The Core Horizon


The Core

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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Transcript


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Across the world,

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a daring and far-fetched experiment is under way.

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I'm going to increase more.

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It's very risky, but it's worth doing, and also,

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if I succeeded, I will be the king. HE LAUGHS

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Scientists are attempting a journey that previous generations

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have only dreamed of.

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I can't imagine a less hospitable place for people.

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High pressures, white hot temperatures.

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Nasty place.

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They are trying to reach the centre of the Earth.

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3, 2, 1...

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What they are glimpsing is a bizarre and alien world.

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We're at a golden age, in terms of the real discovery of the bulk of the deep Earth.

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It's really almost a planet within our own big planet.

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It's like a forest.

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It looks very interesting.

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Their work is opening up a window

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on one of the great mysteries of the solar system.

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The Earth's core.

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A hidden world, 4,000 miles, deep beneath your feet.

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The Goddard Space Flight Centre

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is NASA's mission control for unmanned spacecraft.

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From here, scientists manage many of its most important telescopes and satellites.

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Space engineer Ken LaBel has devoted his career

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to perfecting the smooth running of these explorations of the stars.

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But in February 1997, he was thrown into a space mystery,

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that would offer clues to what is happening deep within our own Earth's core.

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The Hubble Space Telescope was in trouble.

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It's a Friday afternoon. I'm at the office, and the phone rings.

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Engineer who I've been working with called me and said,

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"Well, you know, we newly launched last month, two new instruments.

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"We're seeing some problems we weren't anticipating."

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Two ground-breaking new instruments had been installed on Hubble.

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They were designed to peer into deepest space,

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and to find black holes.

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But as Hubble criss-crossed the Earth,

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the highly sensitive multi-million dollar equipment was malfunctioning.

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The event they were seeing were these current spikes.

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If a signal is just moving along,

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all of a sudden you get some injection of noise so you get a spike.

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The issue for this particular device was that the error

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could end up being deadly.

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It could really take out their system. That was the fear.

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They'd lose this big scientific instrument that people spent

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most of their lives working on.

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What made finding the cause of these potential fatal spikes

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so urgent was that they were happening almost every day.

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One of the first tasks was to plot just where.

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And it soon became clear these weren't random events.

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They were tightly clustered across the centre of South America

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and the south Atlantic.

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It's an excellent indicator that our problem was being

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induced by that specific environment, and not because of a thermal issue,

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or a potentially a power system issue

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or some other type of spacecraft system not working appropriately.

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In fact this region of space has developed

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a reputation at NASA as a place of strange events.

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Astronauts have reported seeing flashes of light there.

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Satellites and space shuttle computers malfunction.

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It's even become known as space's Bermuda Triangle.

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Calling it the Bermuda Triangle is actually a good analogy.

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It's been called that several times over the past 20 or more years.

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It's a known hazard for spacecraft.

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The challenge was now figuring out what in the system was causing it,

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and what we could do about it.

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But this region of space wasn't only of interest to NASA,

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it also held important clues to what's happening in the deep Earth.

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It may be hidden 4,000 miles beneath our feet,

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but the core of our planet is central to life on Earth.

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Because it creates Earth's magnetic field.

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A tool for navigation that's vital for some of nature's greatest spectacles.

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The mass migrations that take place around the world.

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And a tool that helps us explore the planet, too.

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But most importantly of all, it helps protect life itself.

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Because the magnetic field it generates forms a vital barrier

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between us and the dangers of space.

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The core of the Earth and its magnetic field certainly played

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a role in the evolution of life on Earth.

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It shields us from the solar wind, and particles,

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boiling off the surface of the sun.

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Yet, for all the core's importance, though we have travelled high above our planet,

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we've never made it down to reach its heart.

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And that's because the barriers to a physical journey to the core are truly formidable.

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One place on the American continent,

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where you begin to get a sense of the challenges of descending

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into the Earth, is a deserted gold mine, Homestake.

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Dr Bill Roggenthen is a geologist

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and explorer of the subterranean planet.

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He's on the 12-minute journey down, to what is now the deepest laboratory in the USA.

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There's snow at the surface but underground,

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conditions are very different.

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It was chilly at the top.

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It's still early spring here in South Dakota,

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and as we go down, steadily,

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the temperature, at least the rock temperature

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increases at a rate of around over 22 degrees C per kilometre.

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Bill is travelling through the first barrier on any journey to the core.

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The Earth's crust.

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A shell of rock, typically around 35 kilometres thick.

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OK, so now we're standing on the 4,850 foot level,

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almost one-and-a-half kilometres below the surface.

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Homestake mine is the deepest anyone's managed to dig in the USA.

