"Our planet is unique." "An extraordinary piece of engineering, over four and a half billion years old." "And to see how it works, we've created something rather special." "We've collected the latest information from scientists around the world." "We've added satellite maps, sonar and radar images and we've brought it all together to make this." "We've created a virtual planet earth." "And in here we can look at the machinery of the earth." "We'll see how an enormous energy source, buried thousands of miles within the planet, shapes our world, up here on the surface." "I'm going round the world to see this machine in action." "This is mission control, can you hear me?" "It'll be a trip full of surprises." "Sorry, sorry." "It's this machine that causes earthquakes... ..volcanoes... ..and creates mountain ranges." "We discover why diamonds actually are forever, and how turtles are able to use this machine beneath our feet." "Go." "Go." "That was honestly a magical moment, it's quite spine-tingling." "I'm going on a journey to the centre of the earth to reveal just how the earth machine works." "This is Ripon, North Yorkshire, and this is my old school." "Not the most obvious place to start a journey to the centre of the earth, I know, but bear with me on this." "25 years ago I lived there." "That's my bedroom window, next to the tree, just above the lamppost." "And from there I could see this field." "And in this field there lived a donkey." "I used to see it in the mornings." "Then, one morning, I looked out and a whole chunk of the field had gone." "I didn't know it, but a sinkhole had opened up right about here, where I'm standing now." "My first thought was, "Wow!"" "My second thought was, "What's happened to the donkey?"" "And my third thought was "How did that happen?"" "The donkey was fine, by the way." "Shocked, but fine." "There are hundreds of these sinkholes in this area, which means it's not only the donkeys of Ripon that suffer." "Near my old home on a warm spring evening in 1997, a building collapsed." "And it is scary to think that the ground can be so unstable it can suddenly give way beneath us." "Like all sink holes, it was made by water eroding the rock beneath." "This county where I grew up is in fact home to one of the most famous sinkholes of all." "Might not look like much at first glance, but in fact it inspired one of the best known and most loved children's books of all time" " Alice In Wonderland." "This might just be the very place that gave the author, Lewis Carroll, the idea for Alice to fall down a rabbit hole and begin her Adventures In Wonderland." "Lewis Carroll frequently visited Ripon and almost certainly saw this sinkhole." "When I first heard about sinkholes here in Ripon as a kid, obviously all I wanted to know was what's down there, beneath the surface." "Well, now's the chance to find out." "Most of us live in towns and cities and give barely a second thought to what lies beneath our feet." "What would we find if we lift up Trafalgar Square?" "At first, it's a jumble of gas pipes, water mains, electric cables - all the stuff we've put there." "But most of that is in the first 100 feet." "Even our deepest tunnels are only around 200 feet below the ground." "Get below 300 feet and almost all evidence of humanity disappears." "No human being has ever been more than two and a half miles below the surface." "Beyond there, it's uncharted territory." "What we do know is that it gets warmer...much warmer." "And that heat comes from something over 3,000 miles below." "A giant ball of solid metal." "This is the inner core of the earth." "It's almost as big as the moon, and it's as hot as the surface of the sun." "As we'll see, the inner core influences our lives in all sorts of ways." "Yet, up here, we're barely even aware of it." "But we're getting ahead of ourselves." "So let's put it all back for now and start our journey to the centre of the earth at the beginning." "And the beginning is here, the bit we actually we live on." "It's called the earth's crust." "The crust is not just the land above the oceans." "It's the entire outer layer of the planet." "If we take away the sea we can reveal how the crust encases the whole of the earth." "But it's incredibly thin." "If the earth were an apple, the crust would be no thicker than the apple's skin." "It's anywhere from three to 45 miles thick." "But it's not one single piece of rock." "It's broken up into 14 enormous slabs called tectonic plates." "These plates don't stay still." "In fact, they're constantly on the move." "The signs are everywhere, if you know where to look." "And one place to look is here, in the south eastern United States." "This