"Welcome to the Earth Ride:" "fasten your seatbelts for a roller-coaster ride around the only planet in the solar system that supports life." "This is your chance to go to parts of the world you can't normally reach..." "You'll travel to extreme places and meet extraordinary animals!" "Earth is a planet of immense variety, but every form of life depends on one thing... water." "And water gets everywhere..." "whether we like it or not!" "The water on Planet Earth is shared between all living things" "But there's only a limited amount to go around." "So where's all it been, and where's it all going?" "To find out, hop aboard the Earth ride for a blast through nature's greatest spectacles as you take the roller-coaster ride of life!" "All creatures, including you, depend on water none can survive without it." "You are two-thirds water... and the water that's inside your body right now has had a remarkable history." "Some of the water that you'll drink today once filled the deepest oceans." "In every glass are drops that have been shared with other animals." "Whenever you drink, you join them as part of the planet's never-ending water cycle." "The Earth ride will follow water's weird and wonderful course around the world." "Sometimes we'll race along at death-defying speeds... at other moments slow right down to witness the water cycle's most intricate twists and turns." "Water has shaped every habitat on Earth." "It's the only substance that can naturally exist in all three forms..." "As ice it dominates our winter landscape as liquid, it supports the richness of the tropical seas." "And water vapour bathes the rainforests in moisture, creating an explosion of life." "From the driest deserts to the snow-capped peaks, water is constantly recycled around the planet." "And at any moment, there are 12 thousand billion tons of it up in the atmosphere, circling the globe." "But before we start our ride, there's something we need to know:" "what is so special about water?" "After all, it's got no colour, no smell and no taste." "To find out, let's have a closer look..." "inside a single drop!" "This is a water molecule" " H20 two atoms of hydrogen and one of oxygen." "Each molecule is connected to the next by electrical forces called 'hydrogen bonds'." "And these bonds - as we'll soon discover are what makes water so unique." "Water is now the most common substance on the planet's surface but once upon a time, it wasn't here at all." "How did water first appear on earth?" "To answer that, the Earth ride's going to take us back in time to when the world was very young." "Some of our planet's water came from outer-space, where massive quantities of hydrogen and oxygen combined to form 'space ice'." "The average comet is made up of more than a billion tonnes of ice." "We and all other forms of life on earth partly owe our existence to this extra-terrestrial water." "Just think - that makes you part extra-terrestrial too!" "The other main source of Earth's water was from hydrogen and oxygen combining deep within the forming planet." "This produced steam - boiling water vapour which emerged from ruptures in the Earth's crust such as geysers and volcanic springs." "Over the next 3 billion years our planet's atmosphere became saturated with water vapour." "This vapour envelope around the earth helped to protect the planet from the sun's scorching rays." "It also trapped the sun's heat, so as each day flashed by," "Earth's atmosphere began to warm." "Without this the original 'Greenhouse Effect' the average temperature on Earth would still be minus 18oC, and our world would be a frozen wasteland." "Life as we know it could never have begun." "Eventually, the atmosphere had warmed enough for rain to fall." "Rainwater filled the oceans and energy from the sun began to drive the great cycle of water around the planet." "And we're all part of the same loop today." "The rain that fell then has by now circled the globe around 8 million times!" "The water cycle runs on solar power the sun's heat evaporates water from the surface of the seas." "During this process, all its salt is lost, leaving just clean fresh water spread across the globe." "It's our planet's most precious asset." "But each day some is lost into space from the upper atmosphere." "So does this mean that one day, our supply of water will run out?" "To answer that, we're going to the centre of the Earth." "30 kilometres beneath our feet, temperatures exceed 1000 degrees Celsius." "This is the beginning of the mantle the layer between the Earth's crust and the core." "Down here it's mostly hot rock but in deeper parts there is also water... maybe 10 times the volume of all the world's oceans!" "This giant reservoir replaces the water lost to outer space" "It's released as steam when volcanoes erupt!" "Volcanoes shaped our primitive planet long before any life evolved." "Then, as now, most of them were submerged, so they erupted largely underwater and released steam straight into the sea." "More water was released into the oceans through ruptures in the sea floor..." "Prepare to enter the abyss!" "These are 'black smokers', natural