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So You Think You Know Plate Tectonics? Part 6 - Interior of the Earth · PlanetGeo: The Geology Podcast

• 0:03
  SPEAKER_01: 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_02: Hey, you you did it, Jesse.
• 0:14
  SPEAKER_02: That was nice.
• 0:15
  SPEAKER_02: I changed things up on you, and instead of back counting 3, 2, 1, I went 1, 2, 3, and you didn't miss a beat.
• 0:21
  SPEAKER_02: You clapped in on cube.
• 0:22
  SPEAKER_01: I didn't even look confused or anything like that, did I?
• 0:25
  SPEAKER_02: You did a little, you looked a little confused.
• 0:28
  SPEAKER_01: Okay.
• 0:29
  SPEAKER_02: A little bit.
• 0:29
  SPEAKER_02: A little bit.
• 0:30
  SPEAKER_01: I cocked my head at you, like sort of like, what's he doing over there?
• 0:34
  SPEAKER_02: I yeah, you did actually, and I didn't know if the your screen froze up again or whether you were just confused, but you were confused.
• 0:41
  SPEAKER_02: Yeah, generally the latter.
• 0:42
  SPEAKER_01: But sometimes I blame it on the screen freezing up on me.
• 0:45
  SPEAKER_01: So yeah, that's why I was stuck with you know my tongue hanging out of my mouth in a weird goofy pose for a while, staring off into space.
• 0:52
  SPEAKER_01: Yeah, yeah, that's right.
• 0:53
  SPEAKER_01: Um well, I'm used to you just ignoring me and being very impolite and looking at one of your three massive monitors that you have in your recording set up and just staring off into space while you're paying attention to something different.
• 1:04
  SPEAKER_02: I'm not.
• 1:05
  SPEAKER_02: I'm I'm looking at what I have going on.
• 1:08
  SPEAKER_02: So just because I'm not looking straight at you, because you're the one right in front of me, I'm looking at what we have going on over here.
• 1:14
  SPEAKER_02: I'm making sure that our recording is going well.
• 1:17
  SPEAKER_02: Hey, this is complicated business.
• 1:20
  SPEAKER_01: Let me just one thing, Chris.
• 1:21
  SPEAKER_01: Um, I've got a little bit of a bone to pick with you.
• 1:24
  SPEAKER_01: So we were reading, we had a New Yorker article that sort of went through, I forget what the title was, but something about the standards of modern etiquette, like text messaging etiquette, dating app etiquette, all these things that don't really apply.
• 1:37
  SPEAKER_01: But there's one about text message communication, and there's a bit I was noticing this the last couple days.
• 1:43
  SPEAKER_01: You and I have we're not that far apart in age, but there is a bit of a generational divide when it comes to communication, I think.
• 1:52
  SPEAKER_02: I'm really curious to hear what you're gonna say.
• 1:53
  SPEAKER_01: So let's go.
• 1:54
  SPEAKER_01: You and and I'll be curious to hear what listeners think about this because my generation, we're very text-oriented, I think, and we perhaps over-communicate, or we we know why communication is being initiated.
• 2:08
  SPEAKER_01: You so you tend to just call me, and you know, it could be in the middle of the day, whenever you have your you know, half an hour, free hour, whatever, you just call me.
• 2:15
  SPEAKER_01: And if I don't answer, that's it.
• 2:18
  SPEAKER_01: So if I can't get to the call, I'm left wondering what did Chris want for like two hours, maybe five hours.
• 2:26
  SPEAKER_01: And uh what I tend to do is if I call somebody and I don't get them, and I either leave a message rarely, or I just send a text.
• 2:34
  SPEAKER_01: Hey, I'm checking in.
• 2:34
  SPEAKER_01: Hey, I got some thoughts on a script we wrote, or hey, I got some thoughts on an episode.
• 2:38
  SPEAKER_01: So, you know, I would appreciate a little text message every once in a while.
• 2:42
  SPEAKER_02: All right.
• 2:43
  SPEAKER_02: I have a response to that.
• 2:44
  SPEAKER_02: Can I can I answer this?
• 2:45
  SPEAKER_02: I figured you would have some thoughts on this.
• 2:47
  SPEAKER_02: I figured you would.
• 2:48
  SPEAKER_02: Yeah, I called you today because I felt like I needed to talk to you about it.
• 2:52
  SPEAKER_02: Totally get it.
• 2:53
  SPEAKER_02: I didn't want to do this long, rambly text, you know.
• 2:56
  SPEAKER_02: So I don't have time for that.
• 2:57
  SPEAKER_02: So I thought this would be just a one or two minute conversation, right?
• 3:00
  SPEAKER_02: You didn't answer.
• 3:02
  SPEAKER_02: Look, here's the thing my day is not like your day at all.
• 3:06
  SPEAKER_02: You have nothing going on.
• 3:08
  SPEAKER_02: Okay.
• 3:09
  SPEAKER_02: I I have to I have to plan out when I'm gonna pee during the day.
• 3:15
  SPEAKER_02: It's a it's a dilemma.
• 3:16
  SPEAKER_02: I'm serious.
• 3:17
  SPEAKER_02: And so I'm like, oh, okay, I got 30 seconds, I'm gonna quit calling.
• 3:21
  SPEAKER_02: I it's too long to text, and and you don't pick up.
• 3:23
  SPEAKER_02: I'm like, all right, screw it.
• 3:25
  SPEAKER_02: And then I'm I'm on to something else.
• 3:27
  SPEAKER_02: You know, it's so that's why.
• 3:29
  SPEAKER_02: Does that make sense?
• 3:30
  SPEAKER_01: Don't play the busy, uh, busy day card on me here.
• 3:34
  SPEAKER_01: I knew you were gonna do that, and it's a cheap excuse, and I can see right through it, Chris.
• 3:38
  SPEAKER_01: Just a short little text, just say, hey, uh, call me back when you get a chance.
• 3:42
  SPEAKER_01: This thing, you know, that takes you five seconds to send.
• 3:44
  SPEAKER_01: Maybe, maybe with your big thumbs, it takes you a little bit longer because you gotta like delete, delete, delete, delete, and then rewrite it.
• 3:49
  SPEAKER_01: But, you know, just a little communication.
• 3:51
  SPEAKER_02: I yeah, do a fair amount of that.
• 3:53
  SPEAKER_02: But uh, it was interesting.
• 3:55
  SPEAKER_01: It was more interesting.
• 3:56
  SPEAKER_01: It was more interesting too.
• 3:58
  SPEAKER_02: How long have you been harboring this?
• 4:00
  SPEAKER_01: Uh about uh what is it, four hours probably.
• 4:03
  SPEAKER_02: No, I was actually thinking this thought just occurred to you today, or have you been thinking about it?
• 4:08
  SPEAKER_01: No, actually, I mean, I thought I thought of it because we were talking about this New York article where it like sort of went through modern etiquette, and you know, it was mostly for my generation where we grew up with cell phones, or at least we got cell phones when we were in.
• 4:20
  SPEAKER_02: Oh my gosh.
• 4:20
  SPEAKER_02: All right, whatever.
• 4:21
  SPEAKER_02: So listen, you I I don't like the way you text, actually.
• 4:25
  SPEAKER_02: And you text me, and you you are three-word texts, and I'll get 10 of them in a row.
