"This lush sub-tropical island off the coast of Africa emerged from the Atlantic two million years ago." "Today La Palma rises over two kilometres out of the sea." "At its summit the rock suddenly falls away." "The middle of La Palma is a huge rocky chasm, shaped like a horseshoe." "This great natural amphitheatre was first investigated by geologists in the 19th-century." "They worked out it had once been a giant active volcano." "Half a million years ago there was a colossal cataclysm here." "The whole centre of the volcano, 200 cubic kilometres of rock, just collapsed into the sea." "This created a huge tidal wave that raced across the oceans leaving a trail of devastation halfway round the globe." "But events in Las Palma are just one example of the vast forces that are periodically unleashed by our planet and these are an inevitable part of the way it works." "In the course of this series we've seen just how dynamic our planet is." "The Earth's surface is in constant motion driven by its internal store of heat." "As continents collide they create great mountain ranges." "As mountains rise and fall they influence our climate and the climate shapes the life which inhabits the planet" "It's all this change which makes the Earth what it is." "With all this happening around us it's not surprising that to us the Earth seems a very special place, but just how special is it as a planet, and why is it the way that it is?" "To begin to understand what sets Earth apart scientists scientists need to find out how it was formed." "Clustered on La Palma's volcanic summit are some of Europe's most powerful telescopes." "Here astronomers are beginning to throw light on Earth's origins by looking out deep into space." "They now believe that our entire solar system, formed from the debris of dead stars just like the stellar systems they can see forming today." "The Hubble Space Telescope has observed many, many solar systems in the process of formation, last count about 140 and it doesn't seem that our solar system is unique in any sense whatsoever." "Solar systems, clouds of dust and gas in distinct phases of forming into solar systems." "Astronomers now think that solar systems form when those clouds of stellar debris collapse." "You've got clouds of dust and gas in space but those clouds don't collapse without something to help them." "One theory which is a very nice one which we've actually seen in practice is a supernova like supernova 1987 A where you get an enormous Shockwave from the supernova, from the explosion that slams into the S and slams into the, the cloud" "and that starts it contracting and the force of gravity takes over from there." "Here far out in space scientists are observing new solar systems condensing from Stardust, triggered by a nearby exploding star, just as ours was." "About 4'/2 billion years ago the cloud of Stardust and gas that was to become our solar system began to spin." "As gravity pulled the material into the centre, it heated up." "Suddenly the young sun ignited." "The lighter gas was swept far out into the solar system leaving heavier rocky material near the Sun which soon condensed to form rocky planets:" "Mars furthest from the Sun, then the Earth, then Venus." "At this stage was there anything to distinguish one from the others?" "They're very, very similar." "They've all got an iron core, they've all got lighter silicate stuff floating on top." "They seem very similar." "The Earth has exactly the same components as the, the Sun and all the other planets." "But from early on there was one thing which made Earth different from Venus and Mars." "It alone had a large satellite." "Visiting the Moon was the first step in unravelling the history of the inner planets." "17, you are go for orbit, go for orbit." "Dr. Harrison Schmitt is the only geologist to visit an alien world." "Get the comer and get that contact." "If I can't get it..." "While working on the Moon he looked back and saw how much our planet now differs from the others." "We were in a deep mountain valley, deeper than the Grand Canyon of the Colorado of the United States 7,000ft on either side." "We could see mountains rising above us brilliantly illuminated by a sun brighter than any desert sun that you can imagine, but the only real colour that we could see, other than the spacecraft and maybe your colleague wandering around in the distance" "was this beutiful blue and white marbled Earth with a desert beacon here and there that hung always over the same part of the mountain complex in a absolutely stark black background, that was something that one cannot really describe adequately," "it's something that everyone should have a chance to see for themselves." "Something must have happened to make Earth so different from its neighbours." "The Moon enabled scientists to investigate the solar system's distant past." "The Moon has given us a window into the early history of the Earth that we never really expected to have" "I don't think." "We hoped would, would be that way, but when we actually explored it we found we had this beautiful window into that early history, pitted and dusty in some respects, but still one that we could now understand better" "what kind of Earth we had three billion years ago and later." "The crust as it formed began to record on extraordinarily violent period of solar system history in which the debris left over from the formation of the solar system was impacting the Moon and the Earth at