MANNING: Today, we're in the midst of a scientific revolution
in our understanding of the Earth and our relationship to it.
It's a revolution that's had a big impact on my own thinking.
My name is Aubrey Manning.
I've spent my career as a biologist,
but I now realise that those of us who study the creatures that live on the Earth
have a lot to learn from those who study the Earth itself.
As a biologist, what I find so fascinating is that as Earth's scientists learn more and more,
they're revealing just how intimately life and the planet are connected.
We'll never fully understand the history of living organisms
unless we first understand Earth's own story.
(CLOCK CHIMING)
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, I want to explore this new vision of a living planet.
So I've been learning to see the world through the eyes of geologists,
and the essence of that viewpoint is an understanding of time.
To understand the Earth, geologists have had to learn how to travel through time.
WOMAN: There's steam, and I'm collecting the water at the bottom of this.
MANNING: Whether they are collecting gases from the summit of an active volcano
or bringing up mud from the floor of the deep ocean,
geologists are always looking back in time.
But as they've slowly pieced together the planet's past,
they've been forced to an astonishing conclusion,
that the time scales of Earth history are almost inconceivably long,
that time itself is far vaster than they'd ever guessed.
Yet, as I've learnt, this profound insight
flowed from the simplest question one can ask about the Earth.
"How old is it?"
A question which geologists have struggled 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.
(WHINNYING)
(INDISTINCT CHATTERING)
The Barberton Mountain Land is several thousand square kilometres
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 record these outcrops
and so build up a picture of the rocks below the surface.
But as he worked his way across the landscape, Hall slowly realised that something was missing.
However hard he looked, he could find in the rocks none of the usual signs of fossilised life.
Could Barberton be a fragment of the Earth from a time before life began?
Just how old was this place?
(BELL TOLLING)
Hall's question came at a critical moment.
For a hundred years, scientists had been arguing about the age of the Earth
as they challenged ideas which had held sway for centuries.
200 years ago,
most people in the western world would have believed quite literally
in the biblical story of the creation.
In Genesis, it tells us how God created the Earth and all the living things in it,
including ourselves, in just six days.
Of course, the biblical account of the creation implies that Earth history and human history
began at the same moment.
And indeed, the first attempts to estimate the age of the Earth
came from scholars who went to the Bible and took the descendants of Adam
with their different ages and simply added them up,
and came out with the authoritative statement that the Earth had been created in 4004 BC,
which meant that it was just under 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 till much later, 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.
MANNING: 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 are visible.
In this case, this huge mass here has finer vertical rock layers.
MANNING: Everywhere in Barberton, the landscape seems to be made of layers.
By the 19th century, geologists had begun to realise
that the process that created these layers was still at work all around them.
Water can be a powerful agent of change,
destroying rock, but also creating it over time.
As the Komati River flows through the heart of Barberton,
it cuts down through the rocks,
eroding them into sand and silt, which it carries downstream.
Where the rivers flows slowly, the silt falls to the bottom,
layer upon layer, eventually to turn into new rock.
Well, here you have a slab of rock.
Now, this slab represents a riverbed.
Well, yeah, 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.
Originally, they would have been horizontal and they represent a whole history of rivers,
a long history of their position.
MANNING: To 19th-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 over time.
But how much time?
The first person to realise that by studying the rocks
you could learn about the age of the Earth was a Scotsman, James Hutton.
200 years ago, he came to this place, Siccar Point,
about 20 miles down the coast from Edinburgh,
and the discovery he made here changed forever the way that geologists think about time.
At Siccar Point, I was joined by Chris Nicholas,
a geologist who's made a special study of James Hutton's work.
...where he spent much of his life.
Chris wanted to show me a small patch of cliffside
famous to geologists as Hutton's Unconformity.
NICHOLAS: What Hutton saw
was that the grey rock that's down towards the bottom of the cliff
stands vertically.
But on top of it is this horizontal red rock
and between the two, there's a sort of undulating surface.
What did he make of it? What did he deduce from that?
Well, if all rocks were deposited horizontally,
he couldn't work out why this grey one was vertical underneath.
You know, how on earth did they form? What are they doing there?
