The Infinite Monkey Cage - Journey to the Centre of the Earth - Phil Wang, Ana Ferreira and Chris Jackson

Episode Date: February 19, 2025

Brian Cox and Robin Ince slice deep into the lesser explored world beneath us. To join them on the journey from the crust to the core they are joined by seismologist Ana Ferreira, geologist Chris Jackson and comedian Phil Wang.School children learn about the makeup of the earth with an image depicting the earth's core, mantle and crust layered neatly on top of each other, but is this an oversimplification? Our experts reveal that the earths innards are less uniform than we might think and mysteries still abound, including the makeup of some continental sized blobs deep inside the earth. We learn about the incredible heat and pressure as we descend and why that has limited how far humans have been able to explore these deep realms first-hand. We explore the chemistry of the interactions between the earth layers and how they influence the formation of continental plates and volcanoes. Phil has an existential crisis about falling inside gaps between the plates but is reassured his worries are unfounded as Ana explains the latest techniques being used to understand the world deep beneath us.Producer: Melanie Brown Executive Producer: Alexandra Feachem Researcher: Olivia Jani

BBC Sounds music radio podcasts You're about to listen to the Infinite Monkey Cage. Episodes will be released on Wednesdays wherever you get your podcasts from. But if you're in the UK, the full series is available right now first on BBC Sounds. Hello, I'm Brian Cox. I'm Robert Ince. And this is the Infinite Monkey Cage. Today we journey to the middle of the earth, which I think is a wonderful place to go,

because I do actually see Brian as a kind of a Gandalf-like figure, really. This kind of wizardy person talking magical nonsense about ridiculous ideas of the behaviour of subatomic particles, all made up as he talks to his staff. I'm kind of more of a Bilbo, I like to think of myself. But this is the weird thing actually, even though I do see myself as more of a Bilbo, it's actually Brian who has very, very hairy feet. And apparently it was because he was genetically altered

after his first TV series, because they were so worried he might lose the hair on his head that they've now made these incredibly fertile feet of his. And if you actually see him from below the waist he looks not just similar to Pan, that's for everyone who'd like to have a nice dream about Brian tonight. Surprisingly, for the first time in a very long time Robin's introductory reference to Middle Earth is not actually far from the theme of today's show. Today we're looking at what lies

beneath the surface of the Earth. If you could slice through the Earth. Like a Victoria sponge or maybe a Ferrero Rocher. If you could slice through the Earth, what would you find? From the crust to the mantle to the core, what do we know about the deep structure of our planets and what mysteries await as we journey to the center of the Earth? To act as our tourist guides as we drill

down we are joined by a seismologist, an earth scientist and a wangsplainer and they are... My name is Chris Jackson I am a geoscientist and the most exciting thing I've ever dug up was the phone number of an ex-girlfriend who's now my wife. My name is Anna Ferreira. I'm a professor in seismology at University College London. And one of the most exciting things I dug up indirectly was a very deep collision at about a thousand kilometres depth between very hot and very cold materials. Oh, I'm Phil Wang. I'm a comedian. And the most intriguing thing I've dug up was a piece of Roman pottery in Vindolanda, which is an old Roman fort in Northumbria. And all the pottery is all in shards because they were very careless. And I wonder why they're all

broken and why they're all smashed. why aren't there any complete vases? Because it's not like the Roman Empire ended like Pompeii all at once they had time to pack And this is our panel I just want to check Chris. So did you physically dig up the number? No, it was kind of metaphorically. It was a metaphor. Yeah, sorry. I didn't bury her phone number in the ground.

Because I just seemed she was trying to hide her number from you. That's not reasonable. Imagine it's like that Blue Peter. You remember that memory box that they had? Where it was like, and they dug it up 30 years later, but it had all gone damp and everything had gone rotten but that idea if I still be able to read that number in 30 years time. Phil I love your idea about why you know the Roman Empire ended which was due to a lack of crockery to serve their

geese on and so they went they just starved to death. It's got really hungry it's like where's the plates to Tinius smashed again. So Chris, if we were to slice through the earth, could you go through from the surface through to the core and describe what we'd see? I think that one of the best analogs, which fails in terms of the shape, is probably a Cadbury's cream egg in that you cut it open. Let me just qualify that.

