All language subtitles for Walking Through Time The Megaflood That Made Britain Ch4 720p EN

Have you ever wondered why
Britain is an island

and why these cliffs, the
White Cliffs of Dover, look so very

remarkably similar to the ones over
there on the other side in France?

Well, half a million years ago,
they were joined by a land bridge.

It took a catastrophe,
a one-in-a-million event,

to change all of that.

The land bridge that connected us
to the continent was washed

away in the biggest flooding
disaster ever seen in Europe...

..where a lake twice
the size of Wales

drained in a matter of weeks,

gouging out the English Channel.

It was a megaflood and that flood
changed the face of our nation.

As a palaeontologist
and evolutionary biologist,

I'm fascinated by the awe-inspiring
geological events that created

the island of Britain...

The earth must have shook.

Yeah, it would have been deafening.

I mean, a catastrophic event.

..the mysterious lives
of our prehistoric ancestors...

That is beautiful.

..and the mega-beasts
that lived alongside them.

Look at its enormous tusk.

I'm going to set out on foot
to walk through time

and discover this long,
lost world

before Britain became
cut off from the Continent

in a one-in-a-million catastrophe.

My journey through time starts
over half a million years ago

along the beaches of
North Norfolk...

..where mega-beasts and ancient
humans could walk across

the land bridge that connected
Britain to Europe.

My journey continues
down to Kent,

along the North Downs to
the White Cliffs of Dover.

Finally, I'll go under water
off the coast of south-east Britain

to witness the evidence
for the megaflood.

Oh! Wow!

Great visibility. Yeah.

That's cool.

One million years ago
these cliffs didn't exist.

They would just have been
a rolling ridge

stretching as far as the eye
can see into the horizon.

There would have been
no Straits of Dover,

there would have been
no English Channel.

But something happened
to destroy that land ridge

and ultimately turn
us into an island.

First I want to get an idea
of what Britain looked like

when it was connected to
the Continent. What lived here?

What animals? Who lived here?

Were there humans?

The best place to do that
is the coast of Norfolk.

Norfolk was right next
to the span of land that once

connected us to Europe.

My first impulse in any new
place is to get

the lie of the land
from a high vantage point.

Being seven months pregnant
should never get in the way

of a good view.

I've just climbed 133 steps
to the top of the tower

of St Mary's Church
in Happisburgh to get my first

proper glimpse
of the Norfolk coastline,

and what a view.

If I was here 800,000 years ago
or so,

I wouldn't be looking
at the sea at all,

I'd be looking across
a really wide river estuary.

And so all around me I'd be
looking down on lush river delta.

I might even catch the distant
trumpet of a mammoth,

or the trampling of hooves
of a large herd of bison.

In warm periods, this was a world
populated by huge mammals

that came and went from the
Continent across the land bridge.

If I was very lucky,

I might catch
a glimpse of some people

wandering along the river bank.

Evidence for these ancient
species of human

that were so very
different to us today

is found here on the beaches
of Norfolk.

And sometimes, so too are the
remains of very, very big animals.

Alongside me is a deposit that
is known as the Cromer Forest Bed.

In particular this bit is known
as the West Runton Fresh Water Bed

because that's what it is.

We're on a beach but this here,
all of this stuff,

is not beach sediment.

As you peel back the surface,
you can

immediately see it's not sand,

it's soil.

It's the kind of thing that would
be deposited in a really

slow-moving, tranquil river.

I kind of imagine slow waters,

marshes, some grassland
around the edge

and in the distance maybe a forest.

A few stoats might run by,
a mole, squirrel -

very quintessentially English,
until a hyena sticks its head out

and is followed by a sabre-tooth cat
or a lion, or a lynx.

Suddenly, you're in a slightly
different world altogether.

That's West Runton 700,000
years ago.

Here on the beach at West Runton,
something amazing was

discovered that had been hidden
for hundreds of thousands of years.

Here we go.

In 1990, children's nursery
assistant Margaret Hems

and her late husband, Harold,

were searching for fossils
in the run-up to Christmas.

So, Margaret, tell me

a little bit about how you came down
to the beach in the first place.

There was an announcement
saying that there was going to be

a high tide, high winds
and possible flooding at Blakeney

and my husband and I,
we looked at one another and said,

he said to me, "An early start
in the morning." That's what we did.

