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00:00Our world formed through a series of devastating cataclysms.
00:10It could have literally blown the Earth to bits, and then we wouldn't even have a planet
00:13today.
00:16An apocalyptic planetary collision, millions of brutal cosmic strikes, and the most powerful
00:24blast in the universe, a supernova.
00:29Saturn atoms would have been scattered into outer space.
00:34Yet these catastrophes created the planet we know today.
00:39The Earth is an incredibly special place.
00:41It seems like everything has worked out just perfectly.
00:45Could other planets have formed the same way?
00:49If so, the universe could be full of Earths, and full of life.
01:13Our planet is extraordinary.
01:17It provides everything life needs.
01:21Trillions of creatures, plants, and us.
01:28When you look down at the Earth from space, and everything that we know of that's life
01:34is down there on that planet, that beautiful planet, that you now are going around every
01:41hour and a half, and that's almost overwhelming, just the beauty of the Earth.
01:49It's unique in our solar system, but is it unique in the universe?
01:56It's important for us to understand the conditions that led to the formation of the Earth, because
02:01then we can look for those conditions around other stars, and if we find those conditions
02:05there, then that would suggest that other Earths could be forming elsewhere in the universe.
02:14Could there be other planets like ours among the stars?
02:20To find out, we must travel back in time, and discover how the Earth was made.
02:36Rewind the clock four and a half billion years, and this is what you see.
02:45This speck of dust will become the Earth, by combining with countless others.
02:55They're all part of a giant cloud, called a stellar nursery.
03:01The first step of planetary formation is about to start, an event that will transform the
03:15cloud into thousands of infant solar systems, including our own.
03:29The same process is happening today, 7,000 light years away, in the Eagle Nebula.
03:40Our own solar system formed inside clouds of gas and dust, like these.
03:50There are these three trunks of gas, and they're nicknamed the Pillars of Creation, and they're
03:55trillions of miles long.
03:57These are huge structures.
03:59The clouds look dense, but they're actually very sparse.
04:05These gas clouds are incredibly tenuous.
04:08You'd have to compress basically a mountain's volume worth of this stuff, squeeze it down
04:14just to make a little tiny rock like this.
04:17To compress the gas and dust into dense stars and planets takes a supremely powerful event,
04:28one that can only follow the death of a giant star.
04:35In 2007, the Spitzer Space Telescope captured this image, a ball of hot gas behind the Eagle
04:45Nebula, evidence that a huge star has exploded and sent a vast wall of gas racing toward
04:57the Pillars.
04:58There's a wave of hot material approaching the Pillars of Creation, and this may be a
05:04shockwave from a supernova, a dying star.
05:12Supernovas briefly outshine entire galaxies.
05:18Superheated plasma blasts into space at 70 million miles per hour.
05:26A mighty shockwave speeds toward the Pillars of Creation.
05:38When it hits, it will demolish them.
05:42It will also create new worlds.
05:48Supernova shockwaves smash into the Pillars, compressing the thin gas and dust into dense
05:56clumps.
05:58Each is a new star, a new solar system.
06:05Molecular cloud, minding its own business, gets blasted by a supernova explosion, crushing
06:11the cloud down into stars and planets.
06:16Wind back four and a half billion years, and our solar system starts the same way.
06:25A supernova crushes a massive, dusty cloud into a proto-planetary disk.
06:33A thin, nebulous cloud becomes a dense whirlpool of gas and dust, a solar system in the making.
06:46One star is destroyed, a new star is born, our sun and its planets.
06:57This is the first link in the long and unlikely chain of events that made our world.
07:07For Earth to even be here, we had to beat astronomical odds.
07:15A host of different factors have to line up to get a planet just like the Earth.
07:20You have to have the right distance, the right size, the right kind of moon.
07:27On Earth, all the conditions are just right for life.
07:32To get a world like ours, you need a lot of aces.