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Here, the rock temperature is around 29 degrees C.

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Another kilometre down and it would be hotter than the highest temperature

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ever recorded at the surface.

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And, right now, we are doing experiments

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and getting experiments going at this very deep location.

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As scientists probe the inner workings of our planet,

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it's not just the temperature they're contending with...

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..it's also the pressure.

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Any time when you're in the sub-surface

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and you make an opening, nature wants to close it.

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The deeper you are,

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the harder that nature works to try to get rid of that opening.

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Here, the rocks are particularly strong.

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But such is the weight of the ground above, even at Homestake,

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nothing is quite rock solid.

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So these instruments here are measuring the movement

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of the free surface of the rock way back into the rock itself.

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So, even though that movement is very minor, we need to

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monitor it to make sure these excavations are remaining stable.

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In some areas of the crust, it would be impossible to keep an excavation open at this depth

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because, at this intense pressure,

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solid rocks can behave like elastic

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and even change their constituency to become plastic.

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Yet, we're only 0.02% of the way to the centre of the Earth.

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So, even at this depth, why it's a huge amount,

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the pressure at the Earth's core is 50 million lbs per square inch.

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Truly immense.

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That means that at the centre of the Earth,

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the pressure is three million times that at the surface.

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The temperature is over 4,000 degrees Celsius.

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As hot as the surface of the sun.

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We're an ant, if you will, as we, kind of,

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burrow around this part of the world.

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Having said that, it's a tremendous opportunity to go down inside

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and see at least what this small part of the world

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looks like in three dimensions, and that's really exciting.

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The vastly increasing pressures and temperatures mean man will

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never be able to physically dig to the core.

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Scientists have had to search for other means to penetrate any further into the Earth.

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People thought I was a little nuts coming here.

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Famous people bet me money that I wouldn't stay for more than two years, and they all had to pay.

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Professor Rick Aster is one of America's leading explorers

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of the inner planet, though he has barely travelled below the surface.

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As former President of the Seismological Society of America,

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he doesn't need to.

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Next to his lab in New Mexico is the university's test site.

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It has provided him with a perfect landscape for an alternative way of seeing into the underworld.

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Earth tremors - natural and manmade.

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Seismology really is the killer application,

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when you get right down to it.

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It's the only methodology that we have

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to remotely study the deep interior of the Earth with any kind of resolution.

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Today, Rick is blowing up a tonne of high explosives to generate seismic waves.

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Although it's on a small scale, it's exactly the type of thing

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that we would need to look through the interior of the entire planet.

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WARNING ALARM WAILS

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Three seismographs have been set up.

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One, just meters away from the explosives.

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Another, at one kilometre distance.

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And the third, two kilometres from the blast.

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They'll measure how the Earth moves in response to the detonation.

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Particularly with these shallow explosions,

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most of the energy actually goes into the air.

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What I'm interested in is how much goes into the Earth.

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5...

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4...

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3...

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2...

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1.

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-Always impressive.

-HE CHUCKLES

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There's no doubt that that sent a lot of energy into the ground.

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I think we'll see a very strong signal from this explosion.

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This is what you see when you set off one tonne of explosives.

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A supersonic shockwave.

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But, hidden from view,

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a second pressure wave is travelling through the Earth.

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A seismic wave.

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And, it's what happens to this wave, underground,

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that Rick is interested in.

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Very close to the explosion we see a very simple signal.

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We see the seismic waves generated as a very sharp impulse

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travelling through the Earth, passing the seismograph, and it's over in just a second or two.

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At one and two kilometres,

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we see the development of a very rich wave train of scattered energies,

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scattering off the topography, the landscape,

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and scattering off the interior of the Earth, so that the signal is drawn out from this strong signal

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that was generated at the site.

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The further seismic waves travel, the more revealing they can be.

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Because the speed at which they move through the ground changes

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depending on the constituency of the material they pass through.

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The speed of the wave tells us, basically, how stiff the rocks are.

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That can tell us a lot about what's going on within the Earth.

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If you're studying a volcano, for instance,

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the speed of seismic waves slows down tremendously

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when it goes through magma, as opposed to rock.

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But to create seismic waves, which are able to pass all the way through the centre of the Earth,

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and out the other side...

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you need seismic events bigger than this one.

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Earthquakes.

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The shockwaves of major Earthquakes radiate through the globe.

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Scientists have gained a form of X-ray vision into the heart of the Earth

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by analysing the speed at which they travel.

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It's revealed that we aren't simply living on one solid chunk of rock.

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The Earth is made up of different layers.

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First, is the Earth's thin crust.

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The Earth's crust is really, really thin.

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It's about 0.3% of the way to the centre of the Earth.

