All language subtitles for Bbc.men.of.rock.S01E03.MVGroup.org.English-WWW.MY-SUBS.CO

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Whoo-hoo! I'm here! This is it!

Ah, 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!

Ah, 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.

This boulder I'm climbing is
a genuine puzzle.

I mean, it's huge, but the mystery isn't
its size, it's that it's here at all.

The rocks around here are
completely different.

It must be three times my height,
and weigh in at half a thousand tons.

So how on earth did
this alien rock get here?

This one stands completely alone
in rolling Scottish countryside.

Similar rogue boulders lie
scattered all over Northern Europe.

In the early 1800s, people struggled
to understand their presence.

Scientists couldn't ignore them, but
they couldn't explain them either.

The most extreme suggestion of the time,
the one that I like best, was by a Frenchman,

who figured that these huge boulders
were fired from underground caverns

with the force of compressed air.

Much like a cork exploding from
a kid's pop gun.

'The solution to these curious rocks lay in
one of the most powerful forces of nature.

'September 1840,
the Scottish Highlands.

'Two close friends have been travelling
through some of the wildest parts of Scotland.

'800 miles in just two weeks. '

It wasn't easy to get around
the Highlands.

The two men trek for miles,
clamber up steep hillsides and cross

expanses of water to get closer to
the rocks that they want to study.

'They're on a mission to try to
understand the very shape of the Highlands.

'Why it's a land of great peaks
punctuated by magnificent lochs. '

The two men couldn't be
more different.

Louis Agassiz, an adventurous
Swiss scientist.

Serious minded,
a bit of a daredevil.

The other man is
Britain's leading geologist.

William Buckland is
a bit of an eccentric.

He wears his academic gown and top
hat in the field, whatever the weather.

'William Buckland was about the only person
around who believed in the young Swiss scientist.

'Agassiz was just 33, yet had
an idea that would revolutionise

'our understanding of
the geological world.

'Together, they looked at
the shape of the glens.

'They examined the isolated boulders
that dot the Highlands.

'It all struck the young scientist
as strangely familiar.

'He'd seen this type of landscape
back home.

'Agassiz's radical idea had first come
to him in his homeland of Switzerland.

'This is the Morteratsch Glacier
in the Swiss Alps.

'Agassiz grew up with this world of
snow and ice on his doorstep.

'In the late 1830s, he devoted his time
to studying great glaciers like this.

'Vast sheets of ice that covered
the sides of the Alps. '

Those are nice crevasses
over there. Let's cross one.

'Agassiz's journals tell us how he
was lowered right down inside a glacier

'to try to discover
its scale and size. '

Hello! It goes all dark there.
Hard to see how far...

We can't see the bottom.

'With the help of mountain guide
Gian Luc, I hope to do the same. '

Down here... OK.

It's amazing, all this modern
equipment that we've got now,

compared to what they had
150, 170 years ago.

It was much harder than now.

I think when Agassiz came here, he
had a hat made out of marmot skin!

He probably came in lederhosen
and a tweed suit or something.

I just don't know how far it goes,
that's the trouble.

It goes down, and there's a lip,
and then it just goes dark.

When Agassiz went down,

he got himself lowered
40 metres down, right?

When he got to the bottom,
he found...

Agh! He found himself in
not hot water, but cold water.

He was in the meltwater
at the bottom of the glacier.

He ended up being half drowned.

They had to haul him out.
He called it his descent into hell.

All right? Yeah, everything's fine.

'As I climb down, it's hard to forget
that Agassiz nearly died in his crevasse. '

OK? More? Yep.

More.

Keep going, keep going,
keep going, keep going! Hey hey!

Loads of water down here,
and it's streaming down the sides.

The overall sense you get is that
feeling of the ice bearing in on you.

It's really narrow.

What Agassiz really noticed was
the weight of the ice above

compressing down
on the layers below.

And you can tell that pressure's been building
up, because the ice down here is virtually blue.

It's really fine. All of the air
bubbles have been squeezed out of it,

like I'm getting squeezed
at this moment!

'Down here, you get a real sense of
the sheer scale and mass of the glacier.

'In fact, a glacier 100 metres thick will bear
down with a force of 88 tons on each square metre. '

Hey! Hey! Thanks!

'Every summer for five years, Agassiz
returned to the mountains to study the ice.

