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How We Know What's Inside of the Earth (and Other Listener Questions)! · PlanetGeo: The Geology Podcast

0:03
SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
0:12
SPEAKER_00: Chris, how are you doing today?
0:14
SPEAKER_00: I'm doing great.
0:14
SPEAKER_00: How are you doing, Jesse?
0:16
SPEAKER_00: Oh man, I'm doing really well.
0:17
SPEAKER_00: I'm excited for today's episode, to be honest with you.
0:19
SPEAKER_00: But before we get to that, let's do some brief introductions.
0:22
SPEAKER_00: You are Chris Bullheis, a nationally recognized Earth Science teacher from the great state of Michigan.
0:27
SPEAKER_01: And you are Jesse Remink, one of my former students, now a professor of geoscience at Penn State.
0:33
SPEAKER_00: And this is Planet Geo, a podcast where we talk about amazing aspects of our planet and why they matter to our everyday lives.
0:39
SPEAKER_00: So let's get into it here with this episode.
0:41
SPEAKER_00: This is I'm super excited about this episode.
0:43
SPEAKER_00: We're doing our first episode full of listener questions.
0:46
SPEAKER_00: Chris, are you excited?
0:46
SPEAKER_00: That's right.
0:47
SPEAKER_00: I am excited.
0:48
SPEAKER_00: These are really interesting questions.
0:49
SPEAKER_00: So these are great questions.
0:51
SPEAKER_00: These questions come from Mrs.
0:52
SPEAKER_00: White's AP environmental science class.
0:55
SPEAKER_00: And she assigned our plate tectonics episode, if I remember correctly, to her class and asked them to come back with questions.
1:01
SPEAKER_00: And they came back, she kind of sent us an email and summarized the questions for us.
1:05
SPEAKER_00: But these are awesome questions.
1:06
SPEAKER_00: I mean, I was super impressed.
1:07
SPEAKER_00: Yeah, me too.
1:08
SPEAKER_00: So Mrs.
1:09
SPEAKER_00: White's class, you know, congrats to you guys if you are listening to this.
1:12
SPEAKER_00: Great questions.
1:13
SPEAKER_00: Yeah.
1:13
SPEAKER_00: That's right.
1:14
SPEAKER_00: So, Chris, Chris, what are the questions and where are we going to go?
1:16
SPEAKER_00: Summarize this episode.
1:17
SPEAKER_01: Yeah.
1:17
SPEAKER_01: All right.
1:18
SPEAKER_01: So we have basically three main questions.
1:20
SPEAKER_01: Um, the first one is how far have we dug down into the earth and could we ever reach the mantle, or is there a hope of ever reaching the mantle?
1:27
SPEAKER_01: That's the first question.
1:28
SPEAKER_01: Second question is what kind of instruments are used to determine the thickness and structure of the core and a mantle since we don't have samples from them.
1:36
SPEAKER_00: Yeah, that's a very common question, too, right?
1:38
SPEAKER_00: I hear that a lot.
1:39
SPEAKER_01: Yep.
1:39
SPEAKER_01: We're gonna talk a little bit about that.
1:40
SPEAKER_01: We got we got some interesting things.
1:42
SPEAKER_01: And then uh the third thing is um in volcanoes, when they erupt, there's magma underneath that comes out of the surface.
1:48
SPEAKER_01: So what happens to the area of the asthenosphere that lost magma?
1:51
SPEAKER_01: Is there an overall loss of magma?
1:53
SPEAKER_01: Those are the three questions that we're gonna deal with today.
1:56
SPEAKER_01: And then at the end, we're gonna talk a little bit about what is a magma chamber because this is something that's very debated.
2:02
SPEAKER_01: Uh, it's a hot topic right now in research community, correct?
2:06
SPEAKER_01: Absolutely.
2:06
SPEAKER_00: Yeah, absolutely.
2:07
SPEAKER_00: I mean, we yeah, that last question is is a deep, deep question.
2:11
SPEAKER_01: It really is.
2:11
SPEAKER_01: I was so impressed.
2:12
SPEAKER_00: It's it's an awesome question.
2:14
SPEAKER_00: So, all right, so so let's get into these.
2:16
SPEAKER_00: Let's go with how far have we dug down into the earth and have we ever reached the mantle?
2:21
SPEAKER_00: So, how far have we gone, Chris, as humans?
2:24
SPEAKER_01: Well, uh, so we've only gone down about 12 kilometers, which is ish 40,000 feet.
2:30
SPEAKER_00: Yeah, okay.
2:31
SPEAKER_00: Let's step back and think of the structure of the earth.
2:34
SPEAKER_00: You know, the crust.
