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(MEN CHATTERING ON RADIO)

MAN 1: (ON RADIO) Your man's working on it. MAN 2: (ON RADIO) okay.

MAN 3: (ON RADIO) Permission to dive when the swimmers are clear.

MANNING: This submarine is setting out

on a journey to explore the floor of the Atlantic Ocean.

Until recently, what lay at the bottom was a complete mystery.

But under thousands of metres of water

lie twisted rock formations, hot springs and unfamiliar life forms.

It's here in this strange volcanic world that scientists have discovered the key

to how the surface of our planet was created.

The story of how the sea floor gave up its secret began nearly a hundred years ago

on dry land.

The first clues came from looking at the shape of the continents.

Back at the turn of the century,

a young German scientist, Alfred Wegener, puzzled over an observation

that he made and many others had made before him:

That if you look at the coast of Africa here and compare it with the coast of South America

about 7,000 kilometres in that direction, there's a surprisingly good fit.

If you moved them together, they would fit very snugly.

The difference between Wegener and his predecessors

was that he was determined to find out whether this was mere coincidence

or whether it pointed to something more fundamental.

Had the continents truly once been joined together?

It was an extraordinary idea, and Wegener needed hard evidence to back it up.

He thought that he'd found it here, on Table Mountain.

The mountain is part of the South African field area of geologist Maarten de Wit.

Maarten showed me what so excited Wegener.

MANNING: What a fabulous view.

DE WIT: Well, we're right up the westernmost end of the Cape Mountains.

They stretch for about 2,000 kilometres towards the east.

But here they're very abruptly cut off by the Atlantic Ocean.

The next time we see them, 7,000 kilometres across, in South America.

MANNING: And it's the same structure, 7,000 kilometres away.

MANNING: You could see almost the other end of the break, as it were.

Same structure, same rocks.

MANNING: And that wasn't the only evidence

that South America and South Africa had once been joined.

More came from the fossil record.

In particular, the remains of a plant called Glossopteris.

There you are. See if you can find something for me in that one.

MANNING: I'll be damned.

This is a lovely fossil tree fern.

- DE WIT: Look, look at the fine detail there. - Yes, you can see the vein on the leaf there.

These of course are

at that stage where they're being found in all sorts of other places like India, Madagascar,

Australia, South America.

And it was this that made Wegener believe, well,

that kind of distribution of so many fossils in different areas would make a lot more sense

if you put all the continents together in one piece.

- So they would be gathered together in one area? - That's right.

Wegener's ideas were that

much better to interpret this as all the continents being together

and these fossils being explained as being part of one huge supercontinent.

MANNING: Evidence of other similarities between the continents

could be found all over the Southern Hemisphere.

Wegener was forced to the astonishing conclusion that all the dry land on the planet

had once been part of a single land mass,

a supercontinent that he called Pangaea.

He suggested that over millions of years, Pangaea split apart.

New oceans opened up where there used to be land.

He called this idea "continental drift".

Wegener first published his ideas in 1915,

and he went on collecting more information and republishing.

But at first the idea attracted little favour.

Certainly, I can remember in the 1950s, as a zoology student,

continental drift was given little attention.

The trouble was that Wegener couldn't explain how the gigantic blocks of the continents

could sail through the solid rock of the ocean floor.

And without a plausible mechanism, most people,

especially in the Northern Hemisphere, chose to ignore continental drift.

And it remained ignored until new evidence began to emerge

from beneath the waves.

This is the maiden voyage of the research ship Atlantis.

Its destination is the middle of the Atlantic Ocean.

On board is a team of scientists intent on unravelling the secrets

hidden beneath the water.

Among them is marine geologist Joe Cann.

He can sympathise with the difficulty people had accepting Wegener's controversial ideas.

They knew there had to be ways of getting animals and plants from one continent to another

because you had these astonishing similarities, especially in the Southern Hemisphere.

But they couldn't bring themselves to think that the continents were drifting.

Instead, there was a very strong feeling that the Earth was heaving in some periodic way,

that there were... Mountain belts rose and fell.

And that pulsing idea led to people thinking that the ocean floor might rise

to allow the animals to wander across and sink again.

An undulation of the ocean floor from time to time.

It seems very implausible now,

but that's how they felt about it.

And that meant, of course, that the ocean floor had to be the same as the continental crust.

It had to look the same and you'd expect the same sorts of rocks,

the same sorts of materials to make it up.

