Latest / PlanetGeo: The Geology Podcast / So, You Think You Know Plate Tectonics?!? Part 3

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So, You Think You Know Plate Tectonics?!? Part 3 · PlanetGeo: The Geology Podcast

• 0:03
  SPEAKER_02: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:13
  SPEAKER_01: Are you ready, Jesse Rymink?
• 0:15
  SPEAKER_01: Are you ready to do this now?
• 0:16
  SPEAKER_01: You seem like you're down in the jib.
• 0:19
  SPEAKER_01: Okay.
• 0:21
  SPEAKER_01: Oh, I don't know about that.
• 0:22
  SPEAKER_02: I am always ready, sir.
• 0:24
  SPEAKER_01: No, don't call me sir.
• 0:25
  SPEAKER_01: How are you doing, Dr.
• 0:26
  SPEAKER_01: Rymink?
• 0:27
  SPEAKER_01: Mr.
• 0:27
  SPEAKER_01: Bullheis.
• 0:28
  SPEAKER_01: What's up, man?
• 0:29
  SPEAKER_01: Oh yeah, it's been a long, long time since you've ever called me that.
• 0:34
  SPEAKER_01: Yeah, I know.
• 0:35
  SPEAKER_02: It's been, I mean, we might be going on a decade since I've called you Mr.
• 0:38
  SPEAKER_02: Bullheis, man.
• 0:39
  SPEAKER_02: I bet you longer.
• 0:40
  SPEAKER_02: I bet you longer.
• 0:41
  SPEAKER_02: Yeah.
• 0:41
  SPEAKER_02: Oh, yeah.
• 0:42
  SPEAKER_01: As soon as you got out, you were like, oh, I can call him whatever I want now.
• 0:45
  SPEAKER_02: Oh, yeah, that's right.
• 0:46
  SPEAKER_02: It's Chris, it's hey Baldy, all those things.
• 0:49
  SPEAKER_02: Yeah.
• 0:49
  SPEAKER_01: That's right.
• 0:50
  SPEAKER_01: Yeah.
• 0:50
  SPEAKER_01: All those really original digs on me.
• 0:53
  SPEAKER_01: That's right.
• 0:53
  SPEAKER_02: You've probably never heard that before, huh?
• 0:55
  SPEAKER_01: No, never.
• 0:56
  SPEAKER_01: Never been called Mr.
• 0:57
  SPEAKER_01: Clean, Stone Cold, Baldy.
• 1:01
  SPEAKER_01: Never, never got any of that stuff at all ever.
• 1:03
  SPEAKER_01: No, no, no.
• 1:04
  SPEAKER_02: I'm sure.
• 1:04
  SPEAKER_02: I'm sure.
• 1:05
  SPEAKER_02: Yeah.
• 1:06
  SPEAKER_02: Hey, today we are continuing on.
• 1:09
  SPEAKER_02: It's been a while since we talked about our plate tectonics series last.
• 1:12
  SPEAKER_02: I mean, we're going back a couple months now in season two.
• 1:15
  SPEAKER_02: Now we're in season three and we're just kind of launching season three here of Planet Geo, which is really exciting.
• 1:20
  SPEAKER_02: Uh, but we're revisiting some questions, some plate tectonic questions that are under the sort of moniker, Chris, that you came up with that is, do you know plate tectonics?
• 1:31
  SPEAKER_02: Or so, do you know plate tectonics more accurately?
• 1:34
  SPEAKER_02: What was the origin of this?
• 1:35
  SPEAKER_01: The origin was just talking to students, and they, as soon as I said we're gonna get into plate tectonics, I got a really unusual reaction and they thought they, oh, we know this.
• 1:45
  SPEAKER_01: I, you know, we know everything there is to know about plate tectonics.
• 1:48
  SPEAKER_01: And so I wrote a bunch of questions and then flipped them back to the students and said, All right, well, what do you think about these?
• 1:55
  SPEAKER_01: If you know plate tectonics, do these kinds of questions then make sense?
• 1:59
  SPEAKER_01: Are you able to apply what you know about plate tectonics then to our planet?
• 2:04
  SPEAKER_01: And the answer was uh a resounding no.
• 2:08
  SPEAKER_01: They didn't, they didn't know they had no idea.
• 2:10
  SPEAKER_02: It wouldn't do very well on the questions, huh?
• 2:12
  SPEAKER_01: No, but but which is totally okay, right?
• 2:14
  SPEAKER_01: It's it's uh they had the rudimentary understanding of the boundaries and and the features that you get at the boundaries and maybe some of the actions that happen, and that's great, right?
• 2:22
  SPEAKER_01: Well, we can then take that and use it to make our world make more sense because play tectonics is just this really broad, overarching thing.
• 2:31
  SPEAKER_02: Yeah, and I I want to interject this, Chris, because you know, I was initially, as we've talked about, resistant to this idea, but you were right, uh, you turned me around.
• 2:38
  SPEAKER_02: This is really, really a great idea.
• 2:40
  SPEAKER_02: And it's actually, you know, when we were talking about designing our Camp Geo conversational textbook that uh people can go to, there's the link in the show notes there.
• 2:49
  SPEAKER_02: But we were talking about the sort of structure, the layout of that.
• 2:51
  SPEAKER_02: What order should we put things in?
• 2:53
  SPEAKER_02: Where do we put plate tectonics in this?
• 2:55
  SPEAKER_02: You know, we put it pretty high up.
• 2:57
  SPEAKER_02: It's not the first thing, but it's near there because we kind of have you have to understand some of the basic terms before we talk about plate tectonics.
• 3:03
  SPEAKER_02: But plate tectonics is inextricably linked to every other topic in geoscience, right?
• 3:09
  SPEAKER_02: It controls how sediment evolves.
• 3:11
  SPEAKER_02: So there's all these things that feed into plate tectonics.
