0:00:19 > 0:00:22Our planet is unique.
0:00:22 > 0:00:27An extraordinary piece of engineering, over four and a half billion years old.
0:00:29 > 0:00:33And to see how it works, we've created something rather special.
0:00:37 > 0:00:40We've collected the latest information from scientists around the world.
0:00:40 > 0:00:45We've added satellite maps, sonar and radar images and we've brought it all together to make this.
0:00:45 > 0:00:51We've created a virtual planet earth.
0:00:56 > 0:01:00And in here we can look at the machinery of the earth.
0:01:00 > 0:01:05We'll see how an enormous energy source, buried thousands of miles
0:01:05 > 0:01:10within the planet, shapes our world, up here on the surface.
0:01:13 > 0:01:17I'm going round the world to see this machine in action.
0:01:17 > 0:01:20This is mission control, can you hear me?
0:01:20 > 0:01:22It'll be a trip full of surprises.
0:01:22 > 0:01:26Sorry, sorry.
0:01:31 > 0:01:34It's this machine that causes earthquakes...
0:01:36 > 0:01:38..volcanoes...
0:01:38 > 0:01:42..and creates mountain ranges.
0:01:44 > 0:01:49We discover why diamonds actually are forever, and how turtles are able to
0:01:49 > 0:01:52use this machine beneath our feet.
0:01:54 > 0:01:55Go. Go.
0:01:55 > 0:02:00That was honestly a magical moment, it's quite spine-tingling.
0:02:03 > 0:02:06I'm going on a journey to the centre of the earth
0:02:06 > 0:02:09to reveal just how the earth machine works.
0:02:32 > 0:02:38This is Ripon, North Yorkshire, and this is my old school.
0:02:38 > 0:02:46Not the most obvious place to start a journey to the centre of the earth, I know, but bear with me on this.
0:02:46 > 0:02:5025 years ago I lived there.
0:02:50 > 0:02:54That's my bedroom window, next to the tree, just above the lamppost.
0:02:54 > 0:02:56And from there I could see this field.
0:02:56 > 0:02:58And in this field there lived a donkey.
0:02:58 > 0:03:00I used to see it in the mornings.
0:03:00 > 0:03:05Then, one morning, I looked out and a whole chunk of the field had gone.
0:03:05 > 0:03:10I didn't know it, but a sinkhole had opened up right about here, where I'm standing now.
0:03:10 > 0:03:12My first thought was, "Wow!"
0:03:12 > 0:03:15My second thought was, "What's happened to the donkey?"
0:03:15 > 0:03:18And my third thought was "How did that happen?"
0:03:19 > 0:03:22The donkey was fine, by the way. Shocked, but fine.
0:03:26 > 0:03:29There are hundreds of these sinkholes in this area,
0:03:31 > 0:03:34which means it's not only the donkeys of Ripon that suffer.
0:03:36 > 0:03:42Near my old home on a warm spring evening in 1997, a building collapsed.
0:03:44 > 0:03:51And it is scary to think that the ground can be so unstable it can suddenly give way beneath us.
0:03:51 > 0:03:57Like all sink holes, it was made by water eroding the rock beneath.
0:03:59 > 0:04:06This county where I grew up is in fact home to one of the most famous sinkholes of all.
0:04:06 > 0:04:09Might not look like much at first glance, but in fact
0:04:09 > 0:04:16it inspired one of the best known and most loved children's books of all time - Alice In Wonderland.
0:04:27 > 0:04:32This might just be the very place that gave the author, Lewis Carroll,
0:04:32 > 0:04:39the idea for Alice to fall down a rabbit hole and begin her Adventures In Wonderland.
0:04:39 > 0:04:44Lewis Carroll frequently visited Ripon and almost certainly saw this sinkhole.
0:04:49 > 0:04:54When I first heard about sinkholes here in Ripon as a kid, obviously
0:04:54 > 0:04:59all I wanted to know was what's down there, beneath the surface.
0:04:59 > 0:05:02Well, now's the chance to find out.
0:05:14 > 0:05:17Most of us live in towns and cities
0:05:17 > 0:05:22and give barely a second thought to what lies beneath our feet.
0:05:22 > 0:05:26What would we find if we lift up Trafalgar Square?
0:05:53 > 0:05:56At first, it's a jumble of gas pipes,
0:05:56 > 0:06:02water mains, electric cables - all the stuff we've put there.
0:06:02 > 0:06:06But most of that is in the first 100 feet.
0:06:06 > 0:06:11Even our deepest tunnels are only around 200 feet below the ground.
0:06:11 > 0:06:17Get below 300 feet and almost all evidence of humanity disappears.
0:06:18 > 0:06:24No human being has ever been more than two and a half miles below the surface.
0:06:24 > 0:06:27Beyond there, it's uncharted territory.
0:06:27 > 0:06:32What we do know is that it gets warmer...much warmer.
0:06:35 > 0:06:39And that heat comes from something over 3,000 miles below.
0:06:40 > 0:06:43A giant ball of solid metal.
0:06:46 > 0:06:47This is the inner core of the earth.
0:06:49 > 0:06:54It's almost as big as the moon, and it's as hot as the surface of the sun.
0:06:55 > 0:07:00As we'll see, the inner core influences our lives in all sorts of ways.
0:07:05 > 0:07:09Yet, up here, we're barely even aware of it.
0:07:09 > 0:07:13But we're getting ahead of ourselves. So let's put it all back for now
0:07:13 > 0:07:16and start our journey to the centre of the earth at the beginning.
0:07:29 > 0:07:35And the beginning is here, the bit we actually we live on.
0:07:35 > 0:07:38It's called the earth's crust.
0:07:44 > 0:07:49The crust is not just the land above the oceans.
0:07:49 > 0:07:52It's the entire outer layer of the planet.
