"This is our planet, the Earth." "It's an amazing ever-changing world, full of natural wonders." "But there's more to Earth than this, much more." "Because our planet is unique in the solar system, perhaps even in the universe." "Four and a half billion years have made it a world of extraordinary landscapes and a home to life." "My name's Iain Stewart and I want to show you how our remarkable planet works." "In this series, I'm going to explore the four powerful forces that have come together to create our world." "The oceans, that have the power of life and death over all living things." "The atmosphere, the most fickle of forces." "It drives our climate and protects and nourishes us." "Ice, it has carved the world we know and changed the course of human evolution." "But I'm going to start with volcanoes." "They're terrifyingly destructive, but they're also the most fundamental force on the planet." "Volcanoes are part of a global system that continually reshapes our world." "They hold the key to the origins of life on Earth." "They saved the planet from the biggest crisis it's ever faced." "And they've even formed a partnership with life that keeps our planet habitable." "Ethiopia, eastern Africa." "This is the Afar region, bandit country." "So I've hitched a lift with the Ethiopian military." "I'm off to one of the hottest and remotest places on the surface of our planet to see the most powerful force on Earth in action." "We've got plenty of equipment because ahead of us there's some serious climbing." "We've touched down on a dry, brittle surface of recently cooled lava." "once the helicopter leaves, we're on our own for a couple of days." "This place has no water, no shelter, no life, except, I'm told, for a few snakes." "But I think it's really going to be worth it." "I've come all this way to see one of the most remarkable volcanoes anywhere on the planet." "Erta Ale." "The name means the smoking mountain to the local Afar people." "It's reckoned this volcano has been continuously erupting lava for longer than any other on Earth." "But no one's quite sure because it's only been properly studied for the last 40 years." "I've been lucky to see a lot of volcanoes in my time and I've never seen one that has a permanent lake of molten lava in its crater." "But there's another reason why this volcano is very special." "And to see that, I need to get down into the crater and see the lava up close." "How's that feel?" "That's fine." "The rocks here are very sharp and very brittle, so it's actually good that we're on an overhang and that we're not going to" "actually crash into them." "Okay." "Nervous?" "Yeah." "Feeling a little bit nervous, apprehensive really." "You know, it's..." "You know, first time you're ever going to abseil, you kind of didn't want it to be down into an active volcano, but hey." "Then the ledge is..." "This is my one now." "Sit back, sit back." "After, after." "Okay." "That's it." "That's good." "It's a 30 metre vertical drop to reach a wide terrace below." "And the lava lake itself is a little further down." "I've waited until sunset to take a closer look because the lava is at its most spectacular at night." "This is as close as I can safely get." "Oh, wow." "Crikey." "That is magnificent." "I mean, it's taken us a hell of a journey to get here, but that makes it all worth it." "I'm standing on the edge of an active volcano, right next to a big pool of molten lava." "What makes this lava lake more than just pure spectacle is that it's a window that allows us to look deep into the Earth and it helps us understand the forces that shape our planet." "Just take a look at the motion of the lava lake speeded up." "Something intriguing is happening." "The movement of the lava follows a very distinctive pattern." "It wells up on one side of the crater and forms a dark crust as it cools." "Then this crust moves across the surface of the lake driven by the churning action of the lava below." "Finally the crust sinks back down." "As we'll discover, this process of molten rock churning away below the surface affects our entire planet." "That's because this lava lake is connected to a gigantic source of heat that lies deep inside the Earth." "I think it's fair to say that most of us go about our daily lives completely unaware that underneath our feet, our planet is incredibly hot." "I mean, we live on a thin skin of cool rock, precariously located between the cold freezer of space up there and a red hot furnace down there." "And what a source of power this furnace is." "The Earth's heat does far more than just fuel volcanoes." "It created the first atmosphere and the oceans." "It continually reshapes the planet's surface, builds great mountain ranges and moves entire continents." "And it created the conditions for life on Earth to begin." "In fact, you could say that the whole history of the planet has been driven by the massive