A História da Ciência - Episódio 3: Como Chegamos até Aqui? (2010) [HD]

Uploaded by ReVCieN on 16.08.2012

There are some great questions that have intrigued and haunted us
since the dawn of humanity...
The story of our search to answer those questions
is the story of science.
Of all human endeavours, science has had the greatest
impact on our lives,
on how we see the world and how we see ourselves.
Its ideas, its achievements, its results are all around us.
So, how did we arrive at the modern world?
Well, that is more surprising and more human than you might think.
The history of science is often told as a series of eureka moments -
the ultimate triumph of the rational mind.
The truth is that power and passion,
rivalry and sheer blind chance have played equally significant parts.
In this series, I'll be offering a different view
of how science happens. It has been shaped as much by
what's outside the laboratory as inside.
This is the story of how history made science and science
made history, and how the ideas that were generated changed our world.
It is a tale of...
This time, the most personal question we've asked...
How did we get here?
It's a question that provokes fierce argument and huge controversy.
And that's because it gets to the heart of our human origins,
our very significance. And yet, until relatively recently,
it was not a question that people felt they had to keep asking.
Most people believed they already knew the answer,
handed down in religious text or in creation stories.
We and everything else on earth
had been put here by some kind of supernatural power.
What's special about this question
is not how long it took to get answered, but how long it took
to get asked as a scientific question.
And it's a story that begins over here.
'The great voyages of discovery,
of the 15th Century, heralded the start of the modern age.
Advances in navigation and shipbuilding allowed
European adventurers to explore and exploit the rest of the globe.
We're absolutely storming along now, powered by the trade winds.
And over there is the Caribbean island of Jamaica.
In 1494, Christopher Columbus landed here.
It was a completely unknown part of the world,
at least unknown to Europeans. It is the Americas.
The discovery of the Americas sent shock waves through European civilization.
New peoples, new plants, new animals.
The early explorers arrived utterly convinced that they were special,
set apart from the rest of nature. The pinnacle of God's creation.
Yet what they found here would begin to challenge that.
And for me, the story begins with a man called Hans Sloane.
An Irish doctor who arrived in Jamaica in 1687 to take up
the lucrative post of personal physician to the island's Governor.
To be fair to Sloane, he was more than simply an adventurer
in search of a fast buck. He was also a passionate botanist
who loved to go exploring the island on horseback with a guide.
OK, Marlin, are you ready to go? Yep. Lovely.
Elegantly done.
Don't want to be left behind.
My guide, Marlin Beale, is a botanist.
And together we're heading for the Blue Mountains
where Sloane would come face to face with what he described as,
"all that is extraordinary in nature."
I know that Sloane was a doctor and he was particularly interested in plants,
which had any sort of medicinal quality. Yes.
So if you see any, do let me know. Definitely, I will.
'Since most 17th Century medicines came from plants,
'it's not surprising that finding new species
'was high on Sloane's agenda.'
A-ha, here we go.
Smell it. Very pretty.
Yeah. Taste it, if you want.
Which end do I taste?
That end, the cut end.
That's ginger, isn't it?
It's wild ginger.
Interesting, because Sloane wrote quite a lot about wild ginger.
He believed that ginger was very good for the stomach.
I don't know about that. It's certainly good for sea sickness.
If you were doing a two month voyage across the Atlantic, this would be useful.
Sloane also claimed that wild ginger was good for treating cancers.
I'm not sure about that either. Quite tasty though.
Now, an interest in nature wasn't confined to collectors like Sloane.
Because in nature, and particularly plants,
lay the foundations of European imperial power.
Trading vessels criss-crossed the globe, bringing home all sorts of natural produce,
from tobacco and spices to tea and timber,
the botanical booty was practically limitless.
Even the ships, which carried the goods,
were themselves made out of plants.
There were trees for the framework, hemp provided the sails and ropes,
and they used pine resin to produce pitch,
which was used to waterproof the ships.
What distinguished Sloane from most traders and plantation owners
was an interest in all of nature. Not just plants but also animals.
This interest would open the world's eyes to the beauty of God's creation
and crucially to the puzzle of its incredible diversity.
There aren't very many big animals here on Jamaica,
but there are an awful lot of lizards and what Marlin
is about to do is make a little noose I think, is that right?