07:35Somehow, our solar system hit the jackpot, but the big question is, did it happen anywhere
07:42else?
07:46One of the universe's most violent events triggered the birth of our planet, a sparse
07:56cloud crushed into a dense swirl of dust.
08:03Some of this dust will become planet Earth.
08:09But how do tiny dust grains create entire worlds?
08:25A supernova explosion triggers a chain of events that will eventually create the Earth,
08:34the formation of our solar system.
08:38A hot ball of gas grows in the center.
08:44This will become our sun.
08:49The dust that swirls around it will form the planets.
08:56But first, the grains must stick together.
09:02So we have this interesting conundrum, right?
09:04So, this disc consists of gas, and dust particles.
09:07They're about the size of, let's say, particles in smoke, right?
09:11Let's say cigarette smoke, right?
09:13So these are small things.
09:15And somehow we have to get from those little grains to what we see on the Earth.
09:23Gravity is a powerful, attractive force.
09:26It shapes galaxies and solar systems.
09:31But specks of dust are far too small to pull on each other.
09:37Somehow, they clump together to form planets.
09:42So if gravity doesn't bind them, what does?
09:49In Germany, scientists are on the case.
09:54They can simulate how dust behaves in space, inside a huge tower.
10:03Here we do free fall experiments.
10:05So the whole experimental setup, including our dust aggregates, are in perfect free fall.
10:10It is simulation of space, but a very good one, indeed.
10:14I think this is the closest you can get to space on Earth.
10:19Researchers place dust in a container and load it into a launch capsule.
10:27At the base of the tower, they lower it into a super-powerful catapult.
10:35This launches the half-ton capsule from zero to over 100 miles per hour in a quarter of a second.
10:48100 feet up, the capsule reaches the top of the tower, then plunges back down.
10:56A drum of polystyrene balls 30 feet deep breaks its fall.
11:05All this gives just 10 seconds of zero gravity.
11:09Just enough time, they hope, for the dust to stick.
11:14Three, two, one, and go.
11:20Moments after the capsule launches, the dust inside becomes weightless.
11:28The grains clump together, just like the early solar system.
11:41These images reveal how dust particles came together four and a half billion years ago to form the Earth.
11:51The force that binds the aggregates together is not gravity.
11:54They are too small for gravity to be efficient.
11:58We think the force that binds the aggregates together is electrostatic force.
12:05It's the same reason that when you pull your clothes out of the dryer, you know how the clothes sometimes stick to you?
12:12That's the same effect that allows one dust particle to stick to another.
12:17Dust particles join to form balls of fluff.
12:22The little static charges that they have can make them stick when they hit.
12:26And you get something sort of like the dust bunnies that I have a lot of underneath my bed.
12:32These cosmic dust bunnies are planets in the making.
12:38They start out smaller than a pinhead, then grow.
12:44The dust is now in clumps, but it's still just balls of dust.
12:54Turning dust balls into rocks takes a whole new process.
13:01A cosmic electric storm.
13:07Space clouds build up charge just like clouds here on Earth, generating huge bolts of lightning.
13:20Balls of dust can turn into solid rocks by an energetic event like lightning.
13:27Electric bolts smash through the dust balls and heat them to 3,000 degrees Fahrenheit.
13:38In minutes, they cool and fuse into solid rock.
13:45Meteorites today still carry these ancient rock balls inside them.
13:52Tiny globules were once the building blocks of planets.
13:59To form the Earth, these tiny balls must collide, stick, and grow.
14:07Rocks begin to build up by accidental collisions, which can take a long time.
14:11Eventually, the proto-planets, as we call them, the baby planets, get the size of asteroids kilometers across.
14:20The baby Earth is now the size of a few city blocks.
14:25Big enough for a new force to take charge.
14:29Gravity.
14:31At that point, a single asteroid will gravitationally attract a neighboring asteroid.
14:38And so those two asteroids that would have passed in the night are gravitationally attracted and they hit each other.
