"This is our planet, the Earth." "It's an amazing world, full of natural wonders, but there's far more to Earth than its natural beauty." "My name is Iain Stewart and I want to show you how our planet works." "Our planet is unique in the solar system, perhaps even in the universe." "And that's no surprise when you consider the outrageous good fortune it's taken to create our extraordinary world." "What makes the Earth so special is the way that everything seems to come together to create the perfect conditions for life." "It's taken four and a half billion years to turn the Earth from a barren rock into the world we know today." "It's been an incredible journey of catastrophe and renewal." "But now this rare and remarkable planet is facing perhaps its greatest challenge, humankind." "The question is, will it survive?" "Ever since we humans have been able to scan the heavens, we've been looking for signs of intelligent life like us, up there in space." "This array of radio telescopes in America has been part of that search." "These telescopes can see deep into space." "But, so far, we haven't found anything." "Now it could be that we've not been looking for long enough or in the right part of space," "but there is another possibility." "Perhaps we haven't found any signs of life because there's simply nothing out there." "It's hard to believe that we might be on our own." "After all, there are billions of stars in our own galaxy, the Milky Way." "And the Milky Way is just one of billions of galaxies." "You'd think there must be other Earths out there, just like ours." "Capable of supporting life just like us." "It's only a question of finding them." "But now, there's a new theory." "It's called the Rare Earth Theory." "It says that simple life, like bacteria, the type of slime I've seen in hot volcanic pools, may be common in the universe." "But for complex life like plants and animals to evolve requires an extraordinary sequence of events." "And having traveled the world to make this series, what strikes me most is the incredible good fortune it's taken to make our planet a home for such rich and diverse life." "To get an idea of just how lucky Earth has been, let me take you back to what I reckon is the most important day in Earth's history." "This one day was responsible for much of what makes Earth so special." "And yet, it was just a chance event." "This is our planet just 50 million years after it formed." "It's thought that back then Earth had a twin, Theia." "The two planets were born in similar orbits." "The result, a catastrophic collision." "Theia was obliterated, leaving a ring of debris orbiting the Earth." "This may have been a vital first step in creating the conditions for complex life." "That's because Earth consumed a part of its twin," "and became a significantly larger planet." "The result was to increase the pull of Earth's gravity." "Without this," "Earth's atmosphere might have gradually leaked into space." "Even an atmosphere needs gravity to hold it down." "It keeps our planet warm." "It drives the climate." "And provides us with the oxygen we breathe." "But the atmosphere also gives us something else that's vital for life on Earth," "protection." "This is a giant meteorite crater." "It was blasted out of the Earth's crust 50,000 years ago." "Well, there it is, Meteor Crater." "This place really gives you a sense of the destructive power of incoming meteorites." "The blast here would have vaporized a city larger than London." "But the lump of rock that did it measured almost 80 feet across." "The impact exploded with a force 70 times greater than the atom bomb." "But what makes this massive crater so significant isn't how big it is, but how rare it is." "Because although it might not look like it, space is a hazardous place." "There are millions of objects that cross Earth's path at thousands of miles per hour." "With so much debris up in space, Earth should be hit much more often." "Other craters do exist but they're few and far between." "This one is in Namibia." "In some cases, they can only be seen with the latest mapping techniques, like this one in Brazil." "But even with this technology, less than 200 impact craters have been found across the entire planet." "This is partly because erosion continually rubs out the evidence of past impacts, but it's also because of the atmosphere's protective role." "To understand how something as intangible as thin air protects us from meteors, you need to find a meteorite that has survived its fall to Earth." "Meteorites are rare, so you need to go to great lengths to track one down." "Dr Phil Bland is a planetary scientist on just such a mission, leading an expedition out onto the barren Nullarbor Plain in Western Australia, three days` drive from the nearest town." "The Nullarbor is vast, but it's as flat as a pancake." "So it's the ideal hunting ground for meteorites." "Little has changed here for millions of years, allowing meteorites to accumulate undisturbed." "The team are