chimneys on the seabed that spew out superheated water, black with minerals." "It's in such deep, dark places Evolution may have first begun." "And life has been harnessed to water ever since." "Microbes still live here, 2.5 kilometres down surviving under immense pressures." "Instead of relying on sunlight like most living things, they exist on expelled minerals and volcanic heat." "Sea water was the perfect place for life to start... with stable temperatures, physical support and a ready supply of nutrients." "The stage was set for evolution to explode into the oceans..." "Strong currents, powered by the sun, spread life across the globe." "As time went by, the seas became richer and the animals more diverse." "In the warmest seas, near the equator, coral reefs developed into the richest marine habitats on earth." "Today the oceans teem with life..." "in all its shapes and sizes." "This is the biggest fish alive in the seas today - the whale shark." "It's so enormous, it's like a swimming island, with entire communities of fish living around its body." "Yet the whale shark feeds on microscopic plankton, scooped up by a mouth so vast, you could swim through it!" "It's relatively recently that evolution broke free from the sea and reached dry land." "Without the ocean's stable temperatures and physical support, creatures' bodies and behaviours had to alter radically they were like aliens in another world." "The mud-skipper is a modern-day equivalent of those early landlubbers." "It's a fish out of water that solved the problem by walking on its fins and having sealed-up gill slits." "Water availability became the crucial key to survival what land animals needed was new ways to conserve it inside their bodies." "Giant insects evolved water-tight skins, which helped them spread across the globe..." "For a while, they ruled the world." "As more time passed, other animals learned how to manage without so much water." "Huge reptiles started to lay eggs on land, with harder shells to stop them dehydrating." "But even today, these crocodile babies still need contact with the water," "and this caring mother helps them get there." "The reptiles' descendants - the birds held onto the watertight egg design." "Eventually it helped them colonise some of the most hostile places on the planet." "Mammals are good at storing water in their bodies." "Some have even adapted to life in the desert." "But even this one can't completely manage without water's life-giving powers." "A camel can drink 120 litres at a single sitting." "And all this water contains molecules already drunk by many other animals, over hundreds of millions of years of evolution." "Our world is a closed system like this glass it holds only a limited amount of water." "So what happens to a water droplet when it leaves the sea and evaporates into the sky?" "As the water vapour rises, it expands and cools." "It condenses around microscopic particles of dust or pollen, and a cloud is born." "As water droplets in the cloud collide, they swell and fall as rain." "The rain replenishes what was lost and the cycle begins again." "The water-cycle is like a roller-coaster ride a constant process of evaporation, condensation and precipitation." "In a cloud water can exist in all three forms:" "as liquid, vapour and as particles of ice." "As molecules shift from one form to another, the hydrogen bonds connecting them break and reconnect, sucking in or releasing energy." "And it's this rapid transfer of massive amounts of energy inside the cloud that whips up winds and fuels storms." "But this is only the beginning of a raindrop's epic journey from the clouds back to the sea... you're about to take the ultimate white water ride!" "Sometimes the roller coaster will slow and we can experience the effects water has on individual animals." "Then it will speed up again for the next ride." "So how does it all begin?" "Bizarrely, on a hot day most rain starts as ice." "Summer storm clouds are mostly made up of super-cooled water particles, and when one of these collides with an ice crystal floating in the cloud, it grows into a ball of ice - a hailstone." "Gravity takes over and it plummets to earth." "But many hailstones don't survive the trip they melt as they pass into the lower, warmer air and turn into large drops of rain." "Rather than being 'teardrop' shaped, falling raindrops look like burger buns." "They get distorted in the battle between surface tension and the air that's rushing past." "Exactly what happens to a water droplet next depends on where it falls." "It's a projectile packed with energy." "To a small insect, this is equivalent of an artillery bombardment." "In mountain areas, a storm can mean flash floods." "So how do tiny creatures deal with flooding?" "South American Fire ants are powerless to resist." "All they can do is link their legs together and go with the flow!" "Who knows where they'll end up!" "A torrent like this, pouring off the hills, can cut through solid granite." "In the space of 10 kilometres, it can reduce a granite rock 20cm across to a pebble just 2cm wide." "A further 10km downstream and there's