Daniel and Kelly’s Extraordinary Universe - What's Inside The Earth?

Episode Date: May 2, 2019

What would happen if you jumped into a hole that went through the center of the Earth and out the other side? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Oh, I'm all about the crust. The crust makes the pizza. You're a crust guy, huh? Well, it turns out that's just like a planet. All the interesting stuff. stuff in a planet like ours happens on the crust. That's where the good stuff is, right? You know, that totally makes sense because I can't count the number of times I've burnt my tongue on the hot lava of tomato sauce on pizza. It's like a molten core of all that cheese.

Exactly. Exactly. And you always want to bite it before it's cooled off and turned into a nice place to live. You know, you're always got to get in there. But, you know, you're right. The crust is very important and you know that's where you hold the pizza that's where we hold onto our planet so it's a it's a big deal yeah what about um what about the the cheese stuff crust that's like a crust in a crust yeah what is the what is the geological analogy of cheese stuffed crust right that's like underwater uh it's like a subterranean lakes or something of cheese yeah well i'm like does intolerant so. Hi, I'm Jorge.

And I'm Daniel. And welcome to our podcast, pizzas in the universe. Daniel and Jorge explain what makes a pizza a pizza. And what doesn't make a pizza? We have no idea. We do have some idea. Based on my deep expertise of being a particle physicist, I'm here to expound on what's a pizza and what's not a pizza.

Now, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeart Radio. In which we find topics here, there, everywhere, and break them down so that you can understand them while you enjoy your pizza. That's right. We're also the authors of the book, We Have No Idea, which you can find in bookstores and online.

Or just borrow from your grandma because she read it, and she loved it. She loved it. She told us. Are you in touch with everybody's grandma, Jorge? I'm in touch with the cosmic grandma, like the idea. I'm imagining, all of us, I'm imagining some, like, you know, underground internet grandma network that you've typed into.

It's just a giant book club, basically. Can you mobilize them in emergencies to do something important? Yes, I have a big red button here. It says Ray's Grandma Army. Yeah, yeah. Somebody's hungry, quick. Somebody hasn't had lunch. Somebody's looking thin.

Cook, cook. But now today we're going to not talk about something that's out there in the universe and mystery, but today we're going to focus on a question very near us and actually underneath you. That's right. Today we're going to talk about where we all live, the place that you call home. Today's topic is. what's inside the earth or what is the earth made out of we live on it we walk on it we run in it we swim in it but do how many people know what this giant ball that we're riding around space

on is made out of yeah it's a special place i mean as far as we know so far it's host to all life that we've ever seen, right? Everything anybody has ever touched or tasted has been on Earth. So it's an important place, you know. It's the spaceship we are riding through the universe on. And there's a lot going on, right? You can't just ignore it, especially for those of us living in California. You know, we're wondering about like earthquakes and all sorts of crazy stuff.

So it's important to know what's going on inside the Earth. Yeah, magnetic fields and having them move around and shielding us from cosmic rays. It's all because of what's going on inside. you know continental drift and super volcanoes and all sorts of stuff if the earth was just a quiet lump of rock it wouldn't be quite so exciting to live on yeah and lava of course lava who doesn't love a lava who doesn't love a lava lamp you know i was teaching once and i usually like to open my class with asking people for random questions you know get them warmed up hey who's got a totally random question right and somebody once asked me, what does lava taste like?

Wow, that is a good, random question. Of course I said... Pain? Pure pain? Tastes like pain? It tastes like charred tongue. No, I said pineapples. It tastes like pineapples. Does it? Was that with authority?

I have no idea what lava tastes like. No. In like the bill a second between lava, like scorching your tongue, it probably just tastes like a rock right it's just probably like licking a rock salty salty exactly metallic yeah so people out there do not do this investigation do not approach lava do not play with lava do not lick lava um probably doesn't taste like pineapple maybe in hawaii actually and so we got into this question a little bit daniel because we were

wondering we were thinking about ideas for this for an episode and we were wondering what would happen if you dug a hole through the entire earth and jumped into it, right? That's a pretty weird question. Yeah, and you know, this is the kind of thing you see in science fiction all the time, you know, journey to the center of the earth and I was watching

gravity falls and they have the bottomless pit you know, they jump in and fall forever. And so it's a trope that you see a lot of times, you know, people wonder, like, can you get into the center of the earth? And so it's a fun, it's also a fun physics question I ask in my freshman physics class sometimes, like what would happen if you

drill the hole all the way through the earth and then jumped inside, you know, so from the point of view of, like, gravitation. Yeah, but, you know, I'm an engineer, so I kind of got hung up on the question of how you would even make that hole, or could you have a tunnel that goes through the center of the earth? And which led us to the question, what, what is inside the earth? What's going on? What would you drill a hole through? Yeah, exactly. Is it hard or easy? Do you have to, like, dig down 100 meters, and then, you know, it's just like a big pile of soft stuff or is it like diamond down there or you know it's impossible to dig into yeah this is pretty interesting stuff yeah so we might get to that question of what would

