Office Hours - Plate Tectonics Questions/Comments
Jesse Office Hours November 222 - 11:23:22, 2.37 PM
Dr. Jesse Reimink: [00:00:00] Welcome to Planet Go, the podcast where we talk about our amazing planet, how it works, and why it matters to you. don't have anybody. Nobody's on my team. on my side here. What a big
Chris Bolhuis: I'll be on your team,
Dr. Jesse Reimink: You'll be on my side. You'll stick up for me.
Chris Bolhuis: I'm always on your team, jesse.
Dr. Jesse Reimink: you are, you're always on my side.
Chris Bolhuis: I am. I'm a, I'm a loyal, loyal person.
Dr. Jesse Reimink: are, you are. When you go into like pit bull mode, it's pretty good. I, uh, I need somebody in my corner though. Every once in a while I'm not feeling, I'm not feeling the love at the moment.
Chris Bolhuis: Oh, I, I got nothing but love
Dr. Jesse Reimink: Christopher Huis. What's up?
Chris Bolhuis: How you doing, Jesse?
Dr. Jesse Reimink: I'm good man. It's Thanksgiving break here in the US We got a long weekend. What are we recording? This? Yeah. This, this will come on a couple days. Yeah. We got a long weekend ahead of us. It's kind of nice. Uh, I'm looking forward to it. We got nice weather here in Pennsylvania. It's beautiful.
Chris Bolhuis: Yeah, it is beautiful. here too today.
Dr. Jesse Reimink: [00:01:00] So, well, I've said it before. I'll say it again because you weren't super thrilled with how I said it last time. I wasn't emphatic enough for you, but, uh, . I was wrong. Christopher. I was wrong. I will take that one standing up and say I was wrong about the plate. Tectonics ones. We actually got a lot of questions about this do you know plate tectonics theme that we're, I don't know, a third of the way into,
Chris Bolhuis: we're not just questions we touched a nerve. We got, we got emotions too.
Dr. Jesse Reimink: Really good questions, really good comments. Really good thoughts from, from a lot of you. So today we're gonna have office hours. We're just gonna talk about a couple of the, uh, I don't, I wouldn't say more interesting, but a couple of the ones we could talk about for a while. Couple of the questions and comments that we thought we could speak about with some clarity for a little bit.
Chris Bolhuis: I like that. Did you just come up with that? You've never said that before. Office hours. That's, I like that. Pretty clever Jessie. Way to
Dr. Jesse Reimink: stealing it from another podcast that I listen to frequently. So shamelessly stealing. I like it.[00:02:00]
Chris Bolhuis: That's okay. That's what we do, right? As educators, that we steal, we recognize good things, and we steal it and we own it. That is, That is the number one trait of a good educator right there. So, yep.
Dr. Jesse Reimink: So where are we starting, Chris?
Chris Bolhuis: we are gonna start with a kind of a question about plate tectonics, subduction, and the water that is involved in subduction, and really write Jesse the source of the water. the question kind of centered around whether the water was more about water log sedimentary rocks that get dragged down to subduction zones, or is most of the water from water driven out or rung out of the basalt that is subducted down?
Dr. Jesse Reimink: let me interrupt there real quick. Chris, so this comes from Doug, this question, but Doug also pointed out that we might have glossed over some of the important aspects of sedimentary rocks as well, and that's a fair point. We I don't know, we tend to move quickly through sedimentary rocks, you and I, Chris. It's not, I, wouldn't say our necessarily favorite category of rocks. Is [00:03:00] that accurate?
Chris Bolhuis: I, well, no, no, hold on. Now I, I have some things I don't wanna say about that. You just said a mouthful right there. So gimme a second. First of all, I think it's hilarious with what Doug said about sedimentary rocks, cuz we got people that were defending sedimentary rocks and that we glossed over them. And then we got people that felt the other way completely, that we gave sedimentary rocks way too much credit. Um, people are passionate about their sedimentary rocks, either one way or another.
Dr. Jesse Reimink: it's great. I, love it.
Chris Bolhuis: yeah. I do wanna say touching to Doug's point about sedimentary rocks and maybe that we glossed over it. I want to be transparent with this. When I talk about sedimentary rocks with my students in my class, I give them full credit. Sedimentary rocks are arguably the most important rocks on the planet. I mean, they hold all of our water, they hold our. Petroleum, our natural gas. I mean, they hold the things and, and oars also. I mean, they hold the things that literally make the world go round. And so they are [00:04:00] exceedingly important.