So you were walking along the beach
and something caught your eye.

I saw this round piece in the bed
and I knew it was a fossil.

Do have any photos? Yes, I have.

Look at that!

That one seems to be popular.

That is what you found? Yes.

Explain to me the bit that you saw
first. This piece here.

I started digging carefully around
and in the end it was the pelvis.

Wow!

My husband, when he saw that,
said it could only be an elephant

but we didn't know what
kind of elephant.

Margaret and Harold had made
an astonishing discovery -

an almost-complete skeleton of the
largest mammoth known to science.

How does it feel to have been
the discoverer of one of the most

complete mammoth skeletons
ever found?

It is very, very exciting.

It put West Runton on the map,
didn't it?

It's internationally famous.

I remember thinking
while we were digging it out,

I ought to be making my mince pies,
not doing this!

THEY CHUCKLE

Margaret's mammoth is still
undergoing conservation

over 20 years after its discovery.

This remarkable beast
in front of me

is the head and tusks
of the West Runton Mammoth.

Look at its enormous tusk,
it's beautiful.

It's in absolutely exquisite
condition and just this

portion of that mammoth skeleton
can tell us so much.

From the size of its tusks
we can guess it's probably a male.

It could have been over
four metres tall,

probably weighed ten tonnes or more.

That's twice the size of
a male African elephant.

Looking at its teeth, I can tell
that he was probably in his 40s

when he died.

Now, that's an animal that should
have been in his prime.

It was a steppe mammoth,
the ancestor of the woolly mammoth,

which also frequented
the British Isles.

Mammoths like these certainly
didn't evolve in Britain.

Originating from Siberia,

they must have migrated here from
the continent via the land bridge.

In total, over 200 bone fragments
from the West Runton Mammoth

have been carefully catalogued
and preserved.

There are so many bones
and they're all beautiful

and they're all enormous.
Look at this one here.

The femur, the thigh bone.
This is about 1.5 metres in length.

An animal that is over
four metres tall

is going to have pretty long legs.

Now, what's really interesting
about this particular bone

is that it tells us that this
poor thing had a gammy knee.

This side here is lovely and smooth.

That's what you'd expect where it
would join up with the shin

to create the knee socket.

This side should be smooth as well
but it's not.

Maybe a fall, maybe a fight,

but something quite dramatic caused
this knee to pop out

and jump so that it only articulated
on half of the shin bone.

So one whole side of the thigh bone
wasn't in its socket.

It still survived despite
this injury,

in a landscape that had lions,
sabre-tooth cats

and all kinds of predators.

It was still OK
but it wasn't really in

tiptop condition and that may have
been what did for it in the end.

Now, this is fossilised hyena poo,

and the West Runton Mammoth was
surrounded by them.

We know that either in life,

or hopefully for this creature maybe
after it had already passed on,

hyenas got their fill and they ate
an awful lot of it

and they left an awful lot
of that meal behind

in the form of fossilised poo.

Britain was clearly a home to
mega-beasts who had migrated

here from the continent.

Alongside animals like the mammoths,
humans arrived to live

in a Britain which could be
surprisingly comfortable.

In my day job I spend a lot of time
imagining what the past

would look like.

Here on the Norfolk Broads, the
landscape helps you out quite a bit.

Just looking about right now,
I can really get a sense

of what the world would have
looked like around here

a million years ago.

During warm periods,
this part of Norfolk

would've been a water world
much like this.

If you were canoeing here
a million years or so ago,

you wouldn't be on
the Norfolk Broads,

you would be on the ancestral
River Thames,

which flowed all the way from Wales,
right the way up to the sea.

The ancestral Thames was the
original route of the great river

that now runs through London,
hundreds of kilometres to the south.

This river would have run through
heathland, heather,

there might have been some pine
and spruce forests in the distance.

Sturgeon would have been
swimming on their way to the sea.

The first humans who inhabited
Britain are elusive

but astonishing clues to their
presence are found in coastal towns

like Happisburgh.

Happisburgh is
one of the most dynamic

sections of the Norfolk coast.

This here used to be the base
of the steps

that run up to
the top of the cliffs.