The earth's not an oval. But it's basically a series of broadly concentric rings of different kind of compositions or different materials. So I think that's a really good starting point. Or think of an egg which again is egg-shaped because it's an egg. But it's got these different layers and inside each layer there's different features. So what about Scotch egg? Those are... Oh my goodness! It's not vegan or vegetarian compliant

but yeah, Scotch egg would be... But you know, you have vegetarian Scotch egg? That's true. That's one to you Phil, in this quiz. You've come up with a much better metaphor than the professional geology. So as we go in, could you describe those layers? So you know, you have more than

just the simple layers, but let's start simple. So as you say, you've got the crust, which is this thin, very brittle layer where we all live. And for instance, earthquakes happen when that brittle layer breaks. And then beneath that, you have something called the mantle, which at our time scales, it's solid, but over millions of years, it actually flows a little bit like glass, for instance. You might have seen that very old glass is going to be thicker in the bottom and thinner in the top. So it's exactly the same sort of phenomena that happens in the mantle. You have this movement, motion,

flow in the mantle. And then beneath that you have the outer core, which is liquid, and then actually generates our magnetic field of the Earth. And then deep, deep inside you have the so-called inner core, which is solid. You have lots of heterogeneity. You have lots of lateral variations within those layers. So if you were to drill down, so what depths do you find those transitions? So essentially the crust, if it's within the oceans, it's very thin, maybe about seven, six, seven kilometers. If it's within the continents it can be up to something like 70 kilometers, so really much thicker. And then as you go to the mantle, the boundary between the mantle and the core is at about 3,000 kilometers depth. And then that boundary between the outer liquid core and the solid

core is at about 5200 km depth. The bit we experience, which is very real and tangible to us and brings us so many resources, but also presents so many challenges to life on Earth, it's incredibly volumetrically an incredibly small part of the Earth. So the crust is about 1% of the... The bit we live on is about 1% of the total Earth volume. So it is strange when you are giving those numbers of thousands of kilometres.

What we experience of it is so infinitesimally small. And how does the composition change as you go down? We have at the top, we have in the crust, we have rocks. So that's the kind of rocks you'd find on the beach or the rocks we drill into if we were drilling a borehole into the Earth. Then as we go down into the mantle, we have effectively rocks, but as Anna described, these are rocks which are not like rocks as we know it. These are rocks which actually flow like what we call a viscous fluid, like something that's sticky, but it moves over

millions of years very, very slowly. So it's different in terms of how it behaves to the crust, but if you held a piece of mantle material in your hand, it would essentially be a rock. And then as we go down into the outer core, you know, you probably won't want to touch that, would be my guess. Yeah, so it's mostly iron, liquid iron. That's the main, and also some nickel possibly,

but mostly liquid iron that is basically moving, and hence generating currents, and hence then the earth's magnetic field of the earth. This is the internal source for that. And then when you have the inner core is also mostly made from iron and nickel, but solid. The solid, yeah. The outer core, the bit that's moving,

it's under such high pressure that actually, if you brought it to the surface of the earth, I heard, it basically would flow like water. Really? So it's so hot, it's so highly pressured, but if you removed it from that environment and put it to the surface of the earth, the viscosity would basically be as runny as water, which is kind of amazing to think. It's mind-blowing.

It's very difficult to imagine it at our scales. So just to complete that picture, so in terms of temperature and pressure as you go down, can you describe those temperature and pressure gradients down to the centre? Yeah, so for instance, you know, when you are at the sea floor, say five kilometres deep sea, you're at about 500 times the pressure that you have at the atmosphere. And can you imagine, you're 500 times, you would just collapse basically, you know. And then when you are at the discontinuity between the crust and the mantle, you're at about a thousand times. By the time you're at the bottom of the mantle, you're at one million times the pressures that you have at the surface.

I mean, this is crazy. And by the time you are at the center, it's like three million times. It's just... I think the Earth is kind of hard to describe to people like that, because the only kind of physical experience you could ever have of increasing pressure is if you've died to the bottom of a swimming pool right as you dive down over enemy he's been scuba diving you feel that pressure a bit right but like what does it mean like a thousand times that it's it's just so incomprehensible or a million a million yes this pressure is that way and that's why these materials behave in a strange way because iron flowing like water yeah it's an odd concept exactly and I think as well the other, like as the temperature as it changes in

addition to the change in pressure that Anna just described, we have what we call the geothermal gradient. So this is the rate at which the earth warms as we go down into it and the average geothermal gradient for continental crust around the world is between 25 and 32 degrees Celsius per kilometer. So that's why it gets hot, you know, the movie journey to the center of the earth. But just again, just to add some numbers to that, you know, you're talking about hundreds of degrees Celsius, you know, relatively shallow in the mantle, but as you go deeper we're talking about like 3,000 degrees Celsius