• 3:14
  SPEAKER_02: It is sort of the fabric that ties our understanding of our planet together.
• 3:18
  SPEAKER_01: Yeah, right.
• 3:18
  SPEAKER_01: And you you were talking about order.
• 3:20
  SPEAKER_01: I think that in an intro geology like course, one of the first things you have to do is minerals, then you have to go right into rocks, the igneous, metamorphic, and sedimentary rocks.
• 3:30
  SPEAKER_01: Once you're there, you have the foundation then to dive into plate tectonics.
• 3:35
  SPEAKER_01: And that's why we kind of put it high up on that priority list when we started doing this podcast.
• 3:39
  SPEAKER_02: And so that's a great lead-in into the last two episodes that we did in this So You Think You Know Plate Tectonics series.
• 3:45
  SPEAKER_02: We talked about really igneous rocks, a variety of igneous rocks in the first episode, then some sedimentary and metamorphic rocks in the second episode.
• 3:52
  SPEAKER_02: So if you want to kind of catch up in that theme, go back to those episodes or go to the Camp Geo link and learn about the basic minerals and rocks and then plate tectonics, and then come back to this episode and kind of test your knowledge because that's what we're doing right now, Chris.
• 4:05
  SPEAKER_02: And today we're gonna go into planetary tectonics, which is kind of where I exist in my research.
• 4:12
  SPEAKER_02: So it's kind of near and dear to my heart here of like these questions about how has plate tectonics evolved over Earth history, how does it function or not function on other planets?
• 4:20
  SPEAKER_02: Like there's some really deep-seated planetary science questions that are built into this that are near and dear to me.
• 4:26
  SPEAKER_02: So uh I'm excited about this one.
• 4:28
  SPEAKER_01: Yeah, two things that I want to mention here, real quick, before we jump in.
• 4:31
  SPEAKER_01: One is I I bet you I wonder, I'm at I'm gonna ask you a question, actually, Jesse.
• 4:36
  SPEAKER_01: When you started your research in the Northwest Territories, did you ever consider that this is where your interest would go, the direction that you would go?
• 4:44
  SPEAKER_01: I mean, you were just doing research on super old rocks at the point.
• 4:47
  SPEAKER_01: You didn't really know why you were doing what you're doing.
• 4:50
  SPEAKER_01: Is that right?
• 4:50
  SPEAKER_02: No, I mean that that's exactly right.
• 4:52
  SPEAKER_02: When I started a master's, I think this is probably a a similar, similar for most people.
• 4:56
  SPEAKER_02: When you start a master's, you don't really know like why you're doing the things you're doing.
• 5:01
  SPEAKER_02: You kind of trust your supervisor to sort of have the big picture questions in mind.
• 5:04
  SPEAKER_02: I was excited to go fly around in float planes and go way up in the remote north and look at old rocks.
• 5:09
  SPEAKER_02: I mean, that sounded cool to me, right?
• 5:11
  SPEAKER_02: So you're right.
• 5:11
  SPEAKER_02: I had really no idea that of what the big picture questions were, and now that's the motivating factor.
• 5:17
  SPEAKER_02: It's still fun to go fly around in float planes, not as fun as it used to be, but the big motivator is like answering these questions about Earth.
• 5:24
  SPEAKER_02: So great question.
• 5:25
  SPEAKER_01: That's right.
• 5:26
  SPEAKER_01: And you know, which I think is is an important thing for us to come to understand, right?
• 5:30
  SPEAKER_01: But you and I had some deep conversations about this very thing because it's important to you, and and it's always been important to you to do important things, you know, like in and we had this discussion about, you know, you said, Chris, what the hell?
• 5:45
  SPEAKER_01: Who who cares when play tectonics began on this planet?
• 5:48
  SPEAKER_01: And the we we you know, we sat on my front porch and had a few beers and and talked about this many times.
• 5:54
  SPEAKER_01: And it's just really cool to see like the direction that it's taken you, and and now you've fully vested in it and comfortable with the yeah, you know what, we need to know this.
• 6:05
  SPEAKER_01: This is important.
• 6:06
  SPEAKER_01: Um, just kind of it's come full circle.
• 6:09
  SPEAKER_02: It's an interesting, you know, space.
• 6:11
  SPEAKER_02: I I would say that I still on a sort of very deeply personal level, I still struggle with some of the relevance of this.
• 6:17
  SPEAKER_02: Like it is not the most immediately concerning to society of when plate tectonics started on Earth, for instance, right?
• 6:25
  SPEAKER_02: It's extremely interesting to me personally.
• 6:27
  SPEAKER_02: I I love the question.
• 6:28
  SPEAKER_02: I like all the the sort of unknowns in the question that are built into the question, but it's still, you know, part of what motivates me in research is I also have to have something else that's more societally relevant, a research direction that is not just this question about when did plate tectonics start, right?
• 6:45
  SPEAKER_02: So it's always a balance like everything.
• 6:47
  SPEAKER_02: And frankly, I sometimes still struggle with that.
• 6:50
  SPEAKER_02: Uh, but but having it be sort of one direction of a research portfolio is where I've landed to sort of make me happy and stay fulfilled in that.
• 6:59
  SPEAKER_02: So, anyways, it it's a really, really interesting, important question as far as understanding our earth and just a totally cool, like sort of like mind-blowing thing to think wait, we might not have had plate tectonics at some point in earth history and and how did that develop?
• 7:14
  SPEAKER_02: Like it's totally cool.
• 7:15
  SPEAKER_01: That's right.
• 7:16
  SPEAKER_01: I think so too, and I think it's important, but we can talk about that later on.
• 7:19
  SPEAKER_01: But before we begin with the questions, I want to just maybe mention that maybe it's a good idea when we ask the question to push pause and think about how you would answer it.
• 7:30
  SPEAKER_01: You know, we have a lot of different listeners with a lot of different backgrounds, and we have gotten a ton of feedback from this email questions and responses to this kind of series that we're doing.
