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0:00:04 > 0:00:09- Our planet, the earth, has fought - for survival since the beginning.
0:00:10 > 0:00:15- The cosmos is full of dangers, - threatening to destroy the earth.
0:00:18 > 0:00:21- Many things in space could end life.
0:00:21 > 0:00:25- Things like asteroids, supernovas - and black holes.
0:00:26 > 0:00:30- Many times, life on earth - has very nearly ended.
0:00:35 > 0:00:40- There was so much energy, it seems - the earth's surface had melted away.
0:00:45 > 0:00:46- It could happen again.
0:00:47 > 0:00:50- An asteroid from space - could hit us at any time.
0:00:53 > 0:00:57- Something the size of a car - hits the earth once a week.
0:01:01 > 0:01:06- In this programme, we reveal what - will happen to earth in the future.
0:01:07 > 0:01:11- And is there anything we can do - to avoid it?
0:01:15 > 0:01:19- We don't know when - the next extinction will happen...
0:01:19 > 0:01:21- ..but it's inevitable.
0:01:39 > 0:01:40- Our planet - the earth.
0:01:44 > 0:01:48- Home to all types of life - in all sorts of places.
0:01:52 > 0:01:57- It's a quiet, peaceful place - compared to the rest of the cosmos.
0:02:02 > 0:02:04- The universe is full of dangers.
0:02:04 > 0:02:06- Supernovae, asteroids...
0:02:06 > 0:02:08- ..comets and black holes.
0:02:09 > 0:02:14- When you look to the skies, - it's not as quiet as you may think.
0:02:18 > 0:02:21- Earth has seen numerous disasters.
0:02:22 > 0:02:24- Millions of species - were wiped out...
0:02:24 > 0:02:30- ..in a series of catastrophic events - known as mass extinctions.
0:02:38 > 0:02:40- We've had at least five.
0:02:40 > 0:02:43- We've had many, but five stand out.
0:02:49 > 0:02:50- These things happen.
0:02:52 > 0:02:54- Mankind only exists...
0:02:54 > 0:02:58- ..because we've only been around - for a relatively short time.
0:02:59 > 0:03:02- Had we existed - over the earth's entire history...
0:03:03 > 0:03:07- ..extinction events - would have happened to mankind.
0:03:09 > 0:03:15- Without the mass extinctions, which - severely impacted life on earth...
0:03:16 > 0:03:18- ..we wouldn't be here today.
0:03:19 > 0:03:22- It clears the decks - for evolution to change course.
0:03:29 > 0:03:33- Without these events, - we wouldn't be here today.
0:03:36 > 0:03:41- These events happen - every 100 to 150 million years.
0:03:41 > 0:03:43- It sounds like a long time...
0:03:44 > 0:03:48- ..but it means that earth - has experienced these events...
0:03:48 > 0:03:50- ..half a dozen times.
0:03:50 > 0:03:52- And it will happen again.
0:03:54 > 0:03:59- It's hard to believe that we live - in a cosmos that is so dangerous.
0:03:59 > 0:04:01- At the moment, it's quiet...
0:04:04 > 0:04:09- ..but astronomers - have found the latest threat.
0:04:13 > 0:04:17- In November 2012, - astronomers identified a new planet.
0:04:20 > 0:04:23- It's huge and it's on the move.
0:04:26 > 0:04:31- It's lost in space, which - astronomers call rogue planets.
0:04:31 > 0:04:35- A rogue planet is one - which came from another star...
0:04:35 > 0:04:38- ..but veered into our solar system.
0:04:38 > 0:04:42- When I was a kid - watching science fiction movies...
0:04:42 > 0:04:46- ..there'd be rogue planets wandering - around space without a star.
0:04:46 > 0:04:48- I thought that was silly...
0:04:48 > 0:04:52- ..but it turns out - that might actually happen.
0:04:53 > 0:04:57- When planets are forming, - they can interact gravitationally.
0:04:57 > 0:05:00- It's possible that, - when our solar system formed...
0:05:00 > 0:05:04- ..planets were kicked out - into interstellar space.
0:05:08 > 0:05:12- There are 200 billion rogue planets - in our galaxy.
0:05:14 > 0:05:18- And one of them - could be heading our way.
0:05:31 > 0:05:35- But could a collision - with another planet really happen?
0:05:36 > 0:05:38- It already has.
0:05:42 > 0:05:46- Many years ago, a planet - called Theia hits our earth.
0:05:46 > 0:05:49- We have the earth sitting here...
0:05:49 > 0:05:53- ..and a planet the size of Mars - came in and smacked us hard.
0:05:54 > 0:05:58- The two collide - at over 25,000 miles an hour.
0:06:11 > 0:06:15- During that collision, the - earth's surface turned into liquid.
0:06:15 > 0:06:18- It would be impossible - for life to survive.
0:06:19 > 0:06:24- Any life forms would have been - destroyed by such a huge collision.
0:06:34 > 0:06:37- The small planet is destroyed, - but the earth remains.
0:06:40 > 0:06:44- And the debris from this - huge collision creates a moon.
