All language subtitles for our.universe.s01e04.1080p.web.h264-bigdoc

Nightfall…

reveals our planet's
connection to the universe.

A shooting star.

Ancient rock from
the depths of space…

falling to Earth.

Inside it are the chemical
elements that built our universe.

For countless generations,

sea turtles have
roamed the oceans,

gathering cosmic elements
in the food they eat.

And as they've done for
hundreds of millions of years…

every new generation

recycles this same stardust…

to produce the next.

Born in The Big Bang…

…and forged in the
hearts of stars…

…90 chemical elements
have created everything.

Endlessly recycled
and reconfigured

throughout the entire
history of the universe.

And now…

using the same elements,

each new turtle
begins a life cycle…

…that mirrors the
lives of the stars.

On Australia's
Great Barrier Reef…

…something magical has happened.

After 50 days beneath the sand,

chemical elements from across
the cosmos have created life.

Combining to form
the next generation

of green sea turtles.

The eggs have now exhausted their
supply of life-giving elements.

And today, the baby turtles will
take their first taste of air.

And as her brothers and sisters
scramble to make it to the water…

a little female…

is last to be born.

In order to grow to adulthood,

she will need to harvest chemical
elements from across the ocean.

It's a dangerous journey…

…with treachery at every turn.

But for the baby turtles,

the call of the ocean
is irresistible.

From a nest of 100,

sometimes only one will survive.

Sometimes none.

But despite the risk,

the little female knows

she must make it to the water.

She spots an opening…

and takes her chance.

Today…

she's a lucky one.

The hatchling won't stop swimming
until she has left the reef far behind.

Safely past the predators that
gather in the shallow coastal waters,

she'll disappear into the
great void of the open ocean…

to spend her childhood
feeding on atoms.

Atoms whose origins go back through
the entire life of the cosmos.

To the time our universe

was in its infancy.

Expanding from nothing to
everything in an instant.

Our universe was
born in The Big Bang.

At first,

it was nothing but
a hot, dense fog.

But as it continued to expand…

the fog began to cool.

And on the tiniest
scale imaginable…

…something astounding
began to occur.

The first atoms
condensed out of the fog.

Atoms of hydrogen.

The very first element
in the universe.

And in the ocean,

juvenile turtles
are hunting it down.

As they emerge from the blue

to forage in the shallow
waters of the reef.

This is Stella.

One of the lucky ones
that made it off the beach

and into the ocean.

She's already more than 2,000
times her hatching weight

and growing fast.

Feeding on creatures she's found
drifting in the open ocean,

she's harvested one element
more than any other.

Hydrogen.

It makes up more than half of all
the atoms in the food she eats.

And is the most abundant
element in all living things.

From fish

to invertebrates.

Anemones and coral.

Hydrogen atoms formed at
the dawn of the universe

have been passed on
from star to planet,

planet to animal…

and from prey to predator.

Which means, for Stella,

the waters around the
reef are full of danger.

Tiger sharks, hungry
for the same atoms,

hunt sea turtles throughout
their adult lives.

Stella's main defense
is her trusty armor.

Its bone toughened with
calcium and phosphorus.

Elements that date back
to another pivotal moment…

in the life of our universe.

For the first 300 million
years after The Big Bang…

there are no planets
and no stars.

The dark ages of the universe.

Concealed in the gloom,

vast tendrils of hydrogen
gas crisscross the cosmos.

And then, incredibly,

as they were drawn
together by gravity…

…the first stars were born.

This is the cosmic dawn.

The moment the lights came on.

And deep within
those first stars…

a remarkable process began.

Temperatures and
pressures were so extreme…

…that new elements were created.

Atoms of hydrogen were forced
together to make helium.

As they fused,
energy was released.

Creating a chain reaction that
produced increasingly heavier elements.

Including those
essential for life.

Three helium atoms
combined to make carbon.

The element on which
all life is based.

Carbon and helium made oxygen.

The air we breathe.

Oxygen atoms combined
to make phosphorus.

Then silicon and calcium.

The elements that make
up every living thing

were created in the hearts
of the very first stars.

For Stella,

some elements are so important…

…she'll travel great
distances to find them.

The warm, shallow waters between
Australia and Papua New Guinea

are a paradise of
vibrant seagrass.

The prairies of the ocean.

Stella has traveled all the way here
to access their magic ingredients.

As it grows,

seagrass absorbs
elements from outer space

that have found their
way to the ocean floor.

Burgeoning fronds rich
in calcium and phosphorus

provide Stella with precisely
the minerals she needs

to build and sustain
her protective shell.

Hardening her armor
for the trials ahead.

Stella will spend
her adolescent years

searching the ocean

for atoms born in the stars.

Her journey toward maturity…

paralleled in the
story of our universe.

Because three billion
years after The Big Bang…

…the universe was
also coming of age.

It was entering an incredibly
active phase of star formation.

As they grew,

stars were pulled together
into vast galaxies.

Like our Milky Way.

And within those galaxies,

the chemical elements
each star produced…

…were transformed into
planets and moons.

After billions of years,

chemical elements have matured
into the Earth we know today.

Stella is now fully
grown herself.

Over a meter long,

she has a thick shell
covered in green algae.

Ideal camouflage for
cruising coral reefs.

She is now at one
with the ocean.

Atoms from the stars

perfectly adapted
to life at sea.

