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Earth is a living planet.

But it wasn't always that way.

Life had a beginning.

When and how did life emerge
on this planet?

What environments did it live on
throughout Earth's history?

These are some of our planet's
greatest mysteries.

For a long time,
scientists thought

life could not have appeared
very early in Earth's history,

when the planet was under
heavy bombardment by asteroids.

A tremendous number of impacts,
even large one.

Imagine, an object the size
of the moon

that could have collided
with the Earth.

But now, scientists
are finding new clues

in ancient rocks,

on the surface of the moon,

even on space rocks

hundreds of millions
of miles away,

and inside craters made
by massive asteroid impacts.

And they're wondering,

instead of preventing life
from starting,

could violent impacts like these
actually be essential?

Asteroids could have delivered

the basic chemical building
blocks of life to Earth.

Leading some scientists to ask,

"Could asteroids
be the spark of life?"

Right now, on "NOVA."

The Barberton Makhonjwa
Mountains in South Africa.

Here lie some of the oldest
and rarest rocks

visible on the surface
of our planet.

And here, geologists Nadja
Drabon and Phumelele Mashele

are searching for evidence
of the conditions

on the early Earth

to help solve the mystery
of how life got started.

So we'll be going
right here,

right where you see

the purple meet the orange.

Right near the river.

Yeah.

When someone comes into
these mountains, they think,

"Oh, wow, that's a really
beautiful scenery

and really gorgeous."

However, when I come here,

I really start seeing Earthhistory

unfolding layer by layer.

Some of the
Barberton Makhonjwa rocks

are as old as 3.6 billion years.

They've only survived this long
because the mountain range

sits on a relatively stable part
of the Earth's crust.

They date back to a geological
eon called the Archean.

Earth itself had only formed
about 900 million years before.

The Archean world was alien.

There was no breathable oxygen.

Erupting volcanoes poured vast
quantities of greenhouse gases

into the atmosphere.

The sun was a lot weaker
than it is today,

but these gases kept
the planet warm--

warm enough for liquid water
on its surface.

In fact, some of the minerals
found in Archean rocks

suggest the planet
was already an ocean world.

So there was water.

Was there also life?

These Archean rocks are some of
the best preserved in the world.

Could they contain signs
of ancient life-forms?

In this vast landscape,

Nadja thinks she may have found
some traces.

When you look at these rocks
here,

some of these layers look
just really black.

But what I'm seeing here

is really the remains of life
back then.

People have taken
a really close look

through the microscope,
and what they are finding

is remains
of single-cellular organisms

preserved within the rock.

What did these microbes
look like?

Was this the first life
on Earth?

Far from the mountains
of Barberton,

in the city of Orléans, France,

geologist Frances Westall
examines ancient rock samples,

hunting for signs of life.

We have here in front of me
a collection of rocks

from Barbertons in South Africa

and also from the Pilbara
in Australia.

These rocks are more than
three billion years old.

In these rocks,

I have found traces
of fossil microbial life.

These rocky outcrops in the
arid regions of the Pilbara

in the northwest of Australia

are as ancient as those in the
Barberton Makhonjwa Mountains.

Rocks from both locations
have given Frances

and her colleagues

some of the best evidence yet

of what life may have been like
in the Archean eon

over three billion years ago.

To detect ancient life forms,

Frances uses
a scanning electron microscope.

A concentrated beam of electrons
scans the sample

and interacts with atoms
on the surface,

creating signals
that can be translated

into highly magnified images.

But this rock is not
a good conductor of electrons.

So it's coated

with a thin layer of a material
that is--

gold.

In a 3.3 billion-year-old sample
from Barberton,

Frances identifies
what many believe

are fossilized life-forms.

Here you can see
an individual filament.

Here, as well.

Frances thinks each of these
thread-like structures

is a cell about 70 times thinner
than a human hair.

How do we know that they're,
they're microbial fossils

and not something else

that's got nothing to do
with microbes--

minerals, for instance?

One method is to compare them

to microfossils
of modern bacteria

that Frances actually made
in her lab.

She entombed living microbes
in silica.

In nature, silica can fossilize
an ancient organism

by penetrating and coating
its internal structure.

In an extremely old rock sample
from the Pilbara in Australia,

Frances finds a shape that looks

like one of her modern
silica-coated microbes.

