Inside Planet Earth
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00:00:00What do we really know about the planet we live on?
00:00:10This giant spinning ball of rock.
00:00:15The truth is, something extraordinary is going on deep inside the Earth.
00:00:22Unimaginable forces, mysterious processes are happening thousands of miles beneath our
00:00:28feet.
00:00:29And without them, life on our planet would be impossible.
00:00:43The secret to life on Earth lies inside.
00:00:58To discover how and why, we need to crack the Earth open and travel all the way to the
00:01:06core.
00:01:25A century ago, Jules Verne's book, Journey to the Center of the Earth, captured the world's
00:01:30imagination.
00:01:31Of course, in reality, it's an impossible journey.
00:01:39In the center of the Earth, there are titanic pressures and extreme temperatures.
00:01:43They make 99% of the planet beneath us inaccessible to humans.
00:01:47It is easier to design something to descend into the sun than it is to design something
00:01:54to go to the center of the Earth.
00:01:56Because the temperatures are as high or higher than the surface of the sun, but the pressures
00:02:01are unimaginably large.
00:02:06Because scientists can't travel to the core and see for themselves, they have to work
00:02:09out other ways to understand it.
00:02:13It's not easy studying something you'll never be able to see or touch.
00:02:17We can see hurricanes coming.
00:02:20We can see fronts coming that'll have violent thunderstorms.
00:02:24All of that predictive power comes because we can observe the atmosphere.
00:02:29We don't have anything like that in the interior of the Earth because we don't have any detailed
00:02:33measurements of what's happening in the core.
00:02:36We don't really know any of the motions in the core.
00:02:39We don't know how the temperatures are varying.
00:02:41We don't know what storms are brewing down there.
00:02:45But Lathrop is determined to find out.
00:02:47So he's building his very own planet Earth at the University of Maryland.
00:02:53So we've been seven years in construction of this experiment, built to try to match
00:02:59as many parameters as possible with the Earth's core.
00:03:09It's a model of both the outer and inner cores of the Earth.
00:03:14It might look like a crazy experiment, but investigating the Earth's interior is more
00:03:19than just scientific curiosity.
00:03:22Life on Earth's surface, where we live, actually depends on processes taking place deep inside
00:03:28our planet.
00:03:29If we can figure them out, then we'll be closer to understanding how and why life exists and
00:03:36what its future could be.
00:03:37And the hope is, by building a laboratory model of a planetary core, the Earth's core,
00:03:44that we can probe in detail what's happening and work toward getting a predictive science,
00:03:50being able to predict what's going to happen toward the future for the Earth's core.
00:03:55Lathrop is not alone.
00:03:58Around the world, scientists are probing the planet in every way possible to solve the
00:04:03mysteries of the deep Earth.
00:04:06They're studying volcanoes, measuring vibrations from earthquakes to perform seismic X-rays
00:04:12of the planet, building complex laboratory models, and discovering that the world beneath
00:04:22our feet is stranger and more fantastic than they could ever imagine.
00:04:29It's full of incredible riches, monumental structures, and bizarre creatures.
00:04:36They've found there's actually more life beneath the surface than above it, and more
00:04:42water than in all of the oceans.
00:04:46Down here, there are even raging storms more violent than the planet's worst hurricanes.
00:04:53And somehow, this mysterious world deep inside the planet shapes our own.
00:05:00But to discover how is a huge challenge.
00:05:03Almost any basic quantity that you imagine might be changing down there.
00:05:09There's a whole host of interesting questions that you'd like to know about the core, but
00:05:14that you can't unless you go there.
00:05:17There are many mysteries in the deep core, but perhaps none so powerful as gravity.
00:05:25Gravity keeps the moon and thousands of man-made satellites in their orbits.
00:05:30And even out here, it prevents molecules of gas from floating off into space.
00:05:37This immense force comes from the massive, dense interior of our planet.
00:05:44The closer we get to Earth, the stronger this force becomes.
00:05:50By 62 miles up, gravity has collected enough gas to form a cocoon around the Earth.
00:05:56This is the Earth's atmosphere.
00:06:01It protects us from meteorites, absorbs lethal radiation, and insulates the Earth from the
00:06:06freezing temperatures of space.
00:06:13And what's most important, it gives us the air that we breathe.
00:06:19It's simple.
00:06:20No gravity.
00:06:21No atmosphere.
00:06:22No atmosphere.
00:06:23No life.
00:06:29There's another force of nature inside Earth that's just as vital to life.
00:06:35We take it for granted that life gets its energy from the sun.
00:06:39True, its nuclear furnace does warm our atmosphere, drive our weather, and make our food grow.
00:06:47Without the sun, life on Earth would quickly disappear.
00:06:51But forces from deep inside the Earth played a vital role in creating life in the first
00:06:56place.
00:06:59Life survives today because of a careful balance between the energy of the sun on the outside
00:07:03and the energy coming from inside Earth's core.
00:07:11The most visible sign of the seething energy inside our planet are volcanoes.
00:07:21They erupt through cracks in the crust, the planet's fragile outer shell.
00:07:27This layer is only 30 miles thick.
00:07:32All of the Earth's volcanoes release just a tiny fraction of the energy locked beneath
00:07:36the surface.
00:07:41The Earth's inner energy is so powerful, it can thrust rock layers high in the air, creating
00:07:47whole mountain ranges, such as the Guadalupe Mountains in New Mexico.
00:07:53These layers were once a flat seabed, until the Earth's heat pushed them 8,000 feet into
00:07:59the sky.
00:08:02In this churning, heaving action, cracks and fissures let in water, which dissolves the
00:08:07soft limestone rocks below the surface.
00:08:13Here in New Mexico are the magnificent Carlsbad Caverns.
00:08:22One chamber is so large, it could comfortably accommodate a jumbo jet.
00:08:29For Peter Scholl, these caverns are a geological treasure trove.
00:08:37We're 850 feet below the surface of the Earth here in the lower cave of Carlsbad Caverns.
00:08:43We are amongst a bunch of limestone stalactites and stalagmites.
00:08:49This cave has probably a couple of miles of passage.
00:08:52There are other caves that have literally hundreds of miles of passage.
00:08:56In many cases, there are actually rivers that flow through them for tens or even hundreds
00:09:00of miles.
00:09:08The eerie stalactites growing downward and the stalagmites growing upward were deposited
00:09:14by the water over thousands of years.
00:09:26Our journey from the surface to the core reveals more spectacular surprises as we head further
00:09:32downward.
00:09:34Just below the surface, it's cold, dark, seemingly dead.
00:09:38Then, very quickly, everything changes.
00:09:44As we go even deeper, it gets warmer, then hot.
00:09:51The next stop on our journey, a mysterious cave below the Mexican desert.
00:09:57This is what the Earth's inner energy can do.
00:10:03Nearly 40 feet long, these are the largest known crystals in the world.
00:10:08They're what's left of an underground lake rich in minerals.
00:10:13The lake was turned into a boiling cauldron by red-hot magma erupting from below.
00:10:19As the hot water percolated through the crust, these giant crystals grew from the minerals
00:10:24dissolved in the water.
00:10:28Today, the chamber is still a scorching 120 degrees.
00:10:33So hot, scientists can only work 30 minutes at a time, even in their climate-controlled
00:10:38suits.
00:10:40But the deep interior is quite unsuitable for people.
00:10:46Pressures are high, temperatures are high, and early on, people going to mines realize
00:10:51it gets hotter as you go deeper, and so there's this fascination then with this inhospitable
00:10:56interior to what is otherwise a pleasant surface we live on.
00:11:01But the energy inside the Earth can do more than make mountains and hollow out caves.
00:11:06In the 1960s, scientists discovered it can move entire continents.
00:11:12The Earth's crust is formed from seven massive sections called plates.
00:11:18What researchers realized is that these plates were all shifting.
