Original subtitles

Our galaxy, far in the future.

A planet shrouded in turbulence, dense clouds.

Buried deep below,

an alien landscape,

extreme pressures, and a scorched surface

with sky-high temperatures.

But this is not some distant extraterrestrial world.

It's Earth's future, maybe a billion years from now.

We know this because Earth has a twin...

Venus.

And Venus has already descended into hell.

take a look around the solar system...

Eight planets orbiting a central star, the Sun.

Among them is Earth and its neighbor, Venus.

Earth, our home, is an oasis for life.

And Venus, that's the stuff of nightmares.

Plait: Venus and Earth couldn't be more different.

The Earth is this beautiful planet,

and there's water everywhere.

It's ice at the poles. It's water in the ocean.

It's in the atmosphere as water vapor.

But then you look at Venus.

It is the worst place imaginable.

It is so hot on the surface, crushing pressures.

It couldn't be any less supportive of life.

Thaller: To me, the planet Venus

is sort of a classic definition of the word hell.

If you were to transport to Venus

and experience the environment there,

you'd quickly want to return back to Earth.

Narrator: The conditions on Venus

are among the most inhospitable in the solar system.

It's just a horrible place.

It's so hot, and there's no water,

and the atmosphere is so thick.

And it rains sulfuric acid.

It's going to be a competition between whether or not

you're gonna be cooked to death or crushed to death.

Narrator: Earth and Venus may seem like very different worlds,

but they shouldn't.

They're roughly the same size, same mass

and made from the same stuff, and they started out as twins.

Early Venus and early Earth were very similar.

They were twins,

probably nearly identical twins, at their earliest stages.

Given that Venus is so Earth-like in so many ways,

it's really odd that it is so different than the Earth.

And this makes it one of the biggest mysteries

in the solar system.

Somewhere in their two histories,

the Earth and Venus took two very different paths.

Narrator: The result?

Two totally different worlds.

Their paths were so different, you could hardly believe

that one would have been related to the other.

But now, the opposite thing's going to happen.

We're gonna catch up with our twin.

We're gonna evolve to be a lot more like Venus in the future.

Narrator: In the future,

the two planets' paths will converge,

and they will become twin-like once again.

There is going to be hell on Earth.

The oceans will vaporize. The land will melt.

Our hospitable blue planet will vanish,

replaced by a fiery, molten world.

We are actually on the Earth at a time

when there's water and rain,

and it was so easy for life to take hold.

But that's gonna change.

And take a look in at Venus and have a look at our future.

Narrator: And Earth will surpass the horrors of Venus.

A billion years from now,

Earth could be an unimaginably terrible place.

Narrator: How will this happen?

The roots of our home world's destruction

are buried deep in the past of our twin planet.

It's very much true that, in studying the past of Venus,

we are also studying the distant future of Earth.

Narrator: Both planets share a violent birth,

scarred by brutal planet formation,

giant cosmic impacts, and rampant volcanism.

Grinspoon: We're trying to reconstruct things

that happened in the ancient, ancient past.

It's almost like forensic planetary geology.

Narrator: 4.6 billion years ago, hundreds of infant planets

begin to form around the new sun.

Among them, the baby Venus and Earth.

And as they hurtle around the Sun...

Collisions are inevitable.

Planet formation is like a demolition derby.

In a derby, the cars are racing around a track,

going around in circles at different speeds.

Well, it's the same thing with planets.

The material is orbiting the Sun.

It's going around, and they're all going at different speeds,

at different angels, different trajectories.

And sometimes, boom.

Narrator: In this derby, planet hits planet.

Two become one.

Violently.

You have these large bodies that are hitting each other

at really high velocity.

It's really a very hot, violent mess.

Plait: The amount of energy released

in these impacts is huge.

It completely dwarfs

all of the nuclear weapons on Earth combined.

And yet, somehow, on these scales,

you wind up forming gigantic objects that we call planets.

Narrator: Earth and Venus become voracious planet eaters.

But two spectacular collisions will set the twins

on very different paths.

Grinspoon: That was the moment Venus and Earth went through

this divergence to what has now become

these really dramatically different worlds.