Yes. And hopefully we'll capture a few lizards.
Is this the sort of thing that Sloane might have used?
Possibly, because this would be the most conventional method at that time.
Just tight.
What we've got to do now is persuade the lizard to stick its...
It's head inside. So we've got our noose. Very neat.
A beautiful noose for catching lizards in the style of Hans Sloane.
Where are we likely to find them, Marlin?
Well, we can find some on the ground or even on trees.
So, both looking on the ground and on trees is great.
'It was this type of hands on approach...'
I think there's one over here.
'..that enabled Sloane to collect so many different specimens
'of Jamaican wildlife.' MICHAEL YELPS
He jumped. I think he's gone.
Michael. Have you seen something?
Yes. This one right, right there, do you see? Let's have a go.
Brilliant. Is he safe to hold? Yeah.
Maybe a bit feisty. So I'm going to get the noose off of him.
How many different species of lizards are there?
There are many different species, over 20 different species.
I think we've done very well. Yeah.
This book has illustrations of just some of the things that Sloane
captured in Jamaica. A snake there.
There's our friends, the lizards.
I think the one I helped capture, is the one in the middle there.
The book is just full of beautiful drawings.
Birds, fishes...
The thing is that Hans Sloane came to Jamaica not just to revel in its beauty,
but to record everything he saw, which he did in enormous detail, so that other people who
couldn't come here could enjoy and learn from what he had discovered.
After 15 months on the island, Sloane returned to England.
He brought back with him some 800 samples of flora and fauna,
a fully grown crocodile and a recipe for drinking chocolate.
Unlike many explorers who returned from the Americas with tall tales
of giant sea serpents and men whose heads grow beneath their shoulders,
Sloane returned with real data and real specimens.
There was no reason as yet to think that all this diversity had anything to do with us.
But it did unsettle traditional ideas of God's creation of the natural world.
For people who believed that God had created the world
and everything in it, permanent and perfect,
this was also utterly bewildering.
Why had God bothered to make so many small and apparently pointless variations on a theme?
Why so many lizards? Why so many beetles?
The questions started to come thick and fast.
By the time Hans Sloane died in 1753, he had put together
the world's greatest collection of natural objects.
Most of which are still with us today.
In front of me we have part of the Sloane Herbarium.
There are many, many thousands of objects
about 14,000 of these vegetable substances.
Flowers, fruits, dried objects, which we can't press.
'And with that there are about 270 bound volumes
'with many, many thousands of specimens in.'
So vast was Sloane's hoard of wonders
that it was moved to a new type of institution
beginning to appear across Europe.
The national museum.
Private collections, like Sloane's,
could now be seen by a much wider audience.
Bringing nature out of the wilderness and into the every day world.
This new curiosity about life on earth
would bring us closer to the question - how did we get here?
It was fuelled by voyages of discovery and the money to be made from nature,
by obsessive collectors, like Hans Sloane,
who began to document nature's diversity.
And by museums, where ordinary people could see it for themselves.
And it now turned out that all this life also had a history, a rather rich one.
Paris. Just after the French Revolution.
Where the belief that God's creation was fixed and unchanging
was about to be further undermined by a brilliant anatomist
and a taste for new buildings.
Paris is a city in love with its own beauty.
Whatever events may have been dominating the headlines -
the fall of the Bastille, the execution of the King,
one thing has remained constant -
the City's determination to build on its rich architectural heritage.
Buildings began to appear, which were every bit as magnificent as their predecessors.
'While others were added to.'
'For example, the Louvre.
'In the years following the Revolution, it grew
'from a Bourbon palace into a museum large enough to house
'France's rapidly expanding art collection.'
But I'm less interested in what's in there than what's out here.
And in particular this stuff - limestone.
A rock which for centuries had been the mainstay of Parisian architecture.
Now this limestone was hewn from a quarry that is very near to where I'm standing now.
A hidden one, one that is down there.
Deep beneath Paris lies an old network of stone quarries
linked by hundreds of kilometres of connecting tunnels.
Together they form a mirror image of the city above, right down to the street names.
People began quarrying away underneath Paris in the middle ages.
And they went on digging for hundreds of years.
There should be a sign just over here.
Yes, "3R."
