All language subtitles for Wonders of the Solar System E05 Aliens 1080p AC3+DTS_Subtitles06.ENG

We live on a world of wonders.

A place of astonishing beauty and complexity.

There are vast oceans and incredible weather.

Giant mountains

and stunning landscapes.

I'm a physicist, and I'm fascinated by
the way that the universal laws of nature

that made all this, also created
such diverse and different worlds

out there in the solar system.

I think we're living through the greatest
age of discovery our civilisation has known.

We've voyaged to the farthest
reaches of the solar system.

We've photographed strange new worlds,

stood in unfamiliar landscapes, tasted alien air.

But the one thing we haven't found on those worlds

is the thing that makes our planet unique.

Life.

But is that really true?

Is the Earth the only place in the
solar system that could support life?

In this film we will search the
solar system for worlds that harbour
the conditions to support life.

What we find on these worlds may help us answer
the question, are we alone in the universe?

That's not only one of the great
fundamental questions for science,

but one of the great unanswered
questions in human history.

Floating in the Sea of Cortez off the cost
of Mexico is the research vessel Atlantis,

the mother ship for the exploration of
one of the most alien worlds we know.

But it's an alien world on our planet.

The Atlantis is the launch vessel for Alvin,

one of the world's most rugged submarines.

Built like a spacecraft,

it's designed to explore the
deepest depths of the ocean.

And I'm lucky enough to have hitched
a ride down to the sea floor,

two kilometres beneath the surface.

That has got to be the closest thing
to going into space that you can do.

And, given that I'm not going to go into space
any time soon, I think it's the next best thing.

See you in eight hours.

Roger, Alvin. Your checks are
good. Permission to dive.

Roger. Alvin diving.

The parallels to spaceflight are obvious.

As the tiny capsule descends,
we are leaving the familiar world

of the surface of our planet,
and entering a strange, hostile world.

If anything goes wrong,
we will be completely on our own.

MACHINE BEEPS

Beeping is never good.

'Fortunately, Alvin is one of
only a handful of submarines

'that can withstand the colossal
pressure of the deep ocean.'

At the Earth's surface, we're used to one
atmosphere of pressure.

As we descend, the pressure increases
by another atmosphere every ten metres.

And it soon adds up.

We're approaching a kilometre deep.
The pressure outside there is now

100 atmospheres, that's higher than the
atmospheric pressure on the surface of Venus.

Without knowing, if you were asked a question,
could life exist down here, 100 atmospheres,

cold, dark no sign of sunlight at all,

it's pitch black there, you would say no.

Well, I would say no.

But the depths of the ocean are not lifeless.

Illuminated by Alvin's lights,

we find oases of life in the
deserts of the ocean floor.

So we have landed, after about an hour of descent.

We've just stopped in the most incredible place.

Look at those.

We've landed on top of the tube worms.

Amazing things.

This underwater city is one of the most
bizarre environments on our planet.

It's built around a hydrothermal vent,
a volcanic opening in the Earth's crust

that pumps out clouds of sulphurous chemicals
and water heated to nearly 300 Celsius.

And somehow, life has found a way to
thrive in these most extreme conditions.

This is a genuinely remarkable place.

There are mats,

carpets of yellow bacteria.

Look at that. It's not only just bacterial blobs,

there is real complex organisms.

Alien. I want to say that word, alien environment.

It really is alien to us.

For me, the fascinating thing
about finding life down here

is that the conditions on the

deep ocean floor are more similar
in many ways to the conditions on

worlds hundreds of millions
of kilometres away out there

in the solar system than they are to
the conditions just two kilometres
from my head on the Earth's surface.

It's incredibly dark, there is no sunlight,

there's a brutal mixture of hot and cold water,

and just rock and minerals.

So, if life can not only survive but
even flourish in these conditions,

then you've got to feel that it's
much more likely that life can

also survive and flourish out
there in the solar system.

Ever since the invention of
the telescope 400 years ago,

we have looked to our neighbouring
worlds for signs of life.

As technology has improved, we've been able to
search the planets in more and more detail,

and we have found nothing.

