Nova (1974–…): Season 31, Episode 11 - Origins: Earth Is Born - full transcript

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In its infancy,
Earth was a primeval hell,

a lifeless planet bombarded
by massive asteroids and comets.

The moon, much closer to Earth,
loomed large in the sky.

Instead of water, red hot lava streamed
across the surface of our planet.

Volcanoes spewed noxious gases
into the primitive atmosphere.

Scorched and battered,
Earth was a planet under siege.

Yet somehow, the world we call home
emerged from these violent origins.

So how did Earth make
such an astonishing transformation?

How did it change from
a raging inferno like this,

to a place we all know and love,

with firm ground under our feet,

air we can breathe,

and water covering nearly three
quarters of its surface?

A place where life could take hold

and evolve into complex organisms
like you and me?

Well, it turns out,

Earth became a habitable planet

only after a series of devastating
disasters in its early years.

And to see how this happened,

let's imagine all of Earth's four-and-
a-half-billion-year history

condensed into a single day,

just 24 hours on an ordinary clock
or watch like this.

If we start right now,

then the first humans walked
the Earth only 30 seconds ago.

Dinosaurs began roaming
the planet just before 11 p. m.

The first multi-celled animals
evolved at 9:05.

Before that, mostly single-celled
organisms existed,

and we think the first of those

around 4 o'clock on the morning.

Earth was born at midnight on this 24-
hour clock, 4.5 billion years ago,

but its violent history began
well before that,

when huge ancient stars that had
reached the ends of their lives

These supernovas cooked up all the
chemical elements we know today

including iron, carbon, gold and even
radioactive elements like uranium.

Over time, gravity took hold,

and this cloud of stardust collapsed

an enormous rotating disk: the solar

In the center of this disk, temperature

and pressure rose,

and a star, our sun, was born.

Eventually, gases like hydrogen

and helium would be swept to the far
reaches of the disk,

but closer to the sun were dust grains

made of the heavier elements.

They're circling around the
early sun in little racetracks,

and occasionally grains
traveling nearby will collide.

Something like this
happens in your house.

If you look under your bed,

you find that little bits of dust are
collecting together
into large dust balls.

And something like that must be what
happened in the solar system, too.

If they collide slowly, they can add
up to a larger object

and gradually grow.

With enough collisions,

dust grew into pebbles and pebbles
grew into rocks.

And as the rocks grew larger,

so did the collisions.

If they collide head on or at higher

then they'll actually break apart,

like shooting a gun at a wall.

But other times, the rocks stuck

And the larger they got,

the stronger their gravity became.

Because of the gravitational
attraction between these bodies,

you coalesce.

Instead of just making a mess?

and you do make a mess as well?you
build bigger things,

because gravity holds things together.

In time, gravity shaped them into

round planets, or planetesimals,

just a few miles across.

Gradually, they grow from golf ball
size to rugby ball size

and then house size and then township

And then one or two of these objects
would get large faster

than anything else and become the big
boys on the block.

Eventually, some of these
planetesimals grew as big as our moon.

And then they combined to form the
four small,

rocky planets closest to the sun:

Mercury, Venus, Mars and Earth.

But the early Earth bore little
resemblance to the planet

we're all familiar with.

And today, working out exactly

what Earth was like as a newborn
planet is no easy task.

It's sort of like looking
at me as an adult,

and trying to figure out exactly what
I was like as a baby:

When was I born?

How much did I weigh?

Now, a snapshot will give you a pretty
good idea of

what I looked like when I was young,

but the Earth was born 4.5 billion
years ago,

and hardly anything survives from

that time to tell us about
our planet's infancy.

That's because at
midnight on the clock,

the new-born planet was nothing

but a fiery ball of rock covered with

As you go back to these very earliest

the first few hundred million

the Earth was so energetic and
was recycling materials so vigorously

and melting material, that rocks

from that period have not survived.

So to reconstruct
the story of the Earth's infancy,

we look for clues not from the ground
but from outer space.

More than a hundred million miles from

betwee Mars and Jupiter, lies a region
called the Asteroid Belt.

Here, trillions of asteroids, enormous
rocks left over from planet building,
are held in orbit.

Every now and then, a fragment of one
of these asteroids

is knocked out of orbit and set on a
collision course with earth.