This is the old revolutionary calendar
and it means three years after the start of the French Revolution.
At that time, houses being built over my head
would have contained limestone from quarries just like this one.
I'm Gilles. It's a pleasure to meet you. And you.
I guess actually quarrying down here must have been pretty dangerous.
It could be dangerous.
It's the reason why quarrymen put this hand made pillar
to protect them from falling roof, from collapse.
Who actually dug these areas?
It is specific to France when you are owner of the surface,
you are owner of the underground until the centre of the earth.
To the centre of the earth under French law?
Yeah, according to the French law. How interesting.
'As more and more quarries were excavated,
'people began to take a greater interest in the mysterious objects
'they were finding embedded in the rock.'
Ah, it's magical, isn't it? You can see there, a really clear shell.
It must have been very strange for the workmen who first came
down here when they realized they were looking at something which should be on the ocean floor.
What they were looking at, of course, were fossils.
For a long time, people had no idea what fossils really were.
Some people claimed they'd come from the moon.
Others that they were mud's unsuccessful attempt to turn into life.
In fact, it wasn't until the end of the 18th Century
that people fully appreciated they had once been living things.
And this realization opened up a whole new window into the past.
A past that was both ancient and unimaginably different.
Here in France, many of those fossils
ended up in the hands of a brilliant scientist.
A man obsessed by old bones.
His name was Georges Cuvier
and he was widely regarded as the world's leading animal anatomist.
There was barely an animal in existence
whose remains hadn't come his way.
There's a story about Cuvier, which I like, which I think really sums up the man.
It's late at night and Cuvier has gone to bed...
when one of his students dressed in a devil's costume bursts
into his room and cries "Cuvier, Cuvier, I've come to eat you!"
Cuvier opened one eye, calmly looked the student up and down and said,
"All animals that have hooves and horns are herbivores -
"you cannot eat me."
Now the point is that Cuvier had realized
that from a couple of features,
you could work out the essential nature of any animal.
This insight would lead Cuvier to propose a new, and to many minds,
unthinkable story of life on earth.
Now I'm no Cuvier, but I did train as a medical doctor
and so I've seen a lot of bones, albeit human ones.
In here I've got some fossil bones. I'm going to try and see if I can work out where they came from.
Right. I think this is the end bit of the finger.
But in this case is has a big claw attached.
So I'm guessing this comes from a carnivore. I'm going to go and hunt carnivores.
'By examining the form of any body part, Cuvier claimed
'you could discover everything there was to know about its function.'
It's a bit like a crocodile claw, but not really close enough.
'And from its function, its likely source.'
Bigger, but not bad. That's a dog.
I think that's about right.
I guess that this is from a hyena.
Let's see if I'm right.
No, close though, it's from a wolf apparently. Wolf.
Cuvier was clearly better at this than me and this allowed him to
identify many previously unknown fossils coming out of the ground.
But also some remains that would have unsettling implications.
One of the fossils that Cuvier was sent, was this one.
It is, believe it or not, a giant tooth.
You can tell that, because this is the enamel
or biting layer over here.
Now, the people who found this fossil
were convinced it came from an elephant.
But Cuvier had other ideas.
The fossil I've got here is obviously much bigger
than the elephant tooth you've got there,
what other features did Cuvier notice were different?
Well, you see the size of course, you are right.
But, in this African elephant tooth
you can see that the enamel is very different on the grinding surface.
There are diamond enamel lamina.
Here, there are parallel lamina
and they are more numerous than in the African elephant.
So there is a very important difference.
We know that this tooth was coming from Russia
and this tooth was called by Russians, the mammoth.
Ah, it's a mammoth. A mammoth.
So he was able to look at this and go, "It's an elephant,
"but a much bigger elephant,
"and a very different, sort of a third species of elephant."
The revelation that the mammoth was a species totally distinct
from any living elephant was nothing compared to Cuvier's next bombshell.
Cuvier thought long and hard about mammoths
and he came to a surprising and radical conclusion.
Now clearly, mammoths are enormous beasts yet no-one had ever seen one,
which suggested that at some point in the past
mammoths, all of them, must have gone extinct.
And it wasn't just mammoths.
Before long, hundreds of other strange looking fossils
began to be identified as creatures that had mysteriously disappeared
off the face of the earth.