But that doesn't mean the rest
of the solar system is dead,

because we're only beginning to scratch
the surface of what's out there.

There are literally hundreds of other worlds.

Planets and their moons which
we have barely explored.

Among them may be worlds that hold
the conditions to support life.

And the best way to find out
what those conditions are

is to look at the one place
we know life flourishes.

The Earth.

Life is pretty much only chemistry.

It's just the reactions
between atoms and molecules.

And so for life to exist,
you only really need three things.

First of all, you need the right chemistry set.

Now, I'm made of something like 40 elements,

almost half of the known elements,
which is pretty complicated.

But actually 96% of me is only made of four of
them, carbon, nitrogen, oxygen and hydrogen.

Secondly, you need a power source.

You need a battery, something
to make a flow of electrons

that powers the processes of life.

Now here on Earth, most life uses
the power of the sun.

And thirdly, you need some kind of
medium for life to play itself out in,

for processes to happen.

And here on Earth,

you don't have to look very far at all
to find that medium, that solvent.

Because it's this, water.

If you want to see how important water is to life,

there's no better place to come
than the Atacama desert in Chile.

The soil here is more sterile than
a hospital operating theatre.

In fact, scientists have looked for
the most basic form of life, bacteria,

in some parts of the Atacama,
and they found absolutely nothing.

All deserts are characterised
by a lack of moisture.

But the Atacama takes that to the extremes.

The Sahara is 50 times wetter than the Atacama.

There are weather stations here that have
measured 1mm of rainfall in 10 years.

There are river valleys that
have been dry for 120,000 years.

There are rocks that haven't seen
rainfall for 20 million years.

It's this dryness that explains
why nothing can survive here.

Even the most primitive form of
life on Earth, the bacteria,

need water for their survival.

And there are no exceptions.

And this seemingly fundamental
link between water and life

is driving the search for life
out there in the solar system.

Because, wherever we find water,

that will be the best place to
look for life beyond the Earth.

The Earth is the only planet that
currently has liquid water on its surface.

The other planets are either too close to the sun,

like Mercury, and baked dry.

Or they are too far away.

Saturn's rings are made of water,
but in the depths of space,
it's frozen into lumps of solid ice.

But that doesn't mean that liquid water has
never existed elsewhere in the solar system.

And if it has, we should be
able to find the evidence,

because wherever water goes,
it leaves its footprints.

These are the Scablands, a remote part of
the North Western United States.

It's one of the most spectacular
places to come to see how water

carves its signature into the landscape.

The largest flood on Earth
went through this area here.

Jim Rice is an astro-geologist.
He believes that understanding the
events that created this landscape

can help in the search for water on other planets.

We are kind of like CSI arriving at the scene
of a crime, this is the evidence left here.

We've come to piece it together.
I can see this is not a normal river system.

You can see, because it is so straight.

There is no meandering of a river
here, it's just a big hole.

This entire landscape was created
at the end of the last Ice Age.

200 miles to the east lay a huge lake,
held in place by a wall of glacial ice.

When that wall ruptured, over 2,000 cubic
kilometres of water swept out in a single
catastrophic event.

The flood waters were at least 400 feet deep here.

But actually they were another 200 feet
stacked on top of that, coming across here.

So we would be under 200 feet
of water standing right here.

So am I to imagine a wave?

Yeah, a massive wave rolling,
rumbling, this water would

be charged full of big chunks
of ice from that ice dam.

It would be loaded with big chunks of the salt
bed rock being gouged, ripped out of here.

It would be an impressive sight.

As the floodwaters tore across the landscape,
they carved out this 20 mile long canyon.

And at its head, it left these giant horseshoes.

At over 400 feet high and five miles across,

this was the largest waterfall
the world has ever known.

The easiest way of thinking about it is if you
took every river in the world, put them in

the same location, had them flowing at the same
time, these floods are 10 times larger than that.

And how long do we think it
took to sculpt this landscape?

48 hours to a week.

It's instantaneous, geologically.