at the bottom of the mantle. That's why people are sweating in that movie. It's really, it's mind-blowing, it's something completely beyond our human scales. I just wanted to ask, Phil, something just about you, you studied engineering before you gave it all up for showbiz. And was this the kind of world, because some of the machinery that we see and some of these things which are able to start exploring, was that ever part of the interest in engineering? It was a big part. The day I decided I wanted to do engineering was when I went on a school trip to CERN in Switzerland. And the depth of the hole, and the size of the hole they'd made to put the accelerator in, I thought was so incredible. The achievement, I thought

I'm going to learn how to do that. And then a year into uni I discovered dick jokes and I never turned back. I'm fickle basically, I'm fickle. My head is easily turned. You went from one deep darkness to another, I see. I like that moment where you're thinking now I could be part of the true understanding of why the universe is as it is, but I've come up with the pun, chili, chili, wang, wang. And I feel that that might be a better direction to go in. Well, I think also the headlines of all jobs are quite cool,

like science, medicine, the headlines are pretty dramatic. But the reality of the day-to-day work is the same as all work. It's emails, isn't it? I mean it's emails and waking up early and office politics and just grind and spreadsheets misery Yeah, there you go. Yes. I think what once you hit the reality of what a cool job is There any young children listening? Science If there are any young children listening, if you're going into science, this is going to be edited out of this show. Just so you know, we're 198 episodes in

and we forgot to tell you back in 2009, science is boring. I disagree. I was just about to add, coincidentally, last week, I went down, we have a laboratory in the UK called the Bowlby Underground. Oh wow. Which is Bowlby Mine. And it's, I think it's the deepest mine in Britain.

Yeah. Over a kilometre deep. And what you said about the temperature, it's about 35 to 40 degrees down there and it's in Wetherby. So in Wetherby in November, you go down one kilometre and you suddenly it's 35 degrees. You can almost not touch the sides of that mine And that and that mine is absolutely mind-blowing in that it's actually goes out under the North Sea So it goes so far east with the bulby mine if you access the the drifts that go out in this layer called the zekstein

It's a it's a halite rock a salt rock. It goes out under the North Sea So when you're in those distant parts of that mine, you're not only under you know, a kilometer or so of rock You're actually under the North Sea. So when you're in those distant parts of that mine, you're not only under a kilometer or so of rock, you're actually beneath the North Sea. Yeah, and what was interesting to me is it goes to the, we're gonna talk about the dynamic nature of the earth, because we described it just as a fixed thing, but of course it isn't. Yeah, yeah, so it was when the UK was a lot further south

in terms of latitude than where we are now. There was a higher evaporation rate than there was a inflow of fresh brine, so fresh seawater. So we built up these great thicknesses of salt. So, and that's the incredible thing about the geological record, is that it has this little window into this dramatic history of the Earth, and even somewhere as humdrum as, you know, the northeast of England, you know.

It has sampled such a different diversity of climates and different tectonic settings. Very quickly, I'd like to apologize to all listeners in Sunderland, Newcastle South and North Shield. I think you're really smashing them. There's a lot of great stuff that happens there. I do not find you humdrum. Anna?

I was just going to add that what we were discussing before, the scales are so mind-blowing and so beyond us. Not just the spatial scales, the temperatures, the pressures, but also the time scales. We are talking about movements at best of a few centimetres per year, often of millimetres per year. So it's again very, very different. It's a completely different mindset when we think about, you know, these processes. Yeah, and I think as well with geology and the way our planet works is that oftentimes the public's kind of exposure to the planetary dynamics is when it's kind of the Earth is trying to kill them, right?

A volcanic eruption, an earthquake, and they're really dramatic, aren't they? The Earth shakes, something comes out of a big hole in the ground. But a lot of the time the earth is kind of doing its thing but just in a much more kind of modest and humble and quiet way and nobody wants to make tv shows about all the ordinariness of the planet and I think that's a loss. How far first of all has a human being actually managed to go down? How far have they been able to explore? Oh, humans, it's really just of meters basically. Yeah, humans because of the pressures and all of that.

