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00:00 Earth's underground environments are a mostly unknown world.
00:03 There are thousands of complex cave systems, full of strange creatures that never see the
00:07 light of day, with some leading so far down that no human has yet explored them.
00:12 But at these absolute extremes, if we did explore them, then how far could we really
00:17 go?
00:18 This is Unveiled, and today we're answering the extraordinary question; what happens if
00:23 you drill through the Earth?
00:26 Do you need the big questions answered?
00:28 Are you constantly curious?
00:29 Then why not subscribe to Unveiled for more clips like this one?
00:32 And ring the bell for more thought-provoking content!
00:36 First off, what is Earth actually made of?
00:38 At its simplest, it consists of crust, either oceanic or continental, with sections known
00:43 as tectonic plates covering the entire surface.
00:46 The crust is then always made of rock, but of different kinds of rocks in different places
00:50 and at different layers.
00:52 Below this topmost layer, there's the mantle, which is Earth's magma source.
00:56 And then, finally, we have the core, both the inner and outer.
01:00 The core is a thousand miles down, incredibly dense, and billions of years old.
01:05 Here, at the heart of our planet, it's made of super-hot, super-dense iron and nickel,
01:10 and temperatures can be more than 10,000 degrees Fahrenheit.
01:14 We know, then, that inside the Earth isn't exactly a welcoming place… but nevertheless,
01:19 humans are still intrigued by all that's below us.
01:23 Theories about the Earth perhaps being hollow and hosting unknown ecosystems have appeared
01:27 in science fiction for a long time, and although the hollow Earth theory doesn't actually
01:32 hold up, there certainly are strange and genuine underground realms that are intriguing, even
01:38 bewitching.
01:39 The deepest known natural cave on Earth is Virovkina Cave in Eastern Europe.
01:43 At about ten miles long and more than 7,000 feet deep, it's an extreme and unique environment.
01:49 If it were an ocean instead of a cave, its depth would put it firmly in what's known
01:53 as the "Bathypelagic Zone", with pressure hundreds of times greater than what's found
01:57 at the surface.
01:59 Unfortunately, and perhaps unsurprisingly, some explorers have died inside Virovkina
02:03 Cave.
02:04 Ultimately, though, it's very likely that Virovkina is even deeper than we currently
02:08 know, and also that there are other, far deeper cave systems out there that haven't even
02:13 been discovered yet.
02:15 What really puts the scale of the Earth into perspective, however, is that in all cases
02:19 we are still a long way away from reaching down into even Earth's second layer, the
02:23 mantle… let alone further still, to the core and out the other side.
02:28 Do man-made caves offer any improvement?
02:30 To some degree, yes.
02:32 Virovkina Cave is about 1.3 miles deep, but the deepest mine in the world, the Mpana Gold
02:38 Mine in South Africa, is almost double that, reaching 2.5 miles.
02:42 If we abandon "traversable" underground systems - i.e. if we look at the deepest locations
02:47 but ones that humans can't travel down into - then we come to what's truly the deepest
02:52 man-made hole in the world, the Kola Superdeep Borehole in Russia.
02:57 It is more than 7.6 miles deep, and is a real benchmark in the field, given that it was
03:02 a drilling project conceived solely to see how deep it was possible to drill into the
03:07 Earth's crust.
03:08 Thankfully, the borehole is only about nine inches wide and is now sealed off, so there's
03:13 no danger of anybody falling into it.
03:15 But even if you did, you'd still - and again - be way off how deep you'd need to go to
03:20 reach the core, or to emerge out the other side.
03:23 There's simply nothing on Earth, currently, that takes us even close.
03:27 The middle of the core is about 4,000 miles below the surface, meaning we'd need to
03:32 dig an 8,000-mile tunnel to punch through to the other side of our planet.
03:37 The longest still-in-use tunnel in general - going across the Earth and not down into
03:41 it - is the Delaware Aqueduct in the US, but it is only about 85 miles long.
03:46 We'd need, then, almost 100 times more.
03:49 And it would all have to withstand untold pressure and temperature.
03:53 In reality, drilling through the Earth - as simple as it sounds - isn't something that's
03:57 yet technologically possible for humanity.
04:00 But say that money is no object, some kind of tech solution is discovered, and that the
04:05 entirety of our species has, for some reason, decided that we really, really need to create
04:10 this passage.
04:11 What then?
04:12 First, we'd need a material not only to build the tunnel out of, but also our drilling
04:17 apparatus.
04:18 Again, that material would need to be capable of withstanding extreme temperatures and depth.
04:23 There are those highs of around 10,000 degrees Fahrenheit, while the pressure would top out
04:27 at about 3.6 million atmospheres.
