[thunder crashing]
[rainfall]
[dog barking]
[birds calling]
[varied bird calls]
[wings fluttering]
[narrator] The Earth, home to millions of species.
[man talking on radio]
[woman singing]
But what might live... beyond?
There are countless planets throughout the universe.
If life exists on only a fraction of them,
then the universe must be... alive.
[cawing]
[chattering]
All living things have the same needs.
To feed...
reproduce...
and evolve.
By applying the laws of life on Earth
to the rest of the universe...
it's possible to imagine
what could live...
on alien worlds.
All life forms need a planet to live on.
But how many planets are there in the universe?
[man] Think about our star,
the Sun,
with Earth, Mars, Jupiter orbiting it.
For centuries,
people have asked themselves, "What about the other stars?
Uh, do they have planets as well?"
And 24 years ago,
I found one!
Didier Queloz is a superstar astrophysicist.
He has won the Nobel Prize for discovering the first planet
beyond our solar system.
[Didier] I was 28 years old when I found the planet.
I was about to finish my PhD,
and my PhD adviser gave me the key of the equipment.
And after observing a couple of times, the star 51 Peg,
I realized that something was going on on that star.
And frankly, I just panicked at that time.
I thought something was really wrong with my equipment.
And the more I wanted to understand this, the less it made sense.
Until the point I got convinced it must be a planet.
That's likely to be a planet over there.
Could be Jupiter over there.
It's pretty cool.
Distant planets are invisible to telescopes
because they don't emit any light.
But if a planet passes in front of a star,
it casts a tiny shadow,
and there's a minuscule dimming of the star's brightness.
When astronomers detect this dip in light level,
they have found a new planet.
Hello, guys.
Uh... Oh, hey. Here is what the telescope is looking at.
This is a picture of the telescope right now.
Uh, in the middle, you have the... the target we're observing.
So, you analyze this whole field, you process the data,
and, um, if you're lucky enough, you detect this.
There's a little bit of a decrease of the flux,
and this tells me that there is a planet orbiting that star.
[Didier] We know there are a huge number of planets in the universe.
There must be a zillion kinds of different life.
Let's imagine that this is the Earth, here...
Right?
So, imagine that one meter is 20 light-years.
So, I've made two meters as 40 light-years.
This is where you have 51 Peg, where the first planet was detected.
Each of these tiny lights represents a star
where a planet has been found.
Over the next few years,
planets were turning up everywhere.
♪ Planets, planets everywhere ♪
It looks pretty cool right now. [laughs]
A horizon of stars and planets...
all around. [laughs]
Planets beyond our solar system are called exoplanets.
Astronomers have found over 4,000 of them.
And they keep finding more.
They now believe there's at least one planet for every star in the universe.
That means over a million, billion, trillion exoplanets.
More than all the grains of sand on Earth.
A vast canvas for the evolution of life.
The distances are mind-boggling.
The nearest exoplanets are trillions of miles from us.
But they're all subject to the same force that holds the Earth in place.
Gravity.
Imagine a world double the size of Earth,
with twice as much gravity.
This is Atlas.
How would life adapt on such a world?
[alien bird trilling]
Gravity pulls vegetation to the planet's surface.
And yet, seeds can float in the sky.
That's because gravity here is so strong.
Air molecules are densely packed together...
creating a thick, buoyant atmosphere for seeds to drift through.
And where there are seeds...
there are sky grazers.
[screeches]
Giant herbivores with six wings
to ride on the dense pillow of air.
[creatures calling]
Because of the extra gravity,
they weigh twice as much as they would on Earth.
But they don't fall from the sky.
The atmosphere is thick enough to keep them airborne.
Whether on Atlas or on Earth,
flying is always a battle to overcome gravity.
[birds calling]
[man] You might say I have a pretty complicated relationship with gravity.
And you can really feel that gravity is a force pulling you down
as you struggle your way up.
But ultimately, my dream has always been to be able to fly.
