4:00

howling and you were

4:02

up at high altitude and your working

4:04

conditions were somewhere in the neighborhood of

4:06

about minus 40 degrees, awfully chilly. But

4:09

when the sun was out, the wind was

4:11

calmer, and it was only about freezing, those

4:14

were the days that Samantha could get out to her work

4:16

site. You drive out to the airfield

4:18

with all your equipment and whatnot, and

4:21

you board a very small airplane, probably

4:23

could park it in my living room.

4:25

The first thing Samantha did at the site was

4:27

grab a shovel and start digging. My

4:30

biggest thing was also keeping my hands warm and

4:32

keeping my fingers doing what they needed to do.

4:35

It took Samantha's team a couple hours to dig

4:37

a few waist deep holes. Then

4:40

they had to lower down hundreds of pounds of

4:42

equipment. Basically those instruments are what

4:44

are recording the signals from earthquakes.

4:47

These instruments are recording earthquakes that are

4:49

happening all over the world, not

4:51

just in Antarctica. Anything

4:54

above about a magnitude five, anywhere

4:57

in the world, we can see that.

4:59

And those earthquakes help Samantha understand what's

5:02

happening inside the earth. When

5:07

an earthquake happens somewhere, it sends

5:10

energy through the inside of our earth.

5:13

The energy she's talking about is a

5:16

series of seismic waves, which are basically

5:18

huge vibrations. They can come from

5:20

earthquakes, but they can also come from

5:22

things like volcanic eruptions or landslides. Anything

5:25

big enough to shake the earth. And

5:28

as those waves move underground, they

5:30

get altered and distorted. What's

5:33

inside this planet has a big impact

5:35

on those waves. You know, how fast

5:38

these waves move depends on

5:40

what it's moving through, and that's sort of

5:42

the heart and soul of seismology. It

5:45

works a lot like sound, which is also just

5:47

waves of energy. Listening to someone's

5:49

voice sounds different depending on whether you're hearing

5:51

them through a coffee wall, whether

5:55

you're hearing them

5:57

through sand, whether

5:59

you're through them underwater. This

6:04

is how Samantha can study the deep earth

6:07

underneath Antarctica and see

6:09

beyond a wall

6:12

that she can't

6:14

cross. Scientists have been

6:16

doing these type of studies for decades all over

6:18

the world and they've learned the

6:20

basics of what the interior of our planet

6:22

looks like. At its simplest,

6:24

you can think of the earth like a big layer

6:26

cake. The frosting, or the

6:28

very top layer, is the crust. So

6:31

the crust is kind of the thin outer

6:33

skin of the planet that we live on.

6:35

But the crust is only 1% of the

6:37

earth's volume. There's another layer

6:40

below it that's 60 times thicker called

6:42

the mantle. The mantle is kind

6:44

of soft and squishy. It's not molten,

6:46

though it's not liquid. Below

6:48

that, there's the core, the

6:50

center of the earth. Which is

6:52

comprised mostly of heavy

6:54

metals like nickel and iron. And it's

6:57

in between the layer of the mantle

6:59

and the core that Samantha found something

7:01

really strange. When

7:05

seismic waves move through these

7:07

features, they dramatically slow

7:09

down. There

7:13

were some weird areas down there made of different

7:15

stuff from the rest of the mantle and

7:18

they were distorting the seismic waves. These

7:20

areas are called ultra-low velocity

7:22

zones. These structures, they're not

7:25

huge. They're sort of tens of kilometers

7:27

wide, kind of tens of kilometers thick,

7:29

but they have this such different

7:32

characteristics than the material

7:34

around them. So they tend to stand out.

7:37

They almost look like underground

7:39

mountain ranges. It's

7:42

just the material surrounding the mountains, instead of being

7:44

air, it just happens to be the earth's mantle.

7:48

We don't know what they're made of.