Chemical analysis
reveals signatures

of what could be
organic molecules,

which means this might have been
an ancient life-form.

I've been able to reveal
traces of single cells.

We can see cell division.

We can see, also here,
cell division.

These are cells
that are preserved in a rock

nearly three-and-a-half billion
years old,

and they are
exquisitely preserved.

They could be some
of the oldest microfossils

so far found on Earth.

Traces of a variety
of single-celled life-forms

that lived in different
environments

over three billion years ago

have been found in Barberton
and the Pilbara.

Even though they were
single-celled,

they came in a variety
of shapes.

And so, this could not have been
the first life.

Life was extremely diversified
already

by three-and-a-half billion
years ago,

which tells me that it must have
emerged a lot earlier

than we originally thought,

possibly between
4.3 and 4.2 billion years ago.

That would place
the origins of life

within the most mysterious
and inhospitable eon

in Earth's history--

the Hadean.

This was a time
even before the Archean.

Archean rocks may be
extremely rare,

but Earth's Hadean rocks
are nearly unheard of,

because most rocks on Earth
eventually get destroyed,

eroded away, or melted down.

For most of
our planet's history,

Earth's crust
has been broken into plates.

Sometimes,
when two plates collide,

one will slide under the other,

pushing the surface rocks
down into the mantle.

It's as though Earth
is swallowing its past.

Direct evidence of the Hadean
may be long gone,

but what we do know

is that over four-and-a-half
billion years ago,

our planet had just formed
from dust and rock particles

that circled our young sun,

so its surface was unstable.

Scientists named the eon
after Hades

because they believed it
must have been a hellish place,

covered with molten lava
from erupting volcanoes.

On top of that,
giant asteroids left over

from the formation
of the solar system

pummeled the planet.

Could life have emerged,
and survived,

in such hellish conditions?

To find the answer,

scientists must first know
what life actually is.

Karyn Rogers is an
astrobiologist and geochemist.

Karyn and her team study
the origins of life.

At some point
in Earth's history,

there wasn't life.

And there had to,

from that entire planet that
was abiotic,

that had no life on it,

there was a chemistry,
or probably a series

of chemistries and reactions
that were intertwined,

that eventually came into life.

Scientists don't yet know
the exact chemistry

that created life,

but they do know
its building blocks:

molecules containing elements

like carbon, hydrogen, nitrogen,
and oxygen,

which are found
all over the solar system,

can join to form
organic molecules,

including sugars
and amino acids.

These bond to make
even bigger molecules:

amino acids form proteins,

vital for the functions
of a cell.

How do we make the amino acids
that turn into proteins?

How are the sugars that form
the backbone of DNA and RNA

originally synthesized?

So life has all of these
ingredients,

and they need to come together
just right

to eventually get to life
as we know it.

The recipe required
a source of energy

and one of life's most essential
ingredients, liquid water.

So if life did emerge
4.3 billion years ago,

then this ancient,
extremely hot planet

had to also be a wet planet.

The rocks that could prove that
might be long gone,

but for years, scientists
have been gathering clues

from tiny ancient
mineral crystals.

When rocks erode,

some minerals can survive

and get incorporated
into new rocks.

In 2018, here in the Barberton
Makhonjwa mountain range,

Nadja Drabon and her team found
grains of a type of mineral

known to be the Earth's
oldest surviving material,

zircon.

Zircon is an extremely tough
little crystal.

Once it forms,
it's very hard to break down.

Zircon can withstand
billions of years of weathering,

so it retains evidence
about the rock

in which it originally formed.

And that's why the zircons

Nadja and her team discovered
on this mountain

are so special.

So this here is actually
my favorite rock

in the entire Barberton
Greenstone Belt.

That is because we find zircons
about 200 million years older

than the oldest rock on Earth.

Which means Nadja
had discovered

some of the rarest zircons
on the planet,

up to 4.2 billion years old--
from the Hadean.

Chemical analysis of these,

along with even older
Hadean zircons

found in Australia in the 1980s,

revealed that they had formed
in the presence

of a very special ingredient.

By about 4.3 billion years ago,

we've got evidence
for liquid water

preserved within these zircons.

The presence of water
in the Hadean

4.3 billion years ago

is crucial,

because water is one of
the key ingredients for life.

And life as we know it

could not have emerged
without it.

