Richard Hammond Builds a Planet Richard Hammond Builds a Planet

The Earth...

..third rock from the Sun.

And it's unique...

..it has life.

So how do you make a planet like ours?

I'm going to open up the cosmic tool box

and work it out.

We're going to build a planet, up there...

..at the top of this impossibly high tower.

It gives us the perfect platform

to make something really big.

Up here, we can do in seconds

what it takes nature millions or billions of years to do.

We are going to build our planet...

brick by brick.

But to do that, I'm going to need help.

And I'll find it in the most unlikely places.

Right now, I am effectively weightless.

I'm on the ceiling. I am ON the ceiling.

Of course, as with any construction work...

..there will be hiccups.

But out of these mistakes will come real insights

into what makes our planet, our solar system,

exactly right for us - for life.

As an engineering challenge,

it doesn't get much bigger.

I love it here on this hill.

Feels like it was made

for bracing Sunday walks with the family.

And indeed most weekend mornings,

the place is full of parents with their kids,

including me with mine, sometimes.

And when I was on those same family Sunday morning walks,

as a kid myself,

I spent as much of my time looking down as I did up and round.

Rocks, stones, the very stuff of the Earth -

they fascinated me.

And amongst my finds was one I felt particularly important -

a rock the size of your fist.

A rich brown - dimpled, heavy, glinting,

somehow special.

It became one of my most treasured childhood possessions.

I was convinced it was a meteorite -

a rock that had landed here from space.

Morning.

Like most treasured childhood possessions,

it got lost or swapped, probably wasn't even a real meteorite anyway.

But it didn't matter because it had done its job -

it sparked my interest in space,

the idea of "out there".

Like most kids, I suppose, I believed that "out there"

would be full of planets like the Earth.

Each of them full of life,

even if it wasn't quite the same as ours.

But as it turns out,

the planet we live on is very, very special.

As far as we know, our Earth

is the only place in the solar system with life.

To understand why,

we are going to build our own planet...

..at the top of that tower.

And to do that,

first we have to gather up the basic raw materials...

..all the big ingredients we need to start making a planet.

All right, all right!

And here comes my delivery now...

..right on time.

OK, so how much stuff do we need to build a planet like the Earth?

I know that the entire Earth weighs around six septillion kilograms,

that's a six followed by 24 zeros.

But let's be sensible here,

I've ordered the main planetary raw materials

and in the right proportions

but I've had to scale the delivery down...

..a bit.

Now, you'd think that our living Earth

would be made up of countless different things.

But actually, it's constructed almost entirely

out of just four basic ingredients.

So that's what my convoy has delivered.

On these trucks - girders, iron girders.

Like most big construction projects,

we are going to need a lot of iron.

Ah, we need this...

..oxygen.

And over here...

..sand...

..that's rich in silicon.

Magnesium, like you find in alloy wheels.

The convoy has brought the elements

in exactly the same proportion as we'd find on Earth.

So, there are 15 trucks laden with magnesium

because 15% of our planet is made from magnesium.

There are 16 trucks for the 16% that's silicon.

30 trucks carrying oxygen.

And a column of 32 trucks with iron girders

because almost a third of our planet is made of iron.

It is incredible to think that just these four elements

make up 93% of our planet.

The rest is elemental seasoning.

HORN TOOTS

And here's Billy Bob with some of the remaining ingredients...

which are tiny.

Hydrogen...

..aluminium,

a pinch of salt,

calcium.

The question now is

how does all of this turn into a planet?

To find out, I need to take these basic planetary elements

and stick them in a blender.

And I'm going to do that at the top of our tower,

where there's a sky-full of room to break down my ingredients.

The thing is, our planet didn't just pop into existence.

It started out as a swirling cloud of elemental dust,

floating in the great void of space.

So that's how I am going to have to start, as well.

In case you're wondering,

yes, I am...

..scared of heights, that is.

High...really high.

4.5 billion years ago, before the Earth began to form,

this dust and gas was all there was.

So, how do we get from this cloud of dust

to a planet like the Earth?

We need something to bind it all together,

a sort of cosmic superglue.

Now, you might think that'd be gravity. Right?

Wrong.