2:35
SPEAKER_00: So we we talked in the plate tectonics episode about crust and mantle and lithosphere, sthenosphere.
2:41
SPEAKER_00: The crust in continents at least is between 40 and like 150 kilometers deep.
2:46
SPEAKER_00: So, you know, pretty thick stuff.
2:49
SPEAKER_01: Yeah, it depends on what's going on in the crust, whether you have mountains, then you're gonna have thicker crust and so on.
2:54
SPEAKER_01: But yeah.
2:55
SPEAKER_01: So two so 12 kilometers, it ain't much.
2:57
SPEAKER_01: It is a long ways away from getting down even to the moho, which then is the boundary between the crust and the mantle.
3:04
SPEAKER_01: So when you look at this, it's such a small amount.
3:07
SPEAKER_01: Uh it's shocking.
3:09
SPEAKER_01: I don't know if embarrassing is the right word.
3:11
SPEAKER_00: I know, yeah.
3:12
SPEAKER_00: After, especially after our interview with Jackie Faraday when these astronomers were thinking on huge scales and we're thinking, you know, us geologists, we've only really drilled down like a tiny part of the earth.
3:20
SPEAKER_00: It's a little bit embarrassing for our field.
3:22
SPEAKER_00: That's totally and the other thing that's interesting about this is that that borehole or that hole that we drilled, actually, it was drilled by the Soviets.
3:30
SPEAKER_00: It's called the Kola Super Deep Borehole.
3:32
SPEAKER_00: And this was during the Cold War, actually.
3:34
SPEAKER_00: So this was kind of a race between the Germans and the Soviets to drill down.
3:37
SPEAKER_00: It was kind of a scientific, you know, feather in the cap race.
3:41
SPEAKER_00: It took them 20 years to get that that far, and they only stopped because the temperature got too hot, basically.
3:46
SPEAKER_00: The rock, you know, starts to be too hot to actually drill into, and that temperature is almost 350 degrees Fahrenheit or around 180 degrees centigrade.
3:54
SPEAKER_01: Which is also shocking to me, too, because that doesn't seem like that's that hot.
4:02
SPEAKER_01: That you know what I mean?
4:03
SPEAKER_00: We Yeah, your oven gets that hot, right?
4:05
SPEAKER_01: Right.
4:05
SPEAKER_01: And and it shouldn't be something that would inhibit us from going deeper.
4:09
SPEAKER_01: But you know, then of course you have the friction of the drill bit, I assume, and all that kind of stuff going on.
4:14
SPEAKER_01: But taking 20 years, that's amazing.
4:16
SPEAKER_00: And the other thing to note here is that there are plans in the works, or there there's proposals in the works to drill down through the crust and into the mantle in the future, and you know, because it's a really interesting scientific question.
4:31
SPEAKER_00: And we've had a lot of technical advances in drilling, mostly in research or in oil and gas industry, into drilling really deep and using ships, ship-based drilling.
4:41
SPEAKER_00: So, you know, you have this positioning where the ship uses GPS to keep it right over the borehole as kind of a computer-controlled positioning system that helps you have much more pre much more precise drilling down deep into the especially in the ocean.
4:56
SPEAKER_01: Yeah, right, which also has another advantage of the crust is much thinner in the ocean.
5:01
SPEAKER_01: And so you're talking five to ten kilometers thick versus you know 40 to 80 kilometers for the continent, you know, and so that has other advantages of getting us into the mantle and not having to drill quite as deep.
5:15
SPEAKER_00: Yeah, absolutely.
5:16
SPEAKER_00: And the main thing that struck me when we were kind of reading about this is these things are expensive.
5:21
SPEAKER_00: It is expensive to try and drill down into the mantle.
5:23
SPEAKER_00: This one program or this one proposal from the International Ocean Discovery Program.
5:28
SPEAKER_01: Yeah, it was over a billion dollars.
5:30
SPEAKER_00: A billion dollars.
5:32
SPEAKER_01: Yeah, right.
5:32
SPEAKER_01: That's crazy.
5:33
SPEAKER_01: I mean, it's uh it I don't mean it's awesome.
5:36
SPEAKER_00: Okay, yeah.
5:37
SPEAKER_00: To summarize the answer to question number one, how far have we dug down into the earth?
5:41
SPEAKER_00: We've drilled 12.2 kilometers deep into the earth, and the center of the earth is 6,300 and around about 70 kilometers deep.
5:50
SPEAKER_00: So we're not off.
5:53
SPEAKER_00: Yeah, way less than 1% of the uh depth of the total thickness of the earth.
5:58
SPEAKER_01: Wait a minute, are you telling me that the movie the core was like not realistic?
