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MANNING: Today, we're in the midst
of a scientific revolution
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in our understanding of the Earth
and our relationship to it.
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It's a revolution that's had a big impact
on my own thinking.
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My name is Aubrey Manning.
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I've spent my career as a biologist,
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but I now realise that those of us who study
the creatures that live on the Earth
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have a lot to learn from those
who study the Earth itself.
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As a biologist, what I find so fascinating
is that as Earth's scientists learn more and more,
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they're revealing just how intimately
life and the planet are connected.
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We'll never fully understand
the history of living organisms
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unless we first understand Earth's own story.
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(CLOCK CHIMING)
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Recently, scientists have begun
to think of the Earth in a new way,
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almost as a living organism.
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Like a living thing, it is forever on the move,
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driven by the restless energy
locked up in its interior.
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And as the planet has evolved, so has life,
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shaped by the same forces
that move continents and change climates.
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In Earth Story, I want to explore
this new vision of a living planet.
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So I've been learning to see the world
through the eyes of geologists,
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and the essence of that viewpoint
is an understanding of time.
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To understand the Earth, geologists have had
to learn how to travel through time.
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WOMAN: There's steam, and I'm collecting
the water at the bottom of this.
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MANNING: Whether they are collecting gases
from the summit of an active volcano
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or bringing up mud from the floor
of the deep ocean,
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geologists are always looking back in time.
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But as they've slowly pieced together
the planet's past,
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they've been forced to an astonishing conclusion,
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that the time scales of Earth history
are almost inconceivably long,
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that time itself is far vaster
than they'd ever guessed.
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Yet, as I've learnt, this profound insight
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flowed from the simplest question
one can ask about the Earth.
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"How old is it?"
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A question which geologists have struggled
to answer for 200 years.
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At the turn of the century, one such geologist
came to a remote corner of Southern Africa
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called the Barberton Mountain Land.
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His name was Alan Hall
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and he had a commission
from the South African government
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to map this area, looking for gold.
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(WHINNYING)
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(INDISTINCT CHATTERING)
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The Barberton Mountain Land
is several thousand square kilometres
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of rugged terrain cut through by rivers.
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Rocky outcrops dot the hills,
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signs of the bedrock
hidden beneath the landscape.
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Hall's aim was to record these outcrops
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and so build up a picture of the rocks
below the surface.
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But as he worked his way across the landscape,
Hall slowly realised that something was missing.
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However hard he looked, he could find in the rocks
none of the usual signs of fossilised life.
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Could Barberton be a fragment of the Earth
from a time before life began?
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Just how old was this place?
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(BELL TOLLING)
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Hall's question came at a critical moment.
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For a hundred years, scientists had been arguing
about the age of the Earth
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as they challenged ideas
which had held sway for centuries.
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200 years ago,
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most people in the western world
would have believed quite literally
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in the biblical story of the creation.
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In Genesis, it tells us how God created the Earth
and all the living things in it,
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including ourselves, in just six days.
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Of course, the biblical account of the creation
implies that Earth history and human history
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began at the same moment.
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And indeed, the first attempts to estimate
the age of the Earth
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came from scholars who went to the Bible
and took the descendants of Adam
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with their different ages
and simply added them up,
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and came out with the authoritative statement
that the Earth had been created in 4004 BC,
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which meant that it was
just under 6,000 years old.
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But it didn't look that way to geologists.
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When they studied places like Barberton,
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they saw evidence that the landscape
had changed over time,
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that it had a long history.
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Hall's modern-day successor is Maarten de Wit.
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He too is fascinated by the question
of Barberton's antiquity.
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I really got interested
in this part of the world many years ago.
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But the opportunity to come here
didn't arise till much later, the end of the '70s.
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I came down here to Barberton
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and it turned out to be
one of the best moves of my life.
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It's one of these areas
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that has something extremely special to tell
about the story of the Earth.
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MANNING: Maarten, like Hall before him,
has mapped the rocks of Barberton in detail.
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When you do this,
a striking pattern quickly emerges.
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Well, once you start mapping the hills here,
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you'll notice that the landscape
is dominated by stripes,
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stripes of rocks like that one there.
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And if you get your eye in, after a while you'll see,
in fact, all these rock layers are visible.
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In this case, this huge mass here
has finer vertical rock layers.
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MANNING: Everywhere in Barberton,
the landscape seems to be made of layers.
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By the 19th century,
geologists had begun to realise
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that the process that created these layers
was still at work all around them.
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Water can be a powerful agent of change,
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destroying rock, but also creating it over time.
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As the Komati River flows
through the heart of Barberton,
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it cuts down through the rocks,
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eroding them into sand and silt,
which it carries downstream.
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Where the rivers flows slowly,
the silt falls to the bottom,
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layer upon layer, eventually to turn into new rock.
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Well, here you have a slab of rock.
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Now, this slab represents a riverbed.
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Well, yeah, there you can even see
the sand grains.
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These would have been
the sand grains in the river.
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These ridges that you see here, they are ripples.
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I can tell that it would have flowed,
from my hand here, downwards in that direction.
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Now, you can see, if you look downwards,
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that, in fact, there are several of these slabs
stacked on top of one another.
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Here's one.
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There you see another one over here.
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And another one.
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And another one still.
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And more.
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These are dozens of slabs
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and they're all tilted right now.
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Originally, they would have been horizontal
and they represent a whole history of rivers,
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a long history of their position.
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MANNING: To 19th-century scientists,
a world made up of layers
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didn't look as if it had been created
all in one go as the Bible says.
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It must have been built up over time.
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But how much time?
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The first person to realise
that by studying the rocks
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you could learn about the age of the Earth
was a Scotsman, James Hutton.
