For centuries people have dreamt of reaching the centre of the Earth. Now scientists are uncovering a bizarre and alien world that lies 4,000 miles beneath our feet.
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Across the world,
a daring and far-fetched experiment is under way.
I'm going to increase more.
It's very risky, but it's worth doing, and also,
if I succeeded, I will be the king. HE LAUGHS
Scientists are attempting a journey that previous generations
have only dreamed of.
I can't imagine a less hospitable place for people.
High pressures, white hot temperatures.
They are trying to reach the centre of the Earth.
3, 2, 1...
What they are glimpsing is a bizarre and alien world.
We're at a golden age, in terms of the real discovery of the bulk of the deep Earth.
It's really almost a planet within our own big planet.
It's like a forest.
It looks very interesting.
Their work is opening up a window
on one of the great mysteries of the solar system.
The Earth's core.
A hidden world, 4,000 miles, deep beneath your feet.
The Goddard Space Flight Centre
is NASA's mission control for unmanned spacecraft.
From here, scientists manage many of its most important telescopes and satellites.
Space engineer Ken LaBel has devoted his career
to perfecting the smooth running of these explorations of the stars.
But in February 1997, he was thrown into a space mystery,
that would offer clues to what is happening deep within our own Earth's core.
The Hubble Space Telescope was in trouble.
It's a Friday afternoon. I'm at the office, and the phone rings.
Engineer who I've been working with called me and said,
"Well, you know, we newly launched last month, two new instruments.
"We're seeing some problems we weren't anticipating."
Two ground-breaking new instruments had been installed on Hubble.
They were designed to peer into deepest space,
and to find black holes.
But as Hubble criss-crossed the Earth,
the highly sensitive multi-million dollar equipment was malfunctioning.
The event they were seeing were these current spikes.
If a signal is just moving along,
all of a sudden you get some injection of noise so you get a spike.
The issue for this particular device was that the error
could end up being deadly.
It could really take out their system. That was the fear.
They'd lose this big scientific instrument that people spent
most of their lives working on.
What made finding the cause of these potential fatal spikes
so urgent was that they were happening almost every day.
One of the first tasks was to plot just where.
And it soon became clear these weren't random events.
They were tightly clustered across the centre of South America
and the south Atlantic.
It's an excellent indicator that our problem was being
induced by that specific environment, and not because of a thermal issue,
or a potentially a power system issue
or some other type of spacecraft system not working appropriately.
In fact this region of space has developed
a reputation at NASA as a place of strange events.
Astronauts have reported seeing flashes of light there.
Satellites and space shuttle computers malfunction.
It's even become known as space's Bermuda Triangle.
Calling it the Bermuda Triangle is actually a good analogy.
It's been called that several times over the past 20 or more years.
It's a known hazard for spacecraft.
The challenge was now figuring out what in the system was causing it,
and what we could do about it.
But this region of space wasn't only of interest to NASA,
it also held important clues to what's happening in the deep Earth.
It may be hidden 4,000 miles beneath our feet,
but the core of our planet is central to life on Earth.
Because it creates Earth's magnetic field.
A tool for navigation that's vital for some of nature's greatest spectacles.
The mass migrations that take place around the world.
And a tool that helps us explore the planet, too.
But most importantly of all, it helps protect life itself.
Because the magnetic field it generates forms a vital barrier
between us and the dangers of space.
The core of the Earth and its magnetic field certainly played
a role in the evolution of life on Earth.
It shields us from the solar wind, and particles,
boiling off the surface of the sun.
Yet, for all the core's importance, though we have travelled high above our planet,
we've never made it down to reach its heart.
And that's because the barriers to a physical journey to the core are truly formidable.
One place on the American continent,
where you begin to get a sense of the challenges of descending
into the Earth, is a deserted gold mine, Homestake.
Dr Bill Roggenthen is a geologist
and explorer of the subterranean planet.
He's on the 12-minute journey down, to what is now the deepest laboratory in the USA.
There's snow at the surface but underground,
conditions are very different.
It was chilly at the top.
