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00:00Planet Earth. Four and a half billion years of evolution. It's all going to end.
00:18Titanic forces are already at work that will destroy the world as we know it.
00:30Scientific investigators take us on an epic journey into the future of the Earth,
00:41where apocalypses will wipe out all life and destroy our planet.
00:48This is the countdown to the end of the world.
01:00Seven and a half billion years from now, Earth will be consumed by fire and vaporized.
01:16But by then, it will be unrecognizable, a lifeless alien world.
01:27Long before its final moment, our planet could be struck by no less than seven great catastrophes.
01:33One by one, they will turn the jungles into deserts, reshape the continents, and boil away the oceans.
01:47Other disasters will destroy the atmosphere, annihilate the animals, and destroy every plant.
01:54These are just the catastrophes we can predict.
02:00And what of mankind?
02:03We could be the first to go.
02:05This is the story of the death of the Earth.
02:08The first threat to life on Earth comes from the heavens.
02:16Right now, a lump of rock and metal, six miles wide, traveling at 17 miles per second, could be headed our way.
02:25It could strike next week, next month, or next year.
02:30But whenever it does, there will be little we can do.
02:34We would have very little warning before that threat turns into an asteroid impact.
02:42Earth has always been in the firing line.
02:46It could happen tomorrow.
02:48It could be 100 million years from now.
02:51But it's not a matter of if, it's when.
02:55300 million miles out from the Sun, beyond Mars is the asteroid belt.
03:00The rubble of a planet that never formed.
03:04750,000 massive lumps of rock, more than a half a mile across.
03:10It's an inexhaustible source of planetary ammunition that gets knocked out of the belt and sent spinning across space.
03:23NASA astronomer Professor Don Brownlee knows a lot about asteroids.
03:27The record of the devastation they bring is hard to miss.
03:34Just look at the moon in the night. You see it's covered with craters. Huge craters.
03:39Impacts that happened to all the planets that have happened for billions of years throughout our history.
03:45So this will happen.
03:47It already has.
03:5065 million years ago, an asteroid six miles wide slams into the Earth.
03:58The impact throws up millions of tons of rock thousands of feet into the air, fusing sand into glass in a split second.
04:10This one impact wipes out the dinosaurs, a species that had endured for 160 million years.
04:21So what are the odds of this kind of asteroid strike happening today?
04:26Using the visible impact record on the moon and planets like Mars and Mercury, Brownlee has come up with an answer.
04:33The frequency of impact of a 10-kilometer object from space, a comet or an asteroid, of the kind that wiped out the dinosaurs 65 million years ago,
04:46is on the average about one every 100 million years.
04:49When it strikes, it instantly vaporizes every living thing for miles around.
04:59The sheer force of the impact buckles and cracks the Earth's crust, creating powerful earthquakes.
05:06The force of the winds whips up waves, pushing powerful tsunamis onto the land.
05:12Within a few days, the dust cloud blocks the Sun, plunging the planet into freezing darkness.
05:21An endless winter that would last for more than a year.
05:27Hidden within the dust is something far worse.
05:31A sudden overdose of nitric oxide destroys 85% of the ozone layer.
05:36As the dust finally settles, the lack of ozone allows damaging ultraviolet rays to reach the surface,
05:44harming billions of people and killing plants and animals with lethal doses of radiation.
05:51By the end of that first year, at least 70% of all life would have been destroyed.
05:57Those that live underground or hibernate stand a better chance.
06:00This is what killed the dinosaurs.
06:04And one day, the same thing could happen to us.
06:09Not knowing when the next asteroid will strike makes planning difficult.
06:16And worrying pointless.
06:21There is worse to come.
06:24Even if we could plan for the next catastrophe, it won't make any difference.
06:32Ice sheets several miles deep, pushing down from the poles, will be unstoppable.
06:39A global ice age is coming.
06:44How do we know?
06:46It has happened before.
06:47And one of the first clues was pulled from the La Brea tar pits.
06:53To find an ice-loving woolly mammoth was a big surprise.
07:00To find it in the heat of California was a mystery.
07:04Could California have once been covered in ice?