The Scablands reveal the characteristic signature

that water carves into the landscape.

It's a signature that can be seen from
space, and not just on the Earth.

When we turn our telescopes on our next door
neighbour and prime candidate for finding

alien life, the planet Mars,

we find almost identical
features cut into its surface.

The Red Planet is covered in outflow channels.

Straight, wide canyons,
exactly like the Scablands.

And they are filled with
identical geological features.

It all suggests that similar huge floods
once tore across the surface of Mars.

This is a picture of here from the air.

I am sat somewhere around here.

And here are the horseshoe shapes of the
dry folds which are just over there.

This is a picture taken of the surface of Mars,

and you see those typical
horseshoe shapes of the folds.

Also, you see the structures upstream of the
folds, these grooves cut into the landscape.

And you see that here, grooves cut into
the landscape as the water

cascades down and then flows over the folds

and cuts the gigantic valleys
out as it moves downstream.

So, all this adds up, I think,
to an overwhelming smoking gun

that there were vast amounts of
water that flowed very quickly

over the surface of Mars
at some point in the past.

But although the outflow channels are proof
that liquid water once flowed across Mars,

it may not point to the existence of life.

Because if the Martian landscapes
were formed by the same processes
that formed the Scablands on Earth,

the floods that created them may
only have lasted a matter of days.

For life to get a foothold,
you need more than that.

You need areas of standing water.

Lakes and rivers that persist
for millions of years.

In order to look for evidence of that standing
water, we've done the only thing we can,

we have sent an army of robotic
explorers to the surface of the planet.

We have touch down, we have touch down.

Over the last 35 years,

we've landed six robot probes on Mars.

And one of them, Opportunity,
is still rolling across the surface,
investigating the Martian geology.

The Mars rovers has really
captured our imaginations.

I suppose, because they genuinely are
explorers in the old-fashioned sense.

They are the extension of our senses
to the surface of another world.

But they have also been very
important scientifically, because

you can't really get to know
another planet from orbit.

You have got to get down to the
surface, you've got to touch it,

you've got to dig down and
examine it microscopically.

And the Rovers really have, by doing that,

made some extremely important
scientific discoveries.

One of the most significant of those
discoveries was made in November 2004.

The Opportunity rover was examining an
impact feature called the Endurance crater,

when it detected deposits of a remarkable mineral.

This is the world's largest salt works
on the Baha peninsula in Mexico.

And what they do here is pump sea water
into these lagoons and let it evaporate.

What they're after is this stuff,
which is sodium chloride, table salt.

But, at different stages, different salts,
different minerals, crystallise out.

So all the things really that are in
sea water emerge, crystallise out

at different stages of the process.

In one of the lagoons,
pond number nine, the sea water is
at exactly the right concentration

to precipitate out these beautiful crystals
that cover the entire floor of the lagoon.

This is gypsum,

and it's exactly the same stuff that
Opportunity found on the surface of Mars.

Now, what's interesting about that
discovery is how you make gypsum.

You see, its chemical formula is CaSO4.

So it's calcium sulphate.

Dihydrate, 2H2O.

That's water.

So, the only way we know of, the only way to make
gypsum here on Earth, is to have calcium

and sulphate ions in the presence of liquid water.

So, large deposits of gypsum on
the surface of Mars tells you

that there must have been big areas of
water present for a very long time.

The discovery of gypsum has
helped to build a picture

of an ancient Mars that was
much warmer and wetter.

Subsequent discoveries of gypsum
in networks of sand dunes

suggest that large areas of Mars
were once covered in standing water.

And where there is standing water,
there is the chance of life.

This area of the salt flats is, we think,

very similar to areas that have been seen on Mars.

And it certainly looks extremely inhospitable.

It's hard at first sight to see
how anything could live here.

But, if you just dig

a tiny bit below the surface,

then you see that this layer of gypsum
is only a few millimetres thick,

and then immediately the ground
beneath it turns this greeny colour.

It's green because that is bacteria that thrive
in these seemingly inhospitable conditions.