0:07:54 > 0:08:00If we take away the sea we can reveal how the crust encases the whole of the earth.
0:08:06 > 0:08:08But it's incredibly thin.
0:08:08 > 0:08:13If the earth were an apple, the crust would be no thicker than the apple's skin.
0:08:13 > 0:08:17It's anywhere from three to 45 miles thick.
0:08:17 > 0:08:20But it's not one single piece of rock.
0:08:20 > 0:08:25It's broken up into 14 enormous slabs called tectonic plates.
0:08:34 > 0:08:40These plates don't stay still. In fact, they're constantly on the move.
0:08:43 > 0:08:47The signs are everywhere, if you know where to look.
0:08:53 > 0:08:59And one place to look is here, in the south eastern United States.
0:09:01 > 0:09:08This is Florida, famed for its swamps, creeks, 'gators and biting insects.
0:09:08 > 0:09:14But one of the most amazing features here in Florida most visitors never get to see, because it's down there.
0:09:14 > 0:09:19You see, the ground here is not as solid as you might think, in fact it's a bit like Swiss cheese, because
0:09:19 > 0:09:25Florida sits on a huge network of underground caves full of water.
0:09:26 > 0:09:29It's called the Floridan Aquifer.
0:09:29 > 0:09:35It started life when stresses and strains in the tectonic plate caused cracks to open in the crust.
0:09:35 > 0:09:40Over millions of years these cracks were hollowed out by water.
0:09:40 > 0:09:45Today, the Aquifer covers 100,000 square miles
0:09:45 > 0:09:48and provides Florida with nearly all its fresh drinking water.
0:09:53 > 0:09:59But much of the Aquifer has yet to be mapped.
0:09:59 > 0:10:01That's where this lot come in.
0:10:05 > 0:10:07These guys are cave divers.
0:10:07 > 0:10:11They swim underground. Underwater. In caves.
0:10:11 > 0:10:16Connected by tight constricted openings, with no quick way out.
0:10:16 > 0:10:24One man crazy enough to do this for a living is biologist and cave explorer, Tom Morris.
0:10:24 > 0:10:28It's very important to map these underground caves because that's our drinking water.
0:10:28 > 0:10:34So the more we know about what's going on down in that aquifer the better off we'll be up here on top.
0:10:34 > 0:10:40Sadly, because of the risks involved, they won't let an amateur like me go with them.
0:10:40 > 0:10:43I shall be helping them...up here.
0:10:43 > 0:10:45I'll be following them with a tracking device.
0:10:45 > 0:10:50And talking to them on an underground, underwater radio communications system.
0:10:50 > 0:10:52I'm pretty much essential.
0:10:52 > 0:10:56This is the radio that we use to communicate with the divers...
0:10:56 > 0:11:02'Radio expert Brian is rigging me up in this rather strange-looking contraption.'
0:11:02 > 0:11:05- ..Microphone in the other. - So, backpack on back.
0:11:05 > 0:11:07Washing line in hand. We're there.
0:11:07 > 0:11:10Put your headphones on.
0:11:10 > 0:11:14Hey, Tom. This is Mission Control. Can you hear me?
0:11:14 > 0:11:17I can hear you, Richard.
0:11:17 > 0:11:20Well, if we're all ready, I'm ready up here. You guys ready to go?
0:11:20 > 0:11:22Yes, we are. Can't wait!
0:11:30 > 0:11:35To reach the aquifer, Tom and his team must squeeze through a crack in the bed of the lake.
0:11:35 > 0:11:42It's a claustrophobic dive passing through holes in the rock barely wide enough to wriggle through.
0:11:43 > 0:11:46Not the time for a big meal the night before.
0:11:49 > 0:11:51Down and down we go!
0:11:55 > 0:11:59Then it's a tortuous 80 foot descent.
0:12:09 > 0:12:14Up on the surface, Brian's transponder system lets us track exactly where they are.
0:12:16 > 0:12:18They're struggling down through these constrictions.
0:12:18 > 0:12:22So as soon as they get down against this current into the
0:12:22 > 0:12:25- caves themselves, we will start tracking along with them?- Right.
0:12:32 > 0:12:36Far below, Tom has reached the aquifer itself.
0:12:50 > 0:12:55Down here, hidden from view, is an unimaginable, subterranean world.
0:13:06 > 0:13:12The aquifer stretches under the whole of Florida and parts of four other southern states.
0:13:16 > 0:13:21In fact, there's more water held in underground aquifers like this
0:13:21 > 0:13:24than in all the lakes and rivers in the world.
0:13:33 > 0:13:39Up above, we've successfully locked onto the divers' position 100 feet below.
0:13:41 > 0:13:43Hello, Richard. Can you hear me?
0:13:43 > 0:13:47'Tom, how are you? How you doing? What do you see already?'
0:14:06 > 0:14:08We're walking with you now, Tom.
0:14:08 > 0:14:11We think we've got you. We're marking your path.
0:14:13 > 0:14:18Brian, all this that we're doing, mapping it on the surface, linking it to the underground.
0:14:18 > 0:14:20Is it useful?
0:14:20 > 0:14:25The water in this aquifer is the source of most people's drinking
0:14:25 > 0:14:32water in Florida, so by mapping we can help to prevent development over the top of the caves.
0:14:32 > 0:14:39You don't want fertiliser and septic systems and all the rest of that directly over it.
0:14:48 > 0:14:53And while Tom continues to wriggle through impossibly small gaps...
0:14:55 > 0:14:59'To be honest the going is not much easier up here.'
0:14:59 > 0:15:00Sorry.
0:15:00 > 0:15:05'Because wherever the divers lead, so must we follow.'
0:15:05 > 0:15:06Sorry.
0:15:08 > 0:15:10They've gone right under the shop.
0:15:10 > 0:15:13Tom, you're going through a shop.
