Original subtitles

I am gonna tell you about the most incredible place.

We think we know our home, but once you've seen it from space it hits you.

It might be the weirdest place in the whole universe.

Eight astronauts, with over a thousand days in space between them,

can tell us how being up there helped them to truly understand

what goes on down here.

I've been a stargazer ever since I was a kid.

My grandmother even gave me a compass to make it easier to find the North Star.

I love looking out into space and imagining are there other worlds out there?

Is anything living on them?

You know, every day you're finding a new planetary system that

looks pretty similar to Earth.

The possibilities of life somewhere else other than Earth I think are very high.

I like to think that, that there's other life out there.

If there is life out there what would it be like?

Could we talk to it?

I mean, is it gonna wanna fight?

Or will it like romantic movies?

Is there anything out there like you and me?

To find out, we can't just look into space, we also need to look down here.

I'm gonna tell you how clues to alien life are hidden on our strange rock.

Mae Jemison was the first African American woman in space.

But Earth's orbit was not enough for her, she's now head of a star ship initiative,

its 100 year mission to boldly go where no one has gone before.

Growing up, science fiction was my go-to storytelling.

As a little girl as I watched Star Trek, I was fascinated,

because science was one of the characters.

It was right in the middle of it.

And so my love for science really met an incredibly interesting vision.

I was fortunate enough to meet Nichelle Nichols who played Lieutenant Uhura

at a Star Trek convention.

She was really instrumental in the recruitment of some of the first women astronauts

and the first minority astronauts in the US Space Program.

I wasn't one of her recruits, but I'm really happy to say

that she's one of my best friends now.

You're an Andorian, huh?

Yes.

People are always asking me, "Will we find aliens on other worlds?"

And I know they really mean will we find Vulcans or Klingons?

Well, to know how likely that is, we really have to understand how we got diverse,

complex life on this planet.

Scientists believe that somewhere around four billion years ago

life emerged on Earth.

One might imagine that, once we get life out of this primordial soup,

the road to complex creatures like flowers and humans is pretty straightforward.

But hold on, it's not quite that easy.

There was no rule that life had to get bigger.

There was no rule that life had to become more complex.

Life could have stayed simple and small, but it didn't.

Today, we live in a planet inhabited by over eight million different species.

And for that to happen is so unlikely that it makes you wonder

if it could happen anywhere else.

As you look down at the Earth from space, you see the ocean,

the desert,

the grasslands,

you know that life exists in every one of those locations.

And the type of life that's there?

Well, that depends on what food is available.

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The caves have no light source.

When you're away from the entrance it's as dark as dark things get.

The creatures that choose to live in a cave, they do it for a reason.

In a totally dark place any light is incredibly effective.

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The glow worms glow when they are hungry.

The bugs have no idea.

They think, oh light, instinctively fly towards it.

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All of a sudden, they're stuck.

The glow worm is a deceptive creature.

The more you know, the more you see, the more disgusting

and ferocious you realize these creatures are.

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When the glow worm's got its bug, it will bite or puncture into the wall

of the insect and suck out the inside.

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Surely it's a law of nature that life evolves to fit its surroundings.

If we find life on other planets it's likely that it was the best suited to prosper

in the conditions there, an extra-terrestrial Darwinian evolution, if you please.

As human beings, we are constantly asking questions.

Who am I?

Why are we here?

What is the meaning of existence?

Well, it turns out the big question for life is what are we having for dinner?

Food is energy, everything living needs it, and it's a big reason creatures live,

act and look the way they do.

The complexity of life here is staggering.

Just imagine how peculiar a camel might appear if you'd never seen one before.

You might think it was a creature from another planet

but its strange design makes perfect sense

for the way it gets and uses energy,

like its wide,

flat teeth for chewing tough plants.

Or its hump, a mound of fat, stored energy, that allows it to survive months in a harsh

environment without eating.

To sustain a complex creature like a camel requires vast amounts of energy.

Even something like a fly with millions of complex cells is breathtakingly complicated and

requires a steady flow of energy.

But even if you're a tiny microbe, smaller than a pinhead,

you still have energy demands.