preparing to search the ground, scouring the desert like a police search team." "The whole plateau's limestone, so dark meteorites stand out pretty good against the pale limestone, and there's not too much vegetation, so you can see the ground pretty well." "So what am I looking for?" "Something metal and dark?" "BLAN D:" "Yeah." "When they've been out here for a while, they rust a little bit." "They have chunks of metal in them, so you get a kind of a dark, rusty texture." "After searching for quite a while, we've not had much luck." "Hey, guys, I think I've got one here." "That's a beauty." "Is that a meteorite?" "Yeah, it's a lovely one." "This is incredible that it's something from outer space." "That's amazing." "What is amazing is that it actually makes it to the surface at all." "Something that size might have been part of an object the size of a washing machine or a small car at the top of the atmosphere, and as it punches into the atmosphere at high speed, the surface gets melted and stripped off" "and a new surface exposed and melted and stripped off, until you whittle down to something about that big." "But it's heavy, so that small car is a small car of rock weighing tons?" "Yes." "So, thin air does this to solid rock?" "Yes." "That's remarkable." "When meteors hit the atmosphere, they compress the air in front of them which generates intense heat." "Layer upon layer gets stripped away until most are completely burnt up." "We see this process in action when particles no larger than grains of sand burn up as they streak across the night sky." "Shooting stars." "One object that didn't burn up was Theia, Earth's twin." "Earth's early collision with its twin was also vital for our planet in many other ways." "For a start, it probably resulted in Earth's core becoming larger." "And because it's made of iron, the churning of this huge metal core generates a powerful magnetic field." "It's possible to see this magnetic field at work." "This is the aurora." "You're watching the magnetic field deflecting the Sun's dangerous solar wind." "But the huge molten core contributes something else essential for life on Earth," "a way of helping to regulate the planet's temperature." "It's a remarkable system." "Magma heated by the core rises towards the Earth's surface." "As it spreads sideways, the Earth's crust is very slowly dragged apart." "This moves the continents, creating the Earth's restless and ever-changing surface." "But crucially for life, the core does more than just shape the planet." "Where these plates collide, it creates massive volcanic eruptions, which release carbon dioxide into the atmosphere." "Today, we think of carbon dioxide as a dangerous greenhouse gas that leads to global warming." "But throughout Earth's long history, carbon dioxide has played a vital role in keeping our planet the right temperature for complex life to survive." "And there was one final, rather special gift that the collision with Earth's twin bestowed upon our planet." "As the debris from the explosion orbited the Earth, it began to coalesce, until it formed a new planetary body, the Moon." "But because of the way it formed, ours is unusually large, and it's made an unusually big difference to Earth's development." "As the Moon orbits Earth, its gravity pulls the water and the oceans towards it." "The constantly changing tidal Zone this creates provided an evolutionary testing ground for Earth's early creatures." "But the tides would happen without the Moon, and are not the Moon's greatest contribution to life on Earth." "Without the Moon," "Earth's temperature might regularly switch from boiling hot to way below freezing." "Such wild climatic swings would have made the planet uninhabitable." "Yet there's something rather strange happening to the Moon that means we shouldn't take it for granted." "Meet Jerry Wiant." "Every morning, he rides up to the McDonald Observatory in West Texas, and it's thanks to his work that we know something extraordinary about the Moon." "So, how many times do you make this journey?" "Every day for 37 years." "37 years!" "Yeah, on this bike." "You' re joking?" "No, this one bike." "That's it up there, is it?" "Yeah." "Jerry's job is deceptively simple." "Once a day, he fires a laser at the Moon in order to measure its distance from Earth." "Measuring the distance to the Moon is quite simple." "We start with a bundle of light, we send it through a telescope, when it reaches the Moon it hits a reflector, and it comes back toward Earth." "We intercept that with our telescope and what we do is we time when the light left and we time when the light comes back, and that's our data." "Jerry's target on the Moon is a panel made up of individual reflectors that were left by astronauts from the first Moon walk and later Apollo missions." "It takes just 2 . 