happen if you jumped through a hole that goes through the entire earth but uh but today's episode we'll we'll talk about the earlier question which is what is the earth made out of that's right we'll take you on a tour from the very top all the way to the very center of the earth yeah and as usual we were wondering how many of you out there know the answer to this question how many people know what's inside the earth and so Daniel went out there as usual out into the street and asked people random strangers what they

thought was inside the earth here's what people had to say is the earth just one big rock or is it more complex under our feet there are more complex features below our feet so like the mantle core crust

she was there listosphere, mesosphere something like Oh, wow, you know a lot. No, I know that there's, it's not just a big rock, but yeah, I don't know the components of what's inside there. Well, I think there's, like, different layers of rocks, but that's it. Okay. Like, different, like, just different layers and different components like of the earth. It's not just one big rock.

Okay. It's, like, layers, and, like, there's, like, dirt, rock, gravel, like, all that stuff. And they're, like, from some reason, like, my mind went to, like, Minecraft. So then, like, there should be, like, lava in there, yeah. The crust is, like, made out of, like, different minerals, like, different rocks. And, you know. Well, around the earth, the first layer is the crust. Then there's a softer, more hot rock.

And there are two layers of magma at the center. of the core of the earth. Well, it sounds like most people just sort of guess that they just made out of rock and dirt and some lava. Yeah, a lot of people know there's like rock and dirt and gravel. And I love the people who refer to Minecraft as their reference. But, you know, there's some evidence there. Like, you know, Minecraft is a little bit educational.

You dig down deep enough in Minecraft and you get to magma. So, yeah, good job, Minecraft. Yeah, and zombies and that's all I know about Minecraft. There are zombies. Minecraft, you know, says that the universe is pixelated, and I'm pretty sure they get that right also. So, you know, the physics of Minecraft is really pretty solid. Interesting. Just maybe a few orders of magnitude. Exactly. They need a few more bits, you know. It's not an 8-bit universe we live in.

Well, there's the idea that maybe we are all in a video game, right? That's true. Yeah, we could certainly be in a simulation. My kids watched Ready Player 1 last week, and they looked at it, and they were like, whoa, that's pretty cool. He can almost live inside that game. and then you could see the idea of being formed in their minds, wait, what if we're inside a game right now? Really? Wow.

And they weren't even stone. I promise, they weren't even stone. They came up with that question, totally sober. Well, that's a topic of a podcast we already recorded, is are we living in a video game? But today, we're going to focus on what's in the earth. So take us through, Daniel. If we start where we are now sitting or standing

or riding on, and we go down, what do we hit first? Well, the thing to remember is that the earth is huge, right? So it seems like almost flat because the curvature is so small. That's just because the earth is enormous, right? And so remember, as we take our tour down to the center of the earth, the scale of things, from us all the way down to the center is thousands of kilometers, right? So that amazes me already when I learned that the crust, this part that we stand on, you know, the part that's like rock and whatever,

that's only like 50 kilometers thick. And it varies. Under the ocean, it's even thinner. You know, top of Mount Everest, of course, it's thicker. But it's like a tiny little shell. It's like an egg shell around a yoke. And that's the part that we live on. Wait, what do you mean?

So the first layer underneath our feet is called the crust. Is that the official physics name? The crust. That's the official physics slash pizza name. Yeah, it's the crust. It's where you grab onto the planet from, you know. What could you have instead of a crust? Well, if you were like on Jupiter, for example, Jupiter doesn't have a crust.

It has like a metallic hydrogen core and then like helium rain and then like, you know, liquid hydrogen oceans. And, you know, there's no like firm place you can really land. There's no rock on Jupiter. Oh, it's just a... So we're pretty lucky to be a rocky planet that has some crust to it, yeah. Jupiter is just kind of like a big blob of wet stuff. It's like a sun that never took off, right? And, you know, earlier in the life of Earth, when it was really, really young, it was just basically a ball of magma.

And so the surface was all, you know, hot molten rock. There was no cold crust to walk on. Wait, to Earth? And so the Earth, yeah, very, very early on. Oh, we formed from, but I thought we formed from, like, bits of stuff out there in space. How did it turn into a big ball of lava? Yeah, so we did form from bits of stuff, right? Let's rewind a few billion years, and you have like a huge cloud of gas and dust, right, and rubble.

