Megaflood 'made Island Britain'

Research suggests there were eight major incursions
Early immigrations were totally dependent upon land crossings
All but the last incursion - about 12,000 years ago - failed
A number of major palaeo-sites mark the periods of influx
Extreme cold made Britain uninhabitable for thousands of years
Warm climate - high sea level; cold climate - low sea level
Varying depth of rivers and Channel acted as immigration filter





Megaflood 'made Island Britain'
By Jonathan Amos
Science reporter, BBC News

Britain became separated from mainland Europe after a catastrophic flood some time before 200,000 years ago, a sonar study of the English Channel confirms.
The images reveal deep scars on the Channel bed that must have been cut by a sudden, massive discharge of water.
Scientists tell the journal Nature that the torrent probably came from a giant lake in what is now the North Sea.
Some event - perhaps an earthquake - caused the lake's rim to breach at the Dover Strait, they believe.
Dr Sanjeev Gupta, from Imperial College London, and colleagues say the discharge would have been one of the most significant megafloods in recent Earth history, and provides an explanation for Britain's island status.
"This event, or series of events, that caused [the breach] changed the course of Britain's history," Dr Gupta told BBC News.
"If this hadn't happened, Britain would always have been a peninsula of Europe. There would have been no need for a Channel Tunnel and you could always have walked across from France into Britain, as early humans did prior to this event."
Tremor trigger?
The idea of a great flood stems from scientists' understanding of northern Europe's ice age past.


Beachy Head (BBC)
The megaflood cut through the ridge linking Britain with France
It is believed that hundreds of thousands of years ago, when ice sheets had pushed down from Scotland and Scandinavia, there existed a narrow isthmus linking Britain to continental Europe.
This gently upfolding chalk ridge was perhaps some 30m higher than the current sea level in the English Channel.
Palaeo-researchers think it bounded a large lake to the northeast that was filled by glacial meltwaters fed by ancient versions of the rivers Thames and Rhine.
Then - and they are not sure of the precise date - something happened to break the isthmus known as the Weald-Artois ridge.
"Possibly this was just the build-up of water behind. Possibly something triggered it; it's well known today that there are small earthquakes in the Kent area," explained Imperial's Dr Jenny Collier.
Re-routing rivers
Either way, once the ridge was broken, the discharge would have been spectacular.
The Imperial College and UK Hydrographic Office study used high-resolution sonar waves to map the submerged world in the Channel basin.
The images detail deep grooves and streamlined features, the hallmarks of landforms that have been gouged by large bodies of fast-moving water.
The study is the best evidence yet for a long-held idea
More details
At its peak, it is believed that the megaflood could have lasted several months, discharging an estimated one million cubic metres of water per second. And from the way some features have been cut, it is likely there were at least two distinct phases to the flooding.
"I was frankly astonished," said Dr Collier. "I've worked in many exotic places around the world, including mid-ocean ridges where you see very spectacular features; and it was an enormous surprise to me that we should find something with a worldwide-scale implication offshore of the Isle of Wight. It was completely unexpected."
The researchers tell Nature that the ridge breach and the subsequent flooding would have helped reorganise river drainage in northwest Europe, re-routing both the Thames and the Rhine.
Fossil filling
The megaflood theory has been around for some 30 years; but the sonar images represent the clearest narrative yet for the story.
Previous studies of prehistoric animal remains from the past half-million years have already revealed the crucial role the English Channel has played in shaping the course of Britain's natural history.
Andy Currant (AHOB)
The story is also told through Britain's fossil record
Channel's role in pre-history
Piltdown's lessons for science
The Channel has acted as a filter through time, letting some animals in from mainland Europe but not others.
And even when water was locked up in giant ice sheets and sea levels plummeted, the Rhine and the Thames rivers would have dumped meltwater into a major river system that flowed along the Channel's floor.
Scientists can see all of this influence written in the type and mix of British fossils they find at key periods in history.
Professor Chris Stringer is director of the Ancient Human Occupation of Britain (Ahob) project, which has sought to fill out the details of the British Isles' prehistory.
"The timing and method of formation of the Channel has been a long-running argument - after all, it really makes Britain what it is today, geographically," he commented.
"The evidence presented in this paper is spectacular. It certainly explains and reinforces the picture the Ahob project has been putting together of the increasing isolation of Britain from Europe after 400,000 years ago."




