Origins: How Life Began

The National Science Foundation.

TYSON: A hellish, fiery wasteland.

A molten planet hostile to life.

Yet somehow, amazingly, this is where we got our start.

How?

How did the universe, our planet,

how did we ourselves come to be?

How did the first sparks of life take hold here?

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Are we alone in the cosmos?

Where did all the stars and galaxies come from?

These questions are as ancient as human curiosity itself.

And on Origins, a four-part NOVA miniseries,

we'll hunt for the answers.

This search takes unexpected twists and turns.

Imagine meteors delivering Earth's oceans from outer space.

( loud explosion )

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Descend into a toxic underworld

where bizarre creatures hold clues to how life got its start.

And picture the view when the newborn Moon,

200,000 miles closer to Earth than today,

loomed large in the night sky.

This cosmic quest takes us back in time

to within moments of the Big Bang itself

and retraces the events that created us,

this place we call home

and perhaps life elsewhere in the cosmos.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Coming up tonight, the origins of life.

MUMMA: Early Earth was not a Garden of Eden.

There were no clear blue oceans,

there were no plants,

there was no life at all.

TYSON: So where could the building blocks of life have come from?

ZOLENSKY: We think that all the carbon in your body

arrived on the earth in meteorites like this.

TYSON: So it makes you wonder--

if the building blocks of life were delivered

courtesy of comets and meteors,

could any of the tiny ingredients they carry

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] have survived the landing?

( explosion )

And if they did,

how did they generate those first traces of life?

A walk on the ancient surface of the earth offers clues.

These are the oldest fossils in the world

at about 3 1/2 billion years old.

Life evolved on this planet very early and very fast.

TYSON: Journey back to an age

when invisible microbes ruled the planet

and caused the greatest transformation

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] in Earth's history.

MAN: Over a billion or two billion years, the amount of oxygen

that these little creatures produced was enough

to actually change the entire atmosphere of the planet.

TYSON: The story of how life began on this episode of Origins

on NOVA right now.

TYSON: In the endless reaches of the universe, Earth seems unique.

It's a planet shaped and molded by life--

a planet that six billion people call home today.

But when it was born some 4 1/2 billion years ago,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Earth was a violent place,

so hostile it's hard to believe life could ever begin here.

Covered in lava and smothered in noxious gases,

Earth was a planet under siege.

If you were human going back into time,

and tried to stand on the early earth,

it would be just like visiting a planet that was not your own.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] ( meteor thunders )

( explosion )

This was a hazardous world, no doubt about that.

If you were located in the wrong place at the wrong moment,

you were simply vaporized.

TYSON: It was a planet plagued by catastrophe.

If you condense all of Earth's history to just 24 hours,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] then only minutes after it formed,

the entire globe melted and reformed.

Then, to make matters worse,

another planet about the size of Mars slammed into Earth...

( explosion )

a cataclysm that created our moon.

But soon after these disastrous beginnings,

the most radical transformation of all time hit the planet:

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] the origin of life.

So how did life begin?

Well, over the years, people have come up

with some pretty creative answers to this question.

One of my favorites comes from a 17th-century scientist

who wrote down a recipe for creating life from scratch.

Let's see, it says here...

"Take a dirty garment."

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Place it in a vessel.

Next, add wheat.

Then, according to the recipe,

after fermenting for 21 days, mice will appear fully formed.

Of course, we all know that life doesn't form this way.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] But at some point in Earth's early years,

life did emerge out of nonliving ingredients.

And for clues to the real recipe of life,

we have to go back some four billion years

to a time when Earth was nothing like the planet we know today.

MUMMA: When we think of early Earth,

we must recognize it was not a Garden of Eden.

There were no clear blue oceans,

there was no clear water, there were no plants,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] there was no life at all.

TYSON: The young Sun was weaker than it is today.

And its light barely penetrated the atmosphere of carbon dioxide

spiked with the pungent fumes of hydrogen sulfide.