Dr. Jesse Reimink: Absolutely, Chris and I do the same thing in my class. You know, sediments, as you're saying, a lot of what we care about as societies from a minerals and resources perspective comes from sedimentary rocks, and we talk about them quite substantially in Camp Geo as well. So go check out the link in the show notes to get access to our conversational textbook, we have a whole chapter on sedimentary rocks. And Cathy, um, you know, we, we didn't manage to convince you sedentary rocks are super useful, but I do appreciate, uh, Kathy, we, I really appreciated the phrase Igneous rules. Sedimentary rules. That was a really good one. I might, uh, I might steal that one too. in class.
Chris Bolhuis: I gotta interject, Jesse. I, I just had an idea. uh, oh, here we go again.
Dr. Jesse Reimink: Oh no. Chris
Chris Bolhuis: right. I, Hey, it is apparent we need to do a little mini-series on sedimentary rocks. I, we just,
Dr. Jesse Reimink: We did, that. Man. It's called, Camp Geo, chapter three.
Chris Bolhuis: No, but I'm talking [00:05:00] about like, no, no, I understand that. Okay. That was like, I'm talking about the subtleties of sedimentary rocks and why they're so important.
Dr. Jesse Reimink: Yeah. Yeah.
Chris Bolhuis: Okay. We didn't do that in Camp Geo. We just, we did the basics. I'm talking about, all right, what's in 'em? Why are they important? We can talk a little bit about fracking. Uh, the controversy behind that. I don't argue with me. I am, I'm right on this. You need to stop. Okay.
Dr. Jesse Reimink: no, the ego has run away. Oh, no. I've created a monster here. Oh, good. Okay. Right. Let, let, can we come back to Doug's question here a minute, because it's a really interesting one about, so we had
Chris Bolhuis: No. Hold on. I'm gonna say I want listener feedback on this one Set. Ment your rocks, yes or no. Send us an email, planet geo cast gmail.com. We.
Dr. Jesse Reimink: And I want listener feedback on Chris. Hes always right, yes or no. And, uh, send this an email.
Chris Bolhuis: No. Please don't. Please don't. My wife will. be the first one to respond to
Dr. Jesse Reimink: Yeah, Jenny will just mass vote on that one. [00:06:00] Um, so alright, let's come back to Doug's question here, which was basically kind of the idea behind it. Is that like, what is the. Vector. What is the source? How is water getting down into the mantle? Like what rock is kind of bringing it down there? Right? And you know, there's a couple different ways we could envision this. It could be really water log sediments. You know, we've got these clay minerals right on the top of the sea floor that have a ton of water in them, actually, poor space water. Or we could have things like hydrated oceanic crust. The top couple kilometers of the oceanic crust will be basalt, but that basalt will have interacted with water. It won't really have water. Bugs or poer spaces, but it'll have hydrated minerals. And the question is like, how
Chris Bolhuis: Hold on. Yeah, I think you need to define real quick , what hydrated minerals are a second. Can you do that?
Dr. Jesse Reimink: Yeah, absolutely. That's a good point. So Hydrated minerals are mineral groups or a mineral structure that has an OH group. So it basically has an oh group hanging off the end of the mineral formula. [00:07:00] And so things like Amphiboles will have calcium, magnesium, silica, oxygen, and then they'll be some, oh, in the mineral formula, there's an oh group at the end and that can fit. Larger areas within the crystal structure that water will be in there. So, so water, oh, it's not H two O, but it's Oh, , is integral to the mineral structure. And when you put that mineral under high pressure that, oh. Group will be squeezed out and will bond with one hydrogen to form water, and then that water can move through other rocks as well. So we don't think of it as liquid water. We think of it as an oh group, which to us in our nomenclature is water, in effect, in a mineral structure.
Chris Bolhuis: to you chemists out there, you're thinking that's a hydroxide, which you're correct. The hydroxide gets driven off bonds with another hydrogen forms H two Oh. So anyway, um, the question is though, Jesse, that. Really kind of centers around, to me, the way I interpret it, which one is more important because both are at play. We have waterlogged sediments from [00:08:00] sedimentary rock shales, and sandstones and limestones that are, you know, loaded with water in the poorer space. Some of that gets shoved down into the subduction zone. Some of it gets scraped off in informs that a creary wedge, which can lead to the coastal range and all that, but some of it is dragged down in that subduction zone. So that's one source. The other source is, like you said, that hydrated kind of basalt, that is a part of the chemical formula of the minerals that make up basal. So which one is the most important? I think that's really the heart of the question.