is Florida, famed for its swamps, creeks, 'gators and biting insects." "But one of the most amazing features here in Florida most visitors never get to see, because it's down there." "You see, the ground here is not as solid as you might think, in fact it's a bit like Swiss cheese, because" "Florida sits on a huge network of underground caves full of water." "It's called the Floridan Aquifer." "It started life when stresses and strains in the tectonic plate caused cracks to open in the crust." "Over millions of years these cracks were hollowed out by water." "Today, the Aquifer covers 100,000 square miles and provides Florida with nearly all its fresh drinking water." "But much of the Aquifer has yet to be mapped." "That's where this lot come in." "These guys are cave divers." "They swim underground." "Underwater." "In caves." "Connected by tight constricted openings, with no quick way out." "One man crazy enough to do this for a living is biologist and cave explorer, Tom Morris." "It's very important to map these underground caves because that's our drinking water." "So the more we know about what's going on down in that aquifer the better off we'll be up here on top." "Sadly, because of the risks involved, they won't let an amateur like me go with them." "I shall be helping them...up here." "I'll be following them with a tracking device." "And talking to them on an underground, underwater radio communications system." "I'm pretty much essential." "This is the radio that we use to communicate with the divers..." "'Radio expert Brian is rigging me up in this rather strange-looking contraption.'" "..Microphone in the other." "So, backpack on back." "Washing line in hand." "We're there." "Put your headphones on." "Hey, Tom." "This is Mission Control." "Can you hear me?" "I can hear you, Richard." "Well, if we're all ready, I'm ready up here." "You guys ready to go?" "Yes, we are." "Can't wait!" "To reach the aquifer, Tom and his team must squeeze through a crack in the bed of the lake." "It's a claustrophobic dive passing through holes in the rock barely wide enough to wriggle through." "Not the time for a big meal the night before." "Down and down we go!" "Then it's a tortuous 80 foot descent." "Up on the surface, Brian's transponder system lets us track exactly where they are." "They're struggling down through these constrictions." "So as soon as they get down against this current into the caves themselves, we will start tracking along with them?" "Right." "Far below, Tom has reached the aquifer itself." "Down here, hidden from view, is an unimaginable, subterranean world." "The aquifer stretches under the whole of Florida and parts of four other southern states." "In fact, there's more water held in underground aquifers like this than in all the lakes and rivers in the world." "Up above, we've successfully locked onto the divers' position 100 feet below." "Hello, Richard." "Can you hear me?" "'Tom, how are you?" "How you doing?" "What do you see already?" "'" "We're walking with you now, Tom." "We think we've got you." "We're marking your path." "Brian, all this that we're doing, mapping it on the surface, linking it to the underground." "Is it useful?" "The water in this aquifer is the source of most people's drinking water in Florida, so by mapping we can help to prevent development over the top of the caves." "You don't want fertiliser and septic systems and all the rest of that directly over it." "And while Tom continues to wriggle through impossibly small gaps..." "'To be honest the going is not much easier up here.'" "Sorry." "'Because wherever the divers lead, so must we follow.'" "Sorry." "They've gone right under the shop." "Tom, you're going through a shop." "Over here somewhere." "Yeah, right down the aisle." "Tom, you're under barbeque stuff, don't know if that's useful." "Not really, is it?" "No." "They're heading right for the wall." "Oh." "And out." "Can we get out that way?" "Yes." "As we follow the divers we come to a pool in the forest." "Hi, Tom." "I think we've found you." "Do you think you're coming to an opening to the surface?" "'Because if you are, we've so got you.'" "Look, look, lights." "Tom, we can see your lights!" "Well hello, Richard." "Tom, welcome back!" "Did you worry about us?" "It is so good to see our two worlds reconnected by that bit of water." "That's a nice little journey." "We went, oh, gosh, almost half a mile." "We got our new entrance." "And we can put this cave on the map." "It's amazing to think that those vast underground aquifers all started out as these little cracks and developed into something huge." "Rather them than me going down there, but glad to know they're there." "The