6:03
SPEAKER_01: Is that what you're saying?
6:04
SPEAKER_01: It's shocking, right?
6:05
SPEAKER_01: It's shocking.
6:08
SPEAKER_01: Hollywood had it wrong.
6:09
SPEAKER_01: Okay.
6:09
SPEAKER_01: They they well, yeah, they did.
6:11
SPEAKER_01: They did.
6:11
SPEAKER_01: So that's that's I think another topic.
6:14
SPEAKER_00: Yeah, that's another topic, exactly.
6:16
SPEAKER_00: All right, so uh on to question number two, Chris.
6:18
SPEAKER_00: What kinds of instruments are used to determine the thickness and structure of the core and mantle because we don't have samples of them?
6:27
SPEAKER_00: And actually, I was just hassled about this by my future sister-in-law over Christmas about, you know, oh Jesse, how do we know the structure of the earth?
6:35
SPEAKER_00: Like, you don't have samples of them.
6:36
SPEAKER_00: How can you possibly know what it looks like down there?
6:38
SPEAKER_00: So it's a very common question.
6:40
SPEAKER_00: So what's our answer?
6:42
SPEAKER_01: Okay, well, we touched on this with the plate tectonics episode, we touched on this with volcanism episode, seismicity.
6:49
SPEAKER_01: We study seismic waves traveling through the earth, and these can be human-induced seismic waves, these can be uh seismic waves produced by earthquakes, uh volcanic eruptions, or even nuclear bombs.
7:02
SPEAKER_01: And there are two main waves that travel through the interior of the earth, the P waves and the S waves.
7:07
SPEAKER_01: Um, a lot of times they're referred to as body waves because they travel through the body of the earth.
7:12
SPEAKER_01: And the P waves are they're compression waves, they're essentially sound waves, and they they can travel through anything.
7:20
SPEAKER_01: They can travel through solids, liquids, and gases.
7:22
SPEAKER_01: And then the S waves can only travel through solids, they're shearing waves, and so they tear the material that they travel through.
7:31
SPEAKER_01: And liquids and gases don't have any shear strength, and so these S waves are abruptly stopped when they encounter those kinds of materials.
7:39
SPEAKER_00: Yeah, so if you think of you know P waves, compressional waves, think of a slinky.
7:43
SPEAKER_00: The best analogy here is a slinky.
7:44
SPEAKER_00: And if you take a slinky and you just push it in and out, meaning, you know, you're just pushing it in and out where it's compressing towards the other end and then away from the other end, that's kind of the P wave analogy there.
7:55
SPEAKER_00: S waves is if you take the ends of the slinky and you shake it side to side, and it's like this kind of snake-like pattern, right?
8:01
SPEAKER_00: It's kind of snaking along.
8:02
SPEAKER_00: Like a sidewinder, yeah.
8:03
SPEAKER_00: Exactly, like a little sidewinder snake.
8:05
SPEAKER_00: I mean, it's a rough analogy, but it works for this case.
8:07
SPEAKER_00: So P wave and S wave are compression and shear, meaning in and out or side to side, and those side to side waves cannot travel through liquid.
8:16
SPEAKER_00: So, how do how, Chris, does this inform us of the structure of the earth?
8:21
SPEAKER_01: Well, the waves, so when a when any wave travels through material and that material changes, whether it's an abrupt change or whether it's a gradual change, and you get both of those in the interior of the earth, uh, the waves bend, they refract.
8:36
SPEAKER_01: If you think about taking a like a vase of water and putting a rose stem in it, and you can see then how the rose stem looks like it's broken where it enters the water and when it leaves the water.
8:48
SPEAKER_01: And that's just because the the speed of light changes, it's different in water and as opposed to air.
8:55
SPEAKER_01: And so that's a that abrupt bending of the light wave looks like it it it breaks the stem.
9:01
SPEAKER_01: It doesn't, of course, just a visual effect.
9:04
SPEAKER_01: But um, so when these seismic waves travel through the interior of the earth, they encounter these different layers and they up they abruptly bend or they refract.
9:15
SPEAKER_01: And so that changes their trajectory.
9:18
SPEAKER_01: And they also not only do they have these abrupt changes where you go from the crust to the mantle and the mantle to the liquid core and the liquid core to the solid core, you also have this gradual bending of the waves.
9:30
SPEAKER_01: They take this curved path because the density of the rock that they're traveling through with depth also changes.
9:37
SPEAKER_01: So they're really, it's it's it's a complicated thing, actually, studying the geometry of these seismic waves.
9:43
SPEAKER_00: Absolutely.
9:43
SPEAKER_00: I mean, the the people who do who do this, what's called seismic tomography, which is basically think of it as like a CAT scan of the earth.