Whoo-hoo-hoo! [laughs]
The thing I love most about paragliding is that it's so simple and intuitive.
It's just you and the air.
Like the sky grazers on Atlas,
paragliders use their wings to generate lift.
But the atmosphere is less dense on Earth...
so it takes more effort to stay airborne.
[Fiorenzo] Most people don't see air as a substance.
But for me, when I'm flying,
I really see it as a fluid that's moving up and down the valleys
and along the ridges.
It would be really weird to fly in a very dense atmosphere.
You could just be gliding around the whole time, effortlessly.
The best way to gain altitude is to find an updraft,
known as a "thermal."
[Fiorenzo] When you hit the thermal, it's very similar
to when you're in an elevator and it starts.
You feel a push upwards.
Yeah, there we go!
Just the power of nature to pull me up.
When I'm flying and I see a bird circling up,
it means there must be a thermal there.
So we're always constantly looking at them.
You can really feel the balance between the gravity pulling you down
and the air lifting you up.
You can then use your bodyweight to gain speed,
and use that speed to generate more energy
and feel that you're moving through the air.
Gravity may be weaker on Earth than on Atlas...
but the thinner atmosphere means there's less buoyancy.
So, eventually, everything falls.
On Atlas, the sky grazers never need to land.
[screeching]
Their front and back wings are for direction and thrust.
Their long middle wings are for catching thermals.
Despite their weight,
the air is thick enough for them to live a life
in the sky.
But it's not always a peaceful life.
[creatures chattering]
As on Earth, grazers attract predators.
Using hydrogen-producing bacteria to inflate their air sacs,
they take to the skies.
[calling loudly]
Alone, they're no match for their prey...
so they hunt in a pack...
waiting for a sky grazer to stray from the group.
Target sighted, they expel their gas...
and attack from above.
The fastest predator on Earth
uses the same tactic.
[man] My interest in flying falcons is...
their predatory instinct coupled with the speed factor...
and how they use that speed to their advantage.
But just watching a top predator do its thing...
is perfection.
I probably have 30-some birds at this moment.
Each bird is a different personality.
What I love about falcons
is how evolution has made the most perfect specimen.
[imitating bird calls]
-[falcon squawking] -[Vahe chirping]
[laughs]
I do have a relationship with these guys.
Certainly from my end, I do. [laughs]
I don't think the falcons see it that way,
but they certainly see me as part of the team.
Vahe Alaverdian trains captive-bred falcons how to hunt.
[Vahe] These birds are genetically programmed
to be the top-notch avian predators that they are.
What we do as falconers
is try to awaken that predatorial nature in the bird.
Lure training is the very first step.
Come on, buddy! Hup, hup, hup, hup, hup!
I want to put that lure in front of the bird,
and get the falcon to coordinate eye to foot...
Hup, hup!
...and throw its feet out as if it's gonna grab it.
As that happens, I try to pull that away from the falcon
to get it to shoot up in the air and repeat this process again.
I wanna see that bird drop down as vertical as it can.
That's something that they later on will apply to hunting game.
When the falcons are ready, Vahe introduces a prey target...
a racing pigeon.
The falcon can't keep up with the pigeon in a chase,
so its best bet is to drop on it...
using gravity.
[Vahe] When the bird thinks that he's got the advantage,
that's when the wings will get tucked in.
They stoop into a little teardrop shape...
coming down from the heavens.
The kinetic energy of a falcon hitting a pigeon
would be as if you were hit by a cannonball.
In training, the pigeon invariably gets away,
because the falcon is made to stoop from less than a thousand feet.
When hunting for real,
it'll drop from a greater height...
to lethal effect.
[creatures calling]
[screeching]
The predators make their move.
[wailing]
They deploy their wings
to create drag...
destabilizing the sky grazer
to devour it on the ground.
[moans]
But this pack is too small to take down such a large beast.
Today, they'll go hungry.
[calls]
[creatures barking and chattering]
[creatures howling]
The sky grazer climbs to a safe height...
to recuperate.