This exclusive report is about
an object from space buried in ice,

described as a scientific mother lode.

We take you first to the northwest
corner of British Columbia, near the
Alaska border.

Here, a massive meteor plunged through
the atmosphere

leaving a streak across the sky.

A local bush pilot discovered the
debris scattered across this lake,

which was frozen over at the time.

Realizing the importance of the find,

he mailed a few fragments
to NASA meteorite expert,

Michael Zolensky.

He sent samples down frozen in a case,

and so I had a real problem getting

through U.S. Customs because they

wanted to open and thaw these out. And

they were concerned that they were

containing deadly pathogens from Canada

or something.

Zolensky immediately recognized it as
a carbonaceous chondrite,

a carbon-rich meteorite formed from
the very same stardust that built the

The last time we had a major fall of a
carbonaceous chondrite was 30 years

so that means it's about one time
in a career you have
this happening to you.

And to have it happen to me in my

while I was still young enough to take
advantage of it,

was a very exciting thing for me.

A team of scientists scrambled to

as much of
the meteorite as possible.

This was the opportunity
of a lifetime.

More than 400 fragments,
strewn across the frozen lake,

could each contain clues to the very
beginning of Earth.

The scientists hoped that inside,

the fragments would be uncontaminated

in the same pristine condition as when
they formed,

four and a
half billion years ago.

If it lives up to expectations,

this meteorite could reveal

the exact chemistry of the dust grains

that built the newborn Earth.

Meteorites are a window on the past,

and they tell us something
about the conditions

in which the solid planets formed.

This particular meteorite
is really special.

In the first place,

it has the highest carbon
content of any meteorite

and the highest amount of
these preserved interstellar

stardust grains of any meteorite,

and it has a very high
water content as well.

In addition, about 90 other elements

have been identified.

And already they are providing

a chemical fingerprint of early Earth.

And within this meteorite
are radioactive elements

that decay at a precisely known rate,

And since most meteorites formed
at the same time as the planets,

and from the same material,

the age of the meteorite
gives you the age of Earth

and its neighbors.

If you date meteorites,

what you find is that
almost all meteorites

have the same age,

about four and a half to
five billion years old.

They're all the same.

It's pretty monotonous:

within a couple of tens
of millions of years

to hundreds of millions of years,

they are all exactly the same age.

And so what we do is take
the oldest of the ages

and use that as the initial
age of the solar system.

That narrow range of ages

indicates that all
meteorites and planets

coalesced extremely quickly

in the early days of the solar system.

But Earth had barely

taken shape before the first
of several major disasters

struck the young planet.

Earth's gravity was pulling

in huge quantities
of debris from space,

a continual bombardment that generated

enormous amounts
of heat on the surface.

At the same time,

radioactive elements trapped

deep within the Earth were decaying,

producing even more heat,

roasting the planet from the inside.

The combined effect was catastrophic.

By eight minutes after
midnight on our 24-hour clock,

the planet had become a raging furnace.

And when the temperature
reached thousands of degrees,

dense metals such as iron and nickel

in Earth's rocky surface melted.

The outer part of the Earth

would have been completely molten.

We call that a magma ocean.

It's a liquid rock ocean,

hundreds of kilometers thick.

We think the Earth, at some point,

was a big droplet of melt
just floating in space.

When you have a totally
molten object like this,

the heaviest elements?and

that includes things like iron?

would sink to the center
of this droplet,

and the lightest elements?

things rich in carbon
and water for instance,

or light elements
?would float to the top

and float there like algae on a lake.

The global migration of the elements,

known as the Iron Catastrophe,

would have a profound effect
on the future of our planet.

The sinking iron
accumulated at Earth's center

where it created a molten core
twice the size of the moon.

The liquid iron is constantly
swirling and flowing.

And even today this motion
generates electric currents

which turn our planet into
a giant magnet

with north and south poles.

The core is still in constant motion.

And we can see evidence of Earth's
liquid iron core on the cold,

snowy wastes of arctic Canada.

The magnetic field is
constantly fluctuating,

on a minute to minute
or even second to second basis.

And one result of this is the fact

that it causes the magnetic pole

to actually move randomly
over the course of a day.

Every few years,

geologist Larry Newitt sets out

in search of the precise location
of the magnetic north pole

or north on a compass.