Since the atmosphere was thicker and dominated by CO2,

the earth had a reddish tinge to it--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] it didn't have the familiar blue sky.

The oceans would have had an olive-green color,

rather than our familiar blue color.

TYSON: For about the first 600 million years,

comets and asteroids pounded our planet...

( explosions )

a time known as the "Heavy Bombardment."

( explosion )

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

These interplanetary missiles measured up to 300 miles across.

Their impacts vaporized Earth's oceans and melted its crust.

With its extreme temperatures and toxic rain,

seemingly nothing could survive here.

But we now think that in this hellish environment

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] life first took hold.

And today, hidden away in remote corners of our planet,

conditions that in some ways resemble

the extremes of early Earth

can still be found.

Penny Boston and Diana Northup are microbiologists

on an expedition to investigate

how life can survive in those harsh surroundings.

Buried in the depths of this tropical rain forest

is a cave called Cueva de Villa Luz.

<http://www.pbs.org/nova/origins/earth.html>[type:PROGRAM][name:origins research around the world][0669] Located in Southern Mexico,

it's an underground world laced with hydrogen sulfide--

a foul-smelling gas that was present on Earth

some four billion years ago.

WOMAN: These relic, or antique environments,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] like Cueva de Villa Luz,

offer the same kinds of environments

that we would have found on early Earth,

and we're hoping to get clues to work backwards from those.

As you approach the cave,

you begin to get these faint whiffs of the rotten-egg smell.

And as you get closer, this becomes more intense.

TYSON: Hydrogen sulfide can be extremely poisonous,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] so the scientists have to wear gas masks inside the cave

and carefully test them for leaks.

Have you got a leak?

Have you got everything in there?

I think I got everything, yeah.

BOSTON: At the levels at which

humans can't live very long in hydrogen sulfide,

you don't smell it at all.

It will just simply cause you to go unconscious

and die very quickly.

TYSON: But can any other forms of life survive

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] in the deep recesses of the cave so toxic to humans?

Here, hydrogen sulfide-- an invisible gas--

escapes from the underground springs,

reacts with oxygen in the water

and coats the cave with sulfuric acid.

BOSTON: The longer it sits there on the walls,

the more acid it becomes

and so eventually by the time the drop is falling on you

it's a very, very acid environment.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

The slime layer appears pretty thick today.

BOSTON: It's very fatiguing,

and even with the protective masks that we have

we pick up loads of toxic gas through our skins

and perhaps through tiny leaks.

Get a load of those stalactites to your left!

TYSON: Amazingly, despite the extreme conditions,

it appears that life is thriving inside the cave.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] It comes in a strange package--

colonies of single-celled bacteria

that form slimy drips scientists call "snottites."

BOSTON: The snottites are drippy, gooey, mucousy formations

that look like stalactites,

and that's why they were called snottites,

because they resemble strings of snot.

We believe that the snotty, gooey stuff is to protect them

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] against the extreme acidity,

because when we measure the drips on the snottites,

they are as extreme as battery acid.

And so while we find that daunting,

this is where they thrive.

TYSON: Bacteria are among the most primitive

and most common organisms on Earth.

Like all forms of life,

they grow, adapt to their environment and reproduce.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Inside each single-celled bacterium is a molecule of DNA--

the code of life--

which allows them to multiply.

There are millions of bacteria in each snottite.

And down in the underground streams,

Penny Boston has found different kinds of bacteria

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] in slimy clumps she calls "phlegm balls."

In fact, the cave is home

to a huge number of bacterial colonies.

And astonishingly,

instead of being poisoned by the hydrogen sulfide,

these bacteria depend on it for their survival.

BOSTON: They take the hydrogen sulfide

and they get chemical energy out of it.

It doesn't poison them, it's home-sweet-home for them,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] and this is a pretty new finding for these organisms.