The claim that some animals that had once lived had gone extinct
raised uncomfortable questions.
If every creature in God's fixed universe had a place and a purpose,
why had some died off?
The suggestion that most of the creatures
who had ever lived were now extinct was both baffling and disturbing.
The only consolation was that this was still a history of life,
which we humans were separate from.
For now, the most pressing question raised by extinction was one of time.
And whether this fossil record of long lost species was evidence
that the earth was older, much older than previously believed.
The 18th Century was the age of the experiment.
There were experiments on light, liquids,
but also an experiment to establish the precise age of the earth.
The man behind the experiment was Le Comte de Buffon.
A fabulously wealthy French aristocrat, Buffon
was the first person to seriously attempt to measure the age of the earth,
and he did so using some metal balls, a pocket watch and a blacksmith's forge.
Good morning, Brian. Good morning. Hi there, I'm Michael Mosley.
Hello, Michael. I have a present for you.
Two metal balls. I think you know what to do with them.
You might imagine that back in Buffon's day, most people believed
that the world was created in six days and was 6,000 years old.
In fact, a lot of people, including many clerics,
did not take the Bible that literally.
Buffon was not unusual in suspecting that the earth might be very old.
Where he was unusual was he was prepared to do an experiment to find out just how old.
Right, anything I can do?
Give it a nice long stroke, just slow, straight down.
How long will it actually take to heat up to red hot?
Probably the best part of an hour looking at the size of the ball.
The experiment was actually based on a suggestion by Sir Isaac Newton.
He said imagine the world had started off as a red, hot piece of iron.
If you could work out how long it had taken to cool
from that state to the present state,
then you could work out just how old the earth really is.
By timing how long it took for different size balls to cool down,
Buffon was confident he could extrapolate his figures
and establish how long it had taken the earth to reach a similar state.
Do you reckon they're ready yet, Brian?
Well, they're well up to temperature, yes.
It's hot, isn't it?
I'm trying to avoid dropping this on my toes.
Take that down there.
Brilliant. I've got my pocket watch here now.
So, how long do you think before we can actually touch them?
Looking at least 25 minutes or even longer for the small one.
The larger ones much more mass, probably an hour.
'A little later and I'm finally ready to start to plot my graph,
'extrapolating my timings for the two balls,
'to allow for the much bigger diameter of the earth.'
Right. Now for the age of the earth using Buffon's method.
I calculate the age of the earth at 92,000 years.
And Buffon, well, he said it was a suspiciously accurate
74,832 years old.
As we now know, both these figures are in fact way out.
Wildly inaccurate though Buffon's method was,
it would be churlish to let that detract from his legacy.
The important point is, that by doing the experiments
and by publishing the results, Buffon sparked a debate.
Not just about how old the earth actually is,
but how and why every creature on earth came into being.
A debate that would now be intensified
by a new way of looking at the world.
Standing between northern and southern Europe
is one of the world's most formidable natural barriers -
the Alps.
Even as late as the mid 18th Century,
no-one had yet climbed this region's highest peak -
Mont Blanc.
In 1760, a young Swiss aristocrat called Horace Benedict de Saussure
came to the small Alpine village of Chamonix, in the foothills of Mont Blanc.
Now, he came originally to collect plants. But he soon became so enchanted by the mountain
that he offered a reward to the first person who could climb it.
Despite many attempts,
it was 26 years before anyone managed to reach the summit.
de Saussure himself got to the top a year later.
But de Saussure was much more than a rich man with a passion for extreme sports.
For once he'd climbed Mont Blanc, he proceeded to carry out a series
of experiments to discover much more about the mountain.
Going to remote places and getting your hands dirty was a new way
of trying to understand the processes which shaped the earth.
And de Saussure gave it a name...
With its emphasis on direct observation
this new way of looking at the earth would play a vital role
in unravelling not just the mysteries of the planet,
but also the entire history of life on earth including ours.
All across Europe practically dressed men
armed with small hammers headed off into the countryside
in search of the earth's hidden secrets.
Driven by an intense curiosity
that would have surprised their predecessors,
they began to notice a number of strange anomalies in the landscape.
I've come here to the east coast of Scotland
to a place called Siccar Point.
It is wild, windy and rather beautiful.