Newitt spends days at a time on the ice

in temperatures as low as
minus 50 degrees Fahrenheit.

The geographic North Pole
is in a fixed position,

but the magnetic pole is
always on the move.

Over the last century,

its position has changed dramatically.

To identify the pole's
current position,

Newitt measures the strength

and direction of the magnetic field

at about eight different sites

then closes in on it.

Since we don't know where the pole is,

we can't just go there
and take a reading.

So we surround it,

and then I determine its
location by a process of,

well, what amounts to triangulation.

At the time of the most recent survey,

the pole had moved 125
miles off the Canadian coast.

And Newitt and his colleagues
have discovered something curious:

its movement is picking up speed.

Over much of the past hundred years

it's been around ten
kilometers per year.

But since about 1970,

it started to accelerate,

and now it's moving along

at about 40 kilometers per year.

If this keeps up,

it'll reach Siberia in
about another 40 or 50 years,

but of course that's a rather
dangerous extrapolation,

we don't really know
where it's going to go.

Without Earth's liquid iron core,

life would be in trouble.

This swirling ball of molten iron is

what generates the magnetic
field around our planet.

And we need that magnetic field

because every day a deadly stream of

electrically charged
particles bombards the Earth.

Ejected by the sun in
monstrous solar flares,

these particles hurtle through space

at about a million miles an hour,

forming what is known
as the solar wind.

Some think that if the solar
wind ever reached our planet,

it would strip away the atmosphere.

But Earth's magnetic field
creates a protective shield

that deflects these deadly particles.

And you don't have to travel far

to see the fate of a planet
that lost its shield.

Four billion years ago,

Mars had a liquid iron core

and a magnetic field just like Earth's.

Mars built up a thick atmosphere

and supported liquid
water on its surface.

The planet may even have been
home to primitive forms of life.

But Mars is just a fraction
the size of the Earth,

so it cooled more rapidly.

And as it cooled,
its molten iron core hardened.

As a result,Mars stopped generating
its magnetic shield.

And, according to one theory,

this left its atmosphere
to be scoured away

by the solar wind.

Today, the surface of
Mars is a barren desert.

Mars is a stark reminder
of what our world

could have become if
its iron core had cooled,

because without a magnetic shield

a planet is left prey
to the solar wind,

and life, as we know
it, could never flourish.

The time had reached 16
minutes after midnight;

the Iron Catastrophe was over.

But even with the
formation of Earth's core

and magnetic shield,

our planet remained a
hostile and alien world.

Volcanoes spewed clouds
of noxious gases

and Earth was enveloped

in a suffocating atmosphere
of carbon dioxide,

nitrogen and steam.

With no oxygen to breathe

and no ozone layer to block

the lethal ultraviolet radiation,

this was not a hospitable
place for life,

at least life as we know it.

And in the midst of this hellish brew,

the moon was born.

Beginning when I was
about 11 years old,

I used to climb the
stairs to the roof of

this apartment building,

where my family lived,

here in New York City,

a building prophetically
named the Skyview Apartments.

And with simple binoculars,

just like these,

I gazed up above the streetlights,

beyond the buildings
and into the night sky.

And nothing will ever
capture the excitement I felt

when I first turned my
binoculars on the moon.

When I saw that the moon

was packed with mountains
and valleys and craters,

I thought I discovered
an entire new world.

And then I began to wonder,

where did the moon come from

and how did it get there?

Well, little did I know

that about the same time,

the mystery of the moon's origin

was also attracting the attention

of a scientist named Bill Hartmann.

I'm always looking at the moon

and thinking about its phases.

And when I was a little kid

I had a telescope.
I used to be out there

drawing craters on the moon
and was very excited

that I could even see these craters

and mountains and so on.

So it's always had a
special interest for me.

Hartmann has been studying the moon

for the last 40 years.

And when he began his career,

in the late 1960s, he and many other
planetary scientists hoped

that NASA's Apollo missions would solve

the mystery of how the moon formed.

One of the pitches to sell

that program scientifically was

that we were going to
be able to go to the moon

and find these old rocks
from 4.5 billion years ago,

and they were going to tell us

everything about the
origin of the moon.

The Apollo astronauts collected

hundreds of rocks from
the moon's surface.

Scientists calculated their
age using radioactive dating.

To their astonishment,

they discovered that the
moon was millions of years

younger than Earth.