tiny cracks in the ground in Florida are caused by stresses within a single tectonic plate." "But when two tectonic plates meet they cause a different kind of crack." "They create huge splits in the ground called faults." "And some faults can be very bad news indeed." "12.51 on 22nd February, 2011." "The cathedral spire in Christchurch, New Zealand falls as an earthquake leaves 182 dead." "Less than a month later on 11th March an even bigger earthquake struck Japan." "It produced a tsunami with waves of up to 98 feet high, killing perhaps 25,000 people." "And on the other side of the Pacific just a year earlier, 562 people died in powerful quake in Chile." "The Pacific Rim is an area of intense earthquake activity." "In fact, over the last 50 years there have dozens of major earthquakes along the coast of North and South America." "Let's go, let's go..." "The fact is tectonic plates move all the time." "And the evidence is here, in a stadium just across the bay from San Francisco." "The Golden Bears are the American football team of the University of California, Berkeley." "Their home ground, the Memorial Stadium, is one of the oldest and most iconic football grounds in the US." "But the way things are going, the stadium may not be here for much longer." "Stands are crumbling." "Walls are fracturing." "Something strange is going on." "Geologist Roland Burgmann tells me it's all down to a fault called the" "Hayward Fault, which runs right underneath the city of Berkeley." "Roland, talk me through." "Where is the fault in relation to the stadium?" "We're walking on it now." "It goes straight through the middle." "Really?" "Yeah." "So it goes right from..." "See that crack up there?" "It goes right through there, across the field all the way up there." "So really straight through the middle." "The stadium is literally splitting in the middle as that bit goes that way and that bit...?" "That's exactly right." "The western half of the stadium is being dragged north west by four millimetres a year." "Since it was built nearly 90 years ago, the two halves of the stadium have been pulled apart 14 inches." "Yet the real worry for the Golden Bears is that the fault line is moving too slowly." "You say it's moving by four millimetres a year, but here's the strange thing, you say that's not enough." "Right." "It's moving by four millimetres per year and it should be slipping by ten millimetres per year." "So it's not doing the full amount of slip." "That's a slip deficit we call it." "So that means it has to catch up at some point, and we know the way the catch up is happening is in big earthquakes." "And how long ago was the last one?" "So it's been 140 years." "So we are due one now." "Here." "Exactly pretty much between us." "Right there." "'Oh, dear.'" "Probably time to get off the ground." "The Hayward Fault that runs through the stadium is part of the much larger San Andreas Fault system." "All the hills and valleys have been created by the constant movement of the land." "From the air, there's suddenly just a better sense of scale." "I mean, it's all unimaginable, the forces, the size of these things, but just from being up here and tracking the fault round woodlands and round hills, you just get a sense of how massive it is." "Millions of years ago, when the San Andreas Fault tore apart the land, this lake was born." "It filled with water, was extended and is now used as a reservoir for the whole Bay Area." "When the San Andreas Fault shifts just a few feet it can cause a quake." "But the land is always on the move, and, over millions of years, the distance it travels is quite extraordinary." "Rocks found here in northern California started life hundreds of miles away in southern California." "This is part of this sort of 20-odd million year trek, that that whole slab of land has made, inching its way along as it creeps and creeps and creeps and ends up here?" "That's exactly right." "And that means the changes to the landscape here will be dramatic." "San Francisco and Los Angeles sit on two separate tectonic plates, either side of the San Andreas Fault." "Over 9 million years LA will move 350 miles north, so you won't need to drive between the two cities because they'll be side by side." "And then I see something that might not be here after the next big quake hits." "The symbol of San Francisco, the Golden Gate Bridge." "That's the bridge." "Golden Gate Bridge right here." "Disappearing into the fog." "Do you mind if I take a picture?" "Sorry." "It's not very cool." "It's not very "Oh I've been everywhere and seen everything, but..."" "There's a big debate among engineers if it's built safe enough for a big earthquake." "Well, it's