It's still early spring here in South Dakota,
and as we go down, steadily,
the temperature, at least the rock temperature
increases at a rate of around over 22 degrees C per kilometre.
Bill is travelling through the first barrier on any journey to the core.
The Earth's crust.
A shell of rock, typically around 35 kilometres thick.
OK, so now we're standing on the 4,850 foot level,
almost one-and-a-half kilometres below the surface.
Homestake mine is the deepest anyone's managed to dig in the USA.
Here, the rock temperature is around 29 degrees C.
Another kilometre down and it would be hotter than the highest temperature
ever recorded at the surface.
And, right now, we are doing experiments
and getting experiments going at this very deep location.
As scientists probe the inner workings of our planet,
it's not just the temperature they're contending with...
..it's also the pressure.
Any time when you're in the sub-surface
and you make an opening, nature wants to close it.
The deeper you are,
the harder that nature works to try to get rid of that opening.
Here, the rocks are particularly strong.
But such is the weight of the ground above, even at Homestake,
nothing is quite rock solid.
So these instruments here are measuring the movement
of the free surface of the rock way back into the rock itself.
So, even though that movement is very minor, we need to
monitor it to make sure these excavations are remaining stable.
In some areas of the crust, it would be impossible to keep an excavation open at this depth
because, at this intense pressure,
solid rocks can behave like elastic
and even change their constituency to become plastic.
Yet, we're only 0.02% of the way to the centre of the Earth.
So, even at this depth, why it's a huge amount,
the pressure at the Earth's core is 50 million lbs per square inch.
That means that at the centre of the Earth,
the pressure is three million times that at the surface.
The temperature is over 4,000 degrees Celsius.
As hot as the surface of the sun.
We're an ant, if you will, as we, kind of,
burrow around this part of the world.
Having said that, it's a tremendous opportunity to go down inside
and see at least what this small part of the world
looks like in three dimensions, and that's really exciting.
The vastly increasing pressures and temperatures mean man will
never be able to physically dig to the core.
Scientists have had to search for other means to penetrate any further into the Earth.
People thought I was a little nuts coming here.
Famous people bet me money that I wouldn't stay for more than two years, and they all had to pay.
Professor Rick Aster is one of America's leading explorers
of the inner planet, though he has barely travelled below the surface.
As former President of the Seismological Society of America,
he doesn't need to.
Next to his lab in New Mexico is the university's test site.
It has provided him with a perfect landscape for an alternative way of seeing into the underworld.
Earth tremors - natural and manmade.
Seismology really is the killer application,
when you get right down to it.
It's the only methodology that we have
to remotely study the deep interior of the Earth with any kind of resolution.
Today, Rick is blowing up a tonne of high explosives to generate seismic waves.
Although it's on a small scale, it's exactly the type of thing
that we would need to look through the interior of the entire planet.
WARNING ALARM WAILS
Three seismographs have been set up.
One, just meters away from the explosives.
Another, at one kilometre distance.
And the third, two kilometres from the blast.
They'll measure how the Earth moves in response to the detonation.
Particularly with these shallow explosions,
most of the energy actually goes into the air.
What I'm interested in is how much goes into the Earth.
There's no doubt that that sent a lot of energy into the ground.
I think we'll see a very strong signal from this explosion.
This is what you see when you set off one tonne of explosives.
A supersonic shockwave.
But, hidden from view,
a second pressure wave is travelling through the Earth.
A seismic wave.
And, it's what happens to this wave, underground,
that Rick is interested in.
Very close to the explosion we see a very simple signal.
We see the seismic waves generated as a very sharp impulse
travelling through the Earth, passing the seismograph, and it's over in just a second or two.
At one and two kilometres,
we see the development of a very rich wave train of scattered energies,
scattering off the topography, the landscape,
and scattering off the interior of the Earth, so that the signal is drawn out from this strong signal
that was generated at the site.
The further seismic waves travel, the more revealing they can be.
Because the speed at which they move through the ground changes
depending on the constituency of the material they pass through.
The speed of the wave tells us, basically, how stiff the rocks are.