00:11:23In some places, they're pulling apart, in others, smashing together.
00:11:30Mountains are the crumple zones of these collisions, and some are truly spectacular.
00:11:40These are the Swiss Alps, where two continents crash together.
00:11:47High peaks like the Matterhorn testify to the immense scale of the forces unleashed.
00:11:54It's literally a piece of Africa sitting on top of Europe.
00:12:03Every year, these mountains grow by a quarter inch.
00:12:08This activity happens over hundreds of millions of years, far too slowly to see.
00:12:19But speed up time, and the Earth's surface is in constant motion.
00:12:28The Earth that we know, with its continents and oceans, mountain ranges, volcanoes and
00:12:33caves, was shaped and is still being shaped by forces from deep inside the Earth.
00:12:42As we travel even deeper, we discover an unexpected effect of this constant change, this time
00:12:51on life.
00:13:03The Earth is always in motion.
00:13:07Our mountains and continents slide around the Earth's surface, driven by energy from
00:13:11deep inside the planet.
00:13:15But as this driving force reshapes the surface, it reshapes life as well.
00:13:21It can change and transform the course of life.
00:13:26The evidence is here, one and a half miles down, inside a vast coal seam.
00:13:35700 miles long and 120 miles wide, 212 million tons of coal.
00:13:45All the coal on Earth is the fossilized remains of a super-forest that once dominated the
00:13:51surface of our planet.
00:13:58Three hundred sixty million years ago, there was an explosion of life on Earth.
00:14:02It was more diverse, more abundant than it's ever been since.
00:14:07And it was all because of the way that forces inside planet Earth had shaped the surface.
00:14:15Go back in time.
00:14:16That driving energy at the heart of the planet had pushed the continents together into a
00:14:20single giant land mass, wrapped around the equator.
00:14:27On this supercontinent, known as Pangaea, there were vast lowland swamps and tropical
00:14:33rainforests.
00:14:34It was a massive hothouse and led to the creation of millions of new species.
00:14:43This period of time is known as the Carboniferous Era.
00:14:48The closest scientists can get to those conditions on Earth millions of years ago is here, the
00:14:53Okefenokee Nature Reserve in southern Georgia.
00:14:56Dr. Fred Rich is exploring how the inner Earth and life are interconnected.
00:15:05There were large land masses at the equator, so you have to imagine this flat landscape
00:15:12just above sea level, very well watered, in the tropics.
00:15:17And that paleogeography and the weather conditions, the meteorology that followed from that, led
00:15:25to the appearance of forests that were unlike anything that had ever existed on the planet.
00:15:36It wasn't just that the forests were big, the trees were monsters too.
00:15:45Huge plants, some of these are reckoned to have been 70 to 100 feet high, and perhaps
00:15:51as much as five, six feet in diameter, lived across this immense, moist landscape and plants
00:16:02grew until they got so big or so old that they simply fell over.
00:16:08These huge trees and dense forests had a profound effect on the atmosphere.
00:16:14They sucked up carbon dioxide and pumped out oxygen.
00:16:20High humidity, tremendous amount of oxygen exchange, I mean these plants were photosynthesizing
00:16:26so they were understandably, these were oxygen pumps, and they were similarly pulling huge
00:16:31amounts of CO2 out of the air.
00:16:36360 million years ago, the proportion of oxygen in the air was 60% greater than it is today.
00:16:45The high levels of oxygen led to another dramatic effect on the Earth's creatures.
00:16:53It supersized them.
00:16:56There were poisonous centipedes six feet long, two foot cockroaches, even dragonflies the
00:17:05size of seagulls.
00:17:08Dragonflies that we find in this swamp are large and they're certainly numerous, but
00:17:11the dragonflies of the Carboniferous would have been much bigger, easily three or four
00:17:15times the size based on what we have for fossil evidence.
00:17:21Instead of alligators, the dominant predators were giant toads.
00:17:28Alligators would have been replaced by large amphibians.
00:17:32Amphibians probably as large as the alligators that we have in these modern swamps, but looking
00:17:36differently perhaps.
00:17:40New species that changed the evolution of life, all because the energy inside our planet
00:17:45reshaped its surface.
00:17:50This strange lost world existed long before humans, but its story was sealed into the
00:17:55Earth's rocks in coal.
00:18:00The forest first became peat.
00:18:02This was then squeezed under tons of rock, where it started to dry out.
00:18:11Now in the process of this brown, messy sediment becoming coal, the first thing we would need
00:18:17to do is get rid of the water.
00:18:21Earthly processes do that simply by loading the sediment.
00:18:24So the longer the sediment is in the ground, the longer it has been buried, subjected to
00:18:28geothermal heat that's coming from the interior of the Earth, the more the sediment is compacted
00:18:34and the more the water is driven out.
00:18:40So the Earth's internal energy had reshaped the landmass to make life possible, then broke
00:18:45it apart and buried the remains, deeper and deeper, until the heat and pressure transformed
00:18:51the ancient forests into coal, fossilized remains of a lost era.
00:19:03As we go deeper on our journey, there are other riches for humans to exploit.
00:19:10Two and a half miles down, we pass a glittering seam of gold being formed.
00:19:16Boiling fluids full of dissolved gold bubble up through the cracks in the rock.
00:19:24The higher it rises, the cooler it gets, until the dissolved gold finally settles into seams.
00:19:32Miners push the bounds of human endurance to reach these gold seams.
00:19:36But for scientists, there's something even more exciting here.
00:19:41Something quite unexpected.
00:19:47Living organisms.
00:19:50Perhaps the direct descendants of the very first life on Earth.
00:20:03Earth's thin crust, home to life in all its complex, colorful, infinite variety.
00:20:11Below it is an inhospitable, lifeless world, or so it seemed.
00:20:19Scientists are now finding life deep inside Earth.
00:20:25It's a remarkable discovery, made in the world's deepest mines.
00:20:32This is the Witwatersrand region of South Africa.
00:20:36The mines here reach two and a half miles inside Earth's crust.
00:20:42It seems like they stretch a long way down, but in reality, they barely scratch the surface.
00:20:56This is a hostile environment for a human being.
00:21:01It's 130 degrees Fahrenheit, 100% humidity, and extremely cramped.
00:21:09The mines are so deep, the miners have to descend in two stages.
00:21:16A single elevator cable stretching two and a half miles would snap under the strain.
00:21:24So far down, the journey can take two hours.
00:21:33Like the miners, these biologists from Bloemfontein University risk heatstroke as they descend
00:21:38into one of the mines.
00:21:43But they're not interested in gold.
00:21:47They're looking for life.
00:21:50Colonies of extraordinary creatures that thrive in these extreme conditions.
00:21:57Bacteria they believe may be direct descendants of the very first life forms on Earth.
00:22:04Leading the team is Professor Derek Liddauer.
00:22:08You've got communities of bacteria and possibly even fungi we don't know yet, but probably
00:22:15mostly bacteria living in there.
00:22:18And the kind of populations you get in there are usually determined by the chemical composition
00:22:22of the water.
00:22:24But our past experience has been that there's some unique stuff in there.
00:22:34The scientists tap into ancient underground water released during the mining process.
00:22:42The water and the bacteria inside it have remained undisturbed for billions of years.
00:22:51These bacteria are tough.
00:22:54All they need to survive is rock, water and scorching heat.
00:22:59There's an amazing diversity of life underground, even in the deep subsurface.
00:23:06In some areas we can expect life possibly even down to 10 kilometers below surface.
00:23:13And they are extremely sophisticated, very highly specialized for the environment in
00:23:18which they live off the nutrients that they can get in the rocks.
00:23:22It's an extraordinary discovery that has transformed biologists' understanding of the origins of
00:23:27life.
00:23:28The bacteria are the latest additions to a strange group of creatures that thrive in
00:23:33extreme conditions called extremophiles.