7:50

We just know that they're sort of

7:52

shaped like mountains surrounded by superheated rock,

7:54

which is the consistency of tar. They

7:57

can range anywhere from 3 to 25 miles. miles

8:00

high. One of the tallest

8:02

they found is five times taller than

8:04

Mount Everest. It's like the

8:06

Himalayas, but jacked

8:08

up. Before

8:11

Samantha did her research, these underground mountains had

8:13

been discovered in a few limited places. But

8:16

this discovery under Antarctica pointed

8:18

to something larger. It

8:21

was almost like everywhere we looked, it's like, and here's

8:23

another one, and here's another one. You know, like,

8:25

it sort of brought up this question of like, well, are

8:27

these things everywhere? Samantha thinks these

8:30

underground mountains might form a sort of blanket,

8:32

wrapping around the core of the Earth. It

8:35

would basically imply that you have

8:37

a whole other layer inside

8:39

our planet. A new layer to

8:41

fit in this classic Earth layer cake analogy. A

8:44

new layer we don't understand. But

8:46

it's only a hunch. Scientists are

8:49

just beginning to understand what these mountains

8:51

even are. You know, where do they

8:53

come from? What's their origin? What's their source? There's

8:56

just so many unknowns. A

9:01

deep dive on underground mountains after

9:03

the break. Summer

9:21

for this episode comes from Sonos. Hey,

9:24

Sonos, give me some music. All

9:27

right, so I'm standing on the platform here, listening to

9:29

some music on my Sonos Move 2. Classic

9:32

New York, no one really cares, no matter how weird

9:34

I look. But yeah, I just wanted

9:36

to go over everything we learned

9:38

on this little journey here. The

9:41

Sonos Move 2 is easy to use. It

9:43

looks pretty cool. Sounds great, no matter where

9:45

you are, whether you're outside or waiting

9:47

for the subway. It's small enough to be portable,

9:49

big enough to still pack some great bass. It

9:52

syncs up to other speakers around my apartment. It's

9:54

great for showers, great for doing the dishes. Can

9:57

I control it with my voice to move her

9:59

away? I'm pretty sure it would sound great on the subway

10:01

too, but I think I'm gonna... Switch to

10:04

headphones. Don't want to piss too many people off here. Alright.

10:08

Hey, Sonos. Want some music? Thanks.

10:11

You're welcome. One last time, you

10:13

can visit sonos.com to learn more and find

10:15

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12:30

We're inside a giant jump bubble, wrapped

12:33

in a cobalt cocoon,

12:35

700 miles below the surface of the earth. Hell

12:38

of a day. Scientists

12:43

have a few ideas about what these underground mountains

12:45

are and where they come from. The

12:49

first has to do with temperature. The

12:51

mantle material can partially

12:53

melt, so you're getting little

12:55

pockets of molten material. Waves

12:58

move slower through liquid, and since seismic

13:00

waves slow down when they pass through these underground

13:03

mountains, that might mean that

13:05

these mountains are liquidy. So

13:07

in this case, maybe they're less

13:09

like literal mountains and more like

13:11

molten lakes. Little piles of

13:13

melt, if you will. Another

13:16

idea is that a chemical reaction is happening deep

13:18

in the mantle. Water

13:20

down there might be interacting with iron in the

13:22

core. So if you have

13:24

some kind of chemical reaction happening there, that

13:27

could make unique

13:30

property material. But Samantha is

13:32

leaning towards a third option. Maybe

13:35

these mountains might be pieces of ancient

13:37

oceanic seafloor that have sunk deep

13:40

into the earth. Over hundreds of

13:42

millions of years, you're taking

13:45

material at the surface and having it

13:47

dive back into the planet. This

13:50

might have happened when tectonic plates, these

13:52

huge chunks of crust and mantle, hit

13:54

each other and one slid under the

13:56

other. It's a process called subduction.

14:00

materials were once pieces

14:02

of the ocean floor

14:04

that have journeyed all the way

14:06

down to the core. One

14:08

of Samantha's collaborators modeled the movement and

14:10

subduction of tectonic plates and what happens

14:13

in the deep mantle. And

14:15

what he showed was that over

14:17

hundreds of millions of years you

14:20

end up with this fairly continuous

14:23

blanket of this

14:25

material along the core mantle

14:27

boundary. It's not a

14:29

perfect model. It's going to take

14:31

more time and research to nail down where these

14:33

mountains come from. But I

14:36

was also curious about the implications here. So

14:39

yeah, if subducted materials

14:42

are quote the right answer, then

14:44

it's interesting because it

14:48

illustrates how the earth

14:50

functions as one giant system top

14:52

to bottom. Things happening at the

14:54

surface are affecting what's happening very

14:56

deep in the earth and vice

14:58

versa. Some places new stuff

15:00

is getting created and coming out and some

15:03

places it's diving back inside and disappearing

15:06

and getting recycled. So

15:08

it's like basically one big recycling system

15:10

where the whole planet is sort of

15:13

interacting with other parts of itself. Why

15:16

is it important to know where they come from?