That can tell us a lot about what's going on within the Earth.
If you're studying a volcano, for instance,
the speed of seismic waves slows down tremendously
when it goes through magma, as opposed to rock.
But to create seismic waves, which are able to pass all the way through the centre of the Earth,
and out the other side...
you need seismic events bigger than this one.
The shockwaves of major Earthquakes radiate through the globe.
Scientists have gained a form of X-ray vision into the heart of the Earth
by analysing the speed at which they travel.
It's revealed that we aren't simply living on one solid chunk of rock.
The Earth is made up of different layers.
First, is the Earth's thin crust.
The Earth's crust is really, really thin.
It's about 0.3% of the way to the centre of the Earth.
Then there's the mantle,
made of rocks turned malleable by the extreme heat and pressure.
The Earth's mantle is made of rocks that are, in some ways, similar to what we see at the crust,
although their chemistry is a little different.
But then the waves hit something else and, crucially,
they slow down.
To a seismologist, that could only mean one thing.
The fact that seismic waves travel down through
the mantle in a certain manner and then they hit the outer core, which
has a much slower seismic velocity, indicated the Earth had a core.
Indeed, it had an enormous core and it's molten.
It has a viscosity that's not much greater than water.
So it's an enormous ocean of white-hot, molten metal.
Seismology has managed to reveal the Earth's core.
A huge sea inside our planet, the size of Mars.
But that wasn't all seismology detected.
Scientists found signals of something else inside this sea of molten metal -
an inner core.
But for years, quite what it's like remained an enigma.
The biggest breakthrough into the nature of this elusive inner core
has come from a seismologist working as far away from the violence of Earthquakes as you can imagine.
Dr Arwen Deuss took on a puzzle that had baffled every previous seismologist.
So we have this mystery.
We have an Earth which has a solid mantle and a fluid core.
And people have discovered that there was actually an inner core inside this fluid outer core,
but people didn't know for sure if this inner core was solid or fluid.
It was a very difficult problem to solve.
Arwen wasn't to be deterred.
She suspected that the inner core was solid and was determined to prove it.
If you want to prove that the inner core is solid,
there's one specific wave you need to find, which is a tiny wave,
and a really difficult wave to observe in seismograms,
which we would call the shear wave, which can only travel through solid material.
If Arwen could find a shear wave that had passed through
the centre of the Earth, she'd prove the inner core was solid.
But there was a major problem.
How do you differentiate a tiny inner core shear wave,
from the cacophony of other waves reverberating through the Earth?
It's like a needle in a haystack.
It's not something that pops out of the piece of paper
when you look out the seismogram.
So we realised we had to do something different if you want to find it.
We couldn't repeat what other people had done.
The hunt was on.
A new approach to finding an inner core shear wave was needed.
And Arwen found it in an incredible property of the Earth...
The way in which the whole planet resonates
when it has been struck by an Earthquake.
Now when the Earth is hit by a major Earthquake, it's like a big hammer
hits a string of a musical instrument,
and that will start playing all the different tones of the Earth.
Now if we know that there's all these thousands of different tones
happening in the Earth,
what we can do is we can propose two different hypotheses.
We can calculate what all these tones would look like for an Earth with a fluid inner core.
And we can calculate what all these tones look like for an Earth with a solid inner core.
By comparing the predictions, she finally knew where to look for the elusive shear wave.
If she found it, she'd prove the inner core was solid.
So this little peak here is our needle in the haystack.
That is the thing we are going to be looking for in the real data.
All she needed now was an Earthquake to test her theory on.
A perfect candidate was a magnitude 7.9 quake that had
occurred in 1996, under the Flores Sea in Indonesia.
It was big.
And it was deep.
So it's one of the ideal Earthquakes to look for these inner core shear waves.
She started collating the data of this quake
from 47 different seismic stations across the world.
This red box is where you would expect a wave from the inner core to arrive.
Her hope was that the signal would eventually emerge
through the noise created by thousands of other seismic waves.
When we get to 40, we can see a little peak starting to appear.
The question is, when we start adding more stations,
is that bump going to grow or not?