Except...

those cliffs are now all the way
over there.

They've been retreating over
the decades as the sea

has bitten away at them.

That same force of the ocean
a few years ago, May 2013,

scoured away a good portion
of the beach, the foreshore

and uncovered something quite
remarkable

about a metre beneath my feet.

A huge storm had scoured the sand
off the beach

revealing the mud layer beneath.

Over 50 mysterious indentations
in the mud were discovered.

Human footprints.

Their age is truly
awe-inspiring...

..around 900,000 years old.

With only a few hours to record them

before the next tide
wiped them away,

researchers at the site
took 3-D photographs.

So those footprints are now
totally buried? Mmm.

No-one's able to see them any more.

Well, more than buried,
they don't exist any more.

Washed away?
They've been washed away.

David Waterhouse of Norfolk Museums
has brought a 3-D print of one

of the ancient visitors' footprints
to the beach where they were found.

This is the largest one.

This is a size nine.

Probably a male.

These adults were walking due south,

pretty much down the present-day
beach but the smaller footprints

were winding all over the place and
that just happens today, doesn't it?

Exactly... Parents walk along...
Kids running around the outside.

Looking here at the footprints,
the heel is back here.

There you can see the imprint of
what looks like a big toe

and the other toes
just in here.

It's just rather wonderful to think
that this actually was a person

who was walking
on a river bank, here,

maybe as long ago as
one million years ago,

but at least 800,000 years ago.

They're the oldest outside of
Africa, aren't they? They are.

The oldest footprints
outside of Africa. Yeah.

You've got that massive leap
from Africa to Norfolk.

That's why, you know,
it's so special.

This amazing snapshot of human life
was a one-in-a-million find.

The footprints were probably left
by the mysterious Homo antecessor,

one of the earliest known
species of human in Europe.

With a taste for simple stone tools
and cannibalism,

so far their remains have only
been found in Spain.

They would have migrated
here across the land bridge.

Norfolk's rich fossil record tells
us about a world that stretched

from half a million years ago back
to a million years ago or so

where humans, mammoths,
sabre-tooth cats,

a whole diversity of creatures could
come and go freely

between Britain
and Continental Europe.

That connection is underlined again
and again and again

but it was about to change.

Humans and animals would come
and go as the climate warmed

and cooled but an extreme
cold snap would soon trigger

the sequence of events that would
end in the megaflood,

Setting Britain on its way
to becoming an island.

Half a million years ago,

Britain was connected to
the Continent by a huge land bridge

that stretched all the way
from Dover into northern France.

A geological catastrophe
would change all of that

and leave the white cliffs of Dover
plunging into what would

become the English Channel.

I am in Norfolk, looking for
evidence of the people who crossed

the land bridge that once connected
us to Europe so long ago.

Those haunting million-year-old
footprints are not the only

type of evidence for ancient
humanity in the British Isles.

Prehistoric Britons also left behind
traces of their presence

in a unique type of stone.

The people of Norfolk
have always made use of this natural

product of their environment.

And, like any good medieval building
on the east coast of England,

this church is covered in the stuff.

St Mary's, Happisburgh, is a great
example of medieval architecture.

14th-century church, it's made
almost entirely of this stuff -

flint. It was all collected locally

and brought up here
by the barrel load.

I mean, just look at that.

Imagine how many flint nodules
would have been needed to

build this church.
And that's how it came.

Like this, in nodule form.

In certain places, where they wanted
to push the boat out a bit,

they would expertly split it in two

and place it, to reveal the
beautiful lustre of its interior.

And these are all flush with each
other, so it's called flushwork.

This is a great example
of medieval craftwork.

But here in Happisburgh, there's
even finer traditional flintwork

and it goes back
half a million years.

15 years ago,
during an especially low tide,

an extraordinary discovery was
made here on Happisburgh Beach.

It was just this section in the sand

and I could see
this straight line, which is...

It's just relatively unusual.

'Mike Chambers was the man in
the right place at the right time.'

Out there, when the tide is out,
the furthest you can get,

that's where I found it in the clay,
that type of clay.

So, not in the sand.
Not in the sand, no.

It was just this little edge.
So, it came to Cromer Museum first.

Yeah, and it's people like Mike
who know to bring these things in.