And just down there is something truly remarkable, something which an early
geologist who came here described as like looking into the abyss of time.
This is what I've come to see and it is very strange indeed.
It's called an unconformity.
What you have down there is layers of rock that appear to be laid down vertically.
And then just above them a layer of red sandstone, which appears to have been laid down horizontally.
But as odd as this may seem,
to some there appeared to be a startling explanation.
This layer of rock looks as though it was laid down vertically.
But at some point in the past it must have been at the bottom of the ocean
and formed horizontally by layer after layer of sediment.
Then the whole thing rose to the surface, was flipped
through 90 degrees and sank to the bottom of the seas again.
There another layer formed,
until finally the whole thing rose to the surface once again.
All these processes are extremely slow and all this implied
that the earth is incredibly old - practically eternal.
And it wasn't just Siccar Point.
The evidence for slow change was everywhere.
Geologists looked at waterfalls and saw how the constant
flow of water had gradually eroded the surrounding rock.
They saw how rain had inexorably worn away the tops of mountains.
And how the slow movement of glaciers
had carved out entire valleys.
They came to realize that the single most important factor
in why the world looks the way it does
was time and lots of it.
The moment that people first began to think in terms of deep time
is one of the most significant in the history of science.
It would go on to profoundly affect how people see themselves.
But trying to grasp deep time is extremely difficult, because it is so different to human time.
So you have to rely on analogies.
One of my favourites is to imagine the age of the earth as a length from my shoulder to my finger tips.
On that scale, the whole of human history, everything we've achieved in the last few thousand years
would be wiped away by the single swipe of a nail file.
So, why did this concept of deep time take root now?
There was the expansion of quarrying and mining exposing more of the hidden earth.
The fossils of extinct creatures that were being uncovered.
And the emergence of geology - a new scientific view of the planet.
Finally, the pieces were in place to try and answer the question - how did WE get here?
The industrial revolution was a time of rapid, dizzying change.
Great industrial cities spread across Victorian Britain,
their factories drawing in workers from far and wide.
New railways snaked across the landscape cutting journey times
and bringing cheap goods to the masses.
'It was a whirlwind of new ideas, new methods
'and all of it in the name of progress.'
Belief in progress was one of the defining characteristics of the Victorian age.
Factory owners from humble origins had country houses, even seats in Parliament.
Britain was the leading industrial country in the world thanks to the ingenuity of her people.
It was out of this belief in progress that a radical theory
of how WE got here exploded onto the scene.
The theory proposed that not only were societies and nations
capable of progressive change, but also nature.
In 1844, this slim, rather ordinary looking book was first published
and it swiftly became one of THE most controversial books
of the Victorian age.
It was a literary sensation selling tens of thousands of copies
and it was read by everyone of influence from the Queen downwards.
Adding to its mystique was the fact that its author made strenuous
efforts throughout his lifetime to remain strictly anonymous.
The author was a Scotsman -
Robert Chambers.
Robert Chambers was born with six fingers and six toes.
When was young he had an operation to get rid of the extra digits,
which unfortunately went wrong.
Self conscious, Robert now immersed himself in the world of print.
Few changes embodied the Victorian ideal of progress
as much as the 19th Century transformation of the print industry.
The steam-powered printing press ushered in a new age of cheap,
mass-produced books creating a hunger for knowledge right across society.
In response to this demand,
Robert Chambers helped his brother set up a successful publishing firm,
while still leaving enough time to devote to his first love -
Robert Chambers was not a very original thinker but he was well read.
His writing was clear, vivid and above all thought provoking.
It was these qualities plus the fact that he had an insider's knowledge
of the publishing industry, which ensured his book was a huge success.
Chambers called it Vestiges Of The Natural History Of Creation
and in it he presented a compelling case
for the notion that species are not fixed - they change.
That everything had developed from an earlier form.
He called this concept transmutation.
We call it evolution.
Evolution emerged out of a world of progress, a conviction that
all things are capable of change, of improvement.
A history of life that was as diverse as it was baffling.
And a realization that the earth was almost immeasurably old.
But the real significance of evolution to this story is that
it now forced people to confront the uncomfortable question -
how did we get here?
Chambers was not the first person to write about evolution,
but he did take the argument further than others had.