• 4:31
  SPEAKER_02: It's so annoying.
• 4:33
  SPEAKER_02: Okay, just tell me what you want.
• 4:34
  SPEAKER_00: You like the buzz in your pocket, you like the phone buzzing.
• 4:38
  SPEAKER_00: I do that on purpose.
• 4:40
  SPEAKER_02: I I cannot stand it.
• 4:42
  SPEAKER_01: So um well, we have uh we have some work to do in our electronic communication protocols, I would say probably.
• 4:48
  SPEAKER_02: But I am actually offended by this whole discussion because you have notoriously been the person that is you won't respond, you are hard to get a hold of, and uh that was one of the conditions of me doing this podcast with you is like I need access to you, and I need it when I call and when I text.
• 5:07
  SPEAKER_02: Like, I I need to know what's going on.
• 5:09
  SPEAKER_02: That's a very good point.
• 5:10
  SPEAKER_02: So now for you to be criticizing me about this is very hurtful.
• 5:14
  SPEAKER_02: How the worm has turned.
• 5:17
  SPEAKER_00: Okay.
• 5:18
  SPEAKER_01: Going to take my coat off here.
• 5:20
  SPEAKER_01: I'm getting all I'm getting all worked up about this now.
• 5:22
  SPEAKER_01: Uh no, I think uh you're totally right.
• 5:25
  SPEAKER_01: I that was one of your conditions about the podcast is Jesse, you gotta answer when I call, you gotta respond to my text messages.
• 5:31
  SPEAKER_01: And I think I've been pretty dang good about that, actually.
• 5:35
  SPEAKER_01: You actually have.
• 5:36
  SPEAKER_01: You've been good.
• 5:36
  SPEAKER_01: Okay, well, today is part six of So You Think You Know Plate Tectonics.
• 5:42
  SPEAKER_01: And I think we have this really ironed out now, Chris.
• 5:44
  SPEAKER_01: This is gonna be a seven-part series.
• 5:46
  SPEAKER_01: Like we're at a stage, we know the length.
• 5:50
  SPEAKER_01: We're not gonna go ten, we're gonna cut it off at seven.
• 5:53
  SPEAKER_01: And we might pick it back up later on down the road.
• 5:55
  SPEAKER_01: But with the current set of questions, we've got seven.
• 5:58
  SPEAKER_01: So what's part six, Chris?
• 6:01
  SPEAKER_02: Internal dynamics and plate tectonics.
• 6:03
  SPEAKER_02: So, what we're gonna talk about today is the interior structure of the earth.
• 6:07
  SPEAKER_02: You know, we're gonna talk about the chemical properties, the physical properties of the like the layering of the earth and how that's done.
• 6:14
  SPEAKER_02: Um, how do we know what the interior structure is?
• 6:18
  SPEAKER_02: Because this is stuff that most of the time we never get to lay eyes on, and we never will.
• 6:22
  SPEAKER_02: What is the hottest layer of the earth and why is the hottest layer a solid?
• 6:28
  SPEAKER_02: And then we're gonna talk a little bit about the liquid outer core and why it's a liquid, and then we'll wrap it up by talking about the mechanisms for plate tectonics.
• 6:38
  SPEAKER_02: So I think this is pretty basic stuff that I think a lot of our listeners are gonna be it, might be a refresher or it might just be straight up review for things that they already know.
• 6:52
  SPEAKER_02: However, I said that with the last episode on magnetism, and I'm listening back to the episode with my wife, and and Jenny's like, Chris, I have no idea what the heck you're talking about.
• 7:03
  SPEAKER_02: So you know, yeah what you said about most people.
• 7:06
  SPEAKER_02: Like, I don't know if I don't fit into the category of most people, but I do not know what's going on.
• 7:12
  SPEAKER_01: Right.
• 7:13
  SPEAKER_01: It's a fair point, Jenny.
• 7:14
  SPEAKER_01: It's I think this is a common question, though, too.
• 7:17
  SPEAKER_01: Like, especially the parts about how do we know the interior of the earth.
• 7:19
  SPEAKER_01: So I think we should probably start there.
• 7:22
  SPEAKER_01: And the first question that, and again, the structure of this is you basically put together a bunch of questions to ask your class that sort of tested their knowledge about plate tectonics because it is the operating paradigm or the paradigm by which we understand how the earth works.
• 7:38
  SPEAKER_01: So the first one here is what is the interior structure of the earth?
• 7:42
  SPEAKER_01: The chemical and physical behavior is kind of what we're talking about here.
• 7:46
  SPEAKER_01: And Chris, why don't you just run us down on the basic layering of the earth?
• 7:51
  SPEAKER_01: And we have two categories, right?
• 7:52
  SPEAKER_01: Chemical and physical.
• 7:54
  SPEAKER_01: So those are two different categories of layering.
• 7:56
  SPEAKER_02: Um, which one do you want to do first?
• 7:57
  SPEAKER_02: Do you want to do chemical?
• 7:59
  SPEAKER_01: I prefer chemical.
• 8:00
  SPEAKER_01: I'm a Jew, yeah, I like chemistry.
• 8:02
  SPEAKER_02: So that was a dumb question.
• 8:04
  SPEAKER_00: Obviously.
• 8:05
  SPEAKER_02: Okay.
• 8:05
  SPEAKER_02: All right.
• 8:06
  SPEAKER_02: Okay.
• 8:06
  SPEAKER_02: The chemical layering of the earth basically goes crust, mantle, and core.
• 8:14
  SPEAKER_02: Those are the three basic layers that are distinguished based upon their stark chemical compositional differences.
• 8:23
  SPEAKER_02: Okay, so outside in, crust, mantle, core.
• 8:27
  SPEAKER_02: Now, with the crust, there are two kinds of crust.
• 8:30
  SPEAKER_02: We have oceanic crust and continental crust.
• 8:34
  SPEAKER_02: And this layer, when you compare it to the overall size of the earth, the crust is a really thin skinned.
• 8:43
  SPEAKER_02: I mean, it's it's almost like uh it is.
• 8:45
  SPEAKER_02: It's like uh a bowling ball with wax paper over it.
• 8:49
  SPEAKER_02: Yeah, that's the proportion of the crust.
• 8:52
  SPEAKER_02: Very, very thin.
• 8:54
  SPEAKER_02: So let's talk about the two kinds of crust then.
• 8:57
  SPEAKER_02: Oceanic versus continental.
• 8:59
  SPEAKER_02: Jesse, so what's the difference between the two?
• 9:03
  SPEAKER_02: What are the main differences between them?
• 9:04
  SPEAKER_01: Yeah, this kind of goes back to the first uh episode in this So You Think You know, Plate Tectonic series.
• 9:08
  SPEAKER_01: We were talking about igneous rock types, you know, the rock basalt and the rock granite.
• 9:12
  SPEAKER_01: Really, oceanic crust is thin, it's about seven kilometers thick, and it is mostly basalt.
• 9:19
  SPEAKER_01: It is composed mostly of basalt.
• 9:21
  SPEAKER_01: And what does basalt look like?
• 9:22
  SPEAKER_01: Basalt is a dark fine-grain colored rock.
• 9:25
  SPEAKER_01: It basically looks like a black, maybe greenish, maybe slightly brownish rock, fine-grained, can't really see many minerals in it, if any at all.
