Viruses vanquished with a burst from a laser

Scientists in the US have developed a laser technique to selectively wipe out viruses and bacteria whilst leaving human cells unharmed. The approach could be used to improve the safety of blood transfusions and other blood-derived products but
without the risk of harming the cells present. Kong-Thon Tsen and his colleagues at Arizona State University made the discovery when they exposed solutions of viruses including bacteriophages and TMV, a plant virus, to a train of very short (femtosecond duration) bursts from a near infrared (850nm) laser. After an hour the viruses were completely inactivated. The team then repeated the experiment using E. coli bacteria and, again, after one hour the bacteria were all destroyed. But when they exposed solutions of human cells to the same treatment, the cells remained viable and
healthy. The researchers think that the laser pulses rip apart the outer coats of the microbes in the same way that it's possible to smash a glass with sound waves. The bursts of laser light cause a phenomenon called impulsive stimulated Raman scattering (ISRS), which sets up patterns of lethal vibrations amongst the proteins on the outsides of the micro-organisms, breaking them open. But mammalian cells, possibly because they are much larger, require between 20 and 100 times more energy to
trigger the same process, so they're relatively invulnerable to the effect. As a result the team are confident that the technique, which should also be immune to bugs becoming resistant to its effects, could play a major role in the clinical setting. "Although it is not clear at the moment why there is a large difference in laser intensity for inactivation between human cells and micro-organisms such as bacteria and viruses, the research so far suggests that ISRS will be ready for use in disinfection and could provide treatments against the worst, often drug-resistant, bacterial and viral pathogens," says Tsen.

4th Nov 2007

Tuning in to Nano FM

Never mind the Nano iPod, a team of researchers at the University of California at Berkeley have built a working radio made from a single carbon nanotube.

By fixing the tube between two electrodes, it can fulfil all the functions of a radio – acting as an antenna, tuner, amplifier and demodulator.  The team showed that their nano radio could tune into a radio signal generated in the room, and play it back through an attached speaker.    In fact, the first song that was broadcast to the radio was "Layla" by Derek and the Dominos, ironically followed by "Good Vibrations" by the Beach Boys.

But how does it work? When a radio wave passes across the nanotube, it causes a change in the electrons that are streaming along it, and causes the tube to vibrate.  This is the action that effectively “decodes” the radio signal, and transmits the information.  

And by lengthening or shortening the nanotube, the researchers were able to control the frequency of the radio signal that the device could receive.  Using this technique, the researchers could make the radio work across frequencies that are usually used for commercial radio stations.

But aside from the novelty value, the technology could be used for many different applications.  For example, it could be used in radio-controlled devices that could travel in the human bloodstream or microscopic mobile phone devices.  In the long term, the researchers are hoping to develop miniature sensors that can communicate wirelessly.

4th Nov 2007

Plastic poisons worming their way up the food chain

Researchers at Plymouth University in the UK have uncovered worrying evidence of how, thanks to plastic waste in the sea, organic poisons make their way up the seafood chain and ultimately into us. Scientists have known for some time that plastic washed into the sea breaks up into tiny particles, called microplastics, which can absorb oil-based pollutants such as PCBs, nonylphenol and DDT, which are present at low levels in the water. They also suspected that when these particles settle on the seafloor, sediment dwellers like marine worms would ingest them and concentrate their chemical cargo of organic pollutants. Then, when the worms fell victim to predators such as fish and crabs, the chemicals they contained would pass up the food chain. Now Emma Teuten and her colleagues have proved that this is indeed the case. Writing in Environmental Science and Technology, the researchers tested the effects of adding small quantities of plastic mixed with the organic pollutant phenanthrene to tanks containing sediments inhabited by lugworms (Arenicola marina). Compared with control worms, these plastic-exposed animals were predicted to be carrying 80% higher tissue concentrations of the pollutant. "It [plastic] accelerates the mechanism by which contaminants accumulate in the food chain," says Teuten. The team suggest that more research is needed to understand the implications of their findings, including looking at other types of plastics, and how they affect the persistence of pollutants in the environment.