9:50
SPEAKER_00: You know, you go in and you get a CAT scan, you know, you're you're imaging the interior of your body.
9:54
SPEAKER_00: We're doing this with the earth, using earthquakes, using seismic waves, and using seismometers.
9:59
SPEAKER_00: And so someone like Dr.
10:01
SPEAKER_00: Diana Roman, who we interviewed a couple weeks ago, um, you know, uses does this all the time.
10:06
SPEAKER_00: It is extremely complicated.
10:07
SPEAKER_00: These P waves are turning into S waves, S waves are turning into P waves and back to S waves, and there's all sorts of conversions going on.
10:14
SPEAKER_00: It's really complicated.
10:15
SPEAKER_00: But in the simplest sense, to understand the interior structure of the Earth, we have P waves and S waves.
10:22
SPEAKER_00: One of them can travel through liquids and solids, one of them can only travel through solids.
10:27
SPEAKER_00: So if you imagine an earthquake on the other side of the planet, a P wave and an S wave are both coming from that earthquake, and they hit a layer that's liquid in the Earth, the S wave stops.
10:39
SPEAKER_00: It does not get transmitted through that liquid anymore.
10:41
SPEAKER_00: The P wave refracts a little bit, but it continues through there, and then it eventually makes its way to us on the other side of the planet.
10:48
SPEAKER_00: So that is called what we call a shadow zone, which means that there's some liquid down in the earth.
10:55
SPEAKER_00: And this is how we know that the outer core is liquid iron because earthquakes on the other side of the earth or seismic uh activity, atomic bombs, whatever it may be, that produces seismic waves, they don't get transmitted through, at least S waves don't get transmitted through parts of the earth.
11:14
SPEAKER_00: Those must be liquid because S waves don't travel through liquid, the P waves make it through.
11:20
SPEAKER_00: So we can kind of tell where that boundary layer is.
11:22
SPEAKER_00: Because if you produce if you layer a whole bunch of seismometers around the earth, you can kind of get a pretty good idea of the geometry of the interior of the earth by looking at this using this kind of CAT scan of the earth.
11:34
SPEAKER_01: Yes.
11:34
SPEAKER_01: And also when the P waves travel through the liquid uh outer core and then the solid inner core too, they slow down.
11:41
SPEAKER_01: And so when they come out then on the other side of the earth, they they arrive on the order of a couple of minutes slower than what was originally expected before we had this knowledge of really the layering of the earth was.
11:53
SPEAKER_01: And this was also really perfected when we were doing a lot of testing of nuclear bombs, say in the late 50s and early 60s, because you know, these these uh seismic tomographers knew exactly when and where these detonations would take place, and they they give off the PS waves just like an earthquake does.
12:12
SPEAKER_01: And so they were able to really hone in that on the interior structure of the earth due to the testing as nuclear bombs.
12:20
SPEAKER_01: Yeah, yeah.
12:21
SPEAKER_00: I mean, it's super interesting.
12:22
SPEAKER_00: There's there's a lot of uh geological insights that were gained from the nuclear weapons thing, but that's a discussion for another time and place.
12:29
SPEAKER_01: But but I want to talk about this though.
12:31
SPEAKER_01: What brought this question up about hey, really, come on, Jesse?
12:35
SPEAKER_01: We don't how the hell do we know what's going on in there when you know we've never seen it?
12:40
SPEAKER_01: Like, how did this come up?
12:41
SPEAKER_01: First of all give me some.
12:42
SPEAKER_00: Yeah, I don't I I think I can't remember what it is, but I think I walked in the room and and uh Meg was just like, hey, I got a bone to pick with you about the interior of the earth, you know?
12:49
SPEAKER_00: And okay, great, where we're going to this, let's argue it out.
12:52
SPEAKER_00: You know, it's a fair misconception to say you don't have samples, so how the hell do you know what you're talking about?
12:56
SPEAKER_00: And you know, it's inference.
12:58
SPEAKER_00: We are using inference, but we're using pretty damn good inference, and this is very well known.
13:02
SPEAKER_00: We've known this, like you said, Chris, since the 50s and 60s, what the interior structure of the earth is.
13:07
SPEAKER_00: And the other thing is, we do have some samples from this region.
13:11
SPEAKER_00: So there is, especially in subduction zones, so go back to the plate tectonics episode, there are bits of the mantle that have been kind of broken off of oceanic crust, and part of the lithosphere has been thrust up onto the continents, and we can walk on former mantle.
13:29
SPEAKER_00: So it's mantle rocks, it is mantle, but it has been pushed up onto the surface, and so we can go study it now.