That's all left over from other stars that have, you know, had billions of years to burn and then explode and spew their stuff into space, and gravity gradually gathers it back together. And then gravity made the sun, and it gathered all the extra bits together into the planets. And the gravitational pressure, right, the collision between the stuff and the pressure of pulling this stuff together, that's what creates a lot of the heat. also there's when you have a really hot stuff inside the earth and you have things like uranium and all sorts of other stuff emitting radiation so it makes the earth hot right

the gravitational pressure and the radiation from the core made the young earth very very nasty and hot and wet so no place you can go for a nice walk it's being squeezed down into it okay so the first layer is this thing you call the crust and it's made out of just like rocks like the same rocks we see on the surface yeah I mean it is the surface

right and it goes down about 35 kilometers or 50 kilometers depends on on exactly where you are and people have tried i love this people have tried to dig through the crust right to see like how far could we go how deep could we get can we dig you know and um the russians actually have won that race back when there was the soviet union they dug a shaft which was i think 12 kilometers down so it's like you know maybe a third or a fourth of the way through the crust the idea it was almost like a pinprick they didn't really get through the crust yeah and you know all of these things these little holes we're talking about the size of the crust even like the peak of mount everest all these things are tiny features compared to the size of the earth as you're saying it's like a pinprick and remember if you held the earth in your hand none of the features on the earth would even be recognizable they might not even be observable you could probably run your thumb over the earth and not even tell where mount everest was wow it would be like a, it would look shiny, like a shiny marble. Yeah, shiny, slightly

wet marble, exactly. And so, and the outer layer is this crust, which is only, you know, 30 to 50 kilometers thick, so it's really pretty thin. So we would see like just regular dirt and rocks and stuff for 50 kilometers. That's a lot.

I mean, that's like from... Yeah, I know. And it's this conflict in scales, right? Like 50 kilometers seems like a lot, and we tried to dig through it, and it's too far, right? Yeah. And so on one hand, it feels like a lot. On the other hand, it's a tiny little fraction. But this is the kind of thing you discover when you're exploring physics and space and the universe, right?

All these conflict and scales. Like the Earth is huge, but actually it's tiny compared to the sun, which is huge, which is actually tiny compared to the galaxy, right? It's one of the things I love about physics. Yeah. I mean, you can drive 50 kilometers in your car in less than an hour, but if you try to dig 50 kilometers down, it would take you a little bit longer. Yeah, I don't even know how they did it.

this hole that they dug in the Soviet Union that's 12 kilometers deep, it's only like 20-something centimeters wide, right? So they had to have like a crazy drill bit. And, you know, they probably had... A really long extension cord. Like a 12-kilometer extension cord, you know what I mean? Probably they had like Christmas lights and everything. They were using every extension cord in the town probably.

They were in the Soviet Union. That's why they went broke. They're like, everybody, don't use any electronics. Give us your cords. Suveris, Russia, hold drills you. I don't even know what that means. Yeah, exactly. So the crust is 50 kilometers thick.

We've only barely pricked the outer bits of it, right? The deepest mines hardly scratched the surface, and it's a tiny fraction of the size of the earth. Wow, it's just like a little egg shell, really. Mm-hmm, mm-hmm, exactly. It's like if you order a pizza and the crust was like almost invisible, like you could just barely grab it before you got the tomato sauce, right? It'd be like a, I hate it when they cut pieces in squares,

because then you get pieces without crust. You hate that? That's the best way to cut pizza. What are you talking about? No, then you don't get any crust. I thought you were a crust man. Oh yeah, but you have crust on the bottom. I mean, that's what the crust is for, right?

It's a hold up the pizza. The part of the crust without tomato and cheese is wasted. It's a dry. I thought, okay, well, that'll be another episode. Daniel and Jorge argue by pizza. Okay, so let's say you dig through 50 kilometers down and you break through the crust. What do you find? Then you get to something they call the mantle.

And the mantle is basically rocks that have been squeezed really hard, you know, by gravitational pressure, by the crust on top of it. And they're like not fluid, but not exactly solid. It's like a bunch of rocks that are rubbed together really hard and they can slide around a little bit. Wait, what do you mean fluid? They're like grains of sand is fluid or like really the rocks themselves deform and flow? I think it's a little bit of both. I think it's a little bit like the way glaciers flow, right? You hear about glaciers like flowing across the surface of the earth and carving out mountains, right?