14:47Once gravity starts to rear its head, things really speed up.
14:51Because instead of just randomly plowing through material and getting bigger that way, now it's starting to draw material in.
15:00Gravity pulls rocks together, then holds them there to produce bigger and bigger piles of rubble.
15:12So this formation process, which was taking a long time to get to the size where gravity kicks in,
15:17suddenly gets kicked into overdrive and the planet grows very rapidly.
15:23But planets are more than just overgrown rock piles.
15:29These rocks are lumpy and inert.
15:34How did the Earth become round and full of life?
15:48The early solar system is a construction site for planets.
15:54Dust sticks together to form rocks.
15:59Rocks join to form asteroids.
16:04But most asteroids look nothing like Earth.
16:09And when you look at a close-up of an asteroid, it looks like some kind of distorted peanut.
16:14Like a potato that's been sort of bashed.
16:17You can see giant craters and oblong shapes.
16:22The young Earth is one of billions of misshapen space boulders.
16:29To become a planet, it must first become round.
16:35That process only starts when it's several hundred miles across.
16:41When its own internal gravity begins to change its shape.
16:48Once you get enough material, enough mass, the gravitational force becomes stronger.
16:54Any giant mountain will be crushed down by the force of gravity.
16:59The gravity is so strong that can it actually break rocks.
17:04And the rocks itself can act like a fluid making an object round.
17:09Huge outcrops of rock crumble and fall.
17:15The immense self-gravity of the early Earth crushes it into the most efficient shape.
17:25A vast round ball of rock.
17:32A lopsided pile of rubble transformed into a miniature world.
17:45The Earth has a new shape, but it's still just a ball of rock.
17:51Its structure will also soon change.
17:56Cosmic rocks and boulders still rain down from space.
18:02Each collision heats the ground.
18:06There's a huge amount of energy stored in an object that's moving rapidly.
18:10When that hits the Earth, all that energy is dumped into the material and that heats it up and melts it.
18:15And the Earth became molten and stayed that way for a long time.
18:20The young planet is no longer solid rock.
18:24It's a seething, molten mass.
18:29Just like this blast furnace at the Severstal plant in Detroit.
18:36Believe it or not, this process behind me makes life on Earth possible.
18:45They feed in ground-up iron ore.
18:50A mixture of rock and metal.
18:54Just like the early Earth.
19:00Put iron ore in a furnace, and the heat melts everything.
19:10This molten iron is at 2,700 degrees Fahrenheit.
19:16That's about the temperature of the surface of the Earth four and a half billion years ago.
19:22Imagine an entire planet molten.
19:26In the distance, you would see thundering volcanoes spewing out lava.
19:31It would be a scene right out of Dante's Inferno.
19:41Iron is heavier than rock.
19:45Now molten, they separate.
19:50This is amazing. We're witnessing a process which created the very crust of the Earth billions of years ago.
19:56The crust that we walk on every day.
20:02Molten rock rises to the surface and cools to form the crust.
20:08Molten iron sinks underneath.
20:13Inside the Earth, it sank all the way to the planet's core.
20:19The rocky surface is where we live.
20:24But without Earth's molten iron core, none of us could survive.
20:30This process separated the iron from the rocky minerals.
20:36As the iron descended to the center of the Earth, it eventually created a magnetic field.
20:42And that's why we're here today.
20:47Iron is inside the Earth's core.
20:51And generates a powerful magnetic field around the planet.
20:57A cosmic shield against deadly radiation from space.
21:03But the young Earth is still small.
21:09Far smaller than the moon today.
21:15This newly formed world must grow.
21:21It must also avoid being blown to pieces.
21:27Thousands of proto-planets are hurtling around the solar system.
21:33And some are heading straight for Earth.
21:46It's a hundred thousand years since our solar system formed.
21:52The young Earth already looks like a planet.
21:57It's round. It has an iron core and a rocky surface.