'He wanted to find out if the immense pressure
of the glacier was somehow put into action. '

The first clue that Agassiz
noticed was something peculiar

going on with his research hut
that he'd built up on the glacier.

It wasn't where he'd left it.
Every season he came back,

the hut seemed to be closer and
closer to the end of the valley.

He must have thought, "That's a bit odd. Either
the mountains or the hut must be moving. "

About here? From there to there? OK.

'Agassiz was determined to
discover why his hut moved.

'He carried out an experiment,
the first of its kind.

'I'll recreate it with
glacier expert Jurg Alean. '

I think we put
the next one about here.

'It's as simple as it is clever.

'Agassiz drove wooden stakes across the
glacier, one stake every 50 metres or so. '

I think it's pretty good
in line. Yep.

Now, you wouldn't expect something as solid as
this to move, but Agassiz, he suspected otherwise.

He tracked the positions of those stakes
over one year, over two years, and on.

Now, we've not got time to hang around and
wait for that, but I can show you what he found.

'Agassiz discovered
the stakes did move.

'And if they moved, it meant the
entire glacier, millions of tons of ice,

'was also moving slowly
and inexorably down the mountain.

'A remarkable finding.

'His team made beautiful engravings
of vast rivers of ice,

'which flowed down
the valleys of the Alps. '

And those experiments, like the
stake experiment, seem very simple,

but they gave him
really interesting results.

Yes, it was their method of
measuring the speed of the ice,

how much it runs during one year,
or two years or three years.

It was the only way of doing it.

So tell me, how fast were
some of these glaciers moving?

Well, they found out that the ice moved 30 or
even 60 metres in the middle of the glacier.

In one year, that is.

Because, you know, the ice is rock hard,
right? You can hit it and it breaks like glass.

That is beautiful, isn't it?
But on a different time scale,

it's like a slowly-moving fluid.
So it changes from year to year.

'Jurg Alean's webcams expose
the secret life of glaciers.

'In 15 seconds, we can see what
Agassiz took five years to record.

'For me, it's impressive to see an
apparently-immobile glacier really flowing.

'With just sticks and clever logic, Agassiz had
proved that glaciers travel down the mountain.

'And that's not all.

'He found out the pressure of all that ice
grinds out rocks in its path and scoops them up. '

This is the kind of thing that Agassiz
would have been absolutely intrigued by -

a boulder embedded in the ice. There's plenty of
smaller ones, but this is the biggest one I've seen.

And Agassiz realised that it's this rocky debris
that was essentially the teeth of the glacier,

it was this that was
eating away at the land.

'Agassiz had a further revelation.

'In the foothills of the Alps were
huge boulders.

'He suspected they had something to do with
the glaciers further up the mountains. '

Now, here is a familiar sight.

It's one of these
mysterious alien boulders.

The French call them
erratiques - wanderers.

And Agassiz was convinced that
these were transported by ice.

'These boulders fascinated him.

'He and his colleagues mapped their
positions over wider and wider areas.

'What Agassiz found would lead him to an
extraordinary theory about the Earth's past. '

I love old maps, and this one is
especially beautiful.

I mean, look at this picture
of an erratic boulder.

Now, the map itself covers most of
Switzerland, then goes up into France,

and the creamy areas show the
distribution of these erratic boulders.

'The glaciers were
only in the mountains,

'yet many boulders were down
in the lowlands, far from any ice.

'The glaciers seemed to have
once covered a much larger area. '

Trapped within that massive
ice sheet were boulders like this,

boulders that, when the climate warmed and the ice
thawed, were left scattered across the countryside.

It's a beautifully elegant,
but simple, idea.

'If the glaciers had been far more extensive,
then Agassiz believed he should be able

'to find other evidence
of their work in the landscape.

'He proposed that these shallow grooves were created
by rocks in the glacier scraping over the land.

'And even more spectacularly,

'that the great U-shaped valleys of the
Alps were giant grooves carved by glaciers.

'He called the glaciers
God's great plough.

'But Agassiz didn't stop there.

'What if it wasn't only the glaciers of
Switzerland that had melted and shrunk?

'What if, long ago, there'd been ice
everywhere, that had now vanished?'

This is how one of the most radical
ideas in the history of science

began to take shape. The idea that
the climate was once much colder,

and that glaciers smothered
much of the area of Northern Europe.