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Then there's the mantle,

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made of rocks turned malleable by the extreme heat and pressure.

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The Earth's mantle is made of rocks that are, in some ways, similar to what we see at the crust,

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although their chemistry is a little different.

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But then the waves hit something else and, crucially,

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they slow down.

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To a seismologist, that could only mean one thing.

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The fact that seismic waves travel down through

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the mantle in a certain manner and then they hit the outer core, which

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has a much slower seismic velocity, indicated the Earth had a core.

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Indeed, it had an enormous core and it's molten.

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It has a viscosity that's not much greater than water.

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So it's an enormous ocean of white-hot, molten metal.

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Seismology has managed to reveal the Earth's core.

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A huge sea inside our planet, the size of Mars.

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But that wasn't all seismology detected.

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Scientists found signals of something else inside this sea of molten metal -

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an inner core.

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But for years, quite what it's like remained an enigma.

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CLASSICAL MUSIC

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The biggest breakthrough into the nature of this elusive inner core

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has come from a seismologist working as far away from the violence of Earthquakes as you can imagine.

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CLASSICAL MUSIC

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Dr Arwen Deuss took on a puzzle that had baffled every previous seismologist.

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So we have this mystery.

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We have an Earth which has a solid mantle and a fluid core.

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And people have discovered that there was actually an inner core inside this fluid outer core,

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but people didn't know for sure if this inner core was solid or fluid.

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It was a very difficult problem to solve.

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Arwen wasn't to be deterred.

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She suspected that the inner core was solid and was determined to prove it.

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If you want to prove that the inner core is solid,

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there's one specific wave you need to find, which is a tiny wave,

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and a really difficult wave to observe in seismograms,

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which we would call the shear wave, which can only travel through solid material.

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If Arwen could find a shear wave that had passed through

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the centre of the Earth, she'd prove the inner core was solid.

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But there was a major problem.

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How do you differentiate a tiny inner core shear wave,

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from the cacophony of other waves reverberating through the Earth?

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It's like a needle in a haystack.

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It's not something that pops out of the piece of paper

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when you look out the seismogram.

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So we realised we had to do something different if you want to find it.

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We couldn't repeat what other people had done.

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The hunt was on.

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A new approach to finding an inner core shear wave was needed.

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And Arwen found it in an incredible property of the Earth...

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The way in which the whole planet resonates

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when it has been struck by an Earthquake.

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Now when the Earth is hit by a major Earthquake, it's like a big hammer

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hits a string of a musical instrument,

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and that will start playing all the different tones of the Earth.

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NOTES RESONATE

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Now if we know that there's all these thousands of different tones

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happening in the Earth,

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what we can do is we can propose two different hypotheses.

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We can calculate what all these tones would look like for an Earth with a fluid inner core.

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And we can calculate what all these tones look like for an Earth with a solid inner core.

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By comparing the predictions, she finally knew where to look for the elusive shear wave.

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If she found it, she'd prove the inner core was solid.

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So this little peak here is our needle in the haystack.

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That is the thing we are going to be looking for in the real data.

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All she needed now was an Earthquake to test her theory on.

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A perfect candidate was a magnitude 7.9 quake that had

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occurred in 1996, under the Flores Sea in Indonesia.

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It was big.

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And it was deep.

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So it's one of the ideal Earthquakes to look for these inner core shear waves.

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She started collating the data of this quake

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from 47 different seismic stations across the world.

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This red box is where you would expect a wave from the inner core to arrive.

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Her hope was that the signal would eventually emerge

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through the noise created by thousands of other seismic waves.

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When we get to 40, we can see a little peak starting to appear.

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The question is, when we start adding more stations,

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is that bump going to grow or not?

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Arwen added station after station.

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This is what we're looking for. By adding more stations,

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the peak gets bigger, so this is quite exciting.

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She was on the brink of answering this fundamental question about the Earth's inner core.

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We add our last station, 47, and now we have a really large signal there.

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That's our needle in the haystack.

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We've got a really nice, strong, big arrival,

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proving that the inner core is solid.

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This shear wave, which could only pass through solid material,

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had travelled through the centre of the Earth.

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Arwen had discovered that sitting inside our planet

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is a solid metal ball, almost the size of the moon.

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But our solid inner core is proving stranger than Arwen could ever have imagined.

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Say you had an Earthquake at the North Pole and a seismometer at the South Pole,

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then a wave that would travel from the North Pole to the South Pole

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would arrive up to five seconds faster than from east to west if they go through the inner core.

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And we had no idea how to explain that.

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Seismology on its own simply can't unlock all the inner core's secrets

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but it seemed to be the only real way scientists could reveal them.

