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00:00We live in a violent universe.
00:08The universe constantly wants to kill us.
00:11Planets collide.
00:13The entire surface of the earth is liquefied.
00:15That was literally a vision of hell.
00:19Black holes blast out invisible death rays.
00:23It would be apocalyptic beyond apocalyptic.
00:27Planets strike without warning.
00:29It is a real possibility that it could happen in the next 10 minutes.
00:34These cosmic killers have struck time and again, wiping out entire species and pushing
00:40life on earth to the edge of oblivion.
00:43It's happened before, it's going to happen again.
00:46Our species could be next.
00:48There will be disasters in the future and one of them will destroy us.
00:57Not too hot, not too cold.
01:13With water, oxygen.
01:18Our peaceful, plentiful planet nurtures and protects us.
01:24But this lull won't last forever.
01:28There are dangers all around and trouble ahead.
01:32When we look around, we think that the universe is rather gentle.
01:36We have warm breezes and mild seasons.
01:38Actually, the universe is violent.
01:41It is chaotic.
01:43The universe is not a happy, safe place.
01:47There are asteroid impacts and solar flares and supernovae and black holes and colliding
01:51galaxies and all these really amazingly dangerous and violent events.
01:56And the earth is in the crosshairs.
02:05During the planet's four and a half billion year existence, these violent phenomena have
02:11wiped out millions of species in a series of catastrophic mass extinctions.
02:20Mass extinctions due to impacts and other geologic natural processes on the earth have
02:24actually wiped out more species of plants and animals on the planet than exist today.
02:33Mass extinctions are what happens.
02:35It just happens periodically.
02:37And we've lived in a quiet time between mass extinctions.
02:40It's happened before.
02:41It's going to happen again.
02:44The clock is ticking.
02:46With every day that passes, the next mass extinction gets a step closer.
02:52And with every new discovery, the universe gets a little bit more terrifying.
03:01November 2012, astronomers identify a new planet 100 light years from earth, at least
03:10four times more massive than Jupiter.
03:13And it's gone rogue.
03:18Unlike earth and all other objects in our solar system, this planet doesn't orbit a
03:24star.
03:25It really is lost in space.
03:29When I was a kid watching science fiction movies, every now and again there would be
03:32a rogue planet, just some planet wandering space without a star, and I thought that was
03:36pretty silly.
03:37But it turns out that might actually happen.
03:42When planets are forming, they can interact with each other gravitationally, and it's
03:45entirely possible that when our solar system formed, planets were kicked out into interstellar
03:50space.
03:53There could be as many as 200 billion rogue planets in our galaxy.
03:59That's as many rogue planets as there are stars in the sky.
04:03Just one of them could be heading our way.
04:11A collision with another planet sounds far-fetched.
04:16Could it really happen?
04:19In fact, it already has.
04:26Four and a half billion years ago, a young planet veers into the earth's orbit.
04:33We have the earth sitting here, and another planet about the size of Mars came in and
04:37smacked us hard.
04:41The two collide at over 25,000 miles an hour, 12 times faster than a bullet.
04:50The impact destroys the smaller planet.
04:53The earth survives, but only just.
04:57The violence of this is hard to imagine.
04:59Two planets coming together, smashing together into one molten mass.
05:04After an impact of that scale, the entire surface of the earth is literally liquefied.
05:09Imagine the floor of an active volcano with islands of solid rock and lava spurting right
05:13and left.
05:14The entire surface of the planet would have looked like that.
05:17The earth itself, for a little while, would have had an atmosphere of molten rock.
05:21It was like a vision of hell.
05:27Debris, blasted out at 25,000 miles an hour, orbits the molten earth.
05:38Gravity brings the debris together.
05:42The result is our moon.
05:48Our moon emerged from the wreckage of the most cataclysmic event in our planet's history.
05:55From destruction comes creation.
05:58Because without this lump of cosmic shrapnel, life on earth might never have gained a foothold.
06:06The moon's gravity pulls on the infant earth's oceans, spreading nutrients from the land
06:12into the water, and it slows the earth's spin from a 6 to a 24-hour day.
06:20In this calm, fertile environment, one billion years after the impact, life begins.
06:28If we hadn't had that planetary collision a long time ago, we wouldn't have the moon
06:32today.