'Agassiz's theory of a great
and ancient Ice Age was bold.

'But so far, he'd only studied
the area around the Swiss Alps.

'To prove it, he'd have to go
much further afield. '

He hoped to find the killer clues in
a foreign land that showed signs of

having once had glaciers
but which was now ice-free.

And so began
the whole Scottish adventure.

'This is why Agassiz came to be
in Scotland in the autumn of 1840,

'along with fellow scientist
William Buckland.

'He wanted to discover in Scotland the same signs
of ancient glaciers he'd seen in Switzerland.

'If he succeeded, his theory of
a huge Ice Age would be vindicated.

'Together, they toured
the Highlands.

'Agassiz was sure that only huge frozen forces
could've gouged this glen into a U-shape,

'just like
the Alpine valleys back home,

'or carried this rogue boulder
across the land,

'similar to those
he'd found in the Alps.

'But Agassiz's theory of a frozen past didn't just
explain the obvious features of the Highlands. '

It's funny,
that's all that's holding it up.

'One of the most dramatic
is best seen from the air. '

Woo-hoo!

Oh, that was good!

Fantastic!

Great Glen, here we come!

Ah, this is the way to travel!

This is the way to geologise!

None of this horseback rubbish
they had 200 years ago!

Oh, my God!

'As their journey continued
up the west coast of Scotland,

'Buckland was keen to show Agassiz
the highlight of the tour.

'Just north of Ben Nevis is
Glen Roy.

'In this glen was an extraordinary phenomenon
that no-one had been able to explain. '

Agassiz and Buckland came here
because of these peculiar lines

that are etched straight along
the sides of the glen.

Buckland considered these parallel lines
the greatest geological mystery in Britain.

All the great minds of the day,
including Charles Darwin,

would come here
to try to study them.

'The three ledges are each ten metres
wide and tens of kilometres long.

'The lines run parallel
and completely level. '

What makes them so enigmatic, so
weird, is that they're so regular.

I mean, they just look man-made.

They look so man-made that some of
contemporaries of Buckland thought that

that they were created by
some ancient human civilisations,

and the three roads had three different purposes
- one was for humans,

one was for horse-drawn carriages
and the other was for livestock!

'When Agassiz studied them, he
realised they weren't obsolete highways.

'To him, these inscrutable
features screamed "ice".

'He believed he knew what happened. During the
Ice Age, a glacier comes down from the mountains

'and blocks the mouth of Glen Roy
and the river that runs through it.

'Behind this wall of ice,
a lake slowly forms.

'The water level rises to
a certain level.

'For hundreds of years, waves batter the
lakeside, eroding it and creating a flat shoreline.

'As it gets colder,
the glacier increases in height,

'blocks the valley further up,
and the lake level rises.

'Another shoreline is created
higher up the valley's sides.

'This happens three times in all.

'Finally, the climate warms, the
glacier melts and the lake pours out,

'leaving behind
the strange marks on the hillside. '

It's so clear from up here,
but what's astonishing is that

Agassiz worked this out from down there
on the ground, in just a couple of days.

The parallel lines of Glen Roy were the
abandoned shorelines of an ancient glacial lake.

'Glen Roy was the crucial piece
of the puzzle.

'It was now credible that huge
ice sheets used to cover Scotland,

'a country far from
modern-day glaciers.

'And Agassiz believed that ice
as deep as the huge ice sheet that

'covers Greenland today must have
once smothered much of the world. '

For Agassiz,
this beautifully-sculpted

and distinctive landscape provided
the best evidence for his theory.

"It was in Scotland," he said, "that I achieved
precision in my ideas regarding ancient glaciers. "

For the very first time, Agassiz had
confirmed glaciation outside the Alps.

'One of the joys of being
a geologist is that,

'once you've trained your mind
to see what's important,

'you can start to make sense of the world
around you in a completely fresh way. '

For Agassiz and Buckland,
what they saw in places like this

told them that this landscape had
been carved by a massive ice sheet.

In that sense,
they were visionaries.

But not everyone shared that vision.

'Agassiz rushed back to Edinburgh
with his Ice Age theory.

'In 1840, many of the world's most
important geologists lived here.

'He had to win them over
for his idea to be accepted.