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Until now.

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In Japan, one man has pioneered a new technique to investigate the mysterious inner core.

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Because Kei Hirose is a scientist determined to leave the surface world behind,

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and complete an impossible mission to see the centre of the Earth.

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We cannot go into the centre of the Earth,

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but we can recreate the conditions

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corresponding at the centre of the Earth in my own laboratory,

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and it's a kind of journey to the centre of the Earth.

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I'll try to be the first person to reach there.

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It's very risky but it's worth doing,

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and also, if I succeeded...

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..I'll be the king! HE LAUGHS

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This is the SPring-8 Synchrotron Radiation Facility.

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Kei's using its powerful equipment

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in his attempt to recreate the immense temperatures

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and pressures found at the inner core.

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Somewhere rather more convenient to study.

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Oops.

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OK. So, as a diamond it looks beautiful,

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and then I put it on to the seed.

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The first part of his mission is to simulate the pressures

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found at the centre of the Earth.

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It took him ten years and hundreds of shattered diamonds to design an enormously powerful vice,

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using the tips of the jewels.

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Next, we can load the samples, and these are very tiny.

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Between the points Kei puts a sample...

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a shard of iron nickel alloy.

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The material scientists believe makes up the inner core.

0:29:390:29:42

At the Earth's surface, it's composed of lots of tiny crystals.

0:29:450:29:50

Kei hopes to show what happens to its structure

0:29:500:29:53

under the extreme conditions found at the inner core.

0:29:530:29:57

OK, that's fine.

0:29:590:30:02

He uses the vice to raise the sample pressure to that of the inner core.

0:30:050:30:09

It's equivalent to three medium times, atmospheric pressure,

0:30:110:30:16

so it is very high pressure. But we just use a screwdriver

0:30:160:30:22

to increase the pressure, to such extreme conditions.

0:30:220:30:25

It's very simple.

0:30:250:30:28

Part one of the mission complete. Now for stage two.

0:30:370:30:42

Kei has to heat the sample to 4,700 Kelvin.

0:30:420:30:47

A temperature found at the inner core, and on the surface of the sun.

0:30:470:30:53

The beam of an infrared laser will be focused on the sample to raise its temperature.

0:31:010:31:05

At the beginning of the experiment, Kei shines X-rays through the sample to create an image.

0:31:120:31:18

The iron nickel crystals form a pattern of two concentric rings.

0:31:210:31:25

So this image tells us what is going on inside the sample,

0:31:260:31:29

under high pressure and high temperature.

0:31:290:31:32

OK, so let's go.

0:31:340:31:36

As the power of the laser is increased,

0:31:390:31:41

the temperature of the sample rises.

0:31:410:31:44

OK, so the sample is already about 1,500 Kelvins.

0:31:470:31:52

Let's take the X-ray defraction images.

0:31:550:31:58

And as the temperature grows,

0:32:000:32:01

the iron nickel crystal structure begins to change.

0:32:010:32:05

And now the temperature is about, OK, it's about 3,000 Kelvins.

0:32:100:32:16

A uniform circular structure has all but gone,

0:32:160:32:19

and crystals appear to be clumping together.

0:32:190:32:22

Oh, now, the temperature is very high. It's almost close to the temperature at the core.

0:32:290:32:35

You know, I'm very nervous at this moment.

0:32:350:32:38

I'm going to increase more, OK?

0:32:400:32:43

Oh, look at this.

0:32:480:32:49

It is already 4,000 Kelvins, which is the real core temperature,

0:32:490:32:54

and take another pattern here.

0:32:540:32:57

Welcome to Kei's inner core of the Earth.

0:33:020:33:05

For the first time, he has shown how iron nickel alloy crystals

0:33:050:33:09

undergo a dramatic transformation under the pressures and temperatures

0:33:090:33:14

found at the inner core.

0:33:140:33:15

I think we should stop here. It's successful, we are very fortunate.

0:33:200:33:26

We sometimes fail the experiment, but this time we are very lucky.

0:33:260:33:33

Good.

0:33:330:33:34

These X-ray images give us a real insight into the physical nature of the inner core.

0:33:380:33:42

It's iron nickel alloy, but not as we know it.

0:33:440:33:49

So, this is the first image.

0:33:490:33:51

We have rings and it became spotty during heating.

0:33:510:33:58

And the size of the crystal of iron nickel alloy increased

0:33:580:34:02

by 1,000 times at core pressure and temperature, in our experiment,

0:34:020:34:09

just in ten minutes.

0:34:090:34:11

Over millions of years, under the extreme heat and pressure

0:34:150:34:18

found at the core, these crystals could have grown to huge lengths.