TYSON: Conditions on early Earth may have been far worse,

but these bacteria suggest

that primitive life could have thrived

in extremely hostile environments.

But where did the very first life come from?

For more than a century scientists have known

that life is the result of chemistry--

the combination of just the right ingredients

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] in just the right amounts.

Today we know these ingredients

aren't things like dirty garments and wheat,

which people used to think would spontaneously generate mice.

The ingredients of life are actually much simpler.

All living things, from bacteria to mice, to you and me

are made from a small set of chemical elements.

Hydrogen, oxygen, carbon, nitrogen--

four of the most common elements in the universe.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Combined in just the right way,

these are the fundamental ingredients of life.

And carbon is the star of the show.

WOMAN: Carbon's everywhere.

It's all over the universe.

What makes carbon special is the kind of bonds that it makes

both with itself and with other elements.

We know of no other atom that has the flexibility

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] that carbon has to form diverse types of compounds.

TYSON: And the idea that life could have started

when carbon and other ingredients combined

in the harsh conditions of early Earth

was first put to the test in the 1950s

by a young graduate student named Stanley Miller.

( electricity crackling )

To simulate the newborn Earth in the lab,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Miller assembled a contraption made out of flasks and tubes.

( bubbling )

He filled one flask with gases

thought at the time to represent Earth's primitive atmosphere,

and he connected that to another flask with water

to represent the oceans.

And then he did a brilliant thing.

( crackling )

He simply put an electric charge through that

to essentially simulate

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] lightning going through an early atmosphere.

( crackling )

And after sitting around for a couple of days,

all of a sudden there was all this brown goo

all over the... the reaction vessel,

and when he analyzed what was in the vessel now,

he actually had amino acids.

( bubbling )

TYSON: Amino acids are compounds that form when molecules

of carbon and other elements link together.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] They are the essential building blocks of proteins and cells--

vital ingredients of all living things.

Stanley Miller's experiment was headline news

and jump-started the scientific search

for the origins of life.

Life is really chemistry.

<http://www.pbs.org/nova/origins/knoll.html>[type:PROGRAM][name:more of this interview][8420] There's no question about that.

In fact, it's a chemistry that, when you get the recipe right,

it goes, and it goes fairly quickly.

( crackling )

TYSON: That recipe is hotly debated today,

and most scientists think

the environmental conditions on early Earth

were very different

from the ones Miller simulated in his lab.

And another debate rages

about when this recipe first got cooked up.

On our 24-hour clock,

the barrage of asteroids and comets lasted

from about midnight until almost 3:30 in the morning.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] The assault then weakened,

but continued for more than 100 million years.

( asteroids exploding )

It's hard to believe that life could have gained a foothold

during this unstable period,

but new discoveries reveal that life may have existed

as early as 4:00 in the morning, or about 3.8 billion years ago.

( exploding )

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] The evidence comes from some of the oldest rocks on the planet,

found in the remote regions of West Greenland.

MOJZSIS: The geology of Greenland is unique.

It contains a record

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] of some of the earliest geological processes

that we know of on the earth.

The rocks themselves

are thought to be between 3.7 and 3.9 billion years in age.

TYSON: These rocks are so old

that any fossils they once contained have been destroyed.

So to find out if life existed when they formed,

Mojzsis had to look for evidence that is far more elusive.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] MOJZSIS: There may have at one time been small fossils-- microfossils.

But under the conditions of heat and pressure

that these rocks experienced,

such fossils would have been disaggregated and destroyed.

So what we have left behind, then,

are chemical fingerprints of ancient bacteria or microbes.

( whirring )

TYSON: To search for those fingerprints,

Mojzsis first extracts a sample

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] from the ancient Greenland rocks.

Then he will analyze its chemical composition,

looking for carbon-- a signature of life.

( water running )

But carbon comes in several different forms.

And Mojzsis wants to know if the carbon in this sample

is the kind left behind by living creatures.