But then you go visit a glacier and it's just a big piece of ice and you're like, how is this thing flowing, right? Well, it flows very slowly, like glass flows or something like. Oh, I see. If you went up to it and touched it, it would feel solid. But over time, it would be deforming. And, you know, I think there's elements of it that are more liquid and elements of it that are more solid, right? That's what we have magma that creeps up through holes in the crust

and turns into lava when it spews out in volcanoes. By the way, huge Internet debate over what to call magma and what to call lava. Is there really? You mean people argue, you mean people argue on the Internet over things that are not that important? someone on the internet was wrong I can't go to sleep it's magma when it's still underground and as soon as it comes above

ground then you call it lava so if you say that a volcano spews out magma you're going to go like a thousand people online telling you you're wrong that's actually lava or if you say there's lava underground yeah well let's be sure here to not anger anyone on the internet

that's not the point of this podcast is to annoy people and piss them off So this mantle, this kind of liquid rock, is super thick. You would tell me earlier. Yeah, it's like almost 3,000 kilometers thick. So it's a huge chunk of the earth, right? It's much, much thicker than the crust. So if you were to somehow be able to dig all the way through the crust, right,

which seems almost impossible, you'd get to the mantle. And the mantle is really thick. So that's a huge part of the drilling if you wanted to get down to the center of the earth. It'd be like drilling from Florida to California. Yeah, but it'd be super hot and super high pressure the whole time, right? So it's not just like a nice drive across country, right? It's really difficult environment. You need a lot of extension cords for your air conditioning.

That's right. And it's because the mantle is not actually solid that we have earthquakes and tectonic activities and mountains and stuff like that. Oh, it's always shifting and moving. Yeah, you can sort of think of the crust as broken into pieces that are, floating in slow motion on top of this, you know, semi-liquid, semi-solid mantle magma business, right? Oh, I see. And they slide around, they bang into each other.

And all the interesting stuff that happens on the surface is because of that action. I see. Because you're saying it's like the crust is pretty solid. So we are kind of like floating icebergs kind of, right? So the crust is solid, but the rocks underneath is fluid. And so when you move these like solid pieces, that's when you get the crunching and the earthquakes. Mm-hmm. And it's pretty thick, which is good, because you wouldn't want to drive, you know, an entire tectonic plate through something like, you know, as thin as water, and things get pretty crazy.

This mantle is really thick. It's like 10 to the 10 times thicker than tar, right? So it's not something that you can easily sluice through. Wait, what do you mean thicker, like denser? Yeah, they have some measure of thickness, you know, the viscosity, basically. It's more viscous than tar by a factor of 10 to the 10. Oh, I see, I see. viscous okay it's not um if you had a bowl of it how long would it take a drop to form and drop out

actually that's fascinating ever have you seen this experiment the tar pitch experiment yeah yeah it like it um it's like something so thick it just hangs there for a long time yeah it takes like uh you know two decades for a drop to form and fall and they've been doing the experiment for like i don't know 80 years or something and in 80 years they had like four four drops fall and every time one is about to fall everybody's like super excited about it anyway this stuff is much thicker. We take billions of years for a single drop to form. Oh, so let's say, so if we're digging

our tunnel through the center of the earth, we would dig a tunnel and we would be safe. It wouldn't move, would it? Like with the tunnel closing on itself or something? Well, there's a lot of pressure, right? Yeah, it's really thick, you're right, so it might hold itself up, but there's also a huge amount of pressure, right?

There's tons and tons and tons of stuff bearing down, so I think that the tunnel would have to be really strong to survive. And that's my bone with, like, All those movies about Journey to the Center of the Earth. I'm like, where's all the stuff, you know? It always seems to be like fluffy, empty space. Like, they're just like digging through styrofoam peanuts or something.

But in reality, if you dug a tunnel, like the walls would cave in really quickly because it's under so much pressure, right? Yeah, you'd need some super material to stabilize the walls, yeah. Adamantium, probably. All right, let's keep digging down. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys.

Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled. metal, glad. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back.

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we pass the mantle, we're now about 3,000 kilometers into the earth, and then things change, right, after the mantle. Now we hit a new layer which is called the liquid outer core. Yeah, exactly. And you might wonder, like, why do they give these things different

names? Is the earth really just continuous? And this is just like scientists putting labels on stuff because scientists love putting labels on stuff. Oh, like, is there a boundary really? Like, does it do the things suddenly change when you keep digging? They kind of do. Yeah, there really are surfaces. there right like things do change the mantle really is different from the crust and the crust and the

mantle is really also different from this from this core both the liquid outer core and then the solid inner core there really is a change there which is fascinating right why isn't it continuous why isn't it smooth why are there these edges but there are and so you get to this place where it's like liquid rock you know it's like molten metal and rock it's like incredible because it's so hot and under so much pressure that basically all the rocks melt right Right? And you get lava. Yeah, that's right. And remember...

Magma, I mean magma. Magma, dude. There's no lava there. And so it's really hot and really dense. And so you've got this liquid metal and all sorts of rock and other stuff mixing around in there. Right. It's like super duper dense, right? Yeah, it's super duper dense.

It's a... 10,000 kilograms per cubic meter. Per cubic. Oh, I see. 10,000. So it was like five tons or so in a suitcase size. Yeah. Well, you have a cubic meters.

meter-sized suitcase. Wow. I really don't want to travel with you, man. They expand. I just have one bag. It's only a cubic meter. I think you could probably fit your whole family into a cubic meter, man. No. Yes, definitely. Cupid meter is a lot.