incredible rates." "The surface provided scientists with a sort of clock, the more meteorite impacts the older a surface was." "This was true not just on the Moon, but on all the inner planets." "Meteorite craters were to prove crucial in working out the history of Earth's planetary neighbours." "How Mars became a cold, dead world." "How Venus, beneath a permanent cloud cover, developed a surface temperature of molten lead and only on Earth are the conditions right for life." "But why should the Earth have developed so differently from the other rocky planets?" "As scientists continued to explore the solar system, answers to the problem are beginning to emerge from studies of our planetary neighbours " "Mars and Venus." "Mike Carr is an expert on Mars." "He noticed that some geological features on the surface of that planet looked surprisingly Earth-like and that led him to conclude that" "Mars was not always as cold and dry as it is today." "Very early in Mars history there was a, what we call, heavy bombardment where there were lots of meteorite, meteorites hitting Mars and we know we can see parts of Mars that have survived from that time." "We know from the number, I counted the number of craters." "When we look at the oldest terrains on Mars what we see are little river valleys all over the place and they, they appear to have formed by slow erosion of running water." "Well to have water at the surface you have to have warm, warm conditions." "It appears that early Mars was warm and wet and then it changed later." "Four billion years ago" "Mars was not unlike Earth." "The sky would have been full of clouds of water vapour." "From the clouds rain fell." "Streams and rivers formed eroding valleys." "But what kept the young Mars so warm and wet?" "Clues to that puzzle can also be found on the surface of Mars today." "The volcanoes on Mars are huge, absolutely huge." "The crust is stable the volcano sits over the source of the lava and just grows and grows for ever and there's nothing to erode it away and so you get, you get volcanoes of enormous size." "Well Olympus Mons, which is the highest volcano it is 84,000ft high." "It's 550 kilometres across." "It really is a huge volcano." "Olympus Mons is almost three times the height of Mount Everest and half the size of France." "It's the highest volcano in the solar system." "On Earth volcanoes produce a lot of gases, including carbon dioxide, which get added to the atmosphere and carbon dioxide has a decisive effect on the planet's surface temperature." "It's a so-called greenhouse gas acting like a thermal blanket keeping a planet warm." "So 4 billion years ago the huge Martian volcanoes must have been pumping out enough carbon dioxide to keep the planet's surface warm and wet." "But Mars today is dry with no sign of Mollison running water." "Something dramatic must have happened." "The explanation may lie in some mysterious valleys on Mars which Mike Carr thinks formed 500 million years later than the rivers, after the meteorite bombardment." "This whole area here formed after that time." "We know that just by counting all the, all the craters." "For example, this region over here happen to know is, has an age close to 3.5 billion." "It formed shortly after the end of that heavy bombardment." "Here were cliffs hundreds of metres high suggesting water erosion, but no sign of rivers." "They reminded him of a place called" "Dry Falls in America's north-west." "Mike Carr's satellite photographs of Mars show what the two sites have in common." "First there's evidence of deep erosion such as cut this valley here and we see that here." "We also see scour marks on the ground here and you can trace it all the way through here and just above the Dry Falls over here you can see the same scour marks that just go northward from Dry Falls" "so all the things that we see here on this map we also see here in this location." "The explanation for Dry Falls should provide some clues to what happened on Mars." "Geologists have worked out that Dry Falls were created when the last Ice Age ended 12,000 years ago." "As the climate gently recovered, a vast lake of melt water, as big as today's Great Lakes, formed behind a thick dam of ice." "When the dam finally broke the lake emptied, creating a cataclysmic flood." "The flow of water was greater than all the rivers of the world combined." "Enormous boulders and lumps of ice scoured the land." "Their force was so great at Dry Falls that the erosion formed cliffs like Niagara Falls." "This was briefly a giant waterfall." "Could something similar have happened on Mars?" "Mike Carr's Mars images also show evidence of a vast flood, but no sign of where the water came from." "If you follow this large valley here it ends up in a large depression full of rubble and the same we see all these depressions here full of rubble out of which come very large channels." "There's nothing flowing into them and so what must have happened is the water must have come out of the ground." "Somehow the water must have been trapped causing the pressure to build up." "One way of keeping the water under high pressure is by having a cap and the frozen ground is that cap, so temperatures on Mars when these large floods formed were probably very cold so you had a frozen layer" "at the surface half a kilometre to a kilometre thick." "Permafrost, permafrost and that prevented water leaking out onto the surface and it became kind of unstable, very much like an oil well