Narrator: The divergence begins

when a Mars-sized object hits Earth.

The impact makes our planet spin faster.

The core spins with it, generating

a powerful magnetic field around the planet.

[ Humming ]

The field fends off the worst of the Sun's radiation.

Around the same time,

Venus takes a head-on hit from another infant planet.

This impact explains something very weird about Venus.

Oluseyi: Venus is actually rotating

in the wrong direction.

How could that be?

Well, what if it got hit really hard by some object?

That could do it.

Narrator: An object so huge,

Venus stops in its tracks and begins to spin backwards.

If you think about how much energy

and what size you need to change a planet's spin,

that is an incredibly large hit.

Narrator: But the backspin is slow,

243 times slower than Earth.

Without a fast spin,

Venus' core can't generate a strong magnetic field.

It has no protection from the deadly stream

of particles blasted from the Sun.

Venus does not have a strong magnetic field.

And so it has suffered the full brunt

of this wind blasted out from the Sun.

Narrator: The tale of two planets

now splits radically.

Venus will roast

under a violent, suffocating atmosphere.

Earth will give birth to oceans,

life, and intelligence.

But ultimately, these twins' fates

are one and the same.

Earth's future is Venus...

Pure hell.

Narrator: Venus is a vision of hell.

And one day, we'll meet our twin's fate.

It turns out that what Venus went through

in its distant past is what Earth is going to go through

in its distant future.

Narrator: So, exactly how will our blue planet

become a superheated wasteland?

Only Venus can really tell us.

Something happened to Venus long in its past

to make it a completely different planet

with a completely different personality

than the Earth as we know it today.

Man: Two, three, four.

Narrator: We Earthlings sent our first probe

to our sister planet in 1967.

And we've been sending them ever since.

What they found blew scientists' minds...

Rocks that look like granite.

What makes that interesting is that, to make granite,

you need water.

That means that there must have been abundant water

for it to have formed in the first place.

Narrator: Abundant water on a scorched Venus?

Hard to imagine.

But Dr. Lewis dartnell thinks you can get a glimpse

of a wet Venus here in Iceland.

There's the possibility

that, maybe, in the early solar system,

there were not one but two planets with oceans,

two water worlds... Earth and Venus.

And if Venus did once have oceans,

maybe they would've looked a lot like this here,

with a raw, volcanic landscape

descending down into the ocean

with the waves lapping against the coastline,

and maybe a overcast and a misty, hazy atmosphere,

not unlike what we are seeing here today.

Narrator: But Venus couldn't hold on to its water.

Plait: All of that water is gone.

It's just gone. Where did it go?

Something happened, either catastrophically or over time,

to basically dry out this twin of the Earth.

Narrator: The culprit was the young sun.

Since its birth, it's grown stronger.

Krauss: Our sun, when we look out at it during the day,

seems the same today as it was yesterday.

But that's on a human time scale.

On cosmic time scale,

the Sun has been getting hotter and hotter.

Narrator: Every billion years, the Sun gets 10% hotter,

slowly turning up the temperature on Venus.

Not only that,

Venus formed 26 million miles closer to our star.

As it turns out, that distance to the Sun was critical.

It's just an unfortunate circumstance

of being in the wrong place at the wrong time.

Narrator: Earth is far enough from the Sun

to hold on to its water.

But Venus can't take the heat.

Grinspoon: The intensity of its sunlight got sort of

just a little bit too much.

It passed this threshold where Venus

couldn't hold its water on the surface anymore.

Narrator: As temperatures rise,

the oceans start to evaporate.

Plait: All of that water in the oceans,

all of those millions of cubic miles of water,

would become water vapor,

basically steam clouds covering the entire planet,

hiding the surface from the outside.

Narrator: Water vapor is a greenhouse gas.

The clouds covering Venus trap the Sun's heat.

Temperatures on the surface rise.

But the process can't go on forever

because the clouds of water vapor in the atmosphere

start to disappear,

ripped away by the solar wind.

Venus does not have a strong magnetic field.

And so the full brunt of the solar wind

has been slamming into Venus for billions of years.