MANNING: But of course, nobody knew for sure what the ocean floor was made of

because they couldn't see it.

It took a change in world politics to reveal the first hints of what really lay below.

COMMENTATOR: Down away she goes and in a matter of months...

MANNING: During the Cold War, submarine warfare became vitally important.

Nuclear submarines had to be able to navigate the world's oceans safely,

so submariners needed to be sure of the depth of the sea floor.

Flush with navy funding, scientists set out to map the ocean floor in unprecedented detail.

Their tool was the echo sounder.

Ships sent out pulses of sound which travelled to the sea floor and then bounced back up again.

(PINGING)

The time taken for each ping to make the journey gave the depth of the water at that point.

We've basically been using the same types of precision depth recorders

since the end of the Second World War.

As you can see on this record from the 1950s,

basically, you can see that the bottom is a very fine trace here,

very strong fine trace.

But there are also places where the echo-sounder record gets very, very confused.

And in those areas you have to be very careful to interpret them correctly.

MANNING: Two of the first people to do this were Bruce Heezen and his colleague Marie Tharp.

They became experts at making maps from the echo-sounder data.

Their maps at last began to reveal what the bottom of the ocean looked like.

However, their task was far from easy.

The oceans are huge and the ships' tracks were few and far between.

Marie Tharp is retired now. But we met at her home near New York

where she used to work on the data.

THARP: We made this map using that data.

There's an amazing amount of detail here.

How did you extract it from just those tracks? How did you do that?

(CHUCKLING) Well, where we had a track, we took it very seriously and exactly.

But then it'd be so far to the next track that we had to do a bit of inspired guessing

- to fill in the space. - Right.

Actually, in this area we didn't have any data at all,

so that's why we put the legend there.

MANNING: Piecing together the echo soundings

revealed the existence of a vast mountain chain running down the centre of the ocean.

As more data became available,

Heezen and Tharp traced this ridge throughout the main oceans of the world.

It ran on and on, snaking around the entire globe for 60,000 kilometres.

It's an extraordinary discovery. I mean, what was the world's reaction to that?

At first it was one of amazement.

And then sceptical, very sceptical, and finally it was extremely scornful.

And, it was, you know, it was hard to convince them.

It was a shocking thing to say.

MANNING: Marie also noticed something odd about the crest of the ridge,

a feature which looks suspiciously like evidence for Wegener's unfashionable ideas.

Here is the Mid-Atlantic Ridge

and the unusual feature is it has this great big cleft in the middle of it.

There is one there and here's a cleft in the middle, here.

And here's a cleft in the middle, here.

So what did you deduce from these profiles?

Well, I showed it to my boss, Bruce Heezen,

and I had plotted the position of this rift valley along the centre of the ocean where it occurs

and he just groaned and groaned and says,

"No, this can't be. It looks just like continental drift."

Why does that mean continental drift?

Partly because you could spot it was a...

a big rift valley, a big cleft in a mountain range.

That's quite a large valley inside of a huge ridge.

And it looked like a chasm

that would be naturally the feature that formed

if the continents were pulled apart.

FORNARl: Over the course of 20 years since this initial map was made by Bruce and Marie,

they've dedicated their lives to looking at all of the echo-sounding records

that have been collected to produce a global map

that shows us what the bottom of the ocean floor looks like.

And this map is a...

really provides a geologist with a complete understanding

of how different the ocean floor is from the continents.

The ridge system runs down the middle of the Atlantic Basin

between Africa and Europe and North America and South America.

And it's this continuous line of rugged topography that goes all the way down the ocean basins.

Here, into the Indian Ocean and out into the Pacific Ocean, here,

it is continuous throughout the globe.

Now, you don't see that on the continents.

You can see mountain ranges and sometimes they are continuous,

but never for 60,000 kilometres.

You don't see that type of feature on the continent.

MANNING: Today, at last, satellite technology can reveal directly the shape of the ocean floor.

Remove the skin of water

and the backbone of the world can be seen from space.

The discovery of this vast mid-ocean ridge system was a revelation.

But still nobody knew how it had got there.

And then more striking differences

between the oceans and the continents began to emerge,

as scientists developed new ways of looking at the sea floor.

At the end of the Second World War there was a new breed of marine scientist.

And they set out to study the ocean floor

by dropping explosives over the side of the ship, and they had plenty of those,

and listening to them with hydrophones that had been used for submarine detection.