When we think about life we usually think of the big stuff,

you know plants and animals, but the majority of life on Earth are small,

single-celled organisms.

Bacteria.

And they have evolved to eat almost anything.

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So I think, yeah, you go down the King Mast and then you jump into the third hole.

Okay. Well, you know, I've done the checklist, I've got the comms ready.

So good luck.

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This is one of the biggest graveyards of ships in the world.

Around 50 Japanese boats and over 250 aircraft were sunk here

by American forces during the Second World War.

Some were blown up with torpedoes,

others were bombed.

It might seem like useless junk now, but for some kinds of life it's a perfect home.

All that energy that was poured in to make the vessels of the war

is there waiting to be released.

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Rusticles look like stalactites and they are part metal and part microbes.

Microbes extract the chemical energy from the metal, using it to grow and reproduce.

To us iron is just a metal, but for these microbes it's food.

The rusticle is crawling with billions of happy bacteria, all chomping on an

all-the-iron-you-can-eat underwater buffet.

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The first creatures on Earth were microbes.

And in the future when all human life has gone,

bacteria will still be there doing their business.

I love my food but, I mean, I'm a little picky, and that's because I'm not a microbe.

They will eat anything, metal, rocks, oil, plastic,

even human flesh.

But having a big palate like that comes in handy.

Bacteria can survive up on mountain tops.

They can survive in deserts.

They're in the soil.

They're thousands of feet up in the atmosphere.

They're everywhere.

So it doesn't matter what a planet is made of or how poisonous its atmosphere.

Even if there is just a tiny bit of energy to extract,

simple microbes will work out a way to get it.

Out in the universe there, there's gotta be that stuff,

there's gotta be these single cell organisms that are living in environments that life

as we know it here on Earth could probably never tolerate.

Given an unlimited number of planets in an unlimited amount of time,

it's a little bit delusional to think that this is the only place

life could have ever evolved.

Maybe there are microbes on other planets, but there's a big leap between them

and something I can talk to.

Here on Earth, that leap couldn't have happened without a visitor from

93 million miles away.

Over the years, I've had many encounters with aliens and this may come

as a shock to you, but they weren't real.

But if Hollywood is right and there are aliens, they're gonna have needs

and it's gonna be all about energy.

Up to a point in Earth's history, energy came from heat, from volcanic vents,

from lightning strikes.

This energy was readily around.

But, as the Earth started to cool and to change, the weather changed.

A new source of energy was needed.

Some bacteria came up with a new mechanism, let's use the energy from the Sun,

which is readily available.

It was a really pivotal moment in the history of life on Earth.

On the space station, we have this vast array of solar cells that collect

and harness the solar energy from the Sun,

and we use this to run all the systems to sustain life.

If things don't work the way they're supposed to, that can get very tricky very fast.

When you look out the window you see these solar panels that extend the length

of a football field and these eight ginormous solar rays.

They would go from blue to gold to copper color.

Just beautiful.

So I'm out doing a spacewalk and one of the things you're worried about is

the solar panel, trying to maneuver my way around those solar panels and looking down

at plant Earth and the greenery down there and I realize, hey,

planet Earth is really one big solar panel also.

Plants have been converting solar energy and storing it effectively

for billions of years.

This biological magic trick means that, even when there is only

the faintest trickle of sunlight, plants can grow.

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Photosynthesis, we've all heard about it, right?

But have you ever really considered what it means?

What plants do is eat sunlight, streaming from our sun 93 million miles away.

And they use it to make carbon dioxide into starch, granules of stored energy

which plants use to power their growth.

When I see a live plant, their green makes me know life is possible.

Plants make a place feel welcoming, like home.

Every leaf on every plant is like a tiny battery.

Photosynthesis from plants worldwide generate around 100 terawatts of power each year.

To put that into perspective, it's enough to match the energy demand of the modern

world nearly six times over.

Running a planet packed with life takes a lot of energy.

Kudos to the big ball of fire in the sky.

Plants dine out on it.

Once they started, they spread all over the world.

But those first plants were missing something,

which meant there was one place they couldn't go, up.

Bamboo can grow so high because it contains a molecule called lignin.