4th Nov 2007

Making mighty mouse

Researchers at Case Western Reserve University in Ohio have managed to breed some “mighty mice”, capable of running at top (mouse) speed on a treadmill for up to six hours without stopping.

These impressive wee beasties have been genetically engineered to have unusually high levels of an enzyme called PEPCK-C in their muscles.  This enzyme is normally involved in glucose metabolism, and helps our bodies to make energy from sources such as glycogen and fat.

The researchers found that the mice eat 60 percent more than usual, but remain fitter, trimmer and live and breed longer than their normal counterparts.  The mice were also tested on treadmills, and the scientists found that the modified ones could run for nearly twice as long as unmodified mice.  

Lead researcher Richard Hanson compared the metabolisms of the mighty mice to cycling ace Lance Armstrong biking up the Pyrenees.  He points out that these mice use mainly fat, rather than sugar, for energy, and produce very little lactic acid compared to normal animals.  It’s the lactic acid build-up in muscles that causes pains and cramps after intensive exercise.

The mice were bred as part of an on-going research project aimed at understanding the role of the PEPCK-C enzyme in muscle and fat tissue, and according to the researchers, they could tell from the start that these mice were a bit special, and apparently they ran continuously in their cages from an early age.  But as well as being more active and virile, they’re also more aggressive.

The scientists found that these traits continued for at least two years – that’s considered old age in mouse terms.  Some of the female mice were even having babies at the ripe old age of 2 and a half years, which is very unusual – as most don’t breed after they’re about a year old.

4th Nov 2007

Edelweiss, music to the ears when it comes to sunscreen

Researchers studying the high Alpine plant edelweiss may have stumbled on an impressive new sunscreen strategy. Brussels-based researcher Jean Pol Vigneron and his colleagues wondered how the eledweiss plant was able to withstand so effectively the high doses of UV radiation that accompany life at high altitude. To find out they measured how the plant absorbed or reflected lights of different wavelengths, expecting to see the UV being bounced back at them. But they were shocked to see that whilst most wavelengths were reflected, UV wasn't. "It's astonishing, but the plant completely absorbs the UV," says Vigneron. Edelweiss leaves are covered in fine white hairs and the team wondered whether they might be responsible for soaking up the
UV. To find out they studied them under the electron microscope, which revealed that the hairs are made up of tiny fibres, each just 176 nanometres (millionths of a millimetre) across. This diameter means that the fibres are about the same size as the wavelength of ultraviolet light, and can interact with it. The researchers think that the tiny strands steer the UV away from the leaf where it could do harm and into the middle of the hair where it can be soaked up by a material in the centre, possibly pure
water, which is a good absorber of UV. Vigneron suspects that the same trick could also work for sun-lovers seeking better protection than that offered by standard titanium-based creams and lotions currently on the market.

4th Nov 2007

Jumping Flames

Make a flame jump several centimetres using just a humble candle.

What you need

What to Do

Light the candle and wait until it is burning well and has a glowing ember at the end, it works better when the wick is too long.

Carefully pour the excess wax out of the candle.

Blow the candle out gently.

Quickly wave the lit lighter near to but not next to the candle. It works best if you wave it in the smoke.

What may Happen

With any luck the candle should relight without being touched by the flame

What is going on?

It is very difficult to set light to a lump of solid or even liquid wax because the surface area is very low so it can't react with oxygen very fast however it just takes a match to light a candle.

A candle works by melting the wax which is then drawn up the string like wick  by capillary action. The wick is heated by the flame and has a large surface area so the wax vapourises. Now the wax has a huge surface area because it is a gas and it has enough energy to start reacting with the oxgyen in the air to burn.

When you blow out the candle the wick is still hot so the wax continues to evaporate for a few seconds. Eventually this wax condenses into a cloud of tiny wax particles we call smoke.

If you bring another flame to the vapour it can still burn so it will relight the candle.

This is why petrol is much more dangerous than diesel even though it will catch fire at a lower temperature.  Petrol has a much lower boiling point and so will vapourise much more easily, this means there is much more vapour to light if there is a spark.