'He couldn't drag them
up to the Highlands,

'but he could show them evidence
of ice just round the corner.

'He took some top geologists
for a tour around the city.

'I'm with present-day members of the Edinburgh
Geological Society, as we head for a site

'their predecessors visited
- Blackford Quarry, in the city outskirts. '

What he wanted to show them were
scratches and grooves in the rock.

You have to really know what you're
looking for, because to the untrained eye,

these look just like scratches
and grooves in the rock, really.

Look, there's a really nice
set here, if you can see that?

It looks like I've taken my fingernails
and just scratched them along here.

What Agassiz thought was that this was
caused by stones being dragged in the ice

and scouring across the rock.

It ends up being really beautifully
polished and moulded. Lovely.

When Agassiz saw this here at Blackford Quarry,
he famously said, "This! This is the work of ice!"

'Agassiz was convinced there'd been a
glacier here, but what about his companions?'

The people that came with him
probably hadn't seen a glacier.

And it's that feeling, I guess, of trying to
imagine this place here covered in ice, as well.

I mean, that would be
quite difficult.

Especially on a day like this!

It just seems perverse. How many
of you would be convinced of

a completely new theory that Britain
was covered in ice, based on that?

No, no. Is there anyone who would?
I'm interested. Not really.

The silence!

'To most geologists of the time, these tiny
scratches appeared of little consequence.

'So Agassiz turned to
other, grander, rocks.

'One in particular
that's visible from all Edinburgh. '

From the top of Blackford Hill,
you can get a good view of

the gently sloping Royal Mile coming
off the back of the hard Castle Rock.

And it's this kind of feature that Agassiz
believed must have been carved out by ice.

As the ice reached the hard Castle Rock,
it was forced to squeeze around the side.

'All the surrounding area was carved away by the ice,
except for the land protected behind the Castle Rock.

'And so the gently sloping shape
of the Royal Mile was created. '

The thing about geology is that it's often
a lot less clear-cut than you might think.

I mean, on the face of it, those features that Agassiz
pointed out were not exactly blindingly obvious,

and it takes a huge leap of faith
to go from small scratches

or the shape of Castle Rock
to the notion of a great Ice Age.

'Luckily for Agassiz, one man on his tour of
Edinburgh was the editor of The Scotsman newspaper.

'In a tavern round the corner
from the newspaper offices,

'Agassiz's theory was
a hot topic amongst journalists.

'Back then, the very idea of an Ice
Age was scarcely to be contemplated.

'Even so, the editor dared to
publish his scoop. '

And here's the article.
Wednesday October 7th, 1840.

Sandwiched between a review of the Adelphi
Theatre and town-council proceedings is

is the world's first announcement
of the Ice Age.

"Discovery of the former existence
of glaciers in Scotland. "

It's incredible!

"Professor Agassiz conceives that at a
certain epoch all the north of Europe,

"and also the north of Asia and America,
were covered with a mass of ice. "

And he's written, "The ground of Europe inhabited
by herds of giant elephants, enormous hippopotami

"and gigantic carnivore became suddenly
buried under a vast expanse of ice.

"The silence of death followed. "

I mean, it's hard to emphasise
what earth-shattering news

this must have been for
your average reader on that morning.

Is this the equivalent to reading that a
double-decker bus has been found on the moon.

Our understanding of the planet's
past would never be the same again.

This was, essentially,
the arrival of the Ice Age.

Paying close attention to this new idea of an Ice
Age was the most influential geologist of the day,

Roderick Impey Murchison,

a former army officer whose approach to
geology was somewhat like a military campaign.

He was one of
geology's rising stars,

and what he thought of Agassiz's
new theory would make it or break it.

Murchison didn't
believe a word of it.

He asked sarcastically if the scratches
and polishing on London streets would

also be attributed to
the action of ice.

"The day will come," he said,
"when we shall apply it to all.

"Highgate Hill will be
the site of a glacier,

"and Hyde Park and Belgravia Square
the scene of its influence. "

You can just hear
the snort of derision.

'Roderick Murchison was a traditional
man with traditional views.

'He believed the Earth's climate
remained largely steady over time.

'There'd been a gradual cooling since the Earth
formed, but no extreme swings in temperature.

'Resistant to new ideas, Murchison dismissed
the theory of an ancient Ice Age as poppycock. '

And he wasn't above stooping
to underhand measures.