Anyway, it's pretty dense down there. It's pretty hot. It's pretty nasty. But that's important, right? If it wasn't liquid down there, then you couldn't get all sorts of interesting stuff happening like magnetic fields. Oh, this is where the magnetic field comes from. it's this liquid molten core. But it's really a layer, right? Because we're still not down to the core.

That's right. This is the liquid outer core. And we don't really understand the Earth's magnetic field very well. And for those of you interested in that, we have a whole awesome podcast episode just about the magnetic field. But a critical thing for having a magnetic field

is having a conducting fluid. So a fluid that can conduct electricity and move around. And so we think that like currents in this inner-liquid bits of the earth are what provides the, basically the motion for the magnetic field of the earth. Oh, it acts like a giant, like a giant solenoid kind of, right? Like a giant motor?

Yeah, it's like a giant electromagnet, you know? There's currents and they're spinning, and that generates a magnetic field, which causes more currents, which causes more spinning, which causes more magnetic fields. It's called the dynamo. It's pretty cool. Wow. It's like we do have an engine in the middle of the earth. Yeah, we do, exactly.

It's a geological sized engine, right? I mean, building something that big would be incredible, right? These are structures that are powered and that are operating and are bigger than anything humans have ever constructed, right? So we should definitely be in all of them. Wow. Okay, and then if you make it through, and again, it's just like rock. But what does that mean rock?

Like iron or metal, like everything is just kind of mixed in there? So it's mostly iron and there's a bunch of magnesium mixed in there also. and then there's, you know, just some rocks, which you know, silicate rocks and this kind of stuff. And remember where all this comes from, right? Where is all this iron come from? It comes from the heart of a burning star, right? All of this was created in fusion inside a star somewhere else billions of years ago, which was then flung through space and gathered back together.

You know, the Earth doesn't make any of these metals. There's no fusion happening here. So everything that the Earth is made out of and that you and me are made out of had to be formed somewhere else and then exploded through space. Wow. There was an event some time ago that created a whole earth full of these metals. Yeah, exactly. And huge quantities, right? It's not like you've got a spoon full of iron here. Like you have enormous amounts. And it's not also a coincidence that it's iron. It's not random. Iron is the point where fusion stops being energetically favorable, right?

It's the point in a star where squeezing things together to make something heavier stops to release. releasing energy. And then it costs energy to make things heavier. So iron is sort of the natural endpoint for fusion inside stars, which is why you find so much of it. Right. And so you, that's why most rocky planets out there would be made out of iron, right? I'm not sure about that, but I think there must be a lot of iron out there in rocky planets. Yeah. Okay. So, uh, we're now about almost 6,000 kilometers into our tunnel to the center of the earth. And, uh, we just passed. Did we bring enough snacks? Did you pack one cubic meter?

No, no, we're just going for it, Daniel. We're just going, we're holding our hunger here. Is this like a diet? This is like a diet trip? We're like on a lose weight trip to the center of the earth? We're hoping there's a McDonald's down there to the center. Actually, to spoil the surprise, if you do make it to the center of the earth, your weight does drop to zero. Oh, interesting.

Interesting teaser. So we're down and we duck through the mantle, we swam through the molten outer core. So here's where the tunnel idea would collapse, right? Because you couldn't, it's like, it's liquid blackmail down there, right? Yeah, it's totally liquid metal. So you can't just dig a tunnel, right? It's like digging a tunnel through the ocean, right?

You need something to support it. And that's something would have to be super strong and resistant to heat. I don't even know what you could make it out of. You'd have to be like a diamond, diamonds earthship. Yeah, something like that. You'd have to construct a diamond tunnel as you go or something. I mean, this is already implausible, but it sounds impossible. But they did it in movies.

What do you mean? That's right. In Minecraft, you can dig to the center of the earth, so obviously. So let's say you're swimming through this magma for another 2,000 kilometers. and then you'll hit it like a surface, right, if you keep going down to the center. Yeah, you hit a surface, right? And what you hit is this solid inner core,

which is mostly iron and nickel. And it's basically just a huge ball of metal, right? And you might ask, like, why is it solid, right? And it's solid because of all the incredible pressure. It's squeezing it down, right? And it's also interesting to me that it's almost the size of the moon. It's like three quarters of the size of the moon is this just like ball of metal

in the center of the earth. Oh. Wait, why is it metal? Why isn't it like at some point rocks, if you put them under pressure, they'll melt into magma. But at something, if you keep pressing them, they'll actually solidify.