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200 years ago,
he came to this place, Siccar Point,
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about 20 miles down the coast from Edinburgh,
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and the discovery he made here changed forever
the way that geologists think about time.
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At Siccar Point, I was joined by Chris Nicholas,
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a geologist who's made a special study
of James Hutton's work.
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...where he spent much of his life.
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Chris wanted to show me a small patch of cliffside
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famous to geologists as Hutton's Unconformity.
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NICHOLAS: What Hutton saw
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was that the grey rock
that's down towards the bottom of the cliff
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stands vertically.
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But on top of it is this horizontal red rock
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and between the two,
there's a sort of undulating surface.
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What did he make of it?
What did he deduce from that?
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Well, if all rocks were deposited horizontally,
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he couldn't work out why this grey one
was vertical underneath.
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You know, how on earth did they form?
What are they doing there?
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And the way he answered this was to say,
well, what must have happened to this grey rock
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is that it must have been deposited
on the sea bed at one time
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and it must then have been twisted
and brought up so that it's sitting vertically
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and it must then have been eroded off,
so it must have been land.
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It must then have been drowned
under the sea again
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for this red rock to come in over the top
and be deposited.
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And even that has also been lifted up
to give us the cliff face now.
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What Hutton was suggesting here
is that we really have at least three cycles
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of deposition on the sea bed,
then uplift, then erosion.
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Three cycles.
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MANNING: But Hutton could see that the water
eats away at the land only very slowly.
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Each one of his cycles must have taken
a long period of time to complete.
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CHRIS: And he could see no reason
why there were not many cycles
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prior to these ones he could see
in the cliff face here,
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and who knows how many will come after this?
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MANNING: These endless cycles
meant that for Hutton,
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Earth's history was,
to all intents and purposes, infinite.
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Siccar Point represents for us
the discovery of geological time,
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the idea that the history of the Earth
is infinitely longer than human history.
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This idea, this sense of time,
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has informed everything
that geologists have done and thought since.
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They recognise that there's time enough
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for unimaginably slow processes
to have enormous effects on the Earth.
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The significance of this discovery
wasn't lost on Hutton's contemporaries.
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One of them, John Playfair, a mathematician,
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whom he brought here to Siccar Point,
writes most memorably,
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"On us who saw these phenomena
for the first time,
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"the impression made will not be easily forgotten.
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"The mind seemed to grow giddy
by looking so far into the abyss of time."
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But geologists knew
Hutton's abyss was not empty.
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Deep beneath their feet lay clues
to the entire history of the planet,
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locked up in the rock layers.
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200 miles west of Barberton
lie the Rand Goldfields,
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where they sink the world's deepest mine shafts.
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It's a pretty big cage, eh?
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MANNING: For Maarten de Wit,
it's an opportunity to travel back in time.
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(LIFT RUMBLING)
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Okay, now you should be able to get
the impression of
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plunging down at a fairly rapid rate
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and you'll also feel your ears go
from the pressure.
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I can feel it now. Wow.
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(MACHINERY WHIRRING)
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It's the other cage going on the way up.
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- Okay, that's the one...
- On the double drum system.
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If the hoist driver gets it all wrong
and he snaps the brakes on too suddenly...
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- You can feel the stretch now.
- Unbelievable.
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- He got his braking a bit wrong.
- It's pretty scary.
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- Well, you get used to it.
- The first time, yeah.
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So we're travelling through 6,000 metres
of sediments, backwards in time.
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We are now in a part of the world
where we are old enough to be pre-life.
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No wriggling organisms were present at this point.
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(CREAKING)
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MANNING: No matter how far back in time you go,
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every rock contains a detailed picture
of the environment it formed in,
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if you know how to look at it.
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Okay, what we have here now
is a collection of gravel layers,
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and what we are mining from top to bottom
is the selected reef cut,
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and associated with the pebbles and the pyrite
that you see here,
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obviously they are concentrations of gold,
which is the source of our business.
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Well, it looks to me like we're looking at
a section here sliced through a series of riverbeds.
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I mean, we can clearly see the pebbles,
you can see them rounded,
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and of course, we can see the heavy
mineral concentration at the bottom of the beds.
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Looks like we're looking at a stack of riverbeds.
What do you think?
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Could these have been meandering rivers
of some sort?
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Yeah, exactly that.
What one could actually describe these horizons as
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is a series of gravel bars
in their depositional mode
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which have inter-fingered with each other.
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So some sort of meandering river over a flat plain.
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And we're sitting here, a kilometre down now,
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so these beds have been buried by later rivers
and more rivers
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and we know we can go down in places,
even another four, five kilometres.
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So we know that this is a huge stack
of just riverbed after riverbed
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after riverbed after riverbed.
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MANNING: To any geologist,
these rocks are bursting with information
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about what the world was like
when they were laid down.
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Now, as you can see, all this shiny stuff,
iron sulphite, pyrite,
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which should have oxidised,
it should have rusted by now,
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but it's still shining.
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So the pyrite is telling us that we must have had
much less oxygen in the atmosphere at the time.
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That's correct. It probably was the atmosphere
which was dominated by carbon dioxide.
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MANNING: As 19th-century geologists explored
the bedrock in different parts of the world,
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they slowly built up a collection
of random snapshots of the past,
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isolated fragments of the planet's history.
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But how could these fragments be linked together
to form a complete story of the Earth?
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At the Regency resort of Lyme Regis,
I met oceanographer Rachel Mills,
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who showed me other clues locked up in the rocks
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which allowed this jigsaw puzzle
to be put together.
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So here the sea has revealed
what's under our feet in this part of Dorset
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and you can see these amazing layers.
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This is a really striking example of sediments
that were lain down millions of years ago
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that are now exposed here on the beach.