Dr. Jesse Reimink: Yeah, I would agree that that's kind of the heart of, of what this question is getting after, and it's a really interesting one because we can kind of come back to sort of first principles to answer it. So those sediments, as you've said before, Chris, tectonics pushes things up. Erosion knocks things down, things being mountains, those mountains, the stuff exposed above the sea level is continental crust mostly right now. Okay, sure. There's places like Hawaii where there's a little bit of basalt exposed, but [00:09:00] volumetric, it does not affect much about the composition of sediments globally. So the sediments are mostly continental crust and the composition of continental crust is such that it is quite buoyant. And so the sediments, therefore, Will be a composition, which is fsic. It's a pretty buoyant composition. So even if sediments make it down into the slab, they're pretty buoyant and they kind of what we call re laminate, they kind of bounce back up. It's like a bobber. If you got a bobber and a bobber sitting on the surface of the water and you try and tap it down, you can knock it down. You can actually knock it down pretty far if you hit that Bob really hard. But it bounces back up and that's the way to think about sediments as they're kind of in that slab interface. They usually don't make it down super, super, super deep. They can get down a little ways and then they kind of bob back up and kind of get plated to the underside of the crust.
Chris Bolhuis: So let's answer the question then, Jesse, which one is more important, do you think the waterlogged sediments, the sandstones, the shells and the limestones, [00:10:00] or is it the hydrated basalt?
Dr. Jesse Reimink: It's, yeah, it's absolutely the hydrated basalt when it comes to forming volcanoes on subduction zone margins. So forming the ring of fire, it's the oceanic crust, it's the basalt going down because that stuff that generates this kind of conveyor belt where the oceanic crust goes down, it gets dense, and then it's that anchor that pulls the rest of the oceanic plate down with it, which just drags a whole lot more water down very.
Chris Bolhuis: Good point. And then why is this important? And, and I think like , we need to hit on that again, this is very, very important, the water that gets dragged down in subduction zones because that water that gets driven off rises up into that very hot mantle rock and causes partial melting. So the addition of. Lowers the melting point of minerals, which causes then some of those lower temperature pressure minerals to melt and they form then the source of the magma for [00:11:00] the volcanism that occurs on the surface. So it's extremely important.
Dr. Jesse Reimink: Absolutely. it's very important. it is this conveyor belt process, which recycles water from the surface down into the mantle, then to back up the volcano and then out in volcanic gases.
Chris Bolhuis: This leads to one of the most common misconceptions that exist in geoscience is that subduction zones, that oceanic plate melts in the subduction process. And really, it doesn't, it remains relatively cool, relatively brittle. The water that gets driven off of it is important because that melts then the hot mantle rock above the subduction zone. So I think like in introductory, you know, students, when they're first exposed to this, I think it's easy for them to conceptualize that it's the basalt that melts and it's really not. And so that's why this is a really important question from from Doug.
Dr. Jesse Reimink: Yeah, that's exactly right. And because it's not the basalt melting, when the basalt dehydrates controls a lot of where the mantle melts and where it melts and, and the sort of structure of this subduction zone in the details can [00:12:00] vary a lot on earth. Sometimes melting is happening deeper down, sometimes a little bit shallower, depending upon when that slab. Dehydrates when you described it as a sponge being rung out, having the water rung out of it. So when that happens, at what depth that happens really controls where the mantle is melting, which controls a whole bunch of other things, including like economic mineral deposits that often exist in sediments on the top of the, the top of the eventual magnet chamber that reaches a surface. So, great question. Really. Sort of detailed answer there, but it's a, question that points to a really fundamental process, uh, that in a really important consideration when we're thinking about sediments and plate tectonics.
Chris Bolhuis: Good stuff. All right. What's next, Jesse?
Dr. Jesse Reimink: So, yeah. We've got a really, uh, another really insightful question from Kathy about, there's a couple questions tied into here, but it's basically asking about water and how water cycles on a planet through plate tectonics and how it might cycle differently on a planet without plate tectonics, for instance. [00:13:00] If we didn't have plate tectonics, would we just have one global ocean? How much water is being lost to space right now? There's kind of a lot tied up in this question. So, Chris, where did your mind go when you read this Really great question from Cathy, and thank you, cathy.