06:33So, in fact, this most catastrophic event you can possibly think of actually may have
06:38helped life on earth form in the first place and helped us evolve over the next couple
06:44of billion years.
06:47What was a good thing in the past would be a disaster if it happened today.
06:53Now, you don't want a planetary collision now because that would wipe out the entire
06:57planet.
06:58You can't even describe it comparing them to nuclear weapons.
07:03It would be billions of nuclear weapons.
07:05It's enough to melt several miles thick crust on the earth all the way down.
07:11It would wipe out all life on earth.
07:12That would be it.
07:13It would be like a hard restart for the planet itself.
07:17Let this nightmare become a reality.
07:21Right now, even the closest rogue planets are still trillions of miles from earth.
07:28And our neighboring planets have settled into calm, stable orbits.
07:33We're not going to get a planetary collision anytime soon, but all the gravity of the planets
07:37play with each other and change each other's orbits.
07:39So clearly, if you run the clockwork of time forward billions of years, yes, it's entirely
07:45possible that we might have another planetary collision.
07:48You just don't have to worry about it for a long, long time.
07:54Four billion years ago, a devastating collision made life on earth possible.
08:03Two billion years later, that life threatens to destroy itself.
08:23Our blue planet.
08:25In a hostile universe, it sustains and nurtures life.
08:312.4 billion years ago, simple single-celled organisms drift through the nutrient-rich
08:38oceans.
08:40But their world is about to be destroyed.
08:43When you talk about mass extinctions, you have at least two types.
08:48One danger coming from outer space, another from our own very backyard on the planet earth.
08:59The earth circles the sun, but this orbit is unstable.
09:03It changes over hundreds of thousands of years, swinging the planet further out into space
09:11and pivoting on its axis.
09:17Tilted away from the sun, the earth cools.
09:222.4 billion years ago, something turns this natural cooling into a global catastrophe.
09:30It's one of the most dangerous things in the universe, life.
09:37Tiny organisms populate the oceans.
09:42There's no oxygen around, and that's the way most of them like it.
09:47Then a new kind of bacteria evolves, cyanobacteria, and these guys create a serious gas problem.
09:57Imagine earth billions of years ago.
09:59There's no oxygen.
10:00Everybody's happy.
10:01Then cyanobacteria start making oxygen.
10:06It's a toxic pollutant.
10:08If there was a regulatory agency at the time, they would have been outlawed.
10:12Eventually they polluted the whole world.
10:14They had really precipitated an ecological crisis of global proportions.
10:21The great oxygen crisis upsets the greenhouse effect that keeps the planet warm.
10:30Global temperatures plummet.
10:33The ultimate culprit is biology.
10:37Biology makes a mess of the planet, produces oxygen.
10:40The oxygen destroys the greenhouse effect of methane, and that freezes up the earth.
10:462.4 billion years ago, ice creeps out from the poles.
10:57Sunlight bounces off the ice instead of warming the planet.
11:02Temperatures fall, creating more ice, which bounces more sunlight back into space until
11:09the cooling becomes unstoppable.
11:13The ice marches on.
11:18Temperatures plunge.
11:20The blue planet turns white.
11:24It's a snowball earth.
11:27Incredibly, this may have happened not once, but at least three times over the following
11:34billion years as the planet lurched around the sun.
11:41But throughout all of this, against all the odds, a handful of species clung to life thanks
11:48to volcanoes.
11:52Even in an earth that was covered almost entirely by ice, volcanoes would have been punching
11:56through that.
11:57So you'd certainly have pockets of water lying about.
12:01And life was able to carry on and get through these cold periods.
12:11And the whole time, the volcanoes that helped sustain life had been pumping out carbon dioxide.
12:20As this greenhouse gas increases, the atmosphere warms, until 640 million years ago, the last
12:29great snowball earth ends.
12:32And the survivors emerge into a new world.
12:38After snowball earth goes away, things get very interesting.
12:42A lot of opportunities open up for life.
12:45Water's flowing, ice is melting, organic material that's built up that hasn't been decomposing.
12:50So you can imagine that there will be a burst of development.
12:55In the meantime, the cyanobacteria have been churning out ever more oxygen.
13:01Other organisms must learn to breathe it, or die.