The best way to find out what this super-strong planetary glue is

is to discover its power

in the weightless environment of space.

It's why I've come to this Air Force base,

where astronauts are trained.

I'll be honest, I am pretty thrilled right now

because I'm about to boldly go

where quite few have gone before.

I'm not actually going into space.

There were budgetary issues with that.

But never mind because we have come up with

the very next best thing for our purposes.

Where I'm headed is over there.

This plane offers thrill-seekers something unique -

it can cancel out the Earth's gravity.

For me, it means I can recreate the conditions in which

that elemental dust began to make a planet.

Hi, how are you doing? Richard, hey. Good to see you. Welcome aboard.

Are you ready...? I'm ready! Ready for a unique experience?

I don't know, I've never tried it, obviously. Let's see.

'On today's flight, my chaperone is Dan Durda...' Thank you.

'..an expert on space dust.'

All right, Richard. I think...

Which seat are you here? I'm 2F. I'm just...

In the context, having this conversation is hilarious.

I should imagine all astronauts do this.

The attendant service on the space flights

is not quite up to par, though. I was wondering about that.

Do they have, like, a trolley with all the space food on it?

I've got a window seat but there is no window.

That's on purpose. I don't doubt it.

A lack of windows

isn't the only strange thing about this plane.

It's also got a padded interior,

sort of like a flying asylum.

That's because, within 15 minutes,

we are going to experience weightlessness.

And those zero gravity conditions

will allow Dan to show me a fascinating experiment.

Inside this Perspex box

is the next step to building a planet.

We're going to simulate the way the planets formed

in the very earliest days of the solar system.

Instead of microscopic dust particles,

I've got coffee - ordinary coffee.

So in this little box, we're going to see exhibited

what it was that brought stuff together?

Absolutely. So this is what kick-starts the whole process?

Big things have small beginnings.

So it all starts with a coffee?

It all starts with early coffee. Just like my day.

It does all start with a coffee. Even the solar system.

As it turns out! We shall see.

Right, switch the gravity off, then.

That's right!

It doesn't work, it's broken.

The plane is now climbing to 34,000 feet.

Once there, it'll throttle back down to Earth in a steep arc,

perfectly judged so that inside,

we're falling at the same rate as the plane drops.

The result -

a few moments of weightlessness.

Oh, yeah!

Oh, I swam, I did swim.

Oh, that's peculiar.

Oh, look at that! Beautiful. Oh, we got it!

Look at! See, that's what I was trying to show you.

Unfortunately, I'm upside down.

I can't! I can't...it's over there. Here we go.

Hang on, it's...

You come here to do these experiments all the time.

Right, I'm going to watch but I'm going to do it upside down.

Why are you better at this than I am?

I'm really struggling. I'm...

Gravity, there it is. DAN LAUGHS

What are we looking for?

We're now weightless. That's how our planet started.

So these clumps, what's bringing them together?

Electrostatic forces.

Electrostatic's clumping this coffee together.

So this is the effect, this is what starts it all off.

It's hard to concentrate when I'm floating.

That's not gravity causing that clumping.

That's electrostatics. I'm on the roof!

How did I get on the roof? And now I'm on the floor.

Now gravity is coming back into play... And it's all gone. ..and it doesn't work.

That's why we're weightless,

to see phenomena that we can't normally see

when gravity's turned on.

So what's happening here?

These coffee grains, like that first cosmic dust,

rub together as they float.

This means individual grains

get either negatively or positively charged.

And this static charge means they stick together...

..just like the fledgling particles of the Earth

4.5 billion years ago.

This is as near as we're going to get

to being out there with those particles without gravity.

How cool is that?!

Oh! HE LAUGHS

Congratulations! Thank you for that.

I enjoyed it, thank you.

I need you to know that I did that

only because it was the best way of demonstrating

an essential principle in building a planet

and not because I had any fun at all.

It was...yeah, it's quite boring.

I loved that!

So, around our planet-building tower,

we've bound together those first clumps of dust

without gravity present.

But there is a problem.

Electrostatic forces are very strong

but are only effective over tiny distances.

Beyond a certain point,

about the size of gravel,

the dust stops growing.