07:09Could it happen again?
07:11To find out, scientists need a record of changes in the climate, stretching back tens of thousands of years.
07:22It turns up in the layers of sediment at the bottom of the ocean.
07:28Marine geologist Professor Peter Domenical is searching for clues to Earth's frozen past.
07:33Deep sea sediments are really unique archives of past climate change because the sediments in the ocean accumulate very continuously and very slowly over time.
07:48So they present us with this kind of history book of past climate change.
07:52These tiny chunks of rock in the sediment hold the answer to the USA's frozen past and to its future.
07:59Deposited 10,000 years ago, how they got here is astonishing.
08:05Icebergs carry all these rocks and they hold them inside the iceberg and then they melt.
08:10As the iceberg melts, it drops its load.
08:12And that's how we find these big pebbles out in the middle of the ocean.
08:19Icebergs once floated off the coast.
08:22As the bergs melted, the rocks they carried from the north sank to the sea floor.
08:2610,000 years ago, much of North America is in the grip of an ice age.
08:33But what causes a big freeze?
08:36The answer isn't found beneath the geologists' feet, but over their heads in outer space.
08:42The earth orbits the sun in an ellipse that gradually changes shape over time.
08:55The tilt of the earth to the sun also changes.
08:59Calculations suggested that the interaction of these changes could flip the climate from warm to cold and back again.
09:10It's called the Milankovitch cycle, after the man who discovered it.
09:15His orbital calculations showed that the earth flipped from ice age to warmth 10,000 years ago.
09:23The exact age of the sediments Domenical has found.
09:26It was shocking when the evidence came out that there was this very close correspondence between the astronomical calculations and then really the geologic record.
09:37People were just blown away.
09:38But what about the future?
09:43The orbital effect is called the Milankovitch cycle because it happens over and over again.
09:50We're well on our way, actually, into the next ice age.
09:56That's something most people don't really fully appreciate.
10:00The climate was significantly warmer 5,000 and 10,000 years ago.
10:04And then we've been gradually headed into this much cooler climate.
10:08Domenical believes the earth will be plunged into another global ice age within 30,000 years.
10:19If the last one is anything to go by, the next will be worse.
10:24Because in the last ice age, there were just five million humans.
10:29Now, there are six billion.
10:35Could we all survive?
10:40Ice sheets two miles thick could cover the land.
10:45Cities like London and New York may be buried beneath thousands of feet of ice.
10:50Global sea levels could drop 400 feet as water is locked up in ice.
11:00Freezing temperatures might last 100,000 years.
11:06The food chain collapses.
11:08Plants die as they are smothered by ice.
11:11Herbivores can no longer find food and die out.
11:14As civilization collapses and food and shelter become scarce, our base survival instincts kick in.
11:29Dr. Erwin Redliner at Columbia University is an expert in how humans react to catastrophic events.
11:36The bad news is, many won't make it.
11:40The major challenges will be to how to keep ourselves from killing each other because of a natural event like a new ice age.
11:51Enormous migrations of people trying to escape from the extreme conditions have the potential of causing a tremendous amount of deadly competition for resources, for food, for water, for power.
12:06Billions of people could perish, as vast areas of available land are swallowed by ice.
12:16But many humans will survive the big freeze in belts of green north and south of the equator.
12:23Here agriculture will continue, but not enough to support the billions who will now begin a battle to control it.
12:29I think we are hardwired on a genetic DNA level to seek survival at almost any cost.
12:39And I think there's pretty good examples of that.
12:42People who were prisoners of war and people lost in hostile environments.
12:49In a few green areas, humans will survive, but the population will be greatly reduced.
12:55Civilization as we know it will change forever.
13:03And the next ice age is unlikely to be the last.
13:07The great ice sheets will continue to advance and retreat, devastating life and civilizations.
13:13250 million years in the future, it gets worse.
13:21Life will face an even greater threat and be pushed to the very brink of extinction.
13:27The seas will die and the land will become desert.
13:30250 million years in the future, having survived ice ages and perhaps even asteroid strikes.
13:47There now comes an even greater threat.