• 7:40
  SPEAKER_01: So I'm curious about that.
• 7:42
  SPEAKER_01: If you hear us ask the question, push pause, think about how you would answer it, and then resume listening, of course, and see how we go about it.
• 7:49
  SPEAKER_01: Not that we're the developers.
• 7:52
  SPEAKER_02: Very few answers here that are exclusively right.
• 7:55
  SPEAKER_02: You know, that there's a lot of potential good answers here and some potential sort of less good answers.
• 8:00
  SPEAKER_02: But yeah, push pause and reach out to us.
• 8:02
  SPEAKER_02: You can find us on all the social medias at Planet Geocast.
• 8:05
  SPEAKER_02: You can send us an email, planetgeocast at gmail.com, or go to our website, planetgeocast.com.
• 8:10
  SPEAKER_02: There you can kind of find out more information about us, listen to all the past episodes, subscribe and uh support us as well.
• 8:17
  SPEAKER_02: And also the last thing, if you kind of are struggling with some of the terms that we're covering here in this podcast or in this series, our Camp Geo is sort of designed for that.
• 8:26
  SPEAKER_02: So you can go there, you can listen to what it's what we're calling conversational textbook.
• 8:29
  SPEAKER_02: We have images of the rocks, the minerals, the processes.
• 8:33
  SPEAKER_02: We're uploading really cool new schematics to that all the time.
• 8:35
  SPEAKER_02: We're getting some really cool graphics made.
• 8:37
  SPEAKER_02: Um, and so you can go to that.
• 8:38
  SPEAKER_02: It's the first link in the show notes, and there you can kind of bolster your background knowledge before diving into some of these pretty complicated questions about plate tectonics, Chris.
• 8:46
  SPEAKER_02: So, with that, let's get started here with the first question that I think you wrote this one initially is what would Earth look like if plate tectonics was not an active process?
• 8:56
  SPEAKER_02: So, what would the earth look like if plate tectonics was not active?
• 9:00
  SPEAKER_02: And this is a really cool question.
• 9:03
  SPEAKER_02: So, where did your mind go when you were writing this?
• 9:06
  SPEAKER_02: And maybe what did some of your students say to this answer?
• 9:08
  SPEAKER_02: I'd be curious.
• 9:10
  SPEAKER_01: Um, I did not get a good reaction from them on this question.
• 9:14
  SPEAKER_01: In other words, they they really this is something that they hadn't even thought of, you know, and so that makes it difficult just from the onset.
• 9:21
  SPEAKER_01: Like this was never on their radar, so that was a difficult one.
• 9:25
  SPEAKER_01: But we live on an amazing planet.
• 9:27
  SPEAKER_01: I mean, it is just exceedingly beautiful, and you know, that's one of the reasons why you and I are in geology, let's be honest, right?
• 9:35
  SPEAKER_01: This gives us a one of the best excuses on the planet to go and see cool geology, right?
• 9:41
  SPEAKER_02: And we almost on that note, we can go, we can we get to experience those beautiful places in a whole new way because we get to look at the rocks and sort of understand what's going on, even at a basic level, even with just a basic geology understanding, you get to appreciate beautiful areas in a completely different way than other people do, anyway.
• 9:57
  SPEAKER_01: That's right.
• 9:58
  SPEAKER_01: You can't think about words you don't know, right?
• 10:00
  SPEAKER_01: And so the more you know about geology, the more you're able to like think about the world that's around us, and that's really what you and I get excited about.
• 10:07
  SPEAKER_01: So if we're gonna go to see really cool geology, almost always, not always, but almost, it involves some sort of mountains, right?
• 10:18
  SPEAKER_01: And mountains are almost always formed due to some sort of plate tectonic activity.
• 10:26
  SPEAKER_01: And so if I'm gonna summarize it in a really simplistic way, where does my mind go?
• 10:32
  SPEAKER_01: Our planet is gorgeous because of plate tectonics.
• 10:37
  SPEAKER_01: We have the mountains, we have these you know, rivers and valleys and everything in between, largely because of plate tectonics.
• 10:45
  SPEAKER_02: So I guess the inverse of that would be that if if to answer the question directly, if there was no plate tectonics, the Earth would not be beautiful in your kind of answer to this question or where your mind goes, is that the idea?
• 10:58
  SPEAKER_01: Yeah, I I don't want to make any enemies here, but if you take a Mars people and Venus people cover your ears.
• 11:07
  SPEAKER_01: No, but like if you think of a place that is a long ways away from any kind of tectonic activity, um, and is relatively quite flat and to me geologically kind of boring, I think of places like Nebraska or you know, sometimes like Florida, and Florida's got the weather.
• 11:27
  SPEAKER_01: I didn't mean to offend anybody like that, but um they're not to me the most geologically exciting areas, and it's because they are so far removed from any plate tectonics, they haven't been glaciated, um, and so you just end up with just I don't know, bland, flat topography, you know, not much.
• 11:50
  SPEAKER_02: Yeah, that's right.
• 11:50
  SPEAKER_02: And you always phrase this, Chris, as like there's two forces, the forces that push things up, which is uh plate tectonics, and the forces that knock things down, which is erosion on our planet.
• 11:59
  SPEAKER_02: And if you stopped plate tectonics, sort of this is kind of the a little bit the way my mind goes when we discuss this question of removing plate tectonics from Earth, is that if you just stop plate tectonics, stop pushing things up, then the only process you have is pulling things down.
• 12:14
  SPEAKER_02: And you're gonna knock things down, you're gonna erode everything to just at or right around sea level is sort of where erosion is trying to get the land surface is to get it under the water or right near there.
• 12:25
  SPEAKER_02: And so, you know, once that happens and you don't have anything built up anymore, we have a very different planet and it will evolve in a very different manner from that point forward as well, too.