00:23:40In the 1960s, astonished scientists found bacteria living in Yellowstone's boiling acid
00:23:46pools.
00:23:48Then in the 1970s, biologists discovered life one and a half miles down in the oceans, close
00:23:54to vents in the seafloor called black smokers.
00:23:59These life forms thrive on nothing more than volcanic gases.
00:24:05If life exists in such hostile conditions, it suggests a teeming mass of life could exist
00:24:12beneath our feet.
00:24:16It's been estimated that all the bacteria inside Earth could weigh more than all the
00:24:20life above ground put together.
00:24:24It also raises an intriguing possibility that life may have started not on the surface,
00:24:30but deep within the Earth.
00:24:33There's more diversity and more life in the deep subsurface than we have above surface.
00:24:41The implications for this in terms of the evolution of life in the universe are quite
00:24:46astounding because the old concept that life could have started in very calm, serene, warm
00:24:54pools on the surface of the Earth, that may be completely wrong.
00:24:57Life may have started in the subsurface.
00:25:01If life began underground, then somehow, at some time in Earth's history, it found a route
00:25:07to the surface.
00:25:10Perhaps the Earth's inner energy, as it pushed through the crust, took the extremophiles
00:25:14to the top.
00:25:17Or maybe it hitched a ride on a black smoker, a kind of extremophile elevator to ground
00:25:22level.
00:25:23Or floated up in thermal hot springs, boiling up from deep in the Earth.
00:25:31How far down primitive life could survive is uncertain, but to explore what lies beyond
00:25:36the deepest mine pushes technology to its limits.
00:25:42The only way down this far is to drill.
00:25:49But pressure and heat put a limit on even our most sophisticated drill bits.
00:25:55The deepest hole ever drilled bore just 7.5 miles into the Earth's 30-mile crust.
00:26:02In the 1970s, the Soviets raced to drill the world's deepest borehole in Russia.
00:26:07The drill bit was so long, it bent and stretched like a piece of elastic.
00:26:14But even at this depth, we are less than halfway through the Earth's surface layer, the crust.
00:26:20It's only 1,500th of our journey to the core.
00:26:25Seven and a half miles is like traveling from downtown Chicago into the suburbs.
00:26:32But it's another 4,000 miles to the center of the Earth.
00:26:36That's like commuting from Chicago to London.
00:26:42Scientists may be restricted to exploring the thin top layer of the Earth's crust, but
00:26:46their journey of discovery isn't over.
00:26:49They've found other ingenious ways of exploring inside Earth, and in the process, discovered
00:26:55more surprising connections with the evolution of life itself.
00:27:12Life on Earth might have started deep in the Earth's crust, but violent upheavals even
00:27:20further down played a crucial role in pushing life onto the next stage of evolution, one
00:27:27that would lead to all life as we know it.
00:27:30Remarkably, we know this from the ancient rocks of the crust itself.
00:27:43These mountains, in Western Australia's Karajini National Park, are made from rock that's three
00:27:54and a half billion years old.
00:27:57They used to be the bed of an ancient sea.
00:28:01Their red color comes from iron ore embedded right in the rock.
00:28:07Because the iron is evidence of something remarkable.
00:28:12Because they were formed during one of the most important events in the story of life
00:28:16on Earth.
00:28:23The bands of red iron ore were once layers of sediments, and they contain evidence of
00:28:28very primitive life forms.
00:28:32Martin Van Cranendonk is a geologist who spent a lifetime studying these rocks.
00:28:39Each one of these little bands is only about the length of a thumbnail, and was maybe deposited
00:28:43in a year.
00:28:45So you can see here you've got hundreds of feet of deposited sediments that represents
00:28:49hundreds of thousands of years of geological time.
00:28:55These were no ordinary sediments.
00:28:58They contain fossils of rock structures, called stromatolites, created by some of the
00:29:03earliest living things, simple bacteria.
00:29:09It's hard to imagine, but this immense volume of iron-rich rocks was actually formed by
00:29:14tiny microscopic organisms that formed structures such as preserved here in this very old rock.
00:29:22This is an example of a stromatolite that's built by single-celled organisms in this rock
00:29:27which is 3.45 billion years old.
00:29:31This is the oldest fossil on the planet.
00:29:39Incredibly, these bacteria are still making these distinctive rock formations just 400
00:29:44miles to the west.
00:29:48These strange-looking mounds are giant stromatolites built by the bacteria.
00:29:57Well, stromatolites are rocks, but they're rocks that are made by living microorganisms,
00:30:04or as we call them, microbes.
00:30:09And so these stromatolites actually grow by precipitating rock.
00:30:13So they build up layer by layer, but only very slowly.
00:30:18The bacteria also produced something else, something which kick-started a biological
00:30:23revolution, oxygen.
00:30:28If life did start underground, maybe it eventually found its way to the surface, propelled upward
00:30:35by those forces within Earth.
00:30:39And once they'd reached the surface, those bacteria found a new way to harness energy.
00:30:45Not from the rocks and the heat of the deep Earth, but from sunlight, the process we call
00:30:50photosynthesis.
00:30:52And one of the most important byproducts of photosynthesis is oxygen.
00:30:58These stromatolites are incredibly important for us.
00:31:00They're really the precursors to allow life to evolve from the oceans onto land and to
00:31:06breathe air.
00:31:08Without oxygen, complex life as we know it simply wouldn't exist.
00:31:13But oxygen also changed the composition of the planet, creating the iron ore in the crust.
00:31:20At the time, most of the iron on the surface was dissolved in the oceans, making them
00:31:25appear bright green.
00:31:28But the newly released oxygen bonded with all the iron to make iron oxide, or rust.
00:31:35The iron oxide fell to the seafloor, and the seas turned blue.
00:31:40Eventually, the iron oxide formed the deposits we see in the Karajini Mountains.
00:31:47Layer upon layer of iron oxide exists in the Earth's crust, thanks to primitive bacteria.
00:31:55It's the ore from which we extract 1.7 billion tons of iron each year.
00:32:00And it's also rich in oxygen.
00:32:04In fact, there's 20 times more oxygen locked up in the bands of iron ore than there is
00:32:09floating in the atmosphere.
00:32:13It's another example of how the world we know has been shaped by the incredible forces
00:32:18deep inside the planet.
00:32:21But where do these forces come from?
00:32:24We now enter the part of the Earth that holds the answer.
00:32:28The mantle.
00:32:29It's a dynamic mass of churning rock, kept moving by energy from the core.
00:32:35The powerhouse of the planet.
00:32:44Below the 30 miles of surface crust, we now move deeper, further than any human has ventured,
00:32:52into the Earth's mantle.
00:32:55The mantle is the real key to understanding how our world works.
00:32:59When you see flowing lava, it's easy to think that the mantle is liquid.
00:33:04In fact, it's nearly 2,000 miles straight down of hot but solid rock.
00:33:10It makes up 80% of the Earth's volume.
00:33:14Nothing can live here, but what happens at these depths is vital to life on Earth.
00:33:20The mantle may be beyond our reach, but sometimes it reaches us.
00:33:27The solid rock liquefies when the massive pressure on the mantle is suddenly released
00:33:32through fissures and cracks in the crust.
00:33:36The radical change in pressure transforms the rock into lava.
00:33:42The rock of the mantle beneath the Earth's crust is inaccessible, but against the odds,
00:33:47there are some places where mantle rock has been forced to the surface.
00:33:53One of them is on the Lizard Peninsula on the southernmost tip of England.
00:34:08On this peaceful beach is evidence of something violent and powerful, a piece of mantle rock
00:34:14that broke away and was forced upward 30 miles by the churning movements of the crust.
00:34:21For geologists like Robin Shale, it's the perfect place to study mantle rocks, which
00:34:26are normally way beyond his reach.
