Y Cosmos: Diwedd Y Byd

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

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