Now if these bacteria can survive here,

then there seems to be no good
reason why they couldn't also have
survived and even flourished on Mars

when there was water present at some
point in the very distant past.

But although it may once
have been more hospitable,

any liquid water has long since
disappeared from the surface of Mars.

About three billion years
ago, it died as a planet.

Its core froze and the volcanoes that
had produced its atmosphere seized up.

The solar wind stripped away
the remains of that atmosphere.

Any liquid water would have evaporated

or soaked into the soil where it froze.

It left the surface of Mars too cold, too exposed

and too dry to support life.

It's highly unlikely that there will
be life on the surface of Mars today.

But that's not to say that life couldn't
exist somewhere on the Red Planet,

maybe we're just looking in the wrong place.

There are other potential
habitats for life on Mars.

Detailed pictures of the surface
show the entrances to caves,

revealing the existence of a world
beneath the Martian surface.

We know there may be water down there.

Satellite data shows permafrost,
ice frozen in the soil.

Deep below the surface,
that ice may melt to form liquid water.

It all hints at an undiscovered subterranean world

that may be a more likely place to find life.

If you were to imagine the
perfect habitat for life,

then it would surely be somewhere like this.

A warm climate, lots of liquid water,

a beautiful, dense atmosphere.

You see the results everywhere,
just life everywhere you look.

All the life we're familiar with
thrives in pretty much the same

conditions that we do,
driven by the heat and light of the sun.

But this is by no means the only life on Earth.

There's another living planet
hidden beneath the surface

that exists in completely different conditions.

It raises fascinating possibilities
for the caves on Mars.

This is the Cueva de Villa Luz in Tabasco, Mexico,

the Cave of the House of Light.

And it is the definition of
a hostile environment to me.

Because (HE SNIFFS) it's full of
hydrogen sulphide gas, hence

the gas monitor which says at the moment one part
per million hydrogen sulphide, very toxic for me,

which is why I have got this gas
mask in case it all gets too much.

So, it's a place where you, at first sight,

would not expect a great many life
forms to survive and flourish.

Although the cave is a death-trap for us,
that doesn't mean that nothing lives here.

In fact, it's teeming with life.

Look at these fish, just everywhere
in the cave water. And they're

adapted to live in these conditions.

In fact, if you look at them closely,

they're quite pink.

That's thought to be because
they've got lots of haemoglobin

because there's not much oxygen down here,

so they need to have an efficient way
of moving oxygen around their bodies.

Beautiful.

But the really interesting life is
found in the depths of the caves,

where the concentration of poisonous
gas is high enough to set off my alarm.

Down here, far from the light of the sun,

are organisms whose energy source
comes from the air around them.

They use the hydrogen sulphide gas
bubbling up through these springs.

The same gas that could be fatally poisonous to me

is their source of life.

These things are what I came
deep underground to see.

These are snottites. And you can see
why they're called that.

They're really one of the most alien
life forms that I can conceive of

on the Earth

Because they metabolise hydrogen
sulphide, so they metabolise this

faintly acidic and nasty gas
that I'm just breathing in now.

You can almost feel it on your
tongue, actually, the acidity of it.

They metabolise it, they react it with
oxygen, and they produce sulphuric acid.

So their breathing process, if you like,
their version of what I do,

I breathe in oxygen, react that with
sugars and breathe out CO2 and get energy

these guys breathe in hydrogen sulphide
and oxygen and produce sulphuric acid.

In fact, I can test it here with this.

Yes, you see, look at that.

That, well, what looks like water,
that secretion of dripping off the
snottites, has actually got a pH...

well, it's now about between 0.5 and 0.

That's strong acid.

That's as strong as battery acid.

It's actually highly concentrated sulphuric acid.

So, what a strange organism.

Alien in every sense of the word.

Except that it's present on, well,
just below the surface, of our planet.

And the snottites are not alone.

Organisms that can extract energy
from the minerals around them

are found under the ground all over the world.

In fact, this way of life is so
successful that it's thought there

may be more life living beneath the
Earth's surface than there is on it.

And that raises an intriguing possibility.