Chris Bolhuis: I go to this very oversimplified thought that in geosciences there are two opposing forces, forces that lift things up, and that would be plate tectonics and forces that wear things down. Kind of like a big, huge belt grinder from above, just gradually and relentlessly scrubbing everything and making everything flat, and they oppose each other. And so the question really was, well, what happens if plate tectonics stops? What will our planet look like? it is a very interesting thing. Now, you have to understand too, that this is grossly oversimplified in terms of the analogy that I gave. There are more forces going on. But if plate tectonics were to cease. Weathering and erosion then becomes the dominant force, basically it's going to [00:14:00] level everything out, right? The sediments from continental crust are gonna get worn down. They'll be carried by rivers into the oceans. The ocean basins will become less deep than because of, you know, the sediments that accumulate. However, this is where it gets exceedingly complicated because, If you just keep dumping sediments into the ocean basins, the ocean basins aren't just gonna fill up nicely. That's not really what happens. The weight of the sediment is gonna cause them to down warp, you know, and we've talked about that in previous episodes. That's called ISO, or ISO adjustment, which is gonna allow for more sediment a. You know, the net effect, of course, the continents are gonna become, very flat, kind of Nebraska esque, if you will.
Dr. Jesse Reimink: Absolutely. Yeah, I think you're exactly right, Chris. It's if we just stop plate tectonics, no more mountain building, we'd have a lot of flat surface. We'd have a lot of flat stuff right around sea level mostly, but then we'd have to think about how the climate evolves and do we melt all the [00:15:00] glaciers and that raises sea level. A couple hundred meters probably. I don't remember the exact number. We talked about it in our episode with Richard Alley. I'd have to look back and see what the number is there, but a substantial amount. So the sea level change depends a lot on the climate and whether ice is at the poles or not. And the way my mind, well first of all, there's a, a little side question here, which is, are we currently losing water molecules to outer space at the moment? And the answer is partially yes. We lose hydrogen. That's the lightest element. And so some hydrogen is kind of swept away. earth has a pretty strong magnetic field, so we retain a lot of that. But if you kind of remove that magnetic field, then a decent amount could be swept away. Some is retained, by just the gravity pulling at the atmosphere, pulling at the gas molecules. Like for instance, Venus has a. Thick atmosphere, and it retains it and it's super thick, super dense, super toxic. Mars has none. So when we're thinking about these planetary scale processes, it gets really complicated. Like , we have to think about climate, gravity, magnetic fields, tectonics, cycling of [00:16:00] all of these elements. And actually, it's really hard to model these because. They're nonlinear. These things kind of have feedback loops in them that make them really nonlinear. The way I went, and I know I'm rambling, Chris, so stop me here and keep me outta the weeds with this last little point, but I have one more point I wanna make, which is that there's a really good amount of evidence and most of the community agrees that the early earth sort of pre 3 billion years ago, so Earth from four. 3 billion years to about 3 billion years was what we
Chris Bolhuis: Hold on. I'm gonna just let everybody know that I'm gonna take a sip of beer while you're rambling Here because I think I should, I kind of
Dr. Jesse Reimink: I could see you, glazing. I could see you glazing over
Chris Bolhuis: Here we
Dr. Jesse Reimink: You're just about kicking your feet up there on your desk, just like, all right, I'll just sit
Chris Bolhuis: That's right. Yep.
Dr. Jesse Reimink: for him to end.
Chris Bolhuis: have things to say, but I'm gonna wait
Dr. Jesse Reimink: Okay, so basically the ar keyan, what we call the early aian, three older than 3 billion years ago, was a water world continents. Were not above sea level, and my [00:17:00] opinion, you'll get a lot of disagreement about this, but my opinion is that plate tectonics was operative then, so plate tectonics was going on there. Just, we didn't have continents floating above sea level yet. We had all the stuff about plate tectonics, but it was just below sea level, which changes sediments. You don't have as much sediment, uh, production and all that kind of stuff. So, anyway, that's kind of where my mind drifted to as I was reading kathy's
Chris Bolhuis: here. So, alright, here's, can I say where my mind drifted to then in term, because you kinda switched gears, you switched to the other question about water molecules. Right. Um, I think, and, and I want you to correct me if you know if I'm wrong here, Jesse, but you know, generally speaking we're not losing water molecules to space. Earth has enough gravity to hold them. Our magnetosphere holds these things, and generally speaking, we're. but there is something else going on that, our oceans are destined to, to leave us. We're talking now geologic time and in about a billion years, earth is gonna have a real problem because at that point, , the sun will have, heated up [00:18:00] enough and gotten a little bit bigger, which it's doing, which is gonna cause the oceans to, boil away. And so will. turned the way of Venus. If, that's what happens. I mean, you know, that's a, it seems to be the inevitable fate. I think there's a lot of agreement on that, that that's what's gonna happen to the oceans.