Over time, if a water molecule was in the upper part

of Venus' atmosphere,

light from the Sun could break it apart

into oxygen and hydrogen.

And then the solar wind could blow that stuff away.

Plait: Over billions of years,

this torrent of subatomic particles

blasted out from the Sun

has stripped the water out of the atmosphere of Venus

and has desiccated it.

Narrator: Our twin, stripped of its oceans,

is a terrifying vision of our own future.

Lanza: So, if Venus were, in the past,

a lot more Earth-like,

then that tells us that having a habitable world

is something that is actually very precious

and maybe is transient.

It's not something that lasts forever.

Narrator: But that is just the beginning.

Without its water vapor to trap heat,

the temperature stops rising temporarily.

Soon, a new force

will send surface temperatures rocketing again.

It will become so hot,

metal snow will fall.

Narrator: Four billion years ago,

Venus and Earth were twins with oceans.

But soon, the two planets' paths diverged.

Plait: It's pretty amazing how different things

must have looked a billion years after the solar system formed.

The Earth was covered in water,

basically on the path towards life

and a future as we see it today.

Venus was on a path away from life,

on a path toward becoming the hellhole that it is now.

Narrator: The growing sun burned off Venus' oceans,

for Earth, a terrible omen.

Thaller: On the planet Venus,

we think there could have been oceans, lakes, water, and rain.

But all of that came to an end.

That tells you that the Earth's environment has to change, too.

Nothing is forever.

Plait: A few billion years ago,

when you looked in our solar system,

you might have seen two Earths.

Well, a few billion years from now, in the future,

you might look at our solar system

and see two venuses.

Narrator: So we can look to Venus' past and see our future.

We know that temperatures skyrocketed,

and the scarred surface hints at why.

In Hawaii, planetary geologist jani radebaugh

studies the islands' volcanoes.

These volcanoes are a perfect model for early Venus.

What we're seeing out here are lava flows

encroaching on the town of pahoa,

come all the way down from the pu'u 'o'o vent

which is about 15 miles away.

Oh, there's hot. You can see that hot stuff.

You can see hot. Quick, quick, quick, quick.

Right there.

It's really beautiful.

Narrator: Hawaii's volcanic lava fields

look like Venus in miniature.

Both produce the same kind of runny lava,

building flat, shield-like volcanoes.

The big difference

is there are only five active volcanoes on Hawaii.

Venus is covered in them.

Grinspoon: One thing that really jumps out all around the planet

is the number and variety of volcanoes.

I mean, Venus could almost be nicknamed "volcano world."

Venus has tens of thousands of volcanoes all over the planet.

Narrator: But it's not the erupting lava

that turns up the heat.

It's what comes out with it.

Radebaugh: When you think back to the histories of Venus,

I think we must have seen a landscape

very similar to this one,

where you have massive amounts of lava

flowing out of the surface,

dumping huge amounts of gases into the atmosphere,

carbon dioxide, tons of the gas into the atmosphere

every single day.

It would have been amazing to see.

Narrator: Up close on the surface,

jani can see the origin of the gases.

Radebaugh: If we look behind us,

we can see volcanic gases gushing out of steam vents.

We've got carbon dioxide being delivered to the atmosphere.

It's exactly like what has happened on Venus.

Carbon dioxide has been delivered out of volcanoes

over and over and over again throughout its history

so that now we have

just a tremendously thick, dense atmosphere.

The net result of all of these volcanic gases

pouring out of volcanoes, major greenhouse gases,

is that they have been absorbing heat

for billions of years of the history of Venus.

The temperature has been gradually creeping up

until, today, the surface of Venus is 900 degrees.

Plait: It's like if you go into your kitchen

and set your oven to broil,

wait a couple of minutes and stick your head in it,

and even that's not quite hot enough.

It's a crazy, horrible, hellish spot.

Narrator: It's hard to imagine such extreme temperatures.

But probes orbiting the planet

revealed just how insanely hot it is.

Scientists studying the images

noticed something strange on the planet's mountains.

It looks like, on the mountains,

that there's apparently snow-like structures.

Narrator: But this is not like

any snow found on Earth.

So, if you look at the white-peaked mountains of Venus,

you would think that it was snow,

but it's actually metals that have rained down

and deposited on the top of those mountains.

