Original subtitles

Today, we are in the midst of a scientific revolution

in our understanding of the Earth

and our relationship to it.

Recently, scientists have begun to

think of the Earth in a new way -

almost as a living organism.

Like a living thing it is forever on the move,

driven by the restless energy

locked up in its interior.

And as the planet has evolved,

so has life,

shaped by the same forces

that move continents and change climates.

In Earth Story we shall explore this new vision

of a living planet

and the essence of this vision

is an understanding of time.

The most profound question

any scientist can ask about the earth

is also a simple one -

how old is it?

It's a question geologists have been striving

to answer for 200 years.

At the turn of the century

one such geologist came to a remote corner

of Southern Africa

called the Barberton Mountain Land.

His name was Alan Hall

and he had a commission from the South African government

to map this area looking for gold.

The Barberton Mountain Land

is several thousand square kilometers of rugged terrain,

cut through by rivers.

Rocky outcrops dot the hills,

signs of the bedrock hidden beneath the landscape.

Hall's aim was to criss-cross the region,

recording these outcrops,

and so build up a picture

of the rocks below the surface.

It was an immense task.

But as he worked his way across the landscape

Hall slowly realized that something was missing.

However hard he looked,

he could find in the rocks

none of the usual signs of fossilized life.

Could Barberton be a fragment of the Earth

from a time before life began?

Just how old was this place?

Hall's question came at a critical moment.

For a hundred years scientists had been arguing

about the age of the Earth

They were struggling to overcome ideas

which had held sway for centuries.

Ideas sanctioned by the full authority

of religious doctrine.

The book of Genesis relates how God created the earth

and everything in it, including ourselves,

in just 6 days.

The implication was that earth history and human history

had begun at the same moment

and this provided 17th century scholars

with a way to determine the age of the earth.

By simply adding up the ages

of Adam's descendants as listed in the Bible,

they concluded that the planet

must have been created in 4004 BC,

which meant it was less than 6,000 years old.

But it didn't look that way to geologists.

when they studied places like Barberton

they saw evidence that the landscape

had changed over time -

that it had a long history.

Hall's modern-day successor is Maarten de wit.

He too is fascinated

by the question of Barberton's antiquity.

I really got interested in this part

of the world many years ago,

but the opportunity to come here didn't arise

until much later.

At the end of the 70s

I came down here to Barberton

and it turned out to be one of the best moves of my life.

It's one of these areas

that has something extremely special

to tell about the story of the earth.

Maarten, like Hall before him,

has mapped the rocks of Barberton in detail.

when you do this,

a striking pattern quickly emerges.

well once you start mapping the hills here,

you'll notice that the landscape

is dominated by stripes -

stripes of rocks -

like that one there.

And if you get your eye in,

after a while you'll see, in fact, all these rock layers,

all are visible.

In this case this huge mass here

has finer vertical rock layers.

Everywhere in Barberton

the landscape seems to be made of layers.

By the nineteenth century,

geologists had begun to realize

that the process that created these layers

was still at work all around them.

Hall and his contemporaries knew that water

can be a powerful agent of change,

eroding rock, but also creating it... over time.

well take this river, for example,

like many rivers,

cutting through the rocks,

moving material downstream -

sand and silt -

and as it moves down

that material will deposit somewhere

in a quiet spot layer upon layer,

and as these layers get deposited on top of one another

they turn into rock slowly.

well here you have a slab of rock.

Now this slab represents a river bed.

There you can even see the sand grains.

These would have been the sand grains in the river.

These ridges that you see here,

they are ripples.

I can tell that it would have flowed

from my hand here downwards in that direction.

Now you can see if you look downwards

that in fact there are several of these

slabs stacked on top of one another.

Here's one,

there you see another one over here,

and another one,

and another one still, and more.

These are dozens of slabs

and they're all tilted right now,

but originally they would have been horizontal

and they represent all history of rivers.

A long history of deposition.

To nineteenth-century scientists

a world made up of layers

didn't look as if it had been created

all in one go as the Bible says.

It must have been built up overtime.

But how much time?