And the way he answered this was to say, well, what must have happened to this grey rock
is that it must have been deposited on the sea bed at one time
and it must then have been twisted and brought up so that it's sitting vertically
and it must then have been eroded off, so it must have been land.
It must then have been drowned under the sea again
for this red rock to come in over the top and be deposited.
And even that has also been lifted up to give us the cliff face now.
What Hutton was suggesting here is that we really have at least three cycles
of deposition on the sea bed, then uplift, then erosion.
Three cycles.
MANNING: But Hutton could see that the water eats away at the land only very slowly.
Each one of his cycles must have taken a long period of time to complete.
CHRIS: And he could see no reason why there were not many cycles
prior to these ones he could see in the cliff face here,
and who knows how many will come after this?
MANNING: These endless cycles meant that for Hutton,
Earth's history was, to all intents and purposes, infinite.
Siccar Point represents for us the discovery of geological time,
the idea that the history of the Earth is infinitely longer than human history.
This idea, this sense of time,
has informed everything that geologists have done and thought since.
They recognise that there's time enough
for unimaginably slow processes to have enormous effects on the Earth.
The significance of this discovery wasn't lost on Hutton's contemporaries.
One of them, John Playfair, a mathematician,
whom he brought here to Siccar Point, writes most memorably,
"On us who saw these phenomena for the first time,
"the impression made will not be easily forgotten.
"The mind seemed to grow giddy by looking so far into the abyss of time."
But geologists knew Hutton's abyss was not empty.
Deep beneath their feet lay clues to the entire history of the planet,
locked up in the rock layers.
200 miles west of Barberton lie the Rand Goldfields,
where they sink the world's deepest mine shafts.
It's a pretty big cage, eh?
MANNING: For Maarten de Wit, it's an opportunity to travel back in time.
(LIFT RUMBLING)
Okay, now you should be able to get the impression of
plunging down at a fairly rapid rate
and you'll also feel your ears go from the pressure.
I can feel it now. Wow.
(MACHINERY WHIRRING)
It's the other cage going on the way up.
- Okay, that's the one... - On the double 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. - It's pretty scary.
- Well, you get used to it. - The first time, yeah.
So we're travelling through 6,000 metres of sediments, 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.
(CREAKING)
MANNING: 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.
Okay, 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 they are concentrations of gold, which is the source of our business.
Well, it looks to me like we're looking at a section here sliced through a series of riverbeds.
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 beds.
Looks like we're looking at a stack of riverbeds. What do you think?
Could these have been meandering rivers of some sort?
Yeah, exactly that. What one could actually describe these horizons as
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 plain.
And we're sitting here, a kilometre down now,
so these beds have been buried by later rivers and more rivers
and we know we can go down in places, even another four, five kilometres.
So we know that this is a huge stack of just riverbed after riverbed
after riverbed after riverbed.
MANNING: To any geologist, these rocks are bursting with information
about what the world was like when they were laid down.
Now, as you can see, all this shiny stuff, iron sulphite, pyrite,
which should have oxidised, it should have rusted by now,
but it's still shining.
So the pyrite is 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.
MANNING: As 19th-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?
At the Regency resort of Lyme Regis, I met oceanographer Rachel Mills,
who showed me other clues locked up in the rocks
which allowed this jigsaw puzzle to be put together.
So here the sea has revealed what's under our feet in this part of Dorset
and you can see these amazing layers.
This is a really striking example of sediments that were lain down millions of years ago
that are now exposed here on the beach.
So we can actually walk along them and walk over the rocks
as they were on the sea floor.
But what's really exciting about these rocks is what we find in them.
Goodness! Marvellous fossils!
- They're wonderful, aren't they? - Hundreds of them.
That's the thing, in this limestone pavement here we've just walked over
there are hundreds and hundreds of these fossil ammonites.
- Ammonites. - This organism was living in the ocean,
it died, sank to the sea floor and then has been preserved for geological time.
Each layer of limestone, in fact, has its own characteristic set of fossils in it.
And again they've fallen down to the sea floor and they've formed this layer.
MANNING: Ironically, the first people to take a real interest
in these strange shapes in the rocks
were not scientists, but fossil hunters like Chris Moore,
who made a living selling them to tourists.