heat trapped inside it." "To understand where our planet's inner heat comes from, we have to go back four and a half billion years to the time of Earth's own birth." "It was a period called the Hadean, after Hades, the kingdom of hell, which is a good name because this was a hot, hostile and violent world." "You may not recognise it, but this is our planet in its very earliest days." "Little more than a few pieces of rock colliding as they circle the Sun." "These impacts were so violent, they generated immense amounts of heat." "And they also delivered vast quantities of radioactive material to the Earth." "Eventually, when the outer layers of the planet cooled, these two powerful sources of heat were trapped in a huge, hot core." "The centre of our planet is as hot as the surface of the Sun." "This is the source of Earth's vast heat energy." "And it's what fuels volcanoes to this day." "Trapped within our planet, Earth's hot core has been continuously releasing unimaginable amounts of heat." "It gives you some idea how much when you realise that even after four and a half billion years, there's still plenty left." "Earth's inner heat makes the planet's surface incredibly dynamic." "It has created a restless continually changing landscape unlike any other in the solar system." "It's a world of destruction and renewal." "This is Iceland, a place that offers a great opportunity to see exactly how Earth's inner heat is continually reshaping the planet's landscape." "Molten rock usually lies hundreds of kilometres underground but here, as in Ethiopia, it's much closer." "Yet the effect is very different." "Sulphurous fumes and bubbling hot pools hint at the power that is just beneath the surface." "There are naturally heated pools everywhere on the island, which makes going for a dip something of a national pastime." "These hot springs are fabulous for relaxing in, providing you don't mind sharing your bath." "The mineral-rich water is meant to have therapeutic qualities, but the people here might not be quite so relaxed if they knew exactly how the water gets heated." "Right beneath us is a seething mass of red hot molten rock." "Just 20 kilometres beneath Iceland is a vast column of super-heated rock, known as a plume." "Recently, the shape of this hot plume of rock has been mapped." "It's 1 00 kilometres wide and at least 600 kilometres deep." "Created more than 50 million years ago, the plume is sustained by heat continually rising up from the Earth's hot core." "But this giant plume of super-heated rock has done much more than just warm up Iceland's hot springs." "It also created Iceland itself." "In 1 963, we got to see how it must have happened." "A volcano,just below the sea's surface, blasted its way out of the water." "A new island, Surtsey, was born." "This is what Iceland must have looked like 50 million years ago when it first burst above the surface." "But what makes Iceland so unusual is not just that it sits above a hot plume." "This small island is also shaped by the Earth's inner heat in another much more powerful way." "This is Thingvellir." "It's an important place in human history because in AD 930, a group of Icelandic chieftains gathered here to sort out their disputes." "This was the world's first parliament, which then sat here for the next eight centuries." "But there's another reason why this is an important place." "Although they didn't know it, those early pioneers of democracy had set up their parliament in the shadow of a most extraordinary rock face." "From the air, you can begin to see just how unusual this rock face is." "It's a crack in the Earth's surface that runs for hundreds of kilometres." "But what we're looking at is just a tiny part of something much, much bigger." "This is the edge of a gigantic slab of the Earth's crust, which runs unbroken for 7,000 kilometres, right from this point, under the Atlantic, across the USA, all the way to California." "It's what's known as the North American Plate." "The Earth's surface is broken up into seven major chunks called plates." "They're so enormous that they can carry an entire continent and extend far under the sea." "Strip away the Atlantic ocean and you can see a long boundary between two of these plates that runs along the ocean floor until it rises above the waves," "cuts through Iceland, to eventually join up with the rock face at Thingvellir." "It's possible to see this plate boundary from a completely different perspective." "This is a very cold place to go scuba diving." "The water's just four degrees Celsius, but it's worth it because I am actually swimming in the gap between the two giant plates that run through Iceland." "To my left, the North American Plate, and to my right, Europe." "These sheer rock faces were once joined together, but driven by immense geological forces, the land was split apart to create these deep chasms which filled