5 seconds for the light to return to Earth." "Jerry has measured this figure every day for decades." "And his results reveal something remarkable." "The Moon is receding 3 .8 centimeters per year, which kind of surprised me, I didn't really give it a thought whether it was standing still or moving, but it is, it's moving away." "And eventually, we'll lose it." "So the Moon will not be with us forever." "Eventually, it will drift away into space and Earth will lose its climatic stability." "But there's no need to panic." "It'll take billions of years." "Earth's chance collision with its twin was perhaps the critical moment in its history." "By this theory, it ensured that the planet held on to its protective atmosphere." "It gave Earth a magnetic shield against the dangerous solar wind." "And it left us the Moon that provides climatic stability." "If the collision had never happened," "Earth may never have been a home to complex life." "We've seen the extraordinary consequences of just one chance event on the Earth's destiny." "But there's another chance factor that was just as vital, its location." "It's only when you consider our planet's position in the solar system that you really begin to understand how fortunate it's been." "Too far from the Sun, like Mars, and it's simply too cold for life." "A little closer and things improve." "This is where you find the Earth." "We are lucky enough to be in the only place in the solar system, to our knowledge, Â¤hat`s the right temperature for water the most essential ingredient for life to exist on the surface." "Any closer to the Sun, like Venus, and it's far too hot." "Any water would boil away." "Look at the green Zone." "This is the only place in the entire solar system that can support complex life, and Earth is the only planet there." "But it's not just Earth's proximity to the Sun that's important." "We're also lucky enough to orbit the right type of sun." "This is the actual surface of the Sun." "Every second, four million tons of the Sun is converted into pure energy." "It's been doing this for more than four and a half billion years." "And it's this long lifespan that makes our Sun so special." "Many other stars are bigger but at a cost." "The larger the star is, the quicker it burns up and dies." "It took billions of years for complex life to get going on Earth, and it's our Sun's long life that made that possible." "And there's one final piece of good fortune that life on Earth depends on." "Jupiter." "Jupiter is more than three hundred times bigger than Earth, so it has a massive gravitational field." "This attracts dangerous flying objects that might otherwise hit Earth." "Jupiter is Earth's protector." "Scientists have even seen it in action." "In the early 1 990s, a comet was captured by Jupiter's powerful gravity." "It broke up into many different pieces, which smashed into the planet." "Some of the blasts left scars as big as Earth itself." "Without Jupiter it's likely Earth would have been pummeled by huge impacts like this eÂ¤ery 1 0,000 years or so." "Under that kind of bombardment, it's hard to imagine how complex life could ever have got going." "Any planet that's to be a home to complex life needs liquid water a sun that doesn't burn out too quickly and a giant neighbor to protect it from meteorites." "Earth has benefited from all of these." "An environment that remains relatively stable is essential for complex life to survive." "But there's a curious twist." "Too much stability and evolution can get stuck in a bit of a rut." "Every now and then life needs a catastrophe to shake things up." "In the jungles of Mexico lies the evidence of one such catastrophe," "one that turned out to be very important for us humans." "You know, everywhere you go around here, you find these holes." "They' re called cenotes." "There's thousands of them, and most of them haven't even been explored." "But these are the right people to be with because these guys are cave explorers and they' re going to show me a new world, one beneath our feet." "Team leader Bernadette is the first to descend." "Okay, I' m down !" "Wow!" "Look at the size of this." "This is magnificent." "That is beautiful." "So, lower the gear, please." "There's actually much more to this amazing cavern than first meets the eye." "But to understand the scale of what happened here, you have to go deeper still, underwater." "Cave diving is notoriously risky." "It's all too easy to get trapped." "But Bernadette's a professional cave diver so I'm in good hands." "Okay." "Descending into the depths of the cenote is like entering a new world." "Fewer people have visited some of these drowned caverns than the surface of the Moon." "As divers have explored further they've discovered the cenotes are actually part of a huge complex of tunnels and caves." "In fact, when you look from above, you can see there are cenotes scattered across Mexico's Yucatan Peninsula." "And when they're mapped, it becomes clear that they follow a distinctive circular course through the jungle." "They mark out the rim of a giant crater." "Scientific instruments show the structure of the underlying rock has been deformed, revealing the boundaries