0:06:44 > 0:06:45- Our moon.
0:06:49 > 0:06:52- One thing that confused scientists - about the moon...
0:06:53 > 0:06:56- ..was that it's a mixture - of matter from earth...
0:06:56 > 0:06:58- ..and matter not from earth.
0:06:59 > 0:07:04- After going to the moon with Apollo - and analysing the rock samples...
0:07:05 > 0:07:08- ..the idea was introduced - that the moon was formed...
0:07:09 > 0:07:14- ..from a collision between the earth - and something the size of Mars.
0:07:14 > 0:07:18- The moon was created from the debris - of that collision.
0:07:19 > 0:07:22- That's how we think - the moon was formed.
0:07:25 > 0:07:29- Recently, scientists - have discovered more facts...
0:07:29 > 0:07:32- ..about how the moon was created.
0:07:32 > 0:07:33- One of the mysteries...
0:07:34 > 0:07:39- ..is that some of the surface - seems to be denser than other areas.
0:07:39 > 0:07:42- There's a difference - in the gravitational pull.
0:07:43 > 0:07:46- The crust's density isn't uniform.
0:07:51 > 0:07:55- Two years ago, NASA's GRAIL - spacecraft was sent to the moon...
0:07:55 > 0:07:57- ..to solve the problem.
0:07:57 > 0:08:01- We measured - the gravity field of the moon.
0:08:01 > 0:08:05- The moon is lopsided. - It shouldn't have formed that way.
0:08:05 > 0:08:08- One of the ways - of getting around this problem...
0:08:08 > 0:08:11- ..is there may have been two moons.
0:08:11 > 0:08:13- After the collision - and the debris...
0:08:13 > 0:08:16- ..maybe two objects - formed out of the debris...
0:08:16 > 0:08:19- ..and eventually - collided together themselves.
0:08:19 > 0:08:22- So the moon in fact - is not original...
0:08:22 > 0:08:26- ..but two moons that collided - to form the moon we know today.
0:08:30 > 0:08:34- This was the most violent event - in our planet's history.
0:08:36 > 0:08:38- But without it, - there would be no moon.
0:08:39 > 0:08:42- And without a moon, - there would be no life on earth.
0:08:46 > 0:08:50- The moon - creates the tides in our seas.
0:08:56 > 0:09:00- It slows the earth's spin - from a six to a 24 hour day.
0:09:03 > 0:09:06- In this calm environment, - life begins.
0:09:08 > 0:09:12- Without that planetary collision, - we wouldn't have the moon today.
0:09:13 > 0:09:16- This most catastrophic event - that you can think of...
0:09:17 > 0:09:21- ..actually may have helped life - on earth form in the first place...
0:09:21 > 0:09:25- ..and helped us evolve over the next - couple of billion years.
0:09:27 > 0:09:31- But a similar collision would be - a disaster if it happened today.
0:09:33 > 0:09:37- A planetary collision now - would wipe out the entire planet.
0:09:38 > 0:09:42- You can't describe it - comparing it to nuclear weapons.
0:09:42 > 0:09:45- It would be - billions of nuclear weapons.
0:09:45 > 0:09:50- Enough to melt several miles thick - crust on the earth all the way down.
0:09:50 > 0:09:52- It would wipe out all life on earth.
0:09:53 > 0:09:56- It would be like a hard restart - for the planet itself.
0:09:59 > 0:10:00- So could it happen?
0:10:04 > 0:10:09- There's nothing that size in - our solar system which could hit us.
0:10:09 > 0:10:14- There are asteroids - which are around 20km in diameter...
0:10:15 > 0:10:19- ..but that's nothing - compared to a Mars-sized object.
0:10:19 > 0:10:23- In my opinion, there's no chance - of something the size of Theia...
0:10:24 > 0:10:26- ..hitting the earth again.
0:10:32 > 0:10:35- But the threat - might not come from space.
0:10:38 > 0:10:41- It could come - from within the earth itself.
0:10:51 > 0:10:52- .
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0:11:14 > 0:11:16- Our planet - the earth.
0:11:19 > 0:11:23- It has sustained and nurtured life - for billions of years.
0:11:25 > 0:11:30- Millions of years ago, simple - organisms drift through the oceans.
0:11:34 > 0:11:37- But their world - is about to be destroyed.
0:11:38 > 0:11:42- Massive events change the world - - asteroids and so on.
0:11:42 > 0:11:45- But small things - can also change the earth.
0:11:49 > 0:11:51- The earth circles the sun.
0:11:53 > 0:11:55- But this orbit changes.
0:11:58 > 0:12:02- Sometimes the earth - is very far from the sun and cools.
0:12:05 > 0:12:07- It's all part of a natural process.
0:12:12 > 0:12:14- Over 2 billion years ago...
0:12:14 > 0:12:18- ..something turns this natural - cooling into a catastrophe.
0:12:22 > 0:12:25- Tiny organisms live in the oceans.
0:12:26 > 0:12:30- There's no oxygen in the atmosphere, - but they exist happily.