So our planet-building plans have ground to a halt

with nothing to show beyond bigger bits of dust.

We need another force

to somehow grow them more.

I think it's time to introduce a little gravity to the situation.

How, then, does gravity take those bigger bits of dust and gravel,

and turn them into rocks

or even an entire planet?

At a concealed underground laboratory,

I'm told there's a secret device

that will help me find the answer.

Until 2001, this was a gold mine.

Now, it's at the cutting edge of scientific research.

My goal lies

nearly a kilometre and a half straight down.

I'm going deeper underground than I've ever been before.

You know in disaster movies...

..when things go wrong

in things like giant lifts going a mile underground -

the short guy never lasts very long, does he?

Just thinking that out loud.

More and more rock flashing past.

Still plunging.

Still, plunging is better than plummeting.

At the bottom of this shaft is an instrument

that's part of a global gravity research experiment.

Apparently, it's going to help us understand

how gravity can grow a planet from gravel.

In the tunnels of these, the Sandford Labs,

scientists are unravelling the workings of the universe.

ALARM BLARES

I might not look it but I feel a bit like James Bond -

summoned to the underground lair of an international super-baddie.

And here is what I've come to see.

Meet Dr Gnome.

Now the good doctor here is no common or garden gnome.

He is a precision instrument of science.

He's special because he has a super-tough coating

that means he can't be chipped or damaged easily.

So you would think that wherever he went,

he remained exactly the same.

Looks the same.

Same expression -

slightly puzzled.

Well, scientists have taken Dr Gnome all over the world.

And wherever he's been,

he's been weighed with high precision scales.

And it's his weight that helps explain

how gravity can turn gravel into a planet.

It's my job now to weigh him down here,

a mile down beneath the surface,

in laboratory conditions.

So let's zero the machine, pop him on.

And as you can see, the doctor tipping the scales

at 330.95g.

In the interest of thoroughness,

he has been weighed in a number of other locations down here.

And in all of them, we got the same reading.

A kilometre and a half under the surface,

he weighs 330.95g.

And now we must travel back up to the surface

where we shall finish this experiment.

Right then, Doctor, you just sit there. I'll do all the walking.

The doctor has to travel first class.

It's vitally important that he isn't damaged on the way up,

or picks up any dirt that might interfere with readings.

OK, Doctor,

time to weigh you up here, on the surface.

Zero the machine,

let it calm down...

..and here we go.

Look at that!

You are 0.06g heavier up here

than you were down there.

I honestly didn't expect that.

But just to be sure,

he needs to be weighed in some other places.

And sure enough -

331.01g.

The doctor is showing a consistent weight gain

of six hundredths of a gram

up here on the surface, compared to when he was down below.

Have you been secretly snacking?!

I can assure you that Dr Gnome hasn't grown on the way up.

His weight gain can be explained

by Earth's gravity.

Gravity is THE universal force

that attracts one thing to another.

When we measure something's weight,

we are actually measuring the Earth's gravitational pull.

So why has the doctor's weight changed?

Well, it's largely to do with differences

in the amount of rock underfoot.

Up here on the surface, there is a good mile more rock

beneath me and Dr Gnome

than there is in the lab down there,

meaning more planetary bulk pulling down on us,

making for a heavier Dr Gnome up here

than down there.

Nothing's changed about the gnome.

What's changed is gravity.

Our experiment shows that the more massive something is,

the stronger its gravitational pull.

So in space, around 4.5 billion years ago,

when there were no planets, just those elemental clumps,

any difference in the size of those clumps

would have mattered, because of gravity.

If we add gravity to our orbiting swarm of dust,

we start to see the larger bits attracting the smaller bits.

Because they are bigger,

they have a stronger gravitational pull.

The bigger they are,

the bigger they get.

They start to become rocks.

And the larger rocks

draw in the smaller ones.

In space, a rock just a kilometre wide

can grow to a near Earth-sized planet

in just a few million years.

Around our tower,

we can do it in seconds.

And we're seeing something really promising.

The exciting thing is that even though that process

began 4.5 billion years ago -

on Earth, it hasn't finished.

Because if you know where to look,

you can see where gravity is still shaping our planet, today.

