All language subtitles for Bbc.men.of.rock.S01E02.MVGroup.org.English-WWW.MY-SUBS.CO

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Whoo hoo!

I'm here!

This is it.

There's the top just there.

Ah, this is fantastic! What a view!

I'm back.

I was last here 25 years ago.

25 years!

And somewhere around here
I left my hammer.

Ah, look at this! Here we are!

Whoo!

Would you look at this?

Look at this view.
This is what I remember.

This is our ancient heritage
laid out before our very eyes.

Scotland's landscape
has an epic and violent past.

Hidden in these mountains and glens
is the history of the planet.

I'm going to show you
how this landscape was used

by a bunch of brilliant, maverick, eccentric
scientists to solve the greatest mysteries of the Earth.

I'm following in the footsteps
of these pioneers

who blazed a trail
where no-one had been before.

They showed vision and
determination...

.. to piece together baffling
evidence

and uncover the forces
that shape our world.

Wow! God, that's so hot!

It's all out there
if you know what to look for.

Written into the Scottish landscape
is the story of the entire planet.

The remote
northwest Highlands of Scotland.

Ever since people were first drawn to these
mountains, they wondered how they were formed.

How did they come to be so high?

So dramatic?

For thousands of years, people believed
these were the work of a divine creator.

But by the 19th century, a new branch of science had emerged
- geology.

Scientists began to ask bold new
questions about how our Earth was formed.

In 1855, a geologist named Roderick
Murchison was on his way to the Highlands.

Roderick Murchison was
an establishment man.

He'd started off in the Army and then he married
into money, and it was at his wife's suggestion

that he took up geology as a more purposeful
pursuit than his hobby of fox hunting!

Murchison was the most famous
geologist of the day.

Head of the British Geological Survey, he was
an authority throughout the British Empire.

And he started the process that led,
over the next century,

to a true understanding of
the way the planet works.

Murchison believed that he could explain how the
magnificent Scottish landscape had been formed.

Murchison has come up his own big grand scheme,
which he claims can unlock Scotland's geological past,

the story of its landscapes and mountains,
and it's based on one very simple idea.

The start point for Murchison's
grand scheme was very logical.

All of Scotland's
mountains and landscape

were made up of layers of rock, laid
one on top of another over time.

There was much to be said
for this idea.

You can see why if you come to one of the most
dramatic and inaccessible landforms in Britain...

.. the Old Man of Stoer
on the northwest coast of Scotland.

First, there's just the small
matter of getting to the top.

I dare say that what I'm about to do
wouldn't have fazed Murchison at all

but, for me, this is a bit of a leap
into the blue, really.

Literally!

What could possibly, possibly go
wrong?

Ah!

Look at this!

Whoo hoo!

Oh, it's quite far, isn't it?

Blooming 'eck!

This may seem rather extreme,

but when I get there, this stack will show something
very important about how the landscape is formed.

Whoo! Ah!

Final push.

Here we go. Let me touch it.

The stack of Stoer!

I'm here! Almost!

This sea stack I'm standing on
has been scoured by the sea

so that it's completely detached
from the headland

and that means it gives this wonderful three
dimensional slice right down through the landscape.

You feel as if you are on
the top of the world here!

As I abseil down this stack, a close look reveals
something crucial about the way it was created.

These bands of rock around me
are like layers on a cake.

Murchison and the early geologists recognised
that rocks like these started out as soft sediment

laid down by water
and then solidified,

building up one after another
over millions of years.

So that means that the rocks 20 metres below me
are millions of years older than the ones here

and maybe tens of millions of years older
than the ones at the top of the stack.

This idea of young rock on top of old was
the foundation for Murchison's thinking.

But he took it much further.

As he travelled across Scotland, he saw
how exposed rock lay in angled layers.

He believed these layers were
piled up in a simple pattern,

with the oldest rocks on the west of the
country and the youngest rocks on the east.

For Murchison,
it was all so beautifully simple.

He was convinced that the northwest
Highlands were built up

layer upon layer, just like this
stack of slate here.

And if you walked inland
from west to east,

you travelled through a cross
section of younger and younger rocks.

Because Murchison was the top dog
of geology for 40 years,

this grand, but simplistic scheme
becomes dogma.

It was all very logical and plausible
and the evidence seemed to stack up.

Murchison was so sure he was right,
he used his influence

to out-manoeuvre his rivals
and quash any alternative theories.