13:50The surface of the planet is completely unrecognizable.
13:53Life is being pushed to the brink of extinction.
14:04This terrifying vision of the future is caused by the same powerful forces that shape the Earth today.
14:10Plate tectonics was one of the two major scientific advances of the 20th century.
14:17It allowed us to get an understanding that the Earth is really much more dynamic than we ever suspected.
14:24It reveals that the Earth's surface is made up of a series of massive continental plates that are in constant motion.
14:32Where they collide, huge mountains are driven up and massive volcanoes pour out liquid rock.
14:43It shapes the face of our planet.
14:53Armed with this new information, the geological record opened up like a book,
14:58revealing that 250 million years ago, all the continents were united to form a single supercontinent we call Pangaea.
15:08This was a hot, brutal world ruled by dinosaurs.
15:13Could future movement of the tectonic plates transform the Earth once again into a single vast land mass?
15:21We now know how the plates are moving far more accurately than ever before.
15:25And so it became tempting to look into how this might develop if we projected these motions a few million years into the future.
15:37According to Livermore's model, 250 million years in the future, a new supercontinent will form.
15:45Africa plows into the Middle East as Antarctica and Australia fuse together.
15:51One vast land mass surrounded by a giant ocean.
15:57We end up with a supercontinent which is primarily in the northern hemisphere and a southern hemisphere which is mainly ocean.
16:07This will give us a range of habitats within the supercontinent quite different from anything that we see at the present time.
16:13With much of the land hundreds or thousands of miles from the ocean, rainfall becomes non-existent.
16:24No plants grow and as the land absorbs the heat, temperatures soar.
16:30It turns to desert.
16:31If we were looking down on the future supercontinent, what we are likely to see is something really rather like the interior of Australia.
16:40250 million years in the future, this new world will be mostly desert, covering over half of the land.
16:53So hot and dry that few plants or animals survive.
16:5680% of the species we see today could be wiped out.
17:02Those that do survive will have to adapt to less water, less food and rising heat.
17:09Our distant descendants might try to take refuge in the coastal regions.
17:14But even here, there's no escaping the dangers of this new world.
17:21Around the edges here, we're probably going to see continuing volcanism, continuing earthquakes.
17:27The tectonic forces that pushed the supercontinent together are still at work.
17:33Now they begin to buckle and split the land at its weakest points.
17:40The result is massive earthquakes.
17:45Lava exploits these new cracks and bursts out, forming chains of volcanoes.
17:53Molten rock spreads over thousands of miles, incinerating every living thing in its path.
18:00Life on the land will be tough beyond our imagination, causing mass extinctions.
18:06But this is nothing compared with the devastation facing life in the new superocean.
18:17In 250 million years, a single supercontinent will dominate the face of planet Earth.
18:28It has happened before.
18:32By exploring what happened back then, we now know that this single land mass could have a devastating effect on the oceans in the future.
18:42A lethal dose of carbon dioxide may cause a mass extinction, which could wipe out 96% of life in the sea.
18:51But where will this killer carbon dioxide come from?
19:04The biggest natural CO2 producers on the planet are well known, and the supercontinent of the future will have plenty of them.
19:12Volcanoes.
19:14To understand how the carbon dioxide from volcanoes leads to mass extinction in the oceans,
19:22Dr. James Barry has been studying what happens to one particular creature called a brachiopod during similar events.
19:28Oceans became much more acid due to all the CO2 that was released by volcanic ash in over 100,000 years.
19:39And that increased acidity of the ocean has caused not only brachiopods, but many other types of animal life to go extinct.
19:46Dr. Barry is trying to understand exactly what happens when carbon dioxide levels suddenly shoot up.
19:54Among the first to feel it are shellfish.
19:58These brachiopods are a curiosity.
20:01They're one of the earliest sort of real animal life forms that evolved on this planet.
20:06400 million years ago, they were one of the most dominant forms of life on the planet.
20:11But they went from 30,000 species down to about 300.
20:14They're the poster child for how to go extinct.
20:18Brachiopods had survived everything the Earth could throw at them for hundreds of millions of years.