nothing left but sand." "Given enough time, water power can carve up an entire landscape..." "Once water loses height and speed, the raging torrent slows into a gentle cruise..." "Now animals can take advantage of water in amazing ways." "The basilisk lizard is a water walker, but it must run to stay on top." "It gains extra lift by making air bubbles with its feet." "So did our rafting fire ants manage to ride out the storm?" "With queen and pupae safely in their midst, they can now let the water that has almost killed them float them gently in to shore." "Surface tension saved the day." "Once it's slowed down, water has a chance to soak away, and is sucked into living things." "0n the Earth ride we can follow water droplets and enter this inner world." "A tree is about two-thirds water same as you and water travels through it at amazing speeds, up to 60 metres per hour." "Plants need water for 'photosynthesis' they mix it with sunlight and carbon dioxide to make food." "Excess water is expelled as vapour." "From a leaf it's just a short ride for a water droplet to reach other forms of life, perhaps an animal..." "A monkey eats a juicy leaf... and Earth ride takes another turn!" "Trees make so much water vapour that large forests actually create their own weather." "Half the world's rain falls in just one place the Amazon basin in South America." "And 70% of that rain is expelled as vapour by the trees below." "Eventually each water droplet makes its way into the mighty Amazon river, which carries one fifth of the world's running fresh water." "The floodplain is the final fling in a droplet's trip back to the sea." "At last, this water cycle's over and each droplet finally returns to where it started out..." "An average water molecule will stay here for two thousand years or more... until one day it will evaporate and start its epic ride all over again." "By that time, ocean currents may have carried it to the other side of the world!" "Water covers more than two thirds of Earth's surface... only 30% is dry land." "And the amount of life that can exist on land depends on how much water is available." "Plants are the foundation of the food chain without water they can't grow." "They carry water up their roots by a process called capillary action." "Add a little water and the driest ground can spring to life." "Water provides mechanical support without it, a young plant soon wilts." "...but it's incredibly resilient... give it a little drink and it may live again." "Remarkably, one animal has evolved to transport water up its body by capillary action, just like plants." "In the Australian desert, this lizard - the thorny devil can drink from a puddle just by standing in it thanks to the bonds that hold the water molecules together." "The bonds are strong enough for water molecules to be pulled upwards, against gravity... they travel through canals in the thorny devil's skin, until they reach its mouth." "The amount of rainfall each part of the Earth receives limits what can survive there." "The drier it gets, the more the water cycle directly controls animals' lives." "Next, the Earth ride takes you to the places on the globe where the water cycle runs along a knife-edge... the driest spots on Earth." "Here on the East African Savannah, the water roller coaster is in trouble." "There are just two short rainy seasons, producing only about a metre of rainfall each year." "It's too little for trees to grow, instead this is a landscape dominated by grass." "And when the rains do come, it's a deluge!" "0n the face of it, a rainy season should be a good time for predators like this cheetah." "In a storm gazelles turn to face away from rain." "Their vision is blurred and their hearing muted, so they can't spot danger coming." "But in reality, rain causes problems for the hunter too..." "A sprinter, like this cheetah, likes it dry underfoot." "It's hard to corner on a slippery surface..." "This meal slips away." "In drier areas, it's sudden unexpected rainfall that brings far flung desert dwellers together." "A desert is defined as any place where less than half a metre of rain falls each year." "Precious puddles don't last long and these African sand grouse may have travelled up to 60km from their nests to find a drink." "But they have a dilemma... the adults drink their fill, but what about their chicks, who yet can't fly?" "The male grouse has an elegant solution and he keeps it close to his chest." "His breast feathers are four times more absorbent than blotting paper and he uses them to carry water home." "Back at the nest, his thirsty chicks strip his feathers dry." "Deserts are constantly shifting in size, according to subtle changes in the climate." "But over the past century, desertification has gone into overdrive." "Deserts now cover one fifth of Earth's land surface." "Chile's Atacama Desert is as dry as it gets." "There are places here where it has never rained." "For now, there's just no water left to ride." "These rolling dunes may be how we imagine deserts, but they're not always so hot, and not always made of sand." "In fact, the coldest place on earth is