That began to paint a picture

of what the Hadean landscape
was like.

It was not exactly
the hellish place

scientists once thought it was.

We had emergent land,

but maybe not a lot of it.

And we had an ocean
covering most of the planet.

For oceans to exist,
the planet's crust

must have cooled much faster
than scientists once thought.

But where did the water
come from?

Some scientists believe
it was delivered

by asteroids and comets,

but Earth may also have been
born with water

trapped deep inside the mantle,

and volcanic activity delivered
it to the surface as steam.

And, in addition,

we were regularly
getting bombarded

with meteorites and asteroids.

And so they came in one
after another, after another.

Did life have to wait
for a lull in the bombardments

before it could spark?

Or was it hardy enough to emerge
despite the chaos,

snuffed out by an impact
in one place,

only to reemerge in another?

So far, no direct evidence
of these early asteroid impacts

has been found on Earth.

There may be traces of impacts
that happened

around three-and-a-half billion
years ago

back in the
Barberton Makhonjwa Mountains.

While any craters
would have been eroded away,

much tinier clues can survive.

I just found one!

Woo-hoo!

These things are so difficult
to find.

Like, in this whole package
of rocks,

these are the few
that are well-preserved.

This tiny circle is a spherule.

Spherules can form
as a direct result

of massive asteroid impacts.

When you have a giant impactor,

so think about ten kilometers
in diameter or bigger,

when that smashes into Earth,
you actually have so much energy

that it's going
to form a rock vapor cloud

that is going to be ejected out
of the crater

at speeds of up to
40,000 miles per hour.

This rock vapor cloud's
going to start condensing

to form these spherules
that are going to rain out

and blanket the entire globe.

Without visible craters,
these scattered spherules

may be the only remaining
evidence of an impact,

so it's impossible to know

exactly where on Earth
the asteroid hit.

As the spherules rain down,
they form layers.

The thicker the layer,
the larger the original impact.

And the spherule layer
that Nadja and Phumelele locate

is very thick--
almost eight inches deep--

so the asteroid that created it

was probably
more than 20 miles across.

For the impact energy,

what we actually think about
is the mass.

And that would have been
50 to 200 times bigger

than that of the impactor
that killed the dinosaurs.

These rocks tell the whole story
from before the impact happened

to the actual impact event,

and then to how the environment
and life responded.

Before the impact happened,
about 3.26 billion years ago,

here at this location,

we would have been standing
on the seafloor,

on the shallow seafloor.

And there was a little bit of
life present, but not too much.

And then all of a sudden, this
is changing really dramatically.

The asteroid hit the ocean,

triggering an enormous tsunami
that swept across the globe.

Evidence of the big wave
is in the rocks.

And that's what we see here,

these big chunks
that were ripped up

from the seafloor
right below.

What effects did the tsunami
have on the simple life

that may have lived at the time?

Nadja finds clues in sediments

that formed not long
after the impact.

The rocks are red--
an indication of iron,

an essential nutrient for life.

What we think is that
the tsunami that was sweeping by

was bringing iron-rich waters

from the deep oceans
to the surface.

A closer look
at the iron-bearing rocks

reveals another surprise...

...signs that life bounced back
very quickly after the impact.

How could this happen?

So what we think we see
in these rocks

is that these microbes
are starting to respond

to that increase in nutrients
and iron,

and are actually
starting to, to bloom.

When people think
about giant meteorite impacts,

they first think about
the extinction of the dinosaurs.

What we think
what we are seeing here

is that life was not only able

to survive these
really disastrous consequences

for the environment,

life was actually able
to thrive.

So far, evidence
of several giant impacts

that happened between
3.5 and 3.2 billion years ago

has been found
in these mountains.

But what was happening earlier,
during the Hadean,

4.3 billion years ago,

when some scientists think
the very first life emerged?

Traces of that time on Earth
are long gone,

but there is another place
that can tell the story--

the moon,

whose surface has retained
the kinds of scars

that once covered Earth.

We don't have any surviving
remnants of that Hadean Earth.

And so it's easy, I think,

to imagine that that surface
was not cratered.

But the moon actually tells us
otherwise.

MAN [on radio]:
Zero, zero, five, seven, two.

David Kring is an astrobiologist

at the Lunar and Planetary
Institute in Houston.