00:34:30How do they compare with other rocks on the surface?
00:34:35What do they tell us about what's inside planet Earth?
00:34:44The rocks here look completely different.
00:34:47They have colors which vary from greens through to oranges and yellows.
00:34:52This is typical of mantle rocks wherever they're exposed at the Earth's surface.
00:35:01Like no other rocks we know, mantle rock is very hard and very heavy, nearly twice the
00:35:06weight of granite.
00:35:13It's a dense mass of minerals, rich in heavy elements such as iron and magnesium.
00:35:21And it's the source of gemstones such as the distinctive green peridot.
00:35:29Close up, structures are revealed that could only have been formed under extreme temperature
00:35:33and pressure.
00:35:44Here on the Earth's surface, this rock seems solid enough.
00:35:50Deep underground, however, it becomes very different, something that behaves more like
00:35:54fudge.
00:35:56When we look at this mantle peridotite, it appears solid.
00:36:01In contrast, when mantle rocks or fudge are warmer, you can actually stretch and make
00:36:08it flow.
00:36:09And the significance for this is that these weak layers within the mantle allow the overlying
00:36:15plates to move slowly across.
00:36:18A solid that flows may seem strange, but the mobility of the mantle is vital to life on
00:36:24Earth.
00:36:25Because currents of heat circulate upwards from the core through the mantle, the plates
00:36:29of the crust can move around on the surface.
00:36:32Without this shifting geology, there'd be no continents, and the conditions for life
00:36:37would never have existed.
00:36:39Without these zones in the mantle that allow the plates to move across the Earth's surface,
00:36:44we would basically have a geologically dead planet.
00:36:47We would have no plate movement, we would have no mountain ranges, we would have no
00:36:51major ocean basins.
00:36:53So the mantle is absolutely critical.
00:36:59These are the deepest rocks visible on the Earth's surface.
00:37:02To look further into the mantle, scientists must find another way.
00:37:07And they've discovered something that can provide a glimpse of this hidden world.
00:37:15Crystals that formed billions of years ago in the intense heat and pressure 100 miles
00:37:20beneath the surface.
00:37:23Diamonds.
00:37:27We find them only because they are blasted to within our reach by cataclysmic volcanic
00:37:32eruptions.
00:37:44Inside the Earth's mantle, crushed beneath 100 miles of rock, the pressure is 50,000
00:37:51times more than we feel at the surface.
00:37:54It's like carrying 20 titanics on your shoulders.
00:38:00It's in this hostile environment that some of the Earth's greatest treasures are forged.
00:38:07The pressure creates diamonds.
00:38:10It crushes carbon into the hardest mineral known to science.
00:38:16But we don't have to dig 100 miles to find them.
00:38:20Diamonds exist just a few hundred feet below the surface.
00:38:26They were forced up through the crust by violent prehistoric eruptions, triggered by the Earth's
00:38:31internal heat.
00:38:34Today, miners excavate these extinct volcanic vents in search of diamonds.
00:38:42The Letzing Diamond Mine is located in the mountain kingdom of Lesotho, a small country
00:38:48in the heart of South Africa.
00:38:53The diamonds are embedded in rock called kimberlite inside an old volcanic pipe.
00:39:00It's the job of company geologists like Claire Palmer to find them.
00:39:04We're standing within the pipe, the original eruptive pipe that formed.
00:39:10And the original Earth's surface would have been at least 200 meters above our heads.
00:39:15And we're actually, in the mining process, re-excavating that pipe.
00:39:21Most of the diamonds on Earth exploded through the surface during huge volcanic eruptions
00:39:27one billion years ago.
00:39:40These volcanoes erupted at supersonic speeds.
00:39:44So you can imagine the power with which it explodes.
00:39:48Similar to that of Mount St. Helens.
00:39:53The Mount St. Helens eruption moved laterally across the Earth, whereas these eruptions
00:39:58were actually a lot more vertical in their expanse.
00:40:07These violent eruptions exploded minerals from 100 miles down upward to the surface
00:40:12in minutes.
00:40:14Today, the diamonds are locked inside this volcanic rock.
00:40:20There's only one way to get them out.
00:40:42Letzing is a valuable mine.
00:40:46All these diamonds were recovered in just over two weeks.
00:40:50These diamonds are known worldwide for their very high quality and yield the highest dollar
00:40:57per carat in the world.
00:40:59The Letzing diamond mine is famous for its very large diamonds.
00:41:03One of our most famous is the Lesotho Promise, 603 carats, which was recovered in August
00:41:092006.
00:41:10And it sold on tender for 12.4 million US dollars.
00:41:15Not all diamonds are perfect.
00:41:17Some have microscopic flaws.
00:41:20A perfect diamond is worth a lot more money.
00:41:22But for geologists, these flaws are the real treasures.
00:41:27They're tiny fragments of primitive mantle trapped inside the diamond.
00:41:32And they're the deepest samples it's possible to capture.
00:41:35They tell a remarkable story, like time capsules.
00:41:38They hold the key to unlock secrets of the Earth's very early history.
00:41:44From their chemistry, scientists can deduce that most of these diamonds are 3.2 billion
00:41:49years old.
00:41:51They can even figure out they were forged 100 miles down.
00:41:56Diamond samples from different parts of the world show large variation in their composition.
00:42:01That suggests the mantle was a churning, dynamic place, even in the early history of the planet.
00:42:09Below 100 miles, very few rock samples reach us on the surface.
00:42:14But this isn't the end of our journey to the core.
00:42:18There is another way to see what's down there.
00:42:23It's like an X-ray image of planet Earth.
00:42:28Scientists can do this by analyzing the power of earthquakes.
00:42:39Most of the time, we're unaware of the power locked inside our planet.
00:42:50But sometimes, there are violent reminders.
00:42:59Earthquakes are the result of processes taking place deep in the interior.
00:43:05Propelled by the slow movement of the mantle, the great plates that make up the Earth's
00:43:09crust constantly grind into, over, and under each other.
00:43:16Pressure builds until something snaps.
00:43:19When this happens, the Earth shakes, heaves, and rolls.
00:43:23The results can be catastrophic, especially when they happen in populated areas.
00:43:29This earthquake in China in 2008 killed 70,000 people and caused $150 billion worth of damage.
00:43:39Big earthquakes are disasters, but they're also windows on the deep interior of the planet.
00:43:48Scientists can make use of the shattering power of earthquakes to help understand the
00:43:52Earth's most remote depths.
00:43:54They use a worldwide network of devices called seismometers to trace earthquake vibrations
00:44:00as they travel through the planet.
00:44:08The data produced can help fill in our picture of the deep Earth.
00:44:14Professor Ed Guarnero uses this technique to study the mantle, all 1,800 miles of it.
00:44:22When an earthquake happens, the waves travel away from the earthquake through the planet
00:44:27in the interior and on the surface, in the same way when you drop a rock in a pond, you
00:44:31see the rings getting bigger and bigger and bigger from the drop sound.
00:44:35So what we do in seismology is we have these sensitive microphones all over the planet
00:44:39that record the ground shaking, and so we keep track of the precise time it gets here.
00:44:44So when you use a bunch of these instruments in concert, you can start to say something
00:44:49about the material the waves travel through.
00:44:53Just as doctors use sound waves to picture a baby in the womb, the waves from earthquakes
00:44:58can tell scientists about the world concealed deep beneath the Earth's crust.
00:45:04The waves travel through and bounce off structures within the planet.
00:45:10So if you have enough seismic data, you can start to characterize the shapes of things
00:45:15inside the planet that are reflecting the seismic energy.
00:45:21And because earthquake waves travel differently through different materials, we know our planet
00:45:26is made of many layers, like an onion.
00:45:30The waves show the mantle extends downward for 1,800 miles and offer the first glimpse
00:45:36of our ultimate destination, the Earth's core.