• 9:32
  SPEAKER_01: Uh it's what you think of when you have a lava flow.
• 9:35
  SPEAKER_01: If you are picturing a lava flow in your head, it's probably a basaltic lava flow.
• 9:39
  SPEAKER_01: The continental crust is significantly thicker.
• 9:41
  SPEAKER_01: It's about 35, sometimes up to 70 kilometers thick.
• 9:45
  SPEAKER_01: And it is mostly an intermediate rock called andesite, or that's the average composition, but we have a lot of granite in there.
• 9:52
  SPEAKER_01: We do have some basalt in the continental crust, but on average, it's intermediate, what we'd call andesite.
• 9:58
  SPEAKER_01: And so it kind of floats higher and sinks a little bit lower because it's thicker.
• 10:01
  SPEAKER_02: Okay, that's a good point, Jesse, that I want you to expound upon just a little bit.
• 10:06
  SPEAKER_02: That you said that it's andesitic, because this is something new for people that have taken one or two geology classes.
• 10:14
  SPEAKER_02: It's typically said that continental crust is felsic or granitic.
• 10:19
  SPEAKER_02: The opposite of basalt.
• 10:21
  SPEAKER_02: Basalt is black and fine-grained.
• 10:23
  SPEAKER_02: Granite is very light colored, rich in quartz and feldspar, and it's coarse grained, but you just kind of contradicted it a little bit by saying that the average composition of the crust is anticinetic.
• 10:34
  SPEAKER_02: So explain that a second.
• 10:36
  SPEAKER_02: I think you just kind of glossed over it.
• 10:37
  SPEAKER_02: Go ahead.
• 10:38
  SPEAKER_01: Yeah, no, that's that's a good point.
• 10:39
  SPEAKER_01: So the continental crust, this 35 on average kilometers thick piece of continental crust, there are a bunch of different rocks in the continental crust.
• 10:48
  SPEAKER_01: We can look at this on any geologic map, you look and you see all this complexity.
• 10:51
  SPEAKER_01: You see, there's granites over there, there's a bunch of sediments over there, there's some limestone cliffs over there, there's a huge basalt flow over there.
• 10:58
  SPEAKER_01: Like it's an amalgam.
• 10:59
  SPEAKER_01: There's a whole bunch of stuff in the continental crust.
• 11:02
  SPEAKER_01: If we look really, really at sort of the volumes, the volume breaks down into two parts.
• 11:07
  SPEAKER_01: The upper part of the crust is granitic, mostly on average.
• 11:10
  SPEAKER_01: That's sediments, that's granites.
• 11:13
  SPEAKER_01: They're really high in silica, aluminum, potassium, these types of elements.
• 11:17
  SPEAKER_01: So that's kind of a granitic composition, the upper part of the continental crust.
• 11:21
  SPEAKER_01: The lower part, there's some debate about what the composition of the lower crust is because we don't have a ton of samples of it.
• 11:26
  SPEAKER_01: But on average, it's more mafic.
• 11:29
  SPEAKER_01: It's more like basalt than it is like granite, probably.
• 11:32
  SPEAKER_01: And so if you average those two things, you get intermediate.
• 11:35
  SPEAKER_01: If you average mafic and felsic, you get intermediate and you get something on the order of andesitic.
• 11:41
  SPEAKER_02: That makes sense.
• 11:42
  SPEAKER_02: So we talked about the crust then, this really, really thin skin.
• 11:46
  SPEAKER_02: But when we're talking about the chemical compositional layers, the crust can be felsic, it can be intermediate, and it can be mafic.
• 11:55
  SPEAKER_02: That is the chemical composition of the crust.
• 11:59
  SPEAKER_02: Okay.
• 12:00
  SPEAKER_02: The layer right below that is the mantle.
• 12:04
  SPEAKER_02: And there's a boundary that separates them.
• 12:06
  SPEAKER_02: It's called the the moho.
• 12:08
  SPEAKER_02: We we usually just abbreviate it and call it the moho.
• 12:10
  SPEAKER_02: Do you formalize that in your class, Jesse?
• 12:12
  SPEAKER_02: That you teach?
• 12:13
  SPEAKER_01: I just call it the moho.
• 12:14
  SPEAKER_01: But like I said, you like we've belabored before, I think you can get into a lot more detail than than I can in my uh one semester class.
• 12:21
  SPEAKER_01: But yeah, I just call it the moho, the cross mantle boundary done.
• 12:25
  SPEAKER_02: And that's all that it is.
• 12:26
  SPEAKER_02: It's not a layer, it's just a boundary.
• 12:27
  SPEAKER_02: This was discovered, you know, roughly a little over a hundred years ago, because when seismic waves traveled through the crust and they got to this boundary, there was an abrupt change in the velocity of the PS waves.
• 12:40
  SPEAKER_02: And so that that change in velocity was a result of a very sharp compositional difference.
• 12:50
  SPEAKER_02: The the minerals were different, okay.
• 12:53
  SPEAKER_02: And that marks the beginning of the mantle.
• 12:55
  SPEAKER_02: And the mantle, how it's different from the crust, the mantle is ultramafic.
• 13:00
  SPEAKER_02: So it's mafic on steroids.
• 13:03
  SPEAKER_02: You know, we talked about oceanic crust being mafic, basaltic.
• 13:07
  SPEAKER_02: This is ultra mafic.
• 13:09
  SPEAKER_02: So what Jesse, what you're the geochemist in the house.
• 13:12
  SPEAKER_02: So what is the ultramafic?
• 13:15
  SPEAKER_02: What does that mean?
• 13:16
  SPEAKER_01: Yeah, ultramafic is rich in iron and magnesium.
• 13:19
  SPEAKER_01: Silica is a lot lower, something on the order of 45% of the rock will be silica.
• 13:24
  SPEAKER_01: Whereas in a granite, it could be up to 70.
• 13:27
  SPEAKER_01: 75% of the rock can be silica.
• 13:29
  SPEAKER_01: So ultramafic, you'll also hear this termed paritotite or paritotitic.
• 13:33
  SPEAKER_01: Pyritotite is the rock composition of a piece of the mantle, will be a rock paridotite.
• 13:38
  SPEAKER_01: So you'll hear paritititic.
• 13:39
  SPEAKER_01: You will also hear pyrolytic sometimes to describe a mantle that has never been developed.
• 13:44
  SPEAKER_02: I've heard that word in a long time.
• 13:46
  SPEAKER_02: Yeah, it's kind of creeping in.
• 13:48
  SPEAKER_02: It brings me way back.
• 13:50
  SPEAKER_01: In a bunch of these uh, you know, science news publications recently, pyrolytic mantle.
• 13:54
  SPEAKER_01: And uh so it's kind of creeping back in a little bit.
• 13:57
  SPEAKER_01: So those are all three things that broadly mean the mantle.
• 14:00
  SPEAKER_02: So one thing, Jesse, when uh my students see peridotite, I mean, I've you know, they've heard me pronounce it several times, but when they read it, the most common thing that they see, they call it peridote.
• 14:15
  SPEAKER_02: Like, you know, no, that's a gemstone.
• 14:18
  SPEAKER_02: Um, this is peridotite.