and of course if you drill into an oil well the wa, the oil comes gushing out." "Here if a meteorite drilled through that permafrost the water comes gushing out in enormous, in enormous volumns." "So by 3 billion years ago" "Mars had already entered a permanent Ice Age." "Its water was locked up below the surface and was only occasionally released when a giant meteorite punched through the outer layer of permafrost." "Something must have turned Mars from a warm, wet planet into a frozen world." "There's one place on Earth which suggests how this happened." "Here, at Mono Lake in the desert of central California," "Mike Rampino believes there are clues to the events which took place on Mars." "Well this is a very unusual environment in today's world." "In fact it's, it's similar to the kinds of environments we probably saw on Mars 3'/2 billion years ago." "Mike Rampino suspects that the features around this extraordinary lake show what happened to the blanket of greenhouse gas which once kept Mars warm." "It turns out that the key to that question can be seen in these rocks here at Mono Lake." "These rocks are solid rock, but they contain a gas, carbon dioxide, and if we drop a small piece of this rock in acid it will bubble." "The bubbles coming out of the rock are carbon dioxide." "The carbon dioxide in the rocks here has been drawn out of the Earth's atmosphere." "What's happening here at Mono Lake is very similar to what happened on Mars 3º% billion years ago." "These rocks are here because rainwater picks up carbon dioxide from the atmosphere forming a weak acid which begins to dissolve away the granite rocks of the mountains, washing the mineral material and the carbon dioxide into the lake waters." "As carbon dioxide is washed from the atmosphere into the lake, conditions are set up for a chemical reaction that traps it into newly formed rocks." "When that material gets there it's concentrated by the evaporation of the water in this very dry environment." "Eventually the material in Mono Lake produces deposits that form those strange rock formations we were looking at and trap the carbon dioxide." "The water flowing into the lake emerges as bubbling springs where you can actually watch this this process in action." "We can see right here the spring water coming up and combining with the lake water and that's where you get the deposition of the carbonate trapping rock that forms around the lake and we see the formation of the minerals" "that make up these strange rocks at Mono Lake." "Now imagine this going on on a planetary scale in the early history of the solar system, on the Earth or on Mars." "Bodies of water like Mono Lake maybe even larger where this process of formation of limestone is taking place trapping carbon dioxide from the atmosphere and taking the carbon dioxide out of the atmosphere permanently in some cases." "When Mollison was young the carbon dioxide being locked up in its rocks would have been replaced by gas erupting from the huge volcanoes." "But it's clear that eventually this volcanic activity ceased." "One can look at the volcanoes on Mars from orbit and see impact craters on the surface of those volcanoes, ancient impact craters." "It shows that that surface had been sitting there for a billion years without any new flows of lava covering it up." "Mars is much smaller than Earth and its internal store of heat powering the volcanoes was quickly reduced." "Eventually the volcanic activity stopped and all of the carbon dioxide in the atmosphere, or almost all of it, was removed from the Martian atmosphere by this process." "Because its greenhouse atmosphere was soon locked up in its rocks," "Mars quickly froze and it remains frozen to this day." "What about Venus, its surface a mystery beneath the layer of clouds?" "In the 1980s the Russians pulled off an amazing feat of space exploration." "They actually managed to land a probe on the scorching surface of Venus." "Before it burnt up, it sent back this one extraordinary image, looking just like volcanic lava on Earth." "In the 1990s" "NASA's satellite Magellan penetrated the clouds with radar and mapped the entire surface." "The images were clearly of volcanoes." "Suddenly Venus began to appear like parts of Earth, only hotter." "The Magellan mission also provided important information about the types of vulcanism on Venus." "One of the chief scientists was Ellen Stofan." "This Earth volcanic landscape is really fairly similar to what we would see on Venus, but there are some differences." "For example, here we have the products of what's called an effusive eruption where you start getting hot magma that's driven out of the volcano by a lot of gas." "Those red blobs that cool as they come down and they form these, these little pieces of lava." "So these would be the glowing hot pieces and as they fall they cool and turn into this feature which is a cinder cone." "But cinder cones, so common here on La Palma, are rare on Venus." "On Venus we're going to get less of that because of that high, high pressure you're just more likely to get lava lows, so you're going to see a landscape that in a sense is more similar to this sort of eruption" "where you're just getting a lava flow coming out." "On Venus though one of the interesting things are is a lot of the lava flows are extremely smooth and again it's because of this high temperature and this high pressure." "They're so smooth it's more, almost comparable to a parking lot." "Venus's