MANNING: The technique was called seismic profiling.

In the early days it was a fairly hazardous enterprise.

Explosives were simply hurled overboard and detonated.

The shockwaves penetrated deep into the rock beneath the ocean.

(EXPLOSION)

By studying the way the sound was reflected back,

the ocean-going geologists measured the thickness of the ocean crust.

CANN: When they did this, they discovered two very important things.

One was that the ocean crust was much thinner than the continental crust,

six kilometres instead of 30 kilometres,

and the other is that the ocean crust has the same thickness and the same structure

all the way round the world.

Which indicated it formed by the same process all the way round the world.

That was a truly fundamental discovery.

MANNING: The seismic research helped scientists come to realise a crucial fact:

The ocean floor and the continents looked so different,

they had to have been created in entirely different ways.

But the process that created the ocean basins

remained a mystery until another technique began picking up important clues.

It's midnight. The research vessel Atlantis

is approaching the centre of the Mid-Atlantic Ridge,

and Joe Cann is supervising the launch of a dredge bucket.

Over the next couple of hours,

the dredge will be lowered thousands of metres until it touches bottom,

then dragged along as the ship creeps forward.

Zero metres.

In the process, the bucket should scoop up some of the rocks that litter the sea floor.

Bridge, we're going to put another 30 metres of wire out.

WOMAN: About 15. CANN: No, 10, maybe.

The problems are that we've got... We are in 2,500 metres of water.

We've got a dredge being pulled over a rocky bottom with unknown rocks,

some of which are pretty tough rocks.

The ship is going along at half a knot, inexorably.

What we must avoid is being snagged up on a rock down there.

If we get snagged up and don't notice it,

the tension will build up in the wire, the wire parts.

If it parts on deck,

loose end whips around, it could cause a lot of damage, kills people.

In the old days, we didn't know whether the ship was moving over the bottom at all.

We could put wire out, we didn't know where the dredge was on the bottom,

we didn't know where the... we didn't know where the bottom was properly.

And we had to resort to very crude techniques, such as

where the dredge was out, we would sit on the main warp on the afterdeck,

feeling the nubbles coming up from the deep ocean floor.

It's very evocative. Very, very...

Uncomfortable is what it was. Dangerous.

It was very uncomfortable, very dangerous,

but you felt in touch with the ocean floor, like you don't at the present day.

You felt deeply in touch with it through your bottom.

MAN: I have the dredge in sight, dredge in sight.

WOMAN: Roger. In sight.

MAN: Up easy.

CANN: There's certainly rocks in there, I mean...

you can see the bottom of the bag bulging. First one for the new ship. That's impressive.

Oh, yes! Oh, yes!

MANNING: When scientists began recovering rocks from around the mid-ocean ridge,

they found they were mainly volcanic.

These aren't the kind of things that you see in your back garden at home.

They're basalts, they're also submarine basalts.

You can tell 'cause they've chilled to this bright, glassy margin,

chilled against the water when they erupted.

And they're very sharp. The glass is very young and very sharp.

As you can see, I've cut my finger on the fragments.

MANNING: These are young volcanic rocks.

Somewhere 2,000 metres below, volcanoes have been erupting recently.

We know they're young because of the fresh glass and they're also highly magnetic.

If I take my compass out,

it's just an ordinary compass that you use any day,

I take one of these rocks and bring it up to it,

you see, if you look carefully, that the needle deflects a bit.

Not much, about 10 degrees.

But it deflects enough to show that the rock must be very magnetic indeed.

MAN: Here we go.

MANNING: Magnetic rocks would cause small local variations in the Earth's magnetic field

and that gave scientists a new way to investigate the ocean floor.

Okay, it's in the water.

That's a magnetometer and it is towed behind the ship,

it's an instrument that gives us a very detailed reading

of the Earth's magnetic field.

So it's very, very sensitive.

Basically, it can pick up the small variations in the Earth's magnetic field

that are caused by the rocks and the various layers in the ocean crust.

MANNING: Magnetometer surveys started in earnest in the 1950s.

Certain areas were sailed over in a series of tightly packed parallel lines

to ensure that nothing was missed out.

Where the ships went, magnetometers followed behind.

Magnetic rocks distort the Earth's magnetic field,

sometimes making it stronger than expected, sometimes weaker.

These differences are called positive and negative anomalies.