0:12:33 > 0:12:39- But then, a new kind of bacteria - evolves - Cyanobacteria.
0:12:40 > 0:12:41- It changes everything.
0:12:49 > 0:12:54- This is a layer of bacteria - called Cyanobacteria.
0:12:55 > 0:12:58- It lives on the sand's surface - here near Ynys Las.
0:13:00 > 0:13:05- This is how planet earth would have - looked around 2.3 billion years ago.
0:13:05 > 0:13:09- These mats once covered - the earth's entire surface.
0:13:10 > 0:13:15- Evolution was yet to allow - photosynthesis to produce oxygen.
0:13:17 > 0:13:19- But this suddenly changed.
0:13:19 > 0:13:23- There was so much Cyanobacteria - all around the world...
0:13:23 > 0:13:28- ..the atmosphere went from - being anoxic to being oxygen rich.
0:13:29 > 0:13:33- It was the biggest mass pollution - event in the world's history.
0:13:34 > 0:13:39- The oxygen in the atmosphere - upsets the greenhouse effect...
0:13:39 > 0:13:42- ..which keeps the planet warm.
0:13:42 > 0:13:47- With the earth at its furthest point - from the sun, temperatures plummet.
0:13:49 > 0:13:54- This microscopic bacteria - has polluted the atmosphere...
0:13:55 > 0:13:58- ..more than anything known to us.
0:13:58 > 0:14:02- Forget industrial pollution - - it's nothing!
0:14:03 > 0:14:06- Ice starts to creep out - from the planet's poles.
0:14:12 > 0:14:17- Sunlight is reflected off the ice, - and the planet gets even colder.
0:14:23 > 0:14:27- The ice spreads and temperatures - plunge to -74 degrees.
0:14:37 > 0:14:40- The planet - turns into a white snowball.
0:14:45 > 0:14:49- It remains like this - for a billion years.
0:14:56 > 0:15:00- But against all the odds, - a handful of species cling to life.
0:15:07 > 0:15:11- We know it's possible, - because today there are organisms...
0:15:11 > 0:15:15- ..capable of surviving - in the earth's coldest places.
0:15:16 > 0:15:20- Arwyn Edwards from - Aberystwyth University studies them.
0:15:21 > 0:15:26- No animal or other complex organisms - could survive these conditions.
0:15:27 > 0:15:28- But it may be possible...
0:15:29 > 0:15:33- ..for simple organisms - such as bacteria, algae or fungi...
0:15:33 > 0:15:35- ..to survive on the surface.
0:15:40 > 0:15:42- Eventually, a new world emerges.
0:15:43 > 0:15:49- Volcanoes under the ice have erupted - pumping out carbon dioxide.
0:15:51 > 0:15:56- Slowly, this carbon dioxide - begins to warm the atmosphere.
0:15:59 > 0:16:01- The icy world starts to melt.
0:16:03 > 0:16:05- And life takes hold again.
0:16:07 > 0:16:12- After snowball earth goes away, - opportunities open up for life.
0:16:12 > 0:16:17- Water's flowing, ice is melting, - organic material is building up...
0:16:17 > 0:16:20- ..that hasn't been decomposing.
0:16:20 > 0:16:24- You can imagine that there will be - a burst of development.
0:16:25 > 0:16:29- Meanwhile, the Cyanobacteria - churns out ever more oxygen...
0:16:30 > 0:16:34- ..influencing - all organisms on earth.
0:16:35 > 0:16:37- We wouldn't have evolved.
0:16:38 > 0:16:43- We wouldn't have reached the point - of being multi-cell organisms...
0:16:43 > 0:16:46- ..able to walk and talk - and have intelligence.
0:16:48 > 0:16:51- The amount of energy produced - without oxygen...
0:16:52 > 0:16:55- ..is not enough - to create complex organisms.
0:16:59 > 0:17:01- The oxygen - enables life to develop...
0:17:03 > 0:17:06- ..and all sorts - of new creatures appear.
0:17:10 > 0:17:13- But they're not here for long.
0:17:15 > 0:17:17- Another disaster is imminent.
0:17:20 > 0:17:23- The most dangerous thing - in the cosmos.
0:17:23 > 0:17:26- It can kill everything in a second.
0:17:26 > 0:17:28- Gamma rays.
0:17:31 > 0:17:36- Back in the 1960s, - the Cold War was at its peak.
0:17:36 > 0:17:40- America and the Soviet Union - race each other...
0:17:40 > 0:17:43- ..to develop and test - nuclear weapons.
0:17:46 > 0:17:50- One of the ways to know if an enemy - has fired a nuclear weapon...
0:17:50 > 0:17:52- ..is to look for gamma rays.
0:17:54 > 0:17:58- America sent satellites into space - to orbit the earth...
0:17:59 > 0:18:04- ..looking for signs that the USSR - was testing nuclear weapons.
0:18:05 > 0:18:06- They found gamma rays.
0:18:07 > 0:18:09- Far more than they expected.
0:18:12 > 0:18:16- These gamma rays - were not coming from Russia.
0:18:16 > 0:18:18- They were coming from space.