• 14:20
  SPEAKER_02: You got a couple syllables you got to slip into the city.
• 14:21
  SPEAKER_01: I know, just another win for geology naming being so complicated and frustrating for a student to learn.
• 14:28
  SPEAKER_01: Um, and then Chris, just to take it, we've got the mantle, which is a huge amount of the earth.
• 14:33
  SPEAKER_02: Yeah, but then 2,900 kilometers, yeah.
• 14:36
  SPEAKER_01: I mean, it's it's a massive yeah, massive part.
• 14:39
  SPEAKER_01: And then we hit the core, which is the iron nickel alloy part.
• 14:42
  SPEAKER_01: And that's just iron, nickel, alloy.
• 14:45
  SPEAKER_01: There are some what we call quote unquote light elements in there, something silica or lighter.
• 14:50
  SPEAKER_01: We don't really know the composition of the core very well.
• 14:53
  SPEAKER_01: We don't have many samples.
• 14:54
  SPEAKER_01: Well, we don't have any samples of our core.
• 14:57
  SPEAKER_01: We have iron meteorites that we can kind of say are maybe analogous to the core, but we don't know exactly what the core composition is.
• 15:04
  SPEAKER_01: Uh, but it's iron and nickel mainly.
• 15:07
  SPEAKER_01: So that's the chemistry structure.
• 15:09
  SPEAKER_01: Are we good on that, Chris?
• 15:11
  SPEAKER_02: Again, the crust is felsic, intermediate, or mafic, the mantle is ultramafic, and the core is iron nickel.
• 15:20
  SPEAKER_02: So those are the stark chemical differences that separate each one of these layers out.
• 15:26
  SPEAKER_02: So that leads us into the other way that geologists layer the earth or t or think about layering of the earth, and that's based upon physical or mechanical behaviors of the rock.
• 15:37
  SPEAKER_01: And this really brings us to plate tectonics a little bit, because the first layer we would hit outside of the atmosphere in the ocean is going to be a tectonic plate.
• 15:48
  SPEAKER_01: It is the lithosphere, what we call the lithosphere.
• 15:51
  SPEAKER_01: And that is if you bend it, it will break part of the earth.
• 15:54
  SPEAKER_01: It's the cold and crunchy part, and it has the crust, it is all of the crust, and a part of the mantle, the upper part of the mantle.
• 16:03
  SPEAKER_01: And so the lithosphere is crust plus the top of the mantle.
• 16:07
  SPEAKER_01: And just like crust, we have two different categories of lithosphere.
• 16:11
  SPEAKER_01: We have oceanic lithosphere and continental lithosphere.
• 16:13
  SPEAKER_01: Chris, what uh broadly, what are the differences here?
• 16:16
  SPEAKER_02: Uh well, it's just about what sits on top of the mantle.
• 16:20
  SPEAKER_02: If you have oceanic lithosphere, we're talking about oceanic crust sitting on top of the mantle, continental lithosphere is continental crust sitting on top of that.
• 16:27
  SPEAKER_01: Yeah, and the oceanic lithosphere, just to put some numbers on this, is again, this is a pretty thin layer for the most part, but the the we said oceanic crust is about seven kilometers thick on average.
• 16:37
  SPEAKER_01: The oceanic lithosphere is about 35 kilometers thick, plus or minus a few kilometers.
• 16:41
  SPEAKER_01: The oceanic lithosphere, the upper part of the mantle is the residual of the melting to form basalt.
• 16:48
  SPEAKER_01: So you take ultramafic mantle, that paridititic or pyrolytic or ultramafic mantle, you partially melt it and you get basalt.
• 16:55
  SPEAKER_01: The stuff that's left behind, the stuff that's not partially melted, that stuff is what we call depleted, and that forms the lithosphere.
• 17:04
  SPEAKER_01: So that forms the upper mantle, the base of the lithosphere.
• 17:07
  SPEAKER_01: So then those two things go together and form a tectonic plate.
• 17:10
  SPEAKER_01: So that's oceanic lithosphere.
• 17:12
  SPEAKER_01: Continental lithosphere can be anywhere from like 100, 150 kilometers thick to 350 kilometers thick.
• 17:18
  SPEAKER_01: It's it can get very, very thick in some places, and it's a mess, so we don't really understand how it forms necessarily.
• 17:23
  SPEAKER_01: So that's the first thing.
• 17:25
  SPEAKER_02: Because we're not getting many snapshots down to that stuff.
• 17:27
  SPEAKER_02: It's exactly it's deep.
• 17:29
  SPEAKER_02: Yep.
• 17:30
  SPEAKER_02: All right.
• 17:30
  SPEAKER_01: So, Jesse, what's below it?
• 17:32
  SPEAKER_01: What's below the lithosphere?
• 17:33
  SPEAKER_01: Then we go into the asthenosphere, uh, which is convecting mantle.
• 17:38
  SPEAKER_01: This is the mantle that will flow.
• 17:39
  SPEAKER_02: So, Jesse, I think like the best way to describe the asthenosphere is this rock that is hot, it's soft, it's it's plastic-like, and it can then flow in the form of convection.
• 17:51
  SPEAKER_02: And that's really, really important in terms of you know, driving plate tectonics and one of the main mechanisms that we'll talk about at the end of the episode.
• 18:00
  SPEAKER_02: So that's what's below the lithosphere.
• 18:01
  SPEAKER_01: And exactly, and this is because it's hot.
• 18:03
  SPEAKER_01: I mean, it gets hot, it gets weak, it can flow, it's like plastic.
• 18:06
  SPEAKER_01: And, you know, depending on the era of the textbook that you might have in front of you, or you know, what you find on the internet, there are different terms.
• 18:14
  SPEAKER_01: People have historically broken up the mantle, the asthenosphere, into an upper mantle and a lower mantle because there is a big seismic velocity shift.
• 18:23
  SPEAKER_01: There is something happening at about 660 kilometers deep that there's some change.
• 18:28
  SPEAKER_01: But most people these days believe that material goes across that boundary.
• 18:33
  SPEAKER_01: So the whole mantle is kind of convecting across that boundary.
• 18:37
  SPEAKER_01: That boundary is a mineralogical change rather than like a barrier of any kind.
• 18:42
  SPEAKER_01: So this kind of begs the question how we know this.
• 18:46
  SPEAKER_01: And I think the answer is fairly short, right?
• 18:50
  SPEAKER_01: Like, how do we know the interior structure?
• 18:52
  SPEAKER_01: There's basically one way.
• 18:54
  SPEAKER_02: Yeah.
• 18:55
  SPEAKER_02: Yeah, it's based on the study of seismic waves.
• 18:58
  SPEAKER_02: This is geophysics at its best.
• 19:00
  SPEAKER_02: There are two kinds of waves that travel through the body of the earth, P waves and S waves.
• 19:05
  SPEAKER_02: And the way that they refract and reflect when they encounter new compositional layers, when they encounter new physical properties, they do certain things.
• 19:17
  SPEAKER_02: And, you know, for instance, the best thing I think to explain how this works is talking about the liquid outer core.
• 19:22
  SPEAKER_02: How do we know that the liquid outer core is liquid?
• 19:25
  SPEAKER_02: S waves, they're shearing waves, and so they can't travel through a liquid because liquids don't have shear strength.