These appear to be The Transactions
Of The Geological Society from 1842.

In fact they're evidence of a
dastardly deed, a crime against science,

because Agassiz submitted two of
his key papers to this publication,

but as you flick through,
you just don't see them.

As president of the society,
Murchison used his power,

abused his power,
to constantly delay publication.

They never came out.

In effect he censored them.

And in the face of that constant
onslaught from Murchison,

even Buckland's convictions over
the Ice Age theory began to falter.

This ground-breaking theory was
frozen out by a geological bully.

Louis Agassiz left for America.

He felt he'd taken his ideas
on the Ice Age as far as he could.

But the controversy rumbled on.

You know, geologists found it so hard to accept
the idea of the Ice Age for one simple reason,

and that is there was no explanation
as to why the planet

got chilly enough in the past
to create this supposed Ice Age.

I mean, how does the Earth
go cold and then hot again?

What sends it into the freezer,
only to thaw it out?

It just doesn't seem
to make any sense.

For nearly 20 years, the puzzle of the
cause of an Ice Age remained unsolved.

Help came
from a most unlikely source.

In 1859, a man in poor health
and with a patchy employment record

applies for a job
at Anderson College in Glasgow.

James Croll
has variously ran a tea shop,

managed a temperance hotel,

worked in a mill,

and been an insurance salesman.

Croll's career changes yet again
when he lands the job at the college,

not as a lecturer,
for he's got no qualifications,

but as a janitor.

This shy, silent, brooding Scot
had little formal education,

but he did have a brilliant mind.

He would clean the rooms
after the students had left

and had no doubt eavesdropped into
on some of the science classes,

pondering
what was left on the board.

James Croll applied his mind to the
most controversial theory of the day,

the origin of the Ice Age.

In his spare time,
he taught himself physical astronomy

and the complex laws
of motion, light and heat.

Croll fascinates me.

He wasn't interested in the minutiae of
geology. He wanted to get at the big picture.

And what gave him the edge
was while most geologists

were staring at the rocks underfoot,
he was looking to the heavens.

Oh!

Whoa, found the Sun!

Croll's mastery of astronomy gave him an
original take on the most familiar of objects.

That's lovely.

Beautiful colour.

Fantastic, isn't it?
That's its natural colour.

Well, that's it. Because it's so harsh to look
at you just think it's a white, searing thing.

But beautiful orange and red.

In a leap of imagination, Croll made a
connection between the Sun and the Ice Age.

Nowadays, we have modern technology
to map and understand the solar system.

Croll had none of this.

Yet working on his own, he suspected the Ice Age
was all to do with how the Earth orbited the Sun.

This is an orrery,

a kind of amazing contraption that
simulates the orbits of the planets.

It's wonderful to see the choreography
of all the planets turning.

You know, this device
is incredibly simple and elegant,

but it makes you realise just how
hard a job Croll had,

because he had to work out the
orbits of all the different planets

and then try and determine
the influence they had on the Earth.

Croll liked to grapple with these difficult
problems over the course of long walks.

Imagine that this, this is the Sun.

And imagine this rock
is Planet Earth.

I guess that most people
would assume that the Earth

goes round the Sun over a year
in a broadly circular orbit.

Kind of nice and symmetrical.

But the orbit
is actually slightly elliptical.

It's more of an oval.

I'm exaggerating it for effect.

Now, over long periods of time that
ellipse gets more and more skewed.

It gets stretched out
to be even more oval shaped.

All this stretching is caused by
the gravity of the other planets

pulling the Earth out of position.

The thing is when this happens,
the Earth spends more of its orbit

away from the Sun
than it does towards it.

Winters that happen when the Earth
is out here, its furthest distance,

tend to be more intense.

And this position furthest from
the Sun, the most stretched orbit,

comes every 100,000 years.

Croll took into account other
factors which also change over time,

such as the tilt of the Earth.

When these coincide
with the most extreme orbit,

the winter temperature of the Earth
is at its lowest, 20% colder.

Sounds a lot, but it's still not
enough to unleash a full-blown ice age.

Croll believed there had to be something
else to make the Earth even colder.

This beach is becoming
a bit of a science lab.

There are two sets of different ice cubes here, the
same size but slightly different colours of water.

This one here is your regular water,
so it's transparent, it's clear.