0:18:27 > 0:18:31- These spy satellites - found gamma rays coming from space.
0:18:34 > 0:18:36- Gamma rays are full of energy.
0:18:39 > 0:18:42- They're a sign of nuclear reaction.
0:18:42 > 0:18:43- They're also a sign...
0:18:44 > 0:18:46- ..of an explosion in space.
0:18:50 > 0:18:55- So what in space caused - these explosions and gamma rays?
0:18:57 > 0:19:02- Seven years ago, NASA launched - the Fermi Space Telescope...
0:19:02 > 0:19:04- ..to try to find the answer.
0:19:11 > 0:19:14- NASA spent a lot of money - launching Fermi...
0:19:15 > 0:19:16- ..to find the answer.
0:19:17 > 0:19:19- Fermi did indeed - give us the answer.
0:19:20 > 0:19:23- As well as seeing - these gamma explosions...
0:19:23 > 0:19:26- ..it could also pinpoint - their sources.
0:19:29 > 0:19:33- It was clear they weren't coming - from nuclear testing...
0:19:33 > 0:19:37- ..as they were coming from space, - not from earth.
0:19:37 > 0:19:39- So the discovery was...
0:19:39 > 0:19:44- ..that these gamma rays could - happen naturally in the universe.
0:19:46 > 0:19:49- One of the most powerful events - in the cosmos...
0:19:50 > 0:19:53- ..is the process - of creating black holes.
0:19:56 > 0:20:00- When a star dies, - it collapses to form a black hole.
0:20:03 > 0:20:08- Scientists believe black holes could - generate these gamma ray bursts.
0:20:13 > 0:20:17- People believe that large stars - collide and explode...
0:20:18 > 0:20:20- ..to create gamma ray bursts.
0:20:20 > 0:20:22- It's a short, sharp explosion.
0:20:27 > 0:20:30- After the explosion, - a black hole is created.
0:20:30 > 0:20:35- Events like this - cause radiation and gamma rays...
0:20:36 > 0:20:38- ..which can be dangerous for us.
0:20:41 > 0:20:45- The remains of the star - spiral towards the black hole.
0:20:47 > 0:20:50- Everything collides - at huge speeds...
0:20:52 > 0:20:55- ..and the energy - creates the gamma rays.
0:21:03 > 0:21:07- Gamma rays are full of energy, - far more so than X-rays.
0:21:09 > 0:21:12- They can travel - through almost anything.
0:21:12 > 0:21:16- They can reach us - through the universe fairly easily.
0:21:22 > 0:21:26- You're talking about more energy - in a fraction of a second...
0:21:27 > 0:21:30- ..than our sun will create - in its lifetime.
0:21:32 > 0:21:36- The beams are so huge that, - if it reaches the earth...
0:21:37 > 0:21:39- ..everything would be destroyed.
0:21:43 > 0:21:46- If one of these events - creating gamma rays...
0:21:47 > 0:21:50- ..happened in our area - of the Milky Way...
0:21:52 > 0:21:55- ..it would affect - life on our planet.
0:21:56 > 0:22:00- It would be like standing too close - to a nuclear explosion.
0:22:02 > 0:22:06- A gamma explosion from the - further parts of the cosmos...
0:22:07 > 0:22:09- ..would also be bad news for earth.
0:22:11 > 0:22:15- We know this - because it's happened before.
0:22:21 > 0:22:25- Around 200 million years - after the snowball earth...
0:22:26 > 0:22:29- ..the seas are full of life.
0:22:30 > 0:22:34- But for some reason, - 85% of all these creatures die.
0:22:39 > 0:22:42- And the reason may have been - a single gamma ray burst.
0:22:43 > 0:22:47- The first to die are those - closest to the water's surface.
0:22:50 > 0:22:55- The blast is so large, it also - damages the earth's ozone layer.
0:22:55 > 0:22:59- The sun's deadly UV radiation - creates acid rain.
0:22:59 > 0:23:05- There's no escape for the creatures - at the bottom of the sea either.
0:23:14 > 0:23:17- Gamma ray bursts - have wiped out life in the past...
0:23:17 > 0:23:20- ..and it could happen - in the future.
0:23:21 > 0:23:24- Astronomers think the next burst...
0:23:24 > 0:23:28- ..could come from WR 104, - a star which is about to die.
0:23:31 > 0:23:35- This star is quite close to us and - it's about to become a supernova.
0:23:36 > 0:23:39- It's not the only one, - but it's a good example.
0:23:42 > 0:23:46- It's not one, but two massive stars - orbiting each other...
0:23:47 > 0:23:48- ..spiralling ever closer.
0:23:50 > 0:23:54- When the stars collide, - they will create a black hole...
0:23:54 > 0:23:56- ..blasting out gamma rays.
0:23:59 > 0:24:01- The object - is 8,000 light years away...
0:24:02 > 0:24:05- ..so we are within - the kill radius of this object.
0:24:06 > 0:24:10- You could be doing your laundry - tomorrow, look up in the sky...
