“FOG in Channel; Continent Cut Off”. This apocryphal newspaper headline supposedly illustrates the insularity of the British. Weather-wise, nothing could be further from the truth today, as I peer from a gun emplacement atop the White Cliffs of Dover. The view is stunning. Dead ahead is the bulbous headland of Cap Gris-Nez, the closest tip of France. A few degrees to the left, a sharp eye can make out the distinctive silhouette of Calais Town Hall.
Britain is undoubtedly an island, just not by very much. Not even 21 miles separate England from France here at their closest approach – 33 kilometres measured in suspect units from across the sea. The concrete structure I’ve wormed my way into dates from the last time that distance seemed perilously short, when German forces massed on the French coast during the second world war.
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The English Channel carries huge historical and psychological clout. Yet as little as 10,000 years ago, you could have walked across a dry valley in front of me and been in Calais by teatime having hardly got your feet wet.
The full story of how that changed is eye-popping – and we have only recently begun to unearth it. As the political shenanigans surrounding the UK’s decision to leave the European Union continue, this is the story of Britain’s original exit from Europe – a Brexit drama in three acts.
Act 1, Dover
About 450,000 years ago. A ribbon of land stretches into the distance. To the right, a drop plunges perhaps 150 or 200 metres to a plain below. To the left, lapping almost to our toes, are the waters of a huge glacial lake. Small icebergs bob on its surface. We are standing on a vast natural dam. It is cold. Very cold.
Half a million years ago – 50,000 or so years before the scene just depicted – there was no sea where the White Cliffs of Dover are today. There weren’t even any cliffs. There were just chalk hills arcing eastward and slightly south, from present-day England into present-day France. The main axis of this Weald-Artois ridge is still visible on both sides of the English Channel today, in the Downs of Kent and Sussex, and the chalk hills of the Pas-de-Calais.
The ridge was the high point of a strip of land connecting the main body of Europe to a sizeable protuberance stretching out to the north-west. Early humans, possibly Homo antecessor, had imported themselves onto this proto-Britain sometime before 800,000 years ago. That is the date of hominin footprints and stone tools found at Happisburgh, now on the Norfolk coast, some 200 kilometres north of Dover (see Map).
These first Britons were pioneers in a harsh environment, and we know little about them. “We don’t know whether they had the use of fire or whether they were hunters or scavengers,” says archaeologist . “We’re not even sure if they had functional body hair at this point.”
Their world would also look unfamiliar to a modern Brit. To the south of the Weald-Artois ridge, watercourses approximating to today’s Solent, Seine and Somme drained off to the south-west into a bay of the Atlantic. To the north of the ridge, other major rivers carried water towards the Arctic: working eastwards, early equivalents of the Thames, Scheldt, Meuse and Rhine.
“Up until 500,000 years ago, these rivers were disgorging sediment, filling up a huge, low-lying delta plain,” says , a palaeogeologist at the University of Cambridge. Attached to the north of the ridge, this fertile delta covered the southern half of where the North Sea is today, extending from the Netherlands to Britain probably as far up as Yorkshire.
About 500,000 years ago, however, an icy wind began to blow from the north. Earth entered a significant cold period during which global temperatures dropped by more than 2°C. The Arctic ice cap expanded, reaching as far south as the high ground of Finchley in north London – a shock to the established order. Evidence of habitation ceases abruptly.
Geographically, too, changes were afoot. To the south of the Weald-Artois ridge, the Atlantic receded as the burgeoning ice cap sucked up water. To the north, however, the formerly free-draining rivers became trapped by the ice. An enormous glacial lake began to form where the delta had been. “It was like putting the plug in the bath when the taps are still running,” says Gibbard. “The water goes on rising until it can find a way out.”
It seems that way out can only have been through the Weald-Artois ridge. Sediment cores in the English Channel and further to the south-west in the Bay of Biscay show a sudden spike in deposition around 450,000 years ago. They also contain large amounts of glacial material, consistent with that picture.
But how exactly it happened remained a matter of conjecture until the mid-2000s, when marine geophysicist and her colleagues were mapping the floor of the English Channel.