of a colossal meteorite impact crater." "This amazing cavern is part of a bigger story, a much bigger story." "Sixty-five million years ago, this was the site of one of the most catastrophic impacts in Earth's history." "What became known as the Chicxulub meteorite landed here and that triggered the extinction of the dinosaurs." "The meteorite was likely over nine miles across, enough to cause utter devastation across the whole planet." "It exploded with the force of one hundred million million tons of TNT." "The blast sent a giant plume of vaporized rock out into space." "A crater was punched half a mile into the Earth's crust." "It was above this rim of weakened rock that the cenotes formed." "The blast would have been ferocious." "But it was what happened next that made the impact a global catastrophe." "The blast plume that shot into space fell back to Earth." "Many believe that billions of molten particles superheated the air to hundreds of degrees." "Fires swept the planet, choking the atmosphere with soot and dust." "The dinosaurs and most other creatures were doomed." "But fortunately, underground there were some survivors." "It took a few million years, but eventually conditions on Earth returned to normal." "By wiping out the dinosaurs, the impact cleared the way for the rise of a new type of animal, the mammals and, ultimately, for humans." "So from our point of view, this global disaster turned out to be no bad thing." "Catastrophes like the Chicxulub meteorite are disastrous for the life that happens to be around at the time." "But in terms of stimulating the evolution of complex life, they're actually a blessing in disguise." "The extinction of the dinosaurs wasn't the only time that a catastrophe kick-started a major evolutionary change." "In the Italian Dolomites, geological evidence shows how the dinosaurs themselves benefited from a previous catastrophe." "This layer of black rock marks a time when 70% of all life on land perished." "Over 90% of marine life died out." "And when it was over it was the dinosaurs that inherited the Earth." "And in Australia, it's possible to see the last survivors of an even earlier catastrophe." "These mounds are bacterial stromatolites." "They might still rule the Earth today were it not for a colossal ice age, which nearly wiped them out, clearing the way for the first complex life." "Earth has been blessed with just the right balance of stability and the occasional catastrophe." "Too many catastrophes and life never gets a chance to develop." "Too few, and life gets stuck in a rut." "It's taken four and a half billion years to turn the Earth from a barren rock into the world we see today." "It's been a remarkable journey." "But now the planet's facing perhaps its greatest challenge." "Humans." "Just look at Earth from space." "At night, our lights mark out our domination of the world." "By burning fossil fuels like coal and gas, we've changed the very composition of the atmosphere, and with it, the climate." "The human race now moves more rock and soil on the surface of the planet than all the Earth's natural processes put together." "No species has ever dominated the planet like this." "In fact, our influence is now so great that many scientists believe a new geological era has begun." "The Anthropogenic, the human era." "The question is, are we now beginning to threaten the very conditions that make our planet so special?" "A good place to find out is here on the island of Madagascar off the coast of Africa." "It's estimated that 85% of all life here is unique to this island." "Most of it is found in the forests Madagascar is famous for." "These forests symbolize the way our planet works." "They're incredibly complex, and yet everything works together to maintain the health of the whole system." "And just like the whole planet, we're changing the forests here without fully understanding the consequences." "I've joined up with a science expedition to see for myself what's happening to Madagascar's forests." "FISH ER:" "All right, guys, here we are!" "Dr Brian Fisher is cataloguing the life found in the forests to help understand how the delicate ecosystem is changing." "Well, this is it." "This is the end of the road for the vehicles." "We' re heading off on foot now down there into the jungle." "Brian's team is searching for a new species that he's convinced lurk in the undergrowth." "He believes it's a particularly good area for ants." "FISH ER:" "And they live in rotting wood." "They live in the ground, they live under stones." "We' re just trying to peek into their homes, you know, get onto their level." "Check this out." "There are cocoons there, look at that." "Yellow cocoons, look at that." "Yes." "I' m sure this is a new species." "New species of ant?" "Yep, new species in genus Â¤Â¤Â¤" "Oh, look at them all!" "The whole nest structure is right here." "STEWART:" "Oh, yeah !" "Look at that." "FISH ER:" "Oh !" "Look at them all." "So, you only find these ants in a place that's got