And, crucially,
he remembered where it was from.

You can't date the actual flint, but
you can date the sediment around it.

Shall we get it out?
Yeah, I think so.

It's time! Brilliant.

'And here is Mike's discovery -

'at half a million years old,

'the earliest flint handaxe
known in North Western Europe.'

Oh, look at that!

That is beautiful.
It's so black and glossy.

Do we know how
they used these tools?

This was really a butchery tool.

You would use these really
thin edges maybe for skinning.

You could turn it round
and use the thicker bits there

for maybe jointing.
Do we know who made this?

From the shape of it,
the design of it, essentially,

this is a species
called Homo heidelbergensis.

Homo heidelbergensis lived between
600 and 300,000 years ago,

migrating in and out of Britain
as the weather warmed and cooled.

With more sophisticated tools
than antecessor,

heidelbergensis might even have been

among the first humans
to bury their dead.

This handaxe was found
out there, in that direction,

and half a million years ago,
out there wasn't sea. No.

No, I mean, this was a riverbed
we're talking about, isn't it?

We are in a riverbed
and if you kept on going,

the heidelbergensis could walk
all the way to join his mates,

because there was a land bridge
between here and Europe

and this species was everywhere.

But here in Happisburgh,
we have never found any bones,

any fossils of those people.
Yet. Yet!

The humans who created priceless
objects like this would not

stick around for ever.

The glacier that would eventually
cause the mega flood

was moving across Europe,
forcing them to migrate

out of Britain for sunnier climes.

A new ice age was on its way.

Ice ages are periods of intense
global cooling where enormous

ice sheets descend upon the land,
some kilometres thick.

Now, 450,000 years ago,
there was a really big one

and the evidence for that
is right here on this beach.

When we come down on the coast
section here, we find that

the cliffs are almost entirely made
of glacial sediment.

Geologist Martin Warren has been
studying these beaches for decades.

To his trained eye,

the evidence for the Anglian
glaciation that once covered

Britain in huge slabs of ice is
written in the cliffs on this beach.

Here at East Runton we have got this
amazing chalk that has been thrusted

and shoved, to make a hill.

So, there is chalk right up at
the top of the cliff there that

really should be down at beach level

and it has been pushed around
by the power of that ice sheet.

Wow, and you've got a 1km thick
ice sheet that is advancing

and sometimes retreating
and the power of that sheet

is moving
these incredibly large blocks.

I mean, I can see what looks
like some flint up there,

is that correct?

Yes, there is a great sheet
of chalk, with lines of flint

running right the way through it.

With a trained eye
like Martin at your side,

it is hard not to indulge
in a spot of geological foraging.

This looks unusual. Yes, I think
this is a piece of dolerite.

The most likely source of that,
I would think,

is off the coast of Northumbria.

As the ice came streaming
down the east coast,

it would have been bringing
these down.

What is that, 100km, 200km, more?

240, I think, the last time...
if I remember rightly.

How cool. Yeah. Was it rolled?
Was it swept along?

The ice actually
incorporates material

into the base of the ice sheet.

When eventually the ice melts,
it dumps it here in Norfolk.

That's it, isn't it?

We often think of things like
glaciers as being a bit static.

You worry about them melting,

but the whole time
they are moving, moving, moving.

They are, they are very dynamic
and very dirty.

Erratics, like the dolerite,
are rocks carried

to the beach from far away
by an advancing glacier.

They are a telltale clue
that the ice sheet extended

far beyond this area.

Is that something here?
Oh, wow, look at that.

That is an erratic.
A bit of sandstone.

It has got a flat face on it
that has been smoothed off

by the ice sheet and it has
even got grooves and scratches

as it has been scraping along
the bottom of the ice sheet.

That is an absolutely
perfect example of an erratic.

Yeah, moved by an ice sheet
450,000 years ago. Ha!

Britain was being crushed
under the advance of the most severe

glaciation of the past
million years.

This deep cold snap forced humans
and animals to flee this land

and it would set in train
a sequence of events that would

lead to the catastrophic
mega flood that made Britain.

So, 450,000 years ago,
Norfolk would have looked

considerably different than today.

On this spot, there would
have been a huge ice sheet

some kilometres above me.