22:03Yet our baby planet is just a few hundred miles across.
22:09It has a long way to go.
22:14It must grow 4,000 times more massive.
22:20And it has competition.
22:24Thousands of other proto-planets shoot through the solar system.
22:30Often colliding at over 20,000 miles per hour.
22:37You can find proof of this ancient, destructive era in modern day Arizona.
22:45Not Meteor Crater itself. That's just 50,000 years old.
22:51But the asteroid that gouged it out.
22:56That was four and a half billion years old.
23:02Mark Sykes and Marvin Kilgore think the asteroid came from a violent event in the early solar system.
23:12The asteroid flew through space for billions of years.
23:18Then it hit Earth.
23:22They aim to find a fragment of the asteroid.
23:27A remnant from the period of planetary formation.
23:33About six miles from here is Meteor Crater.
23:37And that was an impact 50,000 years or so ago.
23:41And it spewed a bunch of pieces out.
23:45They're convinced the original asteroid was rich in iron.
23:50So they've come prepared with some impressive metal detectors.
23:55Does it work? Oh yeah.
24:01That's the sound we're listening for.
24:07But even with a quad-drawn metal detector, meteorites are hard to find.
24:17Yeah, are you pretty convinced there's nothing there?
24:21Yeah, I'm not detecting anything.
24:28They find metal, but no meteorites.
24:33My great discovery of the afternoon has been this bolt.
24:39And this piece of wire.
24:44It takes hours of searching.
24:48And many false alarms.
24:51Then, with the light fading, the detector sounds again.
25:02How about that? Success at last.
25:05This meteorite is over 90% iron and nickel.
25:10It could only form right in the core of a protoplanet.
25:16The protoplanet it came from must have smashed apart in a brutal collision.
25:23Well, in the early solar system, it was a pretty violent place.
25:28And these protoplanetary embryos would smash into each other.
25:32They would shatter each other, exposing the interior cores like this.
25:37It was a very tumultuous time.
25:40Entire worlds reduced to chunks of rock and metal.
25:46And scattered into outer space.
25:51In the early solar system, these vast collisions are common.
25:58The young Earth is in danger.
26:03The period's name is the Titanomachian.
26:08Literally, the War of the Titans.
26:14All rocky planets, the Earth included, go through this destructive phase.
26:22Sometimes they shatter completely.
26:28Sometimes one consumes the other.
26:34All the big guys are sort of competing with one another in a very violent way, actually,
26:40to see who comes out on top by eating all their neighbors.
26:45The battle lasts over 30 million years.
26:50Finally, thousands of protoplanets have combined into a few full-size planets.
27:00Mercury.
27:01Venus.
27:02Earth.
27:04Mars.
27:06And a fifth planet, Theia.
27:11It's racing toward Earth.
27:15The planet's last giant impact.
27:21Theia is the size of Mars, big enough to destroy the Earth.
27:29If that thing had hit us straight on, it could have literally blown the Earth to bits,
27:33and then we wouldn't even have a planet today.
27:35If this Mars-like object had a direct hit with the Earth,
27:39perhaps there would have been another asteroid belt where the Earth is today.
27:44But Earth is in luck.
27:47Instead of a head-on crash, Theia strikes a glancing blow.
27:59It's the most violent event the Earth has ever known.
28:06The impact turns the Earth back to a molten world.
28:13A vast magma ocean 600 miles deep.
28:20The Earth barely survives.
28:28And the encounter changes our world forever.
28:35Material blasts out into space.
28:40Enough rock to build a mountain as wide as America,
28:46and 10,000 miles high.
28:50It would have been so much energy, so much catastrophe.
28:53Huge amounts of material blasted off and went into orbit around the Earth.
28:57The debris forms a huge ring around the Earth.
29:03This gathers together to form two rocky bodies, both orbiting the Earth.
29:13If something the size of Mars hit the Earth about 4 billion years ago,
29:16lots of material would have been thrown off.