surface is lava flattened by an incredibly high pressure." "The pressure comes from an atmosphere crammed full of carbon dioxide." "What does this mean?" "Clues come from the earliest history of Venus." "It's the same size as Earth, so it wouldn't cool down as quickly as the smaller Mars did." "At about 3º%. billion years ago at the end of this early bombardment that had taken place," "Venus and the Earth are not that different, their atmospheres are very similar at this point, but there is a significant difference." "Venus is closer to the Sun and it's warmer." "It's actually warmer than it is right now on Earth." "Water instead of being a liquid on the surface is right at the point where it's wanting to be a gas, it's wanting to form water vapour in the atmosphere." "Meanwhile you have volcanoes all over the planet and they're not only producing nice volcanic flows all over the place, they're also pumping a lot of gas into into the atmosphere:" "carbon dioxide, silicon dioxide, so you have gases building up in the atmosphere." "Water vapour and carbon dioxide are both a type of gas that if they're in the atmosphere they start to keep the heat from the Sun in, they're not letting the heat escape." "Now that carbon dioxide has nowhere to go, so it just keeps building up and building up and building up in the atmosphere and that starts to cause the surface to warm up so the surface starts warming up and warming up and warming up." "Ellen Stofan believes that as Venus got hotter its climate became unstable." "It goes back to the Whole water question." "Water actually helps to remove carbon dioxide from the atmosphere." "On Venus again the problem is it's just a little too - warm." "There's not that liquid water that's wearing down the rocks." "This whole chemical reaction just isn't taking place, so there's no way to get the carbon dioxide out of the atmosphere." "The carbon dioxide's building up, building up, building up, it's not being fixed into rocks and that's where this runaway greenhouse comes from." "Those processes ran away, the surface heated up and heated up and heated up till it's 500 degrees Centigrade on the surface." "Then it all started at that point when Venus was just a little bit too close to the Sun, a little bit too warm and you end up with the Venus we have now." "Without the ability to bring the carbon dioxide out of the atmosphere, the planet ran away, and that's why it's so hot there today." "The Magellan radar images were put together to form this computerised flyover of Venus." "They show a surface locked into a temperature of nearly 500 degrees." "So the climates of both Earth's neighbours have changed dramatically since they were young and are now at opposite extremes." "By contrast what seems to make the Earth so special is its extraordinary climatic stability over a long period of time." "For example, there's been liquid water on the surface of the planet for nearly 4 billion years and yet we know our dynamic planet is itself anything but stable." "It's constantly changing and evolving." "Is it possible that this constant geological change may even be responsible for the Earth's climatic stability?" "Earth's surface is made up of a few large rocky plates, their edges marked by chains of volcanoes, earthquakes and mountain ranges." "This moving system of rocky plates, called plate tectonics, is fundamental to the functioning of our planet." "It was natural to assume that Venus had a similar system." "As on Earth, the inner heat powering its volcanoes could also drive a system of moving plates." "The Magellan radar camera should have enabled Ellen Stofan's team to detect these plates." "When we looked at the Magellan data of Venus one of the first things we wanted to understand was where the volcanoes, where the faults." "We had a reason for wanting to do this." "When you look at the Earth the whole surface of the Earth is broken up into plates." "It turns out that most geologic activit on the Earth is concentrated at plate boundaries, things like volcanoes, faults, that's where the big earthquakes are, that's where the big eruptions occur, so when we had this Magellan" "global data set of Venus we started mapping out volcanoes, faults, trying to figure out where they all were, looking for patterns and we really haven't found any, and that's really telling us that there are no plates on Venus." "The fact that the Earth has plates on its surface is really critical to how the whole planet operates and since the two planets are so similar and want to know why they went down these different paths." "And then it began to emerge how this unique movement of rocky plates might maintain the climatic stability of Earth." "As they move, one plate can slide beneath another." "This process subduction - buries rock beneath the surface." "Some rock melts and erupts out of volcanoes back onto the surface." "This recycles the rocks." "The circulation of rocks is what links climate with plate tectonics." "There are processes on the Earth, geological processes that take the rocks that form on the surface, that lock up the carbon dioxide, push it down to depth inside the Earth." "Those rocks are heated up and the carbon dioxide is released back through the volcanoes." "There's a cycling of the carbon dioxide in the Earth." "It takes place because the Earth is an active, geologically active planet and has been so for the past 4'/2 billion years." "So on Earth volcanoes pump carbon dioxide into the