But this one has a tiny amount
of black dye in it.

Now all I need to do
is keep them out in the Sun to melt.

What Croll did was apply the simple physics
of reflected light to the Earth's climate.

It's something we all know, that light-coloured
surfaces reflect more sunlight than dark ones.

So what should happen is that these light-coloured,
transparent ice cubes should reflect off,

to bounce off
more of the Sun's energy

and take longer to melt,

whereas these darker ones
will absorb more of that heat

and melt much quicker.

Well, that's the theory.

Look at that. All of the ice
has gone from the black one.

And then there's
one, two, three, four,

five six ice cubes still left there.

I'd call that a success.

The ability of light surfaces to
reflect heat is called the albedo effect.

I don't suppose there's too many
janitors that would have wondered

about the effect of that
on the Earth's climate.

Think of the clear ice cubes as the
ice sheets at the North and South Poles.

Croll argued that every 100, 000
years, the extreme orbit of the Earth

triggers the growth
of these ice sheets.

The more the ice expands, the more
heat from the Sun is bounced away.

The more heat's reflected, the colder
the Earth gets and yet more ice grows.

Eventually, it covers much of the Earth, in an
ice age that can last tens of thousands of years.

The albedo effect is one of the most
powerful drivers of the Earth's climate.

For Croll, it explained how the world could
cool rapidly, cool enough to start an ice age.

Croll writes up his work and gets
it published in a science journal.

The paper comes to the attention
of the Geological Survey.

They're blown away by its original
ideas about the causes of an ice age.

"What genius came up with this?"
they think.

They're astonished to discover that
this character Croll is a janitor.

It doesn't put them off.

They offer this new-found genius
a research job.

No more dead-end jobs.

James Croll has arrived.

A professional position gave him the
space to develop his ideas further.

He spent the next ten years
writing his book, Climate And Time.

There aren't many books
that have changed the world,

but James Croll's book is
as important to climate science

as Darwin's Origin Of The Species
is to biology.

Yet how many people have heard
of it? It's largely forgotten.

And I must confess that even
I haven't read it,

which is why I'm so excited I'm
about to see it for the first time.

So this is it.

This is the hallowed tome.

This is the diagram that lies really,
I guess, at the heart of Croll's book.

Oh, look at that.

It gives it a kind of drama,
this graphic presentation

of variation in temperature.

Croll had calculated the changes in the temperature
of the Earth over the last three million years.

So this is time, this is one million, two
million, three million years in the past.

He saying there's been these swings,
very erratic kind of behaviour,

but behaviour nonetheless
that could be predicted.

Yeah, orderly. Erratic but orderly
at the same time. Absolutely.

The key thing that jumps out
is multiple ice ages.

He carries it back and says there should be an
ice age maybe there, here. Certainly there, yeah.

And then certainly here.
Certainly here.

It prompts all these questions
about the climate in the past.

And in the future.

Actually, down here, 1800AD, his present
day, and he projected into the future,

a million years into the future,
thinking when the next ice ages will be.

It's clear this man has a brain the size of a
planet, never mind actually thinking about planets.

His colleagues thought he was a genius. They
might have been right about that. The genius janny!

I'm absolutely
bowled over by this book.

In this ordinary-looking graph
is a great scientific breakthrough.

It really shows how the temperature fluctuates over
time, which was a real maverick idea, almost heresy.

People had the prevailing notion that
the Earth just cooled steadily over time,

and here it was,
this irregularity.

But what was Croll's genius was to see that
within that irregularity there was order.

It was all to do
with the astronomical changes.

This is what is referred to as the rhythms
of the ice sheet, the kind of pacemaker of it.

Croll gave us the history
of all these ice ages,

the waxing and waning of the ice
sheets over tens of thousands of years.

But when he worked this out, there was
no geological evidence to support it.

His research was theoretical, worked
out entirely from first principles.

This is impressive science.

For me, James Croll
was an unsung hero.

As so often happens in science,
someone else stole his thunder.

When I was learning about
the ice ages in university,

these astronomical principles were attributed
to a Serbian guy called Milankovitch,

and the periods of warming and cooling
were called Milankovitch cycles.

What I didn't know at the time was that Milankovitch
largely based his work on the ideas of James Croll.

So it's nice to set
the record straight,

to give credit where credit's due.