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00:19:35,247 --> 00:19:38,523
So we can actually walk along them
and walk over the rocks
229
00:19:38,607 --> 00:19:40,518
as they were on the sea floor.
230
00:19:41,647 --> 00:19:45,686
But what's really exciting
about these rocks is what we find in them.
231
00:19:48,127 --> 00:19:51,676
Goodness! Marvellous fossils!
232
00:19:51,807 --> 00:19:54,924
- They're wonderful, aren't they?
- Hundreds of them.
233
00:19:55,007 --> 00:19:57,805
That's the thing, in this limestone pavement here
we've just walked over
234
00:19:57,887 --> 00:20:00,879
there are hundreds and hundreds
of these fossil ammonites.
235
00:20:00,967 --> 00:20:03,561
- Ammonites.
- This organism was living in the ocean,
236
00:20:03,647 --> 00:20:08,004
it died, sank to the sea floor
and then has been preserved for geological time.
237
00:20:08,727 --> 00:20:14,165
Each layer of limestone, in fact, has
its own characteristic set of fossils in it.
238
00:20:14,247 --> 00:20:17,922
And again they've fallen down to the sea floor
and they've formed this layer.
239
00:20:24,007 --> 00:20:26,885
MANNING: Ironically,
the first people to take a real interest
240
00:20:26,967 --> 00:20:29,037
in these strange shapes in the rocks
241
00:20:29,127 --> 00:20:32,881
were not scientists,
but fossil hunters like Chris Moore,
242
00:20:32,967 --> 00:20:35,481
who made a living selling them to tourists.
243
00:20:37,087 --> 00:20:41,922
Fossil hunters have a knowledge of ammonites
to rival that of any palaeontologist.
244
00:20:44,207 --> 00:20:47,279
Over a thousand different species
have been found here,
245
00:20:47,367 --> 00:20:50,404
each one with its own particular characteristics.
246
00:20:53,767 --> 00:20:55,883
Now, if you take this one, for example,
247
00:20:55,967 --> 00:20:59,198
these lines across here,
we call them the suture lines.
248
00:20:59,287 --> 00:21:03,075
This fern-shaped pattern separated
each different chamber.
249
00:21:03,367 --> 00:21:05,835
These vary in every different species of ammonite.
250
00:21:05,927 --> 00:21:10,443
And also the general shape of the ammonite,
the number of ribs, the shell structure.
251
00:21:12,767 --> 00:21:14,280
MANNING: Fossil hunters soon noticed
252
00:21:14,367 --> 00:21:17,882
that the ammonites
weren't scattered at random through the rocks.
253
00:21:19,447 --> 00:21:23,838
Instead, each rock layer seemed to contain
its own particular types,
254
00:21:23,927 --> 00:21:25,838
which weren't found elsewhere.
255
00:21:27,047 --> 00:21:31,359
If I pick out a specimen, say, like this one,
256
00:21:31,687 --> 00:21:34,247
you can tell me pretty exactly
where that comes from.
257
00:21:34,327 --> 00:21:38,605
MOORE: Yes, exactly. It comes from the lower part
of the sequence here, in fact, the lowest part.
258
00:21:38,687 --> 00:21:42,999
This is Psiloceras planorbis and
it's preserved in this lovely mother of pearl,
259
00:21:43,087 --> 00:21:44,998
and it's one of the earliest ammonites.
260
00:21:45,087 --> 00:21:49,399
So this is a fairly simple ammonite
at the beginning of their evolution.
261
00:21:49,487 --> 00:21:50,840
- Yes.
- Yes.
262
00:21:51,287 --> 00:21:56,281
So if we go to another one
which is rather different in form,
263
00:21:56,367 --> 00:21:58,198
where does that one fit in?
264
00:21:58,287 --> 00:22:01,085
That comes from about the middle part
of the sequence here.
265
00:22:01,167 --> 00:22:03,806
It's Asteroceras obtusum, that's its name.
266
00:22:03,887 --> 00:22:08,563
Its character, it's got very strong ribs,
with a heavy keel around the outside,
267
00:22:08,647 --> 00:22:12,322
and usually here they're preserved
in this beautiful yellow calcite.
268
00:22:16,487 --> 00:22:19,479
MANNING: Because different layers
contain different fossils,
269
00:22:19,567 --> 00:22:23,606
geologists found they could classify rocks
by their fossil content.
270
00:22:28,247 --> 00:22:33,560
Then scientists in the 19th century
made a very important intuitive leap.
271
00:22:34,887 --> 00:22:40,439
They suggested that where you found
the same fossils in layers of rocks,
272
00:22:40,727 --> 00:22:43,560
then those layers were the same age.
273
00:22:44,447 --> 00:22:48,281
Now, that gave them some kind of sequence,
274
00:22:48,367 --> 00:22:52,963
some kind of measure
across Hutton's abyss of time.
275
00:22:53,327 --> 00:22:56,637
They gave names to these epochs,
names we're fairly familiar with,
276
00:22:56,727 --> 00:23:00,356
Permian, Triassic, Jurassic, Cretaceous and so on.
277
00:23:00,447 --> 00:23:05,885
And they were able to say
that Jurassic rocks here in Dorset
278
00:23:06,127 --> 00:23:09,597
are older than Cretaceous rocks in Kent.
279
00:23:10,567 --> 00:23:14,480
But what they couldn't yet say
was how old they were.
280
00:23:19,607 --> 00:23:22,758
The problem of putting a figure
to the age of the Earth
281
00:23:22,847 --> 00:23:25,645
soon became the most pressing question
in science.
282
00:23:26,567 --> 00:23:30,242
And it attracted one of the century's
most brilliant physicists,
283
00:23:30,687 --> 00:23:32,086
Lord Kelvin.