[howling]
But as a fertile female,
she has company.
Male grazers, competing to be chosen as a mate.
[all calling]
Their oversized tails are a handicap,
making it harder to fly.
But to the female, they're a sign of vitality.
[howling]
The first to reach her gets to mate
and pass on his genes.
[birdsong]
The same principle applies on Earth,
whether up in the sky
or down in the dirt.
Males compete for the right to mate.
[man 1] And running, set...
[man 2] I think when people sit at home watching insects on television,
they imagine the cameraman sitting in the jungle,
in a river or in a hedge,
waiting for this beetle to come across
and reproduce or have a fight in front of the camera.
It doesn't work that way.
This is a ramshackle old shed which is attached to my parents' place,
which is just there.
Huge advantages to having a place attached to your mum and dad's.
You get good dinners in the evening and, uh, teas arriving during the day.
-Have a look and see what we're doing. -Oh!
Oh, gosh.
Oh! What on Earth are they?
[Robert] They are rhinoceros beetles.
The male's got these big horns.
The female doesn't. It's a form of sexual selection,
because the females like males with big horns.
So every time they mate,
they'll mate with a beetle that has a slightly bigger horn
-than the one they've last seen before. -Oh!
And, therefore, that male passes its genes on.
So, over generations, the horns will get bigger.
-[man 1] Anywhere particular? -[Robert] Um, just on the...
on the log facing the other male.
[man 1] Here they go. They're going straight away.
The horns of a male rhinoceros beetle
are like the tail of a male sky grazer.
They've evolved for sexual competition.
-Ha-ha! -That dominant one's done it again.
[Robert] That's a good shot. The shot we wanted.
-[man 1] Yeah. -[Robert] Going into her, yeah.
One, two, three.
-That right? -[Robert] Yeah.
-[man 1] Yep. -[man 3] That's it.
-Can I... Yes. -You putting that in?
Male insects don't always fight to snare a mate.
Sometimes it's enough just to show off their physical prowess.
[man 1] Right, I'm gonna bring the male in front of you.
He's coming in from your right.
Now, uh-- He's flown off.
These are stalk-eyed flies.
[Robert] Stalk-eyed fly is an amazing little thing.
It looks a little bit like an ant with massive eyes on the ends of stalks.
Both the male and the female have eyes on the end of stalks,
but the male has much longer eye stalks than the female.
The males with the long stalks will come up to one another,
and they will, kind of, have a little dance.
And they will try and judge
which of the two of them has the bigger stalks.
There they are. That's the standoff!
The winner of that will remain where they are and the loser will then toddle off.
That winner then will gain access to the female,
and be able to reproduce with her,
and that way can pass on the genetics that he has,
which will include that of a longer eye stalk.
-[Robert] Yes! Got it. -[man 1] Are-- are you on it?
Oh, It's fantastic.
Normally, it's a second and they're gone. This is fantastic.
Why would the male stalk-eyed fly go to the effort
of having these enormous eye stalks?
Well, the idea is that you are conspicuously signaling to the female
that you can have this incredible investment of energy into this resource
that is completely needless.
And if you can still survive,
if you can carry on flying and living and not getting predated upon,
and still have this... wasteful extravagance coming out of your head,
then you're gonna be a pretty good bet to reproduce with.
[creatures howling and barking]
On Atlas,
the long tail of the male sky grazer shows he's an ideal choice...
to father the next generation.
[howling]
But the mother can't lay her eggs in the sky.
[roars]
So she's come down to land.
Because of the gravity, she's too heavy to launch herself back into the sky.
[roars]
[moans]
To create new life, she must surrender her own.
The babies grow up close to where their mothers die.
Now they need to get off the ground and into the air.
[all calling]
[crunching]
But scavengers lie in wait.
Boneless creatures
with no skeleton to give them form.
[calling]
They kill by enveloping and dissolving their prey.
The sky grazers have only just hatched, but already they're in grave danger.