The first person to realise

the profound importance of this question

was a Scotsman, James Mutton.

At Siccar Point on the east coast of Scotland

exposed in the cliff side

there's a small patch of rock

which made a deep impression on Hunt.

Chris Nicholas is a geologist

who has made a special study of his work.

So here we are at one of the most

famous geological localities in the world.

This is Hutton's Unconformity

and what Hutton noticed here

in this cliff

is that at the bottom of the cliff you have these

vertical strata,

overlain by horizontal strata

and between the two

there was an undulating erosional surface.

And what Hutton recognised

was that well if all rocks

were deposited horizontally on the sea-bed,

what on earth was this grey rock doing being vertical

at the base of the cliff there was something wrong here.

And he started to look at rocks in more detail

and he came up with this idea

that what must have happened

is that the grey rock must have been twisted and turned

so that it was vertical,

uplifted out of the sea,

eroded off and then drowned again,

so that the red rock could be deposited on top.

And more than that, it was then uplifted again

to form the cliff we now see.

So there were at least 2 cycles of deposition,

uplift and then erosion

that he could see in this cliff.

And he went on to say "well, these cycles must have taken

an immense amount of time to complete"

because when he looked around him and saw rivers

and the sea eroding today

it doesn't really erode very quickly.

And also he said "well how many cycles

could have taken place before these

and how many will come after this,

we just don't know".

And it led him on to this idea

of the immensity

of geological time

and he came out with a very famous quote of,

well, he could see no vestige

of a beginning and no prospect of an end.

For Hutton the earth was infinitely old.

Siccar Point represents the discovery of geological time

and it's shaped the way

that geologists think and work ever since.

One of Hutton's colleagues,

John Plafare, who was a mathematician

came to Siccar Point with Hutton

and Plafare wrote afterwards

of his experience here

and he said that

"For those of us who

saw the rocks at Siccar Point

their impact was not lost on us

and we grew giddy

looking so far into the abyss of time".

But geologists knew

Hutton's abyss was not empty.

Beneath their feet

lay clues to the entire history of the planet

locked up in the rock layers.

Yeah, we're going down to 128 level,

somewhere between 8 and 10 meters per second.

I mean, it's nothing to be scared about?

No, it's like the Empire State

Building's elevator system.

Yeah.

Not as smooth and probably a bit quicker.

200 miles west of Barberton lie the Rand goldfields,

where they sink the world's deepest mine shafts.

For Maarten de wit,

it's an opportunity to travel back in time.

OK, now you should be able to

get the impression of

at a fairly rapid rate

and you'll also feel your ears

go from the pressure.

can feel it now.

That's the other cage going on the way up.

On the couple drum system

if the hoist driver gets it all wrong

and he snaps the brakes on too suddenly,

you can feel the stretch now.

Unbelievable.

He got his braking a bit wrong. Scary.

Oh you get used to it.

So we're travelling through 6,000 meters of sediment

backwards in time?

we are now in a part of the world

where we are old enough to be pre-life.

No wriggling organisms were present at this point.

No matter how far back in time you go,

every rock contains a detailed picture

of the environment it formed in -

if you know how to look at it.

OK, what we have here now

is a collection of gravel layers

and what we are mining from top to bottom

is the selected reef cut

and associated with the pebbles

and the pyrite that you see here,

obviously there are concentrations of gold,

which is the source of our business.

well it looks to me

like we're looking at a section here

that's sliced through a series of river beds.

I mean, we can clearly see the pebbles,

you can see them rounded

and of course we can see

the heavy mineral concentration

at the bottom of the bed.

It looks like we're looking at

a stack of river bed. what do you think?

That these have been meandering rivers of some sort?

Yeah, exactly that.

what one could actually describe

is a series of gravel bars

in their depositional mode

which have inter-fingered with each other.

So some sort of meandering river

over a flat plane.

And we're sitting here a kilometer down now

for these beds have been buried

by later rivers

and more rivers and we know

we can go down in places

even another 4, 5 kilometers,

so we know that this is a huge stack

of just river bed after river bed

after river bed after river bed.