Over Everest

It’s always been an ambition of man to fly but now the new technology and extreme sports have come together and brought this dream a little bit closer so that adrenaline junkies just like me can rise to even greater challenges than before and it seems that it’s no longer impressive just to have been able to climb mount Everest; now the goal is to fly over it. We sent Meera Senthilingham to the London Science Museum to find out a bit more.

Meera - Imagine what it would feel like to fly and if you could fly what would it feel like to fly over something like Mount Everest, the tallest mountain in the world? Thanks to the new sport of paramotoring, which uses parajets to elevate you into the air and then paragliders to bring you back down, not only are people able to live the dream of personal flight but two Brits have managed to break the world record for the height reached using only a parajet. This year Giles Cardozo and Bear Grylls flew above the summit of Mount Everest and reached a height of 30,000ft. The challenge was known as mission Everest and was sponsored by technology company GKN. Now the equipment they used to accomplish this mission was recently displayed at the Science Museum in London so I went along to see how it all worked and find out just what it took to break this world record. I spoke to Giles Cardozo who not only flew up the mountain but also designed the equipment they actually used to get them up there. So I had to start by asking him just what a parajet actually is.

Giles - Well a parajet is an aircraft that you wear on your back just like a rucksack and a paraglider wing which you attach onto a harness. Using a thrust of this engine on your back with a propeller fitted to it, it moves you into the air and the wing gives you the lift you need. Together you’ve got a complete flying machine. You can fly up to 40mph up to thousands of feet, In this case we flew to 30000 feet with it.

Meera - People do this for social purposes as well. So what kind of heights will they do if they’re just doing this for fun?

Giles - Really, the highest you go is about 5000 feet. Just above the clouds so you have a nice view but 15000 feet is the maximum altitude you can go to with a machine. People never really go that high.

Meera - So what was involved in creating the equipment to take you that extra 15000 feet?

Giles - Well, the most difficult thing really was making an engine that would still breathe where there’s no oxygen or very little oxygen. At 30000 feet there’s only a third of the oxygen in the air. The engine needs oxygen to run, that’s what gives it its power. So we had to make a system that would drive an enormous amount of air or oxygen into the engine to make it produce enough power to keep us flying.

Meera - How did you actually manage that? What kind of details did you have to pay attention to when designing?

Giles - The most important thing was the fuel delivery which is computer-controlled and the supercharging. A supercharger, basically, is a like a tiny impeller which whizzes around incredibly fast. We got it spinning at 3000 times per second. You can imagine that’s rotating very, very quickly. That would blast enough air into the engine. The computer then controls the fuel delivery and between the two of them we managed to keep the engine running and propelling us into the air.

Meera - When you’re doing the flight itself you’re using the engine to propel you but when would you essentially switch it off and use the wind?

Giles - Yes, once you’re up in the air you’ve gotta keep your finger on the throttle. You’ve got a little hand control and you squeeze that hand control and that keep the engine revved up and you keep going higher and higher. Now when you get to the maximum height you want to go you can switch off your engine and the wing keeps flying so you can just glide back down again. So what we did, we just flew to 30000 feet, switched off the engines and glid all the way back down to our starting point.

Meera - At heights like that the actual person himself must need extreme protection just to protect their own body.

Giles - Yeah, we had a wind-chill factor of about -70. We had 3 layers of clothing on board, a whole load of under-liners as well. We had oxygen systems. We’d really pass out under a minute at 30000 feet if we didn’t have oxygen with us and we had a big helmet with two balaclavas on. We had all the kit on to make sure we kept nice and toasty inside our kit.

Meera - The amount of power that the actual engine must need to take you up: it’s 100 horsepower. Could you compare that to something just so people can get an idea of just how much power that is?

Giles - Yes, I mean you’re average family car produces maybe 80-100 horsepower. That’s the sort of 4-6 seater car. We had the engine equivalent power strapped to our backs yet it weighed ten times less. That was the most difficult bit. It was getting an engine which will produce nearly 100 horsepower whilst being able to wear it quite happily on your back and then carrying your fuel with you and everything else. You realise how light the engine had to be to make it possible to actually make it work at all. If we added up everything including fuel, all our helmets, electronics, the whole lot: we weighed about an extra 80 kilos so more than my bodyweight. I think I was fitter before I did this that I’ve ever been in my life.