Just one example
of life on Earth…

exquisitely shaped
from the cosmos.

Stella is now ready for
the next stage of her life.

Because she's about to
become a mother herself.

Inside her body…

she's carrying a
clutch of 100 eggs.

The first of many she'll
have over her lifetime.

Her own precious
cargo of stardust.

All across the reef,

atoms are being
assembled into new life.

Creating one of the richest
ecosystems on Earth.

But our planet…

…is an outlier.

In the rest of the solar system,

the very same elements

have created worlds far
less suited to life.

Closest to the sun,

Mercury is a planet
rich in carbon.

But rather than creating life,

the carbon is baked
into its crust.

On a world scorched
by starlight.

While in the farthest
reaches of the solar system,

Neptune's freezing temperatures

cause carbon and hydrogen
to form clouds of methane.

The suffocating gas that
gives it its brilliant blue.

And even on Mars,

a planet with all the
same ingredients as Earth…

the lack of an
oxygen-rich atmosphere

means complex life
couldn't survive here.

Only on Earth are
conditions just right.

But even here,

competition for
elements is fierce.

And danger…

…is never far away.

Luckily, Stella has become
an expert at hide-and-seek.

Safe for now…

Stella faces the biggest
challenge of her life.

To return to the
Great Barrier Reef

and the island of her birth…

to lay her own eggs in the sand.

But a lifetime spent
wandering the ocean

means she's now 2,000
kilometers away.

How Stella navigates home

is one of the wonders
of the natural world.

Deep within the Earth,

our planet's core
generates a magnetic field…

which gives every place on its
surface a unique magnetic signature.

When she hatched,

her island's signature was
imprinted in Stella's brain.

And to find her way back,

she'll rely on yet
another chemical element.

One that connects her
to the planet's core.

An element that's only
created when stars die.

In a nearby part of the galaxy,

two and a half
million years ago,

a dramatic change took place
in the core of a giant star.

For all its life, it had been
powered by nuclear fusion.

The energy released…

…creating heavier
and heavier elements.

Until the core became so hot,

it started creating…

…iron.

Which caused a fundamental
change to take place.

Because making iron
doesn't release energy.

It consumes it.

As more and more of
the metal was produced,

it spread through the
core like a disease.

Feeding off the star's heat.

Throttling it.

With no heat source
to hold it up.

From this moment onward…

…the star was doomed.

The resulting explosion shone with
the brightness of 10 billion suns.

A supernova which propelled
iron-rich dust across the galaxy.

All the way to our planet.

And even now,

100 tons of stardust enters
Earth's atmosphere every day.

Some left over from the
formation of the solar system.

Some blown here from
distant supernovas.

A direct link between
our planet and the stars.

And it's the iron in this dust

that allows Stella
to find her way.

Because deep in her brain…

…specialized cells are thought
to contain crystals of magnetite.

An iron-rich mineral that aligns
itself to the Earth's magnetic field.

A compass,

pointing her in the
right direction.

Allowing Stella to find the unique
magnetic fingerprint of home.

And so an element
forged in a supernova…

…will now guide her across
kilometers of featureless ocean.

Back to the island…

on which she was born.

But there are other creatures
with magnetic homing abilities.

The tiger sharks have it too.

And it's leading them
back to the same island.

Because for a few
months every year,

thousands of female turtles
come here to lay their eggs.

It's the largest gathering
of green sea turtles

anywhere on the planet.

And as they come to shore,

the feeding begins.

Stella must wait for
the right moment…

to find an opening…

and avoid the onslaught.

When the danger has passed…

she finally swims ashore.

After an epic journey…

Stella emerges onto the sand

she last touched as a hatchling.

The elements she spent
a lifetime collecting…

are now safely
delivered into the sand.

Stella's mission is complete,

and she returns to the ocean…

to begin gathering
stardust once more.

The cycle of her life

mirroring the
grandest cycle of all.

The lives and
deaths of the stars.

Because far away
across the galaxy,

the ashes of
countless supernovas

have come together to
form a giant nebula.

A cloud of stardust tens
of light-years across.

And buried within it are places
where the next generation of stars

are beginning to form.

Called proplyds.

They're like vast cosmic eggs.

Each one bigger than
our solar system.

Inside their shells
of ionized gas,

the force of gravity is
pulling stardust together.

And the stardust
inside Stella's eggs…

is also beginning to take shape.

As the elements she collected
are being transformed…

into something that's starting
to resemble a tiny creature.

And within the proplyd…

gases like hydrogen and helium…

…are feeding an embryonic star.

And what was once an embryo…

is now a tiny turtle…

with shell, flippers, and beak.

Elements reimagined…

for a life at sea.

In the proplyd,

the new star's development
is also nearing completion.

Reborn from the ashes of
the previous generation,

its light now reveals a family
of growing planets in orbit.

New worlds.

But perhaps, new
possibilities for life.

And beneath the sand,

the same stardust,

passed down through countless
generations of stars and turtles…

will start yet another journey.

Each new life

directly connected to the
origin of the universe.

Each new story beginning
at the end of the last.

And so, the story of
our universe continues…

…with Earth's most
precious resource…

…water.

And a family of elephants on a
dangerous mission to find it.

Their journey every
bit as extraordinary…

…as water's journey across the
vastness of space to our planet.

But why is Earth the only
world in the solar system

whose surface is covered
with liquid water?

And why is it so
essential for life?