If so, he believes that life may have existed

when these rocks formed over 3.8 billion years ago--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] a controversial claim.

MOJZSIS: It was a surprise for us

to find evidence of ancient life in these rocks.

We didn't know if it would be there.

You know, just because the stage is set

doesn't mean that the actors are present.

But these samples here represent the first evidence we have--

direct evidence-- of a biosphere on our planet.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] TYSON: If it emerged so early,

life was lucky to miss the greatest cataclysm of all time--

an impact like no other in our planet's history.

It happened when another rocky sphere about the size of Mars...

( exploding )

collided with Earth.

The outer layers of our planet were vaporized,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] and the debris from this collision coalesced

to form the Moon.

That impact was so powerful

that any building blocks of life that existed on Earth

would have been destroyed.

This gives rise to speculation that the ingredients of life

didn't form on Earth at all,

but arrived special delivery... from outer space.

( dramatic movie theme playing )

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] From its size and its appearance,

this thing came from outer space.

We even have reason to believe that...

there's some form of life in it.

TYSON: Hollywood has always been taken with the idea

that life came from outer space.

But it's not as farfetched as it might sound.

Gee whiz.

MOJZSIS: Space is not very far away.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] ( exploding )

Space is only about 20 kilometers that way.

Now, that's, um, that's very close, and space is vast.

TYSON: And a scientist named Don Brownlee designed an experiment

to find out if space might actually harbor

the building blocks of life.

There are 40,000 tons of bits of comets and asteroids

that impact the earth every year.

This is mostly in the form of particles

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] that are less than a millimeter in size.

We breathe them, they're in the food that we eat,

but they are very difficult to find.

You can only find them in very special places.

TYSON: To see if this shower of space dust contains

the ingredients for life,

Brownlee needed to obtain samples uncontaminated

by Earth's atmosphere.

So to get just a few micrograms of dust,

he commissioned a former spy plane

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] to fly close to the edge of Earth's atmosphere.

( engine roaring )

Sticky pads on the plane's wings collected the space dust.

( whirring )

Then Brownlee's colleagues sliced the dust particles

into slivers less than one-tenth the thickness of a human hair.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] And they discovered that these tiny particles

are rich in the seeds of life.

BROWNLEE: When you look at them in an electron microscope,

you see this wonderful array

of minerals and carbon and organic materials

that are 4.55 billion years old

and, we believe, are the building blocks of life.

TYSON: And this extraterrestrial dust

isn't the only possible source of life's ingredients.

In a region of space called the asteroid belt

are huge amounts of debris left over

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] from the formation of the solar system,

and sometimes chunks of debris containing metal and rock

fall to earth, bearing surprising gifts.

One such meteorite landed

in the town of Murchison, Australia, in 1969.

NEWSREEL ANNOUNCER: It's a gold mine, this little chunk of meteorite,

which fell on Australia last year.

For the past six months they've been taking it apart

and have discovered it contains amino acids--

the building blocks of life.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] TYSON: It was the first time that complex organic compounds

had ever been found in material from space.

And if meteorites like it were common,

perhaps they had delivered vast quantities

of the original constituents of life to early Earth.

MAN: Enough organics are present here

that we think that meteorites like this

provide to the early Earth its entire budget of organics.

So all the organics in your body--

all the carbon in your body and in your lunch you had today--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] arrived on the earth in meteorites like this.

If they come to the atmosphere in large enough objects,

they're like little capsules coming in the atmosphere.

They break apart on the earth's surface

and deposit their cargo of organics.

( exploding )

TYSON: More than 70 kinds of amino acids

have been found in meteorites.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

And many are the fundamental ingredients of proteins

that make up living cells.

During the Heavy Bombardment,

millions of meteorites may have seeded the earth

with the stuff of life.

And there might have been

an even more efficient delivery system.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Comets are like giant dirty snowballs made of ice and rock.