20:25Yet it was volcanic eruptions on land that wiped out 99% of brachiopod species in the sea.
20:34Barry's research reveals how.
20:37Brachiopods are highly sensitive to carbon dioxide levels.
20:40The excess CO2 from volcanoes dissolves in the water, making it acidic.
20:47Once it enters the ocean, it combines and reacts with seawater to form carbonic acid.
20:54And that changes the balance of chemistry in the ocean.
20:59As the sea becomes more acidic, the brachiopods die out.
21:03In 250 million years, the hard shells of all marine invertebrates dissolve in the acidic water.
21:13As their inhabitants die, a big link in the food chain collapses.
21:17Their predators starve.
21:20And the lack of food goes right to the top of the chain.
21:24At the same time as the food chain is collapsing, another brutal consequence of a single supercontinent will be reaching its endgame.
21:4180% of marine species live close to the coastline.
21:49With all the land locked up, there's less coast to go around.
21:53Competition for the prime real estate gets fierce.
21:57The coastline of the future supercontinent could be 70% less than it is today.
22:02So the next supercontinent will be deadly.
22:10In 250 million years, an arid desert on land and an acid ocean means a mass extinction that will make the death of the dinosaurs look like a sideshow.
22:21But amazingly, some plants, some animals will survive.
22:29Those that can adapt.
22:31Creatures like snakes.
22:33And spiders that thrive in the heat.
22:40Low hardy bushes and types of captai may be able to evolve.
22:46Life will endure for a billion years to come.
22:49It's only then that the final extinction of life on our planet begins.
22:55The end of all life on land.
23:00A billion years in the future, the world is going to get hotter.
23:05All stars, like our sun, go through a cycle of life and death.
23:10Today the sun is middle-aged.
23:13But in a billion years, it will be that much closer to death.
23:16As it burns through the remainder of its fuel, internal processes will cause it to expand, bringing its surface ever closer to the earth.
23:25The temperature will soar.
23:28It is now 86 degrees and climbing.
23:37For mankind, another 18 degrees higher, and we will have reached our physical limit.
23:43Blood thickens. Strokes and organ failure follows.
23:46Sometime in the next billion years, humanity will cease to function.
23:52At this point, we will have disappeared forever from the face of the earth.
23:57But other kinds of life will be able to survive.
24:01Here at the California Academy of Sciences, Professor Lynn Rothschild searches the history of past extinctions for examples of what creatures might be able to survive in a world twice as hot as today.
24:17What I'm holding here is an ammonite, and these were an extremely successful group of invertebrates.
24:27They were wonderful predators, and they went extinct at the end of the Cretaceous.
24:31Not their fault. They were wonderful at the time, but they went.
24:34As the sun expands and the world heats up, it all comes down to luck.
24:41If you happen just by chance to be better suited to the new world, you'll make it.
24:46If not, it's just bad luck.
24:49And in the brutally hot future earth, we already have a fair idea who's going to be lucky.
24:55We see animals like scorpions, like we have here, spiders, maybe some snakes that come out at night.
25:05And these are so well adapted to living in these hot, dry environments because they prevent water loss.
25:12They do everything they can to keep water inside their bodies.
25:16They stay nocturnal.
25:18Only the most extreme adaptations can survive.
25:21But as conditions become worse, life on land heads toward its final moments.
25:28It begins with the plants.
25:31Atmospheric scientist Professor James Casting is one of only a few people in the world to have figured out what happens to the plants in a billion years from now.
25:43He's discovered that a drastic fall in CO2 will wipe most of them out.
25:49CO2 will drop by a factor of a half.
25:54That will wipe out 95% of the plants on earth.
25:59Geological processes are at work today that absorb carbon dioxide and dump it in deep ocean sediments.
26:09But like all chemical processes, the higher the temperature, the faster it works.
26:14Supercharged by the hot earth a billion years from now, it wipes carbon dioxide from the atmosphere.
26:23It will drop down below the level required to sustain plant life.
26:29And that's the fundamental food source on earth. I mean, carbon dioxide is the food of life.
26:34It's what makes photosynthesis work. And with CO2 gone, it's a very different world.