Meera - And what did it feel like to be at such a height?

Giles - Well, I think I’d dreamt of this moment for such a long time that obviously I was very excited. Also you feel very vulnerable because you’re there amongst these huge mountains, miles and miles from anywhere. I think I was scared but I was also very excited. And just an incredible view, really to top it off. It was just staggering.

Meera - Giles’ flying partner was adventure man Bear Grylls. He must have been facing some personal demons in the mission, having broken his back in three places in a previous parachuting adventure. I asked him how it felt to be hovering over the tallest peak in the world.

Bear - I always thought, God, you know, I wonder if it’s going to be really, really terrifying. Being suspended on these little strings. But it wasn’t, it just felt the most meant-to-be, magical extraordinarily privileged moment even though it was -40 degrees and you’re so dependent on one little oxygen canister for keeping you alive and you’re aware you’re at your most vulnerable point. There was something I think we both felt that this was really meant to be and what a privilege. We’d had screaming winds for days. You know 100mph winds, massive snows. We just had this three hour window of absolutely still weather all the way up to 30000 feet. To get still winds at 30000 feet is unheard of if you speak to any pilot. You know, you always have at least 80mph tail winds or head winds. It all came together in those three hours of which we did feel the luckiest men alive.

Meera - I can’t even begin to imagine the physical endurance required to survive at such a height, let alone having to control something that’s suspending you in mid-air. To get you thinking about how high Mount Everest actually is, and therefore how high in the air the duo were flying on their own I’ll leave you with this comparison from Michael Vor, a member of the GKN team.

Michael - When you think about it, 30000 feet is the height of an [jet] aircraft flying so when you go on your holidays and you’re flying at that type of feet you can imagine looking out of the window and seeing a guy in a parachute basically flying past you, it’s quite a challenge.

November 2007

Dating the Hobbit

Chris - Welcome to the Naked Scientists. Your work has largely been very exciting because you got to do things like date these hobbit people that were discovered a few years back but probably a lot of people are wondering where does man come from and could you possibly set the scene for us? Tell us what the time line is for the evolution of people on Earth and where we all came from?

Chris Turney - Yeah sure, Chris. Essentially the earliest remains of humans are in Africa about 2.5-2.3 million years ago. That’s a species called Homo habilis or ‘handy man.’ Apologies for the remarkably sexist names actually, it’s always man! But anyway, Homo habilis was the first species of our genus. After that it all gets a bit hazy. Traditionally it was always thought that an offshoot of that was Homo erectus (erect man). And the traditional view was that Homo erectus at some point migrated out of Africa and settled across different parts of the world: in Asia - Peking Man; Java Man down in Indonesia. In Europe he eventually evolved into Neanderthals. That was the traditional view and that’s the called the ‘Multiregional’ hypothesis which essentially is that these different species around the world evolved into us: Homo sapiens with a little bit of romantic liaisons on the edge. I wouldn’t say that’s the widely accepted view now but the more accepted view is the ‘Out of Africa’ hypothesis which is that our species (of which the earliest evidence is from about 200,000 years ago) evolved in Africa and then migrated out of Africa somewhere between 50,000 years to 100,000 years ago. They moved out across the world and essentially displaced all these ancient species of human.

Chris - Why do we think that that’s the case? Why have we changed our view that rather than evolving in-situ they actually had to come out of Africa twice?

Chris Turney - Well, there’s always evolution going on around the world all the time but essentially the species, our species, looks like the earliest evidence in Africa and nothing broadly comparable. I guess really, and we’ll come to that again, but the hobbit is also evidence of ‘Out of Africa.’

Chris - How do we know about that magic date of 50,000 years ago? What’s the evidence for that?

