What's Inside The Earth?

What would happen if you jumped into a hole that went through the center of the Earth and out the other side?

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Episode Transcript

Speaker 1 (00:07):
Hey, Daniel, what's your favorite part of the pizza. Oh,
I'm all about the crust. The crust makes the pizza.
You're crust guy. Huh, Well, it turned out that's just
like a planet. All the interesting 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.

(00:31):
It's like a molten core, 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 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 it's a big deal. Yeah.
What about what about the cheese stuff crust? It's like

(00:55):
a crust in a crust. Yeah, what is the what
is the geological analogy of cheese stuffed crust? Right, that's
like underwater, that's like a sub subterranean lakes or something
of cheese. Yeah, well, I'm like those intolerant. So Hi,

(01:30):
I'm Orge 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

(01:53):
Explain the Universe, a production of I Heart 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,

(02:14):
she told us. Are you in touch with everybody's grandma?
I'm in touch with the cosmic grandma. Like the you
like the idea of imagining all of a sudden 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,

(02:37):
there's I have a big red button here, he says,
Raise grandma army. Yeah, somebody's hungry quick, somebody hasn't had lunch,
somebody's looking thin. Cook. Cook. But not today, We're going
to not talk about something that's out there in the

(02:58):
universal 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?

(03:21):
We we live on it, we walk in it, we
running 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

(03:42):
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,

(04:02):
magnetic fields and having to move around and shielding us
from cosmic rays. It's all because of what's going on inside.
Mm hmmm um. You know, continental drift and super volcanoes
and all sorts of stuff. If the Earth was just
a quiet lump of rocket, wouldn't be quite so exciting
to live on. Yeah. And lava, of course, lava. Who

(04:24):
doesn't love a lava? Who doesn't love a love a lamp?
You know? I was teaching ones and I usually like
to open my class with asking people for random questions,
you know, get them warmed up, and who's gonna totally
random question? Right? And somebody wants to asked me what
does lava taste like? That is a good random question.

(04:48):
I said pain, Pure pain tastes like pain, tastes like
charred tongue. No, I said pineapples. It tastes like pineapples,
does it? I have no idea what lava tastes like. No,
in like the bill of second between lava, like scorching

(05:09):
your tongue. Um it probably you just taste like rock, right,
It's just probably like living 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 I probably doesn't taste like pineapple maybe

(05:29):
in Hawaii actually, And so we got into this question
a little bit, Daniel, because we were wondering, we were
thinking about ideas with this up 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 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

(05:50):
of the Earth, and um 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,

(06:11):
so for 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 whole or could you have a tunnel
that goes through the center of the earth? And would
you let 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 like dig down a hundred meters and then you

(06:31):
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 jump through a whole the go through
the entire earth. But 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

(06:52):
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
to earth? And so Daniel went out there as usual,
out into the street and ask people, random strangers what
they thought was inside to Earth. Here's what people had
to say. Is the Earth just one big rock or

(07:14):
is it more complex under our feet? There are more
complex features below our feet and something fel like the mantle,
um core, cross shoe as lissile spear, messile scree or
something like that. I know that there's it's not just

(07:34):
a big rock, but yeah, I don't know the components
of what they send it. Well. I think there's like
different layers of rocks. But that's it, okay, like different,
just different layers and different just difficult that the Earth
it's not just one of big rock, Okay, it's like

(07:54):
layers and like there's like dirt rock, gravel, and thought
it's up and they're like for some reason, like my
mind went to like minecraft. So then like the should
be like lava area across is like made out of
like different minerals, like different rocks. And well around the earth,

(08:19):
the first layers the crust, then um there's soft softer
more hot rock um and there are two layers of
magma um at the center of the core of the Earth. Well,
it sounds like most people, um 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

(08:40):
rock and dirt and gravel. And I love the people
who refer to Minecraft as their their reference. But you know,
there's there's some evidence they're like, you know, Minecraft is
a little bit educationally, you dig down deep enough in
Minecraft and you get to Magma, So yeah, good job Minecraft. Yeah,
and zombies, and that's what that's what I know about minecrafts. Also, Minecraft,