Narrator: Metals like bismuth and lead melt.

Then they evaporate into the atmosphere.

As they rise, they cool

until they finally fall like snow on the mountaintops.

I'm not sure even the imagination

of science-fiction authors would have come up

with something as weird as Venus.

I mean, just think about that.

You have possibly metal frost on the top of mountains.

I mean, how weird is that?

It's pretty insane. Raining metals.

Where would you ever think about that existing?

On Venus.

Narrator: In the future,

metallic snow is forecast for Earth, too.

And our scorching mountain caps

will glitter like Venus.

But Venus tells us

that things will get even worse.

The atmosphere will grow heavy enough to crush cars.

Narrator: Earth and Venus were born twins,

but they took different paths.

Earth slowly evolved into a habitable world.

Venus was covered in thick volcanic gases,

trapping the Sun's heat.

Temperatures rose to 900 degrees.

Extreme temperatures

weren't the only problem on Venus' surface.

The thick clouds of gas kept on building up.

A 155-mile-deep layer of carbon dioxide

piles up around the planet.

We don't think about gases as weighing anything,

but they actually do.

Narrator: Trillions and trillions of tons

of gas press downwards.

There is simply so much air on Venus

that, on the surface, it's pushing down

with a huge amount of force.

Well, atmospheric pressure on Venus is a monster.

Think about it this way.

All right, car.

It's time for you to be crushed, baby.

If you're on Venus, you're gonna have

155 miles of atmosphere above your head.

As a result,

atmospheric pressure is 90 times that on Earth.

So, on Earth, there's about 14.6 pounds per square inch.

On Venus, we're talking about 1,300 pounds per square inch.

So, if you're driving your car on Venus,

this is what might happen.

Narrator: The crusher delivers the same force

as the weight of Venus' atmosphere.

This is pretty serious stuff.

And this is why it's so hard on Venus.

You get down to the surface,

you have the crushing atmosphere to deal with.

Narrator: The extreme pressure and heat

make Venus nearly impossible to explore.

Only one nation has ever gotten a probe to the planet's surface.

Truly, one of the engineering triumphs of the human race

was the Soviet union's venera program.

The Russians sent over a dozen probes to the planet Venus.

And only a few of them were able to survive long enough

to even be able to take pictures from the surface.

Lanza: The venera missions were incredible.

It's such a hostile environment on the surface for electronics.

And they were able to land on the surface and survive.

Narrator: The probe that sent back these images

was crushed and burnt out in 90 minutes.

Some day in the future,

there are going to be interplanetary tour guides

taking people to every planet in the solar system.

And you can imagine going to saturn and seeing the rings

and Jupiter and it's panoply of moons.

There are all these great tourist attractions

in the solar system.

At the very bottom of that list is Venus.

That is the last place in the solar system

I would ever want to visit.

Narrator: The sun's heat and volcanic gases

have transformed Venus into a nightmarish world.

So, why hasn't Earth followed the same path?

Our volcanoes also spew out carbon dioxide.

And we orbit around the same sun.

We're not being crushed and broiled.

That's because Earth formed farther away from the Sun,

staying cool enough to hold on to its oceans.

Grinspoon: Oceans do a lot of things for us on Earth

because not only, obviously, are we water creatures,

and we depend on the water cycle for our existence

in so many ways,

but people don't realize the oceans also help

to regulate the climate of Earth.

Narrator: Our oceans are full of tiny creatures

that eat carbon dioxide.

Richard zeebe from the university of Hawaii

is diving on the island's coral reefs.

He's studying how tiny marine organisms

turn carbon dioxide into rock.

Zeebe: What you see here as this white stuff,

this is what we call calcium carbonate.

And on top of this, where you see these brown layers,

this is essentially the living organism.

This is the coral itself.

It takes calcium out of the seawater

and takes carbonate out of the seawater,

combines them and makes this piece of calcium carbonate.

Narrator: There's over 70 million billion tons

of carbon locked up in carbonate rocks.

This helps regulate carbon dioxide levels

in the atmosphere, keeping temperatures from rising.