Out in Arizona's Badlands,

there is breathtaking evidence

of how gravity is still building the Earth.

This is the Barringer Crater.

When this vast crater was first discovered,

many believed it to be an extinct volcano.

But in fact,

it was created by a meteorite.

This 1.2km wide hole

is an impact crater.

And it's given scientists like Matt Genge

a unique insight into how planets are built.

Matt, how are you? Hello, mate. Sorry about the dust. Wow!

This crater is the scar

left by an incredibly violent impact.

If you look at the crater wall, you can see the strata...

..beds of rock, running across the crater. Yes.

There's this nice red layer of rocks.

Above and below, there's some lighter coloured rocks

and they're actually the same band of rocks.

That layer has been folded over the red layer, red layers,

like the cheese in a sandwich.

But they've been folded over all the way round the crater,

like they've been thrown outwards and have collapsed back.

How big was it? Cos it's a really big crater.

We think the object itself was probably only about 30m in size.

So a couple of double-decker buses back-to-back.

And it made a hole that big? It made a hole that big. Why?

Simply because of how fast it was moving.

So by the time it fell towards the Earth,

it gets faster and faster as it falls towards the Earth,

hits the ground maybe at 26,000mph.

And the energy...

..the kinetic energy associated with that speed

is so huge, it's around two megatons,

that it blew all that material outwards.

The rocks actually flowed like water out of the crater.

So this whole... all this area has been affected?

It's not just the big hole, then,

it's everything around that we're on. Absolutely, yeah.

All of this. In fact, if you were here before the crater was formed,

you'd have had all that rock on top of your head,

so you wouldn't have been very happy. No, that would have been bad.

The meteorite was just 30m wide

but the shockwave of its impact would have been enough

to obliterate a brick wall 60km away.

The Barringer Crater is evidence

of how gravity builds a planet.

Because every meteorite that plummets to the ground

is drawn in by the Earth's gravitational pull.

So when did all this happen, then? How old is that?

So the crater itself is about 50,000 years old.

But we actually know that meteorites like this

have been falling on Earth

throughout the Earth's history, for the last 4.5 billion years.

In fact, in the past,

they were much more frequent.

So back when the Earth was forming,

that bombardment was continual.

There was probably one of them every few minutes.

These were the objects that were making the Earth.

Billions of years later,

meteorite fragments that survived the initial impact

offer a glimpse into the earliest moments

of a planet's formation.

This is rather a special meteorite.

It fell in Mexico

in 1969

and it's called Allende.

We give meteorites names.

And what's special about this meteorite is

it's perhaps the oldest material on Earth.

So it's around 4.5 billion years old.

So that right there

is the oldest thing on Earth?

Yeah.

Wow.

Can I hold it?

Er...no. OK.

But you can touch it, if you like.

Just touch the oldest thing on Earth. Yeah.

Oh, come on.

Wow.

It is kind of a goose-bump moment

because of the significance of a little piece of rock that,

well, frankly, I'd walk straight past.

Well, most people probably would.

But although they're quite rare,

you can find them everywhere.

They fall all over the world.

But not always quite as spectacularly as here!

Yeah, you'd notice that. You'd certainly notice.

But to imagine that some of us are walking past lumps of rock

that contain all the elements you need to build a planet...

You know, you've got the magnesium and the silicon

and the iron and the oxygen.

It's just incredible that this is how we started

and they're just scattered

all over the world.

If you or I were to find an actual meteorite,

and - who knows? - we might,

it's, I don't know, almost a haunting thought

to consider that what you had in your hand

might be 4.5 billion years old

and one of the fundamental building blocks of our planet,

our world,

of our existence.

But the meteorite that you found

might not have landed billions of years ago.

It might have landed the day before you found it.

And that's quite exciting -

they're still arriving. the process is still going on.

It's just that they're late gatecrashers

to some giant planetary party.

Astonishingly, today, 40,000 tonnes worth of meteorites

fall to Earth every year -

the equivalent of 30,000 transit vans

dropping out of the sky -

mostly arriving as dust.

But very occasionally,

as something much bigger.

Early in 2013,

a meteorite fell near the Russian town of Chelyabinsk

that was the largest in a century...