If life can thrive below the Earth's surface,

why couldn't organisms like
snottites survive and flourish

beneath the surface of Mars?

If you think about it, living below
the surface of Mars might actually

be quite a good idea, because the surface
is incredibly hostile.

It's subjected to intense
ultraviolet radiation from the sun.

It's a very cold place,
and the atmospheric pressure doesn't

allow liquid water to exist on the surface.

But, if there is life below the surface of
Mars, then obviously we have a problem.

How could you possibly detect it?

Well, actually, there is a perhaps
tantalising clue that

there might be something interesting
going on below the Martian surface.

These are termites, or white ants.

And they're very unusual
animals because they eat wood.

This is their food.

There are many, many species of these,
billions of individuals across the planet.

And, in the process of digesting
wood, they produce the gas methane.

Because there are so many of them,
they actually produce an estimated

50 million tonnes of methane

and pump it into the Earth's
atmosphere every year.

And it's not just termites.

There's lots of methane
naturally in our atmosphere.

It's all produced either biologically...

or by active geological
processes like mud volcanoes.

And that makes it all the
more surprising that methane

has been detected in the atmosphere
of the supposedly dead planet Mars.

It was telescopes on Earth,
using infrared spectroscopy,

that first identified methane
in Mars's tenuous atmosphere.

Those first measurements appeared
to show only tiny amounts.

But closer observations have revealed that the gas

is concentrated in a handful of
plumes that vary with the seasons.

In the warmer summer months,

thousands of tonnes of the gas is
released from vents in the surface.

Something under the surface
of Mars must be producing it.

It may be coming from previously
unknown geological processes.

But it could be that it's coming
from a biological source.

Now no-one, I don't think,
is seriously suggesting that there

are termites running around
beneath the surface of Mars.

But it's not actually the termites that are
particularly interesting about this story.

It's the way they digest the wood.

You see, they use symbiotic bacteria,
bacteria that live in their guts, called Archaea.

And Archaea, these bacteria that can
digest wood and produce methane,

are the most common organisms
beneath the surface of the Earth.

The snottites are members of the Archaea,

as are many of the microorganisms found
living around deep-sea hydrothermal vents.

In fact, it's Archaea that we find thriving in
many of the Earth's most extreme environments.

So I think it's quite a fascinating
prospect that the methane we see

in Mars's atmosphere might just be
produced by organisms like Archaea,

living below the Martian surface.

But while Mars remains a tantalising possibility,

it's no longer the only place in the solar system

we think could harbour alien life.

Far out, a billion kilometres from the sun,

the solar system becomes a very different place.

The planets, like Saturn,
are made of gas, not rock.

There's plenty of water out
here, but it's frozen solid.

The planets are surrounded by
networks of moons, carved from ice.

They're cold and desolate.

They don't seem likely places to find life.

Any places on Earth remotely
similar are completely barren.

This is central Iceland.

And, at this time of year, in mid-November,
it's an increasingly inhospitable place.

It's about 3 o'clock in the afternoon,
it's already well below freezing.

The sun is dipping below the horizon.

And it will stay this way for another six months.

And there's pretty much no
visible life here at all.

There are no trees, no grass, and just listen.

SILENCE

No insects, no birds.

Nothing.

But it's because these places
are so cold and inhospitable

that they're of increasing
interest to astro-biologists.

Because discoveries in these frozen
places of Earth have raised new hope

of finding life among the icy
worlds of the outer solar system.

And in those frozen wastes

we have found one world that
is of particular interest.

It's one of Jupiter's moons.

Jupiter has a vast network of moons.

The four largest have been known

since they were discovered by Galileo in 1610.

And they're a varied bunch.

Closest to the planet is the tortured moon Io.

It's torn apart by volcanoes that carpet
its surface with bright yellow sulphur.

In total contrast to the heat
of Io comes its neighbour,

the ice moon Europa.

It's about the same size as our moon.

And it's the smoothest body in the solar system.

Its surface is made of an unbroken shell of ice.

Though it's etched with a network
of mysterious red markings.