The Channel is hardly deep – on average little more than 60 metres – but until recently we had only a vague notion of what its bottom looked like. The assumption was that it consisted of gently undulating, perennially shifting sand dunes. The notorious Goodwin Sands, for instance, just north of Dover, lie so close to the surface that they emerge from the waves during extremely low tides, allowing .
But when Collier and her team tested a multibeam echosounder, a new bit of kit that allowed more detailed measurements of the seabed, they found it wasn’t the soggy, sandy bottom they expected. The strong tides in the funnel-shaped English Channel had pulled material around and piled it up in different places, much as the wind might heap up leaves in your garden. “The leaves are mostly on the French side, like all being piled up against the garage,” says Collier.
Denuded of sand, dramatic features were visible gashed into the bedrock on the English side. Chief among them is a straight, streamlined, braided channel running east to west along the Channel floor. A staggering 30 kilometres wide in places, it slices 10 metres down into the rock. It is an ancient floodwater channel, apparently created in one go by a single, unimaginable influx of water. “Someone had thrown a ton of water down,” says Collier. “We’re talking about something like the size of the North Sea going down in two weeks.”
The smart money is on it actually having been the North Sea. In the 1980s, British geologist Alec Smith had proposed that following the build-up of water behind it. In this picture, at some point around 450,000 years ago, water began to flow over the ridge in vast quantities, tumbling down the escarpment and overwhelming the dry valley to the south in a megaflood the likes of which the world has only rarely seen. “The water spills over the bath at the lowest point it can find,” says Gibbard. “And that appears to be at the Dover Strait.”
Smith’s catastrophist idea had seemed rather beyond the pale at the time – but the findings of Collier’s team, , backed it up. A single, unexpected, cataclysmic event had prompted Britain’s exit from Europe.
But this was only the start of a tortuous process. Leave didn’t immediately mean leave. On the morning after the megaflood, it was clear that Britain was actually still part of Europe.
Act II, Westminster
125,000 years ago A shallow, lushly vegetated valley, a little on the swampy side. A wide, sinuous river sweeps past, broadening to a mighty estuary. At the water’s edge, hippos wallow contentedly. It is warm. Very warm. No Big Ben bongs mark the passage of time. In fact, there are no signs of early human activity at all.
Sea levels have fallen and risen as colder times came and went over the past few hundred thousand years. During the coldest of these glacial periods, so much water was locked up as ice that sea levels were almost 120 metres lower than today, and the entire bed of the English Channel was dry land.
The megaflood didn’t change that overnight. The water raced away to the Atlantic, and only over thousands of years did the sea creep back up the English Channel. Around 400,000 years ago, it seems to have poked its way through the newly made breach at Dover. Fossils of marine molluscs from this time in the valleys of the Thames and the Scheldt on the Belgian side share the same characteristics, indicating they were brought there by the same sea. But the part of the valley of the Rhine that is just a little to the north has different fossil fauna, so it was never flooded from the south.
What we can reconstruct is the following: as the ice sheets beat their retreat from Finchley and beyond, they re-exposed the delta where the southern North Sea is now, as well as uncovering an extra strip of glacial material that their bulldozing action had deposited on it. Although low-lying, this strip of land connecting Britain and the present-day Netherlands north of the Thames estuary proved an insurmountable obstacle to the rising waters.
This was a backstop that prevented Britain’s clean exit from Europe for the next 250,000 years.
The backstop was a boon for migration to a depopulated Britain. Early Neanderthals swarmed over the land bridge. Innovations in clothing, hunting techniques and the control of fire had made life in British climes a lot more comfortable, at least during warmer periods. It helped that early humans had, in the meantime, established themselves as the top predators in the region, allowing them to bag the best housing stock: caves. “Around this time, you see a big shift in the ability of people to live happily here,” says Ashton.
But Britain’s relationship with the continent was changing, if imperceptibly. The planet continued to cycle through slightly colder and slightly warmer periods. During each warm spell, the sea inundated the breach at Dover and carved it a little wider. Meanwhile, the land bridge was sinking – as indeed the North Sea floor continues to today – at an average rate of around 10 metres every 100,000 years.