But if only it had been that simple.

That mountainside over there seems at
first glance to be the perfect example

of Murchison's regular succession of
layers of rock stacked on top of each other.

But actually a discovery made in the hills around
here would shatter that neat little picture.

In 1882, a former schoolteacher
came to a windblown shepherd's hut

overlooking Loch Eriboll on the very
tip of Scotland's north coast.

Charles Lapworth was a passionate
amateur geologist, modest and self-taught.

What he discovered here
would demolish Murchison's theory.

When Lapworth came here, he
stayed in this old shepherd's hut

and for weeks braved the elements and went up
daily wandering into the hills to do his work.

And the key to the phenomenal success that he
had up in those hills was his painstaking methods.

He even would wear this special coat
which had all these pockets in it.

It's kind of like a portable
filing cabinet!

And in there he would collect little samples of
rocks and samples of fossils and tuck them away.

That allowed him to cover the ground inch by inch,
collecting samples as he went in incredible detail,

far more detail than that practised by the
so-called expert geologists of the time.

Lapworth suspected that Murchison's
theory was too simplistic

and he was unwilling to accept
the established view.

So he set off into the hills in a
bid to solve the riddle of the rocks.

With little more than a compass and a handful of
tools, for six weeks, he trudged over these hillsides.

WIND BLOWING

Rob Butler has been studying the very same
mountains around Loch Eriboll for decades.

Do you think Lapworth did this -
whoo hoo!

How on earth do you work in these
conditions? It's unbelievable!

It's a little light breeze,
a light breeze!

A light breeze! It's the
strongest wind I've ever had!

I hope you had your porridge for
breakfast. Weighing me down!

Lapworth was driven.

He surveyed the landscape in much more
detail than the Victorian professionals.

And on this cliff face
on the flanks of Ben Arnabol,

he found the evidence that changed
our idea of how mountains were formed.

So, is this it?
Yeah, this is where Lapworth came.

Fantastic.
Yeah. Let's go and have a look.

You can imagine Lapworth seeing
this place, and he could recognise

these should be simply layered and they should simply
go up into younger and younger and younger rocks.

That's what Murchison thought - that
it just goes up and up. But up there,

he went, hang on a minute! Those
don't look like younger rocks to me!

That stuff is the oldest rocks in
Britain, so how could you possibly

get the old rocks sitting on top of
the young rocks that are down here?

So for people like Murchison, they were quite happy
that was just a regular stacked sequence of rocks,

but Lapworth could tell
that it was wrong.

Lapworth had to establish how come you've
got the older rocks sat on top of the younger?

What's going on at this contact?
That's where the action is.

When Lapworth examined the cliff carefully, he
spotted something no one had noticed before -

a thin layer sandwiched between the
old rock above and the young rock below.

What Lapworth recognised was that the
old rocks had been reprocessed and ground,

rather like an industrial mill,
processing and grinding it down

into sort of a very streaky-looking,
smeared-out material.

And this is the brilliant bit because
he realised that this processing

involves a grinding
and, therefore, a horizontal motion.

This thin streaky layer showed Lapworth
something then almost unthinkable.

The ancient rocks above had been grinding slowly
sideways up and over the younger rocks below.

So that slab of rock above
has been sliding towards us really,

it would have been over our heads, and the
bottom of it was all getting crushed along.

Yeah. The old rock started out underneath, so it's
been brought up and over and across. Thrust over.

Murchison had believed the landscape
was made up of sedimentary layers

that got progressively younger
the further east you went.

But Lapworth had discovered evidence

that the formation of Scotland's
mountains must have been much more violent.

It is a truly revolutionary way
of looking at rocks

and the idea that they involve big
motions and grinding processes,

it does change fundamentally the
way in which you view mountains.

Lapworth saw that mountains
could be built in a whole new way.

The layers of rock didn't follow a
simple sequence of youngest rocks

on one side of the country
and oldest on the other.

They could also be thrust up and over each
other by massive sideways movements of the Earth.

This box is a replica of a model
that the Victorians used to explain

how sideways movements
built mountains.

I'm just putting a layer of black
sand along the base of the box here,

and that's going to be our
first geological layer.

I'm going to have to get a move on!

These sand layers represent
the mountainside behind me.

I'm just going to put the lid on.

I'm going to turn this wooden handle
which is going to turn this screw

and send these wooden blocks
into the layers

as if a great sideways force
is crashing in.