And those same rocks
held another secret.

I think the biggest single surprise was

that the materials on the moon

have exactly the same
chemistry as the Earth

and different from any samples

that we have anywhere
else in the solar system.

So that pretty well forced the idea

that the moon has to have formed

from the same basic
material as the Earth.

But even more mysterious was

that the moon rocks
contained very little iron,

just like the rocks on Earth's surface.

In a flash of inspiration,

Hartmann and a colleague came up
with a controversial new theory

for the formation of the moon.

We came up with this very simple idea

that maybe as the Earth was forming

at our distance from the sun,

somewhere nearby, made
out of the same material,

was a second large body
which got pretty big

before it finally plowed
into the Earth.

They proposed that
about 50 million years

after Earth had formed,

a huge planetesimal was still
roaming the solar system.

This massive rock,
about the size of Mars,

slammed into our planet.

The energy of that impact was so great

it melted both the planetesimal
and Earth's outer layers;

the two fused together
forming a new, larger Earth.

At the same time,

this enormous collision ejected into

orbit vast amounts of molten rock.

This debris eventually
coalesced to form the moon.

When Hartmann first went
public with this idea,

in 1974, it was considered
scientific heresy.

So here we come in saying

the moon formed out of
this gigantic catastrophe

that blew off part of
the Earth's mantle.

No one wanted to hear that.

No on wanted to, uh, start
thinking about that kind of model.

All of us were taught, as
junior geology students,

that all processes in geology are slow,

one sand grain at a
time, erosion, and so on.

And people would actually come to us

and say we really shouldn't consider

that model until we've
exhausted all other models.

Ten years passed

before anyone would
take the idea seriously.

And that was only after hundreds
of computer simulations showed

that the moon could have
formed from a giant impact.

Today, Hartmann's big idea is
almost universally accepted.

So it's been a long, slow process.

And it's been really
fun to see a little idea

that you had a long time ago suddenly
blossom forth as a leading theory.

It was 16 minutes past midnight,

50 million years after
our planet was born,

and the moon had arrived.

But the repercussions of this disaster

were just beginning to be felt.

The moon started out
about 200,000 miles closer

to Earth than it is today,

and appeared many
times larger in the sky.

Earth was spinning much faster

making each day less
than six hours long.

And with the moon so close,

its gravitational pull
on Earth was enormous.

Earth's surface rose and fell

up to 200 feet during the
cycle of the moon's phases.

Over time, Earth's rotation slowed
down as the moon drifted away,

a process that continues even today.

The idea of being able to measure

the movement of the moon away from
the Earth has always been a challenge.

And so, when the astronauts went to
the moon, one of the things they did

is they carried out this big
device which was a reflector,

a retroreflector that would beam a laser
beam back in the direction that it came.

On Earth, astronomers
installed a laser so strong

it could target the reflectors.

In 1969, they made their
first measurement of the time

it took for the laser
beam to reach the moon,

hit the reflector, and
bounce back to Earth,

a round trip of about
two and a half seconds.

Doing this year after year after year

we've actually been able to confirm
that the moon is moving slowly away.

We not only get very exact information

on the orbit of the moon,

but we can actually
see the orbit change.

Now about 240,000 miles from Earth,

the moon is moving away at a rate
of one and a half inches every year.

The collision that created the moon

was also a major stroke
of luck for Earth.

That impact was so immense
that it forced Earth's axis

to tilt in relation to the sun,

causing the familiar seasons.

And without the stabilizing
influence of the moon,

Earth would wobble
dramatically about its axis.

Today, the planet would
experience wild climate swings.

But when did a planet
that looks like the Earth

we know begin to take shape?

Earth's hot molten surface

took at least a billion years after

the moon was created to cool

and form a thick skin, its crust,

or so scientists believed.

But no one knew for certain

because Earth is such a
geologically restless place

that none of the original
crust survives today.

Yet startling new evidence is causing

a major rethinking of when
Earth's crust first formed.

The clues to this mystery are embedded
within these rocks in Western Australia.

Here, geologists have extracted
tiny crystals called zircons.

About the size of sand grains,

zircons are nearly as tough as diamonds.

These relics of the early Earth formed

when molten rock
cooled into solid crust,

so the age of the zircon gives you

the age of the crust itself.