It's the bamboo's own internal scaffolding.

Lignin evolved around 400 million years ago and it changed the world.

It provides structural strength for plants and they get to grow tall.

From the outside, plants and trees are beautiful,

but it's the inside that reveals their dynamic, intricate structure.

These memorizing patterns are the storybook of its life.

Because of lignin plants have given our rock a solar-powered skin that harvests energy from

the cosmos, and that harvest supports almost all life here on Earth.

The truth is money doesn't make the world go around, energy does.

Plants store energy.

So, it didn't take long for something to evolve to take advantage.

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When an animal eats a plant it gains the energy that a plant captured from sunlight.

Animals could not exist without plants.

If another planet evolved creatures like goats or like us,

I'm almost certain it would have plants as well.

But plants on this other planet may not be green.

Plants here are only green because our Sun is green.

The majority of light emitted from the sun is in the blue-green wavelength.

It doesn't look green to us because it has light emitted in other areas too,

in red and blue.

And so when you blend all those together they look white.

Most plants here on Earth have evolved to use primarily

red and blue light for photosynthesis.

They reflect back the green light, which is why they look green.

On an alien planet, if there's complex life,

there'll be something like plants

and something like animals that eat them.

But it probably wouldn't stop there, because here on Earth that's not the

last link in the food chain.

How do we begin to imagine what aliens might be like?

Well, if animals have evolved on another planet they might not have arms,

but they'll still be looking over their shoulders,

because chances are there's predators out there.

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There's two ways to load up on the energy you need.

You can be like a fish and spend all day nibbling and nibbling on your ocean greens.

Or you can be like a man o' war

and snatch up in an instant all the energy the

fish picked up from days of nibbling.

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Plants consume sunlight.

Animals eat the plants.

And other animals eat those animals.

It's the circle of lunch.

Every creature on Earth has evolved its own body shape

to maximize its chances of getting a meal without being eaten.

Take cats.

I love cats, particularly house cats.

Cats have a very good sense of themselves, they're very confident.

Cats are fairly pleased with themselves.

And cats have good reason to be pleased with themselves.

Cats are all around the world, from the desert

to the Arctic to temperate climates.

For me, cats represent one of the pinnacles of evolution.

Cheetahs, for instance, have evolved into perfect hunting machines.

But even they may find it hard to catch their prey.

Shiloh is the cocky one, that she's very independent and on her own

and as a cub she was the one that was the strongest.

Odyssey, the male, he's just a, yeah, he doesn't have a care in the world.

As a baby, I lost him almost.

I had to keep him in my bed for two weeks.

He was on a drip, 'cause he was so dehydrated, and he was just the weakest of the three.

I raised them and I gave them their name, so they're like my kids.

They call Marlice Van Vuuran, the Cheetah Whisperer.

She rescues abandoned cubs on the plains of Namibia.

And helps them learn how to eat.

When they're babies and they're around about six,

seven months old they need to chew then,

they need to learn what taste of meat they like.

Who's a good girl?

Where there is a juicy hunk of energy some creature is going to work out

a way to try and get a taste.

The springbok is the ultimate fast food.

If you look at a Springbok, they've kind of developed into a smaller specie;

light-boned, nothing extra.

They've got these long legs that gives them that acceleration and jump.

To catch a Springbok, the cheetah needs to be even faster.

Come. Come babbas. Come.

So Marlice helps the cubs keep in shape.

Come. Come.

The lure is a pulley system, you just connect it to the battery,

a car battery.

We just tie a piece of string to it and we let them just chase it.

It's like a kid, you have to make 'em fit.

By the time they have to really run a 100 meters and catch a springbok they're

gonna be dead if they do it for the first time.

So it's getting them ready for a proper hunt.

They can get from zero to 100 kilometers an hour in a blink of an eye.

Everything is just modified and made for speed.

They have a light bone structure.

They've got long nails; it's like a athlete using spikes.

It's got a very long tail in comparison to the other carnivores,

so it can cut a corner very quickly without flipping or falling.

They normally spot the springbok way before me.

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They need to be at least 100, 120 meters from a springbok

for the springbok not to outrun them.