26:40Deprived of CO2, plant life suffocates and dies.
26:46The last remnants of our green earth turns brown and dead.
26:51One vast desert covers the land.
26:56It's really hard to imagine a future without any plants.
27:00I guess the best way to imagine it is to go up into the desert.
27:03In a way, it's a very beautiful environment, but it is very barren and it doesn't seem like home.
27:07Without plants, the food chain collapses. The plant eaters starve and their predators follow.
27:17Animals, insects, reptiles and mammals.
27:21For life on land, everyone's luck has finally run out.
27:26There is only now one place on the entire planet that does continue to support life.
27:31The oceans.
27:35If you think about why life both originated in the ocean and probably will be forced back into the ocean in the future,
27:43it's because the ocean is far more stable than land.
27:46If you go out into the desert in the middle of any continent here,
27:51the summers are sweltering and the winters are frozen.
27:55During that same yearly cycle, the temperature right offshore here
27:58nearly stays the same year round.
28:06But a billion years in the future, as the dying sun swells and the temperatures rise,
28:13the oceans begin to evaporate.
28:15As the water level drops, they become more and more salty.
28:19To understand what the oceans of the future will be like,
28:23Professor Rothschild has come to these salt ponds outside San Francisco,
28:29where seawater is evaporated to produce salt.
28:32What happens here, and you'd imagine what happened on the Earth,
28:35is that as the concentration of salt goes up, up, up, many of the organisms that we're familiar with,
28:41fish and kelp and algae and manta rays and so on, drop out.
28:45It is the end for life in the oceans as we know it.
28:51Whales, dolphins, jellyfish, coral reefs, pretty much everything.
28:58All gone, unable to survive in the increasing saltiness of the water.
29:03And at some point, you're left with brine flies, a few little worms, and some of the microbes that you see here.
29:14And at the very highest salt concentrations, about ten times the salinity of the ocean,
29:20you only end up with organisms called halophile.
29:23It is the halophiles, tiny organisms, that thrive in high salt environments,
29:28that give the water its red color. This color is no accident.
29:33Now, during the summer, we tend to get tanned.
29:36I've been in the pool, I look a little tanner than I would in the winter.
29:40Well, these organisms also have to protect themselves from a very strong sun, ultraviolet radiation.
29:46And so, instead of tanning, they tend to produce a lot of red pigments, carotenoids.
29:50These are the same kind of compounds that you see in tomatoes and carrots and so on.
29:54And this orangey-red pigment helps protect these organisms from the very high sunlight.
30:01With a blazing sun filling the sky and temperatures rising,
30:06only these incredible survivors called extremophiles can take it.
30:141.2 billion years from now, all other life is gone.
30:18As the Earth becomes a very hostile place, we're back to having a world that's only populated by microbes,
30:30very much the way it was during the early evolution of life on Earth.
30:34Extremophiles clinging on at the ragged edge of survival in the last remnants of the ocean.
30:40The final hammer blow that will end all life is now just around the corner.
30:511.2 billion years from now, plants and animals have been wiped from the surface of the Earth.
30:56Only microbial extremophiles survive in a rapidly evaporating, increasingly salty ocean.
31:03For the oceans, time has finally run out.
31:07The brightness of the expanding sun boosts average global temperatures to a blistering 100 degrees,
31:14nearly double than today.
31:16Professor James Casting is investigating the devastating effect this has on the oceans of the future.
31:22Well, we think that the Earth will start to lose its oceans when the sun gets about 10% brighter than it is today.
31:31His findings confirm evidence gathered by Apollo astronauts in 1972.
31:37Hydrogen is escaping from the Earth.
31:40Water is made up of one part oxygen and two parts hydrogen.
31:44So what the astronauts were seeing was the infinitesimal loss of the oceans into space.
31:51Today, this amount is nothing serious.
31:54But 1.2 billion years in the future, when the temperature is 100 degrees, the process goes into overdrive.
32:02Faster evaporation now saturates the air with water.
32:06As this water rises to the top of the atmosphere, ultraviolet light from the sun splits it into its two component parts, oxygen and hydrogen.