And it was here that geologist
Simon Wilde hit pay dirt

when he found one crystal so old

he's convinced it was formed
in the Earth's original crust.

When we look at the
chemistry in detail,

from the zircons in this rock, we find

that it's consistent with having grown

in a piece of continental crust.

Radioactive dating shows

that the oldest of the zircons

Simon Wilde found in these hills

is 4.4 billion years old,

suggesting that Earth might have cooled

and formed a crust soon
after the moon was formed.

We don't know, of course,

whether the continental
areas were extensive

or whether they were just small
little islands of material.

But certainly what we do know is

that there was continental
crust at 4.4 billion years ago.

This was just 150 million
years after Earth was born,

not a billion years
as previously thought.

But that led to another mystery:

once Earth was cool enough
to form solid ground,

water could collect on its surface,

so when did that happen?

Geologists, including Stephen Mojzsis,

think the answer may lie in
these same tiny zircon crystals.

Zircons are extremely rare,
so to find just a few crystals,

Mojzsis had to pulverize

and sift through hundreds
of pounds of ancient rocks.

An analysis of the chemical
composition of the crystals

revealed that the oldest zircons

contained a high concentration
of a curious ingredient.

It was a type of
oxygen called Oxygen-18,

an isotope that could only be present

in large quantities if the zircon
crystals had grown in water.

The news that water might
have been present so early

in Earth's history was a bombshell.

Not only was there crust present,

which came as a surprise to most of us,

it looks like, from
some of the zircons,

that that crust interacted with
large volumes of liquid water.

The idea that water
settled on Earth's surface

so soon is controversial, but if true,

it suggests a planet
much more like today's

than anyone had ever imagined.

By 200 million years after
the formation of the Earth

you can imagine a landscape of
islands and small continents,

bathed by a primitive ocean.

The time was only 10 minutes
to one in the morning;

the moon existed and so did a planet

with not just land but water.

Liquid water is the key to life;

every living thing
requires it to survive.

And eventually, water would cover

nearly three quarters
of the Earth's surface.

In fact, all the world's oceans contain

nearly one hundred million
trillion gallons of it.

It's an almost incomprehensible amount.

So, where did it all come from?

How would Earth have ended up

with such vast
quantities of this stuff?

Well, strange as it sounds,

these great oceans may have been there

from the very beginning,
just hidden away.

One key to the riddle was volcanoes,

which, throughout Earth's infancy,

pumped huge amounts of
steam into the atmosphere.

Then, as Earth cooled, that
steam condensed into rain.

Drop by drop, water
collected in low-lying areas.

There is nothing mysterious
or surprising about this.

The Earth does it right now.

The main gas that comes out of
Hawaiian volcanoes is water, steam.

So, this is happening all the time.

But some scientists argue
it would take far too long

to create such vast oceans
by volcanic outgassing.

Instead, Earth may have had some help.

The water in our oceans might
have come from outer space,

delivered to the surface by
massive ice-bearing comets.

The evidence for these ancient
impacts is impossible to find today,

since the original
surface of our planet

has long since been
eroded or destroyed.

But there's one place that
preserves a record of impacts

from that early era: our moon.

Every one of those craters was a
meteorite explosion at some time.

The moon's surface is
littered with craters,

some of them hundreds of miles across.

In fact, the moon was ravaged

by more than a million major
impacts in its early years.

Since Earth is much more massive,

its gravitational pull would
have attracted even more debris,

resulting in possibly tens
of millions of impacts.

We all hear about the
impact 65 million years ago

that wiped out the dinosaurs.

And you're getting that kind of impact

something like once a
month on the early Earth.

But this rain of debris left over from

the formation of the
solar system continues

for several hundred million years.

And in this cosmic debris field,

comets containing huge amounts of dust

and ice would have been plentiful,

like dirty snowballs
the size of mountains.

Roughly half their mass was water.

One NASA scientist, Michael Mumma,

wonders if these comets were the source

of the water in Earth's oceans.

One possibility is that
Earth's water was delivered

by the impact of bodies
from beyond the Earth.

These would naturally be the comets,

which are rich inwater.
The proof in that

would be to measure the
composition of the cometary water

and to compare that with the
composition of water in our oceans.

But studying comets
is a tricky business.

In the last 20 years,

just a handful have passed
close enough to study in detail,

including one in 1997
called Comet Hale-Bopp.