So in terms of meters, how many meters would we manage? I think the deepest mines on Earth go to about three and a half kilometers. Some of the deepest mines, and I think they're in South Africa. So that's the deepest I think a human's ever been in terms of entering the crust. Yeah but then it's open right? I was thinking things like you know for instance diving. Yeah diving I guess you know there's Mariana's trench, Mariana Trench in places where people have tried to go deeper. So there is that sort of thing so it depends whether you mean whether people going under the water or going actually into the Earth's crust Going into the Earth's crust is so much cooler than digging a hole

Next time I'm digging a hole and someone says Phil what you're doing? I'm gonna say I'm going into the Earth's crust That's so much more dramatic I remember as a kid I was compared always told about how Comparatively thin the Earth's crust was and I thought it was like a warning I thought I was gonna I was really scared of how thin the Earth's crust was and I thought it was like a warning I thought I was really scared of how thin the crust was I thought they're telling me that like sort of be careful out there and not play wrestling too hard or something through this crust I feel a bit betrayed to learn that it's hundreds of meters

it's important for us that it's quite thin isn't it because there is access to the mantle below there's a a cycle. Could you describe actually, if we would just have a snapshot of the way that the Earth moves, the way that this system, the dynamics of the Earth? So essentially the way things happen is that you have all the time new Earth, if you want a new crust being formed, and also new crust, new Earth dying. And the way that works is that you basically have new crust at so-called mid-ocean ridges. So this is typically in the Atlantic, in the Pacific,

but also in some continental settings where you have this very hot magma rising, you know, typically quite passively. You have molten rock that comes from quite deep inside the earth, hundreds of kilometers deep inside the earth that basically as it's hot it rises and then it spreads laterally. And as it spreads laterally it cools, it ages, it gets denser and then when it gets very very old it eventually sinks down again inside the Earth. These are so

called in subduction zones and some of those areas where you have this cold old material is actually where you also have some of these very big earthquakes, such as in Japan or in South America. The material plunges down. So we say the crust is dying, let's say, and goes into the mantle. It has quite a few transformations. And often, it kind of stops halfway inside the mantle

because you have some transformations going on. But in other cases, it plunges all the way down to the boundary between the mantle and the core and then it might stay there, so we call it you know some graveyards basically of the crust, it might stay there for quite some time, millions of years, but then also at this core mental boundary there are these continent-sized structures that we still do not fully understand exactly their origin. They are very low-velocity regions, hot regions. And from there, because you have the core that

is being heated from beneath, you have stuff that starts coming up. And we call these upwellings, or sometimes also called mantle plumes, that might come all the way up to the surface as well, creating some of the islands that we have, such as for example maybe Hawaii. Yeah, and the cycle just carries on through over millions and millions of years. And where are the subduction zones?

Yeah, so that's like in Japan for instance, that's in South America. So these are plate boundaries. Let's put it like this, most of this activity, new crust coming, old crust plunging, it's mostly at these boundaries of different tectonic plates. But magma can come in through the plates? Yeah. So there's holes in the plates? This is how you can see. This old fear, I'm gonna fall through the crust. We need to answer this carefully. Can I say well done, Loth Phil, because one of the things that really increases ratings is a sense of panic. And you've added now possibly a million new listeners going, my God, the world might end.

It's all cracked and broken. You're totally right, though, to go, so there's holes in the plates? You live on a hole in a plate. I mean, a volcano is a hole in a plate, depending on the source of the magma, right? So if you fell in a volcano, you wouldn't get very far. But I mean, at least theoretically, if the volcanic throat was empty of magma, you'd go all the way down to where that magma had been sourced from, if that makes sense. So there are holes in the... I don't know how to answer this

without like panicking you. This sounds absolutely terrifying and perhaps might even threaten areas like Peterborough and Olmstead at this very moment. So tell us more about why these people might be about to be destroyed. There's no volcanoes in Peterborough, but like, yeah, I think what Anna described is very kind of exciting

as well because there is this slow grind of basically what you're describing is what we refer to as plate tectonics it's the movement of the earth's plates as a function of the addition and loss of material and the thermal gradients you know the way energy is distributed around the earth due to that process. You mentioned that the plates, plate tectonics, how many plates are there? How do they fit together? I'm having like undergraduate trauma now.

Well, there's a bunch of plates and then there's micro plates and then so I don't know, like is there like 10, 11? Around that, yeah. These plates are all sort of moving around in constant motion. So there is that dynamics and it's very slow, it's very gradual, but it's ultimately those processes which lead to the really immediate and dramatic events we see happening because it's the slow grind of the plate that accumulates stress and that stress is released in the form of earthquakes every so often. So that's why we have most of the drama happens at plate boundaries.