(09:01):
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 eight bit
universe we live in. Well, there's the idea that we
maybe we are all in a video game, right, that's true. Yeah,
we could certainly be in a simulation. Um My kids

(09:23):
watched Ready Player one 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 were inside a game right now? Really?
Whoa And they weren't even stoned. I promise they weren't
even stone. They came up with that question totally sober. Well,

(09:46):
that's a that's a topic of a podcast we already recorded,
is that are we living in a video game? But
today's we're going to focus on what's in what's in
the earth. So take us through, Dannuel. If we start
where we are now, sitting or standing or right on,
and we go down, what what do we hit first? Well,
the thing to remember is that the Earth is huge, right,

(10:07):
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

(10:29):
only like fifty kilometers thick, and it varies under the ocean,
it's even thinner, you know, the top amount everest. Of
course it's thicker, but it's like a tiny little shell.
It's like an eggshell around a yoke. And that's the
part that we live on. 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

(10:51):
official physics slash pizza name. Yeah, it's the crust. That's
when you grab onto the planet from you know, what,
what what could you have instead of a crust? Well,
if you were like on you put her. 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

(11:13):
on Jupiter. It's just 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 it's like a sun that never took off right um.
And and you know, earlier in Earth, in the life
of Earth, when it was really really young, it was
just basically a ball of magma, and so the surface

(11:33):
was all you know, hot molten rock. There was no
cold crust to walk on Earth, and so the Earth
yeah verver early on. Oh we form from but I
thought we formed from like bits of stuff out there
in space. How did it try into a big ball
of lava? Yeah, so we did form from big from
bits of stuff. Right, that's rewind a few billion years,

(11:56):
and you have like a huge cloud of gas and dust, right,
and rubble that's all left over from other stars that
have that you know, had you know, billions of years
to burn and and then explode and spew their stuff
into space, and then gravity gradually gathers it back together.
And then gravity made the Sun, and he gathered all
the extra bits together into the planets. And the gravitational pressure, right,

(12:17):
the collision between the stuff and the pressure pulling this
stuff together, that's what 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

(12:37):
nasty and hot and wet. So no place you can
go for a nice walk. It's it's being squeezed down in. Okay.
So the first layer is this good thing you call
the crust, and it's made out of just like rocks,
and like the same rocks we see on the surface. Yeah,
I mean it is the surface, right, and it goes
down about you know, thirty five kilometers fifty kilometers depends

(12:57):
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 can we dig? You know? And um,
the Russians actually have won that race back when there
was a Soviet Union. They dug a shaft which was
I think twelve kilometers down, so it's like, you know,
maybe a third or a fourth of the way through

(13:19):
the crust. It was almost like a pin preak. It did.
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 pin prick. And you remember if you held the
Earth in your hand. None of the features on the

(13:40):
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. It would be
like it would look shiny, like a shiny marble, Yeah, shiny,
slightly wet marble exactly, um and so, and and the
outer layers this crust which is only you know, thirty

(14:00):
to fifty kilometers thick, so it's really pretty thin. So
we would see like just regular dirt and rocks and
stuff for fifty kilometers. That's a lot that I mean,
that's like from yeah, I know, and it's it's this
conflict in scales, right, Like fifty kilometers seems like a lot,
and we try to dig through it and it's too far, right,
and so on one hand, it feels like a lot.
On the other hand, it's a tiny little fraction. But

(14:22):
this is the kind of thing you discover when you
were exploring physics and space and the universe, right, all
these conflict in scales, Like the Earth is huge, but
actually it's tiny compared to the Sun, which is huge good,
which is actually tiny you compared to the galaxy, right,
It's one of the things I love about physics. Yeah,
and maybe you can drive fift kilometers in your car
in less than an hour, but if you try to