Dr. Jesse Reimink: will be kind of a hot house planet like Venus, where it's sort of inhospitable, but the oceans have boiled away and once that happens, it's really hard for tectonics to operate and basically the earth starts to become exactly like Venus. so we'd be outside of the habitable zone at that point.
Chris Bolhuis: That's right. I mean, really we're losing water molecules, but right now, , not, not anything that I think humanity needs to be worried about, but in the future, but not really related to plate tectonics or anything like that, we, we will be losing water molecules a lot,
Dr. Jesse Reimink: so, the last, uh, the last little point I just want to kind of wrap up here is that David sent us a question, well, more of a comment really that gravity is really important [00:19:00] for, formation of subary rocks and the movement of earth plates. And we completely agree with that. You know, gravity is ultimately the sort of driver of a lot of these processes. But I think, you know, that is another thing that we need to consider when we're thinking. Plate tectonics on other planets. And I think Chris, next episode in our, so you think, you know, plate tectonics series, I think is on planetary plate tectonics and what's going on in other planets, which I'm super excited about. But, um, anyways, this is something you need to think about. Cause other planets have very different gravity dynamics have more gravity, less gravity, and that can affect how any potential plate tectonic regime might operate. So that's the only. Comment I have is to say, yeah, great point David. And, um, hopefully we'll come back to that a little bit.
Chris Bolhuis: That's right. Yeah. We can put, we can do the planetary geology next. That's fine. Let's, let's do it. Yeah.
Dr. Jesse Reimink: about that one. near and dear
Chris Bolhuis: We have, we have a It is, it is. Which is a little surprising to me. I mean, you know, I never really, thought of you as a planetary geology kind of guy, but you're really excited. It's kind of your, [00:20:00] your
Dr. Jesse Reimink: Well, everybody's very excited about planetary science and planetary geology, and I'm excited about the early Earth, which is basically another planet. And so I use it to my advantage when it behooves me to sell myself as a planetary geologist. Let's put it that way,
Chris Bolhuis: Yeah. that's, that's interesting. I guess I never thought about it in that perspective, but
Dr. Jesse Reimink: not either until a couple years ago. Uh, which I was like, oh, okay. Yeah, I think somebody said it at a meeting and I was like, oh, that's actually really interesting. I'm gonna use that one again. Back to stealing. Just stealing stuff.
Chris Bolhuis: Hey, don't be ashamed of that. That's what we all do.
Dr. Jesse Reimink: whatever works. Whatever works.
Chris Bolhuis: That's right. Um, so do we, is there a job at NASA in your future then? Is that what you're saying? Is it
Dr. Jesse Reimink: they're recruiting me to run nasa. I don't know if you've heard about this, .
Chris Bolhuis: Okay.
Dr. Jesse Reimink: No, I, I doubt, uh, I'm not nearly smart enough to work at nasa. I have a couple friends who work at NASA and they are very smart, but
Chris Bolhuis: I. would disagree with you there, Jessie. You're selling your,
Dr. Jesse Reimink: I.
Chris Bolhuis: mind a little short. Um,
Dr. Jesse Reimink: Well, [00:21:00] Chris, hey man, I think that's a wrap for office hours today. This was really great. Lots of great questions. Keep 'em coming. And, uh, if you're in the US I hope you're enjoying the long weekend If you wanna reach out, you can send us an email we are Planet Geo cast@gmail.com. Go to our website, planet Geo Cast. Dot com and there you can find out about us. You can subscribe, find social media, links to all of our Instagram and Twitter and Facebook accounts. You can support us there and you can find links. Camp Geo, our conversational textbook for the geosciences. The link is the first one in the show notes too. Click on that. Let us know what you think. We like it more. Content is being uploaded to that all the time. So what's the other thing Chris people gotta do
Chris Bolhuis: they have to share. Podcast with people that care about this planet, or people that should care about this planet. Plus, you know what this is, I love doing this with you, Jesse. I absolutely love doing this with you. It's fun every time we sit across the table from each other and, and [00:22:00] just chat about geology. It doesn't, it just doesn't get any better than that.
Dr. Jesse Reimink: I agree. Having a beer, putting your feet up and listening to me rambling on about random stuff. Pretty good. No, I, I agree, Chris. You know, and it warms my heart. There's no email I like to receive more than, Hey, we just found your podcast. One of our friends shared it with us, and it's awesome. We love it like that, just. That makes me happy. People are willing to share because I think it's a representation that you find it valuable, so do that for us. We appreciate it. All right. Take care.
Chris Bolhuis: Cheers.