A comet like Hale-Bopp would deliver

about 10 percent of the water needed

to fill one of the Great Lakes.

This is a lot of water.

Of course the oceans are much larger,

and so we need many more
comets to fill the oceans.

But we're fortunate; we had many
such comets in the early solar system,

so we have every reason to believe

it was cometary delivery that
brought water to the early Earth.

Mumma thinks that the heat of an impact

would have evaporated
the ice within a comet,

creating storm clouds over
vast areas of the planet.

These clouds produced a deluge of hot,

possibly acidic rain that
continued for millions of years.

At first the rain would
have formed lakes and rivers,

and eventually water would
cover almost the entire globe.

But there's a problem with this theory.

Earth's oceans contain a
mixture of normal water, H20,

nd a much smaller amount
of a more exotic kind,

known as HDO, or heavy water
which contains an extra neutron.

In the comets analyzed so far,

the proportions of
these two kinds of water

don't match the composition
of water in our oceans.

They have twice the amount
of heavy water

that we see in Earth's oceans

so if they were the comets

that delivered the Earth's
oceans they wouldn't fit the bill.

Basically, they don't
have the right properties.

But Mumma hasn't given up.

The comets already studied

come from the outer
reaches of the solar system,

and he thinks comets originating
closer to the sun might be different.

Formed at higher temperatures,

these comets could have a
lower proportion of heavy water

more closely matching our oceans.

And tonight, Mumma
hopes to test this idea

by getting a first hand look
at one of these elusive comets.

If its chemistry is different,

and if the heavy water to light
water is like that on Earth,

it would be the first proof positive,

or the "smoking gun" evidence,

that comets did in fact deliver
water to the early Earth.

But first, the team has
to hunt down the comet.

As soon as he has acquired it,

we should see an image
of it on the screen.

There it is alright,
yes sir, right there.

You can see the elongated material
flowing outward from the nucleus.

Joe, that looks excellent.

With the comet in the
crosshairs of their telescope

they can home in on the
kind of water it's carrying.

People often ask,

"How can you measure water in an object

that is a hundred million miles away?"

We do this by a method
called spectroscopy.

It's a little bit like
taking fingerprints;

the little ridges on your fingers
look different for every person.

And in the same way, the
light that is emitted by

a given molecular
compound is different;

it emits at different wavelengths.

But it turns out this comet is
a very dirty snowball indeed.

There's so much dust on the surface

that it can't reflect enough
light for the team find out

what kind of water is on board.

It did not brighten as expected.

This was a bit of a disappointment.

Comets are quite fickle,
they're unpredictable.

In some ways they are like cats,

they both have tails and they
both do what they want to.

But with astronomers finding
two or three comets a year

from the inner part
of the solar system,

Mumma could soon have another chance
to test his controversial ideas

about the origin of Earth's oceans.

One of the key things that
every scientist keeps in mind,

is you should never fall
in love with your theory.

So it's an idea, it's a hypothesis,

it fits all the known facts.

But it has not yet been proven,

and we must be willing to give it
up and modify it if it is not proven.

But we will learn
something in doing so.

It's still possible that
comets played a role.

In fact, it's hard to imagine
that they played no role.

But it seems more likely
and more physically sensible

to look closer to home for
the source of the water.

Besieged by volcanoes
and battered by impacts,

Earth endured its most extreme
punishment in its early years.

It was beaten, bombarded, mangled,

and melted all in just the first hour
of our 24-hour history of the planet.

The young Earth was still very
different from the planet
we know today.

It was a hostile and forbidding place,

with an atmosphere
full of poisonous gases.

Yet, somehow, these harsh conditions

set the scene for a crucial
phase of Earth's development:

the origin of life.

Very little is left behind from
the Earth's earliest time period,

but what is left behind

has revealed to us a planet much
more complicated than we ever thought,

with different rock types,

liquid water present
and the kind of planet

that we might expect life to emerge on.

Do we know if life was
around 4.3 billion years ago?

Well, who can say? We can say, however,

that the template, the
ground underfoot was there.

Could life have been present? Why not?

But first, the once hellish Earth
would have to undergo another change

as radical as any that had come before.

Catastrophe and cataclysm
transformed the Earth,

now our planet would be ready for
the greatest drama of all time:

the rise of life.