Some comets that hit the early earth

were the size of mountains,

and a large portion of their mass

could have contained organic compounds.

The destructive power of comets and meteors is astronomical.

The meteor that slammed into Earth some 50,000 years ago,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] here in Arizona, blasted a hole in the ground nearly a mile wide

from here...

to here!

And so deep it could hold a 60-story skyscraper.

And as if that weren't enough,

the force of the impact was so great

that it instantly vaporized nearly the entire meteor--

300,000 tons of it.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

So it makes you wonder if the building blocks of life

were delivered courtesy of comets and meteors,

could any of the tiny ingredients they carried

have survived the landing?

And just what happens to things like amino acids

when they slam into Earth with such devastating power?

To answer those questions,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] one scientist came up with an ingenious experiment

using a huge gas-powered gun.

That's good.

Stop, stop.

TYSON: Jennifer Blank simulates

the extreme pressures and temperatures

that are unleashed when a comet smashes into Earth.

BLANK: We set out to test whether or not materials would survive

or whether they would break down, and we expected that,

or we were hoping, that some fraction would survive,

and we figured the parts that didn't survive

would break down into smaller components.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] But in fact what we found was much more exciting.

TYSON: The gun fires a bullet at 5,000 miles an hour towards a sample

that represents the organic molecules inside a comet.

The sample consists of a solution

of five different amino acids-- two of them present

in every living cell.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] ( machinery whirring )

( machine switches off )

The mixture is inserted into a steel capsule.

The gun will send a shock wave through the capsule,

simulating the extreme pressures of a comet's impact.

BLANK: I think it's very hard to just imagine

what kinds of pressures we're generating in these experiments.

If you think about going to the bottom of the ocean,

the pressures you'll have there

are only a hundred times atmosphere.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] So these are hundreds of thousands of times atmospheric pressures.

TYSON: Will Jennifer Blank's experiment

show that the building blocks of life

can survive a crash landing on Earth?

BLANK: Clear the room.

( electronic beeping and chirping )

TECHNICIAN: Okay, charging up.

Okay, bringing up the X rays.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Okay, I'm going to external group.

( high-pitched alarm whistling )

Ready to fire?

Go ahead.

TECHNICIAN: Okay then-- three, two, one.

( gun discharges )

Three, two, one.

Fire.

( machinery clicking )

( slowed-down recording of gun discharging )

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

TYSON: When they remove the capsule, it's undamaged.

But have its contents survived the impact?

The once-clear solution of amino acids

has turned a tarry brown color.

And the analysis revealed

that not only had the material withstood

the colossal pressure of the impact,

but it had transformed into a new compound.

Amino acids,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] combinations of carbon and other basic elements,

had fused together to form more complex molecules

called peptides.

We went from our initial small compounds--

and here's an example of one of them, a simple amino acid--

and we used the energy associated with the impact

to build larger molecules... molecules like this.

This is a peptide,

and we show that we can use the impact energy

to grow larger molecules

from the simplest building blocks of life.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

TYSON: Peptides link together

to form larger building blocks-- proteins--

which make up all the cells in our bodies.

But the leap from nonliving ingredients

to a living creature complete with DNA,

which allows cells to replicate, is staggeringly complex.

No one knows how this process started or what course it took.

It is hard to really get your head around

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] the great leap from nonliving to living.

Well, it's hard enough

that nobody's succeeded in doing it in the laboratory.

I think it's an astonishing mystery

and one that we truly don't understand in any great detail.

TYSON: While we don't yet know how the spark of life occurred,

we can try to figure out where it might have gotten a foothold.

And because the planet was under such devastating assault

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] from comets and meteors, the leap to life

may not have taken place up here on Earth's surface.

To take hold, life might have needed a safe haven--

perhaps underground.

A team of scientists descends

into one of the deepest mines on Earth

to investigate whether microbial life can survive

far below the earth's surface.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

MAN: The mining environment gives us

this fantastic window into the deep subsurface.