(14:44):
dig fifty kilometers down, it would take you a little
bit longer. Yeah. I don't even know how they did it.
This this hole that they dug in the Soviet Union,
that's twelve kilometers deep. It's only like twenty something centimeters wide, right,
so they have to have like a crazy drill bit
and you know, they probably had a really long extension chord,

(15:04):
like a twelve kilometer extension chords, you know what I mean,
probably had like Christmas lights and everything. They're using every
extension chord. And then 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 chord. In Russia, whole drills
you I don't even know what that means exactly. So

(15:26):
the crust is fifty kilometers thick. We've only barely pricked
the like the outer bits of it, right, the deepest
minds hardly scratched the surface. And it's a tiny fraction
of the size of the Earth. Wow, it's just like
a little x X shell really exactly. It's like if
you ordered a pizza and the crust was like almost invisible,
like you could just barely grab it before you got

(15:48):
the tomato sauce, right, it would be like a I
hate it when they cut pieces and squares because then
you get pieces without crust. You hate that. That's the
best way to cut pizza. What are he's talking about? No,
they 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 how the crust is for
to hold up the pizza. The part of the crust

(16:09):
without tomato and cheese is wasted to dry. I thought, okay, well,
well there'll be another episode. Daniel and Horry argue, aby pizza. Okay,
so let's say you you dig through fifts down and
you break through the crust. What what what do you?
What do you find? Then you get to something they
call the mantle, and the mantle is basically rocks that

(16:32):
are being 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 and um,
they can slide around a little bit. Wait, what do
you mean fluid? They're like, um, like grains of sand

(16:53):
is fluid or or like really the rocks themselves deform
and and 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,
and 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, um,

(17:16):
you know, like uh, like glass flows or something like
if you went up to it and touch it, it
would look 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 elements of it that are
more solid. Right. That's why we have magma that creeps
up through holes in the crust and turns into lava
when it's abused out in volcanoes. By the way, huge

(17:38):
Internet debate over whether what to call magma and what
to call lava. Is there really that's what you mean.
People are you? You mean? People are you in 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

(17:59):
you say that a volcano pews out magma, you're gonna
go like a thousand people online telling you you're wrong,
that's actually lava or underground. Well, let's let's be sure
here to to not anger anyone on the internet. That's
not the point of this podcast is to annoy people
and piss them off. So the dismantle, this kind of

(18:21):
liquid rock um is super thick, you're telling me earlier. Yeah,
it's like almost three 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 can get to the mantle, and
the mantle is like, is really thick. So that's a

(18:42):
huge part of the drilling. If you wanted to get
down to the center of the earth, you'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 air conditioning, that's right. And it's because the mantle

(19:04):
is not actually solid that we have earthquakes and tectonic
activities and mountains and stuff like that. It's always shifting
and moving mm hmmm. Yeah. You can sort of think
of the crust has broken into pieces that are floating
in slow motion on top of this, you know, semi liquid,
semi solid mantle magma business, right, slide around and bang

(19:26):
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 that 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. M

(19:47):
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 as thin as water, um
and things, we get pretty crazy. This mantle is really thick.
It's like ten to the ten times thicker than tar, right,
so it's not something that you can easily sluice through
like dancer. Yeah, they have some measure of thickness, you know,

(20:09):
the viscosity. Basically, it's more viscous than tar by a
factor of ten to the ten. Oh, I see, I
see viscus. Okay, it's 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. Have
you seen this experiment, the tar pitch experiment. Yeah? Yeah,
like it it um. It's like something so thick it
just hangs there for a long time. Yeah. It takes

(20:31):
like a you know, two decades for a drop to
form and fall. And they've been doing the experiment for like,
I don't know, eighty years or something, and in eighty
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 is much thicker. We
take billions of years for a single drop to form Oh.
So let's say so we were we're digging our our

(20:52):
tunnel through the center of the Earth. We would dig
a tunnel and we would be safe. We wouldn't move
with 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 that tunnel would have to be really strong to survive.