13:08Many organisms decided that this poison could be useful, it's energetic, and that allowed
13:13them to have an energy source that was so powerful that they could build huge complex
13:18structures, poof, animals.
13:21Snowball earth is an environmental disaster and an evolutionary triumph.
13:30Complex life flourishes.
13:37But most of these creatures will never evolve beyond this point.
13:43Something stops them dead.
13:45It's the most powerful weapon in the universe, and it strikes in the blink of an eye.
14:04In a violent universe, against all the odds, life survives.
14:10But consider this.
14:12At any moment, the universe could pull the trigger on a secret deep space death ray,
14:19obliterating all life on earth.
14:22And until the 1960s, nobody knew it existed.
14:281967, the height of the Cold War.
14:32The United States and Soviet Union raced to outgun each other, stockpiling and testing
14:38nuclear weapons.
14:41America was worried that the Soviet Union would be able to test nuclear weapons in space.
14:46So what America did is launch a series of satellites to go out into space and look for
14:49the telltale flash of gamma rays from nuclear tests.
14:53On July 2nd, 1967, the satellites detect a burst of gamma rays, the most energetic and
15:01destructive form of electromagnetic radiation.
15:05Immediately there was panic in the Pentagon.
15:07Perhaps the Russians are testing super gigantic hydrogen bombs in outer space, and we're just
15:13caught flat footed.
15:14But it's not bombs.
15:16It's something even deadlier.
15:19And then the realization sunk in.
15:21Oh my God.
15:23These flashes are coming from outside the Milky Way galaxy.
15:28They must be billions of light years away.
15:31A new source of energy, second only to the Big Bang itself, had been discovered.
15:37Gamma ray bursts were first discovered.
15:39People assumed that they must be fairly close by.
15:42Of course they have to be close by.
15:43They're the brightest thing that we see in the sky.
15:46And now we know that gamma ray bursts, not only are they not nearby, they're not in our
15:49galaxy, they're not in nearby galaxies, but they're close to the edge of the universe.
15:54They're as far away as anything else that we observe.
15:56And that's completely ridiculous.
15:58Light gets dimmer over distance.
16:01So the further it's got to travel, the dimmer the light should be.
16:05If light from a distant galaxy comes to Earth and it has gamma ray energies, then that explosion
16:10must have been incredibly powerful.
16:13Because it turns out that as light travels through space, the wavelength of the light
16:17gets stretched out.
16:18And this stretching causes the light to lose energy.
16:21And since the light rays have traveled a very great distance through the cosmos to reach
16:26us, and they're still gamma rays, they must have started out with a great deal of energy.
16:31And the amount of energies are unbelievable.
16:33We're talking about the entire energy budget of the sun over its whole lifetime, emitted
16:38over the course of just a few seconds.
16:41These are amazingly violent, amazingly powerful events.
16:47In July 2008, NASA launches the Fermi Space Telescope.
16:52Its mission?
16:53To discover the source of these huge blasts.
16:58What Fermi does is open our eyes to the universe that's there, but gives us such a different
17:03view that we'll really get a deeper and greater understanding of what's going on.
17:08If you had gamma ray eyes, the Milky Way would be blazingly bright.
17:13Across the center of the sky, your vision would be dominated by these very dense, pulsing
17:20stars and supermassive black holes.
17:23And it's black holes that may solve the mystery of gamma ray bursts.
17:28When a truly gigantic star dies, one at least 25 times more massive than our own sun, it
17:36collapses to form a black hole.
17:40Scientists believe black holes are one of the few things in the universe large enough
17:45and powerful enough to generate gamma ray bursts.
17:50Gamma ray bursts are the birth cries of black holes.
17:53When a massive star explodes and becomes a supernova, the core collapses and forms
17:58a black hole.
17:59Material falls around, it swirls into a huge disk.
18:03It gets incredibly hot.
18:05As it's falling into the black hole, it forms a tremendous magnetic field as well.
18:16The remains of the star spiral towards the black hole, accelerating to close to the speed
18:22of light, heating to millions of degrees.
18:29Enormous electromagnetic forces fling some of this matter outwards, hurtling up and down
18:35along the black hole's huge magnetic fields.
18:40The matter collides with debris from the initial explosion.