This glacier would not
only have covered Britain

all the way down to London.

Over thousands of years, a massive
lake also began to develop.

That glacier was dumping all
of its meltwater into an enormous

proglacial lake,
and I really mean enormous -

we are talking
twice the size of Wales.

It would have stretched all the way
from here to the Netherlands

and down the coast some 200km,
where it was dammed

by the enormous chalk ridge.

That ridge was down south,
where the chalk land bridge

once connected us to Europe.

As I travel south, it's like
I am being pushed by that glacier

right the way from Norfolk
all the way to London and beyond,

because of course,
that glacier was the beginning

of something much bigger.

Something was brewing
and it was about to break

and that happened
right down south, in Kent.

The remains of that ancient chalk
ridge are here on the North Downs,

just outside Maidstone in Kent.

I'm actually
currently walking along a ridge,

and there is a thin layer of soil,
but beneath that, it is all chalk.

Now, this ridge that I'm standing
on stretches another 40 miles or so

to Dover and, of course, back then,
it stretched even further

and continued
all the way into France.

The massive glacial lake built up
between Britain and northern Europe.

It was the chalk land bridge
that connected us

to Europe
that held those waters back.

And that ridge
was effectively acting as a dam.

It was holding back the waters
of that massive glacial lake.

Flashes of white in the landscape
reveal the deep chalk beds

under my feet
that make up the ridge.

This is a unique habitat.

Suddenly, I catch sight
of a creature that only

makes its home
on this chalky downland.

One of the things
I really wanted to see

when I came up here on the chalk
ridge was a chalkhill blue.

He is hunkering down, to avoid
this rather strong breeze.

And you get these blue butterflies
on these chalk ridges

because their larvae feed on
a type of plant that only really

grows in these chalky ridges,
the horseshoe vetch.

He is just exquisite.

Today, the ridge
is not just a beauty spot

in a long-forgotten link
to the Continent,

there is another startling piece
of evidence that this is the same

geological feature
that appears in northern France.

And it is evidence
that you can taste.

This corner of south-east England
is a great place to

exploit our deep connection
with the Continent.

It is all thanks to the stuff we are
driving over - the chalk bedrock.

Here in Kent, a British wine grower
is taking advantage of this

wonderful chalk ridge to grow
grapes, to be made into a very

British version of an iconic
French product - Champagne.

Chapel Down vineyard are cultivating
grapes destined for

their award-winning wines, across
94 acres of chalky English fields.

The main feature here on the
North Downs is this chalky soil.

It promotes a much warmer soil
earlier in the spring,

which means these vines can come
out of dormancy much earlier

than some vines
which might be planted on

the colder,
clayer soils of The Weald.

But the added advantage
of chalk is that it acts

a bit like a sponge,
so it will absorb water

and that then releases the moisture
back to the roots gradually.

So, am I looking at, basically,
the same sort of grapes you use

as you would see going into a bottle
of classic Champagne? Yes.

I mean, here we are growing
Pinot noir grapes.

Pinot noir is one
of the main varieties

which they grow in Champagne.

These aren't into
the ripening phase yet,

but they are developing
very quickly.

EU regulations prohibit Chapel Down
from calling their sparkling wine

Champagne,
but that hasn't stopped them

from beating the French producers
in several competitions.

Are people jealous?
Well, I think they are.

They wouldn't say as much,
but we have had the visitors at the

vineyard and they have been pretty
impressed with what they have seen.

I'm imagining, you know,
Champagne vineyard owners

with their binoculars on the ridge,
eyeing up the land.

Who knows? You joke,

I have heard rumours of
the champenoise coming over,

looking at our land and thinking
it might be the next best thing.

Really? But we'll see.
Next best thing?

Well, to what they think.

You're like,
"We know it's the best!" Absolutely.

450,000 years ago, this chalk ridge
that held back the waters

of the glacial lake
was on the brink of destruction.

It was about to give way
in the most catastrophic flood

Europe had ever seen.

I'm investigating a mega flood that
happened half a million years ago.

A catastrophe that helped separate
Britain from the continent

and turn us into an island.

I'm now at the south-east
of Britain in Dover

where I'm seeing the cliffs
as they are meant to be seen -

from the sea.