And Phil, you know, be reassured. We live in what we refer to as an intra-plate setting. So we're away from those boundaries where all the drama is, which is why the earthquakes in the UK are relatively small and we don't have any activity. I've been in an earthquake in Bath. You know, and I've been to the West coast of America, I've been to Japan, but the place I experienced an earthquake was in my mum's living room in Bath. I was at home alone, I was just sitting watching TV, and the whole house just went

to cook like that, just back and forth. And I just texted mum saying like, is there a new washing machine or something? And is it massive? And she's like, no. And then a couple of, like an hour later, there's a new washing machine or something? And is it massive? And she's like, no. And then a couple of, like an hour later, there's a new story about all along the west of the UK, there was an earthquake. So what I'm saying is I'm right to be terrified at all times.

Also, it does lead to more broken crockroot. And thousands of years time when they return to your mother's home, and they'll think, did the the great bath spa Empire collapse Look at all these broken plates. I'm finding a link all these plates made by Ikea The question and then so it's quite there aren't that many of them you said 10 11 Yeah, how you define them so the obvious question is why what why is the planet like that like my mom saying Chris why did you do that thing plate tectonics has evolved over 4.5 billion years there's been more and less plates than that number and it

just so happens we live on a planet where 11 is energetically, if I want to describe it in that way, the optimal number. I've always wondered, are the plates always rubbing up against each other? Are they right next to each other or are they sort of floating around and bumping like bumper cars? The moment you have a gap, it's a new plate. Oh, because stuff comes up to fill it and that's a new plate. Yeah. Oh, okay.

So Ryan was telling me earlier on, because without the tectonic plates, you won't have life on Earth. So, you were saying Venus doesn't have life. Part of the regulation system of our atmosphere is plate tectonics, volcanoes. The bringing of carbon, in the form of carbon dioxide, into the atmosphere is what gives us some of the the ozone layer which actually shields us from you know incoming radiation but also keeps the earth at a kind of hospitable temperature for us our species right you know so actually volcanoes are a fundamental regulator of the earth's kind of climate and therefore you know plate tectonics which is the of the underlying process which dictates how many volcanoes we have and what they bring Up is the fundamental driver for life on earth. And yeah, it's it's a you know plate tectonics as a as a resource

Which was reflecting on Venus runaway greenhouse effect 90 atmospheres pressure what 450 degrees Celsius or so as a fact, 90 atmospheres pressure, what, 450 degrees Celsius or so. In part, that's because there's no way of getting the greenhouse gases out and back into the planet. Yes, we have this constant carbon cycling. So we liberate this carbon in the form of carbon dioxide through these volcanoes. But then we consume that carbon at subduction zones.

And often we consume that carbon weirdly subduction zones. And often we consume that carbon, weirdly, in the form of small fossils, so planktonic foraminifera. These are animals that live in the sea, microscopic. They use the calcium carbonate, the CO2, to build their shells. But the poor suckers, when they die, they go down a subduction zone and get re-entered back into the mantle. So we have volcanoes and fossils are fundamental to life on Earth. Can you believe that? Never thought of it being,

having a role to play in the atmosphere as well. They seem like very separate things to me. There's the crust and the goo and the air. Yeah, but now I'm hearing about subduction zones. So that's another thing to worry about. Are you a warrior, Phil? Are you genuinely a warrior? Yeah, big time. Yeah, ultimate warrior. I'm always looking out for ways I'm going to perish

or get sucked into the earth. It's my ultimate nightmare. You wouldn't get sucked in. Would you get sucked in or you'd just fall? Wouldn't you descend? Knowing Phil's lucky, you'd probably get sucked in. I'll be off chasing plankton. And obviously I'm going to follow it into subduction zone. Because they're just too tasty to leave alone.

How do we know these things? How far have we gone physically down and below that? I mean, so we've never accessed the court, for example, so how do we know it's there, how do we know what it's made of? Yeah, so the deepest borehole that's ever been drilled is in northern Russia. I think it was called the Kola borehole. And they drilled to 12,000, I think it's 12,365 meters down into the earth's crust. So it's the deepest borehole ever drilled. They eventually abandoned it, but it's an incredible kind of feat of like engineering and daring do, you will around like what we're kind of capable of doing, why I don't know. But like, you know, they did it for scientific reasons and everything.