32:17The hydrogen is so light, it floats off into space, lost forever.
32:22What Casting discovered was that from full to empty, the whole process of losing our oceans could take less than 200 million years.
32:35Without water, life cannot exist.
32:38So to find out when this will happen, he had to look at a planet not unlike the Earth that lost its oceans in the same way.
32:45Well, I got interested in the future of Earth's oceans by working on, not on Earth, but on Venus.
32:56Physically, Venus is almost a twin of our planet.
33:00And billions of years ago, it might have been even more similar.
33:06May well have had liquid water on its surface at one time, just as the Earth does now.
33:11But it was too close to the sun, it lost that water by what we call a runaway greenhouse.
33:18It's likely, in my opinion, that Earth will follow the path of Venus at some point in the future.
33:25Studying Venus helped Casting estimate when we will start to lose our oceans.
33:31The answer came as a shock.
33:35Well, up until we had worked on this problem,
33:37many scientists thought that the Earth would retain its oceans for at least another 3 or 4 billion years.
33:43But we were able to show that bad things start to happen much earlier than that.
33:49The oceans could be lost in 1.2 billion years.
33:53With the water gone, dry salt crusts like these are all that will remain of the Earth's magnificent oceans.
34:01Is this the end for life?
34:05Incredibly, a new discovery has shown that even without water, basic life forms can survive.
34:14But for how long?
34:16Although we'd known that organisms could live in very high salt,
34:20we knew that they could also be trapped in solid salt.
34:22But what we didn't know is that while they're in the solid salt,
34:25it's more than them being in suspended animation,
34:28that they are actually still metabolically active.
34:32They're still breathing and eating and excreting and doing all the sorts of things they need to do,
34:40but at a very, very, very slow rate.
34:42So that was really an astounding discovery for us.
34:46In 1.4 billion years, with the oceans finally gone,
34:51extremophiles will survive in the solid salt, but just barely.
34:56These organisms will be able to survive a good deal longer in a salt crust like this,
35:01even in the absence of water.
35:03They won't be able to survive forever like that, but it'll buy them a little time.
35:07Perhaps another few million years.
35:09In that time, their main protection will be the red color that acts as a sunblock.
35:18While they live, they will transform the way our planet looks from space.
35:23People always think of the Earth as this beautiful blue planet,
35:27you know, the pale blue dot in the sky.
35:30But the fact is, for almost half of Earth's future history,
35:34it will be a Barbie planet.
35:36It will be covered with pink salt.
35:44This is the Earth, 1.4 billion years from now.
35:50The extremophiles cling on in an increasingly desperate fight,
35:55but the rising temperatures as the sun brightens eventually defeat them.
35:59By 1.6 billion years into the future, the temperature has climbed to 224 degrees,
36:10far above the boiling point of water.
36:13Life finally loses the battle.
36:16The last remaining extremophile dies.
36:18There are several poignant moments in geologic history.
36:24The Earth losing its oceans will be the most poignant of all,
36:28because that really will be the end of life as we know it.
36:35And unless we've figured out how to colonize other planets,
36:39then life will come to an end.
36:41That's a pretty sobering thought.
36:45The time of the pink Earth passes.
36:49Our planet is reduced to a brown, featureless world.
36:53Unless we have found a foothold on another,
36:56this is the end of life in our universe.
36:58For the next six billion years, our dead world orbits the dying sun.
37:09Only an astronomer can see this far into the future,
37:13to the Earth's final moment of existence.
37:17Dr. Robert Smith, from the University of Sussex,
37:20has unraveled the Earth's ultimate fate.
37:23But his journey of discovery has taken some unexpected twists and turns.
37:28The process begins as the dying sun continues to swell in size.
37:35The sun getting bigger will have severe consequences for the Earth,
37:41because we predict that the sun will get at least 200 times its present size.
37:50All stars go through a cycle of life and death.
37:52Astronomers know this because they can see stars that represent every stage of life that our sun will go through.
38:03In seven billion years, our sun will be close to death.
38:07The sun is now a thousand times brighter, 200 times its present size and still growing.