0:24:10 > 0:24:14- ..and a sudden burst of radiation - rains down from the heavens.
0:24:20 > 0:24:22- Life as we know it - could cease to exist.
0:24:23 > 0:24:25- Plants would be scorched.
0:24:25 > 0:24:28- Animals which depend on plant life - would begin to die.
0:24:29 > 0:24:32- Human civilisation - would have to go underground.
0:24:37 > 0:24:42- There's no point worrying about it - because we're powerless to stop it.
0:24:43 > 0:24:46- And the time it takes - for this to happen...
0:24:46 > 0:24:48- ..is much longer than our lifespan.
0:24:51 > 0:24:54- The cosmos is full of dangers.
0:24:55 > 0:24:58- There are many ways - life on earth could end.
0:24:59 > 0:25:00- But the fatal blow...
0:25:00 > 0:25:04- ..could come from - within the earth itself.
0:25:06 > 0:25:07- .
0:25:17 > 0:25:17- Subtitles
0:25:17 > 0:25:19- Subtitles- - Subtitles
0:25:29 > 0:25:33- Our planet conceals a weapon - which could end life on earth.
0:25:36 > 0:25:39- It is hidden deep beneath our feet.
0:25:40 > 0:25:42- Our planet's core is on fire.
0:25:44 > 0:25:48- If it's unleashed, - it could destroy everything.
0:25:49 > 0:25:51- We know this from experience.
0:25:52 > 0:25:54- Around 250 million years ago...
0:25:55 > 0:25:59- ..marks the biggest mass extinction - the earth has ever seen.
0:25:59 > 0:26:01- The End-Permian extinction.
0:26:01 > 0:26:05- Just over 90% of marine fauna - and 70% of land fauna...
0:26:05 > 0:26:07- ..disappeared from the planet.
0:26:08 > 0:26:13- At that time, a collection - of creatures lived on the land.
0:26:15 > 0:26:20- Strong reptiles like - the scutosaurus and gorgonopsians.
0:26:22 > 0:26:25- But they weren't here for long.
0:26:29 > 0:26:33- Siberia experienced the most - catastrophic volcanic eruption...
0:26:34 > 0:26:35- ..the world has ever seen.
0:26:40 > 0:26:44- Tons of hot magma - surging from deep inside the planet.
0:26:51 > 0:26:55- Lava spews out - for two million years.
0:26:59 > 0:27:02- Everything that's alive suffers...
0:27:05 > 0:27:10- ..well beyond Siberia, - across the whole world.
0:27:16 > 0:27:20- To learn how a volcanic eruption - can have such a global impact...
0:27:21 > 0:27:26- ..scientists examine the most - volcanic country on earth - Iceland.
0:27:29 > 0:27:34- They saw a similar explosion to the - one in Siberia here 200 years ago...
0:27:34 > 0:27:37- ..but on a much smaller scale.
0:27:38 > 0:27:42- Near the village of Laki, - a 17-mile long tear opens up...
0:27:42 > 0:27:45- ..on the earth's surface.
0:27:48 > 0:27:49- Iceland is destroyed...
0:27:50 > 0:27:53- ..and over a million people die - all over the world.
0:27:56 > 0:27:59- These holes - and cracks in the ground...
0:27:59 > 0:28:03- ..would have had jets of magma, - jets of lava flying into the sky.
0:28:06 > 0:28:09- To give you an idea of scale...
0:28:09 > 0:28:12- ..the overall amount of material - that came out of Laki...
0:28:13 > 0:28:16- ..is three and a half cubic miles - of volcanic material.
0:28:16 > 0:28:18- That's a lot of material.
0:28:18 > 0:28:22- It's not just the size of Laki - that makes it so special.
0:28:22 > 0:28:26- What's inside this and what came out - of this is the dangerous thing.
0:28:26 > 0:28:29- It had sulphur gases - associated with the eruption...
0:28:30 > 0:28:31- ..and also fluorine.
0:28:31 > 0:28:33- Quite poisonous gases.
0:28:35 > 0:28:39- The gases have a devastating - impact on people the world over...
0:28:41 > 0:28:45- ..including here in Llanbadarn, - near Aberystwyth.
0:28:45 > 0:28:47- Laki is in Iceland...
0:28:47 > 0:28:52- ..but it affected the whole of the - northern hemisphere and beyond.
0:28:53 > 0:28:58- When it erupted in 1783 and - for the subsequent eight months...
0:28:59 > 0:29:03- ..gases went up - into the atmosphere...
0:29:04 > 0:29:09- ..and were carried by winds - and weather systems across Europe...
0:29:10 > 0:29:11- ..including Wales.
0:29:12 > 0:29:16- It reduced the global temperature - by one degree Celsius...
0:29:17 > 0:29:20- ..which had a big impact - on growing seasons...
0:29:21 > 0:29:24- ..which were vitally important - back then.
0:29:28 > 0:29:31- We're in Llanbadarn, - near Aberystwyth.
0:29:33 > 0:29:37- There's a record from 1784 - by Ellis Roberts.