284
00:23:34,407 --> 00:23:39,720
Kelvin believed that he had hit on a way
of calculating the Earth's age with some rigour.
285
00:23:44,487 --> 00:23:48,639
His method was based on the experience
of Victorian coal miners.
286
00:23:50,607 --> 00:23:54,441
However deep they go,
all miners face a common hazard.
287
00:23:54,527 --> 00:23:57,485
DE WIT: Wow, Gus, it's hot down here, eh?
How hot is it here?
288
00:23:57,567 --> 00:24:00,127
Well, I think it's about 27 degrees.
289
00:24:00,207 --> 00:24:03,802
Right, anywhere in the world you are,
the deeper you go, the hotter it gets.
290
00:24:03,887 --> 00:24:07,436
What's the kind of temperature increase
we see here as we go down?
291
00:24:07,527 --> 00:24:10,519
We have something like 11 degrees per kilometre.
292
00:24:11,407 --> 00:24:14,524
MANNING: As 19th-century miners
had already discovered,
293
00:24:14,607 --> 00:24:17,360
the interior of the Earth is hot.
294
00:24:19,687 --> 00:24:21,882
Where was this heat coming from?
295
00:24:22,447 --> 00:24:25,837
Kelvin believed that it was a relic
of the planet's birth,
296
00:24:26,327 --> 00:24:29,524
heat trapped inside the Earth since its formation.
297
00:24:35,287 --> 00:24:37,721
Kelvin deduced that the Earth
must have been formed
298
00:24:37,807 --> 00:24:40,446
by the steady accumulation of smaller rocks.
299
00:24:40,967 --> 00:24:44,403
The force of their impact as they were pulled
into the growing planet
300
00:24:44,487 --> 00:24:49,242
released an immense amount of energy,
enough to keep the entire globe molten.
301
00:25:01,207 --> 00:25:03,323
Kelvin's idea was very simple.
302
00:25:03,407 --> 00:25:07,366
Any hot body will,
unless you're continuously heating it,
303
00:25:07,767 --> 00:25:09,246
cool over time.
304
00:25:09,967 --> 00:25:14,119
I can get an idea of how long
that coffee's been there from its temperature.
305
00:25:14,687 --> 00:25:18,760
Kelvin applied the same principles
to estimating the age of the Earth.
306
00:25:18,847 --> 00:25:21,725
He collected information about
how temperature increased
307
00:25:21,807 --> 00:25:23,206
as you went down mine shafts,
308
00:25:23,287 --> 00:25:27,519
how heat was transmitted through rocks
and what temperature rocks melted at.
309
00:25:27,607 --> 00:25:29,916
An he applied all this to estimating
310
00:25:30,007 --> 00:25:33,317
how long it was since the Earth
had last been molten.
311
00:25:34,967 --> 00:25:39,358
He worked for many years but in the end
he came up with his best estimate
312
00:25:39,447 --> 00:25:43,156
that the Earth couldn't be much more
than 20 million years old.
313
00:25:48,327 --> 00:25:51,956
For most scientists, Kelvin's argument
appeared watertight.
314
00:25:52,607 --> 00:25:57,317
But to field geologists like Hall,
his number felt far too small.
315
00:25:57,727 --> 00:26:00,639
All around them was layer upon layer of rock.
316
00:26:00,847 --> 00:26:04,760
Even 20 million years seemed too short a time
to lay them down.
317
00:26:07,487 --> 00:26:12,356
Then, just as Hall prepared to leave Barberton,
his commission complete,
318
00:26:12,447 --> 00:26:16,838
back in London, a stunning announcement
began a revolution in geology
319
00:26:17,487 --> 00:26:19,443
and resolved the paradox.
320
00:26:22,727 --> 00:26:28,359
In 1904, Britain's scientific elite
were gathering at the Royal Institution.
321
00:26:30,727 --> 00:26:36,563
A young New Zealand physicist, Ernest Rutherford,
was to reveal to the world what he had discovered
322
00:26:36,647 --> 00:26:39,957
about the new phenomenon of radioactivity.
323
00:26:43,607 --> 00:26:47,395
The human understanding of the Earth,
and of time itself,
324
00:26:47,487 --> 00:26:49,603
was about to change forever.
325
00:26:52,807 --> 00:26:55,958
Tonight, the eminent scientist
addressing the members
326
00:26:56,047 --> 00:26:58,515
is Professor Dan McKenzie.
327
00:26:59,367 --> 00:27:00,959
(AUDIENCE APPLAUDING)
328
00:27:05,407 --> 00:27:10,276
Obviously one of the central issues
for the Earth is how old it is.
329
00:27:10,447 --> 00:27:14,360
And one of the first physicists to try
and make a decent estimate
330
00:27:14,447 --> 00:27:17,007
of the age of the Earth was Lord Kelvin.
331
00:27:17,447 --> 00:27:21,486
And he came out with a number,
which was 20 million years.
332
00:27:23,047 --> 00:27:27,757
Earlier this century, Rutherford came here
to give a talk about radioactivity.
333
00:27:28,127 --> 00:27:32,723
And somewhat to his consternation,
Lord Kelvin was in the audience.
334
00:27:33,527 --> 00:27:35,757
And as he says in his memoirs,
335
00:27:36,247 --> 00:27:42,436
"I came into the room, which was half dark,
and presently spotted Lord Kelvin in the audience
336
00:27:42,527 --> 00:27:45,087
"and realised that I was in for trouble
337
00:27:45,167 --> 00:27:48,477
"at the last part of the speech
dealing with the age of the Earth,
338
00:27:48,567 --> 00:27:51,035
"where my views conflicted with his.
