Narrator: Our world formed
through a series of devastating cataclysms...
It could have literally blown the Earth to bits,
and then we wouldn't even have a planet today.
Narrator: ...An apocalyptic planetary collision,
millions of brutal cosmic strikes,
and the most powerful blast in the Universe,
a supernova.
Our atoms would have been scattered into outer space.
Narrator: Yet, these catastrophes created the planet we know today.
The Earth is an incredibly special place.
It seems like everything has worked out just perfectly.
Narrator: Could other planets have formed the same way?
If so, the Universe could be full of earths...
and full of life.
♪ How the Universe Works 2x08 ♪ Birth of the Earth Original Air Date on August 29, 2012
== sync, corrected by elderman ==
Our planet is extraordinary.
It provides everything life needs --
trillions of creatures, plants,
and us.
Schweickart: Well, you look down at the Earth from space
and everything that we know of that's life
is down there on that planet, that beautiful planet
that you now are going around every hour and a half,
and that's almost overwhelming --
just the beauty of the Earth.
Narrator: It's unique in our solar system,
but is it unique in the Universe?
Dr. Sykes: It's important for us to understand
the conditions that led to the formation of the Earth
because then we can look for those conditions
around other stars.
And if we find those conditions there,
then that would suggest
that other earths could be forming
elsewhere in the Universe.
Narrator: Could there be other planets like ours among the stars?
To find out, we must travel back in time...
...and discover how the Earth was made.
Rewind the clock 4 1/2 billion years,
and this is what you see.
This speck of dust will become the Earth
by combining with countless others.
They're all part of a giant cloud
called a stellar nursery.
The first step of planetary formation
is about to start...
...an event that will transform the cloud
into thousands of infant solar systems,
including our own.
The same process is happening today,
7,000 light-years away, in the Eagle Nebula.
Our own solar system formed
inside clouds of gas and dust like these.
Dr. Plait: There are these three trunks of gas,
and they're nicknamed the "pillars of creation,"
and they're trillions of miles long.
These are huge structures.
Narrator: The clouds look dense,
but they're actually very sparse.
Plait: These gas clouds are incredibly tenuous.
You'd have to compress,
basically, a mountain's volume worth of this stuff,
squeeze it down just to make a little, tiny rock like this.
Narrator: To compress the gas and dust into dense stars and planets
takes a supremely powerful event --
one that can only follow the death of a giant star.
In 2007, the Spitzer Space Telescope
captured this image --
a ball of hot gas behind the Eagle Nebula...
...evidence that a huge star has exploded
and sent a vast wall of gas racing toward the pillars.
Dr. Thaller: There's a wave of hot material
approaching the pillars of creation,
and this may be a shock wave from a supernova,
a dying star.
Narrator: Supernovas briefly outshine entire galaxies.
Superheated plasma blasts into space
at 70 million miles per hour.
A mighty shock wave speeds toward the pillars of creation.
When it hits, it will demolish them.
It will also create new worlds.
Supernova shock waves smash into the pillars,
compressing the thin gas and dust
into dense clumps.
Each is a new star, a new solar system.
Molecular cloud minding its own business
gets blasted by a supernova explosion,
crushing the cloud down into stars and planets.
Narrator: Wind back 4 1/2 billion years,
and our solar system starts the same way.
A supernova crushes a massive dusty cloud
into a protoplanetary disk.
A thin nebulous cloud becomes
a dense whirlpool of gas and dust --
a solar system in the making.
One star is destroyed.
A new star is born --
our sun and its planets.
This is the first link
in the long and unlikely chain of events
that made our world.
For Earth to even be here,
we had to beat astronomical odds.
A host of different factors have to line up
to get a planet just like the Earth.
You have to have the right distance,
the right size, the right kind of moon.
Narrator: On Earth, all the conditions are just right for life.
Krauss: To get a world like ours, you need a lot of aces.
Somehow, our solar system hit the jackpot.
But the big question is did it happen anywhere else?
Narrator: One of the Universe's most violent events
triggered the birth of our planet.
A sparse cloud crushed into a dense swirl of dust.
Some of this dust will become planet Earth.
But how do tiny dust grains create entire worlds?
Narrator: A supernova explosion triggers a chain of events
that will eventually create the Earth...
...the formation of our solar system.
A hot ball of gas grows in the center.
This will become our Sun.
The dust that swirls around it will form the planets.
But first, the grains must stick together.
Dr. Levison: So, we have this interesting conundrum, right?
So, this disk consists of gas and dust particles.