Channel's key role in pre-history
By Paul Rincon
Science reporter, BBC News, Gibraltar

Andy Currant (AHOB)
The remains we find today tell a story of Britain's ancient past
A study of prehistoric animals has revealed the crucial role of the English Channel in shaping the course of Britain's natural history.
The Channel acted as a filter, letting some animals in from mainland Europe, but not others.
Even at times of low sea level, when Britain was not an island, the Channel posed a major barrier to colonisation.
This was because a massive river system flowed along its bed, UK researchers told a palaeo-conference in Gibraltar.
Today the English Channel is 520km long, 30-160km wide, about 30-100m in depth and slopes to the south-west.
Even now, the bed of the Channel is incised by a network of valleys, the remains of the river system, which may have been cut by catastrophic drainage of meltwater from further north.
"It would have been an incredible barrier at times of high sea level, but it would also have been a formidable barrier at times of low sea level for populations trying to move south to north," said Chris Stringer of London's Natural History Museum.
Professor Stringer presented the results here at the Calpe conference, a meeting of pre-history experts from all over the world.
The big flood
The evidence comes from the Ancient Human Occupation of Britain Project (AHOB). This five-year undertaking by some of the UK's leading palaeo-scientists has reassessed a mass of scientific data and filled in big knowledge gaps with new discoveries.
Chris Stringer's co-researchers Andy Currant, Danielle Shreve and Roger Jacobi have been studying how the mammal fauna of Britain has changed over the last 500,000 years.
More details
During that period, animals have colonised, abandoned and re-colonised Britain many times as the climate shifted from warm to cold and back to warm.
The Channel is thought to have formed during a cold period 200,000 years ago or more.
Meltwater from an ice sheet formed a lake, which then overflowed in a catastrophic flood - cutting through a chalk ridge that previously connected Britain to France.
Changes in climate were accompanied by changing sea levels. At the height of an ice age, these would have been low. During interglacial periods, when the climate was warm, sea levels rose.
But even when water was locked up in the ice sheets and sea levels plummeted, the Rhine and the Thames rivers dumped meltwater into a major river system that flowed along the floor of the Channel.
Unusual collections
This means that once the Channel formed, there was never again a simple land crossing to be made from northern France to Britain.
"We find we're getting only a selection of the mammals during the British interglacials that there are in mainland Europe," said Professor Stringer.
For example, at one pre-historic site, researchers found hippopotamus and fallow deer; but unlike mainland Europe at the time, there were no horses and no humans.
"This suggests that the Channel, or the Channel river system, is acting as a filter to prevent the movement of some of these [mammal] forms into Britain," Professor Stringer added.
Once sea levels rose high enough for Britain to be an island, the select fauna that had made it across from mainland Europe could develop in extraordinary ways.
During one warm stage, about 80,000 years ago, fossils from Banwell Cave in Somerset show Britain was populated by some very unusual animals. These included reindeer, bison, and a giant bear similar to a polar bear.
Interestingly, there are no hyena fossils at Banwell Cave, as there were in mainland Europe. Instead, it appears, their role in the food chain may have been taken up by wolves.
"The wolves were developing much larger jaws. Their teeth show incredible signs of breakage and wear as if they're chomping bones like hyenas," said Professor Stringer.
The mammals at Banwell seem to be the kinds of animals normally found today in cold regions. But they lived in Britain during a warm stage and seemed to be adapting to their new environment.
The team thinks the antecedents of these animals must have arrived in Britain when the climate was cold. But when conditions warmed up, sea levels rose and isolated Britain, marooning this cold-adapted fauna in a warm land.




Last Updated: Monday, 16 October 2006, 13:34 GMT 14:34 UK

Piltdown's lessons for modern science
By Professor Chris Stringer
Natural History Museum
A new book reveals how recent research has uncovered a goldmine of information about the history of human habitation in Britain.
Piltdown skull Image: Natural History Museum/BBC
The Piltdown skull fooled scientists for more than 40 years
Here, Homo britannicus author Chris Stringer describes how efforts to search for evidence of early Britons were hampered by wrong turns and false leads, including the granddaddy of all scientific forgeries.
In the early years of the 20th Century, British archaeologists were becoming increasingly desperate for a human fossil to show that our island had deep prehistoric roots.
Our greatest rival, Germany, had the Heidelberg jaw and the original Neanderthal bones. France had Neanderthal fossils and early modern humans at Cro-Magnon to complement their beautiful cave art. Even the Dutch had Java Man, which they had brought back from the Dutch East Indies.
Stone handaxes had been found in Britain, so it was clear that early people had lived here. Some scientists also believed in more primitive stone tools called eoliths, though we now know these were often no more than naturally broken rocks. The absence of a single significant human fossil from Britain was conspicuous.
The time was right for the appearance of Piltdown Man: the earliest Englishman with the earliest cricket bat.
Not cricket
Charles Dawson, a British solicitor and amateur fossil hunter, claimed that some time before 1910, a workman had handed him a thick, dark-stained piece of human skull that had been found in gravels at the village of Piltdown in Sussex.
The "cricket bat" Image: BBC/Natural History Museum
The "cricket bat" would have threatened Dawson's plans
By 1912, Dawson had found more of the skull, and had contacted his friend Arthur Smith Woodward, the keeper of geology at the British Museum (now the Natural History Museum, where I work).
Together, they excavated the Piltdown site, where they discovered more skull fragments, fossil animal bones, stone tools and a remarkable lower jaw.
Additional finds, including a bizarre elephant bone implement shaped like a cricket bat, helped swing the opinions of British sceptics in favour of the discovery. But Piltdown's days were numbered. Discoveries of possible human ancestors in Africa and Asia in the 1920s and 1930s pushed Piltdown into an increasingly peripheral position.
Part of the cleverness of the hoax was the way in which it suited preconceived ideas about what early humans should look like
Finally, in 1953, stringent scientific tests were applied, exposing the lower jaw as a forgery. Later analyses would show the whole assemblage of bones and fossils at Piltdown had been planted.
The human skull was that of a modern person, the jaw from an orang-utan. Both had been artificially stained to match the gravels.
Charles Dawson remains the prime suspect. He was the first person to seriously search for and report fossils at the site and was present when all the major finds were made.
He is now linked with several suspected forgeries, most of which were "missing links" between previously known stages in either evolution or technology.
Sent off course
Dawson was daring to a point, but he took things one step at a time. For example, he waited until experts predicted what size Piltdown Man's canine would be and, lo and behold, the next year a canine turned up of just the right size.
The dig at Piltdown Image: Natural History Museum
The time was right for an early Englishman to emerge
However, I don't think Dawson would have done something as grotesque and outrageous as the "cricket bat", as it would have threatened the entire story he was trying to construct. Martin Hinton, a volunteer in Smith Woodward's department at the British Museum and later the Keeper of Zoology, had the means and motive to create this object.
In the 1970s, a canvas trunk bearing the initials MH was found in loft space above the old Keeper of Zoology's office. Inside were mammal teeth and bones carved in the style of the Piltdown material.
We also know from letters that Hinton was aware the Piltdown finds were suspect. I think he made and planted this absurd object to warn the forgers that the game was up - only to find it hailed as one of the earliest known bone implements.

