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