When the data from the first detailed survey were put together,

the scientists were dumbfounded by the result.

CANN: Stripes of magnetic anomalies.

Now this was, back in 1961, the most amazing thing.

Here's the coast of the United States, here's Canada,

and here is the magnetic anomaly map offshore. Black is positive anomalies.

White is negative anomalies.

And see how they all form these astonishing stripes.

Nothing like this had ever been seen on the continents.

And yet the ocean floor appeared to be made of these parallel stripes

of positive and negative anomalies.

By the early '60s, scientists knew a good deal about the ocean floor,

but none of it made much sense.

In some ways it was a very uniform picture.

The crust was all the same thickness,

it was all much younger than the continents,

and it was nearly all made of volcanic rock.

Also, running down the centre of the basins was a continuous mountain range,

and along the crest was a continuous rift valley.

A pattern like that, to any scientist, demands an explanation.

The turning point finally came in 1962

at a lecture given here in Cambridge

which revived Wegener's idea of continental drift.

Attending the lecture was Fred Vine,

who was just a geology student at the time,

although he was already fascinated by continental drift.

HESS: The birth of the oceans is still a matter of some...

MANNING: The man whom Fred had come to hear was an American geologist, Harry Hess.

Hess explained his ideas of how the ocean basins had formed.

It's a lecture Vine remembers vividly today.

Hess, I guess, was the first person to try to synthesise all the new data,

and it was a pretty daring synthesis and it was regarded as being very speculative

at the time.

MANNING: Hess believed the mid-ocean ridge was a vast crack

where the Earth was splitting apart.

He suggested molten rock was constantly erupting in the crack,

continuously forming new ocean floor.

Hess was basically describing an enormous conveyor belt,

with new ocean crust forming at the mid-ocean ridge

and then moving away.

It explained almost all the observations: The ridge and its valley,

the consistent layer of young volcanic rock, and it also explained continental drift.

The continents didn't sail through the oceanic rock,

they just moved with it.

It was an extraordinary idea.

Hess himself called it "geo-poetry".

Ironically, the one line of evidence that could make it stand up

was the very element Hess left out: Magnetism.

And it just so happened

that magnetism of ocean rocks was the subject of Fred Vine's PhD.

Well, this is where I worked as a graduate student.

This is the first time I've been back in 35 years.

Recognisable?

It's exactly the same. It's incredible.

Still just as tatty, actually.

This is the stables, as you have gathered. This is directly above the stables.

Yeah, I came in here in October, 1962,

to work with Drummond Matthews.

He was a marine geologist attached to the marine geophysics group here.

And Drummond was away at the time, actually.

He was at sea in the northwest Indian Ocean,

surveying a small area of the Carlsberg Ridge,

the mid-ocean ridge in the northwest Indian Ocean, in very great detail.

And I was specifically to work on the magnetic data.

And I think much to Drum's chagrin, in a way, I decided that we had to use digital computers,

which were very new at that time.

Fortunately, here in Cambridge, we had one of the first digital computers in the world.

Actually, it's rather fun, this picture, because this...

I don't think I'm actually in this queue.

But we used to queue up, I think just about on the hour, every hour

to test our programmes.

MANNING: Vine had a programme that analysed the magnetic anomalies.

He entered magnetic data from the survey into the computer.

It then calculated what sort of magnetic field

could cause the anomalies that had been measured.

What the computer told Vine was quite astonishing.

The all-important result that it came up with,

and the rather surprising result in many ways,

was that much of the ocean floor was in fact reversely magnetised.

That is, it's as though it had acquired a magnetisation

when the Earth's magnetic field was reversed.

Exactly the opposite to the present day, where the compasses,

rather than pointing to the north as they do today, would have pointed to the south.

MANNING: The theory that the Earth's magnetic field has repeatedly flipped to and fro

had been hotly debated for years, but no consensus had ever been reached.

Magnetic reversals were just another bizarre concept.

How did you combine this idea of yours

of reversals of polarity on the sea floor with Hess' sea-floor-spreading idea?

Well, basically, we combined what were, at the time, two very speculative ideas.

The reversals of the Earth's magnetic field, true reversals of the Earth's magnetic field

and the sea floor spreading.

We sort of converted Hess' conveyor belts running out symmetrically

about the mid-ocean ridge to tape recorders,

and that if the Earth's magnetic field was reversing as the spreading process was going on

then it would record the polarity reversals of the Earth's magnetic field.