(21:14):
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 if
you dug a truck tunnel, like the walls would cave
in really quickly because it's under so much pressure. Right, Yeah,

(21:35):
you need some super material to stabilize the walls. Yeah,
at of antium probably. All right, let's keep digging down,
but first let's take a quick break. All right, So

(21:56):
we're digging through to the center of the Earth, and
we we passed the crust, and we passed the mantle.
We're now about three thousand kilometers into the earth, and
then we 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

(22:17):
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, like is there a boundary? Really?
Like it doesn't to do the things suddenly changed 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,

(22:40):
both the liquid outer core and then the solid intercore.
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 undre's so much pressure that basically

(23:00):
all the rocks melt, right, and you get lava. Yeah,
that's right. And remember magma magma, magma magma. Dude, there's
no lava that. And so it's really hot and really dense,
and so you've got this liquid metal and and all
sorts of rock and all this stuff mixing around in there, right,
it's it's like super duper danse right. Yeah, it's you're saying.
It's it's a rams per cubic meter cub oh, I

(23:23):
see ten thousand, So it's like five tons or so
in a in a in a suitcase size. Yeah, well
do you have a cubic meter size suitcase? Wow? I
really don't want to travel with you. Man, it's only
a cubic meter. I think you could probably fit your
whole family into a cubic meter man, yes, definitely a

(23:48):
lot um. Anyway, it's pretty dense down there, it's pretty hot,
it's pretty nasty, and 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 that this
is where the magnetic field comes from. Is this liquid
molten core? It's really a layer, right, because were still

(24:08):
not down to the core. That's right, this is the
liquid outer core. And um, we don't really understand the
earth 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 bits,

(24:31):
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 um like a giant solenoid
kind of right, like a giant. It's like a more
a giant electro magnet. 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 called

(24:53):
the dynamo. It's pretty cool. Wow. It's like it's like
we do, haven't. It's like we have an engine in
the middle of Earth. Yeah, we do exactly, and it's
a geological sized engine, right, I mean building something that
big would be incredible, right. This is these are structures
that are powered and that are operating and are bigger
than anything humans have ever constructed, right, so we should

(25:15):
definitely be in all of them. Wow. Okay, and then
if we if you make it through and it's and
again it's just like rock, But what does that mean?
Rock like an 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

(25:35):
all this comes from. Right? Where does all this iron
come from? It comes from the heart of a burning star. Right.
All of this was created infusion 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, that

(25:55):
you and me are made out of, had to be
formed somewhere else and then exploded through base. Wow, Like
there was an event sometime ago that created a whole
earthful of these metals. Yeah, exactly, Um, and huge quantities. Right,
It's not like you've got to scoot a spoonful of
iron here, like you have enormous amounts, and it's not

(26:17):
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 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

(26:37):
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 and rocky planets. Okay, so we're now about
almost six thousand kilometers into our tunnel to the center
of the Earth and bringing up snacks. Did you did

(27:01):
you pack one cubic meter? No, we're just going for
a Daniel. We're just going. We're holding our our hunger here.
It's like a diet trip. We're like, we're weight trip
to the center of the Earth. We're hoping there's a
McDonald's down down there at the center. Actually to spoil
the surprise. If you do make the center of the earth,
your weight does drop to zero. Oh interesting, interesting teaser.

(27:30):
So that we are, we're down, and we we dug
through the mantel, we swam through the molten outer core.
So here's here's where the tunnel idea would collapse, right,
because you couldn't. It's like it's liquid black Man 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, something

(27:51):
to support it, and that's something would have to be
super strong and resistant to to heat. So I don't
even know what you could make it out of. You
have to be like a diamond diamonds earth ship, yeah,
something like something like that. You have to construct a
diamond tunnel as you go or something. I mean, this
is already implausible, but it sounds possible. But they did
it in movies. What do you mean that was in Minecraft?