18:44These high-speed collisions unleash unimaginable amounts of energy.
18:50This is the gamma ray burst.
18:54Gamma ray bursts are fascinating.
18:55You can study them throughout the universe because they're so bright.
18:59But if you move them in really close to the Earth, let's say within 6,000 light years
19:05of the Earth, they become extremely destructive.
19:08The beams are so huge that if a gamma ray burst occurs even closer to Earth, by the
19:15time it reaches the Earth, the beam will be wide enough to engulf our entire solar
19:20system.
19:21Basically, if you were standing on the Earth and you looked up, you would see a flash of
19:26light.
19:27And before you could even say, what's that, you'd be gone.
19:30The amount of energy in the beam that travels across space is so intense, it would basically
19:35light the Earth on fire from that distance.
19:38It would strip off the Earth's atmosphere.
19:40It would boil the oceans.
19:42It would melt the rock.
19:43It would be apocalyptic beyond apocalyptic.
19:49This is the worst-case scenario.
19:52But what if a gamma ray burst hit the Earth from further out?
19:56Would we survive?
19:59People ask what would happen if there was a gamma ray burst within 6,000 light years
20:03of the Earth.
20:04It's actually not the right question.
20:06There have been gamma ray bursts that close to the Earth, and there probably have been
20:10extinctions of life on Earth due to gamma ray bursts.
20:15200 million years after snowball Earth, the oceans are teeming with complex life.
20:23But 440 million years ago, 85% of all these creatures died.
20:33And the killer may have been a single devastating gamma ray burst.
20:39The blast penetrates the ocean's upper layers, killing the creatures that live near the surface.
20:47Creatures living further down survive the initial onslaught.
20:51But not for long, because the blast also damages the Earth's ozone layer, exposing the planet
21:00to the sun's deadly UV radiation, triggering acid rain and lowering global temperatures.
21:07For half a million years, the creatures that survived the gamma ray burst get taken out
21:13by its after-effects.
21:18If a gamma ray burst has wiped out life in the past, it could happen in the future.
21:26And astronomers think the next burst could come from a dangerously unstable star, WR104.
21:35WR104 is the nightmare.
21:39We now have a potential candidate for what may become a gamma ray burster with our name on it.
21:45We are literally staring down the gun barrel of WR104.
21:52It's not one, but two massive stars orbiting each other.
22:01And the stars will die in a massive explosion, spawning a black hole and blasting out gamma rays.
22:11The object is about 8,000 light years away, so we are within the kill radius of this object.
22:17So you could be doing your laundry tomorrow, look up in the sky, and all of a sudden there's
22:22this burst of radiation raining down from the heavens.
22:26The radiation rips off the Earth's ozone layer, creating a toxic smog and exposing
22:32us to the sun's deadly rays.
22:35Life as we know it could cease to exist.
22:38Plants would be scorched.
22:40Animals which depend upon plant life would then begin to die.
22:44Human civilization would have to go underground.
22:47It may sound like the Death Star destroying the Earth in Star Wars, but the difference
22:51is the Death Star isn't going to happen.
22:54A gamma ray burst might.
23:03Our extinction could happen at any time.
23:07And the fatal blow doesn't have to come from space.
23:11It could come from the very thing that makes life possible.
23:16The Earth itself.
23:33Our planet conceals a weapon of mass extinction, primed to detonate at any moment and hidden
23:40deep beneath our feet.
23:45Unleashed, the heat inside our planet can wipe out everything in its path on a massive
23:51scale.
23:53200 million years after a gamma ray burst may have devastated life in the oceans, the
24:00survivors have colonized the land.
24:05Among them is a motley crew of monster reptiles, Scutosaurus and Gorgonopsians.
24:12They're successful, strong and doomed.
24:18Around about 250 million years ago marks the biggest mass extinction that the Earth has
24:23ever seen, the end Permian extinction.
24:26Just over 90% of marine fauna and around about 70 odd percent of land fauna disappeared from
24:32the planet.
24:34The killer is a volcanic eruption, the biggest and most catastrophic the world has ever seen.
24:41250 million years ago in what is now Siberia, the Earth's crust ruptures, pushed beyond
24:53breaking point by a vast plume of hot magma surging up from deep inside the planet.