with water." "It's hard to imagine a force that can move continents apart, yet this is precisely what the Earth's inner heat is able to do." "It happens because hot rock rises, heated by the Earth's core." "Near the surface, the rock spreads in two directions and goes sideways." "It begins to lose heat." "Eventually, the much cooler rock sinks back down." "Through this spreading process, the Earth's crust is very slowly dragged apart and it's this that ultimately causes the continents to move." "The lava lake at Erta Ale is an example of the same process but in miniature." "As we've seen, the movement of hot lava drags the crust across the surface of the lake, just as the continents are pulled across the Earth's surface." "To appreciate the idea of continents moving, you have to step outside human time scales and think in terms of a completely different time frame." "The continents here are drifting apart at two centimetres every year." "In my lifetime, we're talking just a couple of steps." "Even in a thousand years, that's just 20 metres." "It's only when you start to think in terms of millions of years that you realise just what can happen." "225 million years ago, our planet looked very different." "All the continents were joined together in a single super-continent called Pangaea." "As the plates moved, this super-continent broke up." "New oceans formed as continents drifted around the globe." "It's this that has created the shape of the world we know today." "But the plates never stop moving." "In the distant future, our continents will once again be reunited in a new, giant super-continent." "We've seen what happens when the plates move apart." "But when they crash into one another, the effects are even more dramatic." "The collision of the Earth's plates is responsible for the most spectacular mountain ranges on our planet." "To see how they're created, I've come to New Zealand's South Island." "These stunning peaks run 500 kilometres along the west coast, forming a dramatic spine down the island." "According to Maori legend, these mountains are made of the petrified bodies of four Gods who got stranded here on a canoeing trip to Earth." "As they were attempting to return to the heavens, a big storm blew up and capsized the canoe." "They climbed on board and waited for someone to rescue them, but no one came." "As time passed, they slowly turned to stone." "As far as geology goes, there's a slightly different explanation." "It may not be as romantic as Maori legend, but it's every bit as epic." "What was to become New Zealand was once a group of scattered islands." "The collision of the Pacific and Australian plates forced these islands together, creating the familiar outline of New Zealand that we know today." "Along the collision zone, the land was buckled and a line of mountains rose up." "New Zealand's mountains are around five million years old." "That may sound ancient, but it's just a geological blink of an eye." "Yet even in this short timescale, these peaks have grown into giants." "All the world's great mountain ranges form in this way when continents collide." "You can really get a sense of how the surface of the Earth crumples when you look down from space." "These are the European Alps, the South American Andes" "and the Himalayas of Central Asia." "They're all relatively young, born out of recent collisions between plates." "Sometimes you can actually see their growing pains." "Earthquakes are a horrific force of destruction." "Entire cities can be wiped out at terrible human cost." "But this is what happens when our planet builds its great mountain ranges." "In october 2005, a devastating earthquake hit the western Himalayas in northern Pakistan." "The area around the town of Muzaffarabad was completely razed to the ground." "But satellites measuring the height of the surrounding land before and after the earthquake revealed that something else had happened as well." "The red and yellow colours show how the hills to the east of the earthquake's epicentre had actually risen as much as five metres during the earthquake." "This process, repeated thousands of times, has helped build the Himalayas into the greatest mountain range on Earth." "And it's just as well that the Earth's inner heat continues to push mountains up." "Because huge though mountains are, they're continually under attack." "Given enough time, there's a force that can completely destroy them." "It might seem unlikely, but that force is nothing more than water." "(THUNDER RUMBLING)" "Ironically, mountains create the very rain that attacks them." "They're high enough to disrupt the atmosphere and create their own weather." "The higher the mountains are pushed up, the higher the air is forced to rise to cross them." "So the air cools and condenses into clouds, which produce rain." "And it's surprising just how effective the power of water can be." "And