They're about the size of, let's say,
particles in smoke, all right?
We'll say cigarette smoke, right?
So, these are small things.
And, somehow, we have to get from those little grains
to what we see on the Earth.
Narrator: Gravity is a powerful attractive force.
It shapes galaxies and solar systems,
but specks of dust are far too small
to pull on each other.
Somehow, they clump together to form planets.
So, if gravity doesn't bind them, what does?
In Germany, scientists are on the case.
Okay.
They can simulate how dust behaves in space
inside a huge tower.
Blum: Here, we do free-fall experiments.
So, the whole experimental setup,
including our dust aggregates, are in perfect free fall.
It is simulation of space, but a very good one, indeed.
I think this is the closest you can get to space on Earth.
Narrator: Researchers place dust in the container
and load it into a launch capsule.
At the base of the tower,
they lower it into a super-powerful catapult.
This launches the half-ton capsule
from zero to over 100 miles per hour
in a quarter of a second.
400 feet up,
the capsule reaches the top of the tower,
then plunges back down.
A drum of polystyrene balls, 30 feet deep, breaks its fall.
All this gives just 10 seconds of zero gravity,
just enough time, they hope, for the dust to stick.
Three, two, one, and go.
Narrator: Moments after the capsule launches,
the dust inside becomes weightless.
The grains clump together,
just like the early solar system.
These images reveal
how dust particles came together 4 1/2 billion years ago
to form the Earth.
Blum: The force that binds the aggregates together
is not gravity.
They are too small for gravity to be efficient.
We think the force that binds the aggregates together
is electrostatic force.
Marcy: It's the same reason
that when you pull your clothes out of the dryer --
you know how the clothes sometimes stick to you?
That's the same effect that allows
one dust particle to stick to another.
Narrator: Dust particles join to form balls of fluff.
Dr. Levison: The little static charges that they have
can make them stick when they hit,
and you get something sort of like the dust bunnies
that I have a lot of underneath my bed.
Narrator: These cosmic dust bunnies are planets in the making.
They start out smaller than a pinhead,
then grow.
The dust is now in clumps,
but it's still just balls of dust.
Turning dust balls into rocks takes a whole new process...
...a cosmic electric storm.
Space clouds build up charge just like clouds here on Earth,
generating huge bolts of lightning.
Balls of dust can turn into solid rocks
by an energetic event, like lightning.
Narrator: The electric bolts smash through the dust balls
and heat them to 3,000 degrees Fahrenheit.
In minutes, they cool and fuse into solid rock.
Meteorites today still carry these ancient rock balls
inside them.
These tiny globules
were once the building blocks of planets.
To form the Earth,
these tiny balls must collide, stick, and grow.
Rocks begin to build up by accidental collisions,
which can take a long time.
Eventually, the protoplanets, as we call them --
the baby planets --
get the size of asteroids, kilometers across.
Narrator: The baby earth is now the size of a few city blocks,
big enough for a new force to take charge --
gravity.
Marcy: At that point,
a single asteroid will gravitationally attract
a neighboring asteroid.
And, so, those two asteroids
that would have passed in the night
are gravitationally attracted, and they hit each other.
Plait: Once gravity starts to rear its head,
things really speed up
because instead of just randomly plowing through material
and getting bigger that way,
now it's starting to draw material in.
Narrator: Gravity pulls rocks together, then holds them there
to produce bigger and bigger piles of rubble.
Plait: So, this formation process, which was taking a long time
to get to the size where gravity kicks in,
suddenly gets kicked into overdrive,
and the planet grows very rapidly.
Narrator: But planets are more than just overgrown rock piles.
These rocks are lumpy and inert.
How did the Earth become round and full of life?
Narrator: The early solar system is a construction site for planets.
Dust sticks together to form rocks.
Rocks join to form asteroids.
But most asteroids look nothing like Earth.
Marcy: And when you look at a close-up of an asteroid,
it looks like some kind of distorted peanut,
like a potato that's been sort of bashed.
You can see giant craters and oblong shapes.
Narrator: The young Earth is one of billions
of misshapen space boulders.
To become a planet, it must first become round.
That process only starts
when it's several hundred miles across,
when its own internal gravity begins to change its shape.
Once you get enough material, enough mass,
the gravitational force becomes stronger.
Any giant mountain will be crushed down
by the force of gravity.
Dr. Levison: The gravity is so strong
that it can actually break rocks,
and the rocks, itself, can act like a fluid,
making an object round.
Narrator: Huge outcrops of rock crumble and fall.