If all the carbon that is being locked up in carbonate rocks

in these corals would be put into the atmosphere as co2,

that would be certainly bad news for us.

Narrator: Currently, our carbon cycle

helps stabilize our climate.

But in the future, this won't be able to save us.

Forces far greater than the ones at work on Earth

will overpower our systems.

Like Venus, our oceans will burn off.

Temperatures will rocket

as our live-giving sun becomes a monster.

Narrator: Venus' hellish landscape

is a glimpse into Earth's future.

Thaller: There will be no more rain.

There will be no more oceans.

This wonderful, life-friendly environment we enjoy now

just won't be here in some hundreds of millions of years.

Plait: Earth could be an unimaginably terrible place.

Narrator: Right now,

we live just the right distance from the Sun,

where it's just the right temperature

for water to exist as a liquid.

But that's going to change, just as it did for Venus.

Grinspoon: Venus started off, probably, in the habitable zone.

And then the inner limit of the habitable zone crossed

the distance of Venus' orbit.

Well, it's gonna cross the distance of Earth's orbit, too.

There is an expiration date to the Earth.

And that's due to the Sun's evolution.

Narrator: Ever since its birth, the Sun has been getting hotter.

That increased heat devastated Venus.

And, in the future, it will destroy Earth.

In 1.1 billion years,

the Sun is 10% hotter than it is today.

The oceans start to evaporate into thick clouds,

which trap more of the Sun's heat.

Catastrophically, very rapidly on a geological time scale,

the oceans will put so much water vapor into the atmosphere

that we will get a runaway greenhouse effect.

[ Thunder rumbles ]

Narrator: The clouds forming in the atmosphere

trap more and more heat,

driving temperatures even higher.

Spiraling temperatures cause more evaporation,

so the clouds get thicker.

Which led to more heating, which led to more evaporation.

And you can see where this is going.

It's a vicious cycle. It's a positive feedback.

Plait: All of the ocean's water will boil away,

millions of cubic miles of it.

We have all of this water that will go into the atmosphere,

covering the Earth and shrouding it in, basically, steam.

Narrator: Earth has had oceans for billions of years,

but it could lose them in just 10,000.

Krauss: All of the water in the Earth's oceans

will be in the atmosphere.

We'll have an incredibly dense cloud cover system

where the temperatures on Earth

will be approaching 1,000 degrees.

Narrator: Like Venus in the past,

Earth will get hotter and hotter.

But unlike Venus, which topped out at 900 degrees,

temperatures on Earth will keep climbing.

Venus lost its water to space, blasted away by the solar wind.

But Earth holds on to its water.

It's protected by our magnetic shield.

But that is no longer a good thing.

[ Humming ]

Unlike Venus, Earth has a strong magnetic field

which protects it from the erosion of the solar wind.

That water will stay with us.

The Earth could have a thicker, hotter greenhouse atmosphere

than Venus does today, much worse.

[ Thunder rumbles ]

Narrator: This huge volume of water vapor

all pushes down on the surface,

around 4,000 pounds.

That's the weight of the average American car

pressing down on every square inch of Earth.

Surface pressure goes through the roof,

reaching 270 times higher than today.

It is ironic to think that the water on Earth

will one day help contribute to its demise

after all the water has been the source of life on Earth.

But, in the far future, it'll become our enemy.

Narrator: And with no oceans and their microscopic creatures

to absorb the carbon dioxide,

there's no way back for the Earth.

In 1.2 billion years,

a probe visiting Earth would see an alien world,

a scorched, barren landscape.

The pressure is crushing.

Temperatures reach 1,200 degrees.

Molten metals snow down on the mountaintops.

It's so hot, granite rock melts.

The surface liquefies.

At that point, the Earth will become a molten ball

very similar to what it was at the very beginning.

Narrator: Earth and Venus started as twins.

Venus was destroyed by rampant global warming.

Earth will follow the same path, then overtake it.

It is inevitable that the Earth will someday

not only be like Venus, but actually put it to shame.

Narrator: In 1.3 billion years, Earth could hit 3,600 degrees,

four times hotter than Venus.

It will be the hottest and deadliest planet

in our solar system.