Yeah, exactly. They'll solidify. And, you know, the earth is cooling, right? The earth was hot and nasty when it was born, and it's been cooling because space is cold. And eventually it's going to, you know, cool down even more and so the scent it's cooling sort of from the center out i guess you can imagine right like the center is um is getting solid and this solid inner core is growing right as the

the liquid liquid part is sort of falling the falling to the center and and it's growing by i think like a millimeter or two every year wow so we got time we got time before earth freezes over is what you're saying. Exactly. Exactly. You got time to finish that novel you've been working on or whatever before the core of the Earth solidifies. But it's important because then it's sort of game over for life on Earth, right? Because then we wouldn't have a magnetic field. Yes. We need a magnetic field to survive because without a magnetic field, we wouldn't be protected from space weather and space radiation and stuff like that. But, you know, it's going to be a long time before the magnetic field stops because the center of the Earth freezes. But, you know, it has happened like on Mars. We

think Mars used to have a magnetic field. We think it used to have all sorts of interesting stuff going on inside, but now it's basically just a dead rock, right? Wow. And it doesn't have a magnetic field anymore, and we don't think it has a whole lot of stuff going on in the inside, though, you know, we're not 100% sure.

Wow. But yeah, that could be the future of the Earth. But, you know, by then maybe we will have left the Earth and explore the universe or developed ways to make artificial magnetic fields or something else crazy. All right, so that's at the center or the earth. It's a ball the size of the moon made out of metal, really thick and hot and solid metal. That's it? Is it like that all the way to the very center of the earth? We think

so, yeah. We think it's just one big ball of metal. And in fact, some people for a while thought that maybe that ball of metal was just one big crystal, right? You know how metals can form crystals, these regular lattices of atoms that line up. And for a while, people thought it might just be like a huge crystal. But now they're not so sure. They downgraded their diamond rating on the earth. That's right. And we had to go change our insurance policy because the new appraiser said it wasn't worth as much. We have insurance.

Hey, we like it. We love the earth. It doesn't matter. I love you anyway, baby. It's not worth as much, I guess. It's worth everything to me, man. It's our home. Yeah, exactly.

So that's at the center of the earth. But remember, you know, we haven't visited these places. All this stuff we've learned, we've learned sort of indirectly. Yeah, that's the amazing thing. And so let's get into that, but let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. that's harder to predict and even harder to stop.

Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging. out with his young professor a lot. He doesn't think it's a problem, but I don't trust her.

Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him?

Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Have you ever wished for a change but weren't sure how to make it? Maybe you felt stuck in a job, a place, or even a relationship. I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers. I'm Gretchen Whitmer, Jody Sweeten. Monica Patton.

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Listen to these women and more on She Pivots now on the IHeartRadio app, Apple Podcasts, or wherever you get your podcasts. All right, so now we're going to get to the question of what happens if you jump through a hole down through the middle of the earth. But first, I really want to know how we know all this stuff, Daniel. Like if we haven't been able to drill down that deep, how do we know what's all the way down to the center of the earth? It's really an impressive triumph of science, right? Science, we're desperate to know the answer to a question. And sometimes you can't see directly like you'd love to, right? So you have to look indirectly.

You have to look for clues. and we look for ways to figure out what's going on inside and we have a whole bunch of them and then we try to make sure they all tell us the same story and my favorite one is the way we look at the inside of the earth is by looking at the impact from earthquakes and we use earthquakes the way you might like tap on the wall of your house to figure out like

is it hollow or is there a stud there you can tell sort of what's behind the wall by listening to how the sound moves through it oh I've heard of that like if there's an earthquake that happens in one part of the world, then you check with everybody else around the world to see how that wave propagated. That's right, because the wave from the earthquake, right?

Earthquakes are these huge events and they cause a shockwave through the Earth. And that shockwave travels at different speed through different kinds of stuff, right? So you can build a model and you can say, all right, well, if the Earth was all water, how fast would the shockwave arrive in Hawaii or arrive in Russia? if the earth was all, you know, rock, how fast would it move?

Right. And they bounce when it changes medium, right? Like a wave, some of your wave will bounce back if it goes from like air to water or one type of rock to another type of rock. And so that's another way they can tell where these transitions between different kinds of Earth are. Yeah, you get all sorts of interesting reflections. Just like when light hits the window,

most of it goes through but some of it bounces off right you can use a window sometimes like a mirror in the same way as you were saying every time the wave goes through a transition a boundary from one kind of material to another part of it reflects so they can see these reflections that's how we know that there really are transitions there is that every time there's an earthquake the wave travels around the mantle but it also reflects off the mantle interface with the core and then sometimes it goes even deeper and then it reflects off the inner core so we can tell that there really are layers there from these reflections and we can get estimates for their density based on how fast they're moving. We know that that's what the earth looks like because if it was made in any other

way, if it looked like any other way inside, we would see these waves come out differently. That's right. It's sort of like a big ultrasound, right? The way an ultrasound works to see like a baby inside the mom without cutting her open obviously is it sends these tiny little shock waves, ultrasound meaning higher frequency than you can hear into your body. And you're and it listens to how they come back. And based on the speed and et cetera, it tells where the stuff is and where the stuff isn't. So basically, earthquakes are a way to ultrasound the Earth.