That's effectively the deepest point on earth constructed by humans is that borehole as I understand it. There's a borehole being drilled in China and I think it's called Sendikan 1. I think it's in the Tarim Basin in northern China. They started drilling last year and the last news story I could find was the 23rd of March, I think it was this year and they'd reached 10,000 meters in 278 days of drilling. See that's what I find threatening Phil because I imagine what if they go, oh my god, the Earth's core, it's not made of that at all, it's just filled with air. That would have been the perfect end, I think, to the way that we're going. I just want to recall, you know, the audience that we are really talking about such high pressures.

Yeah, it's incredibly challenging to, you know, firstly, there's two, well, there's two main things. One is the temperature we've already talked about. It's just bloody hot down there, you know, so you get down there and it's several hundreds of degrees Celsius and pressure, as Anna described, is incredibly high down there. So just keeping that hole open or basically circulating mud in that hole to keep the hole open by imposing pressure against the borehole wall. So it's an incredibly difficult thing to do. Are there a set of kind of tenets of this is why we're doing it or is it like by imposing pressure against the borehole wall. So it's an incredibly difficult thing to do. Are there a set of kind of tenets of this is why we're doing it?

Or is it like we just need to and we will discover? It's a bit of a mix, you know, of course, if you really want to ultimately to understand all of these impacts on humans, like we were talking about, you know, the process of earthquakes, the phenomena behind volcanoes, how mountains build. Ultimately, you really need to understand how the mantle works. But of course, I have to be fair, it's quite indirect.

It's a very ultimate type of analysis. So it tends to be more really about understanding how our planet has evolved over time. Can we then use this understanding for understanding other planets? So that tends to be really more, it's a more exploratory overall idea. But a lot of the work that we do

at the scale of the planet, really for instance trying to image the planet as a whole, a lot of the techniques that actually we develop and we work really quite hard on imaging techniques, like people in medical teams, hospitals, when you go to do a scan of your body, we use that type of techniques to image the Earth, but we apply them at a global scale,

really to understand these very fundamental questions, but then they can be transferred to small scales. And for instance, to understand geothermal potential, so for energy applications. But for instance, the work I do, it's really, I want to understand how our planet works. So for instance, you know, maybe for about a decade, more than a decade now, we are really intrigued by this continent-sized structures that we have imaged, I mentioned them briefly

before, at the boundary between the mantle and the core. These are really massive structures. We call this region the anti-crust. We know that essentially they are hot. This one I thought the crust was enough danger. Now you have an anti-crust 3,000 kilometers deep beneath your feet. And we don't really know exactly what they are made of.

There are lots of ideas, but it's really intriguing. We know that a lot of these upwellings that I was talking about seem related with them. These upwellings in turn then create islands like we were saying. They actually created, they led to massive eruptions in the past that caused this so-called igneous provinces. We are talking about regions with thousands

of kilometers full of magma. Thankfully, we don't have those mega eruptions now. But this is just an example, you know, understanding really how these big structures that we see inside the Earth then link with the surface and, you know, with the behavior of our planet is ultimately what we try to understand. And you mentioned the imaging there. So how do we image?

So essentially you have earthquakes that occur around the world, and those earthquakes generate seismic waves that propagate inside the Earth. they propagate in many different directions and they probe many different depths inside the earth. And then we have at the surface of the earth so-called seismometers so these are basically like you are listening to the sounds coming from the earth and we have them all around the world and also I must say we have actually access to these data freely. So we put together all the data, these waves that propagate through many different directions.

So they saw the Earth, the waves. And we disentangled the readings so we do lots of advanced data analysis, we do modeling as well to then convert those recordings into images of the Earth's interior. So from hearing the sounds of our Earth, in this case the earthquakes, we basically convert those sounds with mathematical and physical models into images of the Earth's interior.

Because I work with cosmologists, we joke that they look up, I look down, but we use the same type of imaging techniques. And yeah, really fundamental to that is that those waves are of different types and they move in different ways through different materials. So the way those waves move are different through solids and some of them don't move through liquids. So one of the kind of underpinning reasons why we know that the outer core is liquid is because these shear waves don't travel through that region of the Earth's crust. So that's how we found out that the outer core was liquid.