a bit late now." "It's built." "It's there." "Yeah!" "The Golden Gate Bridge may not survive a major quake." "But on the other side of the bay, the Golden Bears have taken dramatic steps to protect their stadium." "They're cutting it in half." "When the work here is finished, the stadium will rest on separate free-floating blocks of concrete so that if a quake hits, the whole stadium will roll with the punches." "Roland Burgmann has returned to check on progress." "So this side of the stadium is going to be a completely separate structure, separated from this side, and the two sides can move independently, even in a large earthquake." "The two sides of the stadium are just going to move their separate paths, thereby there will be much less destruction." "This is a job that's gonna take two years to complete." "It'll cost the Bears a cool $320 million to carry out." "So when the big one hits, there's one place in the Bay Area that Roland thinks will be more than ready." "At least with the work that's being done on the stadium right now, this is going to be one of the safest places to be in the next large earthquake." "It's not surprising that all that pressure between the tectonic plates causes friction that leads to quakes." "But that energy also does something else, something truly awesome." "When two tectonic plates collide, solid land can buckle upwards." "That's the force that forms gigantic mountain ranges like the Alps." "Naturally, I want to see this incredible process for myself and geologist Sarah Rieboldt knows just the place." "This is Mount Diablo, California." "It's not the highest mountain in the world, but what makes this mountain interesting, is what it's made of." "It's going to take a while to get there." "We have only two horsepower." "I'm used to...more." "Sarah, the trip here was lovely, but what have I come to look at?" "All these little white bits - all shells." "Shells?" "Look closely at these rocks." "You can see all these little bits of white, these slivers in here, are re all fossils." "Like this?" "Mm-hmm." "A lot of them are broken up into pieces, but there are larger ones scattered about." "'And these aren't the shells of land animals, 'things you might expect to find almost 4,000 feet up.'" "There's clams, any kind of sea creatures, oysters, things like that." "Now, forgive me then." "Shells, sea creatures..." "Clearly that doesn't belong here, does it?" "Cos we're on a mountain." "Exactly." "For a long time this mountain didn't exist." "It's a very recent mountain." "It was only uplifted about 3 million years ago." "Before that, it was at the bottom of the sea and that's where all of these creatures were living." "So whenever we go anywhere..." "And I've seen this - seashells - and I've seen it on top of mountains in places, and you think, "Wow, the sea must have been really deep at one point" ""because it was over us here." No." "The sea was never here, but neither was this land." "It was down there somewhere." "Exactly." "And is that just a phenomenon unique to here?" "No, there are seashells, sea creatures and things on the tops of lots of mountains, including Mount Everest, which is hard to believe given how high it is." "That's a really out of place shellfish, isn't it?" "Of course, it took millions of years for the land to crumple up and form this landscape." "But because the machine inside our planet never stops working, the Earth's tectonic plates are still moving." "So some of our mountains keep growing." "Even Mount Everest, the highest point on Earth, is still reaching for the sky." "In 1953, it was conquered for the first time by Edmund Hillary and Sherpa Tenzing." "Since then, it's been edging upwards by five millimetres a year." "So if you climb to Everest's summit today, you'll be almost a foot higher than when Hilary and Tensing first reached the summit nearly 60 years ago." "We've explored some parts of the Earth's crust." "Now it's time to go beneath it." "And to find out what happens further down inside the Earth machine." "Let's lift out the east coast of the USA, just cos we can." "Beneath the crust is the next layer." "That's known as the mantle." "It's enormous - over 1,800 miles deep." "And it can get as hot as 2,200 degrees Celsius, hot enough to melt solid rock into a liquid called magma." "And this is the biggest and noisiest way of seeing what magma is." "Because, when a volcano erupts, this magma blasts out onto the surface." "Up here, it's called lava." "And with our virtual Earth, we can look inside the planet and see how it reaches the surface." "The magma collects in chambers around 10 miles below the surface." "But some magma starts life hundreds of