largely desert." "There is water in the Antarctic, but it's all locked up as ice." "So where does all this frozen water come from?" "When conditions are right, ice crystals form in the clouds." "They grow until they are heavy enough to fall as snowflakes." "All snowflakes are six-sided as every water molecule bonds to five others." "They come in a marvellous variety of shapes, but each one has the same basic hexagonal symmetry." "When blizzards fall on mountaintops, the snow compacts and forms the river of compressed ice that will become a glacier." "It takes thousands of years for a single ice crystal to travel the length of a large glacier." "But one day, it will be released either as melt-water or as part of an iceberg." "Today about a tenth of all land on Earth is blanketed by ice." "And ice, like liquid water, is unique." "It's strong enough to carve up bedrock, yet so light, it floats in water." "In fact, water is the only known substance to have a solid lighter than its liquid!" "And if it didn't, what would happen to the penguins?" "And never mind the penguins, if ice sank like other solids do, we wouldn't be here either!" "Life on Earth could never have evolved." "During the winter, seas would freeze solid... ice would reflect the sun's heat back into space and the planet would never have thawed out." "But why does ice float, and why does that prevent our seas from freezing?" "When frozen, water molecules form a rigid, six-sided structure that's less dense than liquid water." "There are gaps between the molecules that make them buoyant." "Water is most dense at around 4 degrees Celsius, the temperature underneath the ice." "So the sea remains unfrozen... and it's home to a spectacular array of life." "But at these extreme outposts of the water ride, penguins and the other animals are particularly vulnerable." "If the roller coaster switches direction, the effects will be most dramatic at the poles." "And at no time in our history has the water cycle changed as rapidly and as dramatically as it is changing right now." "What's round the next bend in the Earth ride, no one knows!" "In recent years we humans have diverted vast amounts of water for our cities and our industry." "We've built some of our greatest cities close to water." "We use it for decoration and because we like its sound." "Water's fun!" "It helps us exercise and to keep clean!" "And to stay hydrated, we should drink at least two litres of it every day." "Since it started out as cosmic ice drifting in outer space, this water's travelled a long way to get to you!" "Strange then that we should take it so for granted!" "But can we - or should we control the water roller coaster, or are we on track for trouble?" "Our manipulation of the water cycle can have surprising consequences." "By building giant dams, we can now store reserves of polar melt-water at lower latitudes." "But moving millions of tons of water across the world has had an astonishing effect... we've actually slowed down the Earth's rotation a day is now measurably longer than it was just half a century ago." "All this consumption raises one big question:" "are we taking more than our fair share of Earth's limited water supply and if so, where will it all end?" "Many factors could affect the water cycle over the next century or so, but scientists predict the largest impact will come from the giant climate shift we know as global warming." "1998 was the warmest year on record, and in 2001 melt-water was discovered at the North Pole for the very first time." "Around the South pole, vast Antarctic ice shelves are also shrinking." "The impact of this climate change on both the poles is not yet clear." "But sea ice does seem to be disappearing." "And that could spell trouble for some animals, including the largest carnivore to walk the Earth today, the polar bear." "The polar bear relies on sea ice as a platform to hunt its favourite quarry, seals." "If sea ice disappears, then probably, so too will polar bears." "The bear is already skating on thin ice, and soon there might be no ice left at all." "At this point, no one can be sure which way the water roller coaster will go next." "Will there be more intense droughts, more flooding, more devastating storms?" "If there are, it's likely it will happen in our lifetime." "These changes to the water cycle could cause lasting damage:" "the sands of time really are running out." "The outcome is uncertain and the Earth ride isn't derailed yet." "And one thing's for sure, we'll be staying on board to the end of the line." "This is one ride you can't stop, slow down or get off!" "Every time we have a drink, we become the next stage in this never-ending roller coaster ride!" "We're linked to everywhere that water has already been to far-flung places and extraordinary plants and animals." "Water is unique and it drives every form of life on planet Earth." "It has allowed life to exist where there was none." "Water remains our most precious resource!" "Without it, there would be no planet, as we know it, and no magical, unending roller coaster ride of life." "Thank you for taking the Earth ride, goodbye."