0:34:180:34:22

We may have very big crystals at the centre of the Earth.

0:34:250:34:29

Maybe up to ten kilometres.

0:34:290:34:33

It's like a forest.

0:34:330:34:34

It looks very interesting.

0:34:370:34:39

Kei believes this forest of crystals makes up the solid inner core of our Earth,

0:34:440:34:48

with the crystals all pointing in the direction of the north pole.

0:34:500:34:53

This could now explain why seismic waves travel through the core faster north to south,

0:34:550:35:01

along the grain of the crystals,

0:35:010:35:03

than east to west, across them.

0:35:030:35:05

We tried many, many times, but we always failed.

0:35:070:35:13

But we finally did and, you know, I realise how important it is.

0:35:130:35:20

And, you know, probably it's a big achievement in my life.

0:35:200:35:27

Kei's discovery is a significant step forward in our understanding of the core.

0:35:300:35:35

But scientists' revelation of a white-hot metallic inner world

0:35:400:35:44

raises another, more fundamental question.

0:35:440:35:47

Why is the core of our planet so very different from everything

0:35:500:35:54

we know at the rocky surface?

0:35:540:35:56

The answer would ultimately turn out to be central to the story of life on Earth.

0:35:580:36:04

Professor Dave Stevenson has made a career out of studying what lies

0:36:130:36:17

beneath the surface of all planets in the solar system.

0:36:170:36:19

I love looking at things that are difficult to understand,

0:36:220:36:26

that are difficult to get to. So I've always been fascinated by cores.

0:36:260:36:32

But one aspect of why

0:36:320:36:36

I find Earth's core so fascinating,

0:36:360:36:39

is that it - I believe -

0:36:390:36:41

contains a memory of what happened in the history of the Earth.

0:36:410:36:47

He believes to truly understand our core, we need to look up to the stars...

0:36:560:37:02

..and go back to our planet's birth, in the violent collisions that

0:37:070:37:11

happened during the formation of the solar system billions of years ago.

0:37:110:37:16

The Earth's core formed through

0:37:210:37:26

a very energetic set of events.

0:37:260:37:31

Let's go back to the beginning.

0:37:310:37:33

Imagine that you were bashing together bodies that were about the size of Mars.

0:37:330:37:40

And when you do that, you produce an enormous amount of heat.

0:37:400:37:45

EXPLOSIVE BOOM

0:37:540:37:56

The early solar system was a brutal and chaotic place.

0:37:560:38:00

But out of this fury, the conditions needed to forge our core were created.

0:38:040:38:10

Heat.

0:38:170:38:18

When you heat a mixture of solid material that is in the form of rock and iron,

0:38:200:38:28

to very high temperatures, the iron will separate.

0:38:280:38:34

It is heavy, and so it will sink under gravity to the centre

0:38:340:38:40

of the Earth and the core will be formed.

0:38:400:38:42

It's this separation of molten rock and metal that makes the outer layers of the Earth so different...

0:38:470:38:54

..from the core inside.

0:38:560:38:57

And the Earth's baptism of fire had another legacy.

0:39:050:39:08

As the intense heat at the centre of our planet escaped,

0:39:100:39:14

it caused the liquid metal within the core to move.

0:39:140:39:17

This ceaseless motion in the depths of the Earth is what creates

0:39:220:39:26

the magnetic field we experience at the surface.

0:39:260:39:30

If you want to generate a magnetic field, the way the Earth does it,

0:39:350:39:40

you need a metal. That's fine, iron is a metal, it needs to be liquid,

0:39:400:39:44

that means it has to be hot. But you also need a temperature difference.

0:39:440:39:49

As the heat flows from the hot inner core to the cooler mantle, it causes

0:39:520:39:57

convection currents to form within the molten metal of the outer core.

0:39:570:40:01

Those motions, through the process of electromagnetic induction,

0:40:070:40:13

is the way in which the magnetic field is generated.

0:40:130:40:17

And it's the generation of this magnetic field that is so vital to life on Earth.

0:40:190:40:26

Because as charged particles are blown off the sun,

0:40:310:40:35

the magnetosphere deflects them,

0:40:350:40:39

creating a safe haven for our planet.

0:40:390:40:42

This magnetic field is providing scientists with new insights

0:40:490:40:53

into what's happening at the centre of the Earth...

0:40:530:40:57

moment by moment.

0:40:570:40:58

Geophysicist, Dan Lathrop, is on a mission to build a remarkable machine.

0:41:130:41:18

He hopes it will do something no supercomputer has managed.

0:41:210:41:25

Recreate the motions of molten metal in the core, to generate a magnetic field.