Going do it really slowly though.

There we go.

There she goes!
Look at that, it actually works!

You can see that this slab of rock
strata has been thrust up and over

the top of this slab of rock strata,

which is exactly what Lapworth
was saying.

Look at it go!

Look at it! It's like a bulldozer,
that's exactly what it's like.

It's beautiful. I never thought
it would be this good.

A whole series of
zig zags are forming

and what we are doing, look behind,
we're building mountains.

And the point is that is exactly
what's going on over there.

Get out of here!

What the amateur Lapworth
had spotted in the Highlands

made a total mockery of
Murchison's grand orderly scheme.

But for Lapworth, the revelation that vast slabs of
rock could move so dramatically left him overwhelmed.

Whether it's the excitement
of his discovery

or the relentless pace of the work,
it all proves too much of a strain.

Nightmares plagued Lapworth.

He tosses and turns at night, imagining the
weight of great sheets of rock grinding above him.

Some say
he suffered a nervous breakdown.

Lapworth did recover and
he published his findings in 1885,

but he was fearful of how
his ideas would be received.

And for good reason.

The geological establishment did not
want to be upstaged by a mere amateur.

There's a final ironic twist
to this story.

Recognising that trouble was afoot,

the Murchison camp sent in their crack team
- Ben Peach and John Horne,

two of the top geologists that were so good and so
inseparable, they were dubbed the Heavenly Twins.

Peach and Horne were
a perfect scientific partnership.

John Horne was analytical, but Ben Peach
was as much an artist as a geologist.

His paintings capture brilliantly
the structure of rocks and mountains.

The Heavenly Twins set off into the
Highlands with a very particular mission.

Their job was to kill off
the Lapworth idea, once and for all.

But to their surprise, instead of
demonstrating that he was wrong,

they proved
that Lapworth was dead right.

Peach and Horne found a whole range of mountains in
the West Highlands thrust up by big sideways movements.

Lapworth was completely vindicated.

Although in his lifetime, sadly, he never received
the credit his brilliant discovery deserved.

The mountains of
Scotland had revealed

that the world was now more violent
than had previously been thought.

Rather than a simple build up
of layer upon layer of rock,

landscapes were also clearly
formed by huge forces

that could thrust billions of
tonnes of rock up and over itself.

This realisation only created
fresh puzzles for the men of rock.

Where did these massive movements
in the earth come from?

What could cause solid rock
to move sideways so powerfully?

The early geologists didn't realise it, but one
of the biggest clues was right under their feet.

It was lying deep underground,

in the very same corner
of the Scottish Highlands.

Just a few miles away from the mountains
Lapworth conquered, is this dramatic cavern.

The mysterious Smoo Caves.

I love exploring caves.

You always feel as if you're
entering a kind of lost world.

For geologists, they're brilliant because they can
let you in, you can see the rock in all its glory.

This rock's made of limestone
and rocks like limestone

can take you to a time and a place
where Scotland was very different.

There's a whole swathe of these types of
rocks running up and down the West Highlands.

What's special about them
is something they contain.

As Peach and Horne
investigated Lapworth's theory,

they made an extraordinary
discovery of their own.

I know this must look like
an overgrown woodlouse,

but this is actually a really
special fossil - a trilobite.

500 million years or so ago, you'd have found
them swimming around in the warm shallows.

You get thousands of them
all over Scotland,

but the ones from this area
were beautifully drawn by Ben Peach.

You can see his sketches here -
look at that! Fantastic artist.

He's got this exquisite
attention to detail,

but even more amazing
is the story they tell.

These seemingly insignificant little
fossils date back 500 million years.

But they're far more
than just ancient creatures.

They were part of a jigsaw of evidence that
would help to explain the movement of mountains.

I'm drawing a map to show something
intriguing about the trilobites.

Something that utterly confused Peach
and Horne and the other early geologists.

It's not the trilobites themselves
that were important,

it was the type of trilobites
and where they were found.

The trilobites that were found
in England and Wales

were the same type they found
right across continental Europe.

But they were completely different to
the trilobites that we find in Scotland.

The Scottish ones were the same
as those that were found

in places like Greenland
and Newfoundland down here.

In other words,
similar to those in North America.

The big question was why?

It was a complete mystery.

The Victorians came up with
all kinds of explanations.

One idea was the trilobites had crossed over on a
bridge of land between Scotland and North America

which was washed away
during the Biblical flood.