Fossil hunters have a knowledge of ammonites to rival that of any palaeontologist.
Over a thousand different species have been found here,
each one with its own particular characteristics.
Now, if you take this one, for example,
these lines across here, we call them the suture lines.
This fern-shaped pattern separated each different chamber.
These vary in every different species of ammonite.
And also the general shape of the ammonite, the number of ribs, the shell structure.
MANNING: Fossil hunters soon noticed
that the ammonites weren't scattered at random through the rocks.
Instead, each rock layer seemed to contain its own particular types,
which weren't found elsewhere.
If I pick out a specimen, say, like this one,
you can tell me pretty exactly where that comes from.
MOORE: Yes, exactly. It comes from the lower part of the sequence here, in fact, the lowest part.
This is Psiloceras planorbis and it's preserved in this lovely mother of pearl,
and it's one of the earliest ammonites.
So this is a fairly simple ammonite at the beginning of their evolution.
- Yes. - Yes.
So if we go to another one which is rather different in form,
where does that one fit in?
That comes from about the middle part of the sequence here.
It's Asteroceras obtusum, that's its name.
Its character, it's got very strong ribs, with a heavy keel around the outside,
and usually here they're preserved in this beautiful yellow calcite.
MANNING: Because different layers contain different fossils,
geologists found they could classify rocks by their fossil content.
Then scientists in the 19th century made a very important intuitive leap.
They suggested that where you found the same fossils in layers of rocks,
then those layers were the same age.
Now, that gave them some kind of sequence,
some kind of measure across Hutton's abyss of time.
They gave names to these epochs, names we're fairly familiar with,
Permian, Triassic, Jurassic, Cretaceous and so on.
And they were able to say that Jurassic rocks here in Dorset
are older than Cretaceous rocks in Kent.
But what they couldn't yet 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.
DE WIT: Wow, Gus, it's hot down here, eh? How hot is it here?
Well, I think it's about 27 degrees.
Right, anywhere in the world you are, the deeper you go, the hotter it gets.
What's the kind of temperature increase we see here as we go down?
We have something like 11 degrees per kilometre.
MANNING: As 19th-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.
Kelvin's idea was very simple.
Any hot body will, unless you're continuously heating it,
cool over time.
I can get an idea of how long that coffee's been there from its temperature.
Kelvin applied the same principles to estimating the age of the Earth.
He collected information about how temperature increased
as you went down mine shafts,
how heat was transmitted through rocks and what temperature rocks melted at.
An he applied all this to estimating
how long it was since the Earth had last been molten.
He worked for many years but in the end he came up with his best estimate
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.
(AUDIENCE APPLAUDING)
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, Lord Kelvin was in the audience.
And as 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."
(AUDIENCE LAUGHING)
McKENZIE: 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.
MANNING: 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.
McKENZIE: 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.
MANNING: Rutherford realised that radioactivity was slowly transforming the Earth's crust.
Hidden inside every rock were minerals containing elements such as uranium.
As time passed, radioactive decay was gradually turning the uranium into lead,
changing the chemical composition of the rock.
This inexorable process begins the moment a rock forms
and new minerals crystallise within it.
Rutherford suggested that by carefully measuring the chemistry of these minerals,
scientists should be able to tell how long ago the rock had formed.
So, after 200 years of controversy and speculation,
the age of the Earth would be found in a few grains of dust.
There's a story that when Rutherford was working in Canada,
he went up to a colleague one day with a sample of rock.
"How old do you think this is?" he inquired.
"Oh, about 10 million years," was the reply.
"I can prove to you," said Rutherford with glee,
"that this rock is more than 500 million years old."
And that was far older than current estimates of the age of the Earth.
And it is indeed remarkable how, as radioactive dating techniques developed,
how quickly scientists' estimate of geological time and the age of the Earth expanded.
McKENZIE: 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, right,
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.
MANNING: The techniques that Rutherford pioneered
have been extended and refined by scientists like Stephen Moorbath at Oxford University.
...sort of lifelong love-hate relationship.
MANNING: Radioactive dating has become the geologist's most powerful tool.
And you've got really here an atomic clock, I mean, which runs at a very constant rate.