forward!" "And forward!" "Hold on!" "It's only when you're fighting the rapids that you can begin to understand how powerful a river can be." "This gorge is hundreds of metres deep and yet it was cut by the river, relentlessly wearing away at the rock, and it's still getting deeper." "Rivers don't just erode the rock, they also carry it from the mountains to the sea in the form of silt." "It happens on a massive scale." "In South America, the Amazon carries away over two billion tons of the Andes every year and deposits it in the Atlantic ocean." "And on the Indian subcontinent, the Ganges river that starts high in the Himalayas grinds away around a billion tons of rock every year, dropping it 3,000 kilometres downriver in the Indian ocean." "If it wasn't for the movement of the plates building new mountain ranges, water would eventually erode away all the land on our planet." "It's hard to imagine, but if the plates should ever stop moving, our planet would become a water world." "It may take an unfeasibly long time, but eventually the land would be worn down and washed out to sea and Earth would be covered in a vast ocean several kilometres deep." "So it's thanks to the collision of the plates continually pushing the land up that we've still got terra firma to stand on." "our world is constantly reshaped by a never-ending battle between the Earth's inner heat that pushes the land up and the forces of erosion that wear it down." "But the Earth's inner heat has made a profound difference to our planet in another way, perhaps the most important way of all." "It began around four billion years ago." "This is Rotorua in the North Island of New Zealand." "It's one of the most volcanically active places on the planet." "This is a landscape where you can travel back in time." "Rotorua is similar to how the early Earth would have looked." "In its early days, the planet looked very different." "Just like here, the ground was hot with perpetual volcanic activity." "Nasty chemicals brought up from below stained the land." "And noxious gases bubbled up from steaming pools." "To us, the young Earth would have been a hellish place." "But ironically, this volcanic activity helped create the right conditions for the most important change in the history of our planet." "Ultimately, volcanoes provided the surface of our young planet with warmth, water and a potent cocktail of chemicals." "And it was this combination which inadvertently prepared Earth for an utterly remarkable event." "No one's sure exactly how it happened, but around four billion years ago, our planet saw the birth of life." "These pools have a unique chemistry that is very similar to what would have existed on the early Earth." "Bruce Mountain has studied these pools for many years." "He's going to show me how the first life on Earth might have begun." "We don't have a time machine to take us back so the only thing we can do is look at things that we think are similar to what they were like and these hot springs are very, very close" "to those that would have been found on the early Earth." "So what's the temperature of this water?" "Well, the water's 75 degrees Celsius, so you'd definitely get burned if you put your finger in there." "And it's full of hydrogen sulphide, which is quite poisonous." "There's a bit of arsenic in the water as well." "Surely there can't be anything living in there." "What am I looking at?" "Oh, there's billions and billions and billions and billions of organisms living in that water, and they form these orange fibres." "It looks like a fur that's covering all the..." "Yeah." "...the rocks." "For the microbes living within the orange fibres, these toxic chemicals in the water are a rich soup of nutrients." "Pools like this were very common on the early Earth." "Fed by volcanic activity, they provided all the right chemicals needed for the emergence of life." "MOUNTAIN:" "Deep down below us, there's a body of magma that's very hot." "Now, the magma itself is giving off gases like carbon dioxide and sulphur dioxide and that provides the food for these bacteria to grow." "So the volcanoes are like a supply chain providing all this stuff?" "They're the heat engine that drives the whole process." "STEWART:" "Volcanic pools like this are one possible place where life might have begun." "But there is an alternative theory, as volcanoes created other places where life could have started." "Like hydrothermal vents." "These too are the result of volcanic activity, but they are found in the deepest parts of the oceans." "Today, they support an extraordinary diversity of life." "But four billion years ago, it's thought that the combination of high temperatures and rich chemicals that the vents produced might have stimulated the emergence of life." "But the role of volcanoes went beyond just kick starting life." "They have played a critical role in nurturing and protecting