• 19:33
  SPEAKER_02: You can't tear a liquid, and so these waves they abruptly halt when they encounter the liquid outer core.
• 19:39
  SPEAKER_02: So by studying the way these waves come back, we've determined like the size and the shape and the nature of the liquid outer core.
• 19:48
  SPEAKER_01: And just to double-click on that, we have some great images that we have made for our Camp Geo conversational textbook that is online.
• 19:56
  SPEAKER_01: This is the first link in your show notes.
• 19:57
  SPEAKER_01: In the earthquakes chapter, Chris, we had some great schematics and gifts made uh that are really, really cool and are uploaded.
• 20:04
  SPEAKER_01: Uh, they should be uploaded soon, if not already.
• 20:07
  SPEAKER_01: So check that out if you want to see this visually really well.
• 20:10
  SPEAKER_01: So that's exactly right, Chris.
• 20:12
  SPEAKER_01: I mean, that's a good example of this.
• 20:13
  SPEAKER_01: You talked originally about the Moho where seismic wave velocities change.
• 20:17
  SPEAKER_01: Seismic waves also bounce off of stuff, so they bounce off of boundaries.
• 20:21
  SPEAKER_01: They also change, they convert energy between P and S wave and between different waves, and so you get all these convergence.
• 20:27
  SPEAKER_01: It gets super complicated, but the complexity is really important because it allows us to really get a good view of the interior of the earth.
• 20:34
  SPEAKER_02: You would be proud of me today because we were talking about magma chambers, and I asked the question in a very Jesse Rhymink way.
• 20:45
  SPEAKER_02: I said, What is a magma chamber?
• 20:49
  SPEAKER_00: Did you have your pinky in the air too?
• 20:51
  SPEAKER_00: And were you a little bit pretentious about it?
• 20:53
  SPEAKER_02: I was.
• 20:54
  SPEAKER_02: I was really pretentious about it.
• 20:56
  SPEAKER_02: And then we talked about how all of the models that you see in books and online and so on have these idealized magma chambers.
• 21:04
  SPEAKER_02: And I'm like, well, no.
• 21:05
  SPEAKER_02: And I use the analogy of a vase filling the vase with marbles, and how a magma chamber is mostly solid and there's a little bit of liquid in there.
• 21:13
  SPEAKER_02: It's all hot, but it's mostly solid stuff.
• 21:15
  SPEAKER_02: And so anyway, we talked about that because that makes me think of it.
• 21:18
  SPEAKER_02: When you talk, I mean, if if magma chambers were idealized like that, they would be very easy to see the footprint of what's below this, all this volcanism, right?
• 21:28
  SPEAKER_02: But it's very difficult to do that because the magma chamber is mostly solid, and so you don't see this stark contrast between the P and the S waves.
• 21:39
  SPEAKER_01: Yeah, anyway.
• 21:40
  SPEAKER_01: No, that's a thought of you too.
• 21:42
  SPEAKER_01: Exactly right.
• 21:42
  SPEAKER_01: Nicely done.
• 21:42
  SPEAKER_01: I am indeed proud of you, Chris.
• 21:44
  SPEAKER_01: Well done.
• 21:44
  SPEAKER_01: Well, well done.
• 21:46
  SPEAKER_02: Gee, thanks.
• 21:48
  SPEAKER_01: Um so I think we can move on from that one because that's a fairly straightforward answer, and we have covered that in previous episodes as well.
• 21:55
  SPEAKER_01: Why is the hottest layer of the earth a solid?
• 21:58
  SPEAKER_01: This is the next question we have in our.
• 22:00
  SPEAKER_01: List here.
• 22:00
  SPEAKER_01: Why is the hottest layer of the earth a solid?
• 22:03
  SPEAKER_01: Which uh this is a a great question, I think.
• 22:06
  SPEAKER_01: Because if you sit down and think about it, it's not very intuitive that that is the case.
• 22:11
  SPEAKER_01: But if you re if you think deeply about it as we talk about, I think it becomes intuitive that this is the case.
• 22:17
  SPEAKER_02: I think so.
• 22:18
  SPEAKER_02: This is something that you know a couple of my students sitting there when I ask this question, they don't have a lot of exposure.
• 22:25
  SPEAKER_02: I'm talking to my upper level geology students.
• 22:28
  SPEAKER_02: Some of them are gonna are gonna know the hottest layer of the earth is the solid inner core.
• 22:32
  SPEAKER_02: And then, of course, that begs the next question.
• 22:34
  SPEAKER_02: Well, then why is the liquid outer core, why is it liquid if that's not the hottest layer?
• 22:41
  SPEAKER_02: And uh a couple of them will be able to think that through.
• 22:45
  SPEAKER_02: And they'll come to the right conclusion.
• 22:46
  SPEAKER_02: They begin to talk about pressure, and that's really what it is.
• 22:49
  SPEAKER_02: You have this geothermal gradient, this steady increase with temperature with depth.
• 22:54
  SPEAKER_02: So the hottest layer of the earth is the deepest layer of the earth.
• 22:58
  SPEAKER_02: And why is that solid then?
• 23:00
  SPEAKER_02: You know, if it's hottest, and it's simple, it really is.
• 23:03
  SPEAKER_02: I mean, it's not intuitive, but like you said, I think it becomes more intuitive if you think it through.
• 23:08
  SPEAKER_02: Pressure squeezes it into a solid.
• 23:12
  SPEAKER_02: In other words, pressure becomes more of an important factor than temperature at that depth, and the liquid outer core, the recipe of temperature and pressure is just right for it to be a liquid.
• 23:26
  SPEAKER_01: And I think again, I don't want to belabor the point, but if you can go back to our Camp Geo chapter on igneous rocks, we again have some cool examples, cool schematics of how melting happens.
• 23:36
  SPEAKER_01: And I think the way I explain this in class is I I think about it from the reverse, not why is it a solid, but why is it not melted?
• 23:42
  SPEAKER_01: And if you think about how melting happens, it makes more intuitive sense.
• 23:46
  SPEAKER_01: So if you start with something that is solid, it's under high pressure, it's being squished.
• 23:51
  SPEAKER_01: And you can think of this like squeezing out a sponge.
• 23:54
  SPEAKER_01: If you squish that, the water comes out of it.
• 23:56
  SPEAKER_01: And if you squish a rock, all the stuff that wants to be water is going to leave it.
• 24:02
  SPEAKER_01: And the magma, the liquid part is going to rise to the surface because it's less dense.
• 24:07
  SPEAKER_01: So if you think of it that way, it makes a little bit of sense.
• 24:09
  SPEAKER_01: Now, think about how we would melt this stuff.
• 24:13
  SPEAKER_01: Well, if it's solid, it's sitting there, it's solid.
• 24:15
  SPEAKER_01: At the same pressure, if you heat it up, usually things will melt.
• 24:18
  SPEAKER_01: So you can add heat to it and it'll melt.
• 24:20
  SPEAKER_01: It'll just sort of increase the temperature, inducing some melting.
• 24:25
  SPEAKER_01: The opposite thing can happen, and this is what's going on in the lower part of the liquid outer core.
• 24:30
  SPEAKER_01: So the bottom part of the liquid outer core, that's gradually cooling down.
• 24:34
  SPEAKER_01: As it cools down, it starts to crystallize.