00:45:41Ed Guarnero's results show intense activity within the mantle.
00:45:45They reveal how convection currents of hot solid rock constantly circulate through the
00:45:51whole layer.
00:45:52It's too slow to observe directly, but speed it up, and it's clear over millions of years
00:45:58the mantle is in constant flux.
00:46:02Resembling mushrooms, the vertical columns in his animations show the steady movements
00:46:07of the Earth's interior.
00:46:10So what we're looking at here is a convection calculation depicting things when they get
00:46:15to the top, they cool off and fall back in.
00:46:18Just like a lava lamp, you know, the blob goes up and then its heat goes away and it
00:46:22falls back in.
00:46:23So that's what's happening here, the cycling of material in Earth's mantle over millions
00:46:28of years.
00:46:29And this is a process that's happening today.
00:46:33These convection currents through the mantle transfer heat from the core to the crust.
00:46:39Heat that drives and pushes the continental plates on Earth's surface.
00:46:44In this way, the roaring energy at the core shapes the world we live in.
00:46:50The crust consists of two kinds of plates, oceanic plates and continental plates.
00:46:57Ocean plates are heavier, so when the two collide, the oceanic plate plunges downwards
00:47:02under the lighter continental plate.
00:47:06Full sheets of crustal plate extend right down to the edge of the core.
00:47:12As that plate descends and drags some of the water down with it, and the water, some of
00:47:17the crust sediments are still saturated, they make their way down, that water can actually
00:47:22be stored in the mantle rock.
00:47:26Over millions of years, descending ocean plates have dragged so much water into the mantle
00:47:31that scientists estimate there's now more water below the Earth's surface than above
00:47:36it.
00:47:38Take all the water from the oceans and lakes and glaciers, everything on the surface of
00:47:44the Earth, and anywhere between 2 and 10 or 12 amounts of that can actually be stored
00:47:52in the Earth.
00:47:53If all this water rose to the surface, there would be flooding on a biblical scale.
00:48:01No land could survive.
00:48:04Eventually sea levels would rise two and a half miles above the peak of Mount Everest.
00:48:10Luckily for us, it will never happen.
00:48:14But some of this underground water does make its way back to the surface.
00:48:19The water carried down by ocean plates into the mantle becomes superheated and drives
00:48:24back toward the surface.
00:48:27A change in pressure liquefies the hot mantle rock, mixed with expanding water, the lava
00:48:32punches up through the crust, where it erupts with spectacular force.
00:48:48Mount St. Helens is the most famous American volcano created at a plate boundary.
00:48:54The pulverized rock and steam that billowed out of the volcano following its 1980 eruption
00:48:59was once part of the plate beneath the Pacific Ocean.
00:49:07There's a ring of explosive volcanoes, like Mount St. Helens, circling the Pacific Ocean.
00:49:14It's called the Ring of Fire.
00:49:18Each one marks the spot where the Pacific plate dives into the mantle below.
00:49:25We're now entering the lower mantle, a region at the edge of scientific understanding.
00:49:31Nobody knows what it looks like, but scientists speculate the hostile conditions here may
00:49:36create bizarre chemical effects.
00:49:41If you were to be able to go into the mantle, you would see exotic things, chemical things
00:49:47that we're not quite, we fully understand right now, but there's evidence for it.
00:49:52And you'd see a lot of different kinds of layering, just like when you're driving in
00:49:56your car and you see a road cut, you can see the layered rock.
00:50:01But in a few places, something disturbs these layers.
00:50:08Plumes of hot mantle rock rise up from the core to the crust.
00:50:16If you happen to live above one of these plumes, the result can be both creative and
00:50:22destructive.
00:50:24So you would see little isolated conduits, the details of which we're not fully clear
00:50:29on, but we think they could be a hundred miles in diameter, very hot material that works
00:50:35its way to the surface and gives rise to these things that we call hotspot volcanoes.
00:50:41You could see in this image, you have hot plumes of material coming up to the surface
00:50:46and the stuff that comes out is what we see coming out of places like Hawaii and Easter
00:50:52Island and Kerguelen Islands and such.
00:50:55And this animation was made with things called tracers, these little black dots.
00:51:00So you can get an appreciation for how slowly the material moves across the core mantle
00:51:05boundary until it finds its little plume upwelling and then, boom, they shoot up quite
00:51:10rapidly.
00:51:20Some of the world's largest volcanoes, Yellowstone, Iceland, Hawaii, sit right above these gigantic
00:51:28mantle plumes.
00:51:32Hawaii's Big Island is evidence of their creative power.
00:51:36Measured from the ocean floor, this is the world's tallest single mountain, 4,000 feet
00:51:41higher than Mount Everest.
00:51:45And every foot of it is made from lava spewed out from the top of a mantle plume.
00:51:51The surface plate is constantly moving while the mantle plume stays still.
00:51:56So the magma keeps punching through the crust in different places and leaves a chain of
00:52:00extinct volcanic islands in its wake.
00:52:08But while mantle plumes have the power to create entire island chains, they also have
00:52:14the power to destroy vast amounts of land.
00:52:21Yellowstone's geysers and mud pools may delight tourists, but they are signs that the park
00:52:26sits on top of a vast mantle plume.
00:52:32With a crater 45 miles long and 35 miles wide, this is one of the world's largest super volcanoes.
00:52:43Geologist Hank Hessler wants to understand its behavior.
00:52:48There's been many destructive volcanic episodes in Yellowstone.
00:52:54Three massive eruptions, one at 2.1 million years ago, which is one of the largest that
00:52:59we as geologists can define on the face of the earth.
00:53:02One at 1.3 million years ago and one at 640,000 years ago.
00:53:09Yellowstone may not look much like a volcano.
00:53:11It's more of a wide depression, but that's just because of its sheer size.
00:53:18Yellowstone is such a big volcano that so much material has been erupted.
00:53:25Hundreds to thousands of cubic kilometers of magma have been forcefully ejected into
00:53:30the air.
00:53:31When all that magma is erupting, the ground actually subsides into the void created by
00:53:37the erupting magma.
00:53:40It's been 640,000 years since Yellowstone last erupted.
00:53:45Heat emissions from the park could be a sign that the next eruption is overdue.
00:53:51If the Yellowstone volcano does erupt, it will unleash billions of tons of ash and gas
00:53:56into our atmosphere.
00:53:58It would block out the sun and plunge the world into a devastating volcanic winter.
00:54:09Mantle plumes are a key part of the earth's interior cooling system.
00:54:14They have the power to create some of the world's most beautiful and dangerous landscapes.
00:54:23The question is, what creates mantle plumes?
00:54:27Nobody knows for sure, but one thing is certain, the answer lies somewhere in the boiling furnace
00:54:34of the earth's core.
00:54:48Eighteen hundred miles down into the earth, just below us, is the core.
00:54:58The earth's outer core is a huge ball of liquid metal, bigger than the moon.
00:55:05The conditions of the outer core are really quite hostile.
00:55:09Temperatures more than 3,000 degrees.
00:55:13The pressure is just mind-boggling, more than a million atmospheres of pressure.
00:55:19If you could strip away the mantle and just have the raw core, it's quite hot and would
00:55:23be glowing intensely, very much like the surface of the sun is glowing.
00:55:27It's that hot.
00:55:30If we could open up a space between the mantle and the core, this is what it might look like.
00:55:42Just inside the mantle, liquid metal meets the mantle.
00:55:45There's probably, you know, a bit of a mushy zone where there's liquid metal mixing in
00:55:49with the last bits of mantle material.
00:55:52And then inside of that is just this vast, deep ocean of liquid metal, which is red hot,
00:56:00flowing.
00:56:01There's all this churning motion and probably things that are analogous to clouds in the
00:56:06sense of bits that are more dense and less dense mixing about as the core convects.