miles further down, and can bring us vital clues about what happens deep inside our planet." "That's why scientists from all over the world travel to the heart of Africa, to take lava samples from one of the most remarkable volcanoes of all." "This is Mount Nyiragongo, in Africa's Great Rift Valley." "It's one of the most active volcanoes in the world and towers two miles above the surrounding countryside." "A million people live in its shadow." "At the bottom of the volcano's crater is a boiling lake of lava." "It is like a vision of hell." "A scorching cauldron, over 750 feet across." "The temperate on its surface is nearly 800 degrees centigrade." "Some scientists think the lava here comes from much deeper down than almost any other volcano on the planet." "Dario Tedesco is one of the world's leading authorities on this volcano." "It's really completely different from other volcanoes." "It really is unique." "There are so many secrets on this volcano that you don't get from the other volcanoes." "Dario leads a team of scientists into the crater." "They're attempting to collect a sample of fresh lava from the lake, but it's a long way down." "The crater is deep enough to accommodate the Empire State Building." "Probably not surprisingly, very few have been to the floor of the crater." "After climbing down for five hours, they reach level ground." "They're still 600 feet above the lava lake." "Time to make camp." "While the team sleep, the super-heated molten rock in the lake churns and boils, spilling over the rim." "When Nyiragongo last erupted in 2002, nearly 400,000 people in the nearby town had to be evacuated." "Because when Nyiragongo erupts, there's no way to outrun the lava." "Nyiragongo's lava can flow at over 60mph, faster than any other lava in the world." "Next morning, and the lake is calmer." "Dario sees another scientist reach the bottom of the crater." "It looks like he is going for the ultimate prize, a sample of lava straight from the lake itself." "It is dangerous, in my opinion." "It is a little crazy." "I mean, I won't do that." "The special suit he wears will deflect some of the incredible heat at the lake's edge, but it will do nothing to protect him if he comes into direct contact with the lava." "He's very, very close." "OK, he's just there." "Really a few centimetres." "He's just on the rim." "He's crazy." "Oh, my God." "Come back!" "It's too long." "Come back!" "Lava begins to bubble over the rim of the lake." "HE SPEAKS FRENCH" "Dario believes the scientist is taking too big a risk." "I kind of agree!" "The lake is becoming more active." "Lava surges over the edge." "The lava lake is now overflowing in three different areas." "Very strong exactly where he was five minutes ago." "Later that day, some perhaps more sensible scientists collect samples from the crater floor." "And those samples are then sent half way around the world to be analysed here, the University of Rochester in New York State." "Geologist Tom Darrah will analyse the sample." "The composition of Mount Nyiragongo lavas are both complex and mysterious." "The lava I am holding in my hand from Mount Nyiragongo is effectively a time capsule of the Earth's history." "Gases and minerals are trapped inside." "The sample is crushed." "Then heated." "So it can be analysed." "The results are ready." "The gases we analyse tells us this volcano is sourced from a very deep location within the Earth." "The source has to be somewhere well below the Earth's crust." "In fact, some scientists think it might come from the very bottom of the mantle, 1,800 miles below." "If so, it suggests something extraordinary and, ultimately, terrifying." "We can see what's happening on the virtual Earth." "Scientists think that an enormous upwelling of intense heat, a mantle plume, is rising from the interior of the planet under this part of the Rift Valley." "In the future, it could cause more volcanoes and earthquakes." "New mountains could rise and new valleys form." "East Africa could be transformed." "Of course, you don't have to mess around with boiling hot lava to get your hands on something that started life miles below the surface." "Burn your hands." "You can do it right here, on the high street." "These diamonds are around three billion years old, so they are pretty ancient." "They were formed in a rare event, deep in the Earth, that only happens every few hundred million years." "Cut and polished like this, they look beautiful." "But they started life as lumps of carbon far below the crust, thrust upwards by a special kind of volcanic eruption." "Magma surges towards the surface and carrying diamonds." "Many will get stuck along the way." "A few will