Arwen added station after station.
This is what we're looking for. By adding more stations,
the peak gets bigger, so this is quite exciting.
She was on the brink of answering this fundamental question about the Earth's inner core.
We add our last station, 47, and now we have a really large signal there.
That's our needle in the haystack.
We've got a really nice, strong, big arrival,
proving that the inner core is solid.
This shear wave, which could only pass through solid material,
had travelled through the centre of the Earth.
Arwen had discovered that sitting inside our planet
is a solid metal ball, almost the size of the moon.
But our solid inner core is proving stranger than Arwen could ever have imagined.
Say you had an Earthquake at the North Pole and a seismometer at the South Pole,
then a wave that would travel from the North Pole to the South Pole
would arrive up to five seconds faster than from east to west if they go through the inner core.
And we had no idea how to explain that.
Seismology on its own simply can't unlock all the inner core's secrets
but it seemed to be the only real way scientists could reveal them.
In Japan, one man has pioneered a new technique to investigate the mysterious inner core.
Because Kei Hirose is a scientist determined to leave the surface world behind,
and complete an impossible mission to see the centre of the Earth.
We cannot go into the centre of the Earth,
but we can recreate the conditions
corresponding at the centre of the Earth in my own laboratory,
and it's a kind of journey to the centre of the Earth.
I'll try to be the first person to reach there.
It's very risky but it's worth doing,
and also, if I succeeded...
..I'll be the king! HE LAUGHS
This is the SPring-8 Synchrotron Radiation Facility.
Kei's using its powerful equipment
in his attempt to recreate the immense temperatures
and pressures found at the inner core.
Somewhere rather more convenient to study.
OK. So, as a diamond it looks beautiful,
and then I put it on to the seed.
The first part of his mission is to simulate the pressures
found at the centre of the Earth.
It took him ten years and hundreds of shattered diamonds to design an enormously powerful vice,
using the tips of the jewels.
Next, we can load the samples, and these are very tiny.
Between the points Kei puts a sample...
a shard of iron nickel alloy.
The material scientists believe makes up the inner core.
At the Earth's surface, it's composed of lots of tiny crystals.
Kei hopes to show what happens to its structure
under the extreme conditions found at the inner core.
OK, that's fine.
He uses the vice to raise the sample pressure to that of the inner core.
It's equivalent to three medium times, atmospheric pressure,
so it is very high pressure. But we just use a screwdriver
to increase the pressure, to such extreme conditions.
It's very simple.
Part one of the mission complete. Now for stage two.
Kei has to heat the sample to 4,700 Kelvin.
A temperature found at the inner core, and on the surface of the sun.
The beam of an infrared laser will be focused on the sample to raise its temperature.
At the beginning of the experiment, Kei shines X-rays through the sample to create an image.
The iron nickel crystals form a pattern of two concentric rings.
So this image tells us what is going on inside the sample,
under high pressure and high temperature.
OK, so let's go.
As the power of the laser is increased,
the temperature of the sample rises.
OK, so the sample is already about 1,500 Kelvins.
Let's take the X-ray defraction images.
And as the temperature grows,
the iron nickel crystal structure begins to change.
And now the temperature is about, OK, it's about 3,000 Kelvins.
A uniform circular structure has all but gone,
and crystals appear to be clumping together.
Oh, now, the temperature is very high. It's almost close to the temperature at the core.
You know, I'm very nervous at this moment.
I'm going to increase more, OK?
Oh, look at this.
It is already 4,000 Kelvins, which is the real core temperature,
and take another pattern here.
Welcome to Kei's inner core of the Earth.
For the first time, he has shown how iron nickel alloy crystals
undergo a dramatic transformation under the pressures and temperatures
found at the inner core.
I think we should stop here. It's successful, we are very fortunate.
We sometimes fail the experiment, but this time we are very lucky.
These X-ray images give us a real insight into the physical nature of the inner core.
It's iron nickel alloy, but not as we know it.
So, this is the first image.
We have rings and it became spotty during heating.
