Office Hours - Pollution and Slab Pull
Dr. Jesse Reimink: Catch your radio voice. Chris,
Chris Bolhuis: I got it. How's it sound?
Dr. Jesse Reimink: It sounds good. Chris Bullis from the basement of the Bull Heights household. How, um, how has your recording voice recovered or has it been damaged with all of your [00:00:30] outdoor work and yelling back and forth between you and Jenny? You seem to be doing this weekend
Chris Bolhuis: Yeah, well, we've cut down probably a hundred trees in my backyard. You're not gonna recognize my
Dr. Jesse Reimink: that, you know what? That kind of hurts my heart a little bit. I don't like cutting down trees.
Chris Bolhuis: Well, these are all like scrub trees. , they're really crappy and they're, they're just, they're getting choked with grapevine, you know, so we're just cleaning out, we're leaving all the evergreens in there so all the pine trees and all the maple trees are staying, but everything else is going, so it's a lot of wood and then [00:01:00] lots of cutting. And so I rented a, uh, a tractor with, has a front end loader on it, and then a backhoe on the back and the seat swivels back and forth. And I'm gonna tell you, if I had a do-over that might be a career choice because I had so much fun driving that thing around. and then yeah, yelling for Jenny, you know, like, Jenny, go do this. And she's yelling back at me and neither one of us can hear each
Dr. Jesse Reimink: just see you in your swivel chair. do you have your little BB gun there or your shotgun to shoot at the [00:01:30] ground, dogs or whatever? You're always hasling the ground dogs on your
Chris Bolhuis: they're, they're, they're my nevius. I was driving the thing and I went past my wood pile and a little chipmunk went skirting across me and it just instantly made me mad. You know, cuz chipmunks, they do so much damage and I'm like, oh, that one got away from me.
Dr. Jesse Reimink: you are living out in it, man. It is. I wish I could have been there. I would've loved to just post up on your beautiful deck there, watching you with a beer in my hand watching you and shouting some directions and
Chris Bolhuis: You, you would've [00:02:00] needed multiple beers. You would've needed multiple beers. It was an all day affair.
Dr. Jesse Reimink: Uh, hey, well, Chris.
by the time this episode launches. Yeah, that's right. We will be together. There is a, a session in your Honor at the Geological Society of America's North. Uh, what is it? North Central I think section? Yeah, the, the section meeting, the regional Geological Survey of America meeting. we're having a session in your Honor, which will be quite fun. , I'm giving a talk. A bunch of other alumni are giving a [00:02:30] talk, so we'll be together. I'm flying to Michigan. It's gonna be great. This is, uh, it'll be a good time I'm, I'm looking forward to it.
Chris Bolhuis: it's a huge honor. you and Dr. Medics from Grand Valley got together and behind my back and put this together. actually coming, she's gonna drive down from, from Northern. She's gonna make a seven hour drive so she can attend the session too, which like, here's, I got, I have to ask you this. my parents found out about it and now they want to go. Is that like, do you think they should or would they just be bored outta their mind?
Dr. Jesse Reimink: I think they [00:03:00] should totally go. That sounds great. I was just talking to our, our little buddy Andrew, who I graduated with, who's also giving a talk and um, and you know, we're talking about what. Our talks should look like, cuz this is a bit of a different thing. You know, this, this happens, let me just back up and explain this, this happens in academia quite frequently when somebody very high profile, high profile research professor or somebody, you know, with, with a, with a great deal of, um, Success in their career retires. Usually there'll be a session in their honor. And so my postdoc mentor [00:03:30] retired and there was a session in his honor and basically a lot of people that he mentored would give talks in the session. And it's a really cool thing to sit there and watch get a feel for how much stuff these people are doing, the mentees are doing. And it's really because of the one person, right? So you kind of get this view of like, wow, there's a lot of stuff going on. That's because of, in this case, Rick Carlson inspired a whole bunch of really cool science, and so our goal was kind of to have a similar thing. So all that to
Chris Bolhuis: So are you, are you guys [00:04:00] pushing me out? Are you guys,
Dr. Jesse Reimink: uh,
Chris Bolhuis: this, is this a, a farewell to Chris Bullis?