It exists at a chilly minus 160 Celsius.

It seems an incredibly unlikely home for life.

The photographs of Europa from space

reveal a vast, icy wilderness.

But, if you look more closely,
then you start to see surface features.

And those features tell you a lot about
what's going on deep beneath the ice.

Close-up, we can see deep cracks that
criss-cross the surface of Europa.

At higher magnification

we see areas where the ice
has been broken into icebergs

and jumbled up before refreezing.

We see the same formations in sea ice on Earth,

where the movements of the ocean have
caused the ice to bend and crack.

It suggests something similar
may be happening on Europa.

But it's the way the cracks are
broken and fractured that provide

the compelling evidence that
there is liquid water on Europa.

You see, as Europa orbits around Jupiter,

Jupiter's intense gravity
stretches and squashes the moon.

And that stresses the ice and
causes it to fracture and crack.

But the position of those cracks is not
quite where you would expect it to be.

And the explanation for that is
that the icy surface of Europa

has shifted, it's moved
relative to the rocky core.

And the only way that could happen is if
there's a layer, or an ocean of liquid water,

surrounding the rocky core that allows
the outer ice surface to slip around.

Measurements of Europa's magnetic field
have confirmed that its icy shell

is sitting on top of a salty ocean
that may be a staggering 100km deep.

That would mean that there is more
than twice as much life-giving

liquid water on this tiny moon
than there is on planet Earth.

But it's not just the
discovery of the hidden ocean

that makes us believe that Europa may
be the most likely home to alien life.

And that's why I've come to this spectacular
ice cave in the Vatnajokull glacier.

You see, the laws of nature are universal.

That may not only apply to laws of physics,
but also to the laws of biology as well.

And if that's the case,

then what we find in these ice caves
of Iceland may tell us something

about what we could expect to find
below the frozen surface of Europa.

It's hard to describe this place.

It's absolutely magnificent.

Visually, the quality of the
ice, it's just completely

transparent and clear.

You can see straight through it.

The cave tunnels into the heart of the glacier,

where the ice has been
frozen for a thousand years.

It's what astro-biologists find in this ice

that makes us think that Europa
could be teeming with life.

NASA scientist Richard Hoover

has spent his career looking
for life in unlikely places.

Well, that went very well.

OK.So, will any organisms that you
find in that ice be living in a
sense that I would understand it?

They're actually alive now, and metabolising?

For a long time it was thought
that ice microorganisms

were present only in a state of
what is called deep anabiosis.

Suspended animation. It's now becoming
quite clear that that isn't necessarily

the case for all the microorganisms,
there may be others that are
actually actively living in the ice.

So in this glacier,
the whole place, this whole cave

may be populated by living
things, not frozen things?

Things existing, living, cell dividing,
reproducing, all the things you do?

All of this.

It's this prospect of finding
things living in solid ice

that has had the greatest impact

on our ideas of where life could
survive in the solar system.

OK, we're at lowest magnification.

So, that is 100,000 millionths of a metre?

Yes. We have bacteria.

So, these are organisms that have been trapped
in that glacier for thousands of years?

Yes, look at this.

Beautiful. You're seeing life in ice.

We now know that some microorganisms

are capable of actually causing the ice to melt,

because they generate,
essentially, anti-freeze proteins.

They change the temperature at which ice
goes from a solid state to a liquid state.

And they could have been
forming little tiny pockets,

maybe only a few microns in diameter,

but if he can make a two or three
micron diameter ball of liquid water,

and he has the ability to move,

then that bacterium is now not in
a glacier, but he's in an ocean.

What are the implications of these discoveries?

The fact that you've got living
bacteria inside ice on Earth,
what are the implications for Europa?

You can clearly have bacteria like this
in the frozen ice near the surface crust.

And the thing that is most exciting to me,

is that surface crust of Europa
has a wide variety of colours

that are highly suggestive of microbial life.

And so there is a very, very strong possibility

that the ice of Europa may contain
viable, living microorganisms.