00:56:17Astronomers can see what the outer core looks like because seismic waves bounce off its
00:56:22liquid surface.
00:56:28And scientists like Dan Lathrop are discovering what's going on inside the core by measuring
00:56:33the powerful electromagnetic energy it produces, the Earth's magnetic field.
00:56:39If you look at the pattern of magnetic field on the outside of the Earth, it's quite clear
00:56:46that that pattern is slowly moving and slowly changing in a way that would be easily described
00:56:52by it arising from a liquid metal that's also slowly moving and slowly convecting.
00:56:58The Earth's magnetism has been known about for more than a thousand years.
00:57:02And for centuries, explorers and sailors have kept detailed records of our moving magnetic
00:57:07North Pole.
00:57:09We now know that birds and animals use it to navigate on their epic migrations across
00:57:14continents and oceans.
00:57:17By the 1950s, scientists understood that something made of metal was responsible for the magnetic
00:57:22field.
00:57:23It was the Earth's core.
00:57:28Dan Lathrop wants to know how the field could be generated.
00:57:32So he's built a model of the core, a sphere filled with liquid metal.
00:57:40It's not iron, but sodium.
00:57:46Iron would be too heavy and dangerously hot.
00:57:53But sodium isn't perfect either.
00:57:56Well, sodium has its pros and cons without a doubt.
00:58:01It's a very good electrical conductor, an excellent electrical conductor, so it gets
00:58:05us closer to being like a planet in the laboratory experiments.
00:58:09The cons are, it's a reactive liquid, it is flammable, burns readily in air, and also
00:58:16reacts violently with water.
00:58:20The 13 tons of sodium safely sealed inside, the 10-foot sphere starts to spin to recreate
00:58:27the Earth's rotation.
00:58:30Heaters keep the sodium molten.
00:58:37Minutes later, magnetic fields spill from the sphere in all directions.
00:58:45Lathrop's experiment confirms the way the Earth's magnetic field is generated.
00:58:50Driven by the heat, the convection currents in the core combine with the Earth's rotation
00:58:55to create a giant dynamo.
00:58:58The dynamo is like an electrical generator, but it's being driven by the motions of the
00:59:03liquid outer core.
00:59:05And that churning motion, sort of turbulent convection in the core, couples to the magnetic
00:59:10field to continuously regenerate the magnetic field.
00:59:13It's like the turning motion of the generator, in this case then it's the churning of the
00:59:17convection.
00:59:20The magnetic field is much more than a geological curiosity.
00:59:25It's vital to life on Earth.
00:59:27The field protects us from our closest, deadliest enemy, the sun.
00:59:34A giant nuclear reactor, enormous storms rage on its surface.
00:59:41These storms fling lethal radioactive particles into space.
00:59:46This is the solar wind, and Earth lies right in its path.
00:59:52But like a stone in a stream, the Earth's magnetic field parts the flow of radiation,
00:59:58converting it around the planet.
01:00:05We sit in a protective pocket of magnetism, the mystery of life made possible by the mysterious
01:00:10core of the planet it inhabits.
01:00:17The Earth's magnetic field is absolutely critical for Earth to be a habitable planet, in the
01:00:22sense that the quite violent radiation coming from the sun stream around the outsides of
01:00:29a bubble formed around the Earth by the magnetic field.
01:00:32So the magnetic field extends a sort of shield, the magnetosphere, which protects us and the
01:00:38atmosphere from most of the radiation.
01:00:41If that weren't there, the solar radiation would be constantly bombarding the atmosphere,
01:00:46actually eating away at the atmosphere, and some of it then directly making it down to
01:00:50the ground level.
01:00:53About 40,000 miles above the poles, the charged solar particles meet the outer reaches of
01:00:59the magnetic field.
01:01:01Here, some are diverted down toward the Earth's magnetic poles, where they create spectacular
01:01:07auroras that glow in the sky.
01:01:10These dazzling displays happen when the particles slam into gas molecules in the Earth's upper
01:01:15atmosphere.
01:01:19Although beautiful, these are a sign of a ferocious battle between the Earth's core
01:01:23and an invading stream of solar radiation.
01:01:29Our magnetic field protects us from other dangers, not just from the sun.
01:01:34Lethal cosmic rays made of radioactive particles permeate deep space.
01:01:41Down on Earth, we're unaware of them, but up in space, it's a different story.
01:01:47On July 20th, 1969, Neil Armstrong was the first man to set foot on the moon.
01:01:54It was one of humankind's greatest achievements.
01:02:04But on their way to the moon, Armstrong and co-pilot Buzz Aldrin saw flashes of light
01:02:09inside the darkened Apollo 11 module.
01:02:14Bizarrely, they even saw the flashes with their eyes shut.
01:02:20When they returned to Earth, they reported what they saw.
01:02:25NASA scientists were mystified.
01:02:31Six years later, they came to believe these light flashes were the result of high-energy
01:02:36cosmic rays penetrating the spacecraft and the crew members' eyes.
01:02:44Armstrong and Aldrin were exposed to these rays because the Apollo craft was near the
01:02:48edge of the safety shield of the Earth's magnetic field.
01:02:59In the years since, at least 39 astronauts have developed some kind of eye cataract a
01:03:04few years after exposure to this dangerous radiation.
01:03:12Without the Earth's magnetic field, we would all be exposed to these dangers.
01:03:18And it's the core that is our great protector.
01:03:23We know the magnetism comes from the rotation of the core and the turbulence of the molten
01:03:27metal within it.
01:03:30But how can we work out exactly what's going on inside the core?
01:03:34Peter Olson is one scientist who's devised an experiment that could offer an explanation.
01:03:40What we have here is nothing more than a large tank of water on a turntable.
01:03:45And what it's intending to simulate is the Earth's outer core.
01:03:51And we're going to inject some heavy dye into this big tank of water, and we're going to
01:03:57see the effects of the rotation on the turbulence.
01:04:03So there's a turbulent plume trying to sink to the bottom of the tank, but it starts to
01:04:09feel the effect of the rotation.
01:04:11And you can see it gets twisted up into kind of a helix.
01:04:16And it's this helical type of flow in the Earth's core that we think is so critical
01:04:22for generating the Earth's magnetic field.
01:04:26Ordinary turbulent motions don't have this kind of helical structure to them, but by
01:04:31virtue of the effect of the Earth's rotation, the turbulence in the core is made helical.
01:04:39These helical columns might explain the Earth's magnetic field.
01:04:44They represent liquid iron columns, which could work like the wire coils inside an electromagnet.
01:04:52As they move with the Earth's rotation, they create magnetism.
01:04:57Two and a half thousand miles below the Earth's surface, could there really be molten columns
01:05:06of liquid iron hundreds of miles high?
01:05:09As a consequence of this turbulent motion of the liquid iron, electric currents are
01:05:15flowing in the core.
01:05:17And the geomagnetic field that we see at the surface is actually the result of these electric
01:05:20currents.
01:05:22So there is no bar magnet or permanent magnet effect of any significance inside the core
01:05:27of the Earth.
01:05:28The magnetic field there is produced by electric currents.
01:05:34This delicate feedback system makes the core seem extremely fragile.
01:05:39Without heat or rotation, it wouldn't work.
01:05:47To demonstrate, Olson simply switches off the tank's rotation.
01:05:51The water keeps moving, but as it slows down, the convection currents gradually collapse.
01:05:58If this happened in the core, the Earth's magnetic shield would soon disappear.
01:06:07As long as our planet keeps turning, this won't happen.
01:06:12But there are signs that something is happening in the core.
01:06:15There is some disturbance, because the Earth's magnetic field is weakening, leaving life
01:06:24more exposed to radiation from space with every day that passes.
01:06:28And there's one place where the magnetic field isn't just getting weaker, it's disappearing
01:06:33altogether and fast.