And the size of the crystal of iron nickel alloy increased
by 1,000 times at core pressure and temperature, in our experiment,
just in ten minutes.
Over millions of years, under the extreme heat and pressure
found at the core, these crystals could have grown to huge lengths.
We may have very big crystals at the centre of the Earth.
Maybe up to ten kilometres.
It's like a forest.
It looks very interesting.
Kei believes this forest of crystals makes up the solid inner core of our Earth,
with the crystals all pointing in the direction of the north pole.
This could now explain why seismic waves travel through the core faster north to south,
along the grain of the crystals,
than east to west, across them.
We tried many, many times, but we always failed.
But we finally did and, you know, I realise how important it is.
And, you know, probably it's a big achievement in my life.
Kei's discovery is a significant step forward in our understanding of the core.
But scientists' revelation of a white-hot metallic inner world
raises another, more fundamental question.
Why is the core of our planet so very different from everything
we know at the rocky surface?
The answer would ultimately turn out to be central to the story of life on Earth.
Professor Dave Stevenson has made a career out of studying what lies
beneath the surface of all planets in the solar system.
I love looking at things that are difficult to understand,
that are difficult to get to. So I've always been fascinated by cores.
But one aspect of why
I find Earth's core so fascinating,
is that it - I believe -
contains a memory of what happened in the history of the Earth.
He believes to truly understand our core, we need to look up to the stars...
..and go back to our planet's birth, in the violent collisions that
happened during the formation of the solar system billions of years ago.
The Earth's core formed through
a very energetic set of events.
Let's go back to the beginning.
Imagine that you were bashing together bodies that were about the size of Mars.
And when you do that, you produce an enormous amount of heat.
The early solar system was a brutal and chaotic place.
But out of this fury, the conditions needed to forge our core were created.
When you heat a mixture of solid material that is in the form of rock and iron,
to very high temperatures, the iron will separate.
It is heavy, and so it will sink under gravity to the centre
of the Earth and the core will be formed.
It's this separation of molten rock and metal that makes the outer layers of the Earth so different...
..from the core inside.
And the Earth's baptism of fire had another legacy.
As the intense heat at the centre of our planet escaped,
it caused the liquid metal within the core to move.
This ceaseless motion in the depths of the Earth is what creates
the magnetic field we experience at the surface.
If you want to generate a magnetic field, the way the Earth does it,
you need a metal. That's fine, iron is a metal, it needs to be liquid,
that means it has to be hot. But you also need a temperature difference.
As the heat flows from the hot inner core to the cooler mantle, it causes
convection currents to form within the molten metal of the outer core.
Those motions, through the process of electromagnetic induction,
is the way in which the magnetic field is generated.
And it's the generation of this magnetic field that is so vital to life on Earth.
Because as charged particles are blown off the sun,
the magnetosphere deflects them,
creating a safe haven for our planet.
This magnetic field is providing scientists with new insights
into what's happening at the centre of the Earth...
moment by moment.
Geophysicist, Dan Lathrop, is on a mission to build a remarkable machine.
He hopes it will do something no supercomputer has managed.
Recreate the motions of molten metal in the core, to generate a magnetic field.
He started small,
but in his search for answers, the models have just got bigger...
What we don't know about the core is really details about the flows,
and details about the magnetic fields inside the core.
We know a bit about what happens at the surface,
but this is a very thick layer of liquid metal
and what happens underneath the surface is really a mystery to us.
The experiment is fraught with danger.
Dan plans to fill his core with 12 tons of molten sodium metal -
a highly volatile element -
and then spin it at up to 85 miles an hour.
This is really as close to a model of the Earth as we're going to have.
This device sets up a swirling mass of liquid metal as a mimic
of what happens in deep Earth, but in a way that we
can directly probe the flows, the rotating motions,
and look at them in more detail than we could ever do for the Earth's core.
He hopes this gargantuan model of the core will help explain
something strange about the behaviour of Earth's magnetic field.
It's never fixed, but constantly fluctuating.
So, while most people think of the Earth's magnetic field
as just being a simple north and south, it's really very complicated.