It's a unique scenario,

because there is nowhere else on planet Earth

that allows you to have access to that sort of sample location

at two, three, 3 1/2 kilometers deep.

TYSON: It takes 45 minutes

to reach the heart of this South African mine.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Conditions here are extremely uncomfortable--

for humans, that is.

The temperature of the rock is 120 degrees Fahrenheit,

and the air pressure is twice that at Earth's surface.

Life down here survives entirely without sunlight.

If they exist, microbes need to find a way

to live in pitch darkness--

drawing chemical energy from water and minerals

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] trapped in the surrounding rocks.

MAN: Microorganisms have been shown

potentially to be able to use these molecules

to provide themselves with energy and support themselves

completely independent of photosynthesis,

and if we can prove that that is the case here,

then that is very interesting,

because that adds credence to the idea that you could have

life originating in the deep subsurface.

TYSON: As the miners drill into the rock,

they break into ancient pockets of water--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] havens for microorganisms.

( indistinct conversation )

HALL: We're not sure

how organisms can live in such extreme environments.

The major thing is there's such low nutrient availability--

there's nothing, really, for these guys

to continually use and process to survive.

And yet somehow they do,

and the question is, how do they do it.

Right.

Three, two, one... go.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] TYSON: The first step is to collect pristine samples of the water

and see if they can grow the microbes it contains.

HALL: I get a very big sense of achievement

if I can actually take something

that's been isolated for 200 million years,

put it in the laboratory

and actually find out what it is this organism needs to survive.

TYSON: In a makeshift lab near the mine,

the team attempts to re-create

the environment deep inside the rock.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] And they have found that these microbes are dining

on a variety of strange gases.

HALL: It turns out, in the deep subsurface

there's an abundance of methane gas and ethane and propane.

Now, for you and I that's not a very exciting diet,

but what we think is that these organisms

may be taking that kind of gas

and actually using that as a food to survive.

TYSON: On such an exotic diet,

the bacteria draw just enough energy

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] to divide and reproduce only once every thousand years--

suggesting a way that life could have survived

deep beneath the surface of the early earth.

( thunder crackling )

And Earth's crust may not have been the only place

where life could have hidden from the heavy bombardment.

( thunderous explosion )

Another safe haven may have been the ocean.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Volcanic activity was intense on the early earth.

( eruptions rumbling and booming )

Chemicals from deep inside the planet

spewed into the primitive seas.

Even today, marine biologists have discovered volcanic vents

on the ocean floor.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Despite scalding temperatures, acid eruptions

and a total lack of sunlight...

they've found creatures of all types thriving down here.

And at the bottom of the food chain

are microbes that live on the noxious hydrogen sulfide gas

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] erupting from the vents.

On early Earth,

primitive life may have survived in similar environments.

MOJZSIS: If all of the bombardment

was occurring near the surface, survivors would be existing

in just these kinds of hydrothermal vent communities

where there's abundant water and nutrients and heat

<http://www.pbs.org/nova/origins/essential.html>[type:PROGRAM][name:why water is necessary for life][19B0] and food in the form of chemical energy.

It has been found that organisms collected there nowadays

are genetically kin to some of the earliest organisms

that we think existed on the earth.

TYSON: By about 3.5 billion years ago,

or 5:00 in the morning on our 24-hour clock,

the bombardment of asteroids and comets had ceased.

With far fewer violent impacts on Earth,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] microbial life could now survive

outside its protective hiding places.

After it reaches Earth's surface,

life would take advantage of another source of energy:

the Sun.

Up here, microbes evolved a green pigment

known as chlorophyll.

This allowed them to trap sunlight

and use it to drive a chemical reaction

that converts carbon dioxide and water into food.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] Called photosynthesis,

it was a clever invention that enabled some bacteria

to grow and reproduce almost without limit.