Seems outlandish today,
but for Victorian geologists,

it was the most plausible
explanation they could come up with.

But then, another strange
piece of the puzzle began to emerge.

On December 23rd 1872,
a ship set sail for an epic voyage.

A three-year journey,
covering 70,000 miles.

The HMS Challenger was the first to
carry out a survey of the ocean bed.

On board was a Scottish scientist, Charles Wyville
Thomson, a pioneer of ocean floor exploration.

Sailors and scientists knew very little
nothing about the depths beneath the waves.

Thomson's survey laid the way

for the first network of deep-sea telegraph
cables and a new era in communications.

To survey the sea bed,
Wyville Thompson's ship had

miles and miles of rough hemp rope
at the end of which was a lead weight.

They would hang this over the edge
and just chuck it overboard really.

The lead weight would
plunge to the bottom.

That was the easy bit. The hard work starts
when you're hauling this thing back in.

It must have been absolutely hell.

You can imagine doing it when
the boat's pitching and tossing.

The rope's just slicing
through your fingers.

It's cold, it's wet,
you're miserable, you're exhausted

and all the time you're trying to count
the number of fathoms you're hauling up.

And at the end of it all, you've got
a single measurement of the depth

and you've got to do that
thousands more times.

After years of painstaking
measurements,

Wyville Thomson and his crew located
something strange on the Atlantic seabed.

Roughly half way to America,
the ocean floor rose sharply.

Instead of five miles to the bottom of the sea,
they discovered it was suddenly less than two.

Wyville Thomson was mystified.

At first, he thinks he's stumbled
upon a submerged mountain,

but as the survey progresses, it
becomes clear this is much bigger.

A colossal ridge running from one pole to the
other, right down the middle of the Atlantic Ocean.

Wyville Thomson had discovered,
not an ancient land bridge

between Britain and America,
but something even more curious.

A chain of underwater mountains
that rises from the ocean floor

and runs 10,000 miles
from the Arctic Sea in the north,

down the middle of the Atlantic
almost as far as Antarctica.

The origins of this Mid-Atlantic
Ridge were a complete mystery.

It was the 20th century before geologists
came up with a possible explanation

for Lapworth's
sideways movements of the Earth,

Peach and Horne's isolated trilobites
and Wyville Thomson's Mid-Atlantic Ridge.

The explanation was based on an idea
people had spotted as far back as the 1500s

when the first
atlases of the globe were drawn.

Take a map of the world and cut
out the landmasses. There we go.

There's South America.

And I'm really not going to do
all these islands, just do that.

I'm sorry to the northern islands of
Canada.

They've got to go.

When you've cut out all the landmasses, you
can do this trick of fitting them together.

Here's South America and Africa and
we can move them close together.

Look at this join here.

It's so snug.

And then here's little Madagascar...

just tuck it in there. Here's India.

Move India up, it tucks in here.

North America, just bring it down...

and it fits snugly into there.

This trick of the maps
led some geologists to think

that all the world's landmasses
were once joined together...

and that they'd slowly drifted apart

and re-arranged themselves
over time.

An idea they began to call
continental drift.

Perhaps Wyville Thomson's
Mid-Atlantic Ridge was a giant scar...

the crack where this ancient
super-continent had split apart.

Continental drift was
a very clever theory,

but what could cause it to happen?

Huge forces were clearly at work.

But the men of rock struggled
to make sense of their discoveries.

Then, early in the 20th century,
a gung-ho geologist -

again, working in Scotland -

found another part of the puzzle.

The Highlands near Glencoe.

For many, a wet and sometimes
miserable experience.

Back in the early 1900s...

Ohh...!

.. an intrepid young geologist, Edward
Bailey, had a bracing daily routine out here.

Oh! Oh!

You think, "It's going to be cold,
it's going to be cold!"

But, boy, it's cold!

Agh, I knew it was going to be cold!

Bailey spent years training himself
to be tough.

As a boy, he invited classmates
to slap him in the face

to test his endurance.

He became a boxing champion

and slept with windows
wide open in winter.

And nothing pleased him more
than his daily, naked swim.

Ah...

When I think about Bailey,

I'm torn between thinking he's an
absolute hero and an absolute nutter.

I mean,
he used to do this every day.

Just dive into some loch
or some river.

And then he'd, kind of, put on his
clothes still wet

and head off into the mountains.