He studies the surface
of the moon

to learn about the early Earth.

MAN [on radio]:
Cherokee, one, zero, zero, zero.

In the early
and mid-20th century,

scientists debated the origin
of the circular structures

on the lunar surface.

Were they huge volcanoes
or were they impact craters?

Ignition sequence start.

Almost immediately,
the Apollo 11 mission

answered this question with the
samples that were collected

and brought back to Earth.

It became evident that nearly
all of those circular features

must have been generated by
impacting asteroids and comets.

It was a turning point,
when scientists realized

that violent asteroid impacts

could reshape the surface
of a planet, including our own.

The craters on the moon
were beautifully preserved,

undisturbed by erosion
or plate tectonics,

like we have here on Earth.

Scientists started
to count them.

The older a planetary surface,

the more time there has been
for it to be hit

by these impacting asteroids,
and therefore,

the greater
the number of craters.

Thousands of craters
larger than a mile wide

have been counted so far.

When the moon rocks from some
of the craters were dated,

scientists were in
for a surprise.

In most cases,

the samples that were returned
by the Apollo astronauts

had very, very old ages,

in what we now call
the Hadean of Earth history,

indicating that there was,
early in solar system history,

a intense period of bombardment.

If the moon suffered
this many violent impacts,

how many and how large
were the asteroids

that hit the early Earth?

How frequently did they impact?

And how could they affect
the emergence of life?

Planetary scientist
Simone Marchi

has been piecing the story
together.

There's one single process
that's very important to me

that I find it very fascinating,

and that is the process
of collisions.

Everywhere we look,

everywhere in the
solar system

there is a solidsurface,

you'll find that there
are craters.

The craters are a reminder
of our solar system's formation

around 4.56 billion years ago.

It began as a disk
of dust and gas

in orbit around the young sun.

The solid materials
collided and clumped together

to gradually form
the rocky planets.

As a result of the formation
of the Earth,

there were still lots of debris,
and asteroids,

and, and other, smaller objects
flying around the sun.

Those object kept colliding
with the surface of the Earth.

About four-and-a-half billion
years ago,

a single object the size
of Mars, or even bigger,

may have crashed
into the young Earth.

This high-resolution simulation
reveals

how the collision flung

enough molten and vaporized
debris into space

to create the moon.

I'm trying to understand the
early evolution of the Earth

and the effects of all those
impacts that were taking place

during the Hadean Earth.

So we do this
by building models.

One of the most important
sources of data

comes from NASA's
lunar reconnaissance mission.

This robotic spacecraft
has made a 3D map

of the moon's surface

at extremely high resolution.

The first thing that we do

is to look at the surface
of the moon.

It is much older than
the surface of the Earth.

The surface of the moon is full
of impact craters,

all the impact craters,

and so we can use
that information

by mapping how many there are,
and their sizes and their ages,

and that will provide us
the primary information

that we need
to build our models.

It took an international team
decades to collect the data,

but they finally created
a computer model

that took what happened
on the moon during the Hadean

and simulated the asteroids

that would have hit the Earth
during the same stretch of time.

And the outcome of that
first modeling was staggering.

We are seeing the entire
surface of the Earth

that is strongly affected
by impacts.

Every single circle
that you see here

is, is an impact,
is a collision.

The prediction was
that there were

a tremendous number of impacts,
even large one.

Imagine, an object
the size of the moon

that could have collided
with the Earth.

That would have basically

wiped out almost entirely,
perhaps, the oceans,

vaporized the oceans

and, and melted a large portion
of the crust of the Earth.

This series
of apocalyptic bombardments

might look like it created
a chaotic hellscape on Earth.

But fossil evidence suggests

that life did emerge
during the Hadean.

So even during asteroid impacts,

there must have been
enough habitable conditions

somewhere on the planet

for life to get a foothold.

If life started on Earth

around perhaps 4.2 billion years
ago or thereabouts,

then the question is
how that was connected

to the impacts that were taking
place at the same time.

The origins of life community
rarely thought about impacts

as part of the origin story.

It's really hard to not think
about them.

We really had to change our,
our sort of frame of mind,

and I certainly did.

To investigate what effects
the asteroid impacts had

on the emergence of life,

Karyn Rogers is recreating the
conditions of the Hadean Earth

in her lab.