25:05The Earth itself can internally generate some very devastating events, millions of years
25:09long events in the form of major volcanic eruptions at the continent scale level.
25:16These are basaltic volcanism events that flood entire portions of the planet with basalt
25:21lava.
25:25Lava spews out for 2 million years.
25:29There's enough to cover the entire United States beneath 1,000 feet of lava.
25:36Then the death toll extends far beyond to the other side of the Earth and deep into
25:42the oceans.
25:43The question is why?
25:48The answer lies in the most volcanic country on Earth, Iceland, with a similar, smaller
25:55eruption just 230 years ago.
26:05June 1783.
26:11A terrible chain of events unfolds that will devastate Iceland and kill up to a million
26:16people around the world.
26:20Near the village of Laki, a 17-mile-long tear opens up in the Earth's crust.
26:28These holes and cracks in the ground that you can see, they would have had jets of magma,
26:32jets of lava flying up into the sky.
26:39To give you an idea of scale, the overall amount of material that came out of Laki is
26:43about three and a half cubic miles of volcanic material, and that's a lot of material.
26:49And it's not just the size of Laki that makes it so special, it's actually what's inside
26:54this and what came out of this that's the dangerous thing, because it had lots of sulfur
26:59gases associated with the eruption, and also lots of fluorine, quite poisonous gases.
27:06Sulfur dioxide spreads out around the atmosphere.
27:10Its droplets form a giant mirror reflecting the sun's warmth away from the Earth.
27:16It's clear that even a relatively small eruption like Laki can cause big, dramatic effects
27:22in terms of the climate.
27:24In the northern U.S. there was one of the coldest winters ever recorded, in fact the
27:28Mississippi is recorded to have frozen.
27:31It's been implicated in causing the big famine in Japan, so the effects potentially for volcanoes
27:37that spew these horrible gases into the atmosphere can be catastrophic on a global scale.
27:44Now picture the Siberian eruptions 250 million years ago.
27:49They're 200,000 times larger than Laki, and last a million times longer.
27:56They release massive quantities of gas, triggering extreme climate change, first cooling, then
28:03heating the atmosphere.
28:07Seventy percent of all land-based creatures die, including the mighty Gorgonopsians and
28:14Scutosaurus.
28:16But worse is to come.
28:18As the oceans warm, they lose oxygen and stagnate.
28:23Organic algae takes over, poisoning the oceans with hydrogen sulfide, killing 96% of marine
28:31life and leaving purple sulfur bacteria to overrun the oceans and turn the water pink.
28:39This is the closest the Earth has ever come to total extinction.
28:46But over 200 million years, the survivors adapt and evolve.
28:52A new group of animals emerge.
28:55They're the largest, most successful creatures the Earth has ever seen, the dinosaurs.
29:03But they too will face annihilation.
29:17Killers prowl the universe, threatening to wipe out life on Earth.
29:27They've struck before.
29:29They will strike again.
29:32And it could happen before you finish watching this show.
29:41February 15, 2013, 9.42 a.m.
29:47It's another cold winter's day in the Siberian city of Chelyabinsk.
29:53When literally out of the blue, a 14,000-ton, 65-foot meteor tears through the atmosphere
30:03at 42,000 miles an hour.
30:06It explodes in the air 18 miles up, unleashing a powerful blast wave, shattering windows,
30:15damaging 7,000 buildings and injuring 1,500 people.
30:22Now imagine what would have happened if the asteroid had hit the Earth in one piece.
30:27And we saw what happened over Russia, over in Chelyabinsk, with an object that could
30:33have hit the Earth.
30:34It could have hit the Earth with the force of perhaps 20 Hiroshima bombs.
30:38If you watch those videos of that meteor in Russia, with the incredible sonic boom, you
30:45could see how even a small object, relatively small in a cosmic sense, could produce a dramatic
30:50event for humans.
30:51The way it works is small objects are hitting the Earth every day, larger objects every
30:57week, larger objects still every year.
31:00And an object the size of the Chelyabinsk meteor strikes, on average, once every century.
31:08What will happen when, not if, the next big one strikes?
31:14The clues lie in the past, in the extinction of the dinosaur.
31:24About 65 million years ago, there was a perfect morning on Earth.