13:35
SPEAKER_00: It's several million years old now, but it is still mantle stuff.
13:39
SPEAKER_00: And the other thing is that again, our diamond episode highlighted this diamonds preserve parts of the mantle in them, and we have diamonds from down to seven, eight hundred kilometers deep in the earth that erupt up.
13:52
SPEAKER_00: So we actually do have samples from very deep in the earth.
13:56
SPEAKER_00: They're diamonds, they're usually not gem diamonds, they're pretty ugly diamonds typically, but industrial, right?
14:02
SPEAKER_00: Yeah, yeah.
14:02
SPEAKER_00: And they do come from very deep and are scientifically very, very useful.
14:07
SPEAKER_01: Yeah, but you know, you're still gonna get the the person out there saying, Come on, really, 800 kilometers when you just said the radius of the earth is 6,378 kilometers, that's really not that deep.
14:19
SPEAKER_01: When you first told me that question, I'm like, really?
14:22
SPEAKER_01: That that was the that was what was said is we've never seen it, so we must not know anything about it.
14:27
SPEAKER_01: It got me thinking because it is a valid point.
14:29
SPEAKER_01: I hear it a lot.
14:30
SPEAKER_01: You know, how often in science do we use indirect evidence, other things that point to what is real?
14:37
SPEAKER_01: We use it all the time.
14:38
SPEAKER_01: I mean, think about it.
14:39
SPEAKER_01: In a chemistry class, we study the the structure of an atom, and we've never really we've never seen an electron, but we study them, we know these things, and we know the structure of an atom without really I've never seen one, you've never seen one, but there's other pieces of evidence that lead us down this path, you know.
14:58
SPEAKER_01: I mean, so much of science works is based on indirect evidence that come to conclusions that are 100% accurate.
15:06
SPEAKER_00: I agree, I agree completely.
15:07
SPEAKER_00: And if some of these things, like the interior structure of the earth, this is a well-known, well-accepted, very well-evidenced, uh effectively fact, but there's a lot of argument in science.
15:17
SPEAKER_00: So do not have the misconception that all scientists agree on stuff because they I've been writing papers that get rejected because people don't agree with what I'm saying.
15:25
SPEAKER_00: There's a heck of a lot of disagreement in science, and that's healthy.
15:28
SPEAKER_00: That's good.
15:29
SPEAKER_00: It's good to have a debate and to have a vigorous debate about things.
15:32
SPEAKER_01: And it's also not to say that, hey, we wouldn't love to be able to drill down to the interior of the earth and and have a product look at it.
15:39
SPEAKER_01: I mean, we would love that, but it's not gonna happen.
15:43
SPEAKER_01: Uh I would want to bring up one other point.
15:45
SPEAKER_01: Meteors give us a really good look at what the interior of the structure of the earth is based on the way the solar system formed.
15:53
SPEAKER_01: When these things formed, nothing happened to them after that.
15:58
SPEAKER_01: They didn't differentiate, there wasn't any metamorphism, they weren't re-melted at some other point.
16:02
SPEAKER_01: I mean, these are 4.5 billion year old meteorites.
16:06
SPEAKER_01: Looking at what they're made of gives us a really good idea.
16:11
SPEAKER_01: And that's another piece of the puzzle is in terms of what the interior structure of the earth is, too, what it's made of, actually from a chemical standpoint.
16:19
SPEAKER_01: And then also, well, let's look at the liquid outer core, for instance.
16:23
SPEAKER_01: I mean, we wouldn't have this electromagnetic field if we didn't have this liquid iron core that was circulating, generating an electromagnetic field.
16:35
SPEAKER_01: So that's a big piece of the puzzle, too, right?
16:37
SPEAKER_01: Yeah.
16:38
SPEAKER_00: Oh no, totally.
16:39
SPEAKER_00: So that is our answer to what kind of instruments are used to infer the thickness in the structure of the core and mantle because we don't have samples.
16:49
SPEAKER_00: The the answer is, well, we do have some samples of them, they don't go super deep, uh, but we infer a lot, but we infer a lot pretty well, and and we're we have a very well understood structure of the earth using seismic waves, using samples for meteorites, and using some pretty sound physical inferences.
17:07
SPEAKER_00: With that, Chris, let's move on to question number three.
17:10
SPEAKER_00: And this question is in volcanoes, when they erupt, there is magma underneath that comes out to the surface.
17:16
SPEAKER_00: And what happens basically in the asthenosphere or in the earth, what happens to that region that lost magma?
17:23
SPEAKER_00: And I think you and I both had kind of different takes on this question because this is a really deep question.
17:27
SPEAKER_00: So it is.
17:28
SPEAKER_01: I it woke me up at night.