29:18We now think that it may have formed not only one moon, but two.
29:24For millions of years, two moons dominate the Earth's sky.
29:33Eventually they drift together and collide.
29:45Two moons merge into one.
29:51The massive moon we see today.
29:56There's no other planet that we know of that has a moon as large as ours,
30:00in comparison to the size of the planet.
30:02We're almost a binary planet, two worlds going around each other.
30:07Without this large moon, we might not even be here.
30:14The moon plays a key role in the survival of life here on the Earth.
30:19The reason is that the moon in its orbit stabilizes the Earth.
30:25The moon keeps the Earth spinning at the same angle.
30:30That steadies our climate.
30:34The fact that the Earth's axis stays in the same direction as it goes around the sun
30:38produces the seasons, but regular seasons,
30:41things that life can depend upon as it evolves.
30:45The Earth is neither too hot nor too cold for life,
30:51thanks to our distance from the sun and our massive moon.
31:01The Earth is not covered in ice or steam, but in liquid water.
31:11Yet that water must come from somewhere.
31:17The newly formed Earth is dry.
31:22To get water, our planet must once again face disaster.
31:38It's half a billion years since the sun first ignited.
31:44Four billion years from now, the first humans will set foot on Earth.
31:52The moon has just formed.
31:56And the Earth is a desert.
32:03One of the more amazing ideas in astronomy is that the Earth started out hot and dry.
32:08There was no water here originally.
32:11As the planets formed, the sun's intense radiation
32:16vaporized the water in the inner solar system.
32:21Farther from the sun, temperatures were cooler.
32:25So in the outer solar system, ice and water collected on comets and asteroids.
32:35While closer to the sun, the young Earth was dry.
32:41So things changed. What happened?
32:44How is it that now we have this wonderful water cycle?
32:47Well, the water probably came from somewhere else.
32:51If you want to have a solar system that has a lot of water in it,
32:54you have to bring it from the outer parts down into the inner parts.
32:58And you can do that through comets and asteroids.
33:03Comets and icy asteroids contain huge reserves of water.
33:09But they're hundreds of millions of miles from the young Earth.
33:15Then something changes.
33:19An event that tosses the asteroids and comets right across the solar system.
33:28Jupiter, Saturn, Neptune, Uranus take a cosmic roller coaster ride.
33:40So this isn't an event that happened when the solar system was young.
33:44It was more of its teenage breakout years where it just started to party for a while.
33:51The young planets have not yet settled into stable orbits.
33:57As their orbits shift, Jupiter and Saturn fall into an intricate dance.
34:05Every time Saturn orbits the sun once, Jupiter orbits twice.
34:12So they always line up at the same spot.
34:16Each time, gravity tugs them in the same direction.
34:21First, they destabilize each other.
34:24And then the entire solar system.
34:28The whole thing just goes kaplooey.
34:30The analogy I like to use is when a bowling ball hits pins, it just goes bam all over the place.
34:36That's what this would have looked like.
34:38Planetary pandemonium.
34:41Neptune and Uranus switch places.
34:45Saturn races outwards.
34:48The giant planets scatter billions of asteroids and comets onto new paths.
34:56Many head for Earth.
35:00These asteroids and comets would have been scattered all over the place.
35:04Some of them hitting the Earth and Moon.
35:07Cosmic missiles bombard the Earth.
35:13We believe that every square inch of the Earth got hit by a comet or an asteroid during this period.
35:19It would not have been a fun time to be here.
35:23The bombardment lasts hundreds of millions of years.
35:30Until finally, the gas planets settle into the stable orbits we see today.
35:38Restoring order.
35:43But Earth itself has fundamentally changed.
35:48Those comets and asteroids were not just made of rock.
35:54But of ice. Frozen water.
36:00Comets, we know, are made out of ice.
36:02Their dirty snowballs are not out of space.
36:04And even asteroids can bring water and ice to the Earth.