• 12:35
  SPEAKER_01: And then the only kind of tectonic activity or or resembling tectonic activity that I can think of without the traditional mechanisms of tectonics would be isostic adjustment, right?
• 12:45
  SPEAKER_01: You know, if you take these mountains and you remove the mass that's on them, then the mantle below is going to respond by uplifting them, at least until they've lost enough mass where you don't get isostasy anymore.
• 12:58
  SPEAKER_01: And you get the same thing with deposition, right?
• 13:01
  SPEAKER_01: We have this going on with the Mississippi River, for instance, when it empties into the Gulf of Mexico.
• 13:05
  SPEAKER_01: The weight of that sediment causes that delta to sink.
• 13:09
  SPEAKER_01: And then that allows for more deposition, which causes it to sink and so on.
• 13:14
  SPEAKER_01: So you get this kind of isostasy, which can be episodic.
• 13:18
  SPEAKER_01: You can have earthquakes and seismicity associated with that, but it's not really plate tectonics.
• 13:23
  SPEAKER_01: But I think like that's what we would be reduced to eventually.
• 13:26
  SPEAKER_02: Let me just build on that, Chris, because that was a that's a great point and a great description of this isostic adjustment kind of thing.
• 13:32
  SPEAKER_02: Because I think it's important when we're talking about this plate tectonic process, especially in the context of other planets and other options.
• 13:39
  SPEAKER_02: It's good to really think about what are the other options.
• 13:42
  SPEAKER_02: So plate tectonics is the Earth's surface is broken up into discrete plates.
• 13:48
  SPEAKER_02: So we have tectonic plates, they migrate around.
• 13:51
  SPEAKER_02: We've got the North America plate, we've got the Pacific plate, the Wanda Fuca plate's almost gone.
• 13:55
  SPEAKER_02: You know, we have all these different tectonic plates that are interacting with each other.
• 13:59
  SPEAKER_02: They're moving horizontally.
• 14:00
  SPEAKER_02: So most of the movement is horizontal in these plates.
• 14:03
  SPEAKER_02: Now, if you remove that, if you say there is no plate tectonics, the question is what else could there be?
• 14:09
  SPEAKER_02: And really what we're talking about is what we call a stagnant lid planet, is one sort of other category of non-plate tectonic planets, which Mars is one of them, the moon is one of them.
• 14:21
  SPEAKER_02: And this is just you have a single lithospheric plate that covers the whole planet.
• 14:26
  SPEAKER_02: And so what you're describing is this lithospheric or lithostatic adjustment.
• 14:30
  SPEAKER_02: It's basically all vertical motion, and and that's the only thing that's going on.
• 14:34
  SPEAKER_02: There's very little like horizontal motion going on, and there could be a little bit, but not a ton.
• 14:38
  SPEAKER_02: And so you get these sort of um these bulges maybe that are forming, but it's all kind of vertical up and down movement, not horizontal where plates are sinking down and diving down underneath of other plates at subduction zones.
• 14:51
  SPEAKER_02: So I just want to kind of level set on sort of what the other alternatives are for a non-plate tectonic planet, basically.
• 14:59
  SPEAKER_01: Right.
• 14:59
  SPEAKER_01: And you bring up a good point.
• 15:00
  SPEAKER_01: I mean, uh really the only thing that we can look to are the other planets that we are close enough for us to study kind of in detail, right?
• 15:08
  SPEAKER_01: And that leads us to the next question, or a sub-question of this really is about Mars.
• 15:15
  SPEAKER_01: Mars has all, all of our solar system's largest volcanoes, the biggest one being Olympus Mons, and it is unbelievably hard to imagine huge.
• 15:28
  SPEAKER_01: It's right.
• 15:30
  SPEAKER_01: So that's the biggest volcano in the solar system.
• 15:32
  SPEAKER_01: And the question is, well, why does a planet that doesn't have plate tectonics, which we tend to think of as the mechanism for generating magma, right?
• 15:42
  SPEAKER_01: Why does it then have these absolutely enormous volcanoes?
• 15:47
  SPEAKER_01: So push pause on that a second and think about it, right?
• 15:50
  SPEAKER_01: Like if it doesn't have plate tectonics, we do, you'd think we have the biggest volcanoes, but actually the answer lies in that because we have plate tectonics, our volcanoes never get to be that magnitude.
• 16:04
  SPEAKER_02: Yeah, I mean it's a great question.
• 16:05
  SPEAKER_02: This is a and a really kind of fundamentally interesting one is why are they there, right?
• 16:09
  SPEAKER_02: So I'm gonna start.
• 16:10
  SPEAKER_02: Maybe I could, Chris, take the first half of this answer and and then you can, I think, build on it, and I think I know where you might go with this this question.
• 16:18
  SPEAKER_02: So, first of all, we have to think of why is there volcanism?
• 16:21
  SPEAKER_02: Why is there melting going on in Mars, right?
• 16:24
  SPEAKER_02: Like if it's a stagnant lid planet, it's got one lid, the lithosphere is all one piece covering the whole planet.
• 16:31
  SPEAKER_02: There's actually something really important that we have to consider, and that's heat.
• 16:34
  SPEAKER_02: Heat has to get out.
• 16:36
  SPEAKER_02: Heat is trying to escape this planet, right?
• 16:38
  SPEAKER_02: And basically what we've done is we've taken a heat blanket, the lithosphere being a heat blanket, and we've just covered the whole planet in a single heat blanket.
• 16:45
  SPEAKER_01: I want to interject something a second, Jesse, because I want you to explain for everybody why there is this heat source.
• 16:50
  SPEAKER_01: You said why it can't get out, but why is there a heat source there?
• 16:54
  SPEAKER_02: Yeah, so there's sort of three ways, or there's three sources of heat in a planet, in a planet like Mars at least.
• 17:02
  SPEAKER_02: First is just accretionary heat.