There are patches of weaker field, patches of stronger field,
all those are moving about the planet, some becoming weaker,
some becoming stronger, in a very complex way.
One thing is clear though.
If the magnetic field is continually changing,
then that must be caused by how the metal moves within the outer core.
Early experiments have already hinted at what could be happening.
Dan injected fluorescent dye into the rotating machine.
The results suggest the core is place of great turbulence,
filled with eddies and currents.
You might think of the core, like the atmosphere of the Earth,
being a very restless place with storms and fronts and bad weather.
Very complicated turbulent motions, very complicated sets of vortices,
all interacting with each other.
And those drive motions like the convection we see in the atmosphere,
billowing upwards motions in clouds.
All of those then are shaped by the rotation of the core.
And these deep motions interact with electric currents,
drive electric currents and cause the Earth's main magnetic field.
Dan's model is opening up a new window on the inner Earth.
Our core may be a dynamo, but it's no simple one.
Vast vortices and whirlpools create a magnetic field constantly in flux.
And that causes unexpected phenomena that scientists are only now beginning to understand.
Dr Jack Connerney has devoted his career at NASA
to studying the magnetic fields of planets
right across the solar system.
Here at NASA's test facility,
he's even got the ability to recreate the magnetic field of any heavenly body.
But something that's really fascinated him
are the changes that are happening to Earth's magnetosphere.
And how they're related to the turbulent molten metal dynamo
that is our core.
The dynamo is electrically conducting fluid in motion,
so when you have motion of that fluid,
it carries with it the magnetic field.
So, if you can look at how the magnetic field evolves in time,
you are actually looking at how the fluid motion
on the dynamo surface is evolving in time.
So, by tracking the change in the magnetic field,
we can essentially image the fluid motion on the surface of the core.
By collating thousands of observations
and the data from many satellites,
scientists have been able to piece together a map
of how Earth's magnetic field has been changing over the centuries.
What they've discovered is that, over the last 180 years,
it's been steadily weakening.
Right now, the Earth field is decreasing fairly significantly,
But, for Jack,
there's one area of the magnetic field that particularly stands out.
It's a region in our magnetosphere
that's been weakening faster than any other.
This is a map of the magnetic field, a contour map,
and what you see here evolving in time, over hundreds of years,
is a patch of very weak field in blue
that slowly expands in size,
becomes progressively weaker and weaker in field magnitude,
and, as it does so, it's going to drift westward, slowly.
This is the map scientists have created
that shows just how a weakness in the Earth's magnetic field
has been growing over 400 years.
The blue patch of field is half the strength of that towards the poles.
And scientists have given it a name.
That weak field is the South Atlantic Anomaly.
This region is still growing and, in just 200 years,
it may cover the entire Southern Hemisphere.
It's evidence that something truly remarkable is happening
deep beneath our feet in the core.
The first place the effects of it are felt aren't here on Earth,
but high in space.
And that's why NASA is so interested in the South Atlantic Anomaly.
And in the core.
It was the South Atlantic Anomaly that was to prove key
to the space emergency that threatened the Hubble telescope.
Two new multimillion-dollar instruments
were repeatedly malfunctioning.
And the upsets were occurring in just one area.
Right in the heart of the South Atlantic Anomaly.
Ken LaBel and his team needed to find out
how the two phenomena could be related.
They knew that the weak field at the South Atlantic Anomaly
has one very significant effect on the structure of the magnetosphere.
In that region of the South Atlantic,
the Earth's magnetic field has a dip in it.
In that region, the magnetic field changes its shape.
It comes closer to the Earth.
As the magnetic shield protects Earth from solar radiation,
then in this dip charged particles like protons
must be able to travel closer to our planet.
Could these protons be causing the trouble with Hubble?
Within two weeks,
we had a test set built,
and we went to one of the cyclotrons in the US to do some testing.
And lo and behold, this part was quite susceptible to protons.
The very culprit we'd expect to see issues with in the South Atlantic Anomaly.
Every time Hubble passed through the South Atlantic Anomaly,
it entered an exposed region of space.
It was bombarded by charged particles.