Here's me with all the gear.

That wasn't the style
for our Bailey. Look at him.

He's got these all-weather shorts.
Look at him, in the snow!

And when the survey told him that
wasn't professional enough,

he told them to stuff the job
and resigned.

No-one could
ever argue with Bailey.

The shorts stayed on.

In 1905, Bailey, came
to the peaks of Glencoe

to join the British Geological Survey
team who were mapping the Highlands.

What they found was evidence of an
explosive era in Scotland's ancient history.

When geologists first started
investigating Glencoe...

they realised there were
lots of volcanic rocks here.

The whole place is stuffed full
of them. But they didn't know why.

What were they doing here
in the heart of the highlands?

Bailey and his team
set off to find out.

Inch by inch, they set out to
carefully map and survey the landscape.

Bailey was often frowned upon

since he took official maps and
completely redrew them as he saw fit.

He was devoted to his fieldwork
in the mountains.

He famously used to eat his lunch straight
after breakfast so he didn't have to carry it

and if his feet got wet while
crossing rivers or fords, no matter,

the holes in his boots
let the water drain out. What a guy!

As Bailey climbed through Glencoe,

he began to follow a dramatic crack
up the side of the mountain.

He and his team traced
the line across the landscape.

And when they drew up their map,
it revealed a giant circle.

Bailey realised this was
no ordinary geological feature.

He wondered if it was the mouth
of a massive volcano.

Then he looked more closely
at the rocks themselves.

Now as Bailey and his team were
going along rivers like this,

they kept finding two types of rock
that started out as molten magma.

One of them is this, it's a granite.
It's got really big crystals.

The other one has got really fine
crystals. You can't really see them.

Molten rock deep underground cools
very slowly

and large crystals
have time to grow.

But molten rock that has exploded
out into open air cools rapidly

so crystals don't have time to form.

We've got one rock that's down deep
and the other rock near the surface,

yet, here, they're found
side by side.

Bailey wants to know why.

Then Bailey made a connection.

The two rocks and the huge circular
crack in the landscape

told him he was stood on the remains
of a very special kind of volcano,

one that would reveal the enormity of
the forces that had shaped the continents.

I'm going to build a model
of how he saw it working.

I know this looks crazy, but I'm making
my own wee miniature version of Glencoe.

I know this barrel
has just got mud and water in it

but, to me, this is a subterranean
pool of molten rock - magma.

Should be red hot really.

The thing is
that this magma is erupting up

and spewing out
at the surface of a volcano.

I'm going to build
the top of that volcano.

When volcanoes erupt,
the lava and ash builds up...

higher and higher, forming
a huge heavy cone at the top.

What Bailey realises is that,
eventually,

the top of the volcano
would get so heavy

that the weight of it
would sink into the magma below.

I'm covered in magma.

I'm covered! What would happen is
the magma would come rushing out.

Bailey realises the volcano has
broken along that circular faultline

and collapsed violently
in on itself,

creating the most almighty explosion

and that explains
why those two rock types -

one at the top of the volcano
and the other deep in its roots -

are now lying side by side.

What Bailey had discovered was a colossal new type of volcano
- a caldera.

Calderas produce the most
explosive eruptions on Earth.

They're a type of mega-eruption

caused when a volcano
collapses in on itself.

As the Glencoe volcano erupted, the
magma chamber below began to empty...

the base could no longer support
the top.

The heavy upper cone
collapsed inwards...

and caused a catastrophic explosion.

Bailey had identified one of the biggest
supervolcanoes in Earth's history.

For 45 years, he mapped monuments
to Scotland's violent volcanic past.

He discovered the country
was covered in volcanoes.

Bailey and his fellow geologists
surveyed a great line of them,

stretching along the islands
of the west coast of Scotland.

Ardnamurchan -
with its perfect ring structure.

The cliffs on Eigg,

solidified sheets of molten rock.

And the mighty Cuillin Ridge
of Skye.

But did Bailey's discoveries have anything to
do with trilobites and the Mid-Atlantic Ridge?

Could his discoveries help explain
the theory of continental drift?

The men of rock now had
several pieces of a jigsaw.

Lapworth had discovered solid rock had been
pushed sideways to form mountain ranges.

Peach and Horne had found fossils in Scotland that
appeared to match those from far side of the globe.

Bailey had revealed the immeasurable
power inside the Earth.