15:18

That's a fair question. I

15:22

mean we have so limited

15:25

understanding of the processes

15:27

inside our planet, how the earth

15:29

has evolved through time, and ultimately that

15:31

has implications for understanding how our magnetic

15:34

field is generated which protects us from

15:36

solar radiation so we can actually live

15:38

on this planet. Wait, you said we

15:41

don't know how the earth's evolved?

15:45

Well, I mean from a very

15:47

general perspective we do but the

15:49

details are fuzzy, right? So

15:52

for example, we

15:54

know we have a magnetic field, right?

15:56

We have a fairly good idea essentially

15:58

how it's created. and why

16:01

it's here, but how

16:04

different parts of the planet sort

16:06

of work together to make

16:08

that field. You know,

16:11

again, the details are fuzzy.

16:15

And so getting a better handle on

16:17

these kinds of things can help us

16:19

learn a lot about how our world

16:21

works and where it's potentially going in

16:23

the future. Yeah. And we live here,

16:25

this planet supports us. And so

16:28

if you don't understand how the planet functions, you're

16:30

not going to understand how life is

16:32

supported. What if we

16:35

don't find out what the answer

16:37

is? So yeah, I don't

16:39

want to disappoint you, but I don't

16:41

know if I can ever definitively answer

16:43

this question. Unless,

16:46

you know, Hollywood becomes reality, and we

16:48

can actually take a trip down to

16:50

the deep mantle. It is

16:53

sort of the inherent nature of the type

16:55

of work that I do. Yeah.

16:57

That we can likely not

17:00

definitively prove this.

17:02

Because the only way you can do that is to physically

17:05

go sample it or

17:07

see it. And we've

17:10

said at this point in time, that's just not realistic.

17:13

We can't do it. So we

17:15

make our best estimates using the data

17:17

that we can. And that's

17:20

sort of at the heart of this kind of science.

17:22

Right. Like that's the edge of the science.

17:25

It is. I mean, we are kind of

17:27

pushing the frontier on this. And I guess

17:29

to be fair, you know, plate tectonics is

17:32

a concept. That whole idea

17:34

only got developed in the 1960s. Yeah.

17:37

I mean, that's my parents'

17:40

generation. So Earth science is

17:42

a fairly young science, right?

17:44

Especially seismology. And so I

17:46

am cautiously optimistic that we

17:48

will have a good explanation

17:51

for this at some point.

17:53

We're not quite there yet.

17:55

But I think we're making

17:57

good headway. If we

17:59

do. figure out the source of

18:01

these underground mountains. What other big questions

18:03

would that open up? I

18:05

think it opens up kind of an

18:08

area of further study

18:11

because there are other things down

18:13

there that we could investigate.

18:15

And I think this kind of helps open

18:17

the door for some of those other kinds

18:19

of investigations too. There

18:21

are other things down there. That seems

18:23

like a very big statement. Like, oh

18:25

my god, really? Well, I

18:27

mean, the aliens aren't coming or anything. So

18:31

for example, there are two appropriately

18:35

named large, low, sheer velocity

18:37

provinces, which are big and

18:40

slow that exist on either side

18:42

of the planet. One's beneath Africa, the

18:44

other one's beneath Pacific, and

18:46

characterized, again, by seismic velocities that move

18:48

much slower through them. But they're huge.

18:50

I mean, the footprint of one of

18:52

these things is about the size of

18:54

a continent. They extend upwards of a

18:56

thousand kilometers or more giant

18:58

features in the Earth's mantle.

19:02

What's causing those? There

19:05

are also what they just

19:07

sort of generically refer to as seismic

19:09

scatters, little blobs of stuff

19:11

in the deep mantle that cause seismic energy

19:13

when they run into it, it kind of

19:16

scatters all over the place. Like when light

19:18

hits a prism, what's

19:20

causing that? Are all these

19:22

things related? Are they all part of

19:24

the same process or not? So there's

19:26

a lot more to be investigated

19:29

in the deep Earth. And

19:31

there's so much variability in that part

19:34

of the planet that is usually

19:37

just glossed over when people talk about

19:39

Earth's structure. But I

19:41

think people are starting to recognize

19:43

how important those details

19:45

are. And I think there's

19:47

a lot of cool room for discovery. So

19:49

this is just one of those things.

19:52

Indeed. So

19:54

we have to get rid

19:56

of this layer kick analogy then. It sounds like it

19:58

may not. Yeah. Well, I mean, you