It's a controversial idea,
but it is a dizzying thought

that the mysterious red stains
on the surface of Europa

could be the visible signs of alien life.

The discovery of the huge ocean of liquid water

under the surface of this tiny moon,
combined with the potential for life in ice,

and the intriguing red markings
that criss-cross its surface,

have made Europa the most fascinating
and important alien world we know.

A true wonder of the solar system,

because it's our best hope of
finding extraterrestrial life.

That question, are we alone in the universe?

Is this the only planet amongst the
billions of planets in our galaxy,

amongst the billions of galaxies in
the universe, that harbours life?

Is, I think, one of the most important questions,

perhaps THE most important
question that we can ask.

Think about what it would mean for us

if the answer was that there was
no other life in the solar system,

in our galaxy, perhaps even in the universe.

How valuable would that make planet Earth?

How valuable would that make us?

But then imagine that the answer is
that, on every moon of every planet

where the conditions are right,
then life survives and flourishes.

That makes us part of a wider cosmic community,

if the universe is teeming with life.

If knowing the answer to the
question is so profoundly important,

then surely striving to find the answer
should be of overwhelming importance.

I believe it's the most important
question you can possibly ask.

Because we have a chance of answering it.

What we've learned from the
extreme places on Earth

is that, if there is life out there in the solar
system, it will almost certainly be simple.

Single-celled organisms like bacteria eking out
an existence in the most hostile of environments.

One thing seems certain.

The only place in the solar system
where there is complex life,

life that can build a civilisation,

is here on planet Earth.

But how did that happen?
What is it that makes our world so special?

Because, after all, everything in the
solar system shares the same genesis.

It was all created out of nothing
more than a spinning cloud of gas
and dust 4.5 billion years ago.

Solid worlds condensed out of the swirling mists.

But those worlds were radically different.

Around the solar system, there are worlds
that erupt with volcanoes of sulphur.

And others with geysers of ice.

There are worlds with rich
atmospheres and swirling storms.

And there are moons carved from ice

that hide huge oceans of liquid water.

But there's only one world where
the laws of physics have conspired

to combine all these features in one place.

On Earth, the temperature and
atmospheric pressure are just right

to allow oceans of liquid water to
exist on the surface of the planet.

And it's big enough to have
retained its molten core

that not only powers geysers and volcanoes,

but also produces our magnetic field

that fends off the solar wind and
protects our thick, nurturing atmosphere.

It's the combination of all
those wonders in one place

that allowed life to begin and
to get a foothold here on Earth.

But, to allow that life to evolve into
such complex creatures as ourselves

requires one more ingredient.

And that's time. Deep time.

The kind of time over which mountains
rise and fall, and planets are formed
and stars live and die.

And it's perhaps that that makes the earth
so rare and so precious in the cosmos.

Because it's been stable enough
for long enough for life to evolve

into such magnificent complexity.

The life we have on Earth today is the
result of millions of years of stability.

And the pinnacle of that is us, humankind.

A species that has developed
to the point where we can bend

and shape and change the world around us.

We have even left our own planet behind

to begin exploring our cosmic surroundings.

You could take the view that
our exploration of the universe

has made us somehow insignificant.

One tiny planet around one star
amongst hundreds of billions.

But I don't take that view.

Because we've discovered that it takes the rarest
combination of chance, and the laws of nature,

to produce a planet that
can support a civilisation.

That most magnificent structure

that allows us to explore
and understand the universe.

And that's why, for me, our civilisation
is THE wonder of the solar system.

MUSIC: "Calling Occupants Of
Interplanetary Craft" by the Carpenters

# Calling occupants of interplanetary craft

# Calling occupants...

And if you were to be looking at the
Earth from outside the solar system,

that much would be obvious.

# Calling occupants of interplanetary craft...

We have written the evidence of our
existence onto the surface of our planet.

Our civilisation has become a beacon that
identifies our planet as home to life.

# We'd like to make a contact with you

# Calling occupants of
interplanetary, anti-adversary craft

# We are your friends

# We are your friends...#

If you'd like to know more about the solar system,

go to bbc.co.uk/science.