And Wyville Thomson had uncovered
a giant ridge on the seabed.

But no-one could understand
how they were linked.

They had observations but nothing
to tie them together.

It would take a geological genius
to solve the puzzle.

I'm at the biggest balloon
festival in Britain...

.. because the theory that united
the men of rock's observations

came not from studying mountains...

but from something much
more familiar to us all.

Heat.

I love watching this - the effort to
get these things off the ground,

all the noise and the action,
the heat when you get close.

And it's a real battle. You can
see them fighting with the balloons

as if the balloon doesn't want to go up
but that hot air just keeps piling in there

until eventually it accepts
the inevitable and just rears up.

And that's really what's
driving it there, just hot air.

It's pure physics in action.

We all know warm air rises.

That's what makes these
balloons lift off.

It's a simple but fundamental principle
of physics. It's called convection.

Heat from the burners warms the huge
bubble of trapped air inside the balloon.

It becomes less dense
than the colder air outside...

.. so up it goes.

And it's this principle that would turn another
man of rock into the unsung hero of geology.

Arthur Holmes was one of the most
brilliant minds of the 20th century.

He was a professor at Edinburgh
University, a geologist and a physicist.

He was fascinated with the heat
deep inside the Earth.

In 1928, he put forward an
extraordinary and controversial idea -

that molten rock could behave
just like hot air

and perhaps heat, convection,
could be driving the movement

of the entire surface of the planet
over millions of years.

I'm meeting geologist John
Underhill who's going to show me

how Holmes's ideas work in the lab.

First, ice goes under one
end of this fish tank.

Just put a couple more in.

At the other end of the tank, John
creates a much hotter temperature.

I'm going to slip this heater,
a hot plate, underneath this end.

And he's using coloured dyes
to track the movement of the water.

I now need to roll my sleeves up
and put the dye into the fish-tank.

First, he puts blue dye
in the cold end.

That's fantastic.

In the hot end, he puts red dye.

It'll show how heat can create
different types of movement.

It's quite hypnotic watching it.

Now we see it starting to spread.

You can see it starting to go up
there. This is convection.

It's beautiful, isn't it?

The hot plate makes the
warm, red water rise,

just like the hot air balloons.

On the other side, the cold
water is denser, so it sinks.

This rise and fall
makes something crucial happen.

This is where
it's going to get really interesting

because it hits the top surface, nowhere
to go, so it starts to go horizontally.

That is gorgeous.

And we can see it moving sideways
and actually starting to come down.

This is the crucial thing.

We've got horizontal motion
of the water column,

so a conveyor belt is set up,
this convection is set up.

This was Holmes's big breakthrough.

The rise and fall of heat
drives sideways motion.

He realised that if this was
molten rock, not water,

you'd have a conveyor belt that powered
massive movements of the Earth's crust.

We're replicating
it in a liquid - water -

but what Holmes is getting at is that
solid earth actually behaves like a liquid.

Absolutely. I think the key insight
that he could bring to all this

was he could imagine that what we are
seeing here happens within the earth

and, thereby, he was able to recognise
the engine that drives continental drift.

Now that was revolutionary. That was
different and it was out of kilter.

He was considered a maverick for even
saying that continental drift was possible.

Holmes proposed that heat from the Earth's
core drives semi-molten rock to the surface.

It splits apart the crust
at the Mid-Atlantic Ridge.

Where it cools, it's forced
back into the inner Earth.

And a cycle of convection
is produced.

This was Holmes's great insight.

Holmes sees it clearly.

Heat from the inner Earth
producing a huge convection cycle.

It's that cycle that moves the continents
sideways on the surface of the globe.

Now, at last, the jigsaw
puzzle was complete.

Lapworth's mountains showed how these sideways
movements thrust old rocks on top of young.

The Glencoe caldera showed where these movements
forced the Earth's crust down into the inner earth.

One part of the crust was forced under the other,
melting to form a deep pool of molten rock...

which burst violently
back to the surface.

And Wyville Thomson's
Mid-Atlantic Ridge

showed where convection
pushed the Earth's crust apart

and new rock
was forced upwards from beneath.

In World War Two, Holmes spent
many hours on fire-watch duty.

He had the time to write down everything he knew
about geology and, also, his most radical ideas.

And in 1944, he published his work.

The Principles of Physical Geology.

It went on to become the single most
important geology book of the 20th century.

This is actually a big deal for me

because this is the original version
of Holmes's book.

