Researchers working on England's North Sea coast have uncovered flint tools dated to at least 780,000 years ago, the earliest evidence of prehistoric humans this far north. The discovery suggests that early humans might have been better adapted to cold climates than previously thought, although some scientists are skeptical.
Discoveries over the past decade or so indicate that early humans left Africa nearly 2 million years ago and spread into Asia and southern Europe. Although early human—or hominin—fossils dated between 800,000 and 1 million years ago have been unearthed in Spain and Italy, there had been little evidence that our species ventured north of the Alps and Pyrenees before about 500,000 years ago. That picture began to change in 2005, when members of the interdisciplinary Ancient Human Occupation of Britain (AHOB ) project, a research collaboration funded by the London-based Leverhulme Trust and made up of more than two dozen scientists from Europe and North America, reported finding stone tools dated to 700,000 years ago on the North Sea coast of England at Pakefield, northeast of Norwich. Yet that human occupation took place during a so-called interglacial period when the weather was fairly balmy .
On the beach. Excavators have found evidence of the earliest known Britons on the North Sea coast.
Credit: Phil Crabb/Natural History Museum
Also in 2005, AHOB geologists working about 60 kilometers up the coast at Happisburgh began finding flint tools in buried sediments of gravel and sand. Between 2005 and 2008, an excavation team led by archaeologists Nick Ashton of the British Museum in London and Simon Parfitt of University College London's Institute of Archaeology, along with AHOB Director Christopher Stringer of the Natural History Museum in London, uncovered 78 such artifacts. They included large flakes with sharp cutting edges. The researchers dated the sediments with a combination of paleomagnetism, which is based on periodic reversals in Earth's magnetic polarity that leave traces in mineral deposits, and biostratigraphy, which utilizes already known dates for the extinction and appearance of animal and plant species to provide age ranges for archaeological layers. Together, the two dating techniques indicate that humans lived in the region between 780,000 to 1 million years ago. This is the earliest evidence for human occupation above 45˚ latitude, at the edge of the so-called boreal zone, the team will report tomorrow in Nature.
At that time, according to estimates from temperature-sensitive beetle species found at the site, mean winter temperatures in this forested region hovered between 0 and –3˚C (at least 3˚C lower than today). The team's climate reconstructions also indicate that plant and animal resources were relatively scarce. This suggests, the authors write, "an ability to survive novel environments as global climate deteriorated" during repeated cycles of ice ages and so-called interglacial periods, in contrast to previous "ebb and flow" models suggesting that hominins moved north only when the weather was warm, such as at Pakefield 700,000 years ago.
Archaeologist Wil Roebroeks of Leiden University in the Netherlands, who thinks the dating is "rock solid," says that researchers should accept the new findings "however surprising [they] may be in the light of previous models" for early human migrations. But Richard Potts, an anthropologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., says the findings "need a lot of testing" by further excavations in the area. One major concern, he says, is the difficulty of carrying out accurate paleomagnetic and biostratigraphic analyses on the kind of coastal sands and gravels in which the stone tools were found. Paul Renne, a dating expert at the Berkeley Geochronology Center in California, agrees. "It's a pity the evidence isn't stronger," Renne says, although he thinks the authors' conclusion is "likely to be correct."
And Potts adds that the new findings do not prove that the Happisburgh hominins were actually adapted to the colder conditions, as the authors suggest. "We don't know yet whether this was a relict population left over from a movement to this latitude during a much warmer time, or whether the artifacts reflect the ability to move into such a novel type of environment."
Source: http://news.sciencemag.org/
No comments:
Post a Comment