|19 July 2009
Cave record of Britain's pioneers
The Cheddar Gorge in Somerset (England) was one of the first sites inhabited by humans when they returned to Britain towards the end of the last Ice Age. New radiocarbon dates on bones from Gough's Cave show people were living there some 14,700 years ago. The results confirm the site's great antiquity and suggest human hunters re-colonised Britain at a time of rapid climate warming.
From 24,000 years ago, an ice sheet extended over much of Britain. Beyond that ice sheet, in southern Britain and much of northern France, the environment resembled a polar desert. Evidence suggests these inhospitable conditions kept people out of north-west Europe for more than 9,000 years. But human groups were able to retreat to ice-free areas (refugia) in southern France, Iberia and elsewhere. After the Ice Age peaked, humans bounced back, expanding from southern refugia to re-colonise northern Europe.
Interest in Gough's Cave was stimulated by the discovery in 1903 of 'Cheddar Man', the complete skeleton of a male individual dating to about 9,000 years ago. In the 1980s, excavations uncovered accumulations of human and animal bones and artefacts that appeared to be much older even than Cheddar Man. However, researchers were perplexed by the radiocarbon dating results. Although the remains seemed to represent a single occupation level in the sediments, the remains appeared to be a thousand years different in age. Since those tests were carried out, there have been significant advances in radiocarbon dating technology, particularly to reduce contamination in the samples. This allows more accurate dating of archaeological materials.
When the bones were sent to be re-tested at the Oxford Radiocarbon Accelerator Unit, the remains fell into a much narrower age range, converging on 14,700 years ago.The latest results were a much better fit with the archaeological findings. Members of the Ancient Human Occupation of Britain (AHOB) project now think the bones from Gough's Cave could have accumulated over just two or three human generations. The new dates correspond precisely to a period of very rapid climate warming which could have occurred over as little as three years: "[The occupation] really is right on the cusp of this warming which we can see in Greenland ice cores," Chris Stringer, head of human origins at London's Natural History Museum, said.
They appear to have been hunting horses: "One of the puzzles from the previous radiocarbon dating was that some of the evidence for human occupation seemed to be divorced from the evidence for horse butchery," said Chris Stringer.
"Now they are right there together, so these people were probably following herds of horses across Doggerland (an ancient landmass once linking Britain to the rest of Europe) because of a large river system in the bed of the English Channel which was blocking the way from France."
Professor Stringer believes humans expanding out of southern France may have circumvented this river system by taking a detour into Belgium or the Netherlands, moving into eastern Britain across land that is now submerged under the North Sea.
However, after the warm period which attracted people back to Britain for the first time in nearly 10,000 years, the climate and environment changed again. Birch forests expanded, which created a less attractive habitat for horses. In turn, the signal of human presence largely disappears from caves and becomes weaker and more scattered across the landscape. Then north-west Europe plunged into the 'short, sharp shock' of the Younger Dryas, a cold climate period which seems to extinguish the signal of human occupation altogether. Cheddar Man, who lived in the cave 10,000 years ago, appears to belong to an entirely new population which arrived from the continent after conditions once again improved, said Professor Stringer.
Source: BBC News (16 July 2009)
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