make into the Earth's crust." "Even fewer will make it onto our fingers." "As we can see on the virtual Earth, diamonds are only found in volcanic regions of the planet." "So when I buy something sparkly for Mrs. H," "I'm buying her something regurgitated from the guts of the planet." "Not that I put it to her like that, obviously" "That wouldn't do." "This is Iceland." "And yes, it's cold." "Yet right beneath their feet, the locals can plug directly into the Earth's machine to power their entire country." "The crust is thin and the Earth's inner heat is so close to the surface that when rainwater seeps into the ground, it's quickly heated and turns to steam." "Power stations capture the steam and use it to generate electricity." "And everywhere you go, Icelanders are finding ways to exploit this natural energy source." "Potatoes?" "Yeah." "I should say this isn't a barbeque, we're not burning any sort of fuel." "Steam, heated in the ground below, is being piped up here and through volcanic lava rock, and that's what's cooking the food." "It's 170 degrees." "It can boil water in ten seconds." "So this really is, if you think about it, a free lunch, cooked naturally." "They even heat this stretch of the North Atlantic, so that they can go for a swim at any time of year." "The seawater out there is a freezing minus four degrees, but these swimmers are splashing around at a balmy 19." "But they don't just use the heat from the Earth's mantle so they can take a dip." "In fact, the whole country runs on power from the Earth's machine." "This is strange." "I'm cold, but warm!" "In Iceland's capital city, Reykjavik, almost every home is heated by plugging into the power of the Earth." "In winter, they even heat the streets and pavements to keep them ice-free." "Icelanders can sleep easy, knowing that this energy will not run out any time soon." "We know that the mantle is beneath the crust." "But what's below that?" "Time to go further down." "We are about to reveal the planet's generator." "The mantle is made of rock." "But the layer below that is an ocean of molten metal." "It's so fluid, it's just like water." "This is the outer core." "And if you thought the mantle was hot, well, the outer core is even hotter." "A lot hotter." "It's calculated to be somewhere between 4,000-6,000 degrees centrigrade." "As this molten metal flows, it does something special." "It creates a magnetic field." "Except this magnetic field is rather big." "Enormous, in fact." "It extends tens of thousands of miles into space." "It's too big for the hangar, but if we shrink the Earth, you'll get the picture." "Of course, without our technical wizardry, all of which I made here in the hangar, the magnetic field is usually invisible to us." "But there is a way we can see it in action." "These are the Northern Lights." "Here, over the snow and ice of the Arctic Circle, a magical procession of lights dances across the night sky." "It's one of the most remarkable things I've ever seen." "Not surprisingly, ancient peoples thought these lights were from the gods." "But it's simply the Earth's magnetic field made visible." "And it's a very good thing it's there." "This is how the magnetic shield works." "The sun is continually throwing out billions of charged atomic particles." "Lethal to most living things, but luckily the magnetic field deflects them." "The Northern Lights are how we see those particles from the sun interact with our atmosphere." "The Earth's magnetic field has another benefit." "In its lifetime, a sea turtle can travel tens of thousands of miles, criss-crossing the Pacific or the Atlantic many times over." "Yet at all times, it will know its exact location and can navigate its way around the Earth." "I've come to North Carolina to find out how they do it." "This is a big day for Coral here." "She's about to be released back into the Atlantic where she'll spend the next 10, 20 or 30 years swimming around it, or even, if she chooses, across it from side to side." "Out there waiting for her are cold waters that could kill her, strong currents, barren stretches of sea where there's nothing to eat." "She'd starve." "But she carries no map." "There'll be no other turtles to follow." "She'll be on her own out there." "But she can navigate all those thousands of miles, all those perils, and find her way back here to breed." "How?" "How does she do that?" "Well, these little fellas at the University of North Carolina are going to help us find out." "Scientist Ken Lohmann has devised an experiment to see how just how these turtles use the Earth's magnetic field." "But first, this young loggerhead turtle needs to dress up in an unusual outfit for a