..nearly 10,000 tonnes, before breaking up.

But such spectacular events are incredibly rare.

In fact, you're more likely to die from falling out of bed

than from being struck by a meteorite.

GLASS SMASHES

Back when the Earth was forming, though,

huge meteorite strikes were constant,

with tens of millions hitting a year.

The thing is, rather than destroying it,

the onslaught built our planet.

Starting 4.5 billion years ago,

it took just 100 million years to reach almost full size.

So now we have a planet that's roughly the same size as Earth

and the same shape.

But at the moment, the surface of our planet

is a molten, fiery vision of hell,

which is going to be inconvenient.

For starters, there's nothing to stand on -

no solid rock.

It's just a fiery, molten sea of magma.

And there's no way life could start

in this volcanic environment.

So how are we going to get a solid surface for our planet?

Back on the desert floor,

Professor Jeff Karlson and his team

are setting up a unique experiment.

They reckon they can show me

how to make land for our planet.

The first step in their challenge -

recreating that early, molten Earth.

And that means constructing what is basically a mobile volcano.

And now we're going to see if we can make it erupt.

All right, Richard? Yeah.

Let's get the helmet on. Yeah.

I'm guessing what we've got in here is not lunch, is it?

It isn't.

Whoa! That's really hot!

So what Bob is stirring there isn't something that looks like lava...

No, it's... ..it's actual lava.

It is real lava, basaltic lava.

We just put in the ingredients, just like a recipe,

and cook up this primordial, primitive material

that makes up our Earth.

It's amazing and exhilarating

but also quite incredibly hot up here. Can I get down?

It's very hot. Yeah. And you can see,

we have to get it that hot so it will flow in a very viscous form.

The recipe for lava that Jeff's team are using

includes the essential planetary ingredients -

iron, magnesium and silicon.

But before this turns to solid land,

we need to make the lava flow.

The spout, here. I see it. Here it comes, here it comes.

The temperatures

reached by this lava are extraordinary.

We know from using our infrared camera,

where it's incandescent orange, there, it's about 1,100 degrees centigrade.

Where it starts to get dark grey, like down at the toe here,

it's about 850 degrees centigrade, now.

Wow!

And now it's coming out here at 1,100 degrees again,

just like the temperature that we're pouring in.

So this is much hotter than that stuff on top? It is.

Looking at what happens here on a small scale

but with the same materials and the same temperatures

and the same behaviours,

you can look back and work out what happened on the early Earth.

Exactly. We're sort of replicating those conditions of the early Earth,

in miniature.

Imagine the whole planet

covered with glowing, incandescent orange lava -

magma oceans.

That is intense.

You can see the little wrinkles and folds

starting to form on the surface

as the surface cools and a crust starts to form.

I can feel wrinkles and folds forming on my face, watching.

So, in order to create land from lava,

we need to cool it down until it turns into a crust.

Simple.

But there's a wrinkle in our plan.

On the early Earth,

the lava didn't cool in the way you'd expect.

There was a reason the surface stayed molten.

Jeff has a, well, slightly unusual demonstration

of what that was.

Site up on the target...

Shooters, fire.

We're going in there? Let's go have a look.

That was quite exhilarating, I'll be honest.

Oh, my God! I can't see the target. OK, what am I doing?

OK, look here, Richard. Here's where all the bullets hit.

Feel how hot it is there, still.

It is, yes. Yes, there's definite heat in there.

Ow, they're really... You could think of these as...

each one of these like a tiny meteorite that struck the Earth

and transferred its kinetic energy to heat energy,

keeping the planet warm.

I think I see where you're going with this

cos I did wonder for a moment.

So these are like meteors.

Right. So, the planet was under bombardment at a time. Right.

And those were going in like these and when they hit,

this is kinetic energy converting into heat.

And what, a meteorite hitting is enough,

is going to make it hot? It is.

It keeps it hot and that's one of the reasons

your planet's not cooling down.

And these meteorites are a lot bigger.

The meteorites are much bigger than our little bullets, of course,

and they're travelling about ten times as fast.

I'd love to get a better idea, a better sense of that moment

when that energy is converted from kinetic into heat.