0:29:37 > 0:29:41- He wrote a poem about the event. - He was a balladeer.
0:29:41 > 0:29:45- Ballads were a way of sharing - information during that time.
0:29:46 > 0:29:48- Balladeers were like - today's newsreaders.
0:29:49 > 0:29:50- This is what he had to say.
0:29:52 > 0:29:55- Seven hundred and six - Lost their lives
0:29:56 > 0:29:58- People previously in rude health
0:29:58 > 0:30:01- Few people survived - To bury the dead.
0:30:02 > 0:30:07- So 706 from this small parish - of Llanbadarn, near Aberystwyth...
0:30:07 > 0:30:10- ..lost their lives - during this period.
0:30:10 > 0:30:14- There were very few people left - to bury the dead.
0:30:20 > 0:30:22- Over a million people are killed.
0:30:27 > 0:30:29- It's a global catastrophe.
0:30:34 > 0:30:38- It's clear that even a relatively - small eruption like Laki...
0:30:38 > 0:30:42- ..can cause dramatic effects - in terms of the climate.
0:30:43 > 0:30:46- The northern US had one of - the coldest winters ever recorded.
0:30:47 > 0:30:48- The Mississippi was frozen.
0:30:49 > 0:30:53- It's been implicated - in causing a big famine in Japan.
0:30:53 > 0:30:58- The effects for volcanoes that spew - these gases into the atmosphere...
0:30:58 > 0:31:01- ..can be catastrophic - on a global scale.
0:31:08 > 0:31:11- But what happened in Siberia - is on a much larger scale.
0:31:21 > 0:31:26- Over 70% of the creatures on - the land were killed by the gases.
0:31:29 > 0:31:33- And things went from bad to worse.
0:31:36 > 0:31:39- The sea became warmer, - losing its oxygen.
0:31:40 > 0:31:44- Toxic algae killed most marine life.
0:31:47 > 0:31:49- It turned the oceans pink.
0:31:53 > 0:31:57- This was the closest the earth - had come to total extinction.
0:32:00 > 0:32:06- But, over 200 million years, - the survivors adapt and evolve.
0:32:08 > 0:32:10- A new group of animals emerges.
0:32:11 > 0:32:12- The dinosaurs.
0:32:15 > 0:32:20- But they too will not live forever - because of another threat.
0:32:21 > 0:32:23- This time from space.
0:32:24 > 0:32:26- The evidence is quite strong...
0:32:26 > 0:32:32- ..that the dinosaurs were killed - by a huge asteroid striking earth.
0:32:32 > 0:32:37- We're talking about an asteroid - a couple of kilometres in length.
0:32:44 > 0:32:48- Meteors and asteroids - strike earth every day.
0:32:48 > 0:32:51- Most are quite small - and don't affect us.
0:32:52 > 0:32:57- But sometimes, as we recently saw - in Chelyabinsk, Russia...
0:32:58 > 0:33:00- ..a larger meteor comes in...
0:33:00 > 0:33:06- ..and we witness the enormous energy - that's carried by these missiles.
0:33:12 > 0:33:14- February, 2014.
0:33:17 > 0:33:22- It's a cold winter's morning - in the Siberian city of Chelyabinsk.
0:33:24 > 0:33:26- Out of the blue morning sky...
0:33:30 > 0:33:33- ..a 65 foot meteor - tears through the sky.
0:33:38 > 0:33:41- It explodes - 18 miles above the earth.
0:33:46 > 0:33:50- It shatters windows, - damages buildings...
0:33:52 > 0:33:55- ..and injures over 1,000 people.
0:33:58 > 0:34:02- When the rock - entered the atmosphere...
0:34:03 > 0:34:04- ..it started to burn.
0:34:06 > 0:34:11- Many people saw this object - as a ball of fire in the sky.
0:34:13 > 0:34:17- If you watch those videos - of that meteor in Russia...
0:34:17 > 0:34:20- ..with the incredible sonic boom...
0:34:20 > 0:34:24- ..you can see how even - a relatively small object...
0:34:24 > 0:34:26- ..can produce a dramatic event - for humans.
0:34:32 > 0:34:35- An object - the size of this asteroid...
0:34:35 > 0:34:38- ..strikes, on average, - once every century.
0:34:39 > 0:34:45- Asteroids and comets are racing - towards our planet right now.
0:34:46 > 0:34:50- When will the next big one strike? - What will happen?
0:34:54 > 0:34:58- The clues lie in the past - - in the extinction of the dinosaurs.
0:35:02 > 0:35:04- It's a quiet morning on earth.
0:35:05 > 0:35:08- In the sky, - a small light can be seen.
0:35:11 > 0:35:14- But the light is moving - and gets brighter.
0:35:16 > 0:35:19- The asteroid is on its way.
0:35:22 > 0:35:24- It's a rock the size of Everest...
0:35:25 > 0:35:29- ..racing towards the earth - at incredible speed.
0:35:29 > 0:35:32- It's moving much quicker than sound.
0:35:33 > 0:35:38- Everything would be over before - you knew it in terms of the impact.