The immense self-gravity of the early Earth
crushes it into the most efficient shape --
a vast, round ball of rock...
...a lopsided pile of rubble
transformed into a miniature world.
The Earth has a new shape,
but it's still just a ball of rock.
Its structure will also soon change.
Cosmic rocks and boulders still rain down from space.
Each collision heats the ground.
Dr. Plait: There's a huge amount of energy
stored in an object that's moving rapidly.
And when that hits the Earth,
all that energy is dumped into the material,
and that heats it up and melts it.
And the Earth became molten
and stayed that way for a long time.
Narrator: The young planet is no longer solid rock.
It's a seething molten mass...
...just like this blast furnace
at the Severstal plant in Detroit.
Kaku: Believe it or not,
this process behind me makes life on Earth possible.
Narrator: They feed in ground-up iron ore,
a mixture of rock and metal...
...just like the early Earth.
Put iron ore in a furnace, and the heat melts everything.
Kaku: This molten iron is at 2,700 degrees Fahrenheit.
That's about the temperature of the surface of the Earth
4 1/2 billion years ago.
Imagine an entire planet molten.
In the distance, you would see
thundering volcanoes spewing out lava.
It would be a scene right out of Dante's "Inferno."
Narrator: Iron is heavier than rock.
Now molten, they separate.
This is amazing.
We're witnessing a process
which created the very crust of the Earth
billions of years ago --
the crust that we walk on every day.
Narrator: Molten rock rises to the surface and cools to form the crust.
Molten iron sinks underneath.
Inside the Earth,
it sank all the way to the planet's core.
The rocky surface is where we live.
But without Earth's molten iron core,
none of us could survive.
This process separated the iron from the rocky minerals.
As the iron descended to the center of the Earth,
it eventually created a magnetic field,
and that's why we're here today.
Narrator: The molten iron swirls inside the Earth's core
and generates a powerful magnetic field
around the planet --
a cosmic shield against deadly radiation from space.
But the young Earth is still small --
far smaller than the Moon today.
This newly-formed world must grow.
It must also avoid being blown to pieces.
Thousands of protoplanets
are hurtling around the solar system,
and some are heading straight for Earth.
Narrator: It's 100,000 years since our solar system formed.
The young Earth already looks like a planet.
It's round.
It has an iron core and a rocky surface.
Yet, our baby planet is just a few hundred miles across.
It has a long way to go.
It must grow 4,000 times more massive,
and it has competition.
Thousands of other protoplanets shoot through the solar system,
often colliding at over 20,000 miles per hour.
You can find proof of this ancient destructive era
in modern-day Arizona.
Not meteor crater itself -- that's just 50,000 years old --
but the asteroid that gouged it out.
That was 4 1/2 billion years old.
Mark Sykes and Marvin Killgore
think the asteroid came from a violent event
in the early solar system.
The asteroid flew through space for billions of years,
then it hit Earth.
They aim to find a fragment of the asteroid,
a remnant from the period of planetary formation.
Dr. Sykes: [ Laughs ]
About six miles from here is meteor crater,
and that was an impact 50,000 years or so ago,
and it spewed a bunch of pieces out.
Narrator: They're convinced
the original asteroid was rich in iron,
so they've come prepared
with some impressive metal detectors.
Does it work?
Oh, yeah.
[ Metal detector clicking ]
[ Tone warbles ]
That's the sound we're listening for.
But even with a quad-drawn metal detector,
meteorites are hard to find.
Yeah, are you pretty convinced there's nothing there?
Yeah, I don't really -- I'm not detecting anything.
They find metal but no meteorites.
Dr. Sykes: My great discovery of the afternoon
has been this bolt...
and this piece of wire.
[ Laughs ]
Narrator: It takes hours of searching and many false alarms.
Then, with the light fading, the detector sounds again.
[ Tone warbles ]
Dr. Sykes: How about that? Success at last.
This meteorite is over 90% iron and nickle.
It could only form
right in the core of a protoplanet.
The protoplanet it came from
must have smashed apart in a brutal collision.
Dr. Sykes: Well, in the early solar system, it was a pretty violent place,
and these protoplanetary embryos would smash into each other.
They would shatter each other,
exposing the interior cores like this.
It was a very tumultuous time.
Narrator: Entire worlds reduced to chunks of rock and metal
and scattered into outer space.
In the early solar system,
these vast collisions are common.
The young Earth is in danger.
The period's name is the "Titanomachia" --
literally the "War of the Titans."
All rocky planets, the Earth included,
go through this destructive phase.