atmosphere, as they do on Venus." "Rain dissolves the carbon dioxide, just as happened on Mars very early in its history and the carbon dioxide is trapped in rocks." "But on Earth most of that rock ends up on ocean floors." "Then it's subducted down as a slab burying the carbon." "The carbon dioxide erupts from volcanoes and so completes a cycle which stabilises the planet." "v This cycle happens only on Earth." "But why does Venus have no plate Mollison tectonics?" "The critical pointer was that it had no oceans where rocks on Earth get buried by subduction." "Subduction is really the key to the whole process of plate tectonics." "It turns out that if you calculate sort of all the forces of what's going on the pull of the slab as it sinks really helps he whole process of plate tectonics go as a system." "And for subduction to keep working it needs a lubricant." "And there's one thing that we know on Earth is we have plenty of water." "The water lowers the melting temperature of basalt makes it easier for the slab to subduct, really doesn't, as you say, it lubricates the whole process." "So water, it seems, is a vital part of plate tectonics on Earth." "Ever since our planet looked like this 31/2 billion years ago the carbon cycle driven by plate tectonics and by water has maintained a temperate climate" "but keeping this astonishing system going over billions of years has required another surprising factor." "For centuries the Paris Observatory has been a centre of research on the Earth's motion through the heavens, motion determined by the force of gravity." "Here, a gyroscope permits Jacques Laskar to demonstrate the way gravity affects the Earth as it spins on its axis." "Well the gyroscope can help us to understand the, the motion of the axis of the Earth." "You see if I put the gyroscope here without it rotating it will just fall down due to the, the gravity, but if I make it rotate now, if I just take it like that and if I, if I put it back" "and if I, it's rotating now instead of falling down it will just slowly ...slowly rotate like that then so its axis will slowly rotate." "In the case of the Earth is roughly the same thing." "The axis of the Earth is tilted and the, the Moon and the Sun are attracting this part to make it go back in the upright position but as with the gyroscope the resulting effect will be to make the axis" "of the Earth slowly rotate in a period of 26,000 year." "In fact if right now the, the axis of the Earth is in the direction of the, of the polar star, but if you were looking 2,000 years ago it would face another star and if, if you want to," "to make observations, star observation now when you want to relate them to observation which were made 50 years ago you need to take this slow motion into account." "This slow rotation of the Earth's axis is controlled mainly by the combined gravity of Sun and Moon, but the planets play a part too and that upsets Earth's stability." "In Jacques Laskar's computer are the orbits of the planets over millions of years." "These shifting orbits produce a fluctuating gravitational pull on the Earth." "They make the Earth's own tilt shift so the red circle drawn here by its axis changes in size." "Although small, these shifts have a major influence on climate." "As the Earth wobbles vast ice sheets wax and wane over much of the globe." "But without the Moon at the Earth's side, it seems these fluctuations could cause catastrophe, worse than any Ice Age." "Now here's the Moon." "You can take it away." "That's something which is difficult to do in reality, but on the computer simulation, ...it's quite easy, so you see I put them on R and the immediate effect you see immediately we are getting to much higher tilt." "You see how it's changing." "With the Moon's gravity removed the Earth comes much more under the influence of the other planets." "They cause chaos in the tilt of its axis and the red circle changes apparently unpredictably." "In reality, the Moon being so close and large, keeps the Earth's tilt within narrow limits." "If the Moon did go away Earth could tip to vertical." "The result would be no seasons and it could go to any degree of tilt, even almost horizontal." "At this angle one hemisphere would stay light for months, the other dark for months as the Earth moved round its annual orbit of the Sun." "Effectively a year would become a day with colossal effects on climate." "And events like this have happened to planets without big moons." "Mars wobbles all the time and Venus appears to have flipped upside down." "No-one can be sure, but Jacques Laskar's calculations suggest, fascinatingly, that the Moon's steadying influence has enabled the Earth's climate to remain stable." "But there's a final surprising twist to the complex story of our climate." "Something with the power to overwhelm the intricate system regulating the planet's temperature." "Astronomers have discovered that the Sun itself is not completely stable." "It's gradually heating up." "Today it burns 25º% more brightly than it did when the solar system was young." "This colossal change should have had an absolutely catastrophic effect on the Earth and yet it appears that our world has hardly been affected." "The evidence for this comes from Greenland where geologists have found the oldest rocks on the Earth's surface." "As it became clear in the very first programme of this series, these rocks paint a vivid picture of the planet nearly 4 billion years ago." "Among is