Once it started, photosynthesis was a runaway success,

and today, it's how all green plants make their living.

As Earth cooled, this new generation of cells

spread across the oceans.

Immense colonies of green slime would take over the world,

kicking off the greatest transformation

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] in our planet's history.

KNOLL: Photosynthesis is the great liberator of biology.

With photosynthesis, the energy is coming from the Sun,

and life could spread,

literally, over the entire planetary surface.

TYSON: And this remote corner of Western Australia

holds clues to how that happened.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] These domed structures, called stromatolites,

are built up layer by layer

over thousands of years by tiny microbes.

These microbes may be similar to life-forms

that dominated our planet billions of years earlier.

And in the arid hills nearby,

there may be evidence of these ancient creatures.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] These rocks have remained unchanged for 3.5 billion years.

Here it's possible to walk on the surface of early Earth.

Martin Van Kranendonk spends months at a time

in this wilderness

studying the geology and producing maps.

In a secret location in these hills

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] is what could be one of the greatest geological discoveries

of all time.

These are the oldest fossils in the world

at about 3.5 billion years old,

and they're composed of stromatolites.

And at this outcrop we can see

two different types of structures

that these creatures formed.

First are these black mats

that have wrinkly textures all through it,

and the second are these larger domes

that form these broad structures.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] The most likely way these things formed

is by the growth of microbes.

TYSON: Like modern stromatolites,

these ancient structures could also have been built

by colonies of bacteria.

And not far away are fossilized ripple marks

which suggest they might have grown in shallow water.

VAN KRANENDONK: Here you can see we've got a smaller structure

that we call the "Mickey Mouse Ears,"

which is this beautiful doubly branching structure,

and there's nothing else that we can think of

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] which would make that except something that was growing

on the bottom of the ocean.

TYSON: So perhaps the ancient stromatolites were formed

by microbes like the ones that build these structures today.

VAN KRANENDONK: These big stromatolites

are composed mostly of rock at the bottom,

and the only living part of the stromatolite

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] is a thin layer on top, and that thin layer on top

is made up of microscopic blue-green bacteria

called cyanobacteria.

TYSON: Named after the blue-green color of their cells,

these cyanobacteria use photosynthesis

to collect energy from the Sun.

They secrete a sticky coating

to shield them from ultraviolet radiation.

As tiny pieces of dust and sediment

settle on top of the sticky cells,

the bacteria migrate closer to the surface to reach the light.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

The layers of sediment build up

by about a half a millimeter a year.

These structures contain living microbes,

just as they have for thousands of years.

VAN KRANENDONK: The amazing thing about these stromatolites

is that the microorganisms which build them are so tiny.

And the structures that you see around me

compared to their size are enormous.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] It'd be like if humans made a skyscraper

that was 105 kilometers high by 70 kilometers across.

These are massive structures

for the size of the organisms that make them.

TYSON: Many different shapes and sizes

of what appear to be fossilized stromatolites

have been found in the rock.

Its seems likely that these structures were formed

by some type of microbe living on the early earth...

perhaps even by the ancestors of today's cyanobacteria.

VAN KRANENDONK: We're looking at sort of a cross-section

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] through the top of these cones

and the layers that were laid down year after year.

And the fact that they're all different sizes

on this one surface shows there was a colony

of microorganisms growing on this one bedding plane.

And that's really fascinating,

because it means that life evolved on this planet

very early and very fast.

TYSON: And it's the cyanobacteria that would bring about

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] the most astounding change in Earth's history--

a change that could have started

as early as 3 1/2 billion years ago.

Over time, stromatolites would spread out across the planet.

As a byproduct of photosynthesis,

the ancient bacteria produced a waste gas: oxygen.

( water gurgling )

The oxygen was absorbed into the oceans at first.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

There it combined with iron erupting from undersea volcanoes

to form iron oxide particles that fell to the ocean floor.