Dr. Jesse Reimink: Yeah. You can't carry banded iron around anymore, so it, it might be time Chris to, to settle in to, you know, the easy life. No, I'm kidding. Uh, but yeah, I think your parents would, would get a lot out of it, probably,
Chris Bolhuis: Okay. All right. Because then, and Jenny's parents want to go to, so,
Dr. Jesse Reimink: Nice. Yeah, then they totally should. Um, alright.
Chris Bolhuis: yeah. You've been ripping on me a lot, by the way, for the whole banded iron thing. You even texted me yesterday about you [00:04:30] think that's pretty funny, don't you? That I
Dr. Jesse Reimink: I do, I'm gonna make, I'm get ready cuz I'm gonna make a lot of hay outta that one that it's gonna be a running joke for
the next year at least I think so just,
just buckle
Chris Bolhuis: I stopped by my parents li uh, yesterday after I dropped off the tractor that I rented, and, they made a comment to your Kermit voice, so, um, my mom thought that was pretty funny, so,
Dr. Jesse Reimink: You did. Okay. So that's actually a great lead in Chris. We're what we're doing today, we have gotten, I just wanna say this and, and, and thank [00:05:00] everyone who has contributed questions and very nice complimentary emails about our podcast. If you're listening to this and you did that for us, that was great. We really, really appreciate that. But because of that, we've gotten a lot of questions and a lot of really good episode suggestions that we're gonna start to kind of chip away at, I think, and it's far too many for one episode. So what we're doing today, Chris, You and I, we've picked one question for each other that we're gonna ask. And so I'm gonna ask you a question from a [00:05:30] listener and you don't know what I'm gonna ask you. And then you're gonna return the favor. And we're kind of gonna use this as just a, a way to sort of chip away at the many, many great questions. So these are coming in no particular order. And Chris, are you ready for your question?
Chris Bolhuis: I think so. Hit me up.
Dr. Jesse Reimink: Okay, this is an easy one, and I'm gonna get to ask you too because of this one right now. So, first of all, your mother, your mother, Joyce. Oh, Joyce. She sent an email and, , it was very complimentary, but it was also, um, [00:06:00] suggesting perhaps that the, the nomenclature in the words are often above her head, and she alluded to the fact that she had trouble keeping the names of her four boys straight in the household. So Geology words are difficult. And so Joyce is ready for a new word. she's got felts bar down and she's ready for a new word. So what's the new word you think that your mother Joyce should learn? The next bit of terminology?
Chris Bolhuis: Okay. Well first of all, I'm taken off guard [00:06:30] because I had no idea that my mom sent you an email. So
Dr. Jesse Reimink: It wasn't just to me, it was to our planet
Chris Bolhuis: all right, that one got past me. So I, I didn't see that. I thought maybe she was hitting you up, on the sly, not letting her son know about it.
Dr. Jesse Reimink: is
Chris Bolhuis: What word? Should my mom, Joyce, add to her repertoire? That's the question.
Dr. Jesse Reimink: Yeah, that's right. She's got feldspar down, so that can't be feldspar.
Chris Bolhuis: Okay. She's got feldspar. All right. That's the basic of the basic mom, just so you know. Um, [00:07:00] let's see this. So there's so many that jump to mind. Do you have one that you think she should know while I'm
Dr. Jesse Reimink: No, this is,
Chris Bolhuis: that, that, that like,
Dr. Jesse Reimink: This is I. She didn't say, Jesse, I want one from you. She said I'm ready for a new word, Chris.