But to do that, they'd have to shoot through my hand

and that's going to hurt, so...

Well, we have a safer way to do that.

A thermal infrared camera's been filming the entire experiment here

and we can show you the images created by that.

In here? Yeah.

So this is a thermal camera looking at what we've just seen.

Right. There's the plate.

Hot areas are going to show up red

and little cooler areas will show up in a bluer, cooler colour

as each one of these bullets strikes the metal.

And there they go, look! I mean, it's really pronounced.

Look at the pieces being blasted off, there.

Watching them go in like that,

I can imagine they were meteorites.

Exactly, much bigger and ten times faster.

And this effect is one of the reasons

why my Planet Earth won't set...

That's right. ..remains molten.

So, to stand a chance of creating a solid surface for our planet,

we need to stop this constant barrage of meteors and asteroids.

On the actual Earth,

this bombardment petered out around four billion years ago.

On the planet we're building,

it can be done in a jiffy.

And reducing the impacts from space helps the surface to cool

so that lava...

..turns to rock.

Perfect!

We now have a planet we can stand on without being burnt.

But there is something pretty important missing.

If we're going to have life on this planet of ours,

we are going to need water.

Incredibly, some water has been with us

from the very birth of our planet,

trapped in dust and rock, and then locked inside of the Earth.

Volcanic activity released this water as steam,

forming rain clouds that then filled the first oceans.

A lot more water arrived from space,

because asteroids and comets actually carried ice inside them,

adding to our already wet planet.

So, we've got water.

We've also got land.

But it doesn't look right.

All that volcanic activity hasn't just pumped steam

into the atmosphere, it's produced a toxic cocktail of gasses.

This isn't a planet for us yet.

So, how do we clean up this poisonous atmosphere?

Well, the answer lies with the oldest living thing on the planet.

On these rocks, there's a thin film of bacteria called a stromatolite.

These ones today are in Australia,

but three billion years ago they were everywhere.

They live on sunlight, and carbon dioxide in water,

and as a waste product, they release oxygen.

For more than a billion years, these bacteria pumped the stuff out

until the air was right for the evolution of complex life...

..including us.

To build our planet, we started with truckloads of raw materials.

And we mixed them together...

..into a cosmic cloud of dust.

We got it to stick together with static electricity.

And then we added gravity.

We bulked the planet up.

Then we stopped the onslaught to cool it down, and make land.

And then we sourced water

and a breathable atmosphere.

But hang on. This isn't right.

There's something seriously amiss with our planet.

This is definitely not how things should be looking.

It's a bad case of the wobbles.

A wobble this big, even slowed down over millions of years,

would be catastrophic.

Without stability, seasonal changes are extreme,

ice ages are frequent,

and the surface is scoured by hurricane-force winds.

It's no good! Our planet has conditions completely hostile to life.

But don't worry, because to stabilise things,

we don't actually have to look too far.

The solution is a moon.

To find out how a moon can stop a planet's wobble,

I've come to NASA in Texas...

..where the answer is kept in a bomb-proof vault...

..wrapped in foil.

And if that isn't enough,

this entire facility demands OCD levels of hygiene.

One man who knows a lot about this object is Harrison Schmitt.

And that's because he found it... on the moon.

Four decades ago, Harrison was an astronaut.

December 6th, 1972.

Dr Harrison Schmitt, better known as Jack.

He would be the first geologist to set foot on an alien world.

We have liftoff at 2.13...

I'm going to meet Harrison, after a final zap in the NASA microwave.

SHRILL BEEP

Harrison. Hey. Hello. Welcome.

I so wanted to shake your hand but it's in there!

A little bit later maybe.

It's great to meet you, and what have you've got in here?

We have one of the Apollo 17 samples.

It's one collected near the lunar module challenger.

And it is a...

..er, really quite a unique type of rock.

That rock formed about 3.8 billion years ago.

That's with a B!

So it's extremely old, it's part of a mass of magma that partially

filled the valley of Tarse Littoral where we landed on Apollo 17.

So let's just get this into context because, for mere mortals like me

to understand, you are standing there as the only geologist ever

to have walked on the moon? That's correct.