MANNING: As volcanic rock erupts and then cools,

it records the direction of the Earth's magnetic field at that time.

If magnetic flips did occur, such reversals would remain locked up in the rock.

Vine's idea was that if the Earth's field would make compasses point north,

then any molten rock erupting at the ridge at that time

would be magnetised in that direction.

(RUMBLING)

If the Earth's field then flipped, any more new rock formed at the ridge

would be magnetised in the new direction.

Each time the magnetic field flipped, so would the magnetisation of the newly-forming crust.

The great strength of this idea, of course, was that it immediately enabled you

to form avenues of normal and reversely magnetised crust

- paralleling the ridge crust. - Right.

- Which could explain this... - The zebra pattern.

- The zebra pattern. The banding. - Yes.

How was this idea of yours received?

Well, at the time, like, it went over like a lead balloon really.

I mean, it wasn't widely accepted at all.

I mean, basically the evidence wasn't very good.

(CHUCKLING) People were really quite rude about it, actually.

MANNING: Fortunately, the hypothesis also made a prediction.

It predicted that the pattern of magnetic stripes

on either side of the mid-ocean ridge would be symmetrical.

So Vine looked carefully at the pattern of magnetism

that had been found in the rocks of the Pacific Ocean.

VINE: The other remarkable thing was, it was a little later when we realised this,

this survey which had been in the literature

for several years does in fact exhibit a symmetry.

MANNING: This strip of positively magnetised rock actually marks a section of ridge.

On either side, the pattern of white and black stripes

stretches out in a mirror image.

So there is indeed a symmetry. It'd been sitting there all the time for four years,

but hadn't been recognised.

MANNING: Now people began to believe Vine,

and they started to find symmetrical patterns in other data.

The theory of sea floor spreading had been tested and proved.

With it, Alfred Wegener's idea of continental drift took on a new lease of life.

At last it was possible to understand how continents could drift

slowly but inexorably across the face of the planet.

But at the heart of the theory lay a feature that no one had ever set eyes on:

The remarkable volcanic mountain chain where oceanic crust is generated,

the Mid-Atlantic Ridge.

Geologists would never be satisfied until they had seen it for themselves.

After six days' straight sail from Bermuda, the Atlantis is sitting directly on top of the ridge.

But a different vessel is needed to make the final leg of the journey

to the ocean floor.

This is a submersible, Alvin, capable of diving to 4,500 metres,

which is roughly three miles deep under the ocean.

Withstands pressures of up to 6,600 psi,

which is about two good-sized elephants sitting on your lap.

The titanium sphere is about two inches thick and inside it sit three people,

the pilot and two observers.

It gets a little thicker up by the view ports.

It's about three-and-a-half inches thick.

The view ports are made of plastic so they're tough and not brittle like glass would be.

MANNING: Alvin dives by being loaded with weights.

When it's ready to surface the weights are dumped

and the sub becomes light enough to float up.

If the submarine was to be stuck on the bottom for some reason,

snagged on anything,

releasing the weights might not be enough.

So the submarine can try to drive up with its thrusters

and if that's not enough, we could drop various pieces of gear.

We could release the science basket, get rid of the science gear.

We can release the manipulators.

We can even try jettisoning our batteries, which would then leave us without power.

If all that's not enough, we can last on the bottom for three days

and if there's no prospect of rescue we can actually release the sphere

from the rest of the submarine and it'll float up on its own.

Unfortunately, it won't float up right side up.

We don't really know exactly how fast or in what attitude. It'll probably spin like a ball

and it might be quite a wild ride.

FORNARl: Matt, I wanted to talk to you a little bit about where we're planning on diving tomorrow.

Can you turn on that light for a second? Thanks.

So we've got this big sea mountain in the middle of the rift valley.

The place where we're going to dive is right here on the summit. It's an area where...

MANNING: The evening before the dive,

project leader Dan Fornari finalises details with Susan Humphris,

the scientist who will be on board the sub.

Matt Heintz has been chosen as pilot.

FORNARl: 500 metres maybe.

So you're not talking more than a kilometre in any direction that you're gonna have to travel...

So, we're going up a nice slope.

Yeah, so I think the thing to do maybe is start down in here

and then work our way up the slope where the dredge went.

It looks like there might be some sort of fairly steep cliff or scarp here

that we'll have to go up and, you know, it looks like it might be about 100 metres high.