Instead of being set apart from the rest of creation,
Chambers was saying we were simply an extension of it.
No wonder he wanted to remain anonymous.
For a society where people fervently believed that
humans had a special place in God's creation,
the claim we were descended from animals was deeply shocking.
And so the backlash began.
There were attacks from the scientific community
on the book's accuracy.
And from the clergy for undermining moral and social order.
One particularly scathing review described it as,
"not merely shallow and superficial, but utterly false throughout."
Harsh. But despite the controversy,
or let's face it probably because of it,
the public simply couldn't get enough of this book.
For all its success, what Chambers' book didn't do
was come up with an explanation of how evolution happens.
The man who answered that question was, of course, Charles Darwin.
A keen geologist and an ardent believer in the earth's antiquity,
Darwin had been working on his own theory of evolution
for several years when Vestiges first appeared.
But, it would be a further 15 years, by which time much of the fuss
surrounding evolution had died down, before Darwin felt ready to publish.
His explanation for how animals evolved had its roots in
the same industrial landscape from which Chambers' book had emerged.
According to Darwin, life was one long struggle for survival.
And just as within the cotton industry,
there was competition between manufacturers,
so in nature there was competition between and amongst species.
Just as new technology might give one factory an edge over another,
so it was in nature.
Any new trait that gave an organism an edge over its rival would prevail
and become more common in later generations.
Gradually giving rise to the appearance of new species.
A mechanism for change that Darwin called Natural Selection.
Darwin's followers must have hoped that his theory of Natural Selection
would help answer the question - how did we get here?
But there were holes in the theory.
Although Darwin acknowledged the critical importance of the environment on driving evolution,
he never fully grasped the incredible extent
to which life on earth is shaped by changes in our violent planet.
Something which has only relatively recently come to light.
While biology raced ahead in the early 20th Century,
geology had more or less settled into a routine.
Stones were dated,
fossils examined, collections expanded.
But, as so often happens in the story of science,
it's the non-specialists, the enthusiasts who shake things up.
One such enthusiast was Alfred Wegener.
He was a German meteorologist, a weather man,
and with his brother, he held a world record for ballooning.
He was not, however, a trained geologist.
But that didn't put him off proposing a radical
and controversial new theory about the forces that shaped the earth.
Forces so powerful as to have shaped even life itself.
The story goes the Wegner was looking at an atlas when he noticed something rather peculiar.
Take a map of the world, a pair of scissors and cut your way down through Greenland
until you get to the cost of South America.
And then it requires a little bit more finesse
working away carefully around Brazil.
And then at the end, just slash away again.
If you move the coast of South America over to the coast
of Africa what you'll notice is that they seem to match very closely.
It's almost as if they were once joined.
Wegner noticed this, but he did nothing about it for around a year,
until he came across some fascinating fossil finds.
Take a look at this.
It's a fossilized leaf and it's about 250 million years old.
It came from a tree fern that is now extinct.
Now, the odd thing these tree ferns grew in the tropics
but these fossils have been found in cold, remote places like this one.
In fact, places even colder than here in Iceland.
So how was that possible?
Then, there were reptiles.
A particular species of reptile found in South America
but mysteriously matched by exactly the same species in Africa more than 7,000 kms away.
In attempting to explain these mysteries, Wegner would transform geology.
Science would have to embrace a new
and very different history of life on earth.
Wegner developed a theory that was logical, but also, on the surface, completely ludicrous.
He suggested that all the great seven continents had once been clumped together
into a single super continent that he called Pangaea meaning, "all lands".
And then Pangaea had simply split apart.
A process that Wegner attempted to illustrate.
Wegner compared the moving continents to the huge floating icebergs
he'd seen on his many field trips to Greenland.
But instead of blocks of ice weighing a few thousand tons,
he was talking about great slabs of rock weighing trillions of tons.
The problem for Wegner was nobody was buying his big idea.
To his eternal frustration, Wegner had no way to explain
how the slabs moved, no hard evidence to convince the sceptics.
One of Wegner's many critics described his ideas as "utter, damned rot."
And you can see why.
The idea that we are floating around seems preposterous.
And it didn't help that Wegner was an amateur geologist,
in many eyes, a jumped-up weather forecaster.