it, too." "During Earth's infancy, the Sun wasn't burning as brightly as it does today." "In fact it was about 30% cooler." "With a dimmer Sun bathing the planet in weaker sunlight," "Earth was actually in danger of freezing." "It was volcanoes that provided the young vulnerable planet with a way to keep warm, but not in the way that you might think." "Earth wasn't warmed up by all that hot lava spewing out, but by an extraordinary gas that volcanoes pumped out." "And that gas was carbon dioxide." "Today we think of carbon dioxide as a dangerous gas, causing havoc through climate change." "But actually carbon dioxide has always been vital to our planet because it traps heat in the atmosphere that would otherwise be lost to space." "To see just how critical carbon dioxide is for Earth, take a look at our near neighbours." "Mars is a frozen wasteland with an average temperature of minus 60 degrees." "That's because its atmosphere doesn't have enough carbon dioxide to keep it warm." "At the other extreme, the temperature on the surface of Venus is hot enough to melt lead, not simply because it's a bit closer to the Sun, but because Venus has an atmosphere with thousands of times more carbon dioxide than Earth." "The early Earth was much more volcanic than it is today because its core was so much hotter." "This provided enough carbon dioxide to compensate for the weak Sun." "It was volcanoes that prevented the young Earth from freezing over, and so early life was able to survive." "But even this was not the end of what volcanoes have done for life on Earth." "About 600 million years ago, they also helped trigger the greatest evolutionary leap in Earth's history." "And a great evolutionary leap was certainly needed because soon after life got started, it got stuck in a bit of a rut." "Shark Bay in Western Australia is home to some of the oldest life forms on Earth." "These strange domes are made up from layer upon layer of bacteria." "They're called stromatolites." "For most of Earth's long history, this was the most advanced life on the planet." "For around two billion years, stromatolites ruled our world unchallenged and there was nothing to suggest that this was ever going to change." "But Earth and the stromatolites were to face a catastrophe, the most serious crisis life has ever faced." "Around 700 million years ago, our planet started to cool." "It was the beginning of an Ice Age, but with a difference." "No one is quite sure why it happened, but it seems that ice advanced from the poles until the entire world was plunged into an interminable frozen winter." "It's been called the time of snowball Earth because the whole planet would have appeared as an icy ball." "Travel out to Jupiter and you can get some idea of what Earth might have looked like." "Europa is one of Jupiter's moons." "It's completely covered in ice, just as Earth would have been at the time of the snowball." "But knowing what Earth looked like doesn't convey just how terrible the conditions would have been." "A blizzard high in the Alps in mid-winter is as close as I can get." "The conditions must have been absolutely horrendous." "I don't think I've been ever as cold in my life." "The temperature must be minus 20 degrees Celsius with the wind, but the thing is during snowball Earth, things were much worse." "(GROANS)" "Today, the average surface temperature of the planet around the world is 1 5 degrees Celsius." "During the time of the snowball, that average surface temperature plummeted to minus 50." "5-0 degrees Celsius." "Those frozen conditions threatened the very existence of life on Earth." "The scary thing about snowball Earth is that our planet could have been trapped in the freezer forever." "Once ice had almost completely covered the planet, most of the Sun's heat was reflected back to space." "It looked like the Earth might never heat up again, but clearly something happened which rescued our planet from the icy grip of the snowball." "And what came to the rescue was volcanoes." "Even though ice covered the entire planet, volcanoes continued to erupt, blasting through the thick blanket of ice." "It must have been an extraordinary time." "The nearest we've experienced was in 2004 when an eruption was filmed bursting through an ice sheet in central Iceland." "This is what would have happened during the snowball era, but on a global scale." "The heat from volcanoes would have melted holes in the ice, but that's not what saved our planet." "It was the tons of carbon dioxide gas they released that did the trick." "As volcanoes continued to erupt, levels of carbon dioxide steadily built up in the atmosphere." "Until, around 630 million years ago, the layer of carbon dioxide became so thick that it trapped enough heat to release the planet from the grip of the ice." "At last, a thaw began." "Fierce storms pounded the planet as ice house became hot house." "Temperatures