FORNARl: Secure propulsion. Hydraulics on.

Good, good.

- MAN: Good luck. - Thanks.

HUMPHRIS: First, when you get in the sub, because it's been sitting out on deck,

it's usually very, very hot and stuffy.

And the first impression is one of being incredibly cramped.

HEINTZ: And we're standing by on the fantail, ready to launch.

FORNARl: okay, roger that, go ahead and commence launch.

HUMPHRIS: I always get the feeling of sort of pent-up excitement,

but some nervousness.

Swinging out over the stern of the ship,

looking out over the waves and realising that all of a minute

you're going to splosh down in there

and the porthole is going to look like the inside of a washing machine.

(BEEPING)

(THUDDING)

Atlantis, Alvin. ID lights on. Vent valve is open. Hatch is shut. Oxygen is on.

Tracking is on 8. 1.

Permission to dive when the swimmers are clear.

- Clear to dive when swimmers are clear. - HEINTZ: Roger. Alvin diving.

- Read off target one. - HUMPHRIS: First target is 34-60-46-42.

Okay, what's the landing target?

MANNING: The sun's rays can't penetrate far into the water.

Eventually the last of the daylight will fade away.

The sub is free falling and Matt and Susan drop at a rate of 30 metres a minute

down into the darkness.

If they could see where they were heading, the view would take their breath away.

1700 metres below, the valley at the centre of the Mid-Atlantic Ridge

stretches out before them.

MAN: Atlantis, Alvin, depth?

HEINTZ: 1623, a hundred off the bottom. I'll call you when we get there.

I'm getting ready to release my first weight.

Okay, one weight away. Listen and you might hear it.

Didn't hear it, but I saw it in the camera.

And that should slow our descent rate. We're down to 60 metres up off the bottom.

HUMPHRIS: Bottom's in sight.

HEINTZ: Atlantis, Alvin. Depth 1712. On the bottom.

MAN: Roger that.

HUMPHRIS: Okay, I'm seeing some structures

that look like maybe this is at the edge of a lava field.

HUMPHRIS: I see some drainback features. HEINTZ: Yeah. I see some collapses.

HUMPHRIS: Collapse pits okay. We might be on the edge of a lava lake here.

Oh, yes. I'm going past some lava pillars on my side.

HUMPHRIS: Oh, yeah. Oh, here it's beautiful.

MANNING: Alvin has landed in the heart of the Mid-Atlantic Ridge,

the place where the Earth's crust is being created.

This is a lava lake where submarine flows of lava have become twisted into dramatic shapes.

The rock here is just a few hundred years old.

The sharp pillars have not been softened by time.

The submersible's journey across the lava lake

takes it between the three peaks of the Lucky Strike volcano.

At this depth, the only light comes from the submersible itself,

as it finds its way along the rugged terrain.

HEINTZ: Ah, well, what do I see here?

- I see some white. - HUMPHRIS: Something white?

HEINTZ: What do you see, port window?

HUMPHRIS: I see what looks like some hydrothermal staining to me.

MANNING: Matt and Susan have detected staining

deposited by hot springs, called hydrothermal vents.

When volcanoes and water mix, hot springs are an inevitable result,

and the presence of these deep sea vents had been predicted.

But the reality turned out to be even more startling than the wildest predictions.

The first time Alvin came across a black smoker, it was piloted by Dudley Foster.

FOSTER: It was like a steam locomotive billowing smoke out of the bottom.

I couldn't imagine what it was. I was just floundered and floored by this.

We stuck the temperature probe into this plume of water

and the probe could only measure it up to 30 degrees.

And that pegged immediately so I moved the probe out of that.

I could see the end of the probe had turned black.

And it looked... I thought, well, this is kind of the dust, whatever the smoky stuff is.

And we got back to the surface, we found that the PVC rod had actually been burned

in the few seconds that it was in this water.

That was our first clue that this was extremely hot.

HEINTZ: Oh, man! Did I open up a nice hole? HUMPHRIS: Oh, look at that!

HEINTZ: Man, that is sweet. I like them. HUMPHRIS: That's a good one.

HUMPHRIS: All right, that should be an easy one to sample.

Once we discovered how hot these hydrothermal vents could get,

we became concerned about the impact on the submersible,

and particularly since the view ports are made out of plastic,

and at the sort of depths we were working,

they can start to lose their strength at about 90 degrees C.