So we're really reliant on these physics-based tools to see down. So I often describe them as CT scans of the Earth. And I'd like to just scare Phil some more. So I'd like to talk about extinction events. You mentioned actually, Anna, you mentioned, so with the Deccan traps in India, that kind of region, what do we know about those extinction events for Phil, when is the next one going to happen? Just like in Old Peterborough. So we have these things called large igneous provinces, we call them lips, and

the Deccan traps is one of these lips. And these are events in Earth history and these are really voluminous outpourings of lava that go on for probably tens of thousands of years. So huge volumes in terms of cubic kilometers of material explode onto the Earth's surface. The lava itself is not the problem, it's the gas that comes with it. So a lot of gases come out of all volcanic eruptions, but especially out of these lips, you get large amounts of carbon dioxide. And that carbon dioxide, as well as other greenhouse gases, I should say, you know, water vapor, and there's other things that are greenhouse gases

that come out with these volcanic eruptions. They then fundamentally change the world's climate over varying timescales. In the case of LIPS, these things go on for long enough to actually lead to, you know, substantial proportion of life on Earth dying. How much do we know about the potential for such events now? We could talk about these big super volcanoes, but also these events. We have a sense from some of the techniques Anna referred to, from global seismology, about where on the planet there are large volumes of melt within the mantle or large volumes of melt, so magma within the Earth's crust.

We have a sense as well as to the dynamics, the timescales over which that material is moving and migrating vertically through the Earth's crust. We can see earthquake swarms, which are effectively the fingerprints of vertically rising magma. So we can map those things. And Yellowstone is one of the very famous examples of the next supervolcano, because there's a large volume of magma resident underneath that part of the Earth's crust. And so the fears are, you know, what's the likelihood? Don't go there, Phil, on holiday. He's shaking his head.

That's not a holiday destination. That's for sure. That's why holiday cancelled. Yeah. But those sorts of areas. So that's why I think for geoscientists, it's always very hard to communicate with the general public because we do know a lot about these dynamics. And the question is, is when might it happen again? And we can't predict.

We could only possibly hope to forecast. And they sound like the same word, but they're actually different things forecasting and prediction. We can safely say there will be another large igneous province forming on Earth, and we could possibly take a guess based on the organisation of the Earth's tectonic plates and the magma where it is now as to where that might be, but the likelihood of it happening whilst humans are on the planet are probably quite small. Just in case you didn't hear the news, humans are dying out next Thursday.

I was just going to add, this is exactly one of the purposes of trying to get our images better and better, to really try to understand exactly where are the regions where there's really potential for these Cygnus provinces to form, and the UK is not one. Now, Annie, you've done some special research about what lies directly beneath us haven't you? Yeah what lies beneath the BBC. Phil we're here at the Radio Theatre, any guesses, any kind of predictions? I mean it's going to be scandalous. Let's be honest. I would like to think an even older radio theatre, maybe one made of a Stone Age BBC with like stone versions of all our favourite television shows.

But for stone people. I don't know. I mean, was London just like a big old mucky delta originally? Is it just like sludge and snails? It's an old Roman town, so I guess there's, spoiler alert, gonna be a lot of broken parts. Yeah. I imagine. Basically the same as Wetherby, though, weren't it?

If you go to the same depth, so a kilometre or so, do you get to 250 million years? Does it work like that? Yeah, beneath London here, if you go down a few hundreds of meters, you eventually go into the chalk. So this is Cretaceous rock, which is 130, up to 100 million years old or even a bit younger than that. And that's where we get our water from. And then above that we have something called the Eocene clay. So that's a clay stone which was deposited in a in a seaway. So that's when you know, London was actually an ocean. So we do have all this history in the rocks beneath our feet here.

And you mentioned where we get our water from. So where's that? From the Cretaceous Chalk. So it's what we call an aquifer. So that's why your kettles and showers get loads of calcium carbonate on is because the water in London this is why northern water is a lot better trying to win them back at the last minute this is why the water has stopped and on tease yes it is a remarkable thought we don't think I don't think of it very

often that the water that comes out of your taps is coming from, was like, it's an aquifer that's in the Cretaceous period that structure was formed. Even more bizarre, the water that you extract or abstract, we should say, from beneath London for us, you know, for people who live here, is that water is tens of thousands of years old,

I think, a few thousand years old. And it comes in in the Chilterns and it comes in in the in the South Down, well the North Downs as well so it actually is ancient rainwater that's percolated down under London. I like the fact that Brian's pretending he uses a tap as we all know he's by a magical spring. So Anna it's time for the reveal then. What shall we find beneath us? What lies beneath us?