31:27I would have loved to have been there to see the giant dinosaurs, you know, the pterodactyls
31:32flying through the air, all of that.
31:34And then something changed, and the Earth would never be the same.
31:37If you would have looked into the sky, you would have seen relatively dim light at first
31:41coming towards you, getting brighter and brighter, and hotter and hotter.
31:45It's a six-mile-wide rock the size of Mount Everest, racing toward the Earth at 25,000
31:53miles an hour.
31:55The first wave of destruction would have started before this object even hit.
31:58There would have been shockwaves, heat and winds going across the entire planet.
32:03Everywhere that was under the path of this asteroid would have been seared, set on fire.
32:07The oceans would have been boiling underneath it.
32:12The asteroid smashes into the ocean off what is now Mexico's Yucatan Peninsula.
32:20It strikes with a force two million times greater than the biggest nuclear bomb ever
32:26detonated, and blasts out a crater 200 miles across.
32:31A superheated shockwave roars out at twice the speed of sound.
32:38Five hundred billion tons of red-hot rock soar to the edge of space.
32:45Two hours after impact, a 300-foot tsunami smashes into the coast of what is now the
32:52USA, reaching as far as North Carolina.
33:01Over the next few hours and days, the debris rains down, setting the planet ablaze.
33:09In the following weeks and months, smoke from the fires adds to the dust blasted into the
33:15atmosphere.
33:17There was so much pulverized rock, all of the burning materials up into the atmosphere,
33:22you wouldn't have been able to see the surface, and on the surface you wouldn't have been
33:25able to see the sun.
33:26And it was like that for a long time.
33:29This ancient apocalypse is a disaster for the dinosaurs.
33:38But without it, we wouldn't be here.
33:42Back then, during the time of the dinosaurs, our ancestors were probably little furry mammals
33:46that were an evening snack for a dinosaur.
33:49When the dinosaurs got wiped out, these small little furry mammals began to expand in size
33:55to take over the niche left over by the dinosaurs.
33:58So one life form replaces another life form in this continual process called survival
34:04of the fittest.
34:06We are here because our ancestors survived the extinction event, and in fact, flourished
34:12because of it.
34:15From our point of view, that extinction event was a good thing.
34:19But we're here for a brief moment, and there will be disasters in the future.
34:24And one of them will destroy us.
34:27There is a one in 5,000 chance that an asteroid the same size as the dinosaur killer will
34:34strike within the next 100 years.
34:37And it could happen at any time.
34:40It is a real possibility that it could happen in the next 10 minutes, but it is a tiny possibility.
34:47So I always say you don't need to prepare very much for winning the lottery.
34:50You may have a similar chance of getting taken out by an asteroid in the next 15 minutes.
34:55In April 2014, scientists make a shocking announcement.
35:01Since the year 2000, 26 asteroids have exploded in the Earth's atmosphere, each with the force
35:09of a nuclear blast, and with some up to 40 times more powerful than the Hiroshima bomb.
35:17And we didn't spot a single one of them before they struck.
35:22Even if we had the technology to detect an asteroid before it hits us, could we destroy
35:28it in time?
35:30The Hollywood favorite, of course, is to go out there and nuke it, blow it to smithereens,
35:33right?
35:34That could actually work in the case of some particular, you know, last ditch effort for
35:38asteroids of just the right size.
35:43But a nuclear bomb could make a bad situation worse.
35:51Smashing an asteroid into large radioactive chunks that inflict damage over a wider area.
36:04But there are also techniques like shining a laser on the asteroid or sunlight, which
36:09would create an artificial cometary jet, if you will, would vaporize some of the water
36:13and the minerals on the surface of that asteroid to gently push it off to the side.
36:19Another fantastic technique, a very robust one, is something we call the gravity tractor.
36:23You just park a spacecraft, the mass of a communications satellite, next to that small
36:28asteroid, and you use the thrusters on the spacecraft to keep it hovering just off the
36:33surface of the asteroid.
36:35And that uses then gravity between the two as a tow line to move the asteroid ever so
36:39gently off course.
36:42Right now, these technologies are still on the drawing board.
36:47But if they do become a reality, we still need months or years to prepare.