The White Cliffs of Dover,
they are iconic and rightly so.

They are gorgeous, especially
on a day like today

with that pure calcite
glinting in the sunlight.

Bright white chalk in places
100 metres high, these cliffs.

But of course, that chalk extends
further down, deeper

and from here in Dover, it
extends across south-east England,

all the way into Norfolk.

But of course, it's their
emotional link to the British Isles

that we really recognise them for.

The last thing that many a sailor
is seeing

when leaving home for distant lands.

The first things that many a war
veteran has seen when coming home.

They are the quintessential image,
if you like, of our island nation.

In many ways, in many of our hearts,
they define Britain.

At their highest point, the cliffs
stand proud of the sea
at 110 metres.

Taller than Big Ben

and the same height as 25 London
buses stacked on top of each other.

You get used to thinking of these
cliffs as being here forever

but of course,
they are dynamic in their own way.

The sea is eating away at them,
day by day

and they are actually eroding at a
rate of about a centimetre a year.

Sometimes, that erosion happens
faster and huge chunks fall off

and you can see on the
cliffside, where it's slumped.

The Straits of Dover have been
Britain's first line of defence

against invasion
for thousands of years.

But the cliffs also
did their duty during World War II,

to protect us from the Nazi threat.

A string of heavy guns
were installed

with their sight
trained on the Channel.

The tunnels that provided protection
and living space for the soldiers

that manned those guns are known as
the Fan Bay Deep Shelter.

Newly opened, the tunnels give me
the opportunity to examine

this ancient chalk, laid down
around 90 million years ago.

Well, here is the chalk,
that's for sure.

It is the same stuff the Channel
Tunnel's going through and taking us

to Europe today. It is
a great tunnelling material.

And look down here.

Really, really striking, solid
layer.

The flint is running
all the way along...

..deeper and deeper in.

You can see the signs of
the handiwork of the people

who were actually living down here.

Look, this is a bit of graffiti.

1940.

Amazing to think that all this stuff
is actually the remnants of

billions of tiny, tiny marine algae
that sunk like rain or snow

to the bottom of the sea floor.

And amongst those tiny organisms,
there was also

some bigger things.
I mean, look at this.

Maybe some kind of mollusc,
definitely a fossil.

So, it would
have taken maybe a million years

just for 20-30 metres of this stuff
to be deposited

and these cliffs are 300 metres
high in places.

That is ten million years
of accumulated animal life

built up there.

It is quite wonderful.

450,000 years ago, this massive
layer of chalk would have

extended across the English Channel
into France.

Dr Jenny Collier
of Imperial College London

has long been fascinated by the
disappearance of the land bridge.

It is actually really easy
to understand that it actually

is the same rock unit going
all the way across.

You can see the white cliffs over
there in France and they continue

right across here
to our Dover cliffs.

When the land bridge existed
all those years ago,

this view would have been
very different.

This would actually all be dry land,
out front of us,

where we've got the sea here.

As the chalk dipped down to
lower levels,

it would have just continued
down into a dry valley,

maybe with a few rivers. Yeah.

Jenny and her team discovered clues
to what removed the chalky

land bridge when they were doing
a sonar survey of the seabed

under the English Channel.

It had long been postulated that
something dramatic

had happened to remove this great
big rock ridge

but no-one really had the evidence
for it and we actually found it

genuinely by mistake, by doing
some surveys down to the west

towards the Isle of Wight.

And we just found this huge,
great big valley,

carved into the floor of the English
Channel about ten miles wide.

A valley as deep as this could
only have been created

by an extremely powerful
flood event.

For Jenny and the team, all evidence
pointed to the huge glacial lake

full to bursting to the
north of the chalk land bridge.

Because we knew we had the lake,
this was obviously a perfect source

of the volume of water we needed and
then we've also got the rock ridge

giving us all the lumps of
material to make the gouges.

And to gouge rock, needs a high
amount of force

so we'd have had lots of ice
on the lake as well,

those would have been
thundering down as well.

The chalk ridge gave way
in a cataclysmic one-off event.

Across a period thought to be
as short as three weeks,

over a million cubic metres
of water per second broke through,

destroying the ridge and crashing
down onto the valley below.