04:30 For context, the deepest known point in the ocean, Challenger Deep in the Marianas Trench,
04:35 has about 1,000 atmospheres of pressure.
04:37 Even it just isn't comparable.
04:39 When thinking of material that could work, you might immediately go to diamond, which
04:43 can cope with up to five times as much for the pressure.
04:46 However, the melting point of diamond is a paltry 7,200 degrees Fahrenheit, so it would
04:52 inevitably melt partway through our journey.
04:55 Which is a shame, because a diamond drill for a diamond tunnel seems like it would be
04:59 a pretty cool thing.
05:01 Scientists have researched this specific problem, however, and before come up with a new material
05:06 that combines hafnium, nitrogen and carbon (hafnium being a lesser-known transition metal).
05:12 But even this fares only slightly better than diamond, with a melting point of 7,460 degrees.
05:19 Even our most thoroughly researched custom materials, then, only get us to the edge of
05:24 the Earth's core.
05:25 And, of course, only in theory.
05:27 Staging any kind of practical test for what we'd need - some kind of new wonder metal
05:32 or element - is basically impossible.
05:35 But hypothetically, say we do have such a material, what other obstacles would our Earth-splitting
05:40 tunnel face?
05:41 The consistency - or rather inconsistency - of Earth is another problem.
05:45 Drilling through rock is one thing, and in fact is the only thing we know… but eventually
05:50 you get to the mantle, full of heavy, molten lava.
05:52 So, in carving our tunnel we would need a craft that can drill through the ground, yes,
05:57 but it would then need to become the most extreme submarine ever, capable of wading
06:01 through magma.
06:03 And then it would need all of those temperature and pressure resistance qualities in order
06:07 to survive the core.
06:09 Anything that could do all of that would be some machine.
06:12 But, hypothetically, say we do have such a machine.
06:16 Next we'd have severe navigation problems, since there would be literally zero visibility
06:21 for the very vast majority of our mission.
06:23 And then the heat remains a major issue, even with an indestructible, hypothetical wonder
06:28 material.
06:29 Because just because something won't melt when subjected to thousands of degrees, doesn't
06:33 mean it won't get so hot inside that humans can't survive.
06:37 The conditions on the inside of our tunnel through Earth would be hellish.
06:41 More than that, they would boil you alive.
06:43 So, here's hoping we develop some ultra-advanced climate control systems, as well.
06:48 But maybe we have all of that, too.
06:50 We've got our tunnel made from an impossible material, the incredible machine needed to
06:54 actually build it, some super-advanced air conditioning, and some sort of vehicle that
06:58 can withstand the entire journey.
07:00 How long would the journey take?
07:02 Again, we have 8,000 miles to traverse.
07:05 The fastest train in the world is currently the Shanghai Maglev in China, which travels
07:10 at 286 miles per hour.
07:12 At that constant speed, we're talking nearly 28 hours to tunnel through the planet, which
07:16 is longer than it would take to just fly between the two points on an airplane.
07:20 But here's where one final and crucial consideration comes into play.
07:24 Because when drilling through the Earth, we're actually not beholden by how fast trains,
07:28 or anything, can move on the surface.
07:30 The force of gravity messes all that up.
07:32 As it's pulling everything directly towards the core all the time, we know that the journey
07:36 to the centre of the Earth would, in reality, be much shorter.
07:39 It would potentially take less than an hour.
07:42 However, there's a catch.
07:43 And a big one.
07:44 Because with gravity pulling you in, how can you ever hope to get away?
07:48 Your journey from the centre of the Earth - the second half, in terms of plane distance
07:52 - just isn't going to happen.
07:54 Unless you manage to conduct the entire journey also in a total vacuum, then no matter what
07:58 you do, gravity will always mean that it's actually impossible for you to leave.
08:02 So, even if you've managed to build a tunnel to withstand the pressure - which means you
08:07 haven't been crushed - you'd still find yourself hopelessly cast adrift, trapped in
08:11 a tomb of your own making, waiting to starve and eventually die.
08:15 Which isn't really the ending we were hoping for.
08:18 But what do you think?
08:19 Would digging a tunnel through the Earth be worthwhile?
08:21 Or would it just be completely absurd?
08:24 Even if it were possible.
08:25 For now, the want to explore is usually to be applauded… but sometimes, even the most
08:29 fundamental laws of physics are telling you that it's probably a bad idea.
08:34 And that's what would happen if you drilled through the Earth.
08:38 What do you think?
08:39 Is there anything we missed?
08:40 Let us know in the comments, check out these other clips from Unveiled, and make sure you
08:44 subscribe and ring the bell for our latest content.