Sometimes, they shatter completely.
Sometimes, one consumes the other.
Dr. Levison: All the big guys are sort of competing with one another
in a very violent way, actually,
to see who comes out on top by eating all their neighbors.
Narrator: The battle lasts over 30 million years.
Finally, thousands of protoplanets have combined
into a few full-size planets --
Mercury, Venus, Earth, Mars, and a fifth planet, Thea.
It's racing toward earth --
our planet's last giant impact.
Thea is the size of Mars -- big enough to destroy the Earth.
If that thing had hit us straight on,
it could have literally blown the Earth to bits,
and then we wouldn't even have a planet today.
Kaku: If this Mars-like object had a direct hit with the Earth,
perhaps there would have been another asteroid belt
where the Earth is today.
Narrator: But Earth is in luck.
Instead of a head-on crash, Thea strikes a glancing blow.
It's the most violent event the Earth has ever known.
The impact turns the Earth back to a molten world,
a vast magma ocean 600 miles deep.
The Earth barely survives.
And the encounter changes our world forever.
Material blasts out into space --
enough rock to build a mountain as wide as America
and 10,000 miles high.
There would have been so much energy,
so much catastrophe.
Huge amounts of material blasted off
and went into orbit around the Earth.
The debris forms a huge ring around the Earth.
This gathers together to form two rocky bodies,
both orbiting the Earth.
Dr. Thaller: Something the size of Mars hit the Earth
about 4 billion years ago.
Lots of material would have been thrown off.
We now think that it may have formed
not only one moon but two.
Narrator: For millions of years,
two moons dominate the Earth's sky.
Eventually, they drift together and collide.
Two moons merge into one --
the massive moon we see today.
Dr. Thaller: There's no other planet that we know of
that has a moon as large as ours
in comparison to the size of the planet.
We're almost a binary planet --
two worlds going around each other.
Narrator: Without this large moon, we might not even be here.
Marcy: The moon plays a key role
in the survival of life here on the Earth.
And the reason is that the Moon, in its orbit,
stabilizes the Earth.
Narrator: The Moon keeps the Earth spinning at the same angle.
That steadies our climate.
The fact that the Earth's axis stays in the same direction
as it goes around the sun produces the seasons,
but regular seasons --
things that life can depend upon as it evolves.
Narrator: Earth is neither too hot nor too cold for life
thanks to our distance from the Sun
and our massive moon.
The Earth is not covered in ice or steam
but in liquid water.
Yet, that water must come from somewhere.
The newly formed earth is dry.
To get water, our planet must, once again, face disaster.
Narrator: It's half a billion years since the Sun first ignited.
Four billion years from now,
the first humans will set foot on Earth.
The Moon has just formed, and the Earth is a desert.
One of the more amazing ideas in astronomy
is that the Earth started out hot and dry.
There was no water here originally.
Narrator: As the planets formed,
the Sun's intense radiation vaporized the water
in the inner solar system.
Farther from the Sun, temperatures were cooler.
So in the outer solar system,
ice and water collected on comets and asteroids.
While closer to the Sun, the young Earth was dry.
So, things changed. What happened?
How is that now we have this wonderful water cycle?
Well, the water probably came from somewhere else.
Plait: Well, if you want to have
a solar system that has a lot of water in it,
you have to bring it from the outer parts
down into the inner parts,
and you can do that through comets and asteroids.
Narrator: Comets and icy asteroids contain huge reserves of water,
but they're hundreds of millions of miles from the young Earth.
Then something changes --
an event that tosses the asteroids and comets
right across the solar system.
Jupiter, Saturn, Neptune, Uranus
take a cosmic roller-coaster ride.
Dr. Levison: So, this is an event that happened
when the solar system was young.
Think of it as more of its teenage breakout years
where it just started to party for a while.
Narrator: The young planets have not yet settled into stable orbits.
As their orbits shift,
Jupiter and Saturn fall into an intricate dance.
Every time Saturn orbits the Sun once,
Jupiter orbits twice,
so they always line up at the same spot.
Each time, gravity tugs them in the same direction.
First, they destabilize each other
and then the entire solar system.
The whole thing just goes kaplooey.
The analogy I like to use is when a bowling ball hits pins,
it just goes "bam!" All over the place.
That's what this would have looked like.
Narrator: Planetary pandemonium.
Neptune and Uranus switch places.
Saturn races outwards.
The giant planets scatter billions of asteroids and comets
onto new paths.
Many head for Earth.