Croll's book came out in 1875.

Queen Victoria was on the throne.

The Industrial Revolution
was in full swing.

New canals, railway lines and roads
cut through the landscape.

All this digging
exposed the Earth itself.

Geologists now had the perfect
opportunity to find real evidence

on the ground
of what Croll predicted on paper,

multiple ice ages.

Step in James Geikie.

He's bought into the notion
of recurring ice ages,

and he's determined to find
the proof of it in Scotland.

Geikie actually worked alongside
Croll at the Geological Survey.

But while Croll theorised,
Geikie liked to get his hands dirty.

In this old railway cutting,
we can uncover layers laid down

over thousands of years
and, just as Geikie did,

reveal our icy past.

I think that's the deepest
we've ever been.

What do you think?
That's looking very, very good.

It might not look much, but what
excites us geologists is what it means.

The top grey layer and the
bottom red one are both ice ages.

They're separated
by a thin black layer.

The thing that jumps out immediately at us is
the black, organic layer in the middle. Down here.

Yeah, and if you pull
a lump of that out,

you'll see there are bits and pieces of
twig and leaf, various bits of vegetation.

So it's like a kind of soil.
It's essentially a soil.

So this soil is from a warm period when
there were trees and other plants around,

very different from the layer above
and the layer below.

Now, underneath that,
we get this red, sandy material

and if we dig through it we see there
are also some very large stones in it.

Then, as we go up through that, we
eventually come to now a sticky, muddy clay

but with very large stones in it.
Yeah.

And this is very similar to the material
we just talked about at the bottom.

And that's what glacial ice
tends to deposit.

So what we are looking at here, then, is essentially
an Ice Age deposit, and then we've got a soil,

so warm period, vegetation comes back,
and then below it another Ice Age deposit.

So ice, non-ice, ice.

That's it.

And it wasn't just here, was it?

They found several of these
sites all over Scotland.

Geikie compiled a huge number of these sites in
his textbook, which he published in the early 1870s,

and he compiled all the sites from the
various railway cuttings around Scotland.

Must have been a cracker of a book!
Railway cuttings of Scotland!

James Geikie had found direct evidence
of multiple ice ages in the landscape.

It was the first indication
that Croll was on the right lines

with his concept of
the natural rhythms of the planet.

But Geikie's research could not reveal
the precise dates of the ice ages.

It was impossible to tie his work in
definitively with Croll's astronomical cycles.

In recent years, scientists have given us
ever more accurate timings of the ice ages.

Here in sunny Cambridge,
the British Antarctic Survey

has a collection of ice
going back nearly a million years.

They use this ice to discover more
about the past temperature of the Earth.

Hello!

I can see what you mean
about wrapping up.

It's quite cool in here, isn't it?

What is the temperature?

It's minus twenty degrees.
Minus twenty.

These are the conditions
we'd work in in Antarctica.

We're wearing the same clothes.

This is what you're getting,
the ice cores.

Yeah, this is the ice
that we're working on.

The cores are drilled out
of the Antarctic ice sheet.

The deeper the core,
the older it is.

By measuring the depth
of the ice samples,

the scientists can work out
when the ice formed.

So this core that
I've just pulled out here

is probably about a 20-year section
of ice that we've got there.

I'm just thinking, if this is 20 years,
then 800,000 years is just ginormous!

Yes, it's over three kilometres down.

We had to drill into the ice
to get an 800,000-year record.

So you don't have it all here,
that's for sure!

Now we can use the band saw
to cut some samples through the ice

and find out
more about the past climate.

Oh, yes. Look at that glistening,
that sugary texture. How old's this?

This piece of ice is around
about 10,000 years old.

So, where's this from? I see
we've got a map of Antarctica here.

From James Ross Island, which is right
on the tip of the Antarctic peninsula.

The Antarctic team is most interested in the
temperature of the Earth at the time the ice formed.

Each sample
has a distinctive chemical make-up.

The scientists use this fingerprint to
measure how hot or cold the Earth was then.

They've found out that over the last 800,000
years, the temperature of the Earth does fluctuate,

and these changes closely
follow the Earth's orbit.

James Croll didn't get
all the details spot-on,

but his general principle
has been vindicated.

What do you know of James Croll?

Not very much.
I only know that he was involved in

some of the early ideas about natural
changes in the Earth's climate.