PILTDOWN MAN IN TIME
1912 - Discoveries publicised
1914 - 'Cricket bat' surfaces
1915 - Charles Dawson dies
1949 - Piltdown ages queried
1953 - Fossil fakes unmasked
Piltdown was particularly damaging for us in Britain, because British scientists clung to it for far longer than they should have done. It clouded their judgment and affected their interpretations of genuine fossils.
For example, when australopithecine fossils started to turn up in South Africa during the 1920s, prominent British-based anatomists like Sir Arthur Keith and Grafton Elliot Smith wouldn't take them seriously because they believed in Piltdown Man.
Lessons learnt
Part of the cleverness of the hoax was the way in which it suited preconceived ideas about what early humans should look like.
Keith and Grafton Elliot Smith thought a large brain was such an important part of humans today that it must have a long and deep evolutionary history. Piltdown had a high, domed skull with a large brain, confirming their belief in the antiquity of these features in the human lineage.
Seven-hundred-thousand-year old stone tool from Pakefield Image: Natural History Museum/Harry Taylor
Stone tools from Pakefield in Suffolk are 700,000 years old
In other countries, Piltdown was viewed with more caution if not downright suspicion. The scientist Franz Weidenreich, who fled Nazi Germany to work in the US during the 1930s, had seen what a potential human ancestor could look like after working on the Peking Man fossils from China. Of course, they looked nothing like Piltdown Man.
He said of Piltdown: "The sooner the chimaera 'Eoanthropus' is erased from the list of human fossils, the better for science."
Weidenreich didn't have an explanation for it and he couldn't say outright that it was a fake; but he knew there was something seriously wrong with it.
In other countries, Piltdown was viewed with more caution if not downright suspicion
Hopefully, the Piltdown saga has taught those of us who study the evolution of humans some important lessons that we should apply today.
Firstly, we mustn't let preconceived ideas run away with us. Secondly, specimens have to pass certain basic tests.
Science thrives on scepticism, which is why the extraordinary discovery of the "Hobbit" fossils in Indonesia has prompted a lively scientific debate over its status.
Science is also self-correcting. In Britain, during the first half of the 20th Century, people simply shut their minds to other evidence and continued to believe in Piltdown because it fitted their beliefs and was the only significant human fossil we had.
Further work
We now have genuine human fossils to speak of from Britain, including a shinbone and teeth from Boxgrove dating to about 500,000 years ago and part of the skull of an early Neanderthal that was unearthed at Swanscombe in Kent.
Homo floresiensis (l) and Homo sapiens (r) Image: PA
The discovery of the "Hobbit" fossils has prompted a lively debate
The first phase of our Ancient Human Occupation of Britain (AHOB) project has pushed back the evidence of humans in Britain by 200,000 years.
We have also shown that humans tried to settle in Britain at least eight times, but on seven of those occasions they subsequently perished as Britain was hit by successive ice advances.
In the second phase of AHOB, due to last until 2010, we plan to uncover further details about these ancient colonisations.
Piltdown Man is now on show once again, at an exhibition in Bonn, Germany, to commemorate the 150th anniversary of the discovery of the original Neanderthal fossil.
It still gets a lot of attention, because it is, as much as anything, a whodunit story.
Once proudly held up as the earliest known Englishman, Piltdown is now displayed as a lesson from the past, of a prehistory of Britain and a stage of human evolution that never was.
Homo britannicus is published by Penguin Books. Chris Stringer is Research Leader in Human Origins at the Natural History Museum in London. He is also director of the Ancient Human Occupation of Britain (AHOB) project.