Chris Bolhuis: Okay, uh, let's, let me think about this a second. Um, I guess my mind right away drifts to the basics of Geology. The unifying thing is plate tectonics, so it probably has to do something with plate tectonics. [00:07:30] So, mom, here you go. The word that you need to know is paleo magnetism.
Dr. Jesse Reimink: Ooh, good one. Okay. And
Chris Bolhuis: be good with this okay. All right, mom, here you go. Paleo magnetism. Paleo is ancient and magnetism is a . Reference to the magnetic record that is preserved in the basaltic or meic rocks on the ocean floor. Usually, not always, but usually. , and this gives us a record then of where [00:08:00] the magnetic north and south pole. Was on the planet at the time that those rocks solidified so very close to the time that they erupted out. and then this, really was the definitive proof that plate tectonics has been happening on earth for a very, very long time. Because it shows reversals. And the only way to get that is to have rock created at a spreading center [00:08:30] and then pushed aside, and then New Rock is created. And so as Earth's magnetic field shuts down and reverses as time goes on, and it just keeps doing this again and again and again, that record is preserved on the ocean floor and the only way to have that is to have plate movement.
Dr. Jesse Reimink: Gotcha. Okay. That's a good one. Paleo magnetism. That's a good one. okay, so that, that was a bit of a cheap one, so I got another one for you a little bit more detailed. Okay. Does that sound all right? Okay. So this question comes from Candace and [00:09:00] Candace. I, I'm gonna kind of summarize this a little bit, but Candace asks about human. Chemical change in plate tectonic cycles. And really what she's after is she says, okay, well the theme here is oceanic crust goes down into the mantle in a subduction zone, the water gets squeezed off that plate and it melts the mantle. Right? And that's how we have ARC vulcanism. Really her question there's a few nuances to it, but basically it's saying, okay, there's a lot of trace stuff that humans have done to [00:09:30] affect the ocean. We have a lot of chemicals that are higher concentration in water than in the background. Before humans, really human progress was substantial. And the question is, how will that, if at all, affect magmas? So if we look 2 billion years in the future, will we see a record of human. Chemical, disturbance in the arc, volcanic record. and would that change how plate tectonics behaves is another kind of side question. So there's a lot of, there's a lot of stuff in here, but what's your knee jerk reaction to that, [00:10:00] Chris?
Chris Bolhuis: Okay. I'm interested to hear your reaction to this question as well, but here's, here's my knee jerk reaction is in terms of how we're affecting humans. The oceans the oceans are getting more carbon dioxide because of, increased greenhouse gases, particularly CO2 being put into the atmosphere. Therefore, the oceans soak those up. And so, I guess that if we were gonna see a change in, you know, several hundred million [00:10:30] years in, in what comes out, if there was anything noticeable in terms of a difference, I, I, it would have to do with carbon dioxide, I would think.
do you think?
Dr. Jesse Reimink: the theme of your answer. I totally agree with, and that's where my mind went as well, is that when we're talking about, you know, trace concentrations of lead or even radioactive materials from nuclear waste, which is something Candace asked about specifically, they're not in a high enough concentration to really affect how melting happens. [00:11:00] Like they're not changing how the mantle melts, and so we don't. I wouldn't think that humans are affecting the plate tectonics system that much like we just, we're not big enough. We don't have that much change. It's the, the, the masses involved and the, the rates of movement are too big. So in that regard, I would say no, we probably don't, but your point is a good one. We're definitely perturbing the carbon . Cycle. And so there could be some sort of unintended consequences about. More carbon maybe going [00:11:30] down in the slab or something like that, but again, there's not much CO2 in magma, so it, like a hundred parts per million is not that much. So if you add 120 parts per million, it doesn't really change the system that much.