“The second megaflood smashed the breach at Dover, opening the strait”
It was becoming less of a bridge and more of a boggy hindrance to the free movement of people. An increasingly detached Britain had turned into a less attractive destination for European migrants, and indeed for the natives. “You see a drop in accessibility during warm periods,” says Ashton. “The only times people could get across were when it was cold.” About 250,000 years ago, evidence of occupation by early humans ceases entirely.
This means there was no one around to observe the moment when Britain truly did first become an island. The evidence for that lies hidden under the Strait of Dover.
French engineers surveying possible routes for the Channel Tunnel in the 1970s had already spotted something strange on the seabed off Dover. They discovered an enigmatic, sand-filled depression that they dubbed the Fosse Dangeard, or Dangeard Pit. But they dismissed it with a Gallic shrug. They didn’t survey it in any detail, and simply diverted their proposed route a kilometre or so to the north – where the tunnel runs today.
It isn’t easy to survey the Dover Strait. More than 500 ships pass its narrowest point every day. Add in the regular ferries plying to and fro between Dover and Calais, and this is a hairy place to be in a jolly little geologist’s boat looking at the sea floor. “It’s a bit like being on the central reservation of a motorway,” say Collier.
In the end, it was Collier’s colleagues from Belgium, in a model of European cooperation, who got to the bottom of what was going on: there was not one, but a series of truly massive pits carved into the bedrock. Together, they formed a belt oriented roughly at right angles to the strait. The deepest depression was 140 metres below the water surface, tripling the strait’s maximum depth measured to its sandy bottom. “They are huge, absolutely huge,” says Collier.
These pits lie where the chalk Weald-Artois ridge would have crossed the strait. And each has the same distinctive profile, deeper at the more northerly end and tapering to a shallow end at the south. “They have a nice scoopy shape,” says Collier. “Just as we should have if we have water coming over a barrier.”
Such plunge pools occur at the bottom of waterfalls too, as the plummeting water scours out the rock beneath. The find seemed to be the clincher for the megaflood hypothesis. The barrier itself has long since eroded away, but the evidence of water cascading over it is still there. “These are some of the biggest palaeo-plunge pools we’ve seen on Earth,” says David Garcia Moreno at Ghent University, part of the team that discovered them.
“The strip of land was a backstop preventing a clean exit from Europe”
But the surveys also revealed unexpected evidence for a second megaflood. If there had been just one flood event 450,000 years ago, the deeply carved river channel indicating the passage of floodwater downstream should start at the plunge pools. And it is there. But the carved channel is also upstream, approaching the Strait of Dover from the North Sea.
Gibbard thinks he knows what was going on. Some 180,000 years ago, history began to repeat itself. Ice again advanced as far south as East Anglia and the central Netherlands, and it blocked the free movement of water to the north.
A lake began to grow again, this time behind the land bridge left behind after the glaciation 450,000 years ago. The flimsy backstop caved in to the water’s pressure. “This second barrier was not made of bedrock, but sediment,” says Gibbard. “So it probably blasted through pretty quickly.” The second megaflood smashed the breach at Dover, opening out the strait to pretty much the width it is now, while also carving out the features to its north.
Just as with the first flood, the effects of this second breach with Europe showed themselves only slowly as the world warmed after the glaciation. By 125,000 years ago, sea levels had once again risen and sat 6 metres higher than they do today. Water stretched up the Thames almost to where the Houses of Parliament now stand. On this occasion, however, the land bridge was overcome as waters flooded in from north and south. Britain was for the first time an island.
If this gives the hippos wallowing in the warm Westminster swamp cause for rejoicing, they don’t show it. People won’t return to British shores for a few tens of thousands of years yet. And getting rid of the backstop wasn’t the final answer either. That required a Norway solution.
Act III, Doggerland
8200 years ago A patchwork of swamp and lagoons. There is evidence of settlement: the odd simple hut, a fire burning here and there. Small fishing boats bob around. But this is no normal day. The sea is receding. Something looms on the horizon: a long, low line of water that is no ordinary wave.