0:41:270:41:32

He started small,

0:41:340:41:35

but in his search for answers, the models have just got bigger...

0:41:350:41:40

and bigger.

0:41:400:41:42

What we don't know about the core is really details about the flows,

0:41:510:41:56

and details about the magnetic fields inside the core.

0:41:560:42:00

We know a bit about what happens at the surface,

0:42:000:42:02

but this is a very thick layer of liquid metal

0:42:020:42:05

and what happens underneath the surface is really a mystery to us.

0:42:050:42:09

The experiment is fraught with danger.

0:42:160:42:19

Dan plans to fill his core with 12 tons of molten sodium metal -

0:42:190:42:24

a highly volatile element -

0:42:240:42:28

and then spin it at up to 85 miles an hour.

0:42:280:42:31

This is really as close to a model of the Earth as we're going to have.

0:42:400:42:44

This device sets up a swirling mass of liquid metal as a mimic

0:42:440:42:48

of what happens in deep Earth, but in a way that we

0:42:480:42:51

can directly probe the flows, the rotating motions,

0:42:510:42:55

and look at them in more detail than we could ever do for the Earth's core.

0:42:550:42:58

He hopes this gargantuan model of the core will help explain

0:42:580:43:03

something strange about the behaviour of Earth's magnetic field.

0:43:030:43:07

It's never fixed, but constantly fluctuating.

0:43:100:43:14

So, while most people think of the Earth's magnetic field

0:43:140:43:18

as just being a simple north and south, it's really very complicated.

0:43:180:43:24

There are patches of weaker field, patches of stronger field,

0:43:240:43:28

all those are moving about the planet, some becoming weaker,

0:43:280:43:32

some becoming stronger, in a very complex way.

0:43:320:43:34

One thing is clear though.

0:43:370:43:39

If the magnetic field is continually changing,

0:43:390:43:42

then that must be caused by how the metal moves within the outer core.

0:43:420:43:47

Early experiments have already hinted at what could be happening.

0:43:530:43:58

Dan injected fluorescent dye into the rotating machine.

0:44:040:44:08

The results suggest the core is place of great turbulence,

0:44:120:44:15

filled with eddies and currents.

0:44:150:44:18

You might think of the core, like the atmosphere of the Earth,

0:44:220:44:26

being a very restless place with storms and fronts and bad weather.

0:44:260:44:30

Very complicated turbulent motions, very complicated sets of vortices,

0:44:300:44:36

all interacting with each other.

0:44:360:44:38

And those drive motions like the convection we see in the atmosphere,

0:44:380:44:43

billowing upwards motions in clouds.

0:44:430:44:45

All of those then are shaped by the rotation of the core.

0:44:450:44:50

And these deep motions interact with electric currents,

0:44:500:44:54

drive electric currents and cause the Earth's main magnetic field.

0:44:540:44:58

Dan's model is opening up a new window on the inner Earth.

0:45:030:45:07

Our core may be a dynamo, but it's no simple one.

0:45:090:45:14

Vast vortices and whirlpools create a magnetic field constantly in flux.

0:45:160:45:21

And that causes unexpected phenomena that scientists are only now beginning to understand.

0:45:210:45:29

Dr Jack Connerney has devoted his career at NASA

0:45:420:45:45

to studying the magnetic fields of planets

0:45:450:45:48

right across the solar system.

0:45:480:45:50

Here at NASA's test facility,

0:45:520:45:55

he's even got the ability to recreate the magnetic field of any heavenly body.

0:45:550:46:01

But something that's really fascinated him

0:46:030:46:06

are the changes that are happening to Earth's magnetosphere.

0:46:060:46:09

And how they're related to the turbulent molten metal dynamo

0:46:090:46:13

that is our core.

0:46:130:46:15

The dynamo is electrically conducting fluid in motion,

0:46:190:46:23

so when you have motion of that fluid,

0:46:230:46:26

it carries with it the magnetic field.

0:46:260:46:29

So, if you can look at how the magnetic field evolves in time,

0:46:290:46:33

you are actually looking at how the fluid motion

0:46:330:46:38

on the dynamo surface is evolving in time.

0:46:380:46:41

So, by tracking the change in the magnetic field,

0:46:410:46:45

we can essentially image the fluid motion on the surface of the core.

0:46:450:46:50

By collating thousands of observations

0:46:520:46:55

and the data from many satellites,

0:46:550:46:57

scientists have been able to piece together a map

0:46:570:47:00

of how Earth's magnetic field has been changing over the centuries.

0:47:000:47:05

What they've discovered is that, over the last 180 years,

0:47:090:47:12

it's been steadily weakening.

0:47:120:47:14

Right now, the Earth field is decreasing fairly significantly,

0:47:160:47:20

fairly rapidly.