• 24:37
  SPEAKER_01: At the same pressure, it's starting to crystallize.
• 24:39
  SPEAKER_01: So the inner core is growing as the outer core is crystallizing metal, basically metal crystals are crystallizing right at the base because that's the highest pressure part of the liquid outer core.
• 24:51
  SPEAKER_01: And the same thing happens in the mantle, too.
• 24:53
  SPEAKER_01: If stuff upwells, it decompresses, it can melt.
• 24:57
  SPEAKER_01: Now, kind of just think about the earth.
• 24:58
  SPEAKER_01: We've got rock down below, then liquid ocean on top of it, then gas above it.
• 25:02
  SPEAKER_01: That's because of the pressure differences, and those things are happy at those pressure differences.
• 25:06
  SPEAKER_02: Yeah, if you take really, really hot rock and do nothing else to it but lower the pressure on it, that rock can become liquid.
• 25:16
  SPEAKER_02: It can melt.
• 25:16
  SPEAKER_02: And that's a it's a very important thing that happens uh in generating ocean floor.
• 25:22
  SPEAKER_02: This rising and convecting a stenosphere.
• 25:25
  SPEAKER_02: Well, it's that rock, we we just said it's right near its melting point.
• 25:28
  SPEAKER_02: As it rises up toward the surface towards lower pressure, it partially melts, and that's what comes out then on the ocean floor.
• 25:36
  SPEAKER_02: So it's a this pressure relief melting is really I think important in understanding why the liquid outer core is liquid, even though it's a lot of fun.
• 25:44
  SPEAKER_01: And I think that it is quite an intuitive thing because if you just ask people what's more dense, a solid or a liquid, they'll usually say a solid is more dense, the vast majority of people.
• 25:54
  SPEAKER_01: I mean, unless you're thinking about ice in water, but heavy things or solid things sink.
• 25:59
  SPEAKER_01: That's intuitive.
• 26:00
  SPEAKER_01: And so, you know, of course, the solid stuff is going to be at the bottom.
• 26:03
  SPEAKER_01: And that is the case with the mantle mostly, uh, and especially with the core, which leads us very nicely into the next question.
• 26:11
  SPEAKER_01: Why is the liquid outer core liquid?
• 26:13
  SPEAKER_01: Which is kind of the inverse of why is the hottest layer of the earth a solid, right?
• 26:17
  SPEAKER_01: Right.
• 26:17
  SPEAKER_01: Yeah.
• 26:18
  SPEAKER_02: I think I don't know.
• 26:19
  SPEAKER_02: We think we've kind of answered it, haven't we haven't we?
• 26:21
  SPEAKER_01: I yeah, I would agree.
• 26:22
  SPEAKER_01: Yeah, yeah.
• 26:22
  SPEAKER_01: I think we've gotten that I think we're done.
• 26:24
  SPEAKER_01: But I think, Chris, the the one important thing, and and actually a fun visual that I've uh at least a visual I find quite fun, is thinking about liquid iron metal convecting.
• 26:35
  SPEAKER_01: That's the liquid outer core, that's where a magnetic field uh is generated, which we talked about in the last episode in this series.
• 26:42
  SPEAKER_01: Think about that hitting the base of the mantle, which is solid.
• 26:45
  SPEAKER_01: The mantle's solid down there, the lower mantle is solid.
• 26:48
  SPEAKER_01: And so you've got this liquid convecting underneath of it.
• 26:51
  SPEAKER_01: And you think about how does that happen?
• 26:54
  SPEAKER_01: Why is there solid above liquid at the core mantle boundary?
• 26:59
  SPEAKER_01: And I I think that's kind of a fun visual to think about and to think about why that might be the case.
• 27:05
  SPEAKER_02: Um, do you want to answer why that is the case?
• 27:08
  SPEAKER_02: Are you just gonna leave us hanging?
• 27:09
  SPEAKER_01: Well, I yeah, we we can answer.
• 27:11
  SPEAKER_01: I mean, it's just that metal is more dense than rock.
• 27:14
  SPEAKER_01: So even liquid metal is more dense than solid rock.
• 27:18
  SPEAKER_01: So solid rock will float on top of liquid metal of iron, nickel, alloy.
• 27:22
  SPEAKER_01: So that's it's just a density difference, even though there's this phase difference that's seems inverted to our intuition.
• 27:27
  SPEAKER_01: So all right, Jesse.
• 27:29
  SPEAKER_02: That brings us into the last part of this episode, which are the mechanisms for plate tectonics so this is an opportunity for you to show us how overeducated you are.
• 27:39
  SPEAKER_02: Uh always, always my favorite part of the day.
• 27:43
  SPEAKER_02: It is the truth.
• 27:44
  SPEAKER_02: Like you just light up like a light bulb.
• 27:46
  SPEAKER_01: That's always what I'm trying to do.
• 27:47
  SPEAKER_01: I'm just trying to find people out there in the world who I can show how overeducated I am, too.
• 27:52
  SPEAKER_02: Okay.
• 27:53
  SPEAKER_02: Well, let's go then.
• 27:54
  SPEAKER_02: All right.
• 27:55
  SPEAKER_02: I don't know.
• 27:56
  SPEAKER_02: We've talked about this actually, and I think we've talked about it on Planet Geo before.
• 28:00
  SPEAKER_02: The main mechanism for plate tectonics is always everything you read talks about how convection is this main mechanism.
• 28:08
  SPEAKER_02: I just it just doesn't do it for me.
• 28:10
  SPEAKER_02: That you know, there's something missing in this, and I think that I don't know, I'm asking you this.
• 28:17
  SPEAKER_02: Does the literature um I'm sure that that you're coming across things that are contradicting this as the main mechanism for plate tectonics at the research level?
• 28:28
  SPEAKER_01: Uh yeah, absolutely.
• 28:29
  SPEAKER_01: I think actually there's there's more of a consensus around one of the other mechanisms.
• 28:35
  SPEAKER_01: So let's just list the mechanisms.
• 28:37
  SPEAKER_01: Can you just list the four mechanisms that we're talking about here, Chris?
• 28:39
  SPEAKER_01: So we and then we can dive into them.
• 28:40
  SPEAKER_02: Convection, number one, because that's always the one first listed.
• 28:44
  SPEAKER_02: Slab push and slab pull, and then mantle plumes.
• 28:48
  SPEAKER_02: Those are the four main mechanisms, or slab pull and slab push kind of work together.
• 28:53
  SPEAKER_02: So maybe three if you combine them and lump them together in one.
• 28:57
  SPEAKER_01: Yeah.
• 28:57
  SPEAKER_01: And I'll just kind of give you a visual.
• 28:59
  SPEAKER_01: Let's just work through visuals of these four really quickly.
• 29:01
  SPEAKER_01: Convection, the mantle, we talked about the asthenospheric mantle, that's convecting.
• 29:05
  SPEAKER_01: So if this is convecting and upwelling, this stuff, when the convecting part rises to the surface, it hits the base of the lithosphere, it spreads out laterally, it moves right and left, and that could kind of drag the lithosphere along.
• 29:18
  SPEAKER_01: So that's one idea.
• 29:19
  SPEAKER_01: That's convection.
• 29:20
  SPEAKER_01: It's kind of the the mantle's convecting, it's causing upwelling, and it's moving stuff.