Over the next several hundred million years,

the planet literally rusted.

There may have been other forces at work,

but eventually, all the iron was turned into oxide,

building up, layer after layer,

one of the most valuable mineral deposits on Earth:

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] iron ore.

Located in Western Australia,

this is one of the world's largest iron mines.

The iron here was originally deposited

on the floor of a primordial ocean.

( sirens wailing )

MAN: We're at the firing position.

We'll fire in ten seconds with a five-second countdown.

( man responds over radio )

TYSON: Every week they excavate

a half a million tons of iron ore

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] used to make steel

for everything from cars to skyscrapers.

MAN: ...four... three... two... one.

Fire.

( explosions )

TYSON: In a more pristine state,

thousands of ancient layers of iron ore

are preserved in the Karajini Gorge,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] just 30 miles from the mine.

The layers exist

because different amounts of iron oxide

were deposited at different times of the year.

Cyanobacteria produced oxygen in varying amounts

as water temperature changed with the seasons.

All over the world, vast amounts of iron ore

were laid down in similar ways.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] On our day-long clock,

this process continued until 1:00 in the afternoon.

Eventually, oxygen produced by cyanobacteria

began to build up in the atmosphere.

Slowly but surely, this transformed the planet.

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4]

Over the next eight hours or so,

tiny microbes raised the level of oxygen

from less than one percent to today's 21%.

The time was about 9:00 p.m.

It's amazing to contemplate,

but without cyanobacteria, there would be no oxygen

and Earth would still be smothered in noxious gases.

Plants, animals and humans would have never evolved.

We're sitting here today

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] breathing an oxygen-rich mixture of air.

We couldn't be here without that oxygen,

but that oxygen wasn't present on the early earth,

and it only became present

because of the activity of photosynthetic organisms.

BOSTON: Life has made this environment what we know.

It's allowed us to live on the surface.

It allows us to breathe.

It allows large organisms like we are

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] to function at very high rates of activity.

TYSON: The oxygen also helped protect life

from the Sun's lethal ultraviolet radiation

by creating a layer of ozone in the upper atmosphere.

One of the fascinating properties of that

is that it actually screens out--

just sort of like a sunscreen does on your skin--

screens out this harmful radiation.

TYSON: With the protection of the ozone layer,

life was able to diversify into more complex organisms.

It took only the last three hours of the day

<http://www.pbs.org/nova/origins/life.html>[type:PROGRAM][name:a brief history of life][0B27] for all other life-forms on our planet to evolve.

The first multicellular life emerged

at six minutes past 9:00 in the evening.

Then came fish...

and insects...

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] and reptiles.

By about ten minutes to 11:00 in the evening,

dinosaurs roamed the earth.

The first primates appeared at 20 to midnight.

And with less than 30 seconds to go,

the first humans made their appearance.

BROWNLEE: It's only been the last

ten percent of the earth's history

where there was life on the surface of the earth

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] that you would see with your naked eye.

So for most of Earth's history

life has basically been invisible on the earth.

Over a billion or two billion years,

the amount of oxygen that these little creatures produced

was enough to actually change

the entire atmosphere of the planet.

MOJZSIS: Multicellular life that we're most familiar with--

animals, plants--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] their environment was made possible

by the slow, toilsome task of bacteria

to oxygenate the atmosphere.

TYSON: Microbes ruled the earth

for more than three billion years--

two-thirds of its history.

These tiny organisms had transformed an entire planet.

Without them, complex life-- humans included--

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: How Life Began][14B4] would have never evolved.

To order this program on VHS or DVD,

<http://www.pbs.org/nova/origins>[type:PROGRAM][name:NOVA: Origins: Back to the Beginning][D337] or the book,

Origins: Fourteen Billion Years of Cosmic Evolution,

please call 1-800-255-9424.

Captioned by Media Access Group at WGBH access.wgbh.org

NOVA is a production of WGBH Boston.