It's fantastic leafing through it.

Great stuff. This, when it came out,

almost immediately made
the geologists' best-sellers list...

and I guess it became our bible,
really.

I had, I think, the fifth edition which got me
through university. So it's dear to me. The thing is,

Holmes really wrestled with the idea of whether
to put his theory of convection into this book

and he kind of slides it in at the last minute,
the very last diagram in the book. There it is.

This is the first time that convection as a
mechanism for moving continents was laid out.

You can see here the hot magma
rising up as currents,

moving sideways and descending back
down again.

It's interesting here,
I just noticed, he says,

"This is to illustrate a purely hypothetical
mechanism for engineering continental drift. "

He's hedging his bets here,
covering his back.

He knows it's controversial so he's going, "If
it did happen, this is one way it might happen. "

But you get the impression,
the very fact he's got it in there,

he knows, he really believes in it.

It seemed like the perfect theory.

Now all it needed was the proof.

It came from a horrifying source.

The Cold War brought an
unexpected revelation.

When a worldwide treaty banned
nuclear tests in the atmosphere,

bombs were then detonated
underground.

The Americans needed
a method of surveillance

to monitor tests around the world.

They set up a global network of seismometers
to listen in on the tremors in the ground.

Then, as they look for telltale
vibrations from enemy nuclear tests,

they found something completely unexpected
about the structure of the Earth.

The seismometers detected, not just
nuclear tests,

but geological events
across the world...

.. volcanic eruptions
and earthquakes...

.. each tremor a pinpoint on a map...

.. until a pattern emerged.

This all looks a bit psychedelic

but this is the most important recent
development in the history of geology.

The world map of tectonic plates.

It explains how the planet's most
devastating events -

earthquakes and volcanoes -
all lie along plate boundaries.

What it really shows is where
the geological action is.

Like over here in the middle of the Atlantic
where two vast slabs of crust are spreading apart.

Or over here along the edge of the Pacific
where two slabs are colliding together.

You can see right around the
Pacific, the so-called Ring of Fire.

All these surface motions are
powered by convection from below.

Just as predicted by Holmes.

Heat deep in the Earth has driven
our entire geological history.

For millions of years,

the tectonic plates have moved back
and forth the surface of the planet

to create the globe
we recognise today.

The movement of continents explains
the mystery of why fossils from Scotland

are so similar to those found thousands
of miles away across the ocean.

The fossils of Scotland
match North America

because they were
very close together.

Scotland was once part of an arc of
islands strung out

along the edge of a vast continent,
Laurentia, with America at its heart.

500 million years ago,
Scotland was on the Equator

and part of an ancient
North American continent.

Thousands of miles away,
separated by a vast ocean,

England was part of a
different continent too.

Over millions of years, those two
ancient continents collided...

.. and Scotland finally
came together with England

in an incredibly slow but immensely
powerful act of union.

Today, you can still see the results
of this great geological clash.

These cliffs became crumpled when
the two continents collided.

They sit on the border between
England and Scotland at St Abbs.

Layers of rock that were laid down
flat on the ocean floor

have been thrust up
vertically out of the ground.

For geologists, it's one of the most
remarkable places in the British Isles.

These rocks are so crumbly!

This whole thing just feels...
really precarious!

These buckled rocks look like they've
been in some kind of giant pile-up.

These ones are angled in one direction. Just down
there, they're angled in the opposite direction.

It's because this whole coastline
is the site of a giant collision,

albeit a very slow one,
between England and Scotland.

This clash between
the ancient continents

forced the rock layers into
striking shapes and angles.

It's this collision with England that
forced up the mountains of the Scotland,

fuelled volcanic eruptions
and shaped the landscape.

Finally, I'm returning to
the Scottish mountain

where I was inspired to become
a geologist, a man of rock.

Dun Caan on the Isle of Raasay
near Skye.

This mountain top
is so important to me

because this is where I first learned
to read the rocks, read the landscape.

The fact that we can do that today is all down to countless pioneers
- amateurs and professionals.

People like Lapworth,
people like Bailey.

It was because of them that we understand
Scotland, and through it the world.

Next time, I'll look at the
daredevil scientist

who revealed that our land had been
gripped by a great and ancient ice age.

I'm getting squeezed!

And the humble janitor who wondered if the
causes of the Ice Age lay in the heavens.

Oh. The sound of the Ice Age.