a lot of biodiversity, it's unique." "Right." "You can't support this on a marginal habitat because they require, underneath it, a whole system of interactions to be happening." "Look at that one stinging me right now." "Look at that." "It's an encouraging find." "The fact that this part of the forest is teeming with insect life means that here, at least, it's still pretty healthy." "And by convention, whoever discovers a new species gets to give it a name." "In a very generous gesture," "Brian chose to name the new ant after me." "Say hello to Cerapachys iainstewarti." "Bit of a mean-looking critter if you ask me." "The more we find out about these forests, the more we're discovering how vital they are to the well-being of the whole planet." "They' re like the lungs of the Earth." "As they grow, trees absorb huge amounts of carbon dioxide from the atmosphere through their leaves." "The remarkable thing is that even as carbon dioxide levels in the atmosphere rise, trees respond by growing faster so absorbing more carbon dioxide." "In fact, since humans started pumping greenhouse gases into the atmosphere, the world's jungles have absorbed around" "2 5% of all the carbon dioxide we've produced, helping to reduce the effects of global warming." "So, healthy forests like those I've experienced in Madagascar play a vital role in regulating the planet's climate." "But the pristine natural beauty of this island isn't all that it seems." "This is one of the most famous places in Madagascar." "These giants are the baobab trees, the island's national symbol." "They' re actually a symbol of something else as well." "The only reason you can see them is that all the other trees have been cut down." "The baobabs remain because to the local people, they're sacred." "Right across Madagascar, the forest is under attack." "Wherever you go, you catch the smell of wood smoke, the smell of farmers clearing the jungle because the local practice, known as Â¤Â¤ uses fire to open up new land." "These days, there's only about a fifth of the island's original jungle left." "Of course, deforestation is not a problem that's confined to Madagascar." "In Bolivia, this area of rainforest covering more than 20,000 square miles was turned into farmland and towns in just 20 years." "Each year across the planet, an area of forest about the size of South Carolina is destroyed." "So not only are we increasing the levels of greenhouse gases in the atmosphere, we're also reducing the ability of the planet to deal with the problem." "you only have to go back to Mexico, the place where the meteorite that wiped out the dinosaurs landed, to see our influence on the planet from a very different perspective." "Just inland from the ocean, here in Mexico's Yucatan Peninsula, the jungle stretches unbroken for hundreds of miles." "But every now and then, you stumble upon a strange mound of stones like this." "Some of them are enormous, the pyramids of a lost civilization." "This is the pyramid of Nor Uxmal." "It was built more than a thousand years ago by the Mayans, and was at the heart of a city of 50,000 people." "Today, little remains of that once-thriving culture." "There are lots of theories for why the Mayan civilization disappeared." "Some say it was war, others that drought finished them off, but there's one thing for sure and that's they' re not here now." "It's a reminder that no civilization will last forever." "In the human imagination, the 2,000-year rise and fall of the Mayan Empire seems incredible." "But it's nothing compared to what's happened here over Earth's lifetime." "This area hasn't always been jungle." "At times it's been beneath the sea." "At other times, it may have been covered in ice." "And 65 million years ago, this is where the Chicxulub meteorite landed." "But even that hasn't left much of a trace." "Earth and life recovered, sometimes even benefited, from this and from every other major catastrophe." "It's this ability to deal with catastrophe that's a truly special thing about Earth." "Our planet is really tough, and there's nothing to suggest that that's going to change anytime soon." "In the long run," "Earth can cope with anything we can throw at it." "We could clear all the jungles, but a jungle can re-grow over a few thousand years." "We could burn all Earth's fossil fuels, flooding the atmosphere with carbon dioxide, but even then it would take the planet only a million years or so for the atmosphere to recover." "Even the animals we're wiping out may eventually be replaced by others equally rich in diversity, as the relentless work of evolution continues." "So in changing this world, we're altering the very environment that has allowed the human race to thrive." "We could be creating conditions that threaten the long-term survival of our civilization." "So, all this stuff about saving planet Earth, well, that's not the problem." "Planet Earth doesn't need saving." "Earth is a great survivor." "It's not the planet we should be worrying about, it's us."