0:15:13 > 0:15:17Over here somewhere. Yeah, right down the aisle.
0:15:17 > 0:15:20Tom, you're under barbeque stuff, don't know if that's useful.
0:15:20 > 0:15:22Not really, is it? No.
0:15:26 > 0:15:29- They're heading right for the wall. - Oh.
0:15:29 > 0:15:31And out.
0:15:31 > 0:15:34- Can we get out that way?- Yes.
0:15:41 > 0:15:46As we follow the divers we come to a pool in the forest.
0:15:46 > 0:15:48Hi, Tom. I think we've found you.
0:15:48 > 0:15:52Do you think you're coming to an opening to the surface?
0:15:52 > 0:15:55'Because if you are, we've so got you.'
0:16:01 > 0:16:05Look, look, lights. Tom, we can see your lights!
0:16:10 > 0:16:12Well hello, Richard.
0:16:12 > 0:16:15Tom, welcome back!
0:16:15 > 0:16:18Did you worry about us?
0:16:18 > 0:16:22It is so good to see our two worlds reconnected by that bit of water.
0:16:22 > 0:16:25That's a nice little journey. We went, oh, gosh, almost half a mile.
0:16:25 > 0:16:27We got our new entrance.
0:16:27 > 0:16:30And we can put this cave on the map.
0:16:30 > 0:16:37It's amazing to think that those vast underground aquifers all started out as these little cracks
0:16:37 > 0:16:41and developed into something huge.
0:16:41 > 0:16:44Rather them than me going down there, but
0:16:44 > 0:16:46glad to know they're there.
0:17:08 > 0:17:15The tiny cracks in the ground in Florida are caused by stresses within a single tectonic plate.
0:17:15 > 0:17:20But when two tectonic plates meet they cause a different kind of crack.
0:17:22 > 0:17:26They create huge splits in the ground called faults.
0:17:28 > 0:17:34And some faults can be very bad news indeed.
0:17:43 > 0:17:4812.51 on 22nd February, 2011.
0:17:48 > 0:17:55The cathedral spire in Christchurch, New Zealand falls as an earthquake leaves 182 dead.
0:17:57 > 0:18:03Less than a month later on 11th March an even bigger earthquake struck Japan.
0:18:03 > 0:18:09It produced a tsunami with waves of up to 98 feet high,
0:18:09 > 0:18:12killing perhaps 25,000 people.
0:18:12 > 0:18:15And on the other side of the Pacific
0:18:15 > 0:18:21just a year earlier, 562 people died in powerful quake in Chile.
0:18:21 > 0:18:27The Pacific Rim is an area of intense earthquake activity.
0:18:27 > 0:18:31In fact, over the last 50 years there have dozens of major
0:18:31 > 0:18:35earthquakes along the coast of North and South America.
0:18:35 > 0:18:37Let's go, let's go...
0:18:41 > 0:18:46The fact is tectonic plates move all the time.
0:18:47 > 0:18:52And the evidence is here, in a stadium just across the bay from San Francisco.
0:18:54 > 0:19:00The Golden Bears are the American football team of the University of California, Berkeley.
0:19:00 > 0:19:02Their home ground, the Memorial Stadium,
0:19:02 > 0:19:06is one of the oldest and most iconic football grounds in the US.
0:19:06 > 0:19:13But the way things are going, the stadium may not be here for much longer.
0:19:14 > 0:19:17Stands are crumbling.
0:19:17 > 0:19:20Walls are fracturing.
0:19:20 > 0:19:23Something strange is going on.
0:19:26 > 0:19:30Geologist Roland Burgmann tells me it's all down to a fault called the
0:19:30 > 0:19:34Hayward Fault, which runs right underneath the city of Berkeley.
0:19:34 > 0:19:39Roland, talk me through. Where is the fault in relation to the stadium?
0:19:39 > 0:19:44- We're walking on it now. It goes straight through the middle.- Really?
0:19:44 > 0:19:45Yeah. So it goes right from...
0:19:45 > 0:19:47See that crack up there?
0:19:47 > 0:19:50It goes right through there, across the field all the way up there.
0:19:50 > 0:19:53So really straight through the middle.
0:19:53 > 0:19:56The stadium is literally splitting in the middle as that bit goes that way and that bit...?
0:19:56 > 0:19:58That's exactly right.
0:20:01 > 0:20:08The western half of the stadium is being dragged north west by four millimetres a year.
0:20:08 > 0:20:14Since it was built nearly 90 years ago, the two halves of the stadium have been pulled apart 14 inches.
0:20:14 > 0:20:22Yet the real worry for the Golden Bears is that the fault line is moving too slowly.
0:20:22 > 0:20:25You say it's moving by four millimetres a year,
0:20:25 > 0:20:29- but here's the strange thing, you say that's not enough.- Right.
0:20:29 > 0:20:35It's moving by four millimetres per year and it should be slipping by ten millimetres per year.
0:20:35 > 0:20:37So it's not doing the full amount of slip.
0:20:37 > 0:20:39That's a slip deficit we call it.
0:20:39 > 0:20:43So that means it has to catch up at some point,
0:20:43 > 0:20:47and we know the way the catch up is happening is in big earthquakes.
0:20:47 > 0:20:48And how long ago was the last one?
0:20:48 > 0:20:50So it's been 140 years.
0:20:50 > 0:20:52So we are due one now.
0:20:52 > 0:20:57- Here. Exactly pretty much between us.- Right there.
0:20:57 > 0:20:59'Oh, dear.'
0:21:01 > 0:21:04Probably time to get off the ground.
0:21:20 > 0:21:26The Hayward Fault that runs through the stadium is part of the much larger San Andreas Fault system.
0:21:29 > 0:21:34All the hills and valleys have been created by the constant movement of the land.
0:21:36 > 0:21:40From the air, there's suddenly just a better sense of scale.