Chris Bolhuis: It is the second most abundant gas typically that's in magma though, you know, anywhere from 10 to 15% of the dissolved gas in magma is carbon dioxide. Obviously, water's the most abundant one, but yeah, I forgot about that part of the question because when you read that to me about the nuclear waste, I automatically dismissed that. And, and so when I answered it, I [00:12:00] didn't address that, is because I was thinking, okay, because really this is on the spot. I had no idea what you were gonna ask me. And so it is, it's a little bit of pressure to be honest with this is, but that's okay. It's fun. So,
Dr. Jesse Reimink: well, you did good job, Chris. I, I, I think we're on the same page about this question, and it's a really insightful question actually. Like, you know, we talk a lot about how humans are perturbing the carbon cycle. And this is a huge, like, big, big cycle that operates on. Relatively short timescales. And so it's sort of an obvious and [00:12:30] interesting question of, okay, can humans affect billionaire timescale processes on earth? And, and I think at the moment it does not look that way. But, um,
Chris Bolhuis: Right,
Dr. Jesse Reimink: it's a good question.
Chris Bolhuis: Okay. Okay. Good. Good deal. All right. I have one for you, Jesse. Uh, I think this is right up your alley. Actually, I didn't, I wanna make sure you get your Geology correct. So, I'm, I'm giving you, this is, this is a softball right
Dr. Jesse Reimink: Is this gonna be
Chris Bolhuis: So,
Dr. Jesse Reimink: Is my ans am I gonna have to stay outta the
Chris Bolhuis: Probably you're gonna get all doctor in everybody, but, all right. This question [00:13:00] is from Ava. , she is a master's student at Georgia Institute of Technology, and she's currently doing research on aerospace engineering. And so this question goes back to, , our episode on, so you think, you know, plate Tectonics part six, the Interior of the Earth. And we had a little bit of a discussion about the mechanisms for plate tectonics. And I pointed out that slab pole is becoming, you know, a very primary driving force for plate tectonics, which is a, a little bit of a shift. And I made the [00:13:30] comment kind of off the cuff that, , that doesn't answer how. Slab pull began there. There seems to be a gap in it. I can see it once it starts, how it would become a major driving mechanism. But our, how does it start? And, and so she says her background is that she's taken this class where she's learning about planet formation and it seems intuitive to her that as the body cooled the outer shell or the crust would form cracks. Right. And. Because they're, they're shrinking in volume [00:14:00] and she says, would this not be a viable explanation for some kind of beginning to the process of slab pull?
Dr. Jesse Reimink: Ah, okay. hmm. Great question, first of all. So, okay, we're imagining a magma ocean planet where the whole thing's molten and then the skin is kind of cooling down and starts to crack, right? That's kind of the visual we have in our head, I think. Um, can that start plate tectonics? Um, probably can start plate tectonics, but what we're talking about [00:14:30] specifically is a slab pole, which is basalt turning to elote at depth, and so that it has to get deep down. And then once
Chris Bolhuis: Can you hold on a second? Sorry, I don't want to interrupt your train of thought, but I think a lot of people have heard us talk about Basalt a lot, but what about elote again, can you please explain that a second?
Dr. Jesse Reimink: sure. Eloy is the Christmas tree rock. It's a stunningly beautiful rock, but it's garnet and sodium rich pyroxene. And so, uh, what we call oocyte, there's another word for [00:15:00] Joyce to look up oocyte, but, but, um, It's basically basalt that's been metamorphose to high pressures and low temperatures. So it only really forms in subduction zone settings for the most part. and once that rock forms, it's super, super dense. It's more dense than the mantle around it. And because it's kind of a cool rock it because it's very, very dense. And so that's the anchor that pulls the slab down. That's the anchor that does the pulling in slab pull. , So I guess [00:15:30] let me back up and say that there's a lot of debate about how plate tectonics might have started, and there are theories out there that range from a meteorite impact that kind of hits the earth and punches through the lithospheric lid. And then you could potentially have that dense stuff start to kind of drag down through the hole that the meteorite punched through the lithosphere. , there's other ways to do it that are not really dependent upon slab pull, but. Slab pole is like the modern [00:16:00] mechanism and has been operating for the last like two and a half billion years. So it's a great question. I don't have a clear answer. I will answer the last part that just cooling the outer part of the earth is probably not the thing that did it. So, Plate tectonics doesn't seem to turn on right away. After a planet cools down from a magma ocean phase, the planet needs to cool more than that. To actually have this slab pole mechanism start to be an important uh, driver.