01:06:44Deep inside the Earth's core, something mysterious is happening.
01:06:49Swirling currents of molten metal are creating a magnetic field that envelops the planet.
01:06:56We depend on this field to protect us from deadly solar radiation.
01:07:01But scientific data shows that magnetic field is weakening.
01:07:07Over the past century, the strength of the planet's magnetic field has declined by nearly
01:07:1110 percent, and scientists aren't sure why.
01:07:16During most of mankind's history, the magnetic field has been very strong, and now it's weakening.
01:07:24The Earth's magnetic field has been studied for about 160 years, and what people see is
01:07:30that the magnetic field has slowly and steadily dropped in its strength.
01:07:35In one region, the magnetic field is a third weaker.
01:07:41It's here, over the Atlantic Ocean, just off the coast of Brazil.
01:07:46It's known as the South Atlantic Anomaly.
01:07:50This disruption in the magnetic field stretches a quarter of the way around the globe, and
01:07:55it's growing.
01:07:59Every day in this area, cosmic radiation reaches closer to the Earth's surface.
01:08:05This protection that we get from the solar radiation from the magnetic field is already
01:08:10weaker in that patch.
01:08:12So it already has implications mostly for astronauts and people who run satellites.
01:08:19It's really come into prominence since the advent of long-term orbiting spacecraft.
01:08:24For example, the Hubble Space Telescope has had enormous problems over the years as it
01:08:29passed through the South Atlantic Anomaly.
01:08:33The problem is so bad that when the billion-dollar Hubble Space Telescope is above the area,
01:08:38vital instruments are routinely shut down for protection.
01:08:47And near the core, under the South Atlantic, something even stranger is happening.
01:08:53The magnetic field here hasn't just weakened, it has totally reversed.
01:09:00If you look at what the magnetic field would be at the edge of the core, the magnetic field
01:09:05down there has already reversed in that patch.
01:09:09Now this could be a sign, if this becomes deeper and broader, that we're headed toward
01:09:14a reversal.
01:09:16A reversal is a total change in polarity of the Earth's magnetic shield.
01:09:21The North Pole flips to the South, and the South moves north.
01:09:26What a reversal is, is when those North and South Poles reverse, so that you have a long
01:09:33steady period where they're in one orientation, and then there's a reversal, and then a long
01:09:39steady period in opposite reversal.
01:09:44Reversals have happened before.
01:09:45We know this because when lava cools, it preserves evidence of the Earth's magnetic field.
01:09:52Crystals inside the molten lava line up with the field.
01:09:57When it solidifies, it creates a record of its strength and direction at that exact moment
01:10:01in time.
01:10:04Studies of prehistoric lava flows indicate that the last reversal happened 700,000 years
01:10:09ago, when our ape-like ancestors roamed the Earth.
01:10:14You might think that if the field is so stable that it can persist for billions of years,
01:10:19why should it suddenly decide to change?
01:10:22But it does.
01:10:23We know that the Earth's magnetic field has reversed many hundreds of times.
01:10:26What we don't know is when will it do it next.
01:10:29Neither do we know what will happen when it does.
01:10:32The weakening magnetic field and the South Atlantic Anomaly are the signs that we're
01:10:36about to experience the next reversal.
01:10:40It could happen within the next 1,500 years.
01:10:43The rate of decrease is about 6% per century.
01:10:49Now that doesn't sound like very much, perhaps, but in geologic terms, that's extremely rapid.
01:10:57No one knows what a reversal will mean for life on Earth.
01:11:01But while the magnetic field reverses, we would lose its protection for several months.
01:11:09Solar radiation would penetrate our electrical systems.
01:11:16Surges would overload the world's power grids.
01:11:26At the same time, bats, birds, and whales could become disoriented, as their internal
01:11:31navigational systems are scrambled.
01:11:36There could even be an increased incidence of cancer, as solar radiation attacks our
01:11:41cell's DNA.
01:11:46We might see auroras appearing all over the planet, even over our major cities.
01:11:57No one knows exactly when the next reversal will happen, but the answer could lie even
01:12:02deeper inside the Earth, in the inner core.
01:12:07It's the least understood, most remote, and inaccessible place on the planet.
01:12:13And somewhere, in this hidden, hostile world, lies the key to the Earth's future.
01:12:20The inner core is a rotating sphere of solid metal floating inside the liquid outer core.
01:12:28Billions of amps of electricity leap across its surface.
01:12:32Hotter than the outer core, the inner core's heat is the ultimate driving force behind
01:12:37the Earth's magnetic shield.
01:12:42The pressures are so high towards the center of the Earth, because of the overlying weight
01:12:47of so much material, that despite the fact that it's hot, the material is still solid.
01:12:55Seismic studies tell us something else about the inner core.
01:12:58Slowly but surely, it's growing.
01:13:02Every year, it expands by one millimeter as the planet loses heat.
01:13:08Nobody has ever seen this process with the naked eye, but in the lab, scientists can
01:13:12use their imagination to show something similar.
01:13:16So as the Earth cools, the inner core grows by iron crystallizing onto it.
01:13:23We could imagine what that looks like by looking at ice crystallizing onto this cool sphere.
01:13:33A lot of people who think about the core sit around and argue about what's that surface like?
01:13:42Is it rough?
01:13:43Is it smooth?
01:13:44Is it mushy?
01:13:45What we know is that from the earthquakes passing through, if it is rough, the thickness
01:13:51of that is less than a mile or so, but that still leaves lots of room for mushy zones
01:13:58or cavernous pits and little mini mountains.
01:14:01We really have no idea what that surface looks like, but if you look at any other surface
01:14:06on the Earth, on other planets, elsewhere in the solar system, they're all rough.
01:14:12Even the surface of the ocean is rough, of course, moving about with the waves.
01:14:15And so my expectation is that things are quite rough and quite complicated.
01:14:21Exactly how rough and complicated is open to debate.
01:14:26Stan Lathrop believes the inner core's surface is probably covered in a forest of metallic projections.
01:14:34They're called dendrites.
01:14:36There's most likely a sort of rough surface of these iron crystals, perhaps dendrites
01:14:41poking out, and the whole core itself has a sort of crystalline order to it.
01:14:47So while it's roughly spherical, it has crystalline bits growing out from it, continuously growing larger.
01:14:54As the core cools, the dendrites grow.
01:14:59It's a sign that heat is constantly being transferred from the inner to the outer core.
01:15:04The Earth is slowly cooling just from its origin, and whenever you have something which
01:15:11is hotter on the inside and colder on the outside, it tends to get flows going, vortices.
01:15:17Think of them sort of like big, tumbling, cloud-like motions, but it's in the liquid
01:15:21metal in the core.
01:15:25This heat transfer is fundamental to life on Earth.
01:15:29It powers the outer core and the Earth's magnetic shield, but it won't last forever.
01:15:37With planet Earth losing heat every second, every day, one thing is certain.
01:15:43The inner core will keep growing and cooling.
01:15:47In the distant future, the whole core will freeze solid.
01:15:53For life on Earth, the consequences of that are unthinkable.
01:16:11The inner core of planet Earth is a mysterious place, hotter than the surface of the Sun,
01:16:17yet it's solid metal.
01:16:19The core radiates incredible heat energy outward.
01:16:22At the same time, it crushes everything down around it with intense gravity.
01:16:29There's no way to see it or sample it.
01:16:32How did it get there?
01:16:33Where did it come from?
01:16:35There are clues.
01:16:39The Earth shares its origins with the other rocky planets, Mars, Venus, and Mercury.
01:16:45In the beginning, just after the Sun lit up, before the planets existed, great clouds of
01:16:51cosmic debris orbited the newly ignited star.
01:16:56These early building blocks crashed into each other with massive force.
01:17:01The bigger the objects became, the greater their gravitational pull, until eventually
01:17:09whole planets formed.