And as you can see all this shiny stuff,

iodine sulphite, pyrite,

which should have oxidized -

it should have rusted by now -

but it's still shining.

So the pyrite are telling us that

we must have had much less oxygen

in the atmosphere at the time.

That's correct. It probably was the atmosphere

which was dominated by carbon dioxide.

As nineteenth-century

geologists explored the bedrock in different parts of the world,

they slowly built up a collection

of random snapshots of the past,

isolated fragments of the planet's history.

But how could these fragments be linked together

to form a complete story of the Earth?

Here at the Regency resort of Lyme Regis

on Britain's south coast,

19th century scientists

found the key to this puzzle.

Every year oceanographer, Rachel Mills,

brings her students here to see a place

where the past is vividly etched into the rock layers.

These rocks hold a different sort of clue

to the earth's history.

The beach is a great place to come and do geology

because here we have the sea

eating away continuously

at the cliffs exposing the rocks

that normally are under our feet in dorset,

but here we can walk along the beach

and actually see the rocks that were laid down

millions of years ago.

The striking thing about these rocks is that

here we have a cliff which seems to have this alternating

light/dark, light/dark, light/dark,

which is repeating in a sort of regular basis

as we move up through geological time,

up this cliff.

Now if we look at these rocks in a bit more details

we can see there's a lot of interesting information

in here which we can pull out as geologists

to tell us about the conditions under which they formed.

Now the dark, soft layers,

have been laid down in an ocean environment,

a shallow sea.

I can break this with my fingers,

so you can see it falls apart very easily

and that's why it erodes very easily here on the beach.

And essentially it's made from clay particles

that have been transported by rivers to the ocean

and then very little has happened to it since then.

The light layer is strikingly different.

It's much, much harder

and that's why it stands out

in these platforms across the beach.

Basically this rock is limestone

and it is formed by the shelly remains of organisms

that lived in the ocean at that time,

but later on it has been cemented,

which makes it hard.

But what's most exciting about these rocks

is what we find in them.

And so this layer which I'm walking across at the moment

is one of these limestone pavements

which is full of hundreds and thousands of fossils.

And this is a really nice example here

of a fossil ammonite.

And this organism lived in the ocean

millions of years ago.

It died, sank to the sea floor,

and then has been preserved for geological time.

Ironically, the first people to take a real interest

in these strange shapes in the rocks

were not scientists but fossil-hunters

who made a living selling these beautiful objects to tourists.

Fossil hunters at Lyme Regis

soon acquired an intimate knowledge

of the different ammonites they found along the beach.

There were over 1,000 different species

in this locality alone.

Significantly these fossils increased in size,

complexity and diversity

as you moved higher up the cliff.

In other words they seemed to evolve through time

Now each layer of limestone

has a characteristic assemblage of fossils in it

which allows geologists

to go anywhere else in the world

and if they find the same assemblage of fossils

they then can say

"That rock was laid down at exactly the same

as these rocks here in Lyme Regis".

This was a great leap forward for geologists

in the 19th century

because it allowed them to divide up geological time

into the familiar time-scales that we now use -

the Triassic, the Jurassic, the Cretaceous -

and so with this understanding of how fossils evolve

and change through time

we can put together a timescale.

By classifying rock layers

according to their fossil content,

scientists were able to tell how layers

in one part of the world

related to layers found elsewhere,

whether they were younger or older.

But what they still couldn't say

was how old they were.

The problem of putting a figure

to the age of the Earth

soon became the most pressing question in science -

and it attracted one of

the century's most brilliant physicists-

Lord Kelvin.

Kelvin believed that he had hit

on a way of calculating the Earth's age

with some rigour.

His method was based on the experience

of Victorian coal miners.

However deep they go,

all miners face a common hazard.

wow, it's hot down here. Hey! How hot is it here?

well I think it's about 27 degrees.

Anywhere in the world you are,

the deeper you go, the hotter it gets.

what kind of temperature increase

do we see here as we go down?

we have something like 11 degrees per kilometer.

As nineteenth-century miners had already discovered

the interior of the Earth is hot.

where was this heat coming from?