339
00:27:51,767 --> 00:27:54,918
"To my relief, Kelvin fell fast asleep."
340
00:27:55,007 --> 00:27:56,759
(AUDIENCE LAUGHING)
341
00:27:58,567 --> 00:28:02,276
McKENZIE: Rutherford realised
that various elements
342
00:28:02,367 --> 00:28:06,724
inside the Earth were radioactive,
like uranium and thorium and potassium,
343
00:28:06,807 --> 00:28:10,516
and that these generated
an important amount of heat,
344
00:28:10,607 --> 00:28:14,646
and that this completely changed
the basis of Kelvin's calculation,
345
00:28:14,727 --> 00:28:18,766
because instead of the Earth cooling all the time
it actually had heat sources in it
346
00:28:18,847 --> 00:28:24,046
and that you couldn't any longer use
that argument to estimate the age of the Earth.
347
00:28:24,607 --> 00:28:28,839
MANNING: Rutherford had removed
a central plank of Kelvin's argument.
348
00:28:28,927 --> 00:28:32,636
Not all the heat inside the Earth was left over
from its formation.
349
00:28:32,727 --> 00:28:38,324
Instead heat was continuously being generated
within the planet by radioactive decay.
350
00:28:39,047 --> 00:28:42,835
McKENZIE: But on the other hand,
what this then allowed you to do
351
00:28:42,927 --> 00:28:46,158
was to use the decay of these things, right,
352
00:28:46,247 --> 00:28:50,320
to not make an estimate,
but actually measure the age of the Earth.
353
00:28:54,487 --> 00:29:00,005
MANNING: Rutherford realised that radioactivity
was slowly transforming the Earth's crust.
354
00:29:02,567 --> 00:29:06,879
Hidden inside every rock were minerals
containing elements such as uranium.
355
00:29:11,567 --> 00:29:17,324
As time passed, radioactive decay
was gradually turning the uranium into lead,
356
00:29:17,807 --> 00:29:20,446
changing the chemical composition of the rock.
357
00:29:25,047 --> 00:29:28,881
This inexorable process begins
the moment a rock forms
358
00:29:28,967 --> 00:29:31,276
and new minerals crystallise within it.
359
00:29:32,447 --> 00:29:36,759
Rutherford suggested that by carefully measuring
the chemistry of these minerals,
360
00:29:37,207 --> 00:29:41,166
scientists should be able to tell how long ago
the rock had formed.
361
00:29:48,327 --> 00:29:52,684
So, after 200 years of controversy
and speculation,
362
00:29:53,087 --> 00:29:56,841
the age of the Earth would be found
in a few grains of dust.
363
00:30:01,207 --> 00:30:04,836
There's a story that when Rutherford
was working in Canada,
364
00:30:05,167 --> 00:30:08,477
he went up to a colleague one day
with a sample of rock.
365
00:30:08,847 --> 00:30:11,486
"How old do you think this is?" he inquired.
366
00:30:11,647 --> 00:30:15,356
"Oh, about 10 million years," was the reply.
367
00:30:15,447 --> 00:30:18,086
"I can prove to you," said Rutherford with glee,
368
00:30:18,167 --> 00:30:21,477
"that this rock is more than
500 million years old."
369
00:30:21,567 --> 00:30:25,162
And that was far older than current estimates
of the age of the Earth.
370
00:30:25,247 --> 00:30:29,798
And it is indeed remarkable how,
as radioactive dating techniques developed,
371
00:30:29,887 --> 00:30:35,325
how quickly scientists' estimate of geological time
and the age of the Earth expanded.
372
00:30:39,087 --> 00:30:44,480
McKENZIE: What Rutherford did, really,
at a stroke, was to lengthen geological time
373
00:30:44,567 --> 00:30:47,400
by a factor of something like 100.
374
00:30:47,727 --> 00:30:51,845
And this was greeted by the geologists
with a great sigh of relief.
375
00:30:52,247 --> 00:30:56,399
And it is really one
of the major achievements, right,
376
00:30:56,487 --> 00:31:00,560
of the 20th century, that we now can date rocks
377
00:31:00,647 --> 00:31:05,118
and minerals and things of that kind
with greater and greater accuracy
378
00:31:05,207 --> 00:31:10,884
and see how the whole history
of the solar system and the Earth has unrolled.
379
00:31:12,807 --> 00:31:15,162
MANNING: The techniques
that Rutherford pioneered
380
00:31:15,247 --> 00:31:20,446
have been extended and refined by scientists
like Stephen Moorbath at Oxford University.
381
00:31:20,527 --> 00:31:23,724
...sort of lifelong love-hate relationship.
382
00:31:25,327 --> 00:31:29,605
MANNING: Radioactive dating has become
the geologist's most powerful tool.
383
00:31:32,927 --> 00:31:37,398
And you've got really here an atomic clock,
I mean, which runs at a very constant rate.
384
00:31:37,487 --> 00:31:41,321
You know that uranium will always decay
to lead at the same rate,
385
00:31:41,407 --> 00:31:43,921
no matter what the temperature
or the pressure or...
386
00:31:44,007 --> 00:31:48,523
Absolutely constant, it never changes,
in no known physical or chemical process.
387
00:31:48,607 --> 00:31:52,395
- No matter how hot or cold it is.
- Nothing at all. It's completely invariable.
388
00:31:52,487 --> 00:31:55,479
The rate of radioactive decay is always the same.
389
00:31:57,287 --> 00:31:59,596
MANNING: It's a universal clock.
390
00:32:00,047 --> 00:32:04,165
And that's vital, because
to finally determine the age of the Earth,
391
00:32:04,247 --> 00:32:07,717
scientists needed a rock
with a very special history,
392
00:32:08,087 --> 00:32:11,682
a rock left over from the time
when the Earth was forming.