• 17:03
  SPEAKER_02: So this is heat left over from when the planet formed.
• 17:06
  SPEAKER_02: A lot of that gravitational energy of things colliding together is stored as heat in the planet, and so it's hot inside of it.
• 17:13
  SPEAKER_02: The second one is radioactive decay.
• 17:15
  SPEAKER_02: So there is uranium, thorium, and potassium in Mars, in the interior of Mars, and as those elements decay away, they release energy which becomes heat.
• 17:23
  SPEAKER_02: And so that heat has to escape as well, or is trying to escape.
• 17:27
  SPEAKER_02: And the third one is um we don't quite have a great idea of the interior picture of Mars, but at least on Earth, the crystallization of the core is releasing heat.
• 17:36
  SPEAKER_02: So the liquid outer core, when crystals form, they release heat, latent heat of crystallization.
• 17:42
  SPEAKER_02: So they actually are pushing heat, and there's heat coming out of Earth's core into the mantle as the inner core is crystallizing.
• 17:48
  SPEAKER_02: So that probably is going on to some degree at Mars as well, or it did in the past at least.
• 17:52
  SPEAKER_01: Maybe I can interject something with that, the you know, the heat from crystallization.
• 17:56
  SPEAKER_01: It's it's like this evaporation is a cooling process, right?
• 18:00
  SPEAKER_01: So when liquid molecules evaporate, the result is that it's a cooling process.
• 18:05
  SPEAKER_01: And we feel this when we, you know, our our bodies get wet from sweat or you know, just got out of a pool or something like that.
• 18:11
  SPEAKER_01: Evaporation happens, and we feel that almost immediately, the cooling process of that.
• 18:16
  SPEAKER_01: Well, crystallization is the opposite of evaporation.
• 18:19
  SPEAKER_01: So condensation is a warming process, then it's the opposite of what we feel when we get out of a pool.
• 18:25
  SPEAKER_01: So it's a warming process, and that's the heat that you're talking about.
• 18:29
  SPEAKER_02: Exactly.
• 18:29
  SPEAKER_02: That's a great, great analogy, Chris.
• 18:31
  SPEAKER_02: Absolutely great analogy.
• 18:32
  SPEAKER_02: So the you know, why is the planet melting?
• 18:34
  SPEAKER_02: Why is there volcanism?
• 18:36
  SPEAKER_02: Well, the interior of the planet's solid, but it's it's heating up because there's all this heat and it's got this heat blanket over it that can't escape.
• 18:42
  SPEAKER_02: The lithosphere, the single lid, the stagnant lid, is not allowing heat out.
• 18:46
  SPEAKER_02: So that heat builds up and eventually will start melting.
• 18:49
  SPEAKER_02: And it'll do this partial melting.
• 18:51
  SPEAKER_02: We've talked about this uh, you know, ad nauseum on Campgeo because it's such an important thing, but it starts this partial melting, which produces magma, and that stuff wants to escape too.
• 19:00
  SPEAKER_02: And so it'll eventually puncture through this stagnant lid.
• 19:03
  SPEAKER_02: It'll build up and kind of create a volcano that breaks through the single lithospheric plate.
• 19:09
  SPEAKER_02: And then what happens from there, Chris?
• 19:10
  SPEAKER_02: Why does it get so big?
• 19:12
  SPEAKER_01: Yeah, that's the whole thing.
• 19:14
  SPEAKER_01: You did a really good job, by the way, of explaining how the heat goes and it creates its own plumbing network, right?
• 19:19
  SPEAKER_01: It just for whatever reason, you get this center where there's melting that's taking place below the lid and it finds a way to the surface.
• 19:26
  SPEAKER_01: Well, because there's no tectonics, the plates then there it's one rigid lid that has a plumbing system leading to the surface.
• 19:36
  SPEAKER_01: Because the plates aren't moving, the magma just keeps erupting out of that one eruptive center.
• 19:42
  SPEAKER_01: Whereas on Earth, it creates an avenue, but then the plates move and it creates a new avenue, and the plates move, and you just keep getting this.
• 19:50
  SPEAKER_01: So you get volcanism on Mars that just piles up and piles up and piles up, and over time then you get these just absolutely massive volcanoes because they're not going to be strung out in a chain like you would get here on Earth.
• 20:08
  SPEAKER_02: Right.
• 20:08
  SPEAKER_02: And you use this great analogy in class, Chris, which I've stolen shamelessly, is that you hold a lighter, you have a little hand lighter, you light it, and you hold a piece of paper over it.
• 20:16
  SPEAKER_02: And on Earth, that piece of paper is the tectonic plate and it's moving.
• 20:20
  SPEAKER_02: And so think of Hawaii.
• 20:21
  SPEAKER_02: There's a hot spot, which is the lighter, and a piece of paper which is moving over that hot spot, which creates a linear scar in that piece of paper.
• 20:29
  SPEAKER_02: And also on top of that, it would be in our analogy here, we'd be piling up lava on top.
• 20:34
  SPEAKER_02: And in Hawaii, we have this chain of volcanoes.
• 20:36
  SPEAKER_02: Olympus Mons, you're just holding the lighter underneath a piece of paper, and that paper's not moving.
• 20:40
  SPEAKER_02: So you just burn a single big hole in the piece of paper, right?
• 20:44
  SPEAKER_02: And it piles up and all that lava piles up and creates a huge volcano.
• 20:48
  SPEAKER_02: So that's a a really great explanation, Chris, of how this or I guess of why Mars has the solar system's largest volcanoes and Earth does not, which is an interesting juxtaposition there.
• 21:03
  SPEAKER_01: Right on.
• 21:03
  SPEAKER_01: So let's move on to the next question, which I gotta I'm a little worried about you and this because this is your thing.
• 21:10
  SPEAKER_01: Um the next question is you know, Jesse, I'm looking at you over your shoulder, and you have these Harvard classics there, which I gave you a long time ago.