0:21:40 > 0:21:46I mean, it's all unimaginable, the forces, the size of these things, but just from being up here
0:21:46 > 0:21:53and tracking the fault round woodlands and round hills, you just get a sense of how massive it is.
0:21:59 > 0:22:05Millions of years ago, when the San Andreas Fault tore apart the land, this lake was born.
0:22:08 > 0:22:14It filled with water, was extended and is now used as a reservoir for the whole Bay Area.
0:22:16 > 0:22:22When the San Andreas Fault shifts just a few feet it can cause a quake.
0:22:22 > 0:22:26But the land is always on the move, and, over millions of years,
0:22:26 > 0:22:29the distance it travels is quite extraordinary.
0:22:29 > 0:22:36Rocks found here in northern California started life hundreds of miles away in southern California.
0:22:36 > 0:22:40This is part of this sort of 20-odd million year trek, that
0:22:40 > 0:22:42that whole slab of land has made,
0:22:42 > 0:22:45inching its way along as it creeps and creeps and creeps and ends up here?
0:22:45 > 0:22:48That's exactly right.
0:22:51 > 0:22:55And that means the changes to the landscape here will be dramatic.
0:22:55 > 0:23:03San Francisco and Los Angeles sit on two separate tectonic plates, either side of the San Andreas Fault.
0:23:03 > 0:23:10Over 9 million years LA will move 350 miles north, so you won't need
0:23:10 > 0:23:14to drive between the two cities because they'll be side by side.
0:23:20 > 0:23:25And then I see something that might not be here after the next big quake hits.
0:23:25 > 0:23:30The symbol of San Francisco, the Golden Gate Bridge.
0:23:30 > 0:23:31That's the bridge.
0:23:31 > 0:23:34Golden Gate Bridge right here.
0:23:34 > 0:23:36Disappearing into the fog.
0:23:36 > 0:23:38Do you mind if I take a picture?
0:23:38 > 0:23:40Sorry. It's not very cool.
0:23:40 > 0:23:43It's not very "Oh I've been everywhere and seen everything, but..."
0:23:43 > 0:23:48There's a big debate among engineers if it's built safe enough for a big earthquake.
0:23:48 > 0:23:49Well, it's a bit late now. It's built.
0:23:49 > 0:23:52- It's there.- Yeah!
0:23:57 > 0:24:02The Golden Gate Bridge may not survive a major quake.
0:24:02 > 0:24:09But on the other side of the bay, the Golden Bears have taken dramatic steps to protect their stadium.
0:24:11 > 0:24:13They're cutting it in half.
0:24:18 > 0:24:24When the work here is finished, the stadium will rest on separate free-floating blocks of concrete
0:24:24 > 0:24:28so that if a quake hits, the whole stadium will roll with the punches.
0:24:31 > 0:24:36Roland Burgmann has returned to check on progress.
0:24:36 > 0:24:42So this side of the stadium is going to be a completely separate structure, separated from this side,
0:24:42 > 0:24:46and the two sides can move independently, even in a large earthquake.
0:24:46 > 0:24:50The two sides of the stadium are just going to move their separate
0:24:50 > 0:24:53paths, thereby there will be much less destruction.
0:24:57 > 0:25:00This is a job that's gonna take two years to complete.
0:25:00 > 0:25:05It'll cost the Bears a cool 320 million to carry out.
0:25:08 > 0:25:10So when the big one hits,
0:25:10 > 0:25:16there's one place in the Bay Area that Roland thinks will be more than ready.
0:25:16 > 0:25:20At least with the work that's being done on the stadium right now,
0:25:20 > 0:25:25this is going to be one of the safest places to be in the next large earthquake.
0:25:46 > 0:25:54It's not surprising that all that pressure between the tectonic plates causes friction that leads to quakes.
0:25:54 > 0:26:02But that energy also does something else, something truly awesome.
0:26:04 > 0:26:09When two tectonic plates collide, solid land can buckle upwards.
0:26:18 > 0:26:23That's the force that forms gigantic mountain ranges like the Alps.
0:26:46 > 0:26:51Naturally, I want to see this incredible process for myself
0:26:51 > 0:26:56and geologist Sarah Rieboldt knows just the place.
0:27:02 > 0:27:05This is Mount Diablo, California.
0:27:05 > 0:27:09It's not the highest mountain in the world,
0:27:09 > 0:27:13but what makes this mountain interesting, is what it's made of.
0:27:17 > 0:27:20It's going to take a while to get there.
0:27:20 > 0:27:22We have only two horsepower.
0:27:22 > 0:27:25I'm used to...more.
0:27:29 > 0:27:33Sarah, the trip here was lovely, but what have I come to look at?
0:27:33 > 0:27:36All these little white bits - all shells.
0:27:36 > 0:27:38- Shells?- Look closely at these rocks.
0:27:38 > 0:27:42You can see all these little bits of white, these slivers in here,
0:27:42 > 0:27:45- are re all fossils.- Like this?
0:27:45 > 0:27:47Mm-hmm. A lot of them are broken up into pieces,
0:27:47 > 0:27:49but there are larger ones scattered about.
0:27:49 > 0:27:52'And these aren't the shells of land animals,
0:27:52 > 0:27:57'things you might expect to find almost 4,000 feet up.'
0:27:57 > 0:28:00There's clams, any kind of sea creatures,
0:28:00 > 0:28:02oysters, things like that.
0:28:02 > 0:28:05Now, forgive me then. Shells, sea creatures...
0:28:05 > 0:28:08Clearly that doesn't belong here, does it? Cos we're on a mountain.
0:28:08 > 0:28:12Exactly. For a long time this mountain didn't exist. It's a very recent mountain.
0:28:12 > 0:28:15It was only uplifted about 3 million years ago.
0:28:15 > 0:28:20Before that, it was at the bottom of the sea and that's where all of these creatures were living.