01:17:11When a planet forms, it forms from a hodgepodge of all sorts of different materials.
01:17:16And so the heavier bits would tend to fall under gravity and accumulate into the interior
01:17:21of the Earth.
01:17:22We know that the bits of material that made up all the inner planets had quite a bit of
01:17:26iron in them, just raw metallic iron.
01:17:29And that would tend to sink down eventually to form this massive core of the Earth.
01:17:36The solar system is now complete and stable, but the process of formation, called accretion,
01:17:41is not quite over.
01:17:45The spare parts left over from the creation of the solar system, asteroids, comets, meteorites,
01:17:51still orbit the Sun and still crash into the Earth, like the one that created this, Meteor
01:17:57Crater in Arizona.
01:18:00It was formed by an impact 50,000 years ago.
01:18:07And for cosmochemist Menakshi Wadhwa, it offers a glimpse of the forces and the materials
01:18:13that created the Earth's core.
01:18:18So Meteor Crater that you see here was created by the impact of an object probably that was
01:18:24about 300, 400 feet across.
01:18:27And this was an event that was a sudden catastrophic event.
01:18:32A lot of energy was released, something like 20 megatons or so.
01:18:40Imagine a planet growing from billions of impacts like this one, each one delivering
01:18:45iron, nickel, and the other elements that make the world around us.
01:18:49They also delivered an enormous amount of heat energy.
01:18:56You can see that there were large blocks that were ejected out from the crater and
01:18:59there were actually material probably tossed out to hundreds of miles from the crater as
01:19:03a result of the impact.
01:19:07The impact here was so powerful, it vaporized the meteorite, but a few fragments survived.
01:19:15So this particular meteorite is, it's called a Canyon Diablo meteorite, and it's an iron-rich
01:19:20meteorite, which was part of the impactor that created Meteor Crater.
01:19:26It's very difficult, of course, to actually sample a piece of the Earth's core, but these
01:19:30meteorites right here provide us a window into looking at planetary interiors.
01:19:36And you can actually learn something about core formation processes by looking at iron-rich
01:19:40meteorites.
01:19:42Close up, you can see the crystalline structure of the metal that exists right at the heart
01:19:47of our planet, a planet that's unique in the solar system.
01:19:51But what makes Earth so special?
01:19:54If the other rocky planets were made the same way, how come they're so different today?
01:20:02What happened to them might shed light on the future of our own planet.
01:20:10Scientists look to them for clues that can tell them more about the fate of the Earth's
01:20:13core.
01:20:15And the planet that interests them most is Mars.
01:20:21It's our nearest neighbor.
01:20:23Like Earth, water once flowed on its surface.
01:20:26It had a thick atmosphere, but that was billions of years ago.
01:20:31Today, the planet is a frozen desert.
01:20:36Most of its water and atmosphere have vanished.
01:20:40But even though Mars has a metal core, its magnetic field is tiny.
01:20:46Are these conditions a coincidence?
01:20:49Or is Mars a vision of Earth's future?
01:21:04In 1996, NASA launched the Mars Global Surveyor.
01:21:08Its mission?
01:21:09To unlock the secrets of the red planet.
01:21:11As America begins its journey back to the red planet.
01:21:14But in the process, it unlocks some of our own planet's secrets, shedding new light on
01:21:21the very center of the Earth, the inner core.
01:21:26The Global Surveyor's data astonished scientists.
01:21:31It showed Mars' magnetic field is very weak, but Mars' crust is intensely magnetized.
01:21:40The implications for our planet are immense.
01:21:46Like Earth, Mars once had a powerful magnetic field, but at some point, the Martian core
01:21:52cooled and froze, and its magnetic field collapsed.
01:21:59The question is, could it happen to our planet?
01:22:07Mario Acuna was one of the scientists who built the magnetic sensors that gathered the
01:22:11Mars data.
01:22:13He used it to create a map of Mars' magnetized crust.
01:22:17He discovered that in one area, there is no magnetism at all, and it corresponds with
01:22:23a particular physical feature.
01:22:25One of the things that we observe is this very large hole in Mars, if we want to call
01:22:31it a hole.
01:22:32It's really the remnants of a gigantic impact that took place very early in Mars' history.
01:22:41This hole is an enormous meteor crater.
01:22:44It was clear that the rocks here, unlike those in the rest of Mars' crust, hadn't been magnetized.
01:22:50So the crater must have formed after Mars' core stopped working.
01:22:58Scientists think the meteor impact here released so much energy, it liquefied the planet's
01:23:02crust at the point of impact.
01:23:09Crystals in the cooling lava would have recorded the surrounding magnetic field just like they
01:23:14do on Earth.
01:23:15But in the gigantic crater on Mars, the rocks bear no record of being magnetized.
01:23:23Scientists theorize that's because the magnetic field no longer existed when the impact occurred.
01:23:30The continent-sized crater was created four billion years ago.
01:23:35It means the dynamo in Mars' core stopped working when the planet was in its infancy.
01:23:42For the first time, we could time when the dynamo disappeared.
01:23:47And since Mars was formed only 4.5 billion years ago, that means that the dynamo only
01:23:52lasted a few hundred million years.
01:23:58The reason for Mars' premature death lies in its size.
01:24:05Mars is half the diameter of Earth, so it cooled more quickly.
01:24:10Its core froze, and its magnetic shield collapsed.
01:24:15The fate of life on Mars was sealed.
01:24:20The planet lay exposed to the solar wind.
01:24:27Its atmosphere and water eroded away.
01:24:32The fact that the magnetic field disappeared had a tremendous effect on the loss of water
01:24:36by Mars.
01:24:37We're looking for something like 1,500 feet of water over the entire planet Mars that
01:24:45have disappeared from Mars.
01:24:52Earth is much larger than Mars, so its core is still hot, still working.
01:24:58But the lesson of Mars is unavoidable.
01:25:00Eventually, Earth's own core will cool until the convection columns inside the outer core
01:25:06collapse, and then our magnetic shield will come down.
01:25:14Without it, solar radiation will strip away both our atmosphere and liquid water.
01:25:20Then, Earth will become a dead and desolate place.
01:25:25But we don't need to panic just yet.
01:25:30The extreme temperatures in the inner core suggest we have plenty of time left, perhaps
01:25:37even billions of years.
01:25:43Nearly 4,000 miles from the surface, we have reached our destination, the very center of
01:25:49the Earth.
01:25:50This is the hottest part of the planet.
01:25:56Temperatures reach 12,000 degrees, hotter than the surface of the sun.
01:26:03And with no gravity, it's like nothing else on Earth.
01:26:08The very center of the Earth is probably the most unearth-like place on the planet, in
01:26:13the sense that gravity gets weaker as you go down, and when you hit the center, there's
01:26:18no gravity left, there's no direction which means down.
01:26:23Gravity is absent.
01:26:24The temperature is the hottest spot on the Earth, and so it's a sort of white-hot, gravity-less,
01:26:30very high pressure, just crushing pressures of all the weight of the rest of the Earth
01:26:34all pushing down on you.
01:26:36So it's extremely inhospitable and extremely strange at the same time.
01:26:43The world beneath our feet may seem like an alien place, but our journey has shown it's
01:26:49very much part of life above ground.
01:26:54Everything about it is just right.
01:26:57The Earth spins at precisely the right speed, and it's exactly the right size to allow some
01:27:03heat loss from the core, but not too much.
01:27:09As a result, we have our magnetic field.
01:27:12The mantle is just mobile enough to allow currents of heat to move upward, so we have
01:27:17our continents to live on.
01:27:22And our gravity is just the right strength to bind our atmosphere and oceans to the surface.
01:27:30From the crust to the core, every layer, every rock, every piece fits together to make life
01:27:37upon the surface possible.
01:27:41The secret of all life as we know it lies deep inside planet Earth.