393
00:32:19,687 --> 00:32:26,525
This rather inconspicuous-looking object,
it's part of a meteorite which fell in Mexico,
394
00:32:26,767 --> 00:32:30,726
at a place called Allende in February, 1969.
395
00:32:31,727 --> 00:32:38,644
And it is actually the oldest known object
that we know of that exists on Earth.
396
00:32:46,247 --> 00:32:50,365
It's the oldest object
that can be held by human hands.
397
00:33:16,087 --> 00:33:22,925
It has an age of 4,566 -
plus or minus two - million years.
398
00:33:23,687 --> 00:33:29,717
Actually, most meteorites that hit the Earth
are only just slightly younger.
399
00:33:29,807 --> 00:33:32,526
- They're all within quite a narrow age...
- All within a narrow,
400
00:33:32,607 --> 00:33:36,202
round about 4,550 million years.
401
00:33:36,287 --> 00:33:42,522
And this is regarded as part of the material
from which the solar system,
402
00:33:42,607 --> 00:33:46,282
our sun and planets,
actually came together, accreted.
403
00:33:46,487 --> 00:33:52,357
They are the remnants of the raw material
from which the solar system is made.
404
00:33:53,447 --> 00:33:57,599
So this meteorite gives us an idea
405
00:33:57,687 --> 00:34:01,726
of the age at which the solar system
and the Earth was forming.
406
00:34:01,807 --> 00:34:03,035
Yes, it does.
407
00:34:03,127 --> 00:34:06,597
We believe that the Earth formed at this time also,
408
00:34:06,687 --> 00:34:09,759
and by a kind of indirect
but very strong reasoning,
409
00:34:09,847 --> 00:34:14,079
it's believed that the Earth is also
about 4,550 million years old.
410
00:34:14,167 --> 00:34:19,036
So in a way,
the meteorites give us an absolute age
411
00:34:19,127 --> 00:34:21,004
for the Earth and the solar system.
412
00:34:21,087 --> 00:34:22,759
- Yes, it's the limiting age.
- Limiting age.
413
00:34:22,847 --> 00:34:24,803
- It's as old as you can get.
- Yes.
414
00:34:24,887 --> 00:34:29,244
If you wanted anything older
you'd have to get outside the solar system.
415
00:34:31,847 --> 00:34:35,840
MANNING: Meteorites told scientists
when the Earth started to form.
416
00:34:35,927 --> 00:34:41,047
But to know what the infant planet was like,
they needed to find a remnant of the early crust
417
00:34:41,127 --> 00:34:43,516
miraculously preserved at the surface.
418
00:34:44,287 --> 00:34:47,085
The search was on for the oldest place on Earth.
419
00:34:49,407 --> 00:34:54,322
That quest took Stephen Moorbath
to the edge of the great Greenland icecap.
420
00:35:02,247 --> 00:35:07,526
In 1971, Vic McGregor and I
heard about this area,
421
00:35:07,607 --> 00:35:13,637
which is about 150 kilometres northeast
of Nuuk, the capital of Greenland.
422
00:35:14,367 --> 00:35:19,725
And a mining company was up there
exploring a big iron ore deposit
423
00:35:19,807 --> 00:35:23,243
and Vic and I were very keen to see this area.
424
00:35:23,847 --> 00:35:27,681
Vic made the first reliable geological map
425
00:35:27,767 --> 00:35:32,557
and he suggested that some of these rocks
might be very old indeed.
426
00:35:39,487 --> 00:35:41,955
MANNING: This place is called Isua.
427
00:35:45,167 --> 00:35:48,716
For Stephen, it was to prove
the discovery of a lifetime.
428
00:35:51,487 --> 00:35:56,436
MOORBATH: We're standing right in the middle
of the oldest known rocks on the Earth.
429
00:35:57,567 --> 00:36:04,279
And they extend from the lake there
over to the other lake here.
430
00:36:16,647 --> 00:36:22,244
Well, back in 1971, when we first came up here,
we collected many of the rock types
431
00:36:22,327 --> 00:36:28,277
and then took them back to our laboratory
to do the radioactive dating analysis,
432
00:36:28,367 --> 00:36:32,201
and we found that
many of these rock types around here
433
00:36:32,287 --> 00:36:36,519
have ages of nearly 3,800 million years,
434
00:36:36,767 --> 00:36:40,806
which is still the oldest age
435
00:36:40,887 --> 00:36:45,756
of any terrestrial rocks which are
sort of as extensive as this.
436
00:36:46,487 --> 00:36:49,001
Well, it came as quite as a surprise.
437
00:36:49,087 --> 00:36:55,401
The age itself is very old
in relation to the age of the Earth.
438
00:36:55,487 --> 00:36:58,957
But also, what's interesting is
what these rocks can tell you
439
00:36:59,047 --> 00:37:01,481
about the environment of the early Earth.
440
00:37:02,047 --> 00:37:05,244
MANNING: One outcrop in particular
caught Stephen's eye.
441
00:37:05,647 --> 00:37:10,198
MOORBATH: As you can see, it's full of thousands
and thousands of round pebbles
442
00:37:10,287 --> 00:37:15,281
set in a fine-grained matrix
of mud, clay and shale.
443
00:37:15,527 --> 00:37:19,679
And this sort of rock,
which geologists call a conglomerate,
444
00:37:19,807 --> 00:37:23,482
were formed at a beach or a shoreline
445
00:37:23,607 --> 00:37:27,395
and the erosion by water
446
00:37:27,767 --> 00:37:30,076
has rounded these pebbles
447
00:37:30,447 --> 00:37:33,484
and it shows without any doubt that water existed
448
00:37:33,567 --> 00:37:36,718
at the surface of the Earth
3,800 million years ago,
449
00:37:36,807 --> 00:37:40,595
which at that time came as a complete surprise.