Dr. Levison: These asteroids and comets would have been scattered
all over the place, right,
some of them hitting the Earth and Moon.
Narrator: Cosmic missiles bombard the Earth.
Dr. Levison: We believe
that every square inch of the Earth got hit
by a comet or an asteroid during this period.
It would not have been a fun time to be here.
Narrator: The bombardment lasts hundreds of millions of years
until, finally, the gas planets settle
into the stable orbits we see today,
restoring order.
But Earth itself has fundamentally changed.
Those comets and asteroids were not just made of rock
but of ice, frozen water.
Comets, we know, are made out of ice.
They're dirty snowballs in outer space,
and even asteroids can bring water and ice to the Earth.
Narrator: Our oceans are full thanks to the cosmic hailstorm.
Kaku: So next time you're drinking a glass of water, realize
that you're probably drinking comet and asteroid juice.
Narrator: The arrival of water is the final step
to create a habitable planet.
A sequence of catastrophes has created a world
that's perfect for life.
But has it happened elsewhere among the stars?
Or are we alone?
Narrator: How did we get here?
Planet Earth only exists
because of a chain of extraordinary events,
a lucky throw of cosmic dice.
Krauss: Five billion years ago,
the odds would have seemed extremely slim
that a planet like Earth
would form in a rather unremarkable arm
in the Milky Way galaxy.
It's like trying to throw two sixes
but with dice that have thousands of sides.
Narrator: We know it happened once, else we wouldn't be here.
But what are the odds it happened elsewhere?
That other planets have life?
Life like ours needs a planet
with the right temperature and size,
a stabilizing moon, a protective magnetic field,
and just the right amount of water.
The conditions must be perfect.
Yet, amazingly, there may be
countless earth-like planets out there, waiting to be found.
Thanks to the sheer scale of the Universe,
we may find one any day now with the Kepler Space Telescope.
Geoff Marcy is mission co-investigator.
Marcy: It has only one goal,
and that's to discover earth-size planets
around other stars that you see in the night sky.
Narrator: Earth-size planets are hard to spot.
Before Kepler, astronomers took 20 years
to discover around 500 planets.
Most were gas giants
hundreds of times bigger than Earth.
Since Kepler, that number has exploded.
Marcy: Kepler has already discovered
a couple thousand planet candidates.
Many of them are members of multi-planet systems --
two, three, four, five, and even six planets
all orbiting the same star.
So, we're finding an absolute avalanche of planets
out there among the stars.
Narrator: Kepler has found one planet only twice the size of Earth
and the right temperature for life.
We don't know yet if this planet has other earth-like attributes,
like liquid water.
But even if it doesn't,
there are many more planets out there.
Kepler has found only a tiny fraction of them
because it only looks at a small part of the sky.
Plait: It's not even looking at the whole sky.
It's looking at a very tiny slice of stars
in the galaxy.
And, in fact, if you were to look up,
you could cover it with just your thumb.
Narrator: In the whole of our galaxy, there are 200 billion stars.
Many will have planets.
Marcy: Based on our knowledge from Kepler and other searches,
something like half of those stars,
perhaps even more, harbor planets.
Narrator: That means at least 100 billion planets
have formed in the Milky Way.
Earth-like worlds may be rare,
but it seems a safe bet they're out there somewhere.
So, the odds of getting an earth-like planet
are extremely small --
much smaller than getting a double six at craps.
But if you have a lot of dice, you're guaranteed to get sixes.
Narrator: And if you have a lot of planets,
you're guaranteed to get earths.
There are so many planets in our galaxy,
even if the chances are one in a million,
there should be thousands of earth-like worlds.
Marcy: Our Universe, at large,
has hundreds of billions of galaxies,
each of which is more or less like our Milky Way.
So, the number of planets in our Universe
is virtually uncountable.
Narrator: Alien earths must be everywhere.
Plait: Now, we haven't discovered even one of them yet.
But statistically speaking, it is a rock-solid certainty.
There are millions of billions of planets like the Earth
out there.
Narrator: And with that many earth-like planets,
surely, some of them will have intelligent life.
Plait: I would bet everything.
I would bet my house
that there is another Earth out there somewhere.
Marcy: There really can be no doubt that, elsewhere in our Universe,
there are other smart critters who are asking themselves,
"Gee, I wonder if there are any other intelligent species
out there in the Universe?"
The story of the birth of our planet
reveals that we cannot possibly be alone in the Universe.
The question is not "Are we alone?",
"it's how far away are our neighbors?"
"And when will we meet?"
== sync, corrected by elderman ==