Chris Turney - Well, really it’s constrained really. We’ve got evidence of modern humans in Europe around 40,000 years ago (55-40,000ya). Really the lynchpin is essentially Australia actually. There’s not a lot of evidence of modern humans between Africa and Australia. There’s lots of stone tools but there’s very little modern human remains. There’s a little bit in Borneo and essentially it’s in Australia. Australia opens up all sorts of interesting angles because essentially even during an ice age when the sea level drops 120m, it’s always been an island. So people must have actually built boats to get across so the early stages therefore were 50-60,000 years ago.

Chris - So people were building boats 50,000 years ago? That’s really something isn’t it?

Chris Turney - Well, that’s right, We’ve got no direct evidence of it and, of course the alternative is a pregnant woman on a mat of vegetation or an elephant swimming across with people on him but I think basically a boats is probably a more likely one.

Chris - So tell us about the colonisation of Australia because that in itself’s an interesting story. Because people didn’t know exactly when the first settlers arrived there unless, I guess, you and your various techniques came along?

Chris Turney - Well, it’s been an interesting story actually. If you went back to the 1960s the earliest ages based on radio carbon dating were essentially around 10,000 years ago. And over time, gradually, it’s been pushed back and pushed back. Until about ten years or nearly 20 years ago now it was about 40,000. There’s a limit to radio carbon dating and 40,000 was traditionally quite close to how far back you can detect with that method. Then other methods came along and they started coming up with ages of 50 and 60,000. There was nothing close to that. So my research interest was really seeing if we could push back radio carbon dating and were those ages real artefacts of the method or were they real?

Chris - If we could just explore that a little bit, Chris – why is carbon dating restricted to those dates that you mention? Why can’t it go on ad infinitum?

Chris Turney - Well it all comes really down to this quirky concept called the half-life which essentially after a period of time half of your radioactive element disappears. So a radioactive carbon or C14 has a half-life of about 5,500 years. Every 5,500 years you lose half. After about seven or eight half-lives you’ve essentially got very little left. I guess the thing is if you took a piece of coal which is millions of years old and you added to that carbon 1% of something from your body (modern carbon) you’d come up with an age of 37,000 years if you measured that. That doesn’t mean the coal’s 37,000 years it’s just how far back it can really date.

Chris - How did you crack that nut?

Chris Turney - A combination of things. In Australia and South East Asia, probably lots of places in the world. Early archaeological remains, a lot of the artefacts are found associated with charcoal and charcoal’s great as there’s lots of it. It’s a product of burning. In many environments it can survive for quite a long time. The problem is it soaks up everything in the ground. If you’ve got smelly feet you can use a bit of charcoal. If it sits in the ground for 40,000 years it can pick up a lot of contamination so the method that we use was to clean up the carbon out of the charcoal and then we had a special vacuum line where we basically heated up the charcoal, burnt off all the contamination and cleaned up the sample for dating.

Chris - What did that show you about Australia?

Chris Turney - Well essentially when we actually tested it out, intriguingly some of the early sites became younger. Some stayed the same age but a few crucial ones actually became quite a bit older. One of them got back to around 52,000 years.

Chris - So that says people were knocking around Australia must have had the capacity to get across the water 50,000 years ago but also, what about the climate then? Obviously Australia’s struggling now with not enough rainfall, Murray Darling river’s down to a trickle because so much is having to be taken out for irrigation. Was it always like that?

Chris Turney - No. Australia swings backwards and forwards with aridity, all the time. Essentially, this is pretty unusual what’s happening at the moment. We’ve been doing a lot of work out there trying to reconstruct the climate and try and get a better handle on what’s happened in the past.

Chris - So what do you think has happened?

Chris Turney - Essentially, I think we’re in a lot of trouble unfortunately. We’re gonna have to start doing something pretty seriously.

Chris - But if you look at say, the timing of the arrival of people. One of the things that indigenous peoples in Australia have been doing for 40,000 years is burning stuff. So is there any evidence that they have brought about any of the change that you see in Australia?