The surprise element is crucial to them.

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Almost 90% of the times they get away.

It's rough being a predator.

Cheetahs are living on a knife edge.

They use almost as many calories catching their food as they get from eating it.

But there's other ways to get food besides catching it.

If you can't out run 'em, outthink 'em.

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These wiseguys have worked out an angle, trading sunglasses for food.

It brings in the maximum amount of calories for the minimum amount of effort.

Monkeys are smart, but we've got a bigger racket.

We've hacked the entire planet to feed over seven billion of us.

Hello.

I'm Mae Jemison.

Right now, I'm aboard the space shuttle Endeavour,

over 300 kilometers above the Earth

and travelling at over 7,000 meters per second.

My first view from space was the city of Chicago.

No kidding. My hometown.

And it looked just like the map I learned when I was a child,

because the concrete of the city seemed to be separated from the

green of the farms that surrounded Chicago.

Chicago prospered because of its ability to transfer food

from the place that it was grown to humans that were far removed from that locale.

The Chicago stock markets, the agriculture around Chicago, the corn fields,

all of that is about a manipulation of the food web.

It's something we humans do really well.

Our eating skills are epic.

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Our brains are so big and complex that we have managed to figure out all sorts of

clever ways to get our food.

Chemicals to fertilize crops.

Genetic manipulation to modify them.

Nourishment to make animals grow up big and fast.

And even robotics to process them.

Here on Earth there are over eight million different

types of complex life,

all feeding 24 hours a day, every day of every year,

including over seven billion human beings.

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If it's edible it's going to get eaten.

Plants eat sunlight.

Animals eat plants.

And other animals eat animals.

But there wouldn't be anything larger than a microbe to eat.

No cucumbers, no fish, no steak and fries.

None of this food chain would exist without a freak event we think

only happened once in the whole of Earth's history.

Our planet is like a huge restaurant where everything

is eating everything else.

Humans are at the best table, just eating, eating and eating.

But is this joint a franchise?

Are there other branches out there in the universe?

The answer to that revolves around the strangest meal that ever happened.

Every complex life form on this planet, including you and me,

has relied on the same solution for what seemed like an insurmountable hurdle,

getting enough energy.

Around two billion years ago, when nothing lived on Earth except microbes,

we think one microbe ingested another.

Nothing particularly remarkable, happened all the time.

But this time the microbe was engulfed but not digested.

It actually survived in the host and became a part of it.

This remarkable microbe had a superpower.

It generated energy using oxygen,

allowing it to extract 15 times more energy from its food.

This is the moment when life as we know it really began.

The microbe that survived led to what we now call mitochondria;

a big complex cell that could connect with other cells to make big creatures,

all of them using oxygen to break down their food.

Mitochondria inhabit every single cell of every complex life form on this planet.

That means they power everything from flies

to trees to cheetahs and us.

Think about it, we all carry the same machinery in us.

And we wouldn't be the complex,

complicated organisms that we are today without mitochondria.

If we didn't have that one moment, Earth would have no plants, no plant eaters,

no meat eaters, no us.

Life on Earth would be just bacteria chewing on rock and each other.

It took trillions of bacteria swallowing trillions of bacteria for more than

two billion years before that one failed meal, which suggests it kinda rare.

How rare?

Maybe Earth only rare.

For an alien planet out there to evolve over those billions of years and to be

exactly like it evolved here on Earth, well that's like rolling those dice and hitting

a one, you know, a billion times in a row.

The overwhelming probability, if you find a planet with life on it,

it's probably gonna be very simple life.

You know, we're not gonna I always say see Mr. Spock.

You know, we're not gonna necessarily find the bipedal character that looks very

humanoid just walk in through the door and say, "Hey, I evolved on a different planet

and there are a whole bunch of us around."

But do I think simple life exists in other places?

Absolutely.

Looking up at all those points of light,

we'll always wonder is there life out there somewhere?

Maybe there is, maybe even a lot of it.

But there's a good chance that, as we gaze up at those stars,

there'll be nothing remotely like us looking back.

Next time, the greatest mystery in the universe could be right between our ears.

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Captioned by Cotter Captioning Services.