swung from minus 50 Celsius to plus 50 in just a few hundred years, as Earth endured the most extreme climate change in its history." "Fortunately, over time our planet's climate stabilised and Earth slowly returned to normal." "It had been a close call, but a few pockets of life had survived the snowball." "We've got a lot to thank volcanoes for." "They saved our planet from a desolate fate as nothing more than a lifeless frozen wasteland, but as if that's not enough, when volcanoes triggered the end of snowball Earth, it set the stage for the greatest leap forward" "in the history of life on our planet." "I've come to South Australia to see what happened to the evolution of life after snowball Earth." "Palaeontologist Jim Gehling is taking me to see some of the rarest and most ancient fossils in the world." "The remains of the creatures that finally ended the era of the stromatolites." "Jim, where exactly are we going?" "We're going to a secret location in the Flinders Ranges." "This site is so valuable that we have to actually be very careful about who we take in there and who actually finds out about it." "We're going to see one of the most fantastic things." "It's the place where you can get a look at the very first fossil evidence of complex life on Earth." "STEWART:" "The area we're about to visit was once at the bottom of the sea." "600 million years ago, the oceans were the only place where life could be found." "For a billion years, all that the Earth had seen was microscopic single-celled creatures." "The best they could do was to form these domes of slime, which we call stromatolites." "So then in comes this snowball, global glaciation and wipe out, and how did life get affected by that?" "Within a short time after the end of the snowball, we see a revolution in the history of life." "We see a sudden increase in size and complexity of the single cell creatures and soon after, you find impressions on rocks of the very first large creatures, things you can see with the naked eye, which we believe are the oldest multi-cell creatures," "the Ediacara fossils." "STEWART:" "These fossils may represent the most important leap forward in the history of life on our planet, but that doesn't mean they're easy to spot." "This is a very old surface and if we clean it off and then push this putty onto the surface," "you can actually see the impression..." "Look at that." "...of a thing called Parvancorina." "You know, it looks like somebody's signet ring." "It's like a trademark." "Exactly, yeah." "And that's really all the fossil is." "It's the impression of this soft-bodied creature as it was preserved instantly on the sea floor about 560 million years ago." "These are nothing like the fossils I'm used to." "I mean, that..." "I would never, ever have spotted that." "Parvancorina wouldn't attract much attention today, but this animal had made a gigantic evolutionary leap." "Unlike single-celled microbes, this was a complex creature with a head, skin and internal organs." "Under here we can actually see the imprint of quite a large creature, at least the size of your hand." "This is Dickinsonia and it has got the finest segments that you can actually believe." "Oh, yeah." "Just as it catches the light." "So, can you see that?" "Once you get it the right angle you can actually see the details of these body segments." "There are about three there." "There's another one, there." "It's like it was impressed there yesterday." "Every little detail is preserved on these sands." "It's beautiful." "Dickinsonia could grow to over a metre long." "It's thought they lived on the sea floor soaking up nutrients through their skin." "Here for the first time we're seeing life that's become multi-celled, it's large." "These are the creatures that gave rise to the life that we know today." "For around 50 million years, the Ediacarans lived in an ocean free of predators." "Slowly, they evolved into more complex animals, but that came at a price." "These new animals now came equipped with rigid skeletons and shells, gripping claws and protective armour." "The Earth had changed from a soft, peaceful garden of Eden into a savage world of predator and prey." "This intense competition now drove evolution at a frenetic pace." "For more than two billion years, our world had been dominated by microbes." "Now, complex multi-celled life exploded into many new shapes and sizes." "Emerging from the sea, animals and plants went on to conquer the land and the air." "Volcanoes had ended the terrible time of snowball Earth and in doing so, led to a great evolutionary leap forward." "But Earth's powerful volcanoes had one further role to play in the story of life on Earth." "It's a role that's still vital to the survival of complex life like us to this day." "It involves an amazing alliance, a partnership between volcanoes and life that regulates the temperature of the