Even after that initial, successful bid to go it alone 125,000 years ago, for most of the time since, says Gibbard, you could have walked from Brighton to Calais, or across what is now the North Sea.
Whenever the temperature was down just a tick, the shallow bottoms of these seas meant they drained away entirely to become open plains watered by major rivers. One of those rivers would have been clearly visible from my eyrie atop the White Cliffs. In colder periods over the past 100,000 years, the Channel river, running roughly along the course first carved by the megaflood 450,000 years ago, was fed by the combined southerly flowing waters from the Thames, Meuse, Scheldt and Rhine.
These waterways were important migration routes for megafauna such as mammoths, woolly rhinos, bison and indeed humans. “People probably followed the animals,” says Gibbard. “They were major routeways. They were sources of fresh water and there was vegetation.”
Early humans took advantage of them to recolonise Britain during colder phases. Late Neanderthals arrived about 60,000 years ago, followed by small groups of Homo sapiens maybe 40,000 years ago. “They are big hunters and they are able to cope on a seasonal basis at least,” says Ashton.
The last glacial maximum, some 21,000 years ago, gave them pause for thought. It was the starting point of the third – and so far final – act in Britain becoming an island.
Once again, an ice sheet covered most of Britain, and lower sea levels meant there was a land link to what is now Denmark and the Netherlands. But this time the ice sheet wasn’t connected to the wider polar ice cap. With no hindrance to the flow of water, there was no repetition of the megaflood events of 450,000 and 180,000 years ago.
By 9000 years ago, the world was considerably warmer and the sea was pushing its way back up through the Strait of Dover. To its north, there was still dry land. Known as Doggerland after the Dogger Bank, a sandy feature on the bottom of today’s North Sea, its pleasant, wooded valleys and meandering rivers would once have been a paradise for the stateless hunter-gatherers of the period. As the planet warmed further, the area became wetter and marshier, a low-lying lagoon archipelago.
The coup de grâce, 8200 years ago, was dramatic. An undersea earthquake triggered huge submarine landslides off the coast of Norway, known as the Storegga slides. They dislodged something like 3000 cubic kilometres of material, and created a huge tsunami that raced across the North Sea. Whatever was left of Doggerland didn’t stand a chance, overwhelmed by waves 5 metres high. Once again, the land bridge that connected Britain with Europe was washed away. For a third time, water rushed through the Strait of Dover – and Britain was left in glorious isolation again.
Epilogue
The never-ending story of Britain’s divorce from Europe, embedded as it is in flows of ice and water, is a tale of European integration. “What’s happening in Scotland affects what happens in northern France. What happens in Germany affects what happens in southern England,” says Garcia Moreno. “There are no boundaries in geology.”
The complications inherent in such a picture mean our story isn’t definitive – but all the evidence suggests we aren’t too wide of the mark. The clincher for the idea of repeated floods opening out the Strait of Dover could come from drilling into the sediment held in the depressions there, and then into the bedrock below them, to date what was laid down when. “That will give us a minimum age for the incision of the valley floor,” says Garcia Moreno. “Then we can possibly unravel which process produced this infilling, where it came from and when.”
His team recently won the promise of funding to do just that – from Europe, naturally – but lost it again for lack of a strong, stable boat from which to do the drilling. So we must wait a while yet for that confirmation.
Meanwhile, where next for Britain? Will the shadowy geological forces of remain once again thwart its destiny as an independent island, as so often in the past? History certainly suggests that when a new glacial period arrives, it will suck up seawater and sink global sea levels to make the Strait of Dover dry once more.
But that new cold spell might never come. The billions of tonnes of carbon dioxide we are pumping into the atmosphere each year are likely to ensure that temperatures, and sea levels, will rise still further.
If so, Britain will cut a diminished figure on the world stage in the future – but it will have a wider moat. Sceptics of continental integration can rejoice that Britain will never again be part of Europe. But the story of Britain’s future in Europe won’t be about Brexit. It will be about climate change.
Article amended on 12 March 2019
We corrected the sequence of the Thames, Scheldt, Meuse and Rhine