Chris Turney - Well, some people have argued that. Yes we’ve done a lot of dating and looking at reconstruction of what vegetation was like and there does seem to be a coincidence between changes in vegetation, at least in NE Australia, and burning. So some people have argued that actually, human arrival caused catastrophic collapse of vegetation and it dried out. Other people disagree with that view. It’s an interesting debate going on.

Chris - If we could just turn finally to the hobbit story which was really exciting a few years ago. How do these hobbits, these little people fit into this whole picture of the colonisation of Australia and what else was going around the world at the same time?

Chris Turney - That was great fun. We were basically interested in trying to work out when Homo erectus died out across Indonesia and one of the early sites that we were interested in was led by a colleague, Mike Morewood ate the University of Wollongong. Mike was interested in the island of Flores and working with the Indonesian colleagues. He went back to one of the key sites that had been excavated before and there’d been burials found in the surface and lots of stone tools. Essentially when they were digging down they’re looking for Homo erectus. They came across an entirely new species of human, Homo floresiensis.

Kat - There’s been various arguments about whether it really is genuinely a new species or not. I’ve heard people say oh well it’s just a pygmy or something like that. How do we know that it is genuinely a new species, an offshoot?

Chris Turney - Well there’s quite a lot of evidence now presented in that shape of a skull, the shape of the whole skeleton actually, the pelvis and feet, the wristbones more recently and the brain size as well. Typically, if you look at the history of science as well, whenever a new species of human is discovered there’s usually some question about a diseased individual. When the first Neanderthal was found someone claimed it was a giant bear. Another person was a Mongolian Cossack. You’ve got lots chasing back Napolian in 1840. Another was that it was a child that suffered from rickets, got bashed over the head and a bit of arthritis. So it’s par for the course really.

Chris - Just looking briefly at the timeline, Chris. How many years were there hobbit people around on Earth?

Chris Turney - Well, some of their traits are remarkably ancient, possibly 2 million years or so. They certainly arrived in Flores by a million years ago and the most recent evidence we’ve got is 13,000 but there’s some tantalising stories from the locals, Ebu Gogo, the ancestor who eats everything and the locals insist that they arrived in the island just before the Dutch turned up a couple of hundred years ago. Mind-blowingly there might have been another species of human being on the island.

Chris - Thank you very much Chris Turney.

Chris has also written a book on this subject called Bones, Rocks and Stars: the Science of when things happened. This is currently available in hardback and will be out in paperback on November 13th.

November 2007

Ancestral Fires

Kat - We’re no going to speak to Dr Anne Skinner who’s from William’s College in Massachusetts. Good evening Anne. 

Anne -   Hello.

Kat - Now, I understand that you’ve been studying how humans have used fire in history. So can you put it in a bit of context? How far back did we previously think humans have been using fire?

Anne -   Prior to the work that I did a few years ago the earliest of dates for fire were about 300,000 years ago. That is, controlled use of fire by human beings.

Kat - So we’re talking about camp fires here, basically?

Anne -   Yes, yes.

Kat - What have you done now?

Anne -   So what I did, about in the 1980s some bones were found in Swartkrans Cave which is in South Africa. They’d clearly been burnt. The layer in which they were found was dated to about 1 and a half million years ago and the question was, ‘how did these bones get burnt?’ And, ‘could that be evidence that they were deliberately burnt as a result of human activity?’ So I used a technique that’s called electron spin resonance – we won’t have to spend a lot of time on that – to look at the remnants of the burning process. If you burn something long enough you get soot. But if you don’t burn it quite long enough you have some other organic materials in it. And the actual ones that you find will depend on how hot the fire was.

Kat - So will that be the difference between whether it was a campfire or say, just an accidental bush fire?

Anne -   Right. Because at the time it was not a forested area. If it was an accidental fire it would be a grass fire about 300 degrees centigrade maximum. Camp fires go easily up to 500/600 degrees centigrade. So if these bones had been heated well over 300 that would suggest that the fire that had heated them had been deliberately assembled by the people who were also assembling the bones.

Kat - So it was basically a barbecue?

Anne -   Not really, there’s no sign that they were cooking. This has been billed as the earliest barbecue or as South Africans call it, a braai. First of all, if you actually cook something to 600 degrees centigrade it isn’t fit to eat any more.