Yeah, I'm trying to bring him
out the ice closet really.

But I was just thinking, he would
love to have got his hands on this,

to have seen what you're doing with these ice
cores, because this is really nailing it, isn't it?

I'm told if I come out with this slice
of ice I can hear something weird.

I don't hear anything at all.

What I should be hearing is that as the
ice starts to melt, the air bubbles pop.

CRACKLING

Oh!

Crackle crackle.

What I'm hearing is the sound of the atmosphere
from thousands of years ago coming out.

The sound of the Ice Age!

These days, we've learnt more about the ice
ages than Croll could have ever dreamt of...

.. where they began, how long they
lasted, and how extensive they were.

The last ice sheet to cover most of the
British Isles was just 20,000 years ago.

You might assume it started in the
North Pole and spread southwards,

but reading the rocks reveals that Britain's Ice
Age began in the middle of the Scottish Highlands.

In the British Isles, the ice sheet
was born here, Rannoch Moor.

It reached a maximum
thickness of a kilometre,

a thousand metres of ice, which is
similar to present-day Greenland.

This was the beating heart
of the Ice Age.

From here, glaciers moved slowly down these valleys
towards the sea, carving out these magnificent glens.

We now know there have been ten major
ice ages in the past million years.

So what does the future hold for us?

Today, scientists follow
in the footsteps of James Croll.

They too predict
that an ice age is coming.

On this boat
on the west coast of Scotland,

they work out where the glaciers
of the next ice age will go.

he best way of doing this is to look
where the ice went the last time.

Now, this is the Firth of Lorne.

I've been here loads of time,
but never like this.

This is like a mill pond.

It might seem odd
to study glaciers out at sea,

but thousands of years ago,
this wasn't sea,

it was land, land covered by ice.

During the ice ages, so much water
gets locked up in the ice sheets

that around the world sea levels fall,
and they fall by as much as 150 metres.

When the ice sheets melt,
the sea floods back,

and so by mapping the sea bed,
John Howe and Tom Bradwell

can find the tracks
of these ancient glaciers.

You can see on here the footprint of the glacier
or an ice sheet as it's come down the loch.

And we can see these beautiful
ridges that cut across,

and this was produced by a glacier.

Presumably they get
better preserved on the sea bed

because there's nothing
to erode them or to change them.

We see these features preserved
better offshore than onshore. Gosh!

For the first time, we can
actually see where the ice got to.

They're real limits.
This isn't guesswork.

We're getting real data on where the
ice got to at a certain point in time.

The team has made a computer model that shows
what the next ice age in Britain could be like.

How far these giant glaciers would extend
depends on how far the temperature drops.

An eight-degree fall would plunge
Britain into a full-blown ice age.

So that's telling us what, that the ice is going
to maybe in the future cover this area again?

Absolutely.
There will be another huge ice sheet,

hundreds of metres of ice,
and the ice will just scrape across.

And remove the remains of us,
really, the cities.

Everything that we think
as so familiar will be gone.

Squeezing us down!

It will all be bulldozed away.

Oban will be trashed.

It's not just towns in Scotland
that will be obliterated.

The next ice age
will be a global catastrophe.

Millions of people
will be displaced.

America, Europe and Asia
will be gripped by ice.

This is one of the things
geology is so great at.

You have to imagine
strange other worlds.

You get tantalising clues here and there,
but actually a lot of it's in your head.

How do you visualise this with, I don't know,
several hundreds of metres of ice above you?

It's just hard to do.

But how soon will this happen?

The million-dollar question. When will
the Earth go into the next ice age?

40,000 to 50,000 years from now,
there will definitely be an ice age,

and Scotland will be plunged back into the conditions
that we saw about 12,000 to 20,000 years ago.

But that timing, then, is still
based on those natural rhythms

that Croll and Milankovitch
really tied down?

That's right, those natural frequencies are
going to exist into the future, and we know that.

Looking back into the past, over the last two
million years, we've seen this natural frequency.

This is a vision of our future, and we've only come
to realise it thanks to the pioneers of the past.

People like Louis Agassiz who opened our eyes
to the power of ice that carved our landscape.

And James Croll who looked up to the heavens
to solve the mystery of Earth's ice ages.

These men of rock gave us the tools
to make sense of our planet.

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