450
00:37:49,367 --> 00:37:53,724
MANNING: At Isua, the ice has uncovered
a tantalising glimpse of the early Earth.
451
00:37:54,767 --> 00:37:59,921
But the search for a place where rocks might yield
a more detailed picture of the young planet
452
00:38:00,007 --> 00:38:02,726
took geologists to the other side of the globe,
453
00:38:04,727 --> 00:38:08,402
to the Barberton Mountain Land, in South Africa,
454
00:38:09,847 --> 00:38:12,281
field area of Maarten de Wit.
455
00:38:16,087 --> 00:38:20,956
Well, it turns out that the oldest rocks
in Barberton are about 3,500 million years old,
456
00:38:21,047 --> 00:38:24,357
some of them slightly older,
up to 3,700 million years.
457
00:38:24,447 --> 00:38:26,438
There are older rocks elsewhere in the world,
458
00:38:26,527 --> 00:38:30,725
but what's so special about Barberton
is that it's so incredibly well-preserved,
459
00:38:30,807 --> 00:38:32,763
almost in a pristine state.
460
00:38:38,287 --> 00:38:41,324
MANNING: Hall's original suspicion
turned out to be correct.
461
00:38:41,407 --> 00:38:45,719
Barberton is the oldest extensive piece
of the Earth's ancient surface.
462
00:38:46,287 --> 00:38:49,484
Here the rocks at last really begin to speak.
463
00:38:50,687 --> 00:38:53,679
DE WIT: And it's not till you've walked
for weeks and weeks on end,
464
00:38:53,767 --> 00:38:57,476
all of a sudden you find one tiny little outcrop,
and you say, "Bingo! I've got it.
465
00:38:57,567 --> 00:38:59,364
"That's what they've been trying to tell me.
466
00:38:59,447 --> 00:39:02,405
"That's what makes it exciting.
That's why I'm a geologist."
467
00:39:06,527 --> 00:39:11,601
MANNING: What the rocks of Barberton reveal
is that 3.5 billion years ago,
468
00:39:11,687 --> 00:39:13,803
the Earth was a world of volcanoes.
469
00:39:17,127 --> 00:39:19,960
That's amazing, all these little globules.
470
00:39:20,047 --> 00:39:23,084
The physics of the formation
is very like the formation of hailstones.
471
00:39:23,167 --> 00:39:25,237
These globules form in volcanic clouds
472
00:39:25,327 --> 00:39:29,684
where very large volcanoes erupt violently,
like Mount Saint Helens, for example.
473
00:39:37,647 --> 00:39:41,435
And as the volcanic hailstones form,
they fall back to Earth,
474
00:39:41,527 --> 00:39:43,836
in this case on a layer in a lake.
475
00:39:43,927 --> 00:39:48,125
The biggest ones settle to the bottom
and the smallest ones follow.
476
00:39:49,327 --> 00:39:51,921
MANNING: And as in Greenland,
there's abundant evidence
477
00:39:52,007 --> 00:39:54,567
that the volcanoes were surrounded by water.
478
00:39:56,047 --> 00:40:00,723
Look, these are the volcanic rocks
that are so characteristic all over Barberton.
479
00:40:01,007 --> 00:40:04,920
And it's these funny shapes, these bulbs
and these contorted things
480
00:40:05,007 --> 00:40:07,760
that we see all over this face here
481
00:40:08,007 --> 00:40:11,443
that tells us that these volcanic rocks
were erupted underwater.
482
00:40:11,527 --> 00:40:12,846
(RUMBLING)
483
00:40:15,447 --> 00:40:20,396
DE WIT: And the shape is a reaction of the lava
as it erupts underwater
484
00:40:20,487 --> 00:40:23,365
against the cool water that wants to cool it down.
485
00:40:24,687 --> 00:40:27,326
And as it freezes it forms this bulb,
486
00:40:27,447 --> 00:40:31,725
it's like squeezing toothpaste out and piling it up
on top of one another.
487
00:40:34,207 --> 00:40:37,756
Everywhere in Barberton we look,
it is these kind of rocks
488
00:40:37,887 --> 00:40:42,915
that allow us to reconstruct
that there were huge tracts of ocean
489
00:40:43,207 --> 00:40:45,516
in this part of the world at that time.
490
00:40:47,687 --> 00:40:50,838
MANNING: But where was all this water
coming from?
491
00:40:53,087 --> 00:40:54,486
Look at this rock.
492
00:40:56,407 --> 00:41:00,764
See these textures on the rock?
It's very delicately preserved,
493
00:41:00,967 --> 00:41:03,117
almost as if birds have been walking on this.
494
00:41:03,207 --> 00:41:05,277
They're actually little crystals.
495
00:41:10,367 --> 00:41:14,326
They almost look man-made
but they're really natural crystals growing.
496
00:41:17,847 --> 00:41:20,645
These rocks came from very high temperatures,
497
00:41:20,727 --> 00:41:24,402
crystallised out from magmas
that came from deep in the Earth,
498
00:41:24,487 --> 00:41:30,039
very rapidly to the surface,
high in volatile content, high in water.
499
00:41:32,807 --> 00:41:34,718
MANNING: The volcanoes erupting here
500
00:41:34,807 --> 00:41:38,163
were producing vast quantities
of water vapour with the lava.
501
00:41:39,087 --> 00:41:42,682
It was this water which was condensing
to form the primitive ocean.
502
00:41:53,727 --> 00:41:57,037
The combination of volcanic activity and water
503
00:41:57,127 --> 00:42:01,166
produced an environment where
a fascinating new process could begin.