0:35:38 > 0:35:44- Had we been there to see it, - we would have died instantly.
0:35:48 > 0:35:53- The asteroid smashes into the earth - off Mexico's Yucatan Peninsula.
0:35:54 > 0:35:57- It strikes - with a force much greater...
0:35:57 > 0:36:01- ..than the biggest nuclear bomb - ever detonated.
0:36:03 > 0:36:06- It creates a crater - 200 miles across.
0:36:08 > 0:36:10- A superheated wave roars out.
0:36:12 > 0:36:17- Red-hot rocks soar into space, - before falling back down...
0:36:17 > 0:36:19- ..setting the planet ablaze.
0:36:21 > 0:36:25- Two hours later, - a 300 foot tsunami hits the coast.
0:36:27 > 0:36:33- Over the next months, dust and - smoke hangs in the atmosphere.
0:36:34 > 0:36:39- It had a devastating effect on the - animals which existed at the time.
0:36:39 > 0:36:43- The dust that was thrown - into the atmosphere...
0:36:44 > 0:36:48- ..darkened the planet for a year, - shutting down photosynthesis.
0:36:49 > 0:36:53- Anything which relied on plants - to give it life...
0:36:53 > 0:36:56- ..couldn't survive these conditions.
0:36:57 > 0:37:02- When that happened, it created what - we refer to as a mass extinction.
0:37:04 > 0:37:08- The dust in the atmosphere - blocked out the sun, so plants died.
0:37:09 > 0:37:14- As a result, animals - such as dinosaurs became extinct.
0:37:17 > 0:37:20- This was the end for the dinosaurs.
0:37:22 > 0:37:24- But for us, it was the beginning.
0:37:27 > 0:37:30- That's how life as we know it began.
0:37:31 > 0:37:35- Evolution happened - because of one small animal...
0:37:35 > 0:37:39- ..that survived - the asteroid hitting the earth.
0:37:40 > 0:37:43- Evolution led us to life - as we know it today.
0:37:46 > 0:37:51- By removing the dinosaurs, - the mammals were allowed to grow.
0:37:51 > 0:37:56- In the same way today when you - destroy foxes, the rabbits thrive.
0:37:58 > 0:38:00- That's how evolution works.
0:38:01 > 0:38:03- There's a one in 5,000 chance...
0:38:03 > 0:38:07- ..of a similar asteroid hitting - earth within the next 100 years.
0:38:09 > 0:38:11- It could happen at any time.
0:38:12 > 0:38:18- If a kilometre-wide object hits - the earth, it's curtains for us.
0:38:19 > 0:38:22- And it could strike without warning.
0:38:23 > 0:38:27- It could happen tomorrow - or 1,000 years from now.
0:38:27 > 0:38:31- One thing's for certain - - another one will come.
0:38:33 > 0:38:37- Asteroids travel fast - and are difficult to spot.
0:38:42 > 0:38:46- The Chelyabinsk asteroid - came from the sun's direction.
0:38:47 > 0:38:52- Many asteroids could be - on a collision course with us...
0:38:53 > 0:38:58- ..but we won't see them if - they come from the sun's direction.
0:39:00 > 0:39:03- If an asteroid is heading our way...
0:39:03 > 0:39:06- ..we need to spot it - sooner rather than later.
0:39:10 > 0:39:14- The Spaceguard Centre in Powys - looks for asteroids.
0:39:14 > 0:39:20- Spaceguard and other similar centres - have spotted over 10,000 asteroids.
0:39:26 > 0:39:30- Some were a few inches long. - Others were 25 miles wide.
0:39:36 > 0:39:41- Some of them may be travelling on - a collision course with the earth.
0:39:43 > 0:39:47- It's important to monitor it - and to think what we could do...
0:39:48 > 0:39:53- ..if an asteroid or a comet - strikes the earth in the future.
0:39:59 > 0:40:04- Recently, scientists have discovered - just how fragile the earth is.
0:40:05 > 0:40:07- Since the year 2000...
0:40:07 > 0:40:12- ..26 asteroids have exploded - in the earth's atmosphere.
0:40:12 > 0:40:16- Some were 40 times more powerful - than the Hiroshima bomb.
0:40:19 > 0:40:23- And we didn't spot a single one - of them before they struck.
0:40:24 > 0:40:29- Even if we can detect an asteroid - before it hits, can we destroy it?
0:40:30 > 0:40:33- The way to avoid - being hit by an asteroid...
0:40:33 > 0:40:38- ..is to spot it soon enough - and attempt to change its course.
0:40:38 > 0:40:41- There are several ways to do that.
0:40:42 > 0:40:46- One way, the one used for dramatic - effect in Hollywood films...
0:40:47 > 0:40:48- ..is to blow it up.
0:40:48 > 0:40:52- But a nuclear bomb - could make things worse...
0:40:52 > 0:40:55- ..smashing an asteroid - into large chunks...
0:40:55 > 0:40:58- ..capable of more destruction - on earth.
0:41:02 > 0:41:08- So scientists are looking for - another way to save the earth.