Chris Bolhuis: Okay. Interesting take. My take on this too is that, there's [00:16:30] something else to consider with this question because plate tectonics. it turns on and it turns off in certain areas, and so just cooling and contracting isn't enough to talk about. plate tectonics, starting up again in a different area, you know what I mean? And, and so like, I, it doesn't explain everything. it is just kind of where my mind went with it. You know, we talk about the, these super continents in the past, like Rodinia and Pangea, where they, they [00:17:00] seem to come together at. Somewhat regular intervals, and so you're talking about how you get spreading that stops and then it comes back together and then it spreads again. That has nothing to do with initial contraction of the continent.
Dr. Jesse Reimink: That's a really good point, Chris, and that, that makes me think of something else that I think helps, helps clarify some of this is that what do you need to form, eclogite? You need a basalt that's cool and deep. And so [00:17:30] if you have a mid ocean ridge, imagine like a mid ocean ridge system that's forming new basalt really, in the middle of the ocean. But if the ocean's really small and compact and that plate is subducting like. A hundred miles away, that plate is still really hot when it hits the subduction zone and it starts going down the trench, like it hasn't cooled off very much, and so that slab will be less likely to form eclogite and actually form this slab pull mechanism. If you have a a plate that. Is [00:18:00] forming at a mid-ocean ridge like the Pacific Ocean, and it's thousands of miles away from the subduction zone. It cools off. There's a long time for that plate to cool off and reside under the ocean before it hits the subduction zone. And that forms what we call a cold subducting slab. And that is much more likely to form eclogite and form a lot of eclogite. And so the anchor is bigger there. And so on an early earth, an early planet, the plates are all really hot. Like the first little crust that's forming, those are still really hot plates, [00:18:30] unlikely to have slab pull happen. what you said, just made me think of, of that, to kind of clarify this, so back to the super continent cycle, if you have a super continent, all the continents are in one place on the planet. Let's say they're all in the South Pole, then there's like maybe a mid ocean ridge on the North pole the subduction zone's happening around the continent on the South Pole, and the plate has to traverse the entire planet halfway around the planet. That's a really cold plate by the time it hits the subduction zone. And so this is a really important thing for like how much volatiles get down into the [00:19:00] mantle, um, and, and how the subduction zone actually operates. So, great
Chris Bolhuis: And my, yeah.
Dr. Jesse Reimink: that,
Chris Bolhuis: I think that you're right because as you're talking, my mind is just, just going in a thousand different directions because I'm thinking, alright, well, you know, the severe orogeny that led to the, you know, Laramide, orogeny began, on the order of 120 million years ago. in other words, what I'm saying is that's a long time after the cooling and contracting of the crust. That would've happened after Thea collided with Earth and formed our [00:19:30] moon and all that. So it doesn't explain more recent, plate tectonics.
Dr. Jesse Reimink: No. That that's absolutely true. And, and I think I alluded this, I kind of threw some criticism at the modelers and said that, you know, we don't actually know how to break the lithosphere. Like what? it doesn't just happen randomly. And so probably what's happening is that it's re reactivating old sutures. So old breaks in the lithosphere are getting reactivated by later tectonic forces, cuz we don't really know how it breaks. It's, it's really hard. Like the lithosphere is [00:20:00] really thick. It's, you know, it's really sort of hard to break. You have to. Put a crack that's like hundreds of kilometers deep through the lithosphere to get a subduction zone starting. That's a hard thing to do,
Chris Bolhuis: You know that, that brings up an interesting point that that is a very important principle in tectonics, are these cracks that form that get reactivated. Yeah. I think of, of the Tetons, you know, you have this, the, the Buck Mountain Fault that happened during the La Miroy. And then much, much, much later. Extensional processes take over, but the [00:20:30] faulting happened along a preexisting weakness, the Buck Mountain Fault, which, you know, so it, it is a very important principle. Those, those preexisting cracks.