0:47:200:47:21

But, for Jack,

0:47:240:47:26

there's one area of the magnetic field that particularly stands out.

0:47:260:47:30

It's a region in our magnetosphere

0:47:350:47:38

that's been weakening faster than any other.

0:47:380:47:41

This is a map of the magnetic field, a contour map,

0:47:450:47:49

and what you see here evolving in time, over hundreds of years,

0:47:490:47:53

is a patch of very weak field in blue

0:47:530:47:57

that slowly expands in size,

0:47:570:48:00

becomes progressively weaker and weaker in field magnitude,

0:48:000:48:05

and, as it does so, it's going to drift westward, slowly.

0:48:050:48:09

This is the map scientists have created

0:48:110:48:14

that shows just how a weakness in the Earth's magnetic field

0:48:140:48:18

has been growing over 400 years.

0:48:180:48:20

The blue patch of field is half the strength of that towards the poles.

0:48:230:48:29

And scientists have given it a name.

0:48:290:48:31

That weak field is the South Atlantic Anomaly.

0:48:330:48:36

This region is still growing and, in just 200 years,

0:48:410:48:44

it may cover the entire Southern Hemisphere.

0:48:440:48:47

It's evidence that something truly remarkable is happening

0:48:530:48:56

deep beneath our feet in the core.

0:48:560:48:58

The first place the effects of it are felt aren't here on Earth,

0:49:020:49:07

but high in space.

0:49:070:49:09

And that's why NASA is so interested in the South Atlantic Anomaly.

0:49:130:49:17

And in the core.

0:49:170:49:18

It was the South Atlantic Anomaly that was to prove key

0:49:220:49:25

to the space emergency that threatened the Hubble telescope.

0:49:250:49:28

Two new multimillion-dollar instruments

0:49:300:49:34

were repeatedly malfunctioning.

0:49:340:49:36

And the upsets were occurring in just one area.

0:49:360:49:40

Right in the heart of the South Atlantic Anomaly.

0:49:410:49:45

Ken LaBel and his team needed to find out

0:49:510:49:54

how the two phenomena could be related.

0:49:540:49:56

They knew that the weak field at the South Atlantic Anomaly

0:49:590:50:02

has one very significant effect on the structure of the magnetosphere.

0:50:020:50:07

In that region of the South Atlantic,

0:50:070:50:09

the Earth's magnetic field has a dip in it.

0:50:090:50:13

In that region, the magnetic field changes its shape.

0:50:130:50:17

It comes closer to the Earth.

0:50:170:50:19

As the magnetic shield protects Earth from solar radiation,

0:50:190:50:24

then in this dip charged particles like protons

0:50:240:50:28

must be able to travel closer to our planet.

0:50:280:50:31

Could these protons be causing the trouble with Hubble?

0:50:360:50:40

Within two weeks,

0:50:420:50:44

we had a test set built,

0:50:440:50:45

and we went to one of the cyclotrons in the US to do some testing.

0:50:450:50:50

And lo and behold, this part was quite susceptible to protons.

0:50:500:50:54

The very culprit we'd expect to see issues with in the South Atlantic Anomaly.

0:50:540:50:59

Every time Hubble passed through the South Atlantic Anomaly,

0:51:030:51:07

it entered an exposed region of space.

0:51:070:51:10

It was bombarded by charged particles.

0:51:120:51:16

So, each of these events that we're seeing,

0:51:190:51:22

those nine events in the first ten days,

0:51:220:51:25

was a single proton hitting the sensitive portion of these devices.

0:51:250:51:31

But, making the equipment completely proton proof

0:51:310:51:36

was simply too difficult, even for NASA.

0:51:360:51:39

Something else needed to be done.

0:51:390:51:42

It was determined after a lot of work,

0:51:420:51:45

both in testing and in environmental predictions,

0:51:450:51:49

trying to come up with risk analyses,

0:51:490:51:52

that, every time instruments pass the South Atlantic Anomaly,

0:51:520:51:56

they turn off.

0:51:560:51:59

It's never an even battle when you are dealing with

0:52:020:52:05

something on as large a scale as the core and the magnetic field.

0:52:050:52:09

So, a good story in the end for those instruments.

0:52:110:52:15

Hubble's delicate sensors were now safe

0:52:180:52:22

from the strange behaviour of the core deep under the South Atlantic.

0:52:220:52:26

But the Anomaly is evidence of changes deep within the Earth

0:52:300:52:34

that could ultimately have consequences for more than just satellites.

0:52:340:52:39

To understand what these changes might be,

0:52:470:52:49

scientists began mapping the magnetic field far below the ground.