(28:15):
You can dig to the center of the earth, so obviously.
Uh so there, Let's say you're you're swimming through this
magma for another two thousand kilometers and then then you'll
hit You'll hit it like a surface, right, if you
keep going down to the center. Yeah, you hit a surface, right,
and um, what you hit is this this solid inner
core which is mostly iron and nickel, And it's basically

(28:37):
just a huge ball of metal, right, And you might
ask like why is it solid? Right? It's solid because
of all the incredible pressure it's squeezing it down, right,
And and it's also it's interesting to me that it's
almost the size of the moon. It's like three the
size of the moon. Is this just like ball of
metal in the center of the earth? Huh? Way, why

(29:01):
is it metal? Why isn't it like 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 um 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,

(29:23):
cool down even more. And so the center it's cooling
sort of from the center out, I guess you can imagine, right,
like the center is um it's getting solid, and this
solid in your core is growing right as 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.

(29:48):
We got time before Earth freezes over, is what you're
saying exactly Exactly, You've 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

(30:08):
wouldn't be protected from space weather and space radiation and
stuff like that. Um. But you know it's going to
be the long time before the magnetic field stops because
the center of the Earth freezes. Um. But you know
it has happened, like on Mars. We think Mars used
to have the 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, and it

(30:29):
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. Um, wow, but yeah,
that could be the future of the Earth. But you know,
but 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 that's
at the center of the Earth. It's a ball the

(30:50):
size of the moon made out of metal, really thick
and hot and and solid metal. And that's it. Is
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 like regular lattices of

(31:11):
atoms that lineup, and for wild 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 have to go change our insurance
policy because the new appraisers said it wasn't worth as much. Hey,
we like it. We love the Earth. It doesn't matter.

(31:32):
I love you anyway, baby, So it's not worth as much.
I guess it's worth everything to me, man, it's our home. Um, yeah, exactly.
So that's the descent 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, um.
And so let's let's get into that. But let's take
a quick break, all right. So now we're we're gonna

(32:07):
get to the question of of what happens if you
jump through all down through the middle of the earth? Um.
But first I really want to know how we know
all this stuff, Daniel, Like, if we 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 were desperate to of the answer to your question.
And sometimes you can't see directly like you'd love to write,

(32:30):
so you have to look indirectly, 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'll 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

(32:50):
your house to figure out like is it hollow? 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

(33:11):
from the earthquake. Right, earthquakes are these huge events, and
they cause a shock wave through the earth, and that
shock wave 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 shock wave arrive in Hawaii or arrive
in Russia? If the worth if the earth was all
you know, rock, how how fast would it move? And

(33:33):
they bounced when they when it changes medium, right, like
a wave, some of some of some of the your
wave will bounce back if it if it goes from
like air to water, or one type of rock to
another type of rock. And so that's another way can
they can tell where where are these um transitions between
different kinds of earth are. Yeah, you get all sorts

(33:55):
of interesting reflections. Just like when light hits the window,
most of it goes through, but some of it ounces off. Right.
You can use a window sometimes like a mirror. In
the same way as you were saying. Every time a
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,

(34:16):
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 that's what the Earth looks like because

(34:37):
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, you know the way 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 it listens to how they come back,

(34:59):
and based on the speed and etcetera, it tells where
the stuff is and where the stuff isn't. So basically,
earthquakes are a way to ultrasound the Earth. Those guys
are the only ones who celebrate when this an earthquake.
They're like, 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,

(35:20):
or neither. Yeah, And so that's really that's, um, 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 the Earth is this, in which case
we would see the reflections looking at that, and then
you compare what you predict to what you observe in
the tweet and tune and this tells us a lot
about what we know about the inside of the Earth

(35:41):
without ever going there. Wow, that's pretty cool, got science, man, science,
you are awesome. Yeah, buy yourself a pizza, a real pizza,
not one with pineapples on it. And um, you know,
we have some direct evidence, like we have dug down
pretty far to see what the crust is made out of,
and um, you know, sometimes things do crack open and

(36:03):
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. Um, 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,

(36:30):
it's 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 in 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,