36:10Our oceans are full, thanks to the cosmic hailstorm.
36:16So, next time you're drinking a glass of water, realize that you're probably drinking comet and asteroid juice.
36:24The arrival of water is the final step to create a habitable planet.
36:34A sequence of catastrophes has created a world that's perfect for life.
36:43But has it happened elsewhere among the stars?
36:47Or are we alone?
37:03How did we get here?
37:07Planet Earth only exists because of a chain of extraordinary events.
37:15A lucky throw of cosmic dice.
37:21Five billion years ago, the odds would have seemed extremely slim
37:24that a planet like Earth would form in a rather unremarkable arm in the Milky Way galaxy.
37:29It's like trying to throw two sixes, but with dice that have thousands of sides.
37:38We know it happened once, else we wouldn't be here.
37:43But what are the odds it happened elsewhere?
37:48That other planets have life.
37:53Life like ours needs a planet with the right temperature and size,
37:59a stabilizing moon, a protective magnetic field, and just the right amount of water.
38:09The conditions must be perfect.
38:16Yet amazingly, there may be countless Earth-like planets out there waiting to be found.
38:26Thanks to the sheer scale of the universe.
38:32We may find one any day now with the Kepler Space Telescope.
38:41Jeff Marcy is mission co-investigator.
38:46It has only one goal, and that's to discover Earth-sized planets around other stars that you see in the night sky.
38:54Earth-sized planets are hard to spot.
38:59Before Kepler, astronomers took 20 years to discover around 500 planets.
39:07Gas giants hundreds of times bigger than Earth.
39:12Since Kepler, that number has exploded.
39:17Kepler has already discovered a couple thousand planet candidates.
39:23Many of them are members of multi-planet systems, 2, 3, 4, 5, and even 6 planets all orbiting the same star.
39:31So we're finding an absolute avalanche of planets out there among the stars.
39:38Kepler has found one planet only twice the size of Earth, and the right temperature for life.
39:48We don't know yet if this planet has other Earth-like attributes, like liquid water.
39:57But even if it doesn't, there are many more planets out there.
40:04Kepler has found only a tiny fraction of them, because it only looks at a small part of the sky.
40:14It's not even looking at the whole sky. It's looking at a very tiny slice of stars in the galaxy.
40:20And in fact, if you were to look up, you could cover it with just your thumb.
40:25Across the whole of our galaxy, there are 200 billion stars.
40:32Many will have planets.
40:35Based on our knowledge from Kepler and other searches, something like half of those stars, perhaps even more, harbor planets.
40:44That means at least 100 billion planets have formed in the Milky Way.
40:52Earth-like worlds may be rare, but it seems a safe bet they're out there somewhere.
41:00So the odds of getting an Earth-like planet are extremely small, much smaller than getting a double six at craps.
41:08But if you have a lot of dice, you're guaranteed to get sixes.
41:14And if you have a lot of planets, you're guaranteed to get Earths.
41:22There are so many planets in our galaxy, even if the chances are one in a million, there should be thousands of Earth-like worlds.
41:36Our universe at large has hundreds of billions of galaxies, each of which is more or less like our Milky Way.
41:44So the number of planets in our universe is virtually uncountable.
41:49Alien Earths must be everywhere.
41:53Now, we haven't discovered even one of them yet, but statistically speaking, it is a rock-solid certainty.
42:00There are millions of billions of planets like the Earth out there.
42:06And with that many Earth-like planets, surely some of them will have intelligent life.
42:14I would bet everything, I would bet my house that there is another Earth out there somewhere.
42:21There really can be no doubt that elsewhere in our universe, there are other smart critters who are asking themselves,
42:28gee, I wonder if there are any other intelligent species out there in the universe.
42:36The story of the birth of our planet reveals that we cannot possibly be alone in the universe.
42:46The question is not, are we alone?
42:50It's how far away are our neighbors?
42:54And when will we meet?