• 29:24
  SPEAKER_01: Think about a boiling pot of water where you see the water moving away from the center of the pot where it's hottest, and that's that's kind of convection.
• 29:32
  SPEAKER_01: If you put some stuff on the surface, it'll spread laterally.
• 29:36
  SPEAKER_01: Um, slab push, or sometimes called ridge push, is basically the hot part of the oceanic plate right along the mid-ocean ridge where oceanic plate is being formed.
• 29:46
  SPEAKER_01: That stuff's high and it's hot, higher elevation, hence the ridge and it's hot, and that is kind of sloughing off to the sides.
• 29:52
  SPEAKER_01: It's pushing the plate away from the ridge.
• 29:54
  SPEAKER_01: That's the ridge push mechanism or slab push.
• 29:57
  SPEAKER_01: Slab pull is really the main one where consensus, I think, has been built around this being a main driving force.
• 30:03
  SPEAKER_01: Is when an oceanic plate subducts, it's diving down into the mantle.
• 30:08
  SPEAKER_01: At some point, it becomes super dense, converts to eclogite.
• 30:11
  SPEAKER_01: That behaves like an anchor.
• 30:13
  SPEAKER_02: You could see dropping big words here.
• 30:15
  SPEAKER_01: There we go.
• 30:16
  SPEAKER_01: And it pulls the plate down.
• 30:19
  SPEAKER_01: The plate it sort of behaves like an anchor with an anchor rope, and it kind of drags the rest of the anchor chain down off the boat, pulls it away.
• 30:27
  SPEAKER_01: The last one, what did you say?
• 30:28
  SPEAKER_01: Mantle plume stresses that.
• 30:29
  SPEAKER_02: Well, let's uh I'm not ready to leave this yet.
• 30:32
  SPEAKER_02: So it's being pulled and pushed in the same direction.
• 30:36
  SPEAKER_02: You know, and it's all connected.
• 30:38
  SPEAKER_02: That's why it's called slab often.
• 30:41
  SPEAKER_01: Slab push and slab pull is what you're referring to, those two, right?
• 30:44
  SPEAKER_02: That's right, that's right.
• 30:45
  SPEAKER_02: And they're being pushed and pulled at the subduction zone in the same direction.
• 30:51
  SPEAKER_02: But I want to ask you, because this is this doesn't quite make sense either.
• 30:55
  SPEAKER_02: If slab pull is a main driving mechanism, what causes the subduction then?
• 31:01
  SPEAKER_02: You it's kind of like putting the cart before the horse or the horse before the cart.
• 31:05
  SPEAKER_02: Like, you know, what do you do?
• 31:06
  SPEAKER_02: Uh you know, something had to cause the subduction zone to begin with.
• 31:11
  SPEAKER_01: I think this is uh this is a really interesting question and a really deep question because you sort of ask the people who model the planet uh from a plate tectonics or geodynamics standpoint, and we don't actually know.
• 31:23
  SPEAKER_01: It's hard to do with modeling.
• 31:25
  SPEAKER_01: You don't just start with a lithosphere and a sthenosphere, and then the lithosphere breaks and subduction starts.
• 31:30
  SPEAKER_01: That actually doesn't really happen in these models.
• 31:32
  SPEAKER_01: So we don't actually know how you break the lithosphere to start a subduction zone system.
• 31:36
  SPEAKER_01: There's a whole bunch of ideas about potential ways to do it.
• 31:38
  SPEAKER_01: It's hard to really model the physics of this accurately enough to do it.
• 31:42
  SPEAKER_01: There's a bunch of ideas, but you're keying in on a really important point, is that this is a sort of a chicken or the egg argument.
• 31:49
  SPEAKER_01: Once it's started, it's easy to keep it going.
• 31:51
  SPEAKER_01: And actually, if you start subduction in one place, it's easy to start plate tectonics globally that way because of this slab pull mechanism.
• 31:58
  SPEAKER_01: But how do you get that going in the first place?
• 32:00
  SPEAKER_01: Is a is an open question.
• 32:01
  SPEAKER_01: You kind of have to have some horizontal movement due to convection or due to uh the sort of slab push mechanism.
• 32:09
  SPEAKER_01: A big, huge mountain range piles up, think Olympus Mons on Mars.
• 32:12
  SPEAKER_01: It's a huge thing.
• 32:13
  SPEAKER_01: That's sort of sloughing off to the sides and getting really dense, and that could potentially pull stuff down.
• 32:19
  SPEAKER_01: There's other people who suggest giant impacts early on in Earth history.
• 32:23
  SPEAKER_01: A big impact punches through the lithosphere, and then you start subduction.
• 32:27
  SPEAKER_01: Basically, slab pull can start on the edges of that.
• 32:30
  SPEAKER_01: So there's a whole bunch of different ideas about that, but it's a great question.
• 32:33
  SPEAKER_02: Which leads us into the last part of this, then the other kind of newer mechanism of plate tectonics, mantle plumes.
• 32:41
  SPEAKER_02: So let's talk about mantle plumes a little bit.
• 32:43
  SPEAKER_02: Um Jesse, why is this so new and and why is this becoming I don't know, I kind of get the feel that it's becoming more and more prominent.
• 32:53
  SPEAKER_02: It's getting traction.
• 32:55
  SPEAKER_01: I think it it's uh so why is it becoming new?
• 32:59
  SPEAKER_01: Well, we've started to see that, and this is because of seismic imaging technique development, so really advanced computer models that can really tease apart the details of this really complicated seismic waves that are penetrating through the earth, and people do what's called tomography, which is imaging the whole earth.
• 33:17
  SPEAKER_01: And we've seen that there are what are called, we've had listener questions about this before.
• 33:22
  SPEAKER_01: They're called LLS VPs, large, low shear wave velocity provinces, like the most boring name in the world, right?
• 33:30
  SPEAKER_01: But basically what these things are are huge, huge piles of either hot or chemically different stuff at the base of the mantle.
• 33:39
  SPEAKER_01: And there's two piles.
• 33:40
  SPEAKER_01: There's one kind of under Africa, and there's one kind of on kind of under the Pacific, and these things are thought to feed mantle plumes, or maybe they are the mantle plumes, and they feed the plumbing systems that feed Hawaii or Yellowstone or these different ocean island basalt provinces or volcanic island chains.
• 34:00
  SPEAKER_01: So these things are like big piles of stuff down in the mantle that are piled up on the core mantle boundary, and they come up, I forget what it is, maybe 1,500 kilometers high or a thousand kilometers high.
• 34:10
  SPEAKER_01: So these things are are really big, and they're like 10% of the mantle is these things, these LL SVPs.
• 34:18
  SPEAKER_02: And okay, so they rise up.
• 34:20
  SPEAKER_01: So they've been newly identified.
• 34:21
  SPEAKER_01: That's the answer to that.
• 34:22
  SPEAKER_02: Okay, so they rise up, they will plume out or pool at the base of the lithosphere.
• 34:29
  SPEAKER_01: Let me interrupt there real quick, Chris, and say the LLSVPs are down there, and those are kind of not moving, at least that we see, but these there's little plumes coming off.
• 34:37
  SPEAKER_01: So think of like little jets of stuff coming off of them that are then feeding the magma system, and this is what you're talking about.