0:28:20 > 0:28:24So whenever we go anywhere... And I've seen this - seashells -
0:28:24 > 0:28:26and I've seen it on top of mountains in places,
0:28:26 > 0:28:30and you think, "Wow, the sea must have been really deep at one point
0:28:30 > 0:28:32"because it was over us here." No.
0:28:32 > 0:28:34The sea was never here, but neither was this land.
0:28:34 > 0:28:36- It was down there somewhere.- Exactly.
0:28:36 > 0:28:39And is that just a phenomenon unique to here?
0:28:39 > 0:28:44No, there are seashells, sea creatures and things on the tops of lots of mountains,
0:28:44 > 0:28:47including Mount Everest, which is hard to believe given how high it is.
0:28:47 > 0:28:50That's a really out of place shellfish, isn't it?
0:28:53 > 0:28:57Of course, it took millions of years for the land to crumple up
0:28:57 > 0:28:59and form this landscape.
0:29:03 > 0:29:07But because the machine inside our planet never stops working,
0:29:07 > 0:29:11the Earth's tectonic plates are still moving.
0:29:11 > 0:29:13So some of our mountains keep growing.
0:29:15 > 0:29:20Even Mount Everest, the highest point on Earth,
0:29:20 > 0:29:22is still reaching for the sky.
0:29:22 > 0:29:25In 1953, it was conquered for the first time
0:29:25 > 0:29:28by Edmund Hillary and Sherpa Tenzing.
0:29:31 > 0:29:36Since then, it's been edging upwards by five millimetres a year.
0:29:39 > 0:29:41So if you climb to Everest's summit today,
0:29:41 > 0:29:46you'll be almost a foot higher than when Hilary and Tensing first reached the summit
0:29:46 > 0:29:47nearly 60 years ago.
0:29:56 > 0:30:01We've explored some parts of the Earth's crust.
0:30:01 > 0:30:04Now it's time to go beneath it.
0:30:07 > 0:30:13And to find out what happens further down inside the Earth machine.
0:30:19 > 0:30:24Let's lift out the east coast of the USA, just cos we can.
0:30:31 > 0:30:34Beneath the crust is the next layer.
0:30:34 > 0:30:36That's known as the mantle.
0:30:36 > 0:30:41It's enormous - over 1,800 miles deep.
0:30:42 > 0:30:48And it can get as hot as 2,200 degrees Celsius,
0:30:48 > 0:30:53hot enough to melt solid rock into a liquid called magma.
0:30:58 > 0:31:04And this is the biggest and noisiest way of seeing what magma is.
0:31:04 > 0:31:07Because, when a volcano erupts,
0:31:07 > 0:31:10this magma blasts out onto the surface.
0:31:12 > 0:31:15Up here, it's called lava.
0:31:18 > 0:31:20And with our virtual Earth,
0:31:20 > 0:31:25we can look inside the planet and see how it reaches the surface.
0:31:29 > 0:31:34The magma collects in chambers around 10 miles below the surface.
0:31:38 > 0:31:43But some magma starts life hundreds of miles further down,
0:31:43 > 0:31:48and can bring us vital clues about what happens deep inside our planet.
0:32:03 > 0:32:07That's why scientists from all over the world
0:32:07 > 0:32:09travel to the heart of Africa,
0:32:09 > 0:32:14to take lava samples from one of the most remarkable volcanoes of all.
0:32:18 > 0:32:23This is Mount Nyiragongo, in Africa's Great Rift Valley.
0:32:23 > 0:32:26It's one of the most active volcanoes in the world
0:32:26 > 0:32:31and towers two miles above the surrounding countryside.
0:32:31 > 0:32:34A million people live in its shadow.
0:32:38 > 0:32:43At the bottom of the volcano's crater is a boiling lake of lava.
0:32:56 > 0:32:59It is like a vision of hell.
0:33:01 > 0:33:06A scorching cauldron, over 750 feet across.
0:33:08 > 0:33:13The temperate on its surface is nearly 800 degrees centigrade.
0:33:16 > 0:33:19Some scientists think the lava here
0:33:19 > 0:33:21comes from much deeper down
0:33:21 > 0:33:24than almost any other volcano on the planet.
0:33:29 > 0:33:34Dario Tedesco is one of the world's leading authorities on this volcano.
0:33:34 > 0:33:38It's really completely different from other volcanoes.
0:33:38 > 0:33:39It really is unique.
0:33:39 > 0:33:43There are so many secrets on this volcano
0:33:43 > 0:33:45that you don't get from the other volcanoes.
0:33:50 > 0:33:53Dario leads a team of scientists into the crater.
0:33:56 > 0:34:03They're attempting to collect a sample of fresh lava from the lake,
0:34:03 > 0:34:05but it's a long way down.
0:34:05 > 0:34:10The crater is deep enough to accommodate the Empire State Building.
0:34:10 > 0:34:17Probably not surprisingly, very few have been to the floor of the crater.
0:34:43 > 0:34:48After climbing down for five hours, they reach level ground.
0:34:48 > 0:34:53They're still 600 feet above the lava lake.
0:34:53 > 0:34:56Time to make camp.
0:35:11 > 0:35:14While the team sleep, the super-heated molten rock in
0:35:14 > 0:35:19the lake churns and boils, spilling over the rim.
0:35:30 > 0:35:35When Nyiragongo last erupted in 2002,
0:35:35 > 0:35:40nearly 400,000 people in the nearby town had to be evacuated.
0:35:40 > 0:35:44Because when Nyiragongo erupts,
0:35:44 > 0:35:47there's no way to outrun the lava.
0:35:47 > 0:35:55Nyiragongo's lava can flow at over 60mph, faster than any other lava in the world.
0:36:10 > 0:36:13Next morning, and the lake is calmer.