I mean, today, the flow rate over
Niagara Falls, for example,

it would be 300 times that.

That must have shook.

Yeah, it would have been deafening,
a very dangerous place to be

and just a phenomenal,
catastrophic event.

Would you have needed something else
to fragment the ridge,

to sort of kick it off?

We know there are small
earthquakes in this area

and perhaps there was a small earth
tremor that just set it off.

A seismic event, this time
a volcanic eruption, was the trigger

for a similar but much smaller
glacial flood in Iceland in 2010.

This footage, shot from a news
helicopter at the time,

is both fascinating
and slightly horrifying.

It gives you an idea of just
how ferocious

and apocalyptic these events can be.

Jenny and her team have only ever
visualised the underwater channel

using sonar.

They have never set eyes on it.

So, we have come to Gosport to
do something

that has never been done before.

This is going to be
an interesting day.

It is pretty exciting. We are
going out to roughly halfway

between Britain and France in the
middle of the English Channel

and we're going to go deep
underwater, 70 metres deep,

to see what is down there.
Hopefully, we will find some

evidence of the mega flood that
Jenny has seen on her sonar scans.

However,

the wind's picking up...

..we are in the middle of a shipping
channel, we are diving deeper than

most people tend to dive in this
area, it is completely unexplored

and we don't really know
what is going to happen.

I'd like to say I was confident...

I am confident, no, I am completely
confident we are going to do well.

Unfortunately, there is a lot
working against us so we shall see.

But I'm not going to
put on a wet suit.

Adrian Glover from the
Natural History Museum

has brought along a submersible,
remote-operated vessel,

nicknamed Rex, to act as our
eyes underwater.

So it is a mini sort of
remote control submarine

but with a tether, a line that
connects it to your computers here?

That's right. We're way too deep
for diving, where we're going.

That is what an ROV brings you, the
ability to work beyond scuba depths.

We're going to see, hopefully,

evidence of the sides
of these channels.

It is the freshness of the landscape
which is so remarkable and it is,

I say, the tides have just swept it
all out for us. Brilliant.

The trip to the edge
of the underwater valley

will take a good three hours.

We've just left port and we are
passing the Isle of Wight over
there.

We are in the sheltered part
of the Channel right now.

I can see the ships passing by out
there, lots of container ships.

Yeah.

Onwards.

But enough worrying about getting
run over by a tanker,

it is time to do some science.

What we're looking at on this map is
actually a map of the sea floor

and it is these reds, these yellows,

these greens...are all telling you
the depth and this blue,

that is the deepest bit yet
and that is where we are headed for.

We are on our way out to the middle
of the English Channel.

Here,
we'll send Rex down to the seabed.

Through Rex's onboard camera,

We hope to gaze into the
half a million-year-old mega flood
valley itself.

'It's been a three-hour journey to
the middle of the English Channel.

'Thankfully,
the weather has improved.'

We're very close,
within 100 metres or so.

Almost there.

'Finally, we're at the spot
where we'll send our

'remote-operated submarine,
Rex, underwater.'

So we're now,
I guess, about here. Cool.

'Along with scientist Jenny Collier,
I'm hoping to get a glimpse

'of the ancient channel carved by
the mega flood that made Britain.'

So, are we almost here?
Well, we are here. We're here?

So, what Graham's doing
is just bringing the boat around,

so we're just doing
a couple of profiles

just to make sure
we're on the cliff edge.

'The skipper positions the boat
over the valley

'that Jenny's team
found on the seabed.

'We want to drop Rex on to
the edge of the valley

'so he can get a good look down the
slope of the mega-flood channel.'

Probably we're going to have Rex in
the water in about 20 minutes' time,

but we want to make sure
we've got no uncertainties,

it's exactly where the cliff edge
is going to be.

It looks so featureless out there.

Expanse of water. Nice and calm.

But it does belie what's beneath us.

It's action stations. The team get
to work, preparing for the dive.

OK, Adrian, we're all hooked up,
ready to power up.

OK, vertical thrust,
to check, coming up now. OK.

Main thrust is all good.

And lights check.

Lights OK. Happy.

With a clean bill of health...

Off she goes.

..Rex is over the side
and on his way.

All yours, Adrian. Copy that, John.

OK, we're going down very fast.