You know that uranium will always decay to lead at the same rate,
no matter what the temperature or the pressure or...
Absolutely constant, it never changes, in no known physical or chemical process.
- No matter how hot or cold it is. - Nothing at all. It's completely invariable.
The rate of radioactive decay is always the same.
MANNING: It's a universal clock.
And that's vital, because to finally determine the age of the Earth,
scientists needed a rock with a very special history,
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 in Mexico,
at a place called Allende 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 two - million years.
Actually, most meteorites that hit the Earth are only just slightly younger.
- They're all within quite a narrow age... - All within a narrow,
round about 4,550 million years.
And this is regarded as part of the material from which the solar system,
our sun and planets, actually came together, accreted.
They are the remnants of the raw material from which the solar system is made.
So this meteorite gives us an idea
of the age at which the solar system and the Earth was forming.
Yes, it does.
We believe that the Earth formed at this time also,
and by a kind of indirect but very strong reasoning,
it's believed that the Earth is also about 4,550 million years old.
So in a way, the meteorites give us an absolute age
for the Earth and the solar system.
- Yes, it's the limiting age. - Limiting age.
- It's as old as you can get. - Yes.
If you wanted anything older you'd have to get outside the solar system.
MANNING: 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 icecap.
In 1971, Vic McGregor and I heard about this area,
which is about 150 kilometres northeast of Nuuk, the 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.
MANNING: This place is called Isua.
For Stephen, it was to prove the discovery of a lifetime.
MOORBATH: 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 sort of as extensive as this.
Well, it came as quite as 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.
MANNING: One outcrop in particular caught Stephen's eye.
MOORBATH: 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.
MANNING: At Isua, the ice has uncovered a tantalising glimpse of the early Earth.
But the search for a place where rocks might yield a more detailed picture of the young planet
took geologists to the other side of the globe,
to the Barberton Mountain Land, in South Africa,
field area of Maarten de Wit.
Well, it turns out that the oldest rocks in 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.
MANNING: 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.
DE WIT: And it's not till 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."
MANNING: 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 Saint 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 settle to the bottom and the smallest ones follow.
MANNING: And as in Greenland, there's abundant evidence
that the volcanoes were surrounded by water.
Look, these are the volcanic rocks that are so characteristic 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 underwater.
(RUMBLING)
DE WIT: And the shape is a reaction of the lava as it erupts underwater
against the cool water that wants to cool it down.
And as it freezes it 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 tracts of ocean
in this part of the world at that time.
MANNING: But where was all this water coming from?
Look at this rock.
See these textures on the rock? It's 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,
crystallised out from magmas that came from deep in the Earth,
very rapidly to the surface, high in volatile content, high in water.
MANNING: 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 thought, "What is that?"
And I didn't have a clue what it was. I'd never seen anything like this before.
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 said, "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.
MANNING: And in fact, just recently, Maarten has made another remarkable find.
Well, these sedimentary rocks have 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.
MANNING: From the unique rocks at Barberton,
Maarten has been able to build up an extraordinarily vivid picture of the young Earth.
Looking back as far as they can see, more than three-and-a-half billion years,
scientists have found a planet studded with volcanic islands.
The intense heat of the young Earth meant the volcanoes were much more active
than volcanoes today.
As the lava cooled, it steadily added to the growing landmasses.
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.
Sedimentary layers started to form.
And gradually the shallow ocean that covered the young planet grew deeper.
Since the scientific study of our planet began,
geologists have been learning to travel through time.
Thanks to places like Isua and Barberton,
they've 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.
A planet shaped throughout its history by the same forces of heat and water still at work.
How those forces have transformed the Earth from a planet covered by a single shallow ocean,
dotted with volcanic islands, to the world we know today,
that's the story we'll be telling over the next few programmes.
We'll start next time with the place where the Earth's crust is formed,
as we'll voyage to the bottom of the deep ocean.
MAN ON RADIO: Atlantis, Alvin. Depth 1712 on the bottom.
MANNING: We'll be following the journey of the research submarine Alvin
as it ventures thousand of metres below the waves.
On board are scientists intent on studying at first hand
the strange volcanic realm where new ocean floor is continuously being created,
the next stage in Earth's story.