this deposit of rounded pebbles in a muddy matrix, the remains of an ancient beach or shoreline." "This is unequivocal proof that then, as now, there was liquid water on the Earth, so despite the steady increase in the Sun's activity" "Earth's temperature has changed little in 4 billion years." "Something which controls the planetary climate must be reacting to the changing Sun so keeping the world cool, but what?" "The answer may lie here in one of the most famous of all landmarks:" "the white cliffs that look out over the English Channel." "This thick layer of white rock has enormous significance for global climate and has been a special interest of geologist Rory Mortimore." "It's an extraordinary deposit because it covered so much of the globe at a particular period in the Earth's history." "But it's not only the height of the cliffs which matters." "It's what they're made of: chalk." "There's something special about chalk." "It's not formed by a purely geological process." "It's made by living things." "It forms by a rain of plankton onto the seabed." "They die in cycles and they come through in blooms in the oceans so we have what 200 metres of chalk behind us on this magnificent cliff and in 200 metres of chalk if you took," "I don't know, perhaps every metre would be made up of many millions of cocaliths." "They are so small that we cannot see them with the naked eye and even with an ordinary light microscope they're almost impossible to see." "As these tiny organisms grow they use carbon dioxide from the atmosphere to build their shells." "When they die and sink to the sea floor these shells can become compressed to form chalk and other limestones." "They're locked into the shells of each of the cocaliths is a percentage of carbon dioxide so in limestones like chalk we have locked in vast amounts of carbon dioxide and we can give you an idea of just how much by looking at this core of chalk" "which weighs about 6 kilograms and locked into it we have about 1,300 litres of carbon dioxide and that is an enormous amount of carbon dioxide locked into the rocks." "Today almost all the carbon locked up in the rocks is found in deposits like limestone, chalk and coal made from living things." "In other words, on Earth today it's life that pulls carbon dioxide from the atmosphere, locks it up and keeps our planet cool." "So at some point in Earth history, possibly billions of years ago life must have taken over a key role in the carbon cycle which keeps the Earth's temperature stable." "And of course living things react to changes in sunlight." "Perhaps as the energy from the Sun increased life flourished drawing ever more carbon dioxide from the atmosphere." "That gradually lessened the greenhouse effect and so kept the Earth from overheating." "If life has played this crucial role in controlling the climate, we can perhaps begin to answer the question we started with:" "what makes our planet special is above all a unique partnership between the Earth and living things." "That partnership can be seen in miniature here in La Palma." "At its heart lies the planet's interior energy which drives plate tectonics and the Earth's vulcanism." "On La Palma they've grown accustomed to regular volcanic eruptions and lava flows." "This was a river of lava which flowed out of the volcano on June 24th 1949." "It came down the mountainside, passed close to a village and went straight into the sea." "Throughout Earth history geological upheavals like these have been one of the driving forces of evolution." "Living things today are the descendant of those that survived the many cataclysms unleashed by the planet." "Like the pine trees on La Palma's volcanic slopes whose insulating bark enables them to survive the fires triggered by volcanic eruptions." "It's a remarkable thought that the planet's activity shapes life, but perhaps even more astonishing is that through the carbon cycle life plays a major role in maintaining the Earth's activity." "Whole hillsides of bananas on La Palma are also part of the planet's carbon cycle which began here with gases released in the last volcanic eruption." "Some of the carbon dioxide which came out of the volcano about 30 years ago is now fixed in these bananas and if they are eaten some of that carbon dioxide will then be breathed out." "Rainwater may dissolve it and it will end up in the ocean where living things will use it to make their shells shells which may eventually form new rock deep on the ocean floor." "From there it will, in time, be subducted and perhaps 100 million years from now the carbon dioxide will be erupted again from a volcano to complete this remarkable cycle." "For millions of years this partnership has controlled the level of carbon dioxide in our atmosphere keeping the Earth's climate in the narrow zone where water remains liquid neither freezing as on Mars, nor boiling away as on Venus." "In turn, liquid water has lubricated the motion of the plates and of course without it life would be impossible." "So every part of this astonishing system is essential." "Life to draw down the carbon dioxide the earth's activity to return it to the atmosphere and water to keep the whole cycle running." "Our world isn't just a rock spinning in space." "Instead it is n intricate system where change to one part affect all the other." "As living being we ourselves are part of that system." "Our won story inextricably tied to that of the Earth, our ancient astonishing living home."