• 34:43
  SPEAKER_01: So this magma will kind of rise up, hit the base of the lithosphere, and pool.
• 34:47
  SPEAKER_02: Yes.
• 34:48
  SPEAKER_02: Okay.
• 34:49
  SPEAKER_02: So how is this a mechanism for plate tectonics?
• 34:52
  SPEAKER_02: This kind of pooling at the base of the lithosphere.
• 34:56
  SPEAKER_01: I think it does a lot of stuff.
• 34:57
  SPEAKER_01: I mean, you can envision this providing a bunch of heat and kind of eroding the lithosphere above it.
• 35:02
  SPEAKER_01: The mantle plume can kind of destroy lithosphere because it's just punching a ton of heat into this system, a bunch of magma.
• 35:08
  SPEAKER_01: It can also focus other plate tectonic scenarios.
• 35:13
  SPEAKER_01: So, for instance, Iceland.
• 35:15
  SPEAKER_01: Iceland has a mantle plume under it and the mid-ocean ridge system running through it.
• 35:19
  SPEAKER_01: And some people would argue that the mantle plume has captured the ridge system.
• 35:24
  SPEAKER_01: So the ridge system is kind of locked on this mantle plume source and it's not migrating around like other ridge systems might.
• 35:30
  SPEAKER_02: I gotta interrupt you here, though, because yeah, we see that with Iceland, but you know, we don't see that with Hawaii.
• 35:36
  SPEAKER_02: It's a well-established that we have this mantle plume beneath Hawaii, but we don't see a divergent boundary there.
• 35:43
  SPEAKER_02: We don't see that with Yellowstone either.
• 35:45
  SPEAKER_02: We don't see that extension.
• 35:47
  SPEAKER_02: How does this fit into the plate tectonics theory then?
• 35:52
  SPEAKER_01: The mantle plumes are a little bit independent in some ways of plate tectonics.
• 35:58
  SPEAKER_01: Now they can interact with the plate tectonic surface of the earth, like in places like Iceland, where they can kind of capture a ridge.
• 36:03
  SPEAKER_01: They also, there's some thoughts that mantle plumes, especially big mantle plumes, could potentially break the lithosphere, so it could form a triple junction where the mantle starts to break apart, or where the lithosphere starts to break apart.
• 36:14
  SPEAKER_01: So, for instance, where we're from in Michigan, there's this big mid-continent rift system, which is a failed rift.
• 36:20
  SPEAKER_01: The continent almost broke apart there.
• 36:22
  SPEAKER_01: And the idea was maybe there's a plume that hit the base of the lithosphere, tried to break it, but didn't.
• 36:27
  SPEAKER_01: And so plumes can sometimes break continents in half by by doing this.
• 36:32
  SPEAKER_02: Makes sense.
• 36:33
  SPEAKER_01: All right.
• 36:34
  SPEAKER_01: So I think that kind of covers it, Chris.
• 36:36
  SPEAKER_01: Yeah, this is uh this was a fun episode, fun conversation.
• 36:39
  SPEAKER_02: It was, it was.
• 36:40
  SPEAKER_02: Um, I I so I talked to my mom, Joyce.
• 36:43
  SPEAKER_02: Okay, yep.
• 36:44
  SPEAKER_02: Um, and so she sent me a couple of questions, not really questions today, because we you and I talked about this, like uh which which kind of try to keep her in mind as we go through this.
• 36:55
  SPEAKER_02: And I know that today we probably lost her a little bit, and and I think she might be sleeping by now, but she she did make two points.
• 37:02
  SPEAKER_01: Okay, are these like notes on things like you know, Jesse should do this better, Chris?
• 37:07
  SPEAKER_01: You should do this better.
• 37:08
  SPEAKER_02: No, no, so no, not really, not really.
• 37:10
  SPEAKER_02: She I think she's gonna come up, she's making lists of questions that she wants to ask us.
• 37:15
  SPEAKER_02: But two things today is I I was over there, I usually try to go over there on Friday afternoons after work and and you know, spend an hour, an hour and a half with them, and so on.
• 37:23
  SPEAKER_02: I'm a I'm a good son, okay?
• 37:25
  SPEAKER_02: And so my mom, uh we were just talking and I dropped a word, I said perseverate, and like that word shocked her.
• 37:34
  SPEAKER_02: So she texted me today and said, What are you gonna perseverate on today?
• 37:38
  SPEAKER_02: And so that was her first first point was using that word in a sentence, okay?
• 37:45
  SPEAKER_00: What were you gonna perseverate on?
• 37:47
  SPEAKER_00: Yeah, I think tectonics, mom.
• 37:49
  SPEAKER_01: I think we perseverated on the uh the chemical structure of the earth.
• 37:53
  SPEAKER_01: We perseverated on that one today.
• 37:55
  SPEAKER_02: We did.
• 37:56
  SPEAKER_02: We we absolutely did.
• 37:57
  SPEAKER_02: The second point that she made is she thinks that your voice is very melodic.
• 38:02
  SPEAKER_02: So it Well, I well, I don't know if it's a good thing, though, because it does tend to put her asleep.
• 38:09
  SPEAKER_01: Well, that's okay.
• 38:10
  SPEAKER_01: I mean, you know, if there's anybody who wants me to be the voice of their, you know, do some audio recording for advertising, I'm open to it.
• 38:16
  SPEAKER_01: I can be the voice for car company or you know, maybe Rock Hammers, Estwing, maybe Estwing wants me to be the voice of Rockhammers for them.
• 38:24
  SPEAKER_01: I'd be up for that.
• 38:25
  SPEAKER_00: Okay.
• 38:26
  SPEAKER_01: So it I sound better on the radio than you do, Chris.
• 38:29
  SPEAKER_01: It sounds like.
• 38:29
  SPEAKER_01: And coming from your mother, who I don't know how to take it.
• 38:32
  SPEAKER_01: Who's genetically predisposed to appreciate your voice more than mine.
• 38:37
  SPEAKER_02: Well, uh, like I said, I don't know if it's a good thing because you do put her to sleep.
• 38:41
  SPEAKER_02: So you might be melodic, but you're boring.
• 38:43
  SPEAKER_02: And and so I don't I don't know.
• 38:46
  SPEAKER_01: I'll I'll take it.
• 38:47
  SPEAKER_01: I agree with both of those, probably.
• 38:49
  SPEAKER_01: All right.
• 38:50
  SPEAKER_01: Hey, that's a wrap for this episode.
• 38:52
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• 38:53
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• 38:54
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• 38:58
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• 38:59
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• 39:01
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• 39:07
  SPEAKER_01: See pictures of Chris as well.
• 39:08
  SPEAKER_01: There's a lot of pictures of Chris on there.
• 39:10
  SPEAKER_01: And uh last thing, go to our Camp Geo conversational textbook, first link in your show notes.
• 39:14
  SPEAKER_01: There you can learn all the basics with images, where basically we put podcast meets textbook.
• 39:20
  SPEAKER_01: That's what's going on there.
• 39:20
  SPEAKER_01: So, first link in your show notes, check that out.
• 39:23
  SPEAKER_01: Right on.
• 39:24
  SPEAKER_01: Cheers.
• 39:24
  SPEAKER_01: Peace.