And therefore, when you saw these rocks on the moon, they would have

meant more to you anyway because of your training and knowledge. I hope so.

Your brain must have been just screaming!

You were looking at that rock.

Well, you can't believe where this geologic setting was.

It's a valley deeper than the Grand Canyon of the Colorado

here in the United States.

The mountains on either side are 6,000-7,000 feet

above the valley floor.

This was off the valley floor.

It's the moon that saves the real Earth from the disastrous

climatic effects of wobbling.

But how exactly the moon keeps us stable

is tied into its mysterious origins.

Until the Apollo programme,

we had no real idea of how the Earth got its moon.

Finding out was an important goal for Harrison Schmitt

when his Apollo 17 module touched down on December 11th, 1972.

Feels good, stand by for touchdown.

Stand by, down at two.

Feels good. Ten feet.

That's contact!

Harrison had just three days

to collect as many lunar samples as possible.

Late in the mission, things got a little tense.

Harrison had just half an hour of oxygen left

and he was getting a bit carried away with his work.

I've got to dig a trench, Houston.

Fantastic, sports fans!

It's trench time!

They got to leave at a certain time,

regardless of what they got.

There isn't enough time to do it, no matter which way we want to do it.

We need more time.

We need to make it clear, we've got to pull out.

We'd like you to leave immediately.

OK.

By golly, this time goes fast!

We're on our way, Houston.

Once Harrison and NASA were able to examine the rocks,

they began to understand fully just how the moon had formed,

and the massive stabilising effect it brought.

What the scientists discovered was an extraordinary connection.

It seems this moon rock was made of pretty much the same stuff

as Earth rock.

The oxygen isotope ratios in the rocks are identical

to those ratios that we have here on Earth

and it tells you that the Earth and the moon formed in, basically,

almost identically the same part of the solar system.

And this information that you brought back has helped

people narrow down the theories as to how the moon came to be

where it is and like it is. No question about that.

The primary hypothesis right now is giant impact.

Soon after the Earth formed,

another planet-sized rock crashed into it.

The impact threw huge chunks into orbit.

And these clumped together to make the moon.

When first formed, it was much, much closer than it is now.

One of the primary reasons that we still are here on this planet

is that the Earth is a stable planet and it's been stabilised by the moon.

With the moon there, there's a gravitational stabilisation

that occurs that keeps the Earth wobble down to an absolute minimum

and that makes a big difference for us, because

if you wanted to have major climate change on Earth, introduce a wobble.

It doesn't mean that life wouldn't be here

but it would be a very difficult and different kind of life that we

would have to deal with

with this wobble over fairly long periods of time.

So, let's see what happens to our planet when we add a moon.

Our planet and its new moon are two dancers

locked in a gravitational embrace,

steadying themselves as they swirl round and round.

Having a moon has one other vital effect.

Tiny variations in its gravitational pull on our planet's oceans

have given it tides,

and that's more important than you might think.

Without the tides, early life on Earth may never have left the sea,

because the tides created damp strips along the coast

that tempted life onto land.

And the actual positioning of the moon is crucial.

Ever since its formation, it's been drifting away from the Earth.

But when it was closer, it generated immense tides.

If we had them today, every few hours, New York and London

would disappear under tens of metres of water.

And if the moon was further away, the planet's spin would slow

and the days would be longer.

But put it at just the right distance, which in reality

is about 239,000 miles, and we have the stability we need.

So, there it is - the perfect planetary relationship.

After trial and error, I have built my planet and its moon...

..and got them working just right.

In reality, this whole process took four and a half billion years.

The sheer scale of it all is understandably mind-blowing,

especially when you realise that with just one element

out of place...

..nothing works, and life stops.

So what holds the Earth and moon in place?

They need a sun to orbit around,

and other planets to make our solar system...

..all of which is just a tiny part of a Milky Way galaxy

with 300 billion stars.

And that galaxy is just one amongst half a trillion other galaxies.

So, to keep it all working, we're going to have to build a universe.

And to build a universe,

I'm going to need

a lot of help.

Oh, this is really difficult!

Oh, my God, it's beautiful!

Do I look faintly ridiculous? Yes!

I'll be honest. I'm faintly nervous.

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