0:41:13 > 0:41:16- One of the ways - which appeal to me...
0:41:17 > 0:41:20- ..is to paint - one side of the asteroid white.
0:41:21 > 0:41:25- The sun's rays will have a greater - effect on the white side...
0:41:26 > 0:41:31- ..and it will gradually alter - the asteroid's course.
0:41:40 > 0:41:44- To survive, we need the - right technology and enough time.
0:41:51 > 0:41:56- The earth has experienced - destruction many times.
0:41:56 > 0:41:59- Each time, - some form of life has continued.
0:42:01 > 0:42:07- But inevitably the end will come - and life on earth will vanish...
0:42:08 > 0:42:10- ..thanks to the sun.
0:42:18 > 0:42:19- .
0:42:28 > 0:42:28- Subtitles
0:42:28 > 0:42:30- Subtitles- - Subtitles
0:42:41 > 0:42:46- Despite the earth's turbulent past, - we are still here.
0:42:51 > 0:42:54- But eventually - we will face extinction...
0:42:56 > 0:43:00- ..threatened by the thing - which gives us life - the sun.
0:43:05 > 0:43:09- The lifespan of the sun - will be around ten billion years.
0:43:10 > 0:43:15- We know this because of the amount - of hydrogen left in the sun's core.
0:43:16 > 0:43:19- We're halfway through - that fuel now...
0:43:19 > 0:43:24- ..so in around five billion years, - the hydrogen will start to run out.
0:43:24 > 0:43:29- The process of burning hydrogen - through fusion will slow down...
0:43:30 > 0:43:34- ..and the sun will become - very unstable.
0:43:38 > 0:43:42- Unfortunately, the sun is getting - bigger and bigger.
0:43:42 > 0:43:47- Ultimately, this means it will run - out of energy and come to an end.
0:43:48 > 0:43:54- As with any star that dies, it will - destroy everything around it.
0:43:58 > 0:44:02- As the sun dies, it will swell - and appear brighter.
0:44:04 > 0:44:07- The outer layers of the sun - will expand outwards.
0:44:08 > 0:44:12- It's more than likely that it will - expand into the earth's orbit.
0:44:22 > 0:44:26- If we're still here on earth, - we'll perish.
0:44:26 > 0:44:31- Other species may find a way - to adapt but not for long.
0:44:35 > 0:44:39- Five billion years from now, - the sun runs out of hydrogen.
0:44:39 > 0:44:42- It starts - the last stage of its life...
0:44:42 > 0:44:46- ..bloating to 100 times - its current size.
0:44:49 > 0:44:53- When the sun reaches the end - of its lifespan and expands...
0:44:53 > 0:44:56- ..it will swallow the planets - nearest to it.
0:44:57 > 0:45:00- So Mercury, Venus - and probably the earth too...
0:45:01 > 0:45:03- ..will disappear into the star.
0:45:17 > 0:45:20- The death of the sun - is also our end.
0:45:23 > 0:45:26- There's no doubt, it will happen.
0:45:33 > 0:45:37- But life may have developed - somewhere else in the solar system.
0:45:40 > 0:45:42- As the sun expands...
0:45:42 > 0:45:47- ..the planets which are further out - will now get more heat and light.
0:45:51 > 0:45:57- The moons around Jupiter and Saturn - which seem to have water on them...
0:45:57 > 0:46:02- ..may offer hope - as a place where life can flourish.
0:46:04 > 0:46:07- Scientists believe - there may be life...
0:46:08 > 0:46:11- ..under the ice - on one of Jupiter's moons.
0:46:11 > 0:46:13- Europa.
0:46:13 > 0:46:17- In the distant future, - when the sun is swollen...
0:46:18 > 0:46:22- ..temperatures will rise - and the ice on Europa will melt.
0:46:22 > 0:46:26- It could then be possible - for humans to survive there.
0:46:27 > 0:46:31- Must we escape to a distant moon - and start a new life?
0:46:32 > 0:46:37- Imagine you know full well - there's an asteroid on its way...
0:46:37 > 0:46:40- ..and it will hit the earth - in two years.
0:46:41 > 0:46:45- Enough time to prepare spacecrafts - to take some people away...
0:46:46 > 0:46:50- ..but most people know there's no - room for them on those spacecrafts.
0:46:53 > 0:46:58- We can't control the cosmos but we - may be able to control our future.
0:46:59 > 0:47:04- It's possible that we will break - this cycle of extinction...
0:47:04 > 0:47:06- ..by escaping to another planet.
0:47:07 > 0:47:11- A lot of money is being invested - by NASA and other agencies...
0:47:11 > 0:47:16- ..who are searching - for other habitable planets.
0:47:16 > 0:47:22- We may survive the next extinction - by moving to another planet.
0:47:23 > 0:47:26- Our greatest hope - is our intelligence.
0:47:34 > 0:47:38- We may be the first species - in the earth's history...
0:47:38 > 0:47:42- ..to overcome - an extinction event and live on.
0:48:12 > 0:48:14- S4C subtitles by Eirlys A Jones
0:48:14 > 0:48:15- .