Kelvin believed that it was a relic of the planet's birth -

heat trapped inside the Earth since its formation.

Kelvin deduced that the Earth must have been formed

by the steady accumulation of smaller rocks.

The force of their impact

as they were pulled into the growing planet

released an immense amount of energy -

enough to keep the entire globe molten.

But Kelvin knew that any hot body,

unless it's being continuously heated,

will cool overtime.

The longer the earth had been cooling,

the colder it would be.

So he set about collecting information

about how temperature increases as you go down mine shafts,

how heat was transmitted through rocks

and what temperature rocks melt at.

He applied all this to estimating how long it was

since the earth had last been molten.

After many years of calculation

Kelvin finally concluded that the earth

couldn't be much more than 20 million years old.

For most scientists Kelvin's argument appeared watertight.

But to field geologists like Hall,

his number felt far too small.

All around them was layer upon layer of rock -

even 20 million years seemed too short a time

to lay them down.

Then, just as Hall prepared to leave Barberton,

his commission complete,

back in London a stunning announcement

began a revolution in geology...

and resolved the paradox.

In 1904

Britain's scientific elite

were gathering at the Royal Institution.

A young New Zealand physicist, Ernest Rutherford,

was to reveal to the world what he had discovered

about the new phenomenon of radioactivity.

The human understanding of the Earth,

and of time itself,

was about to change forever.

Tonight, the eminent scientist addressing the members

is Professor Dan McKenzie.

Professor McKenzie, we're ready.

Obviously one of the central issues

for the Earth is how old it is

and one of the first physicists to try

and make a decent estimate of the age

of the Earth was Lord Kelvin.

And he came out with a number

which was 20 million years.

Earlier this century Rutherford came here

to give a talk about radioactivity

and somewhat to his consternation

Kelvin was in the audience.

And he says in his memoirs,

"I came into the room

which was half dark

and presently spotted Lord Kelvin in the audience

and realised that I was in for trouble

at the last part of the speech dealing

with the age of the Earth

where my views conflicted with his.

To my relief Kelvin fell fast asleep.

Rutherford realised that various elements

inside the Earth were radioactive,

like uranium and thorium and potassium

and that these generated

an important amount of heat

and that this completely changed the basis

of Kelvin's calculation

because instead of the Earth cooling all the time

it actually had heat sources in it.

And that you couldn't any longer use

that argument to estimate the age of the Earth.

Rutherford had removed

a central plank of Kelvin's argument.

Not all the heat inside the Earth

was left over from its formation.

Instead, heat was continuously being

generated within the planet

by radioactive decay.

But, on the other hand,

what this then allowed you to do

was to use the decay of these things,

right, to not make an estimate

but actually measure the age of the earth.

Rutherford had laid the foundations

for an entirely new branch of the Earth sciences,

geochronology -

the direct measurement of the ages of rocks.

One of its most distinguished practitioners

is Stephen Moorbath.

what Rutherford suggested

was that you could actually use

the phenomenon of radioactivity to date rocks

and he suggested that if you had a rock

which has a certain amount of uranium in it,

the uranium would in the course of time

decay to the element lead

by radioactive decay

and one could measure the rate of that process

so that if you took a rock

and measured the amount of uranium

and the amount of lead,

and then you could calculate

the actual age of the rock.

So Rutherford -

well some of his younger colleagues actually -

started to measure,

take rocks and measure the uranium and lead content.

Every rock contains its own radioactive clock.

That clock starts ticking when the rock forms

and new minerals crystallize within it.

Immediately the chemical composition of these minerals

slowly starts to change

as radioactive decay turns one element into another.

So after nearly two centuries of scientific endeavour,

the age of the earth would be revealed

by a few grains of sand.

And they suggested that they found that rocks

were as old as a few hundred million years

and then very soon afterwards

it was found that there were rocks

which were 1,500 million years old,

and this is a completely different order of magnitude

to the estimates of the age of the earth,

and the age of rocks

that had been given before radioactivity

which tended to give figures like

10, 20, 30 million years.

what Rutherford did really at a stroke,

was to lengthen geological time

by a factor of something like 100.