Dr. Jesse Reimink: Yeah, those cracks actually don't heal very easily. Uh, especially in the crust. They can, they can heal in the mantle a little bit faster, just cause it's hotter. But in the crust, you're, you're totally right. Like it's really, really amazing when you go around and look at faults. Big, big, huge, you know, faults like the Teton fault, they're often very, very often reactivated old faults, just, and it makes sense, right? Like if you start squeezing [00:21:00] something, It's gonna break where it's already been broken. I if it doesn't have time to heal. So they're not like human bones, which, you know, they say get stronger where they break it. It's not like that. It, it remains weak for a long time.
Chris Bolhuis: So thanks again, Ava. That was an awesome question and um, yeah, it really, really made my mind go a thousand miles an hour there.
Dr. Jesse Reimink: That's the thing, Chris, I think all these questions, we got a lot of questions and, and most, the vast majority of them are not simple and not short answers [00:21:30] really. And so we're gonna have a bunch of episodes over the next many months that are based on many of these questions. I think that's our plan at least. So, so stay tuned to more office hours, uh episodes, and more episodes that are directly based on questions we've gotten cuz they take a while to explain.
Chris Bolhuis: Hey, I have one thing, um, way off topic. This is gonna seem like it comes outta the blue, but I was at a, I was at a track meet. , the other day and I came across, uh, our maintenance guy who takes care of the stadium and does an [00:22:00] awesome job. Well, his son is on the track team and he is also an avid listener of Planet Geo. But he always makes comments to me about like, you know, the t Rexes and, you know, how many t rexes are in Ottawa County, bull Heis, you know, stuff like that. And I, I passed by him at this track meet and I shook hands with him and he made a comment to me and he said, Give him hungry water Coach. And I, and I, I shook his hand and I, I walked away and I was thinking, you know, Rob hasn't made a, [00:22:30] he hasn't made a comment about Planet Geo in a long time. And I'm, I'm like, I wonder if he still listens. And then 20 seconds later, I remember, wait a minute, he just made a reference to an old episode about, about dams with hungry water. Yeah. Remember how the water
Dr. Jesse Reimink: water.
Chris Bolhuis: other side and it's
Dr. Jesse Reimink: Yeah. It's hungry. It wants that sediment. That's a great one. I love that. I actually had this just recently. A uh, colleague, of mine was like, yeah, you know, I we're kind of friends and he said, you know, I, there's a whole bunch of people who come up to me and I I talk about you. And [00:23:00] then they say, oh yeah, the, the guy from the podcast, the Planet Drew podcast. So
Chris Bolhuis: The guy from the
Dr. Jesse Reimink: yeah, he is like, he's like, dude, he's like, dude, it's really annoying, you know? Anyway. Yeah, it's fun. It's fun. So thank you very much. We appreciate all the questions, all the nice emails, uh, that, have questions and episode suggestions. Keep 'em coming. We are not ignoring them, even if we don't get to replying, uh, you know, in a timely manner. Uh, we're not ignoring them and we're putting together lists of, of these things to do over the [00:23:30] summer, really. So, hey. If you like Planet Geo, please give us a subscribe, a like, and a review and a rating. Those are really powerful for us. , you can go to our website, planet geo cast.com. There you can subscribe, you can listen to old episodes, see transcripts, learn a little bit about us and you can support us as well. We always appreciate that and, and we're very appreciative to everybody who has supported us in the past. So, I think that's a good wrap, Chris. stay tuned for more Office Hours. Episodes coming your way.
Chris Bolhuis: Cheers.[00:24:00]
Dr. Jesse Reimink: Peace.