0:52:490:52:55

As we step down and look deeper and deeper inside the Earth,

0:52:550:53:00

the field both grows in magnitude

0:53:000:53:03

and it becomes more complex in structure and polarity.

0:53:030:53:07

Scientists discovered that the simple North-South divide

0:53:090:53:12

we experience at the surface

0:53:120:53:14

breaks down at the level of the core.

0:53:140:53:17

Under the South Atlantic, there are patches, indicated in green,

0:53:190:53:23

where the magnetic field has actually flipped and points North.

0:53:230:53:28

The combined effect of these patches,

0:53:310:53:34

where the polarity of the field is reversed,

0:53:340:53:37

is such to weaken the field over the South Atlantic.

0:53:370:53:40

That weak field is the South Atlantic Anomaly.

0:53:400:53:43

What could be happening

0:53:520:53:54

in the molten metal ocean of the outer core to create these patches?

0:53:540:54:00

Dan Lathrop thinks he knows.

0:54:000:54:03

It's really the moving liquid metal's ability

0:54:080:54:12

to drag and stretch and twist the magnetic field.

0:54:120:54:15

In the same sense as we talk about a storm,

0:54:180:54:21

when the air is being a particularly violent or unusual patch of weather,

0:54:210:54:25

then there's some sort of flow structure down in the core under the South Atlantic

0:54:250:54:29

that changed in such a way as to forcibly reverse the magnetic field.

0:54:290:54:34

When scientists looked at the Earth's entire magnetic field at the level of the core,

0:54:360:54:42

they discovered this perfect storm under the South Atlantic wasn't a one-off event.

0:54:420:54:47

In fact, there are multiple patches where the field has flipped.

0:54:500:54:54

Could these changes be harbingers of an even bigger shift?

0:54:560:55:01

So, there's a very good chance that that South Atlantic Anomaly,

0:55:030:55:08

that reversal at the level of the core, could deepen and spread,

0:55:080:55:12

and that these small reversed patches in the Northern Hemisphere

0:55:120:55:15

could also deepen and spread,

0:55:150:55:16

and result in an overall reversal of the North-South pattern,

0:55:160:55:20

the biggest structure in the magnetic field.

0:55:200:55:22

So, if enough of these storms joined forces

0:55:240:55:28

in the molten metal of the outer core,

0:55:280:55:31

the Earth's magnetic field could reach a tipping point...

0:55:310:55:35

..and flip.

0:55:360:55:38

It's not a change that would happen overnight.

0:56:060:56:09

The shifting flows of the core

0:56:090:56:12

could take between 1,000 and 10,000 years to reverse our field.

0:56:120:56:17

During this period, though,

0:56:210:56:23

there would be some intriguing phenomena that we would all notice.

0:56:230:56:28

During the reversal, the structure of the Earth's magnetic field

0:56:280:56:32

could be more complicated than what we have now.

0:56:320:56:36

So, instead of a north and south main pole,

0:56:360:56:38

one could have two north poles and two south poles,

0:56:380:56:41

or poles occurring at the Equator.

0:56:410:56:44

The animals that rely on the core's magnetic field to navigate

0:56:460:56:50

would have to find some other means to guide their migrations.

0:56:500:56:54

And, the wandering magnetic poles would bring the Northern lights

0:56:570:57:01

to unexpected locations.

0:57:010:57:04

It wouldn't be the first time the flows of the outer core

0:57:050:57:09

have undergone a dramatic change.

0:57:090:57:12

Magnetised rocks contain a history of the core's turbulent past.

0:57:160:57:21

We have very solid evidence that the Earth's magnetic field

0:57:210:57:25

has reversed many hundreds of times in the Earth's history.

0:57:250:57:29

So, the fact that we've seen so many changes and reversals,

0:57:310:57:35

and so many changes in the historical times of the field,

0:57:350:57:38

really gives us a view of the outer core being a very active place.

0:57:380:57:42

It's not a question of IF the Earth is going to reverse its magnetic field, but WHEN.

0:57:420:57:46

How soon this might be is one of the many mysteries of the core.

0:57:500:57:55

But these remarkable experiments

0:57:560:57:59

are now creating a real picture of the deep Earth

0:57:590:58:03

to replace the fantasies of science fiction.

0:58:030:58:07

We may never be able to go there.

0:58:110:58:13

But we have a sense of what a journey might be like.

0:58:150:58:19

One thing is certain, though...

0:58:220:58:24

..this strange inner world is only STARTING to reveal its secrets.

0:58:260:58:31

Subtitles by Red Bee Media Ltd

0:58:480:58:51

E-mail [email protected]

0:58:510:58:54

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.


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