We're now at 40 metres. Wow!

OK, still going down.

Well, it looks like a lot of snow,

but clearly it's not,
cos it's underwater.

Going through a layer
with quite a bit of

resuspended bottom sediment,
I suspect.

'Worryingly, the water seems
to be full of suspended sediment.'

OK, coming up on 45 metres.

4-5 metres.

'If the seabed is covered
in mud and sand,

'we might not be able
to see the drop off.'

We're at 56 metres now. I suspect
any moment now we should touch down.

There's the sea floor. Oh, yeah.

Great visibility. Yeah. That's cool.

'At 60 metres down, there it is.'

We are basically
on a slope on the seabed.

'Rex's position marker shows
that he is sliding down into

'the vast flood channel discovered
by Jenny and her team.

'Through Rex's camera,

'we are gazing at something
never before seen by human eyes.'

It looks like a drop off.

We're seeing off the edge.

These are really prominent sides.
It's like a precipice.

What you expected?
It's better than I expected.

We're pushing it
a bit at the boundaries.

There's a reason why people
don't do this very often.

That's right. I'm quite nervous.

My heart rate is going up
and I find this quite stressful,

and we're recording the data,

we're getting images of an area
of the sea floor that,

basically, nobody ever looks at,
because it's so hard to get to.

So, here's the edge of that
60-metre contour.

Down each of these contour lines,
getting deeper and deeper and deeper

and, as you can see,
Rex is this little red spot here.

He's being bounced down
the edge of this slope.

'At first,
the drop off looks barren,

'but marine biologist
Adrian's eagle eyes

'spot a thriving community
of sea life.'

Oh, that is a coral.

So, that is what's called
a Dead Man's Finger,

Alcyonium Digitatum.

'As a suspension feeder,

'the Dead Man's Finger
can thrive in the gloomy depths.'

You get these kinds of corals
in UK waters.

This is an anemone.
Oh, look, yeah. It's beautiful.

See that sea anemone
on the bottom right?

There's actually really
very high biodiversity here.

It's quite interesting.

If you just take
a few square metres of this,

you'd find many, many species.

'All these species are adapted
to fast-flowing currents.

'They feed
on the nutrient-rich water

'flowing at high speed around them.

'And, if it wasn't for these rapid
currents, the drop off might

'never have been discovered
during the original sonar survey.'

Many people have said to us,

"It's 400,000 years old,
why's it still there?"

And actually we think
probably in the past,

it was covered with sediments,
but today, because of these extreme

tides we have, it's all swept clean
and we're seeing that today.

So it's being revealed to us for
the first time in 420,000 years?

Absolutely, absolutely.
It's remarkable.

It's great to see the mega flood
channel with the naked eye.

There's a boulder.
Small boulders there in front of us.

There's a bit of chalk.

'And it seems we have also found
lots of chalk boulders.

'They could be debris
from the chalk ridge

'that once connected us to France.'

A few lumps about this big,
based on the size of Rex's pincers,

you do wonder, don't you,
how far they've rolled

and when they first landed there?

The mega flood probably only raged
for a few weeks but in the aftermath

of the catastrophe, the chalky
ridge would have been obliterated.

In the hundreds of thousands
of years to come,

Britain would have been accessible
during periods of low sea level.

That huge chalk ridge
that connected us to Europe

was a thing of the past.

We saw with our own eyes
the evidence for this mega flood.

It really brings it home to you
that the shape of the seafloor

that lies beneath, which you don't
get at all any sense of when

you're out here, particularly on
a calm day, definitely a privilege.

My journey has taken me from
the first humans in Britain

to the mega flood that destroyed
the chalk land bridge.

It's been a story of mammoths.

Priceless objects.

Amazing connections to the continent
and fantastic scientific discoveries

that fundamentally changed
the way we think about Britain.

But, after all this talk
about us as an island nation,

I can't help feeling
how connected we are to Europe.

We think of ourselves
as an island nation, don't we?

But it took a catastrophic event
of unimaginable scale to tear

us asunder from the Continent.

A connection that had lasted
millions of years, gone in a moment.

And you haven't got
to look very deeply

at the surface of our country
to discover our European roots.

So, Europe is closer than you think.

Subtitles by Ericsson