged to a previously unknown pterosaur - a flying reptile that lived alongside the dinosaurs. Pterosaur vertebrae up to six inches long were also uncovered in the sandy rocks.

          The scientists believe the creature had a wingspan of up to 20 feet and was a relative of an enormous North American species called Quetzalcoatlus, whose wings spanned nearly 50 feet.

          Another major find was a three foot long bone from a giant sauropod - a plant eating dinosaur with a long neck and tail which stood on four legs.

          The researchers suspect the bone is a fore-limb from a creature at least 65 feet long.

          But there is an outside chance that it is the lower end of a thigh bone belonging to a dinosaur nearly 100 feet long - making it the biggest sauropod ever known.

          Dr Martill said: 'Most people have no idea how diverse sauropods were - I think nearly 100 have been described. There were lots of different families.


          'We think this one might be linked with brachiosaurus, but it is different. The bone we found has some unusual features - it's unusually robust for a humerus. We're 95 per cent confident that it is a humerus but if its part of a femur it would mean this creature was unimaginably enormous.

          'Plant eaters are uncommon in this deposit, extremely rare in this region and to find one this large is very exciting. It’s a major discovery.'

          The finds are now being examined in detail by expedition leader Nizar Ibrahim, from University College Dublin, who is carrying out the work for his PhD.

          He said: 'It's amazing to think that millions of years ago the Sahara was in fact a lush green tropical paradise, home to giant dinosaurs and crocodiles and nothing like the dusty desert we see today.

          'Even to a palaeontologist dealing in millions of years it gives one an overwhelming sense of deep time.'

          He added: 'Finding two specimens in one expedition is remarkable, especially as both might well represent completely new species.'

          The team spent a month in the desert and travelled more than five thousand miles by Land Rover, battling sandstorms and floods.

          Having discovered the giant sauropod bone they had to return to the nearest town to get more water and plaster to protect it, a trip which involved crossing flooded rivers in their Land Rover at night with water coming in through the doors.

          It almost proved impossible to retrieve the heavy sauropod fossil, which had to be carried on a stretcher down the side of a mountain through pouring rain.

          'When we had managed to get the bone in the Land Rover, the extra weight meant we kept sinking in the sand dunes,' said Dr Martill.
          The team hopes to return to the region to search for more fossils in November.

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          • #6

            December 17, 2008 -- Paleontologists claim they have unearthed a new type of pterosaur and a previously unknown sauropod dinosaur in the Sahara Desert.

            The probable pterosaur was identified by a large fragment of beak from the giant flying reptile, and the probable sauropod, an herbivore, was represented by a long bone measuring more than a yard long, indicating an animal nearly 65 feet (20 meters) in length. Now extinct, both would have lived almost 100 million years ago.

            The fossils were found in southeast Morocco, near the Algerian border, during a month-long expedition.

            "Finding two specimens in one expedition is remarkable, especially as both might well represent completely new species," said University College Dublin graduate student Nizar Ibrahim, who led the expedition and was accompanied by Moroccan scientists Samir Zouhri and Lahssen Baidder as well as University of Portsmouth researchers Darren Naish, Robert Loveridge, David Martill and Richard Hing.

            Ibrahim will undertake a detailed analysis of the sauropod bone, which he and Martill expect is a new species and genus of sauropod. He will also examine the pterosaur remains, which are particularly uncommon because their bones, optimized for flight, were light and flimsy and seldom well-preserved.

            "Most pterosaur discoveries are just fragments of teeth and bone so it was thrilling to find a large part of a beak, and this was enough to tell us we probably have a new species," Ibrahim said.

            The team traveled more than 5,000 miles by Land Rover in an overland trip that went through the Atlas Mountains. Sandstorms and floods challenged the team. For instance, having discovered the giant sauropod bone, they had to return to the nearest town to get more water and plaster with which to protect the fossil, a trip which involved crossing flooded rivers at night with water coming in through the vehicle's doors.

            At one point during the fieldwork, heavy rain in the Atlas Mountains flooded the Ziz River. To retrieve the bone, the team had to manhandle the fossil in its plaster jacket down the side of a mountain, clearing thousands of stones to make a safe path to carry it on a wooden stretcher.

            "There was a point when we wondered if we would make it out of the desert with the bone, but we had worked so hard to find it so there was no way I was leaving it behind. It took us five days to get the bone out of the ground and down the mountain — and that was not the end of our problems," Ibrahim said.

            Martill, one of the Portsmouth researchers, added: "When we had managed to get the bone in the Land Rover, the extra weight meant we kept sinking in the sand dunes and on several occasions everybody except the driver had to walk while we negotiated difficult terrain. Our journey home was equally eventful. While crossing the Atlas Mountains, we got caught in a snowstorm and total whiteout. But it’s all been worth it."

            The team was also excited to discover some rare dinosaur footprints, including some that record several animals walking along the same trail, as well as hundreds of dinosaur teeth, bits of giant crocodiles and some probable new species of fish.

            Ibrahim said: "It's amazing to think that millions of years ago the Sahara was in fact a lush green tropical paradise, home to giant dinosaurs and crocodiles and nothing like the dusty desert we see today. Even to a paleontologist dealing in millions of years, it gives one an overwhelming sense of deep time."

            The fossils will return to Morocco for display after study in Dublin, said Zouhri, a geologist at the Université Hassan II in Casablanca.

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