(36:52):
we know we live on the surface, but like a thousand,
two thousand years ago, people must have had a very
primitive understanding of what the Earth was made out of. Well,
they probably thought what I talk which is just a
giant rock, right, yeah, And people I think, like more
than add years ago were able to make density measurements
of the Earth. Right, they know the size of the Earth.
They know basically know how big it is, and you

(37:14):
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 a
d years ago were able to measure the average density
of the Earth and discover that it was more dense
on average than it was in 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,

(37:41):
So that's 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 two thousand
kilometers thake uh. And then down to a little um
crystal diamond ball the size of the moon um iron nickel, right,

(38:04):
you can you can advertise it on the internet. It's
a crystal diamond, and then they'll be disappointed when you're
sending them just an iron nickel ball. But sure, go ahead,
we'll call it like an iPhone. You know, it's a
metallic nickel exactly, exactly right. So okay, let's say let's
get down then to what we set out to answer,
which is what would happen if you jump down a

(38:26):
hole through the earth. Well, we were already established it's
impossible to dig that hole. Yeah, so let's 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 whole 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,

(38:49):
and that that corn middle doesn't really um 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 whole there's a tunnel going through the

(39:11):
center of the Earth out to the other side. Okay,
and what happened? What what what happens to be jump into? Yeah,
So that 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

(39:32):
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.
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 a

(39:53):
kilometer down falling eating your snack. Now there's a whole
bunch of earth 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 one that 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

(40:15):
that's on the other side is 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

(40:36):
of the 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

(40:58):
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 it we're standing on the moon
as you're digging down, you would you would start to
feel weightless, Yes, exactly. So as you so you jump
into this hole, right, and just before you jump, you're
feeling the full gravitational force of the Earth. And as

(41:20):
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 drill through, you're falling through and
you get to the center and you would be floating
around in space just like no, because you'd have you'd

(41:42):
have a huge velocity, right, you'd have to have been
pulled down from a bunch of stuff, so you have
a huge amount of velocity and you 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. 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

(42:05):
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 stake. Now now
it's pulling you back, polling 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

(42:27):
side and then just stop with the same speed that
you had just when when you jumped in. Yeah, which
is zero, right, So I'm assuming that the tunnel on
the other side comes out of 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

(42:48):
of go back and forth, oscillating back and forth through
the earth forever, up and down, up and down. Have
you calculated how long would take you to do that
take that trip? I have 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 um less than the elevation where you're going

(43:11):
to come out on the other side, and you're not
gonna make it, right, if you start on the Death
Valley and you want to come out the amount everest,
and you're not gonna make it to the top amount everest, right,
You're just gonna fall back down into the hole. Yeah, exactly, exactly.
But if the Earth was a perfect sphere and you
jumped onto one side, then you come out the other
side of exactly the same height above the surface. But

(43:31):
if you slow yourself down and you stopped at the core,
then you would be waitless and you'd be floating there. Yeah, exactly,
because the earth gravity would be pulling on you from
every direction simultaneously, which is like having no gravity. Wow.
And that would be a pretty awesome moment, right, and
be like at the center of the Earth, the entire
Earth around you. Right. Yeah, I hope you're not clustrophobic.

(43:52):
It would 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 live are h all right? Well? That that
that's um that's what the Earth is made out of.
And if you dropped a pizza down a hold that
goes through the center of Earth, they would just come
right back to you, right eventually. Yeah, Or you could

(44:15):
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're somebody would grab It's a totally
realistic way. I bet Elon Musk is working on that
pizzas and the bonuses. It would be warm because it
would heat up on the way you could you could
dump it in frozen and it would come out nice

(44:35):
and coasting. This is a great business opportunity. I hope
the lawyers are scribbling this down as you're talking. All right, Well,
thanks for joining us. I hope that, um, 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.

(45:01):
If you still have a question after listening to all
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email us at feedback at Daniel and Jorge dot com.
Thanks for listening and remember that Daniel and Jorge Explain
the Universe is a production of I Heart Radio from

(45:23):
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