17:30
SPEAKER_01: This this question woke me up.
17:31
SPEAKER_01: So, Mrs.
17:32
SPEAKER_01: White, whoever your student is, I've been teaching for 25 years and I've never had this question in any of my classes.
17:39
SPEAKER_01: It's an amazing question.
17:40
SPEAKER_01: Such a good question.
17:41
SPEAKER_01: It really is.
17:42
SPEAKER_00: Yeah, totally deep question.
17:43
SPEAKER_00: And and uh so Chris, take it away.
17:45
SPEAKER_00: Where did you take?
17:46
SPEAKER_00: Oh, actually, there's a follow-up here.
17:47
SPEAKER_00: Is there an overall loss of magma?
17:49
SPEAKER_00: Is the follow-up.
17:50
SPEAKER_00: So take it away.
17:51
SPEAKER_00: What were you thinking about when you woke up in the middle of the night?
17:54
SPEAKER_01: So, yeah, we had two totally different takes on this.
17:56
SPEAKER_01: The way I interpreted the question was this student is asking, okay, if we have material coming from the mantle, coming through the crust, coming out of volcanoes, then what replaces the magma that came out of the mantle?
18:12
SPEAKER_01: You can't just have this void, then, right?
18:14
SPEAKER_01: I mean, if this this stuff came from wherever it came from, what replaced it?
18:19
SPEAKER_01: That's the way I interpreted the question.
18:22
SPEAKER_00: How did you interpret the question?
18:24
SPEAKER_00: I interpreted it as uh what is the magma chamber actually look like?
18:27
SPEAKER_00: Which you might remember.
18:29
SPEAKER_00: I think it went crazy.
18:30
SPEAKER_00: This is not the question.
18:32
SPEAKER_00: When I came out to uh your SummerSides field trip uh a year and a half ago, I gave a little like lecture spiel on this.
18:40
SPEAKER_00: Little.
18:40
SPEAKER_00: I well, I took a two-hour nap while you so did the rest of the class, I think.
18:47
SPEAKER_00: I looked around and everybody was tired.
18:49
SPEAKER_00: I mean, in fairness to me, it was after kind of a long hike, and you had just given some random old man belaboring lecture that put them to sleep initially.
18:58
SPEAKER_00: So I took I took sleepy students and I put them to sleep with my lecture, but I think you got them to the edge.
19:05
SPEAKER_00: All right, so anyway, go you interpreted the question how?
19:07
SPEAKER_00: I interpreted the question of what does a magma chamber look like?
19:10
SPEAKER_00: Is there actually magma down in the in the earth?
19:13
SPEAKER_00: So, yeah, we answered this question kind of two separate ways, Chris.
19:16
SPEAKER_00: But before we get into our like different uh interpretations of this question, I kind of want to step back and say, why is this important?
19:22
SPEAKER_00: Like, why did we stay up at night thinking about this question?
19:25
SPEAKER_00: It's an awesome question, and it has some real-world implications here because magma chambers or volcanoes and eruptions of this scale are obviously important for humans.
19:36
SPEAKER_00: You know, where volcanoes are, when they're gonna erupt, that's important for humans.
19:40
SPEAKER_00: Go back, listen to our interview with Dr.
19:42
SPEAKER_00: Diana Roman.
19:43
SPEAKER_00: They're important for humanity.
19:45
SPEAKER_00: The other thing is that these magma chambers or these volcanic systems also are really important for producing metal deposits that are economically important.
19:54
SPEAKER_00: So things like gold, things like iron oxides, things like lithium, they're often found in these former volcanic centers, these former magma chamber areas is where we find economic mineral deposits that are really important to society.
20:08
SPEAKER_00: So it's an important question, and this is kind of why we stayed awake listening to it.
20:12
SPEAKER_01: Yeah, but I think before we answer the question directly, Jesse, I think we need to talk about what a magma chamber is, then.
20:19
SPEAKER_01: There are so many misconceptions out there about what a magma chamber looks like, you know.
20:23
SPEAKER_00: I Yeah, so when you're teaching your kids, what like what does your class think a magma chamber is or looks like?
20:28
SPEAKER_01: My students think that a magma chamber is what you get beneath, you know, a string of volcanoes, and it's it's like a a pipe leading down to this big, vast opening miles beneath the volcano that is this magma chamber that is mostly, if not all, liquid.
20:46
SPEAKER_01: That's how most people envision what a magma chamber looks like.
20:50
SPEAKER_00: Yeah, and that's that's what the textbooks often say, right?
20:53
SPEAKER_00: Yeah, it shows a big liquid, a vat of liquid many kilometers down deep in the earth.