Shall I show it? So first of all, I have to say, I'm sorry to disappoint you. This is a global model that we have produced, but we have done this cross-section. So it's a section going, like if you slice a cake, let's imagine it goes from the surface of the cake to the outer core, which is here at the bottom. I must say it was produced by my colleague, William Sturgeon, who is sitting here. We are here in London. That's London.

And then this is Iran, just to give you a scale. This is really a global scale model. So it goes from what, west of Iceland all the way over to Iran on this cross section. And we're in the middle. We are in the middle here. This was a special cut for tonight. And essentially what you see is beneath London in this area here there's this whole of this blue stuff which is pretty much boring stuff.

It's cold, stable material, so not much happening there. You know there's going to be a twist, don't you? And then you can see this low, again, hot stuff in the lower mantle, very deep, but somehow it avoids London. So we are quite safe, quite in a very stable region, this blue area here. Well, I see there was good news. So Phil, just to end, in terms of all the things that have terrified you today, what was number one? Was it falling into

the volcano? Was it the anti-crust? The anti-crust sucks. The idea that I could keep falling through magma and hit something hard is just creepy I think. And I think the holes in the plates scared me the most, because I always assumed that the volcanic action happened on the edges of the plates, but now I learn there are plate holes to look out for as well. So that's quite scary. I'm very scared of this giant hole in China that I'm just going to trip and fall down that. There's a lot to be afraid of. I'm going to leave tonight terrified but thankful. By the way, this map is called the seismic velocity anomaly. That sounds funny, doesn't it? It sounds like one of the 60s science fiction films that you...

Sounds like a bad one. Yeah, anomaly sounds like it's wrong. Or a Doctor Who thing. There's been a seismic velocity anomaly. Yeah. So we also asked our audience a question and we wanted to know what do you think might be found in the centre of the earth? So Brian what have you got? I don't know I'm not good under pressure. That's Nathan Joyce. Well done Nathan. Oh we can almost pack this up on the first one.

What have you got, Phil? How can the Earth have a centre if it's flat? Very good question. Very good question. I saw, actually, the security guys wandering around. I thought, what are they doing? They're looking for the flat earther. The deep state? I think that's probably the same person as this. LAUGHTER

A viewing platform with overpriced cafe and souvenir shop. LAUGHTER So, thank you very much to our fantastic panel, Professor Chris Jackson, Professor Anna Ferreira and Phil Wang. CHEERING AND APPLAUSE So... ..very, very excited about next week's show, cos next week, Brian is going to give me £1 million

so I can start building my dream sea monkey sanctuary in Bucharest. LAUGHTER I'm not... Yeah, yeah, you are. We're going to do a show about altruism and I thought the best way of proving it was by you, because you're very, very rich, giving me money to make a sea monkey sanctuary in Bucharest

because that's better than the... Normally you just spend it on fine wines and velvet mittens. LAUGHTER LAUGHTER Sorry? velvet mittens. LAUGHTER LAUGHTER Sorry? Velvet mittens? You do. You've got everyone out here knows the number of velvet mittens you've got. It's ridiculous. Velvet on the inside for your pleasure,

on the outside for the pleasure of others. Brian, he's 360 degrees pleasure, that man. Yeah, yeah. And when you see his alpaca jodpus, you will be really impressed by the way he's sitting there with his velvet mittens thinking of my sea monkeys. What is the jodhpurs? Are they big trousers? Yeah, they're wide at the top, thin at the bottom, kind of horse riding ones, or the Erich von Stroheim director ones, yeah. And they're just like shaved alpaca. And it does make him walk weird as well. It does make him walk a bit like an alpaca. It's like he becomes... So his pan-like legs become possessed by the alpaca-like trousers.

It's going to be one of the harder edits for the end of the show, isn't it? Thank you very much, everyone, for joining us. Bye-bye. I'm Hannah Frye and I'm Dara O'Briain. And in the all new series of Curious Cases, things are getting curiouser and curiouser. We'll be looking the universe squarely in the eye and demanding an answer to your everyday mysteries. Including... Can you actually die of boredom? Why do some people taste music?

And how many lemons would it take to power a spaceship? We will shine a light on the world's most captivating oddities. Brought to us by you, you delightful bunch of weirdos. I don't think you're allowed to call a spaceship. We will shine a light on the world's most captivating oddities. Brought to us by you, you delightful bunch of weirdos. I don't think you're allowed to call them that. But I love them really. Curious Cases on Radio 4 and available now on BBC Sounds.