"This is our planet, the Earth." "It's a remarkable, 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 is Iain Stewart and I want to show you how our planet works." "I'm going to explore 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 possibly 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." "I've come all this way to see one of the most remarkable volcanoes anywhere on the planet." "It's called Erta Ale." "The name means smoking mountain to the local Afar people." "It's reckoned that the lava lake has been active for at least 90 years, making it one of the longest known eruptions." "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." "Sit back, sit back." "After, after." "Okay." "That's it." "That's good." "It's close to a 100-foot drop to the terrace below." "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." "Look at that." "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." "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." "This process of molten rock churning away below the surface affects the planet on a global scale." "But the Earth's heat does far more than simply fuel volcanoes." "It continually rebuilds the planet's surface and it created the conditions for life on Earth to begin." "To understand where our planet's immense inner heat comes from, you have to go back four and a half billion years." "This is the time of our planet's birth." "you may not recognize it, but this is the Earth." "Little more than a few pieces of rock colliding as they circle the Sun." "But these impacts produced immense amounts of heat, as did underground radioactive decay." "Eventually, when the outer layers of the planet cooled, these powerful sources of heat were trapped in a huge, hot core." "The centre of our planet is around 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." "Earth's hot core has been continuously releasing unimaginable amounts of heat since its formation." "Even after four and a half billion years, there's still plenty left." "Volcanoes are the most obvious examples of the Earth's inner heat in action." "But this inner heat also continually reshapes the surface of the whole planet." "It creates a restless, constantly changing landscape." "Iceland is a great place to see exactly how the planet's inner heat is able to transform the surface of the Earth." "Magma usually lies many miles beneath the surface but here, in Iceland, it's much closer." "And that has a dramatic effect." "Sulphurous fumes and bubbling hot pools with hundred-degree-plus temperatures 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." "But the people here might not be quite so relaxed if they knew exactly how the water gets heated." "Just 12 miles beneath Iceland is a vast column of super-heated rock called a plume." "It's over 100 miles wide and at least 370 miles deep." "Created more than 50 million years ago, the plume is sustained by heat continually rising up from Earth's hot core." "This giant plume does more than just warm up Iceland's hot springs." "It also created Iceland itself." "In 1963, there was an event that showed 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 more than 50 million years ago when it first burst above the surface." "Iceland owes its existence to the plume of super-heated rock beneath it." "But it's also shaped by the Earth's inner heat in another even more dramatic way." "This extraordinary rock face at Thingvellir shows how." "From the air it's clear just how unusual this rock face is." "It's a crack in the Earth's surface that runs as far as the eye can see." "But even this is just a small part of something far bigger." "To the left is a gigantic slab of the Earth's crust, which runs unbroken for over 4,000 miles, from here, 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 vast chunks called plates." "They're so enormous they can carry an entire continent, even extending under the ocean." "Strip away the Atlantic and the long boundary between two plates that runs along the ocean floor is exposed," "until it rises above the waves, and cuts through Iceland," "to eventually join up with the rock face at Thingvellir." "These sheer rock faces were once joined together but driven by the churning force of molten rock beneath them, the land was split apart." "It happens because hot rock from the Earth's interior rises up." "Near the surface, the rock spreads sideways in two directions." "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 land masses to move." "225 million years ago, our planet was unrecognizable." "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 world we know today." "But the churning heat beneath us means the plates never stop moving." "In the distant future, our continents may once again be reunited in another giant super-continent." "This is what happens when the plates move apart." "But when they collide, the results can be even more dramatic." "The collision of the Earth's plates is responsible for the most spectacular mountain ranges on the planet." "Like the Southern Alps in New Zealand." "These stunning peaks run 300 miles along the west coast, forming a dramatic spine down the island." "Tens of millions of years ago, the collision of the Pacific and Australian plates created the New Zealand 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, many over 10,000 feet high." "All the great mountain ranges formed in this way as the planet's inner heat forced the continental plates to collide, crumpling the surface of the Earth." "The European Alps, the South American Andes," "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." "They happen with the Earth's plates push against each other and get stuck." "Stress builds up until it's suddenly released." "In October 2005, a devastating earthquake hit the western Himalayas in northern Pakistan." "Much of the area around the town of MuZaffarabad was completely flattened." "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 colors show how the hills close to the epicenter had actually risen as much as 1 6 feet during the earthquake." "From earthquakes to mountains, geological forces are shaping our world." "They have helped build the Himalayas into the greatest mountain range on Earth," "soaring reminders of the power of our planet." "Despite their size, mountains are continuously under attack." "(TH U N DER RUMBLING)" "And the force that can eventually destroy the highest peak is nothing more than water." "(THUNDER RUMBLING)" "Mountains create the very rain that attacks them." "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 !" "Bring it down !" "Hold on !" "This gorge is hundreds of feet deep." "It was carved out by New Zealand's Shotover River relentlessly wearing away at the mountain range, and it's still getting deeper." "As rivers erode the rock, they also carry vast quantities of silt from the mountains down to the sea." "It happens on a massive scale." "In South America, the Amazon River carries away over two billion tons of