0:36:18 > 0:36:22Dario sees another scientist reach the bottom of the crater.
0:36:22 > 0:36:29It looks like he is going for the ultimate prize, a sample of lava straight from the lake itself.
0:36:31 > 0:36:33It is dangerous, in my opinion.
0:36:33 > 0:36:35It is a little crazy.
0:36:35 > 0:36:37I mean, I won't do that.
0:36:37 > 0:36:40The special suit he wears will deflect some of the incredible heat
0:36:40 > 0:36:48at the lake's edge, but it will do nothing to protect him if he comes into direct contact with the lava.
0:37:07 > 0:37:08He's very, very close.
0:37:21 > 0:37:23OK, he's just there.
0:37:23 > 0:37:25Really a few centimetres.
0:37:34 > 0:37:37He's just on the rim. He's crazy.
0:37:38 > 0:37:41Oh, my God.
0:37:41 > 0:37:43Come back!
0:37:43 > 0:37:45It's too long. Come back!
0:37:50 > 0:37:53Lava begins to bubble over the rim of the lake.
0:37:55 > 0:37:59HE SPEAKS FRENCH
0:38:17 > 0:38:21Dario believes the scientist is taking too big a risk.
0:38:21 > 0:38:23I kind of agree!
0:38:29 > 0:38:32The lake is becoming more active.
0:38:32 > 0:38:35Lava surges over the edge.
0:38:48 > 0:38:52The lava lake is now overflowing in three different areas.
0:38:52 > 0:38:57Very strong exactly where he was five minutes ago.
0:39:01 > 0:39:08Later that day, some perhaps more sensible scientists collect samples from the crater floor.
0:39:09 > 0:39:14And those samples are then sent half way around the world to be analysed
0:39:14 > 0:39:18here, the University of Rochester in New York State.
0:39:18 > 0:39:22Geologist Tom Darrah will analyse the sample.
0:39:27 > 0:39:29The composition of Mount Nyiragongo lavas
0:39:29 > 0:39:31are both complex and mysterious.
0:39:31 > 0:39:34The lava I am holding in my hand from Mount Nyiragongo
0:39:34 > 0:39:37is effectively a time capsule of the Earth's history.
0:39:40 > 0:39:44Gases and minerals are trapped inside.
0:39:49 > 0:39:52The sample is crushed.
0:39:55 > 0:39:57Then heated.
0:39:59 > 0:40:01So it can be analysed.
0:40:11 > 0:40:13The results are ready.
0:40:14 > 0:40:20The gases we analyse tells us this volcano is sourced from a very deep location within the Earth.
0:40:20 > 0:40:25The source has to be somewhere well below the Earth's crust.
0:40:25 > 0:40:32In fact, some scientists think it might come from the very bottom of the mantle, 1,800 miles below.
0:40:35 > 0:40:42If so, it suggests something extraordinary and, ultimately, terrifying.
0:40:44 > 0:40:48We can see what's happening on the virtual Earth.
0:40:48 > 0:40:54Scientists think that an enormous upwelling of intense heat, a mantle plume, is rising
0:40:54 > 0:40:58from the interior of the planet under this part of the Rift Valley.
0:40:59 > 0:41:04In the future, it could cause more volcanoes and earthquakes.
0:41:08 > 0:41:12New mountains could rise and new valleys form.
0:41:20 > 0:41:23East Africa could be transformed.
0:41:38 > 0:41:41Of course, you don't have to mess around with boiling hot lava
0:41:41 > 0:41:45to get your hands on something that started life miles below the surface.
0:41:45 > 0:41:49Burn your hands. You can do it right here, on the high street.
0:42:02 > 0:42:10These diamonds are around three billion years old, so they are pretty ancient.
0:42:10 > 0:42:15They were formed in a rare event, deep in the Earth,
0:42:15 > 0:42:18that only happens every few hundred million years.
0:42:19 > 0:42:22Cut and polished like this, they look beautiful.
0:42:22 > 0:42:28But they started life as lumps of carbon far below the crust,
0:42:28 > 0:42:32thrust upwards by a special kind of volcanic eruption.
0:42:36 > 0:42:40Magma surges towards the surface and carrying diamonds.
0:42:40 > 0:42:42Many will get stuck along the way.
0:42:42 > 0:42:45A few will make into the Earth's crust.
0:42:45 > 0:42:49Even fewer will make it onto our fingers.
0:42:57 > 0:43:05As we can see on the virtual Earth, diamonds are only found in volcanic regions of the planet.
0:43:09 > 0:43:13So when I buy something sparkly for Mrs H,
0:43:13 > 0:43:18I'm buying her something regurgitated from the guts of the planet.
0:43:18 > 0:43:20Not that I put it to her like that, obviously
0:43:20 > 0:43:22That wouldn't do.
0:43:32 > 0:43:34This is Iceland.
0:43:34 > 0:43:37And yes, it's cold.
0:43:37 > 0:43:40Yet right beneath their feet, the locals can plug
0:43:40 > 0:43:45directly into the Earth's machine to power their entire country.
0:43:45 > 0:43:50The crust is thin and the Earth's inner heat is so close to the surface
0:43:50 > 0:43:56that when rainwater seeps into the ground, it's quickly heated and turns to steam.
0:43:56 > 0:44:02Power stations capture the steam and use it to generate electricity.
0:44:02 > 0:44:08And everywhere you go, Icelanders are finding ways to exploit this natural energy source.
0:44:18 > 0:44:21- Potatoes?- Yeah.
0:44:21 > 0:44:27I should say this isn't a barbeque, we're not burning any sort of fuel.
0:44:27 > 0:44:33Steam, heated in the ground below, is being piped up here and through volcanic lava rock,
0:44:33 > 0:44:35and that's what's cooking the food.
0:44:35 > 0:44:37It's 170 degrees.
0:44:37 > 0:44:39It can boil water in ten seconds.