20:58
SPEAKER_00: And that's fair enough because we go around and we look at rocks that are form of magmas, and they look kind of like that.
21:04
SPEAKER_00: But this has been a relatively new revelation in the scientific community, is that this is not actually what magma chambers look like.
21:11
SPEAKER_00: Magma chambers are not actually magma chambers, they're not a big vat of liquid, it's actually more like a bunch of crystals with a tiny bit of magma kind of interspersed.
21:22
SPEAKER_00: It's think of you know, one of these vases and you fill it up with the clear marbles and then you pour water into it.
21:29
SPEAKER_00: It's more like that.
21:30
SPEAKER_00: It's mostly marble and a little bit of water, it's mostly crystals and a little bit of liquid magma.
21:35
SPEAKER_00: And this is a new revelation.
21:37
SPEAKER_00: The evidence for this goes back to our understanding the liquid outer core, right, Chris?
21:42
SPEAKER_00: Because if there was a big vat of liquid in the earth, we should see it.
21:45
SPEAKER_01: And we don't see that with study and seismicity, studying seismic waves, we don't see this big belly underneath volcanic centers, including Yellowstone, which is one of the biggest volcanic centers on the On the planet, we would expect to see this huge magma chamber below that, and we just don't see it.
22:07
SPEAKER_01: We see what you described.
22:09
SPEAKER_01: It's this mush of mostly crystals with some magma in there and very, very hot, soft rock that's inner in between the spaces.
22:19
SPEAKER_01: You know, that's really what this bears out.
22:22
SPEAKER_00: And this was one of the things when I started graduate school, which was, you know, a decade ago, which this is one of the things that really kind of struck me, is that it's different from the textbook.
22:33
SPEAKER_00: I had gone through all of high school, all of undergrad, envisioning magma chambers as this big vat of liquid of boiling rock.
22:39
SPEAKER_00: And then to realize actually, this this probably wasn't actually what it looked like.
22:44
SPEAKER_00: This was kind of one of these, like, whoa, mind blown kind of moments.
22:47
SPEAKER_01: Um yeah, it is, it's one of those things that that I struggle with, and honestly, Jesse, because the model of a magma chamber and how everybody thinks of it, it's still effective.
22:58
SPEAKER_01: It it's not exactly how it looks, but it's still really effective.
23:01
SPEAKER_01: And to try to take that to what it really is is actually very difficult.
23:06
SPEAKER_00: You're you're totally right.
23:07
SPEAKER_00: The analogy of a big vat of magma, it works to understand the first principles.
23:13
SPEAKER_00: It doesn't work in the details, though.
23:15
SPEAKER_00: And we've actually never seen, we've never imaged a real big magma chamber on Earth.
23:21
SPEAKER_00: Instead, what we see is areas where it's a little bit hotter, there is some liquid there, maybe 10% or something like that, but not anywhere near 100%.
23:30
SPEAKER_00: And this is what happens during volcanic eruptions.
23:33
SPEAKER_00: This is what actually gets tapped during a volcanic eruption.
23:36
SPEAKER_00: And so the other important point here is that it's like 10% or 5% magma in 90 or 95% crystals, and it's actually pretty big.
23:45
SPEAKER_00: That's a huge area to make up the magmatic volumes that we see.
23:49
SPEAKER_00: It has to be a huge area that is 5% melt, as opposed to a small area that's 100% melt, right?
23:56
SPEAKER_00: That may encompass the entire depth of the crust.
23:59
SPEAKER_00: It's exactly right.
24:01
SPEAKER_00: They're called transcrustal, so they kind of go for 30 kilometers deep or 40 kilometers deep in the crust of a little bit of melt everywhere, which is really important for how the earth operates.
24:11
SPEAKER_00: It's really important for plate tectonics, it's really important for forming mineral deposits, and it kind of gets back to the question of what happens when that magma erupts, Chris.
24:20
SPEAKER_00: So what happens when that magma erupts?
24:22
SPEAKER_01: Well, up higher near the surface, okay, higher up in the magma chamber, is where you might get what people think of as a smaller, more traditional looking magma chamber, where something happens, degassing below that adds volatiles to this super hot rock and it causes it to lower the melting point and you generate more magma or an injection of fresh magma from below, and it it causes that heat, causes some melting higher up in this magma chamber.
24:52
SPEAKER_01: That's where you know a lot of this magma that comes out of volcanic eruptions comes from.
24:57
SPEAKER_01: And so, to answer the question then, like what happens?
25:00
SPEAKER_01: How does it respond?
25:00
SPEAKER_01: We can't just have this void beneath the surface of the earth.
25:03
SPEAKER_01: So, what happens, Jesse?