And this was greeted by the geologists

with a great sigh of relief

and it is really one of the major achievements

of the 20th century

that we now can date rocks and minerals

and things of that kind with greater and greater accuracy

and see how the whole history

of the solar system and the Earth has unrolled.

But to finally determine when our planet began,

geologists still needed to find a rock

left over from the time when the Earth was forming.

This rather inconspicuous looking object,

it's part of a meteorite

which fell at a place called Allende

in Mexico in February 1969.

And it is actually the oldest known object

that we know of, that exists on Earth.

It's the oldest object

that can be held by human hands.

It has an age of 4,566,

plus or minus 2, million years.

Actually most of the meteorites

are in approximately the same range -

just a few million years younger -

and its these little white inclusions here

that give this fantastically old age.

And it comes from the outer

reaches of the solar system.

It's really a kind of residue of the material

from which the whole solar system accreted,

came together, compacted.

It's the building block

of all the planets and the sun

and that formation of the solar system

and of the earth happened a few tens,

perhaps a hundred million years

after the formation of this object,

between about 4,550 to 4,450 million years ago.

Meteorites told scientists

when the Earth started to form.

But to know what the infant planet was like,

they needed to find a remnant of the early crust

miraculously preserved at the surface.

The search was on for the oldest place on Earth.

That quest took Stephen Moorbath

to the edge of the great Greenland Ice Cap.

In 1971

Vic MacGregor and I heard about this area

which is about 150 kilometers north east of Knud,

capital of Greenland,

and a mining company was up there

exploring a big iron ore deposit,

and Vic and I were very keen to see this area.

Vic made the first reliable geological map

and he suggested

that some of these rocks might be very old indeed.

This place is called Isua.

For Stephen it was to prove the discovery of a life-time.

we're standing right in the middle

of the oldest known rocks on the Earth.

And they extend from the lake there,

over to the other lake here.

well back in 1971

when we first came up here

we collected many of the rock types

and then took them back to our laboratory

to do the radioactive dating analysis

and we found that many of these rock types around here

have ages of nearly 3,800 million years

which is still the oldest age

of any terrestrial rocks

which are as extensive as this.

well it came as quite a surprise.

The age itself is very old

in relation to the age of the Earth

but also what's interesting is

what these rocks can tell you about

the environment of the early Earth.

This is a particularly interesting unit here

because as you can see

it's full of thousands and thousands of round pebbles

set in a fine grained matrix of mud,

clay and shale.

And this sort of rock

which geologists call a conglomerate,

were formed at a beach or a shoreline

and the erosion by water has rounded these pebbles,

and it shows without any doubt that water existed

at the surface of the Earth 3,800 million years ago,

which at that time came as a complete surprise.

At Isua the ice has uncovered

a tantalizing glimpse of the early earth.

But geologists' search for a place where rocks

might yield a more detailed picture of the young planet

took them to the other side of the globe.

The Barberton Mountain Land,

in South Africa.

Field area of Maarten de wit

well it turns out that the oldest rocks

at Barberton are about 3,500 million years old.

Some of them slightly older,

up to 3,700 million years.

There are older rocks elsewhere in the world

but what's so special about Barberton

is that it's so incredibly well preserved.

Almost in a pristine state.

Hall's original suspicion turned out to be correct.

Barberton is the oldest extensive piece

of the Earth's ancient surface.

Here, the rocks at last really begin to speak.

And it's not until you've walked

for weeks and weeks on end,

all of a sudden you find one tiny little outcrop

and you say "Bingo, I've got it.

That's what they've been trying to tell me.

That's what makes it exciting. That's why I'm a geologist. "

what the rocks of Barberton reveal

is that 3.5 billion years ago

the Earth was a world of volcanoes.

That's amazing,

all these little globules.

The physics of the formation

is very like the formation of hailstones.

These globules form in volcanic clouds

where very large volcanoes erupt violently,

like Mount St Helens, for example.

And as the volcanic hailstones form,

they fall back to Earth,

in this case on a layer in a lake.