0:44:45 > 0:44:52So this really is, if you think about it, a free lunch, cooked naturally.
0:45:08 > 0:45:14They even heat this stretch of the North Atlantic, so that they can go for a swim at any time of year.
0:45:14 > 0:45:20The seawater out there is a freezing minus four degrees,
0:45:20 > 0:45:24but these swimmers are splashing around at a balmy 19.
0:45:26 > 0:45:30But they don't just use the heat from the Earth's mantle so they can take a dip.
0:45:30 > 0:45:35In fact, the whole country runs on power from the Earth's machine.
0:45:35 > 0:45:38This is strange. I'm cold, but warm!
0:45:44 > 0:45:46In Iceland's capital city, Reykjavik,
0:45:46 > 0:45:50almost every home is heated by plugging into the power of the Earth.
0:45:53 > 0:45:57In winter, they even heat the streets and pavements to keep them ice-free.
0:46:00 > 0:46:07Icelanders can sleep easy, knowing that this energy will not run out any time soon.
0:46:16 > 0:46:20We know that the mantle is beneath the crust.
0:46:20 > 0:46:22But what's below that?
0:46:24 > 0:46:26Time to go further down.
0:46:28 > 0:46:32We are about to reveal the planet's generator.
0:46:35 > 0:46:37The mantle is made of rock.
0:46:37 > 0:46:42But the layer below that is an ocean of molten metal.
0:46:42 > 0:46:47It's so fluid, it's just like water.
0:46:47 > 0:46:49This is the outer core.
0:46:51 > 0:46:56And if you thought the mantle was hot, well, the outer core is even hotter.
0:46:56 > 0:46:59A lot hotter.
0:46:59 > 0:47:05It's calculated to be somewhere between 4,000-6,000 degrees centrigrade.
0:47:07 > 0:47:12As this molten metal flows, it does something special.
0:47:12 > 0:47:14It creates a magnetic field.
0:47:19 > 0:47:22Except this magnetic field is rather big.
0:47:22 > 0:47:27Enormous, in fact. It extends tens of thousands of miles into space.
0:47:27 > 0:47:32It's too big for the hangar, but if we shrink the Earth, you'll get the picture.
0:47:39 > 0:47:42Of course, without our technical wizardry, all of which I
0:47:42 > 0:47:47made here in the hangar, the magnetic field is usually invisible to us.
0:47:47 > 0:47:51But there is a way we can see it in action.
0:47:58 > 0:48:01These are the Northern Lights.
0:48:03 > 0:48:06Here, over the snow and ice of the Arctic Circle,
0:48:06 > 0:48:11a magical procession of lights dances across the night sky.
0:48:11 > 0:48:15It's one of the most remarkable things I've ever seen.
0:48:18 > 0:48:23Not surprisingly, ancient peoples thought these lights were from the gods.
0:48:23 > 0:48:28But it's simply the Earth's magnetic field made visible.
0:48:28 > 0:48:31And it's a very good thing it's there.
0:48:38 > 0:48:42This is how the magnetic shield works.
0:48:42 > 0:48:47The sun is continually throwing out billions of charged atomic particles.
0:48:47 > 0:48:53Lethal to most living things, but luckily the magnetic field deflects them.
0:48:53 > 0:48:59The Northern Lights are how we see those particles from the sun interact with our atmosphere.
0:49:09 > 0:49:13The Earth's magnetic field has another benefit.
0:49:16 > 0:49:21In its lifetime, a sea turtle can travel tens of thousands of miles,
0:49:21 > 0:49:25criss-crossing the Pacific or the Atlantic many times over.
0:49:29 > 0:49:36Yet at all times, it will know its exact location and can navigate its way around the Earth.
0:49:38 > 0:49:42I've come to North Carolina to find out how they do it.
0:49:45 > 0:49:47This is a big day for Coral here.
0:49:47 > 0:49:51She's about to be released back into the Atlantic where she'll spend the
0:49:51 > 0:49:54next 10, 20 or 30 years swimming around it,
0:49:54 > 0:49:59or even, if she chooses, across it from side to side.
0:49:59 > 0:50:02Out there waiting for her are cold waters that could kill her,
0:50:02 > 0:50:06strong currents, barren stretches of sea where there's nothing to eat.
0:50:06 > 0:50:08She'd starve.
0:50:08 > 0:50:10But she carries no map.
0:50:10 > 0:50:12There'll be no other turtles to follow.
0:50:12 > 0:50:14She'll be on her own out there.
0:50:14 > 0:50:19But she can navigate all those thousands of miles, all those perils,
0:50:19 > 0:50:23and find her way back here to breed. How?
0:50:23 > 0:50:26How does she do that?
0:50:33 > 0:50:41Well, these little fellas at the University of North Carolina are going to help us find out.
0:50:41 > 0:50:45Scientist Ken Lohmann has devised an experiment to
0:50:45 > 0:50:50see how just how these turtles use the Earth's magnetic field.
0:50:50 > 0:50:58But first, this young loggerhead turtle needs to dress up in an unusual outfit for a turtle.
0:50:59 > 0:51:02These are little bathing suits we've produced for the turtles.
0:51:02 > 0:51:07They're cloth harnesses that encircle the carapace, or the shell, but they don't
0:51:07 > 0:51:11prevent the turtle from moving its flippers in its normal way.
0:51:14 > 0:51:19The harnesses enable Ken to track their movements.
0:51:19 > 0:51:24He creates a magnetic field around the turtles' tank.
0:51:24 > 0:51:29With the field turned on, the turtle knows which direction to go.
0:51:37 > 0:51:40If we to were to reverse the magnetic field, the turtle
0:51:40 > 0:51:43in all likelihood would turn around and swim in the opposite direction.
0:51:48 > 0:51:55And as soon as Ken changes the magnetic field, the turtle does change direction.