In some ways,

the early Earth was
a big experimental laboratory

doing prebiotic chemistry.

We can do experiments

that were similar to what
the early Earth was doing,

and hopefully discover

the chemistry that eventually
led to life.

Karyn's team can create
tiny Hadean environments

with the same temperatures,
pressures, gases,

water composition,
and types of rocks

that may have existed
at the time...

...echoing the places which may
have had the chemistry needed

for simple molecules to join

and eventually lead
to the first cell.

So what we think
about the origins of life,

there are a few different ideas

that have been around
for a while

that people have been studying
for quite some time.

One of them is a hydrothermal
system origin of life.

These are hot water systems
heated by volcanic activity.

One of the really special things
about hydrothermal systems

is that they can provide energy
either for life

or maybe the chemistry
that allows life to emerge.

Hydrothermal systems can appear
on land,

where magma pushes
towards the surface,

creating hot springs
and geysers,

like the ones at Yellowstone,

and in the deep sea.

Here, the cold seawater descends
into fractures in the rock

and interacts with the minerals.

Heated by magma, it reemerges
through chimney-like structures,

now enriched with the types
of organic molecules

necessary for life.

We have really hot
hydrothermal fluid

coming out of a chimney.

It's full of metals,
and it's mixing with seawater.

And so when those two fluids
come together,

they could also provide energy

to do organic chemistry
that might lead to life.

So, did the very first
primitive cells

emerge and survive
in hydrothermal systems?

And if so, where?

On land? In the deep sea?

Or somewhere else?

Was that even possible under
a steady barrage of asteroids?

Well, when we think about life
surviving on the Earth,

we think about things
that allow it to thrive

and things that
might actually destroy it.

And probably one of the most
prominent sort of events

that destroyed life

was the impact
that killed the dinosaurs.

66 million years ago,

long after the Hadean ended,

a space rock
bigger than Mount Everest

hurtled toward our planet.

It was a moment
that would change

the evolution of life on Earth.

A vivid reminder of the havoc
and devastation

that an asteroid impact
can wreak.

That one impact alone

wiped out 75% of Earth's species

after it hit
the Yucatán Peninsula.

The Chicxulub impact crater
was produced by an asteroid.

It hit with an energy

equivalent to 100 million
megatons of energy.

That's a tremendous blast.

David Kring has studied rocks

from beneath the Chicxulub
impact crater.

Looking at tiny slices of the
rock under a microscope...

...he found quartz crystals
that had been shocked

and deformed
by the intense pressure

generated by the impact.

But he also saw something
much more surprising:

minerals like anhydrite, which
are produced hydrothermally

in the presence
of very hot water.

So this is evidence

that the impact event
heated the Earth's crust,

heating the water
within the Earth's crust,

and then generated a vast,
circulating hydrothermal system.

This system
would have been similar

to volcanically driven
hydrothermal systems,

where some scientists believe
life first emerged.

But this one was much larger.

As David probed further,

he found something else
locked inside the minerals.

Signs that ancient microbes
were living

in Chicxulub's hydrothermal
system

just after the impact.

We now have evidence

that it hosted
a microbial ecosystem.

They provided the habitat
in which

these organisms thrived and grew

throughout the crust
of the Earth

beneath the floor
of the Chicxulub impact crater.

And it wasn't just Chicxulub.

As scientists surveyed
the 200 known impact craters

and structures on Earth,

they discovered that about
a third of them show signs

of the same type
of hydrothermal activity.

And so we began to realize
that this was a common process

that would have occurred
in impact craters

throughout the Hadean period.

What did these ancient
hydrothermal systems look like?

There could be clues

inside one of Earth's
best-preserved craters.

About 15 million years ago,

an asteroid hit
Southern Germany,

making an almost 16-mile-wide
crater known as Ries.

The impactor
was about the same size

as a medieval town
called Nördlingen,

built inside the crater,

which is nearly invisible today.

Even from the highest tower,
the rim is hard to make out.

But human-made quarries
have exposed the secrets

that lie beneath the crater.

All along the rock walls,

excavation has exposed
strange, vertical,

pipe-like structures.

Planetary geologist
Livio Tornabene

is at Ries Crater to learn
more about these formations,

which are visible
as rust-colored rock.

It's really bounding
this pipe structure.

I mean, it looks
like it disappears,

but it probably
goes into the rock.