the Andes every year and deposits much of the sediment in the Atlantic Ocean." "And on the Indian subcontinent, the Ganges River that starts high in the Himalayas grinds away close to a billion tons of rock every year dropping millions of tons almost 1 , 900 miles down the river 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." "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 geological forces that push 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, possibly similar to Earth millions of years ago." "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." "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 be 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?" "There's billions and billions and billions and billions of organisms living in that water, and they form these orange fibres." "For the microbes living within the orange fibres, these toxic chemicals within the water are a rich soup of nutrients." "Pools like this were very common on the early Earth." "Fed by volcanic activity, they may have provided all the right chemicals needed for the emergence of life." "MOU NTAIN :" "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 neighbors." "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." "Volcanoes 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 a great evolutionary leap in Earth's history." "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, perhaps 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." "No one is quite sure why it happened, but it seems that our entire world was plunged into an interminable winter." "Some scientists have called it the time of snowball Earth because the whole planet may have appeared as an icy ball." "Others believe that the Earth was cold but not completely frozen." "Travel out to Jupiter and you can get some idea of what Earth might have looked like." "Europe is one of Jupiter's moons." "A frozen landscape that might mirror parts of Earth millions of years ago." "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." "Today the average surface temperature of the planet around the world is 1 5 degrees Celsius." "700 million years ago, it was much colder." "That average surface temperature plummeted to minus 50, 5-0 degrees Celsius." "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." "It was volcanoes that came to the rescue." "They erupted with tremendous force, even blasting through the ice sheets that covered much of the planet." "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 millions of years ago, 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 it 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 its endless winter." "At last, a thaw began." "Fierce storms pounded the planet and Earth's cold and slushy climate began to warm." "In just a few hundred years, temperatures would rise dramatically." "and Earth would never be the same." "Fortunately, over time our planet's climate stabilized and Earth slowly returned to normal." "Volcanoes had set the stage for a dynamic new era." "In South Australia, there's evidence for what happened to the evolution of life after Earth's long winter." "Five hours' drive out of Adelaide, paleontologist Jim Gehling is traveling to see some of the rarest and most ancient fossils in the world." "We' re going to a secret location in the Flinders Ranges." "It's the place where you can get a look at the very first fossil evidence of complex life on Earth." "STEWART:" "The area Jim's visiting was once at the bottom of the sea." "600 million years ago, the oceans were the only place where life could be found." "But a warmer Earth brought change." "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." "Stromatolites were the Earth's dominant life form." "Were it not for the violent climatic changes triggered by volcanoes at the end of the snowball era, they might still rule the planet today." "Instead, new life forms arose." "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, 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." "Once you get it at 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 three feet 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 two billion years, our planet had been dominated by stromatolites." "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 created the conditions for a great evolutionary leap forward." "But the planet's powerful volcanoes had one further role to play in the story of life on Earth." "A role still vital to the survival of complex life." "It involves an amazing alliance, a partnership between volcanoes and life which regulates the temperature of the planet." "It may be hard to believe, but working together volcanoes and life fine-tune the Earth's temperature by controlling the amount of carbon dioxide in the atmosphere." "This extraordinary 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 color the ocean green." "The oceans absorb carbon dioxide from the atmosphere and plankton use this carbon for both photosynthesis and to make their shells." "When the plankton die, they fall to the sea floor and here, over thousands of years, their shells 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." "So if that was the end of the story, our planet would have run out of carbon dioxide and steadily got colder and colder." "But fortunately, a special type of volcano doesn't allow that to happen." "They're called subduction volcanoes." "Where plates in the Earth's crust collide, the rock on the sea floor containing carbon from the plankton shells is carried deep into the Earth." "This is called subduction." "As it descends, this layer of rock is heated and melts, releasing carbon dioxide." "This gas is returned back into the atmosphere during an eruption." "The remarkable cycle is complete." "It's uncanny how life and volcanoes keep just the right amount of carbon dioxide in our atmosphere," "keeping 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 powerful on Earth." "you can see just how explosive they are by looking at one of the most famous eruptions ever recorded." "On May 18th, 1980," "Mount St Helens in the Pacific Northwest was ripped apart." "Within minutes, over 100 billion cubic feet of the mountain slid down into the surrounding countryside." "Since the eruption, Mount St Helens has been fairly quiet." "But inside its vast crater a giant cone of rock is growing." "Forced up by 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 back into the atmosphere the carbon that's locked in the rocks below." "The whole elaborate system works a bit like a thermostat, maintaining the right temperatures for life." "Ever since our planet formed four and a half billion years ago," "Earth's inner heat has been continuously struggling to escape." "In fact, you could say that the whole history of the planet has been driven by the immense heat trapped inside it." "No force on Earth is more dramatic more destructive, and more violent than volcanoes." "They're the life force of our planet."