• 21:20
  SPEAKER_01: I'm I'm starting to think that you need to start reading more of those and less of your science papers because every time we get together now, you come up with these weird things like, oh yeah, read a paper on this, and I don't know.
• 21:32
  SPEAKER_01: I think you need to become a little bit more well-rounded, Jesse.
• 21:35
  SPEAKER_01: So you're a little bit too big about any one of those books.
• 21:37
  SPEAKER_01: And all right.
• 21:40
  SPEAKER_01: So here we go.
• 21:42
  SPEAKER_01: Is there granite on other planets?
• 21:46
  SPEAKER_01: That's the next question.
• 21:47
  SPEAKER_01: That's the question.
• 21:48
  SPEAKER_01: Okay, so push pause, think about that.
• 21:50
  SPEAKER_02: And if you haven't listened to sort of part one in this series, you know, we talked about how plate tectonics helps explain the formation of granite on Earth, and so in that episode, we kind of alluded to the fact that plate tectonics might be intimately related with granite production.
• 22:05
  SPEAKER_02: So the question then is is there granite on other planets?
• 22:08
  SPEAKER_02: Chris, what did you think about?
• 22:09
  SPEAKER_02: Well I think I wrote this question.
• 22:10
  SPEAKER_02: So what did you think about?
• 22:12
  SPEAKER_02: Where did your mind go with this?
• 22:14
  SPEAKER_01: Well we don't know of granite on any of the other planets in our solar system.
• 22:20
  SPEAKER_01: You know, Mars on down to to Mercury.
• 22:22
  SPEAKER_01: So there's no granite.
• 22:23
  SPEAKER_01: There's a ton of basalt but no granite.
• 22:27
  SPEAKER_01: Okay.
• 22:28
  SPEAKER_01: And out of my question went to silicates right away.
• 22:33
  SPEAKER_01: The silicate minerals, you know, the sheet silicates and the framework silicates of the most abundant mineral group on the crust on the continental crust I should say of the earth.
• 22:42
  SPEAKER_01: And so that's where my mind went and and it interesting when I saw that you wrote this question, yours went a different direction.
• 22:49
  SPEAKER_01: You right away went to water you know which I want to talk about because I want to hear your answer because I have some thoughts on this about water.
• 22:57
  SPEAKER_01: So you have this this punchy kind of title up there.
• 23:01
  SPEAKER_01: I think it comes from a paper that you read.
• 23:02
  SPEAKER_01: It's called No Water, No Granites, No Oceans and No Continents.
• 23:08
  SPEAKER_01: So why don't you talk about this a little bit and why water is important in the formation of granite.
• 23:14
  SPEAKER_02: Yeah so that title No Water, no granites, no oceans, no continents, kind of flows together.
• 23:19
  SPEAKER_02: I mean it says if there's no water then there's no granites.
• 23:22
  SPEAKER_02: Therefore if there's no oceans on Earth then there's no continents on Earth.
• 23:25
  SPEAKER_02: And it's mostly pretty accurate.
• 23:29
  SPEAKER_02: So why is water tied to the formation of granites is the first question here.
• 23:33
  SPEAKER_02: Well the way that melting happens we've talked about minerals and rocks that have water in them and we don't mean like a water molecule like in a pore space in the rock.
• 23:43
  SPEAKER_02: We mean a mineral group in the rock that has an OH group hanging on the end of it or an OH group that's part of the crystal structure.
• 23:50
  SPEAKER_02: So that's for our intents and purposes water in the rock is hydrous minerals minerals that are hydrated.
• 23:56
  SPEAKER_02: And rocks that have hydrated minerals in them melt at much lower temperatures than rocks that do not have hydrated minerals in them.
• 24:04
  SPEAKER_02: So if you try and melt the mantle which has very little water in it as default you try and melt the mantle it's really hard you've got to get to high temperatures at any given pressure to melt the mantle.
• 24:15
  SPEAKER_02: If you add water to that system you can melt it at much lower temperatures and much lower pressures at the same sort of conditions, right?
• 24:22
  SPEAKER_02: So adding water to the mix makes things melt quicker.
• 24:25
  SPEAKER_02: It also kind of changes the composition of melts that are produced.
• 24:29
  SPEAKER_02: So the partial melting happens at different pressures and temperatures but also the melt composition that is produced changes dramatically as well.
• 24:39
  SPEAKER_02: So true granites like real granites on earth which has a specific definition it has potassium feldspar sodium doc.
• 24:47
  SPEAKER_01: Yeah getting into the weeds here doc that's all right all right come back come back to reality.
• 24:52
  SPEAKER_02: All right the main point here can I just all right go ahead.
• 24:55
  SPEAKER_02: Well I can let me let me just try and make the connection here to the end of this statement.
• 24:59
  SPEAKER_02: So if we so water helps it is really instrumental to producing granite and therefore oceans on Earth are where all this hydration happens where a lot of water is mixing with rocks is interacting with rocks.
• 25:10
  SPEAKER_02: So the idea there at the the later part is if you didn't have oceans we wouldn't have continents which kind of ties that uh comes full circle there.
• 25:19
  SPEAKER_01: So okay so two things I want to say Jesse one is that when water is involved in melting you called it partial melting and the general rule is is like this so ultra mafic which means ultra rich in iron and magnesium the composition of the mantle if you partially melt that you generate a magma that is less mafic than what you started with.
• 25:41
  SPEAKER_01: So now you go from ultramafic to mafic if you partially melt that you go to intermediate in composition and if you partially melt that you go to a felsic end member composition which is granite.
• 25:51
  SPEAKER_01: Okay so that's the general rule of of what you were just describing there in a detailed kind of way.
• 25:57
  SPEAKER_01: The second thing that I want to say is though both Mars and Venus we are exceedingly confident that both of them had water at one point.
• 26:09
  SPEAKER_01: Yet there's no granite.