That's amazing. Those guys are the only ones who celebrate when there's an earthquake. They're like, yay, huge earthquake. We get a new picture of the inside of the Earth. We get to tell the Earth there's a boy or a girl. Oh, my God. Or neither. Yeah, exactly.

What? They're twins? What? Yeah. And so that's really, that's the primary way we know about it. And to do that, you have to build models, right? And so you say, well, maybe the earth is this, in which case we would see the reflections looking like that. And then you compare what you predict to what you observe

and the tweak and tune. And this tells us a lot about what we know about the inside of the earth without ever going there. Wow, that's pretty cool. Go science, man. Science, you are awesome. Yeah, buy yourself a pizza. A real pizza, not one with pineapples on it.

And, you know, we have some direct evidence. like we have dug down pretty far to see what the crust is made out of. And, you know, sometimes things do crack open and magma comes out from the earth and turns into lava. And we can sample that and see what it is, right? And we can look at rock outcroppings, you know, places where, like, the crust has been lifted up so we could see what used to be underneath, stuff like that. Wow. But it's pretty amazing that basically the earth is not a big ball of rock, right?

Like it's this kind of active, moving, squishy, dynamic ball of stuff. Yeah, yeah. There's a lot of stuff going on, right? It's not just a rock. If it was just a rock, then life on Earth would be very different. Maybe impossible, right, without the magnetic field to protect us and our atmosphere. So we should be grateful that there's a huge engine humming under our feet that all this stuff is happening. You know, and I wonder, something I was trying to figure out but couldn't is, like, when we first became aware of this.

You know, because as humans, you know, we know we live on the surface, but like 1,000, 2,000 years ago, people must have a very primitive understanding of what the Earth was made out of. Well, they probably thought what I thought, which is just a giant rock, right? Yeah, and people, I think, like, more than 100 years ago, were able to make density measurements of the Earth, right?

They know the size of the Earth. They know how big it is, and you can figure out, you know, with the strength of the gravitational force, and from that, you can figure out what the mass of the Earth is, and that tells you, like, what's the average density? So, like, more than 100 years ago, we were able to measure the average density of the Earth

and discovered that it was more dense on average than it was on the surface, which suggested that, like, something denser was going on under our feet. But that was really the first clue. Wow. Cool. All right. So that's what the Earth is made out of. It's a thin crust on top of a fluid rock,

on top of a giant layer of magma, 2,000 kilometers thick, and then down to a little crystal diamond ball, the size of the moon. Iron nickel, blob, yeah. But yeah, you can advertise it on the Internet as a crystal diamond, and then they'll be disappointed when you send them just an iron nickel ball. But sure, go ahead. We'll call it like an iPhone, you know, it's a metallic nickel. Yeah, exactly, exactly.

All right. So, okay, so let's get down then to what we set out to answer, which is what would happen if you jump down a hole through the earth? Well, we're already established it's impossible to dig that hole. Yeah, so let's imagine it's possible that aliens come and have some super digging technology and some super tunnel technology, and we can actually make that hole all the way through the earth and out the other side, right, through the very center. And hold it open because, you know, the magma wants to flow in, the liquid. rock wants to crush it in and that core in the middle doesn't really

it's so dense it doesn't want to get drilled through right yeah exactly so you need a lot of legal paperwork before you can jump into this hole but let's assume that we figured out all the physics and all the law aspects of it and that we're ready to jump right before we do that we want to do some science

okay so there's a hole there's a tunnel going through the center of the earth out to the other side and what happens if you jump into it Yeah, so it's really fascinating because you have to think about the force of gravity. So you're on the surface of the earth. The whole earth is pulling you towards the center of the earth, right? Because the whole earth is a smaller radius than you do, right?

Every little bit of it is pulling it. But you can think about, you can treat it gravitationally as if it was just like a particle at the center of the earth that was pulling on you because it's all under your feet. Right. But once you jump into that hole, then some parts of the earth are no. longer on the inside. Some of them are like on the outside. So imagine you're like halfway down this hole. Like let's say you're like a kilometer down falling, eating your snack. Now there's a whole bunch of earth the earth above you that's now pulling you back, right? Actually the earth above you on average doesn't have any effect on you. There's

the stuff that's just above you, yeah, that's pulling on you. But there's like this kilometer thick shell of earth, right? And the stuff that's on the other side is pulling. pulling on you and the stuff that's above you is pulling on you, it all cancels out. So if you're inside a shell, then all the gravitational forces cancel out. What? Yeah. Yeah. I mean, imagine, for example, what happens when you get to the center, right?