HUMPHRIS: 18, 74, 216, 241, 256,

303, 291, 321, 321.

MANNING: The water pumping out of this vent is at 321 degrees centigrade.

We work very close to these structures

because we reach out with a manipulator and sample them,

put probes in them and do a lot of work around them.

But frequently there are several and you can easily bump up next to one

and several times, the fibreglass skin on the submarine has actually been burned,

come back with several layers of glass burned away

and the paint charred black.

MANNING: It's a hazardous environment for the sub and its crew,

but no one had imagined it could also support life.

HUMPHRIS: Okay, let's see if we can smoke some of these shrimp. These look great.

HEINTZ: Come here, shrimp.

HUMPHRIS: Are you getting any? HEINTZ: I'm... I'm working it.

HEINTZ: I've got something stuffed in there. I'm getting some bacterial mat.

- Okay, well, keep trying on the shrimp. - Shrimp are pretty resilient.

They're saying, "No, no, no, no. I'm not going in there."

I know, they can move around pretty fast.

HEINTZ: Get in there. Get in there. Get in there!

HUMPHRIS: Okay, well.

However many we've got, maybe we should call it quits.

I'll look up our range and bearings for our next site.

MANNING: Shrimp, mussels and fish have all been found thriving around the smokers.

They survive where most scientists expected life to be impossible,

in the pitch dark, cut off from the sun's energy, which fuels every other ecosystem on the planet.

At the bottom of this complex web of life, supporting the whole thing, are bacteria.

Those bacteria feed off the rich cocktail of chemicals

spewing out in the superheated water.

All these living things are totally dependent on the Earth's own energy.

Locked up in the rocks of South Africa

is evidence that this strange world has existed for billions of years.

Well, here we are in Barberton Mountain Land,

walking on some of the oldest rocks that have ever been found on Earth.

And the particular rocks I'm walking on are ocean floor rocks.

Very old ocean floor.

And we now know that this ocean floor and all these rocks everywhere around us here

are 3.5 billion years old.

Come up here. This is where the rock's been cracked open in two.

Look, this hand here fits with that hand over there.

And we can see these pillows, these bulbs in cross-section very nicely.

This is very characteristic of how lava forms

or the sort of shapes lava forms as it hits the ocean floor.

MANNING: Underwater eruptions are very different to lava flows on land.

Lava erupting into water rapidly cools, forming a skin.

As more lava wells up from below

it continuously pushes out new buds onto the ocean floor,

like pillows of solidifying rock.

Anywhere you go today, you see these kind of fossils with these shapes,

you know you're walking on rocks that were once covered by water.

MANNING: And like the oceans today, the ancient oceans also had black smokers.

Three-and-a-half billion years ago,

hot water streamed out of this rock.

The mineral deposits are not the only traces the smokers left behind.

And when we look at these flinty rocks in detail,

under the microscope, we find very ancient bacteria.

So that, I think, makes a very solid case

for the sorts of hypotheses that are hanging around,

that make people believe perhaps these kind of associations,

the pillow basalts and the black smokers are the sort of areas,

the niches, where life might have originated.

MANNING: Could it be that life on our planet first evolved at a hydrothermal vent?

On board Atlantis, biologists are studying the bacteria from black smokers

to see how closely they're related to the earliest forms of life.

HUMPHRIS: Judy, which sample are we working with?

We start with the slurry. It's been settling...

MANNING: Analysis of their DNA shows that deep-sea bacteria

are the most primitive forms of life on the evolutionary tree.

These bacteria really could be the direct descendants

of the first living things on Earth.

The work on the evolution of life all stemmed from a simple observation,

the matching of two distant coastlines.

In the last few decades the deep ocean has begun to lay bare its secrets to science.

We've finally come to understand how truly dynamic our planet is,

and how the sea floor is being continuously remade.

As a biologist, I'm fascinated by the links we've discovered

between the Earth's activity and the origin of life.

The energy which fuelled the first living thing is the same energy

that is still remaking the surface of our planet.

But if you think about it, there's a problem.

For billions of years, new sea floor has been continuously produced

at mid-ocean ridges,

so unless the Earth's been getting steadily bigger over all that time,

there must be somewhere on the planet where crust is being devoured

as fast as it's being made.

Solving that paradox will take us on our next programme

to the volcanoes ringing the Pacific

and also explain how the land we live on came into being.

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