• 26:11
  SPEAKER_01: So do you have a thought about that?
• 26:15
  SPEAKER_02: It's a great question.
• 26:16
  SPEAKER_02: I would kind of wiggle out of it and say that we don't know that we don't have granite.
• 26:22
  SPEAKER_02: Like we haven't found a ton of granite on either planet.
• 26:25
  SPEAKER_02: Now on Mars it kind of goes back to this resurfacing question or this volcanism question.
• 26:30
  SPEAKER_02: Like there could be an argument especially on Venus we'd need to have a look at the interior of the planet we'd need to drill down and evaluate is the middle part of the crust does it have granite in there or not?
• 26:42
  SPEAKER_02: Because you can envision a scenario where there were some sort of continents, pseudo-continents around and then the planet sort of died from a plate tectonic standpoint, became a stagnant lid planet and then it got resurfaced the surface is all basalt because of this sort of heat pipe volcanism that's pumping stuff out like Olympus Mons and just resurfaced the planet.
• 27:00
  SPEAKER_02: So it's an open question I would say particularly for Venus about how much granite.
• 27:04
  SPEAKER_02: Now I I want to say one thing there are andesites on these other planets.
• 27:10
  SPEAKER_02: There's little tiny fragments of andesite that have been found on Mars.
• 27:13
  SPEAKER_02: And actually there's one that's been found on an extinct protoplanet like what's called a chondritic protoplanet and it is 4.56 billion years old and it's a little andesite classed fragment intermeteorite and it has an andesite composition which on Earth we think that's a subduction zone volcano but on other planets it has some chemical differences that say okay it's not a it's it's not an andesite like we think it forms, but it is an andesitic composition.
• 27:41
  SPEAKER_01: Interesting.
• 27:42
  SPEAKER_02: So maybe the water wasn't around long enough to distill it all the way maybe is that is that a thought that's out there that's that's yes either the water's not around long enough or we have uh this process that we've talked about on Campgeo is fractional crystallization.
• 28:00
  SPEAKER_02: We talked about Bowen's reaction series previously in PlanetGeo here.
• 28:03
  SPEAKER_02: We have an episode on Bowen's reaction series where if you take a magma early form minerals start to crystallize out which changes the composition of the magma and it gets more evolved.
• 28:12
  SPEAKER_02: So you can actually produce andesite if you crystallize something like 80% of a basalt what you're left with is andesite.
• 28:19
  SPEAKER_02: So you can produce small volumes of andesite on any planetary body really if you have a big basaltic magma chamber just by this Bowens reaction series fractional crystallization process but it does not produce huge continents like we think of on Earth.
• 28:33
  SPEAKER_02: So there there is a difference here I guess in the volumes that we're speaking about.
• 28:37
  SPEAKER_01: Okay interesting interesting all right well anything else that you want to add to this discussion then about water granites oceans like what about what I've originally said to my question where my mind went to the silicates themselves like is Earth unique and you know like I think about this that maybe we should do an episode Jesse on the condensation sequence in planet formation.
• 29:00
  SPEAKER_01: Just that one topic you know I think that be especially with your deep background in geochemistry I think you would have a ton to add to this and I can just kind of sit in the background and direct you and keep you out of the weeds too bad you know too much.
• 29:12
  SPEAKER_01: But I think it'd be a really cool topic that would that kind of follows with what makes Earth so unique.
• 29:18
  SPEAKER_01: But what do you think?
• 29:19
  SPEAKER_01: The silicates um what's your thought?
• 29:22
  SPEAKER_01: I think you're you're exactly right and it's first of all tell us what a silicate is a second.
• 29:26
  SPEAKER_02: A silicate is a mineral that has a silica SI as a primary constituent phase.
• 29:31
  SPEAKER_02: So it you know that is a building block for silicate minerals usually it's an SiO4 bond as a silica tetrahedron bond and then you you add some other cations to it to make a mineral calcium, magnesium, iron, something like that.
• 29:43
  SPEAKER_02: So that's the bulk of planet Earth, we have this core part which is metal and then we have the silicate part which is the mantle and the crust and the the lithosphere most of our planets in our solar system have that same sort of breakdown.
• 29:56
  SPEAKER_02: We have cores and we have silicate parts of the planets.
• 29:59
  SPEAKER_02: Now that's because our solar system has generally the same composition and so if you form rock from our solar system it's going to be like a silicate based rock.
• 30:09
  SPEAKER_02: There is some pretty active research in the exoplanets people looking mainly astronomers who look at other stars and look at other planets around other stars and they see that the star has a different what's called metallicity a different ratio of silica and an iron and magnesium in those different proportions and the idea is that you would generate planets around those stars that have different proportions of iron, magnesium, silica, calcium to what our solar system has.
• 30:37
  SPEAKER_02: So for our intents and purposes most people who study silicates in the sol our solar system kind of use Earth as a good analogy for the rest of the planets.
• 30:46
  SPEAKER_02: But that does not necessarily mean that other planets in other solar systems exoplanets have the same process.
• 30:52
  SPEAKER_02: So I think Chris your question is too many variables yeah yeah too many variables but I think your question's a great one when we start to consider exoplanets that are orbiting other stars.
• 31:01
  SPEAKER_02: We really have to consider are silicates the main mineral group or are they a little bit more of a a a smaller you know a a less important mineral group than they are on our planet for instance.
• 31:13
  SPEAKER_00: Interesting.
• 31:14
  SPEAKER_00: Okay.
• 31:15
  SPEAKER_02: Yeah great question I think I get it I'm not sure it gets pretty so it gets pretty armor it gets kind of like this plate tectonics discussion where like if we don't uh think about what we know on earth then how do we think about it?
• 31:29
  SPEAKER_02: Like there's so many other options out there you know you can make a soup you uh you can make a recipe using the periodic table and generate some random compositions how relevant are they to other planets like in other solar systems it's kind of it gets really complicated really quick and there's very few constraints so it kind of gets um difficult to understand for sure.