So, each of these events that we're seeing,
those nine events in the first ten days,
was a single proton hitting the sensitive portion of these devices.
But, making the equipment completely proton proof
was simply too difficult, even for NASA.
Something else needed to be done.
It was determined after a lot of work,
both in testing and in environmental predictions,
trying to come up with risk analyses,
that, every time instruments pass the South Atlantic Anomaly,
they turn off.
It's never an even battle when you are dealing with
something on as large a scale as the core and the magnetic field.
So, a good story in the end for those instruments.
Hubble's delicate sensors were now safe
from the strange behaviour of the core deep under the South Atlantic.
But the Anomaly is evidence of changes deep within the Earth
that could ultimately have consequences for more than just satellites.
To understand what these changes might be,
scientists began mapping the magnetic field far below the ground.
As we step down and look deeper and deeper inside the Earth,
the field both grows in magnitude
and it becomes more complex in structure and polarity.
Scientists discovered that the simple North-South divide
we experience at the surface
breaks down at the level of the core.
Under the South Atlantic, there are patches, indicated in green,
where the magnetic field has actually flipped and points North.
The combined effect of these patches,
where the polarity of the field is reversed,
is such to weaken the field over the South Atlantic.
That weak field is the South Atlantic Anomaly.
What could be happening
in the molten metal ocean of the outer core to create these patches?
Dan Lathrop thinks he knows.
It's really the moving liquid metal's ability
to drag and stretch and twist the magnetic field.
In the same sense as we talk about a storm,
when the air is being a particularly violent or unusual patch of weather,
then there's some sort of flow structure down in the core under the South Atlantic
that changed in such a way as to forcibly reverse the magnetic field.
When scientists looked at the Earth's entire magnetic field at the level of the core,
they discovered this perfect storm under the South Atlantic wasn't a one-off event.
In fact, there are multiple patches where the field has flipped.
Could these changes be harbingers of an even bigger shift?
So, there's a very good chance that that South Atlantic Anomaly,
that reversal at the level of the core, could deepen and spread,
and that these small reversed patches in the Northern Hemisphere
could also deepen and spread,
and result in an overall reversal of the North-South pattern,
the biggest structure in the magnetic field.
So, if enough of these storms joined forces
in the molten metal of the outer core,
the Earth's magnetic field could reach a tipping point...
It's not a change that would happen overnight.
The shifting flows of the core
could take between 1,000 and 10,000 years to reverse our field.
During this period, though,
there would be some intriguing phenomena that we would all notice.
During the reversal, the structure of the Earth's magnetic field
could be more complicated than what we have now.
So, instead of a north and south main pole,
one could have two north poles and two south poles,
or poles occurring at the Equator.
The animals that rely on the core's magnetic field to navigate
would have to find some other means to guide their migrations.
And, the wandering magnetic poles would bring the Northern lights
to unexpected locations.
It wouldn't be the first time the flows of the outer core
have undergone a dramatic change.
Magnetised rocks contain a history of the core's turbulent past.
We have very solid evidence that the Earth's magnetic field
has reversed many hundreds of times in the Earth's history.
So, the fact that we've seen so many changes and reversals,
and so many changes in the historical times of the field,
really gives us a view of the outer core being a very active place.
It's not a question of IF the Earth is going to reverse its magnetic field, but WHEN.
How soon this might be is one of the many mysteries of the core.
But these remarkable experiments
are now creating a real picture of the deep Earth
to replace the fantasies of science fiction.
We may never be able to go there.
But we have a sense of what a journey might be like.
One thing is certain, though...
..this strange inner world is only STARTING to reveal its secrets.
Subtitles by Red Bee Media Ltd
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For centuries we have dreamt of reaching the centre of the Earth. Now scientists are uncovering a bizarre and alien world that lies 4,000 miles beneath our feet, unlike anything we know on the surface. It is a planet buried within the planet we know, where storms rage within a sea of white-hot metal and a giant forest of crystals make up a metal core the size of the moon.
Horizon follows scientists who are conducting experiments to recreate this core within their own laboratories, with surprising results.