Horizon (1964–…): Season 48, Episode 4 - The Core - full transcript
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.
Nasty place.
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.
Truly immense.
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.
5...
4...
3...
2...
1.
Always impressive.
HE CHUCKLES
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.
Earthquakes.
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.
CLASSICAL MUSIC
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.
CLASSICAL MUSIC
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.
NOTES RESONATE
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.
Until now.
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.
Oops.
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 million
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.
Good.
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.
EXPLOSIVE BOOM
The early solar system
was a brutal and chaotic place.
But out of this fury,
the conditions needed to forge
our core were created.
Heat.
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...
and 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,
fairly rapidly.
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...
..and flip.
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.
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.
Nasty place.
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.
Truly immense.
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.
5...
4...
3...
2...
1.
Always impressive.
HE CHUCKLES
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.
Earthquakes.
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.
CLASSICAL MUSIC
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.
CLASSICAL MUSIC
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.
NOTES RESONATE
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.
Until now.
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.
Oops.
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 million
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.
Good.
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.
EXPLOSIVE BOOM
The early solar system
was a brutal and chaotic place.
But out of this fury,
the conditions needed to forge
our core were created.
Heat.
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...
and 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,
fairly rapidly.
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...
..and flip.
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.