What happens when you get to the center? Is there any gravity there? No, because every point, every little bit of Earth is pulling you equally in all directions. Exactly. And that's true for any shell that you're on the inside of. So if you're halfway down the Earth, then you only feel the gravitational force of the part of the earth that's closer

to the center than you are, right? A sphere of that radius. The stuff that's above you, you don't feel. Like, let's say we're digging the tunnel and we only get halfway there and we stop. And we stand there on the bottom of that hole. You're saying I would weigh half as much.

Like, I could jump. It would feel like we're standing on the moon. As you're digging down, you would start to feel weightless. Yes, exactly. So you jump into this hole, right? Just before you jump, you're feeling the full gravitational force of the Earth. As you go down, the gravitational force starts to go down, and it goes down linearly so that when you get to zero, when you get to the center, there's no force on you anymore.

Which makes sense, as you were saying, because you're pulled in every direction. Wow. So if you open, like if you drill through, you're falling through, and you get to the center, you would be floating around in space, just like Earth. No, because you'd have a huge velocity, right? you'd have been pulled down from a bunch of stuff so you'd have a huge amount of velocity and you'd shoot right through the center

right the center would be your highest speed it's like on a roller coaster you start at the top right and it rolls you down a hill and you get to the bottom of the hill right then you're going really really fast if there's no friction you would just keep going yeah because you've been falling all this time exactly unless it's like a party down there

and people hanging out and ready to catch you you just shoot right through the center of the earth and then gravity would start to slow you down again on your way through the other side of the tunnel. Right. It would start, no, it's pulling you back to the center. It's pulling you back. It's slowing you down.

And it's just enough gravity to slow you down so that you would emerge from the tunnel on the other side and then just stop. With the same speed that you had just when you jumped in. Yeah, which is zero, right? So, assuming that the tunnel on the other side comes out at exactly the same elevation, right? If you, then you would come right out of the tunnel

and you just sort of like hover right above the tunnel for a second before falling back down again. And if you didn't do anything, you would just sort of go back and forth, oscillating back and forth through the earth forever. Wow. Up and down, up and down. Have you calculated how long it would take you to do that, take that trip? I've not done that calculation, actually. Leave it as homework for the listener. But you have to be careful because if you jump, if your elevation, your distance from the center of the earth when you jump is less than the elevation where you're going to come out on the other. side, then you're not going to make it, right? If you start on Death Valley

and you want to come out to Mount Everest, you're not going to make it to the top of Mount Everest, right? You're just going to fall back down into the hole? Yeah, exactly. But if the Earth was the perfect sphere, and you jumped on one side, then you would come out the other side at exactly the same height above the surface. But if you slow yourself down and you stopped at the

core, then you would be weightless and you'd be floating there. Yeah, exactly. Because the Earth's gravity would be pulling on you from every direction simultaneously, which is like having no gravity. Wow. And that'd be a pretty awesome moment, right? It'd be like at the center of the earth,

the entire earth around you, right? That would be pretty crazy. Yeah. I hope you're not claustophobic. It'd be pretty hard to climb back out, right? That's kind of the problem. Yeah, that would be a very long climb. Oh my gosh.

Wow. I hope somebody built a ladder. All right. Well, that's what the earth is made out of. And if you dropped a pizza down a hole that goes through the center of Earth, it would just come right back. to you, right? Eventually. Yeah, or you could deliver pizza to the other side of the earth just by dropping through

that hole and it would just like come on out the other side and float there for a second while they grabbed it. Somebody would grab it. It's a totally realistic way. I bet Elon Musk is working on that pizza to the system right now. And the bonus is it would be warm because it would heat up on the way. You could dump it in frozen and it would come out nice and toasting. This is a great business opportunity.

I hope the lawyers are scribbling this down as you talk. All right, well, thanks for joining us. I hope that that wasn't too hardcore for you guys out there. I hope we didn't get too crusty on you. All right, thanks for joining us. See you next time. Thanks for tuning in. If you still have a question after listening to all these explanations,

please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge. word or email us at Feedback at Daniel and Jorge.com. Thanks for listening and remember that Daniel and Jorge

Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport.

The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever. wherever you get your podcasts. Why are TSA rules so confusing? You got a hoot of you. I'm take it off. I'm Manny. I'm Noah.

This is Devin. And we're best friends and journalists with a new podcast called No Such Thing, where we get to the bottom of questions like that. Why are you screaming? I can't expect what to do. Now, if the rule was the same, go off on me. I deserve it. You know, lock him up. Listen to No Such Thing on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. No such thing.

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