38:22The heat literally dissolves the face of the Earth, wiping away the last of its uniqueness.
38:28As the sun gets bigger early, mountains will start to melt.
38:35And instead of having high mountains and deep ocean depths, everything will flow into a uniform sphere.
38:44It will be featureless and very, very hot.
38:51Earth's surface is now melting in two and a half thousand degree heat.
38:55The surface runs with liquid metal.
38:59Our planet is utterly unrecognizable.
39:02A totally alien world.
39:04The end is now close.
39:07But Dr. Smith's calculations revealed a last minute escape might just be possible.
39:137.5 billion years in the future.
39:25The mountains and oceans have been erased from the Earth's surface.
39:29The temperature is over 2,500 degrees.
39:33It has been lifeless for six billion years.
39:36Now the Earth itself is about to die.
39:43At the heart of the dying sun, helium is reaching a critical stage.
39:50It's becoming so dense, its atoms so crowded, that the core is becoming explosively unstable.
39:57It now takes on its final form, a red giant, 256 times bigger than it is now.
40:07It fills the sky.
40:09First of all, you would see the size of the sun beginning to increase.
40:17It would get redder, it would get brighter.
40:18At the moment we're used to seeing it about the size of the full moon.
40:23Then it would get bigger and bigger, it would feel more and more of the sky.
40:28Until eventually when it would become a red giant, it would probably feel something like half the sky.
40:33As the sun burns up the last of its fuel, it expands outwards.
40:38Now almost 200 million miles in diameter and swallowing everything in its path.
40:47Is this the fate of planet Earth?
40:51When Dr. Smith first tried to find out, the figure showed that as the sun gets bigger, it loses its gravitational grip on the Earth.
40:59The chain is broken, and our planet drifts off into space, potentially escaping a fiery death.
41:10It seemed that Smith had saved the planet.
41:13It was a good feeling that we'd saved the Earth, and indeed some of the newspaper headlines said exactly that.
41:21But then one of Smith's colleagues took another look, and produced new calculations about the red giant.
41:27These seem to suggest a radically different picture.
41:35When we came to look at the calculations again, we realized that we'd missed something out.
41:41We realized that there was a missing effect which we had to take into account, and that's to do with tides.
41:49What they hadn't taken into account are the tidal effects of the Earth on the sun.
41:54The Earth's gravity will create a tidal bulge on the surface of the sun, in much the same way as the moon affects the rise of the ocean tides on Earth today.
42:07This bulge, in turn, creates a drag on the Earth, pulling it back towards the sun.
42:13Smith set to work, using the new data to find out just what would happen now.
42:20We didn't know what to expect when we first put in this additional effect.
42:25We hoped that even when we put in the tides, the Earth would still escape.
42:30Smith announced a very different set of results.
42:35The news was bad.
42:37The tidal effect chains the Earth to the sun.
42:40When we came to look at this problem again and put in the extra effects, and realized that the Earth would in fact not survive, we decided to call our paper Doomsday.
42:54The surface of the Earth is now nearly 2,500 degrees, hot enough to melt metal.
43:03The outer fringes of the sun reach out to engulf the Earth.
43:07We tried to imagine what it would look like to see the Earth disappearing.
43:24Just be like an asteroid crashing through this Earth's atmosphere.
43:29It will burn up completely.
43:31It will vaporize.
43:32It will disappear, become part of the sun, and it will be as if it has never been.
43:3712 billion years of planetary history ends.
43:42The death of planet Earth, engulfed in flame, vaporized by the sun, reduced to atoms.
44:07It's sort of dust to dust.
44:08But it's not such a bad fate, because those atoms, your atoms, your dog's atoms, your car's atoms, they go out into space, and what do they do?
44:17They end up forming new stars, new planets, and maybe even new people.
44:21It's a cruel act of fate, that life-giving stars will one day go bad.
44:28Big changes are coming.
44:31By understanding how Earth worked in the past, and how it works today, science is beginning to understand what the future may bring.
44:39The death of the Earth is already laid out in front of us.
44:45It's written into its geological past, and literally into the stars above us.
44:51альcy.
44:52RACE
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