• 31:47
  SPEAKER_01: Well that leads us into our last question which is a good way to wrap up this episode I think which is why does plate tectonics make Earth a beautiful planet?
• 31:56
  SPEAKER_01: And I think you know I think we've already kind of covered it but it's a good summary right to me it's undeniable that plate tectonics makes Earth beautiful because I love the mountains and so do you and it it it obviously then we have mountains on this planet because of plate tectonics.
• 32:14
  SPEAKER_01: But we also have these massive deep impressive valleys because of plate tectonics too it's because we have this really well first of all because we have an atmosphere you have to have that to have the weather and erosion part of it you have to have an atmosphere okay the uplift which accelerates weather and erosion and the like one of the things that makes mountains so beautiful is how caught up they are how jagged and carved they are right and that's because of water whether that be ice water or running water this is what makes mountains truly beautiful in my opinion glaciated mountains are you know they're just amazing right and so all of this is intertwined with you know you get accelerated weather and erosion if you have plate tectonics rapidly uplifting mountains.
• 33:06
  SPEAKER_01: You can't separate them.
• 33:07
  SPEAKER_02: Absolutely and Chris that really sort of points right in the direction that I was thinking with this answer to this question of why does plate tectonics make Earth a beautiful planet is that plate tectonics makes Earth a habitable planet.
• 33:19
  SPEAKER_02: Plate tectonics is instrumental in keeping our oceans and keeping an atmosphere intact and has all these really important feedback loops that maintain a a moderate climate the only reason we're here is because in large part plate tectonics has been operative on our planet for a long time.
• 33:34
  SPEAKER_02: So that's kind of where I went is like we wouldn't even be able to see it's a beautiful planet unless we had plate tectonics going on you know so um can you give me I wanna I wanna I want to take that a little bit further Jesse can you provide an example of why that's the case like that's a really interesting thought and it's one that I had not I had and it didn't occur to me.
• 33:55
  SPEAKER_02: So the main thing there's there's feedback loops like the main thing that controls climate is the the sort of CO2 content of our atmosphere with our kind of gas makeup of our solar system.
• 34:07
  SPEAKER_02: And so CO2 content controls the the temperature of the planetary surface and when you push mountains up what happens is CO2 is drawn down.
• 34:16
  SPEAKER_02: We've talked about this before the carbon cycle we've talked about how we get salty water and stuff like that chemical erosion pulls CO2 out of the atmosphere by making rocks and and dissolving rocks and putting them in the ocean basin.
• 34:30
  SPEAKER_02: Now if carbon's going down that way what's putting it up into the atmosphere well carbon is going up in most volcano chains.
• 34:36
  SPEAKER_02: So volcanoes are outgassing CO2 in this active feedback loop so we have this this sort of modulating effect and you can think of it this way what happens if I just increase a bunch of volcanic activity and I put a bunch of CO2 into the atmosphere well if we do that weathering's going to happen faster.
• 34:52
  SPEAKER_02: So more weathering means that we're gonna start drawing down CO2 more rapidly and it's gonna go into the oceans.
• 34:57
  SPEAKER_02: So we have to have oceans we have to have uplift plate tectonics to regulate CO2 in this manner and it's a feedback loop.
• 35:04
  SPEAKER_02: We can kind of bounce up to some extremes and down why will weathering accelerate if there's more CO2 into the atmosphere because the reactions will go so if you just it's think of it like a basic chemicals chemical reaction if you put more product in or more reactant in it'll drive the reaction faster in the other direction.
• 35:23
  SPEAKER_02: So if you have a bunch of rust forming on your truck um and you know let's say you suddenly clean off a bunch of rust well that reaction will happen faster because you you cleaned it off and so there's new surface that can be rusted right or if you put a bunch of oxygen you put it in an oxygen chamber that rusting is going to happen really fast.
• 35:44
  SPEAKER_02: So as soon as you add more reactant or product it drives the reaction in the other way the speed of it does that sort of make sense there yeah that yeah you did that that really drove it home.
• 35:54
  SPEAKER_02: I just have another idea I think this is a really good idea and I don't want any pushback on this I think that we need to do a series I'm I'm a yes man now Chris I'm just a sycophant who just goes with whatever you say I think that you and I need to do a series on the carbon cycle oh yeah that sounds it's too big of a topic we can't do this in one or two episodes but we could do a little mini series on the carbon cycle uh what do you think that's a good idea isn't it I think it sounds great I think it sounds great and you know what we're gonna we're probably gonna tie it up with our carbon cycle chapter on Camp Geo that we're putting together pretty soon I'm guessing so um yeah I think it sounds great.
• 36:33
  SPEAKER_01: That's true.
• 36:33
  SPEAKER_01: Yeah okay good deal all right all right man well we're gonna pick up with uh some more questions and and you're gonna have your work cut out for your next episode talking about when plate tectonic started on earth keeping me out of the weeds I think so that's that's right episode four in this series is going to start with the question about when did plate tectonics start on earth and why is this an important question to answer.
• 36:53
  SPEAKER_01: This is Jesse's research it's been his research it's gonna it's you know it's it's consumed massive parts of his life so he has a lot to say I'll do my job.
• 37:02
  SPEAKER_02: I'm I'm good at it yeah so all right man hey that's a wrap you can follow us on all the social medias at Planet GeoCast send us an email planetgeocast at gmail.com and go to our website planetgeocast.com where you can subscribe you can follow us you can support us we always appreciate that and um yeah leave us a review and a rating we really appreciate those still helps the algorithm and gosh check out campgeo we we love hearing feedback on that a couple of you have gone there have found some sort of minor errors in our labeling and we really appreciate that uh sort of feedback so go check it out and let us know what you think also share planet geo with somebody else that really helps us out too and that's yeah we love that we love that all right cheers peace