504
00:42:05,447 --> 00:42:09,156
My eye caught these structures by accident,
505
00:42:09,247 --> 00:42:11,841
and when I looked at them,
I thought, "What is that?"
506
00:42:11,927 --> 00:42:16,443
And I didn't have a clue what it was.
I'd never seen anything like this before.
507
00:42:16,527 --> 00:42:19,837
That same year I went on a conference
to New Zealand
508
00:42:21,447 --> 00:42:23,483
and during that conference I had a chance
509
00:42:23,567 --> 00:42:26,400
to sit around some of the mud pools
in New Zealand,
510
00:42:26,647 --> 00:42:30,276
and when I was looking at them,
while I was looking at this bubbling mud,
511
00:42:30,367 --> 00:42:32,244
I all of a sudden remembered these structures
512
00:42:32,327 --> 00:42:36,115
and said, "Wow! That's it!
That's got to be what it is."
513
00:42:36,567 --> 00:42:39,365
Ancient mud pool structures,
frozen in the rock here.
514
00:42:39,447 --> 00:42:43,520
And what gives it away as a mud pool is,
of course, all these intersections.
515
00:42:50,967 --> 00:42:55,483
What is even more interesting to think about
is the warmth of this area
516
00:42:55,567 --> 00:43:00,800
and the sort of niche it might have created
for bacteria, for example, to be swimming around.
517
00:43:00,887 --> 00:43:04,721
And this is, of course, one of the sites
we might be thinking about
518
00:43:04,807 --> 00:43:06,877
where life might have started.
519
00:43:10,167 --> 00:43:14,638
MANNING: And in fact, just recently,
Maarten has made another remarkable find.
520
00:43:20,647 --> 00:43:23,366
Well, these sedimentary rocks
have locked inside them
521
00:43:23,447 --> 00:43:27,520
the very earliest signs of life on this planet.
They're very tiny.
522
00:43:27,727 --> 00:43:32,482
And when you look through the microscope
at these rocks, you'll see tiny little bacteria.
523
00:43:38,127 --> 00:43:43,724
And it's these bacteria that are the first
well-preserved signs of life on this planet.
524
00:43:48,527 --> 00:43:50,882
MANNING: From the unique rocks at Barberton,
525
00:43:50,967 --> 00:43:55,836
Maarten has been able to build up
an extraordinarily vivid picture of the young Earth.
526
00:44:00,727 --> 00:44:05,482
Looking back as far as they can see,
more than three-and-a-half billion years,
527
00:44:06,367 --> 00:44:09,803
scientists have found a planet
studded with volcanic islands.
528
00:44:12,407 --> 00:44:16,320
The intense heat of the young Earth
meant the volcanoes were much more active
529
00:44:16,407 --> 00:44:17,886
than volcanoes today.
530
00:44:21,927 --> 00:44:26,000
As the lava cooled,
it steadily added to the growing landmasses.
531
00:44:34,007 --> 00:44:38,523
But there were no plants to soften the contours
of the newly created land
532
00:44:38,687 --> 00:44:41,918
and without plants, no oxygen in the atmosphere.
533
00:44:55,687 --> 00:44:59,839
But around bubbling volcanic pools,
bacteria thrived.
534
00:45:11,807 --> 00:45:15,766
And the volcanoes also produced
vast quantities of water vapour.
535
00:45:15,927 --> 00:45:19,522
As it rained back to the surface,
it eroded the new rocks.
536
00:45:19,927 --> 00:45:22,282
Sedimentary layers started to form.
537
00:45:24,607 --> 00:45:29,158
And gradually the shallow ocean
that covered the young planet grew deeper.
538
00:45:34,407 --> 00:45:37,285
Since the scientific study of our planet began,
539
00:45:37,367 --> 00:45:40,677
geologists have been learning
to travel through time.
540
00:45:40,927 --> 00:45:43,725
Thanks to places like Isua and Barberton,
541
00:45:43,807 --> 00:45:46,765
they've been able to achieve something
quite remarkable,
542
00:45:46,847 --> 00:45:49,122
to show us our world being born.
543
00:45:57,967 --> 00:46:02,643
This is the Earth as it is at the very limit
of our scientific imagination.
544
00:46:05,847 --> 00:46:11,479
As far as the record in the rocks is concerned,
this is the beginning of the Earth's story.
545
00:46:17,887 --> 00:46:23,917
A planet shaped throughout its history
by the same forces of heat and water still at work.
546
00:46:34,767 --> 00:46:40,125
How those forces have transformed the Earth
from a planet covered by a single shallow ocean,
547
00:46:40,287 --> 00:46:43,677
dotted with volcanic islands,
to the world we know today,
548
00:46:43,807 --> 00:46:47,243
that's the story we'll be telling
over the next few programmes.
549
00:46:47,767 --> 00:46:52,045
We'll start next time with the place
where the Earth's crust is formed,
550
00:46:52,527 --> 00:46:56,076
as we'll voyage to the bottom of the deep ocean.
551
00:46:58,047 --> 00:47:02,962
MAN ON RADIO: Atlantis, Alvin.
Depth 1712 on the bottom.
552
00:47:03,967 --> 00:47:07,243
MANNING: We'll be following the journey
of the research submarine Alvin
553
00:47:07,327 --> 00:47:10,444
as it ventures thousand of metres
below the waves.
554
00:47:11,567 --> 00:47:15,480
On board are scientists intent
on studying at first hand
555
00:47:15,567 --> 00:47:20,595
the strange volcanic realm where
new ocean floor is continuously being created,
556
00:47:21,327 --> 00:47:23,477
the next stage in Earth's story.