0:51:55 > 0:51:59So turtles really are sensitive to the magnetic field.
0:51:59 > 0:52:04And how they do it is all down to a mineral in their head.
0:52:04 > 0:52:11Magnetite is a magnetic mineral, it's actually the same mineral that compass needles are made of, and
0:52:11 > 0:52:16it appears likely the turtles use magnetite crystals in their heads
0:52:16 > 0:52:19to perceive the magnetic field.
0:52:19 > 0:52:24And it turns out that the turtles can do far more.
0:52:24 > 0:52:29They can use the field not only as a source of directional information,
0:52:29 > 0:52:34but also as a way of figuring out where they are within the ocean.
0:52:34 > 0:52:40So in effect, they have a global positioning system that is based on the Earth's magnetic field.
0:52:40 > 0:52:43Look at this, she knows!
0:52:43 > 0:52:47That's how Coral is going to be able to swim out into the Atlantic
0:52:47 > 0:52:52and then, years later, find her way back to this exact beach.
0:52:52 > 0:52:57Coral, look at this. Look at all that lovely ocean waiting for you.
0:52:57 > 0:53:00Right now, she's tuning herself in
0:53:00 > 0:53:03to that magnetic field.
0:53:03 > 0:53:05She knows where she is,
0:53:05 > 0:53:07which is more than I do!
0:53:07 > 0:53:11All the hair on the back of my neck is standing up with what we're doing here.
0:53:14 > 0:53:18She's desperate now!
0:53:18 > 0:53:19She's desperate now.
0:53:19 > 0:53:25We're in a good spot. Here we go.
0:53:25 > 0:53:29So, we pick our moment, Coral, this is your moment, my darling.
0:53:29 > 0:53:31Good luck! You're built for this!
0:53:33 > 0:53:36Coral. Go, go, go!
0:53:43 > 0:53:46- And she's gone.- There she goes.
0:53:47 > 0:53:50That was honestly a magical moment.
0:53:50 > 0:53:53It's quite spine-tingling.
0:53:53 > 0:53:58I don't know about everyone else with us, but suddenly you're aware that's a
0:53:58 > 0:54:01very, very big ocean out there and a small turtle in it.
0:54:01 > 0:54:07But she's tapping into something even bigger, the Earth's magnetic field.
0:54:07 > 0:54:09It is magical.
0:54:09 > 0:54:11And she's out there now, doing it.
0:54:23 > 0:54:26Our journey's nearly over.
0:54:26 > 0:54:28The best bit is yet to come.
0:54:28 > 0:54:32We have travelled more than 3,000 miles down into the Earth.
0:54:32 > 0:54:38We've gone through the crust, through the mantle and through the outer core.
0:54:38 > 0:54:41We are now at our final destination.
0:54:41 > 0:54:42The centre of the Earth.
0:54:47 > 0:54:50This is the inner core.
0:54:50 > 0:54:55And down here, something strange happens.
0:54:55 > 0:55:03That layer of molten metal that formed the outer core has now become solid, crushed by pressures around
0:55:03 > 0:55:07four million times greater than on the surface of the Earth.
0:55:09 > 0:55:12And it's hot. Really hot.
0:55:12 > 0:55:16Up to a staggering 6,000 degrees centrigrade,
0:55:16 > 0:55:20the same temperature as the surface of the sun.
0:55:20 > 0:55:25And it is this heat that is the key to how our planet works.
0:55:30 > 0:55:36All the volcanoes, the earthquakes, the never-ending movement of the land, it's all
0:55:36 > 0:55:42powered by this huge fiery ball of solid metal over 3,000 miles below.
0:55:42 > 0:55:46The inner core is the engine room to the whole planet.
0:55:50 > 0:55:55The core transfers its heat to the molten rock in the mantle,
0:55:55 > 0:55:59forcing it to rise upwards in vast plumes.
0:56:03 > 0:56:10These rise to the surface through the mantle towards the crust, and with nowhere else to go they spread out,
0:56:10 > 0:56:13pushing the continental plates across the face of the planet.
0:56:15 > 0:56:19They cool and fall back to start the cycle all over again.
0:56:23 > 0:56:27The cycle takes millions of years.
0:56:27 > 0:56:31And that is how the continents get pushed across the face of the planet.
0:56:31 > 0:56:34It's how the Earth works.
0:56:34 > 0:56:35Simple as that.
0:56:35 > 0:56:39Many scientists believe this cycle will continue
0:56:39 > 0:56:44until all the continents are forced together into one huge land mass.
0:56:44 > 0:56:50If so, our climate, our landscape, everything will change beyond recognition.
0:56:50 > 0:56:54In 10,000 years this place could be covered in sheet ice.
0:56:56 > 0:56:59In a million, it could be sand dunes.
0:57:04 > 0:57:09In 100 million years, I could step from here onto the northern coast of Russia.
0:57:11 > 0:57:15And in 250 million years, all the world's land masses will have
0:57:15 > 0:57:21joined together to create one massive super-continent.
0:57:21 > 0:57:28As long as the Earth's core continues to spin, continents will continue to drift across the face of the planet.
0:57:28 > 0:57:36New land will emerge, mountains will rise and each and every one of us will be for ever on the move.
0:58:13 > 0:58:20Next time. We look at how the Earth machine affects the ocean floor, and how this affects us.
0:58:20 > 0:58:23- Have you ever had anybody panic completely?- Yes.
0:58:24 > 0:58:28We drain the oceans to reveal vast underwater canyons.
0:58:28 > 0:58:30Seeing as I'm already dressed.
0:58:30 > 0:58:37Huge volcanoes, massive mountain ranges and metal snails!
0:59:00 > 0:59:03Subtitles by Red Bee Media Ltd
0:59:03 > 0:59:06E-mail subtitling@bbc.co.uk