25:05
SPEAKER_00: Well, what happens is it basically collapses down in on itself.
25:08
SPEAKER_00: Instead of there's not stuff that comes up and takes its place necessarily, instead, the crust kind of relaxes down into the hole.
25:15
SPEAKER_00: And this is how we form calderas, like the Yellowstone caldera, is that you erupt a whole bunch of magma out of this distributed network of mostly crystals and a little bit of magma.
25:26
SPEAKER_00: That magma gets evacuated out the the volcanic center, and then basically the crust collapses back down into that void.
25:35
SPEAKER_00: And this is how you form a caldera that in Yellowstone, what is it, 30 miles by 40 miles or something on that on that order?
25:41
SPEAKER_00: Right, that's correct.
25:42
SPEAKER_00: Yeah, 30 by 45 miles.
25:43
SPEAKER_00: Yeah.
25:43
SPEAKER_00: So so basically this this huge area from human perspective, it looks like a huge area and a huge amount of magma.
25:49
SPEAKER_00: But when you think of it as a trans-crustal magma system that goes really deep, it goes 20 kilometers deep and it's 5% partial melt or 5% magma, it's not that much actually.
26:00
SPEAKER_00: So what gets pushed out the magma chamber is actually not that much when you think of the whole crust of the earth.
26:06
SPEAKER_01: Because the crystals in the magma, the magma chamber, what we think of as a magma chamber, which is not really a magma chamber, it's more of a crystal chamber, right?
26:15
SPEAKER_01: Is gonna still support what's above it.
26:17
SPEAKER_01: Well, back to your analogy of the vase full of marbles that has water in it.
26:21
SPEAKER_01: You know, if you pour water in enough where the water you have a little bit of water sitting on top, and then you evacuate the water uh during an eruption, let's say, then that will collapse down where there was magma, but where the marbles are is still gonna support uh everything that's above it.
26:39
SPEAKER_00: The flowers will still stand upright if you remove all the water out of the vase, right?
26:43
SPEAKER_01: Like oh, I thought you were gonna give me a warm and fuzzy flower analogy.
26:46
SPEAKER_01: Yeah, yeah.
26:47
SPEAKER_00: If you got some beautiful roses, if you bought some beautiful roses for Jenny, you know, and they're still gonna stand upright.
26:53
SPEAKER_00: Never fear, Chris.
26:54
SPEAKER_00: You can have a volcanic eruption in your vase.
26:56
SPEAKER_00: Uh um, so so this question number three, let's go back to it and kind of tie it up.
27:01
SPEAKER_00: You know, when volcanoes erupt, what happens to the magma underneath?
27:06
SPEAKER_00: What replaces it?
27:07
SPEAKER_00: The answer is that it's more complicated than that question, in that the magma's pretty well distributed.
27:13
SPEAKER_00: There's not much of it in any one area.
27:16
SPEAKER_00: And when it does erupt, the stuff that's removed, the ground just kind of collapses back down on itself.
27:22
SPEAKER_00: So there's not this big gaping hole in the earth that magma has left.
27:27
SPEAKER_01: This question, this very insightful deep question, really comes back to the misconception of what a magma chamber doesn't really look like.
27:36
SPEAKER_00: That's right.
27:37
SPEAKER_00: That's right.
27:37
SPEAKER_00: Yeah, absolutely.
27:38
SPEAKER_00: So we've highlighted many things in that question.
27:41
SPEAKER_00: Obviously, with the length of our answer, we've stumbled on some very interesting insights into how the earth works there.
27:47
SPEAKER_00: And actually, very interesting scientific debates going on in the geological community right now.
27:52
SPEAKER_00: So, with that, I think we've answered all the questions.
27:55
SPEAKER_00: I think we're good, yeah.
27:57
SPEAKER_00: So, again, thank you, Mrs.
27:58
SPEAKER_00: White's AP Environmental Earth Science class.
28:01
SPEAKER_00: That's right.
28:02
SPEAKER_00: You guys are awesome.
28:03
SPEAKER_00: That was great.
28:04
SPEAKER_00: Awesome questions.
28:06
SPEAKER_00: Totally.
28:06
SPEAKER_00: And uh yeah, with that, we'll wrap it up for this week.
28:10
SPEAKER_00: And as usual, if you enjoyed this podcast, if you got something out of it, give us a like, a share, subscribe on your podcast uh service, and share it with somebody who might be interested in this as well.
28:21
SPEAKER_00: We would really appreciate it.
28:22
SPEAKER_01: Yep, you got it.
28:23
SPEAKER_01: All right.
28:24
SPEAKER_01: All right, that's a wrap.
28:25
SPEAKER_01: See you next time.