Probably have to see this
in three dimensions,

and it would be sort of

branching out
and trying to find

the quickest route
up to the surface.

After decades of research,

scientists believe they know
how these pipes were formed.

Here, we're, we're actually
below the surface of the,

of the deposit as it would have
been 15 million years ago.

It's really well-preserved,
and for a crater this size,

it would have produced
a lot of melt

that would have been
superheated.

The heat from the melt
released water from the rock

and turned it into gas.

The energy of the escaping steam
forged pathways

up though the hardening rock,

creating what scientists
call degassing pipes.

The darker color of the pipes

is evidence
that liquids and gases

once flowed through them.

We know that there was fluid
here

running through these rocks,

there was heat,
there were available nutrients,

and that is definitely
the combination

that you want to look for
when looking for life

here on Earth, or on Mars,

or elsewhere
in the solar system.

These degassing pipes
were like the plumbing

of a vast hydrothermal system.

With every excavation,
more are exposed.

So how large
were the hydrothermal systems

that formed during the Hadean?

The Chicxulub crater may help
scientists in their estimates.

So, Chicxulub is
a good model

for some of the smaller
impact events

that occurred during the Hadean.

At the Southwest Research
Institute,

geologist Amanda Alexander

runs one of the latest
Chicxulub models.

The blue-green color shows
the areas where the impact

would have fractured the rock,
allowing water to flow through,

creating a hydrothermal system.

It was much bigger
than scientists thought.

About ten times larger than was
previously expected,

and about 100 times larger
than we think

is the current
Yellowstone hydrothermal system.

And this astonishing estimate

is for only one crater.

So the Chicxulub impactor was
about 14 kilometers in size,

but the impacts that were
happening on the Hadean

were much larger
and much more frequent.

Impacts like these would have
been occurring

over the half-billion-year
duration of the Hadean.

So at some point,

vast hydrothermal systems might
have covered much of the planet.

All of this research
is leading to a remarkable idea.

It's looking more and more
like asteroid impacts

were double-edged swords.

While they were certainly

bringers of chaos
and destruction,

they might have created
ideal conditions for life.

But what about
the raw ingredients?

How can we know
if they were present

at asteroid impact sites?

Danny Glavin
is an astrobiologist

at NASA's Goddard Space Flight
Center near Washington, D.C.

He's been looking
for the ingredients of life

in space rocks.

Meteorites are really
fascinating objects.

These are fragments
of asteroid material

that are constantly bombarding
the Earth.

Something like 5,000 metric tons
of material

is falling to the Earth
each year.

In 1969,

what would become one of the
world's most studied meteorites

fell to Earth
in Southeast Australia.

It was named Murchison,
after a nearby town.

This meteorite
was a treasure trove,

containing hundreds
of amino acids

and other fundamental
building blocks of life.

The way we extract
these meteorite samples

to look for the chemical
building blocks of life

is, we start with a small chunk,
maybe the size of a sugar cube,

start chopping it up,
grinding it up.

We make kind
of a meteorite flour,

and then we take that powder
and we put it in a test tube,

with water, to extract it.

So we're making kind of
a, a meteorite tea, if you will.

We take the liquid water,

we purify it
through several steps--

we want to remove the salts
from the extract,

so that we can really focus
on the amino acids

and detecting them.

And then the final step is,

we inject that liquid
into a mass spectrometer

to separate out
the individual amino acid peaks

and identify them by name.

But there's a problem
with studying meteorites

that have made their way
to Earth's surface.

One of the challenges
with meteorites,

that, as soon as they hit
the atmosphere

and hit the ground,

they, they immediately
become contaminated.

Lift off of OSIRIS-REx.

To boldly go to the asteroid
Bennu and back.

We really do need to go
to space,

to go to asteroids
and bring back pristine samples

that have never seen
the Earth's biosphere.

In 2016, NASA's OSIRIS-REx
mission

headed to the asteroid Bennu.

Bennu is slightly taller
than the Empire State Building,

and, from a distance, it looked
like it would have had

the same kind of rocky makeup
as meteorites like Murchison.

In October 2020,
OSIRIS-REx bounced off Bennu

and grabbed a sample
of its surface material.

We fired the nitrogen
to collect the sample.

There was a huge plume
of material.