36:57Rogue planets, ice ages, gamma ray bursts, volcanic eruptions, and asteroid strikes.
37:07We've survived the worst the universe can throw at us.
37:12But our species will still face extinction.
37:16It's as inevitable as the sun rising.
37:35We are the survivors in a cosmic battle to the death.
37:40But eventually, the universe will win, and we will face extinction, threatened by the
37:47thing that gives us life, our creator, the sun.
37:58We orbit a giant nuclear bomb, the sun, but you know, it's not going to explode, it's
38:02too small to explode, but what happens with the sun is that every day it's a little
38:06bigger than it was the day before.
38:10Since the sun's birth, hydrogen has been fusing into helium in the sun's core.
38:17As the helium accumulates, the core gets denser.
38:22With 150 million tons of helium squeezing into the core every second, the gas compresses
38:30and heats up.
38:31Right now, the temperature inside the sun's core is 27 million degrees, and it's getting
38:38hotter all the time.
38:41What happens when you heat up a gas?
38:43It expands, and so that's what the sun is going to do.
38:47As the sun swells, it will appear brighter.
38:51In two billion years, the sun will be about 15% brighter, and that will lead, if the earth
38:57remains in its present orbit, inevitably to a runaway greenhouse effect.
39:02The oceans will evaporate, and the surface temperature of the earth could easily be a
39:06thousand degrees.
39:07So if we don't do anything in two billion years, we'll be toast.
39:14If we're still here on earth, we'll perish.
39:19Other tougher species may find a way to adapt and survive, but they'll be living on borrowed
39:25time.
39:28It's going to fill up the sky.
39:29From horizon to horizon, the sky will literally be on fire.
39:34Five billion years from now, the sun runs out of hydrogen and enters the final, apocalyptic
39:41stage of its life, bloating to 100 times its current size.
39:48Our sun is now an angry red giant.
39:52Now, red giant stars are so big, they will actually eat up their own planets.
39:56We know of examples of red giants that go all the way out to where the orbit of Jupiter
40:00is in our solar system.
40:02The sun will not get quite that big, but it'll probably get about out to Mars.
40:05And eventually, in fact, the sun will be so large that the earth will be located inside
40:10of the sun, which certainly won't be a very pleasant place to be.
40:15The red giant's bloated body absorbs the earth, vaporizing our planet until it's nothing
40:22more than gas and dust inside a dying star.
40:31The death of the sun is the ultimate mass extinction event.
40:35There's a 100% chance it will happen, a 100% chance it will destroy our planet and
40:45any life left on it.
40:49But life on earth may not be the only life in the solar system.
40:57As the sun brightens, you can imagine a wave of habitability going out.
41:01So right now, it's on earth, it'll go to Mars, it'll go to Jupiter and its moons.
41:08Scientists think Jupiter's moon Europa may already harbor alien life in a deep, liquid
41:13ocean beneath its frozen crust.
41:16But out at Jupiter, it'll be much warmer, but not so warm that it would destroy everything.
41:22So even when the earth is gone, if there's life on Europa, it may be able to endure that.
41:28Will our species go on?
41:30Can we survive the loss of our home planet?
41:35The universe is like an ecosystem.
41:37Living things are going to survive based on the law of survival of the fittest.
41:43What decides if you're fit in this universe is if you're able to leave your planet and
41:47go out and populate other planets.
41:49So the only species that are going to live on forever are the ones that can leave their
41:53planet.
41:56We can't control the universe, but we may be able to control our fate.
42:02Inevitably, in the long term, the earth is going to become uninhabitable.
42:06It's just the way the universe works.
42:07It wasn't made for us, it doesn't care that we exist, and it won't care when we go away.
42:13The only people who care about that are us, and we might be able to do something about
42:17it.
42:18In that sense, we have a fighting chance.
42:21Our intelligence is our greatest asset.
42:24It's the end result of four billion years of extinction and evolution.
42:29And it may give us a chance to do something no other species has done before.
42:35Break the cycle of creation and destruction and live on.
42:41Everything that you and I are is a consequence of the way the universe works.
42:45The universe is violent, the universe is dynamic, it's constantly pushing us to change.
42:49And here we are, these incredibly evolved, interesting creatures, we're a direct consequence
42:54of the violence, which in turn was our creation.