planet, and once again it happens because volcanoes have the power to change our atmosphere." "To show how this extraordinary partnership works, I'm going to Sicily." "This is my favourite place on the entire planet." "I'm 2,500 metres above sea level, on the island of Sicily, and, as you can see, this is pretty cold and windy, but the Phoenicians called this place the Furnace." "The Romans called it the Burning and for the Arabs, it was the Mountain of Fire." "We know it as Mount Etna." "And even after thousands of years, it's still one of the most active volcanoes in the world." "It may be hard to believe that volcanoes as destructive as Etna could ever develop a partnership with life." "But in fact working together, they fine tune the Earth's temperature by controlling the amount of carbon dioxide in the atmosphere." "This process begins in an unlikely place." "The oceans, with tiny creatures called plankton." "They may be individually microscopic, but they're so abundant that when they come together, they can be seen from space." "Every year they proliferate into huge blooms that colour the ocean green." "And it's because the plankton are so abundant that they can help regulate the climate of the planet." "The oceans absorb carbon dioxide from the atmosphere and the plankton use this carbon to grow." "When the plankton die, they fall to the sea floor and here, over thousands of years, they are slowly transformed into rock." "In this way, huge amounts of carbon dioxide, the very gas that keeps our planet warm, are removed from the atmosphere and locked away on the sea floor." "So if that was the end of the story, our planet would steadily get colder and colder." "Fortunately, volcanoes like Etna don't allow that to happen." "Etna is a special type of volcano." "It's formed where two of the Earth's plates are colliding." "In this case, the African plate with the European one." "What happens is that one plate gets forced down, or subducted, underneath the other." "That action produces volcanoes and subduction volcanoes produce some of the largest and most powerful eruptions on the planet." "Where the plates collide, the rock on the sea floor containing carbon from the dead plankton is carried deep into the Earth." "As it descends, this layer of rock is heated." "So the rock melts, releasing carbon dioxide." "And gas is returned back into the atmosphere during an eruption." "The remarkable cycle is complete." "It's uncanny how working together, life and volcanoes keep just the right amount of carbon dioxide in our atmosphere, maintaining our planet at a comfortable temperature." "But this process that has sustained all life on the planet comes at an enormous cost." "Subduction volcanoes are the most violent on Earth." "You can see just how explosive they are by looking at one of the most famous eruptions ever recorded." "on May 1 8th, 1 980," "Mount St Helens in the United States was ripped apart." "Within minutes, 2.8 billion cubic metres of the volcano were blasted out over the surrounding countryside." "For the last 25 years, Mount St Helens has been fairly quiet." "But inside its vast crater, a giant cone of rock is growing." "Forced up by the pressure from beneath," "Mount St Helens is building for another eruption." "The irony is that subduction volcanoes are so highly explosive and destructive because they're so gassy, yet it's the release of the gas that's crucial to the Earth." "That's the key to recycling carbon that's locked in the rocks back into the atmosphere." "The whole elaborate system works like a finely tuned thermostat maintaining the right temperatures for life." "But, of course, it must be hard to accept just how important volcanoes are to our world when it's your own home that gets destroyed." "In 1 992, a few months before I first came here, the volcano was spewing out masses of lava." "And I remember the news footage of the farmer who lived in this house here, and with the lava coming up to his front door, he sits down for a farewell meal, drinks a final glass of red wine," "daubs a sarcastic remark, grazie governo, on the wall and leaves his home to the lava." "Ever since the planet formed four and a half billion years ago," "Earth's inner heat has been continuously struggling to escape." "We see the result as volcanoes, but that's just one part of it." "To me, nothing has been more important to the history of our planet than the heat trapped inside it." "No force on Earth is more dramatic, more destructive, more violent than volcanoes, but they're so much more than just a force of destruction." "They're the life force of our planet." "Quite simply, without volcanoes, I wouldn't be here and neither would you." "Next time, the atmosphere." "It's immensely powerful, but, at the same time, highly sensitive." "It's destructive and yet it also protects us." "Now it's changing fast with potentially devastating consequences."