And now, there's no going back.
[calling and squeaking]
[insects chirping]
[animal howling]
[meerkat grunting]
Every day on Earth,
young animals have to overcome terrible odds,
if they're to survive.
Sixty percent of meerkats don't make it to their first birthday.
[woman] For a young meerkat, in their early life,
there's a lot of danger here.
They're vulnerable for many months after they're born...
but particularly in the first month or two after they emerge from the burrow.
Predators are everywhere, and a constant danger.
There are snakes in this area
that will eat a young meerkat.
-[snake hisses] -[meerkat chatters]
[barking and chattering]
A young meerkat is safe within a group,
but if it lags behind, it's vulnerable.
Scorpions are a constant threat.
[squeaking]
[Kirsty] The young are really completely incompetent,
and totally ignorant when it comes to dealing with scorpions, initially.
But they can't avoid this danger forever.
They're going to eventually have to learn how to neutralize the threat.
[whimpers]
The first time that a young meerkat faces a scorpion
and it has to deal with it itself
is probably a terrifying encounter.
This is a real moment of truth.
[yelping]
It's a real rite of passage, because once they've managed to do that themselves,
then they really are at a stage where they can start to forage by themselves
and become independent and be a useful group member.
So, they've really managed to escape the vulnerability of being a pup
and made that transition into being an adult.
It's one step on the road to adulthood,
but it's by no means plain sailing after that.
There are a lot of threats out there,
and it will have to continue to learn in order to reach adulthood.
[creatures roaring]
If the young sky grazers are to grow up,
they have no choice.
It's time to fly.
[screeching]
[predators chattering]
Even in the air, they're still not safe.
On Atlas, survival is a game of chance.
Life goes on from one generation to the next.
At least for now.
The strong gravity of Atlas pulls asteroids onto a collision course.
Most burn up in the atmosphere.
But there's a constant threat something big will get through...
and reset the course of life on the planet.
Because gravity is weaker on Earth than Atlas,
asteroid strikes are less frequent.
But when they do occur, they can be catastrophic.
[birds calling]
[man] This is the Yucatán Peninsula.
27,000 square miles of tropical jungle.
But hidden within the jungle are numerous sinkholes called cenotes.
These are entrances to vast underground cave systems.
There's no surface rivers or streams in the peninsula,
so the only source of water is underground in caves.
But the really interesting thing is the location of these cenotes.
Although there's probably 10,000 or more cenotes across the peninsula,
in the northwest corner...
they occur in a very well-defined semicircle.
If we follow that semicircle out into the Gulf of Mexico...
we now have a complete circle that marks what one would expect
from the edge of an asteroid impact crater.
[Thomas] 65 million years ago,
gravity pulled an asteroid into our solar system.
It smashed into our planet,
causing the extinction of 75 percent of life on Earth.
The asteroid strike generated enough debris
to block out sunlight for two years.
A world plunged into darkness.
Nothing could grow.
This would happen on Atlas
if a big enough asteroid hit the planet.
[Thomas] Cenotes are difficult places to survive...
just like the Earth was 65 million years ago.
What are the characteristics that a species needs to survive an extinction?
Somebody's in here.
So, crocodiles are very resilient animals.
They live both in the water and on land.
They're generalists. They don't require a specific diet.
They'll eat almost anything.
Whatever is available is good enough,
they'll take it.
Here in this cenote,
one's fallen in, gotten trapped, no way out...
Somehow, some way...
he's succeeded.
They're survivors.
In a changing world, it pays to be a generalist,
not a specialist.
If a big enough asteroid hits Atlas,
the sky grazers and predators would be doomed.
[screeching]
They're too specialized to cope with change.
The generalists are the boneless scavengers.
Like crocodiles, they eat anything...
and live anywhere.
On this imagined high-gravity world,
they could be the great survivors.
How might life adapt
on a different world,
where creatures are trapped
between a searing desert
and a frozen shadowland?
A world of extremes.