Wegner went back to meteorology and his theory was shelved
until a series of unexpected discoveries made during the height of the Cold War.
In the 1950s, as the Cold War intensified, the United States
and the Soviet Union found themselves engaged in a game of cat and mouse deep beneath the ocean.
A game that demanded a much more accurate picture of this underwater landscape.
And so the oceanographers set to work.
They began taking thousands of photographs of the ocean floor.
Echo soundings plotted the rise and fall of deep sea ridges...
..while drill rods were sent down to establish the composition of the sea bed.
But, in mapping the oceans, the scientists discovered something entirely unexpected.
They found that the sea floor didn't consists of one thick uniform crust,
as used to be thought, but a number of thin interlocking plates.
And that the boundaries to those plates featured mountain ranges...
..deep rift valleys...
..even volcanoes.
And this entire landscape was floating on a bed of molten rock constantly on the move.
And you can also see evidence of this on dry land.
I've come to Thingvellir in Iceland, one of the wonders of the world.
It is one of the few places on earth
that you can actually see with your own eyes
the joins in our patchwork planet.
This may look like an ordinary cliff edge, but it's actually the start of an enormous great slab of rock
which extends all the way from here in Iceland,
across the Atlantic Ocean, across North America to the Pacific Ocean.
It is called the North American Plate.
And just over there, well, that is the beginning of another enormous plate.
It is called the Eurasian Plate, and it extends all the way from here to Shanghai.
Now, if I was to stand here long enough, say, a few thousand years,
I'd notice the gap between me and Eurasia was getting wider.
Scientists have measured this movement.
It ranges from a very gradual seven millimetres a year here at Thingvellir,
to almost ten centimetres a year elsewhere.
Over hundreds of millions of years,
this shifting of the earth's plates has transformed the face of our planet,
a never-ending cycle of change that Wegner had called continental drift.
Sadly, Wegner didn't live long enough to see his theory vindicated.
In 1930, he went on an expedition to Greenland.
There, in temperatures of minus 60, he died of cold and exhaustion.
He was buried on the ice.
Because of continental drift, his body is now two metres further away from home.
But continental drift has done much more than shape the earth.
By showing how a fossilised tree fern could travel all the way from the tropics to the ice,
or why it is that a single species of reptile can be found on what are now two widely separated continents.
The theory also takes us closer to solving the mystery of how we got here.
And that's because when the earth moves in this way, the results can also be incredibly violent.
When the earth's plates collide...
..they can trigger volcanic eruptions so powerful as to block out the sun for months on end.
As those same plates grind against each other,
so they cause devastating earthquakes...
..which themselves can spawn mega-tsunamis, that destroy everything in their way.
While it's easy to imagine that all this violent upheaval
brought with it nothing but death and destruction, the truth is very different.
It's now clear that throughout our four and half billion year history,
the balance of our planet has been absolutely central to the creation of new life.
Because, every time our planet experiences violent change,
a new opportunity for life opens up...
..making continental drift one of the great drivers of evolution.
And here are just a couple of ways it has changed life on earth.
Some 30 million years ago,
the plate boundary separating Africa from Arabia began to pull apart,
causing the land in between to fall away.
A 5,000 km gash in the earth's crust,
that we know as the East African Rift Valley.
As a new landscape of broken savannah formed,
it allowed the ancestors of many today's animals to gain a foothold, and to flourish.
And then there is climate change, when continental drift has also played a major role...
..not least by accelerating the onset of ice ages,
by pushing land towards the poles, and altering the flow of ocean currents.
Changes which have forced animals to adapt in the most remarkable of ways.
And, just occasionally, we're subjected to violence...
..from beyond our planet,
so extreme, that many species are wiped out altogether...
..only for others to take their place.
And so, what of us?
How did we get here?
Well, we are just the latest in a long line of lucky survivors,
born out of death, destruction, and the immensity of deep time.
And if this great experiment that is life on earth
were to be run again...
..we might never even show up.
It's now clear that the story of life, and the story of our planet,
which were once seen as separate, are actually intrinsically linked.
The evolution of new life has been driven by climate change,
by asteroid impacts, and by the slow-motion collision of continents.
It turns out that we and every other living creature
are marching to the drum beat of our violent planet.
Next time, an ancient human ambition...
the search for limitless power.
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