Chris - I dunno, you’ve obviously not tried my wife’s cooking, Anne.

Anne -   Also, you couldn’t have counted on having the fire all the time. That is, probably what happened was that there was a lightning strike, some bushes caught of fire and they dragged burning wood back to the cave and used it to protect themselves against the leopards which were around.

Kat - That would suggest that humans were using fire one and a half million years ago. That’s quite a dramatic difference from 300,000.

Anne -   It is. Oh yes! In some ways it’s not that remarkable if you stop to think that 1.8 million years ago some of our other ancestors were as, Chris was saying, migrating up into the Caucasus and I know climate was milder there. But I’m sure they would have appreciated having at least some knowledge of the properties of fire in the winter time in the Caucasus.

Chris - Thank you very much Anne, it’s brilliant to hear your work.

November 2007

The Big Flood

Chris - When did Britain become an island in its own right and for a long time that’s been a big question but some scientists from Imperial college reckon they solved the puzzle earlier this year. One of them is with us this week and it’s Jenny Collier. What do you think happened? How did we become the island that we’re very proud of having?

Jenny - Well, it’s been something that’s been known about from other scientists for some time, particularly people looking at the human occupation of Britain. So we’ve been hearing a lot about very ancient ancestors of ourselves, humans. But humans first came to Britain about 700,000 years ago (at a very famous site of Boxgrove). Basically during this period, this is the quaternary, so the ice ages were coming backwards and forwards. Living in England was a bit marginal, if you like. Ancient man was coming backwards and forwards. Crossing to France and back into Britain basically as the ice came down and retreated. What the archaeologists have known for some time is that there’s a big gap. Basically the humans were coming backwards and forwards for some time and then, for some reason, about 100,000 and 60,000 years ago there’s no evidence for any humans at all. What we did in our group at imperial as a group of geologists was to go out and do a marine geophysical study in the English Channel where we literally measured the water depth. We found evidence for a catastrophic, large volume flood, which we think effectively cut Britain off. This helps explain why ancient man couldn’t get back in.

Chris - Two questions, then Jenny, what do you look for on the sea bed that tells you there was a flood? What’s the giveaway sort of signature of a flood?

Jenny - What we do in terms of telling a catastrophic flood from a normal fluvial process, as you might imagine, if you’ve got a very high volume of rapid-discharge water you get all sorts of scours and eddies, a whole group of landforms which you can put together and say they can only be formed by high volume water discharge and that means it’s not a fluvial river. Frankly it’s enormous. I’ve been working in a lot of exotic places and I never expected to find something quite so astonishing.

Chris - So a massive flood about, when? 500,000 years ago?

Jenny - Yes, we haven’t dated it yet so from a geological point of view the only way we could date it – we call it the smoking guns. We’ve got the bit that’s been carved out. The bit that’s been found. We need to go and look towards the edge of the shelf to find out where the sediments that have been carved out had been dumped. We haven’t done that yet.

Chris - Where do you think this massive flood came from and what triggered it?

Jenny - Well, that’s right. So we’ve got this great big flood channel and basically it points to the straits if Dover and it’s been well known. Again, mainly from people looking at animals and also plants that the straits of Dover was a land bridge that survived throughout these glacial fluctuations so man was happily trotting backwards and forwards across between the England and France across this land bridge which was just a geological structure. We made this hypothesis that the only way to get such a sudden water release would be to have a catastrophic breaching of the rock dam across the straits of Dover which would have releases basically a lake that built up in the southern North Sea.

Chris - And where did that Lake come from?

Jenny - Well as you imagine during a glacial period there’s a lot of – we’re on the edge of the glacier so there’s all sorts of melt water coming from the ice itself. All of the rivers from the northwest of Europe (so for example the Rhine) use to go through the North Sea out into the Atlantic, would all get trapped and build up a big lake which would be dammed behind this straits of Dover rock ridge.

Chris - And that’s what cut us off from France and made us country in our own right. Jenny thank you very much.

November 2007