When we imaged
the sample collector,

we saw there was a bounty
of material

from asteroid Bennu
in the collector,

so we had done our job.

It took just under three years

for the sample
to be returned to Earth.

Altogether, the mission
brought back about 122 grams,

the largest sample ever
collected from an asteroid.

The precious space dust
was divided up

and sent to labs
around the world for analysis.

Danny's lab
got about five grams.

So you're looking
at a very tiny speck of Bennu.

Even in a particle
as small as a half a millimeter,

we can extract these samples
and look for amino acids

and other chemical building
blocks of life.

Bennu was rich in carbon,
the element of life.

14 of the 20 amino acids
found in life on Earth

were also detected, along with
all of the chemical bases

of our genetic code.

Which begs the question,

what would happen
if an asteroid that created

a vast hydrothermal system
on impact

also delivered
the building blocks of life

directly to that site?

Could those building blocks
survive

such a violent,
destructive event?

Nobody really knew what happened
to these organic compounds

once they got delivered.

And we do know

that when impactors
hit the Earth,

they create
hydrothermal systems.

And nobody asked,

"Gee, what happens
to those organic compounds

in those hydrothermal systems?"

So we did lots and lots
of experiments.

Meri Herrero Perez

conducts the experiments
under early Earth conditions.

Meri takes a mineral thought
to be on the Hadean Earth

and found in impact craters
today.

To this she adds a mixture
of simulated Hadean water

and soluble organic compounds,
including amino acids,

like those present
in some meteorites.

She then places these
ingredients into a chamber,

where they're exposed
to the conditions

typical of a hydrothermal system
made by an impact.

It requires liquid water,
energy, and heat.

Hydrothermal systems
made by impacts

cool over a long period of time.

So the experiments are conducted
using a range of temperatures.

Meri conducted hundreds
of these trials,

each lasting seven days.

I remember the first time
that I looked

at all the experiments

that needed to be done.

It was 180, and I thought that
that was a lot.

But the actual thing is,
I ended up doing

probably more than double
or triple that.

After the tests,

Meri used a nuclear magnetic
resonance spectrometer

to help identify the structures
of any molecules

that may have formed
during the experiment.

The results
were beyond surprising.

The first time I saw the results
of a successful experiment,

I did not believe
what I was seeing.

I thought I had done it wrong.

And then I spoke with Karyn,
and we, we could understand

that there was more complex
chemistry happening

that we envisioned.

Our question was, is,
did these molecules start

to react with each other
as they went

through this impact-generated
hydrothermal system?

There was always a possibility
that they just broke down

and never led to life,
but what we found is,

instead, these molecules

actually got together and
made new and bigger molecules.

And we're still trying
to figure out

what those new
and bigger molecules are.

But as you make
bigger molecules,

you really are pushing
in the right direction

to build the complex chemistry

that could eventually
lead to life.

Exactly where and when
that complex chemistry

made the leap to biology,
and life first emerged,

remains a mystery.

Many scientists still believe
that hydrothermal systems

created by volcanic activity

deep in the sea
or on the surface

are the best candidates.

But some scientists
are rethinking

what role asteroid impacts
might have played

in the origins of life.

We always think

about an asteroid's colliding
with the surface of the Earth

as a very negative event.

Maybe that's what we needed

in order to get the chemistry
necessary

for life to form.

Those very same impact events
were perfect crucibles

for the origin
and early evolution of life.

They really generated
an environment to life

that allowed it to evolve
to what it is today.

Many lines of evidence have led
to a remarkable hypothesis,

that life might have begun as
a result of those huge impacts,

rather than in spite of them.

Perhaps over four billion years
ago,

a space rock laden
with the building blocks of life

hit the Earth, creating
a vast hydrothermal system,

one of hundreds of thousands
that covered our planet,

each one with the water,
the energy, and the ingredients

to brew the chemistry of life.

And these asteroid impacts
were happening

all over the solar system.

On Mars, the remains
of hydrothermal systems

have been discovered beneath
many asteroid impact craters.

And inside one
four billion-year-old crater,

NASA's Perseverance rover
has collected

the most tantalizing evidence
yet

of potential microbial life
on the Red Planet.

Who knows what discoveries
may await

on distant, rocky surfaces

elsewhere
in our own solar system,

and beyond,

that might finally reveal,
once and for all,

that we are not alone?