The biggest ones settled to the bottom

and the smallest ones follow.

And as in Greenland there's abundant evidence

that the volcanoes were surrounded by water.

Look! These are the volcanic rocks

and they're so characteristic

and all over Barberton.

And it's these funny shapes,

these bulbs and these contorted things

that we see all over this face here

that tells us that these volcanic rocks

were erupted under water.

And the shape is a reaction

of the lava onto the rocks on the water,

against the cool water that wants to cool it down.

And as that freezes and forms this bulb

it's like squeezing toothpaste out

and piling it up on top of one another.

Everywhere in Barberton we look it is these kind

of rocks that allow us to reconstruct

that there were huge tracks of ocean

in this part of the world at that time.

where was all this water coming from?

Look at this rock.

See these textures on the rock.

Very delicately preserved -

almost as if birds have been walking on this.

They're actually little crystals.

They almost look man-made

but they're really natural crystals growing.

These rocks came from very high temperatures,

crystallized out from magma

that came from deep in the Earth

very rapidly to the surface,

high in volatile content, high in water.

The volcanoes erupting here

were producing vast quantities

of water vapour with the lava.

It was this water which was condensing to

form the primitive ocean.

The combination of volcanic activity and water

produced an environment where

a fascinating new process could begin.

My eye caught these structures by accident

and when I looked at them I asked "what is that?"

You know, I didn't have a clue what it was.

I'd never seen anything like this before.

In that same year

I went on a conference to New Zealand

and during that conference

I had a chance to sit around some of the mud pools

in New Zealand

and when I was looking at them,

while I was looking at this bubbling mud,

I all of a sudden remembered these structures

and I thought "wow, that's it.

That's got to be what it is. "

Ancient mud pool structures frozen in the rock here

and what gives it away as a mud pool

is of course all these intersections.

what is even more interesting to think about

is the warmth of this area

and the sort of niche it might have created

for bacteria, for example, to be swimming around.

And this is, of course, one of the sites

we might be thinking about

where life might have started.

And in fact, just recently Maarten

has made another remarkable find.

well these sedimentary rocks,

they've locked inside them

the very earliest signs of life on this planet.

They're very tiny

and when you look through the microscope at these rocks

you'll see tiny little bacteria.

And it's these bacteria

that are the first well preserved signs

of life on this planet.

All geologists are time travellers

but few have travelled as far as Maarten de wit.

He has ventured back in time

almost as far as the rocks will take him,

to a planet very different from the world we know today.

It's quite remarkable to think that

geologists over the last 100 years

have been able to collect all this data to allow us

to piece together what the early earth,

the young earth, the juvenile earth

might have looked like 3.5 million years ago.

And in many ways Barberton

has played a very big role in this.

The unique preservations of all the features in Barberton

allow us to have to very firm picture

of what that planet,

the skin of the planet, might have looked like.

There would have been lots of continents,

little continents, rocks basically,

with lots of volcanoes reaching the surface.

So we would have seen a tremendous amount of volcanic activity.

Gasses, lava flows everywhere.

This whole process would have been

driven at a faster rate than we see today.

There's more energy inside the planet

through this huge amount

of radioactive heat that's trying to escape.

All this volcanic activity was constantly

adding new material to the growing continents.

But there were no plants to soften the contours

of the newly created land

and without plants no oxygen in the atmosphere.

But around bubbling volcanic pools bacteria thrived,

And the volcanoes also produced vast quantities of water vapour.

As it rained back to the surface,

it eroded the new rocks.

On the bottom of the primitive ocean

sedimentary layers started to form.

80-90%, 95% perhaps of the planet would have been ocean

and we know from our observations that

the oceans must have been shallow.

Shallow oceans over most of the planet.

Since the scientific study of our planet began,

geologists have been learning to travel through time.

Thanks to places like Isua and Barberton

they have been able to achieve something quite remarkable -

to show us our world being born.

This is the Earth as it is at the very limit

of our scientific imagination.

As far as the record in the rocks is concerned,

this is the beginning of the Earth's story.

Subtitles: Thor