For Earth and its inhabitants, it's the end of the road.

We could never survive the extreme temperatures

or the crushing pressure.

Maybe we'll escape to space.

But there's one absolutely crazy way we could stay here...

Move our planet further away from the Sun.

Narrator: Earth of the future will become

the most inhospitable planet in the solar system.

Its oceans will boil off, and its surface will melt.

A billion years from now,

Earth could be an unimaginably terrible place.

Right now, today, Venus is the evil twin of Earth.

But in the distance future,

Earth could be the evil twin of Venus.

Narrator: Earth's surface temperatures

will reach 3,600 degrees

with pressures 270 times greater than today.

Plait: At these kind of temperatures,

where rock on the surface of the Earth is molten,

it's hard to imagine any place there could be life.

Narrator: But there is hope.

Astrobiologist Lewis dartnell thinks

that some forms of life could survive

such terrible conditions.

We're here on top of a volcanic outcrop in Iceland

with this howling Gale whistling past our ears,

the stench of hydrogen sulfide, of sulfurous fumes,

filling our nostrils.

And this is about as close as you get can on Earth

to high up in the venusian atmosphere.

About 30, 35 miles above the surface of the planet Venus,

the air pressure is about the same

as on the Earth's surface.

The temperature is pretty similar, as well.

But the cloud droplets are full of concentrated sulfuric acid,

many, many times more concentrated than battery acid.

It's a hostile, horrible environment.

But bizarrely enough,

there's good reasons to think that there may be life,

venusian life, high up in the clouds

that are kind of high-altitude aerial biosphere.

Narrator: High above Venus, there are nutrients,

solar energy, and traces of water.

If life can live up there, then perhaps it might survive

high up in the clouds of future Earth.

You can easily imagine these micro-organisms evaporating

in water particles and being transported

to the upper atmosphere.

Even though it turned into this toxic greenhouse planet,

life could potentially still survive

in that upper atmosphere.

Narrator: But what about us?

We couldn't survive the high temperatures

or pressures at the surface.

And a life in the clouds doesn't seem likely.

What's our future?

Oluseyi: If there was this life on Venus,

clearly, they weren't advanced enough

to stop the changes in their atmosphere

that led to Venus' current state.

The question is, are we?

Narrator: Maybe we'll leave our planet

and find a new home.

But there is a more outlandish solution...

Stay on Earth and move it farther from the Sun.

Moving the Earth is at least imaginable because, in fact,

as objects exchange gravitational energy,

they move in or out in the solar system.

It's happened to our planet.

So I could imagine engineering things

where we directed large asteroids and comets

close to the Earth, but not to hit it.

Narrator: The gravity from these large objects

would slowly alter our orbit.

Krauss: Gravitational energy would be exchanged,

and the Earth could slowly move out.

Narrator: Each gravitational jolt

would only move Earth a short distance.

But do it thousands or millions of times,

and we could push the Earth away from the Sun,

in theory, at least.

Over a billion-year period, it's possible to imagine.

It would require incredible technology

and incredible coordination.

The technology is possible.

Whether humanity as a species could ever coordinate it

is something I'm a little more skeptical about.

Narrator: It's a crazy option, but if we don't do something,

Earth and all of us will die,

and we'll become just like Venus.

Earth and Venus were probably born together

as identical twins, but then their paths diverged.

But now, lifetime is gonna send that cycle all the way back,

and they'll die as identical twins again.

Narrator: In the grand scheme of things,

they'll just be two charred twins

spinning to oblivion in a backwater of the universe.

On the cosmic scale, life is short.

When you look at how Earth evolved and how Venus evolved,

you can see the difference,

even though it's two almost twin planets,

how life and habitability could change over time.

So, habitability isn't always a permanent thing.

Krauss: On human scales,

the universe seems the same every single day.

But, of course,

that's because human life and human civilization

is but a brief instant in cosmic time.

On cosmic scales, the universe evolves and changes,

and that makes the history of the universe remarkable.

Narrator: Our tale of two planets converges in the end,

a cautionary tale about forces beyond our control.

Maybe a billion years of learning from Venus

will ultimately save us from the same terrible fate.