turtle." "These are little bathing suits we've produced for the turtles." "They're cloth harnesses that encircle the carapace, or the shell, but they don't prevent the turtle from moving its flippers in its normal way." "The harnesses enable Ken to track their movements." "He creates a magnetic field around the turtles' tank." "With the field turned on, the turtle knows which direction to go." "If we to were to reverse the magnetic field, the turtle in all likelihood would turn around and swim in the opposite direction." "And as soon as Ken changes the magnetic field, the turtle does change direction." "So turtles really are sensitive to the magnetic field." "And how they do it is all down to a mineral in their head." "Magnetite is a magnetic mineral, it's actually the same mineral that compass needles are made of, and it appears likely the turtles use magnetite crystals in their heads to perceive the magnetic field." "And it turns out that the turtles can do far more." "They can use the field not only as a source of directional information, but also as a way of figuring out where they are within the ocean." "So in effect, they have a global positioning system that is based on the Earth's magnetic field." "Look at this, she knows!" "That's how Coral is going to be able to swim out into the Atlantic and then, years later, find her way back to this exact beach." "Coral, look at this." "Look at all that lovely ocean waiting for you." "Right now, she's tuning herself in to that magnetic field." "She knows where she is, which is more than I do!" "All the hair on the back of my neck is standing up with what we're doing here." "She's desperate now!" "She's desperate now." "We're in a good spot." "Here we go." "So, we pick our moment, Coral, this is your moment, my darling." "Good luck!" "You're built for this!" "Coral." "Go, go, go!" "And she's gone." "There she goes." "That was honestly a magical moment." "It's quite spine-tingling." "I don't know about everyone else with us, but suddenly you're aware that's a very, very big ocean out there and a small turtle in it." "But she's tapping into something even bigger, the Earth's magnetic field." "It is magical." "And she's out there now, doing it." "Our journey's nearly over." "The best bit is yet to come." "We have travelled more than 3,000 miles down into the Earth." "We've gone through the crust, through the mantle and through the outer core." "We are now at our final destination." "The centre of the Earth." "This is the inner core." "And down here, something strange happens." "That layer of molten metal that formed the outer core has now become solid, crushed by pressures around four million times greater than on the surface of the Earth." "And it's hot." "Really hot." "Up to a staggering 6,000 degrees centrigrade, the same temperature as the surface of the sun." "And it is this heat that is the key to how our planet works." "All the volcanoes, the earthquakes, the never-ending movement of the land, it's all powered by this huge fiery ball of solid metal over 3,000 miles below." "The inner core is the engine room to the whole planet." "The core transfers its heat to the molten rock in the mantle, forcing it to rise upwards in vast plumes." "These rise to the surface through the mantle towards the crust, and with nowhere else to go they spread out, pushing the continental plates across the face of the planet." "They cool and fall back to start the cycle all over again." "The cycle takes millions of years." "And that is how the continents get pushed across the face of the planet." "It's how the Earth works." "Simple as that." "Many scientists believe this cycle will continue until all the continents are forced together into one huge land mass." "If so, our climate, our landscape, everything will change beyond recognition." "In 10,000 years this place could be covered in sheet ice." "In a million, it could be sand dunes." "In 100 million years, I could step from here onto the northern coast of Russia." "And in 250 million years, all the world's land masses will have joined together to create one massive super-continent." "As long as the Earth's core continues to spin, continents will continue to drift across the face of the planet." "New land will emerge, mountains will rise and each and every one of us will be for ever on the move." "Next time." "We look at how the Earth machine affects the ocean floor, and how this affects us." "Have you ever had anybody panic completely?" "Yes." "We drain the oceans to reveal vast underwater canyons." "Seeing as I'm already dressed." "Huge volcanoes, massive mountain ranges and metal snails!" "Subtitles by Red Bee Media Ltd" "E-mail subtitling@bbc.co.uk"