So You Think You Know Plate Tectonics?? Part 1

Jesse Reimink: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.

Chris Bolhuis: Well, Dr. Reimink, how are you doing?

Jesse Reimink: Christopher. Hi. are you? In a better mood now,

Chris Bolhuis: Um, so I don't know. Not, not really. I don't know what's going on. I'm, uh, I'd rarely do I find myself in the mood I'm in. I don. Cheer me up, Jessie

Jesse Reimink: I'm so excited to spend an hour with you today. This is just the, the best. Chris sits down and he goes, Uh, I'm pretty cranky today. . Oh, good. It's great to see you too, man. Uh,

Chris Bolhuis: but how often do I say that ever?

Jesse Reimink: it's true. It's pretty rare. You're usually in a, in a decently good mood.

So without much intro here, What the heck are we doing,

Chris Bolhuis: well, we, you and I, I feel like we went back a year and a half in time because we actually had arguments over what we're gonna do now,

Jesse Reimink: It's still not clear. If we're, we might break up over this still. I, we haven't quite resolved our issues here,

Chris Bolhuis: I am onto something and you need to just like relax and trust and we'll all be good. But

Jesse Reimink: there was a point where you said, Just trust me. Just trust me, Jesse

Chris Bolhuis: Did. So we are gonna do a series on plate tectonics. Okay. And the reason for this, I want to tell everybody like the backstory on this. Um,

Jesse Reimink: Yeah, let me just interject here because you, you called me in the middle of the day, which you rarely do because your, schedule is like back to back to back with classes. But you called me in the middle of the day, which usually means something's up usually it's like, oh, something's wrong. But you were all fired up and this is what you're all fired up about when you called me in the middle of the

Chris Bolhuis: yeah, So here's what got me going. I, my blood was really going, I was excited and riled and, uh, all of that, all those emotions wrapped up into, into this thing. Well, here's what happened. , I introduced like our next unit in my classes. What we're gonna do, we're gonna talk about plate tectonics, and I'm really excited because, you know, plate tectonics is, that was my aha moment , when I'm in college and this professor just opens up about the power of the earth. I was hooked right there. That was my day, That was my moment. And so when I get to teach this to my students, , I'm super excited about it. Right? Well, I got, this reaction, like, they were not impressed. Like, Ah, Mr. Boyce, we know about plate tectonics. I'm like, oh, do you know

Jesse Reimink: the the vein in your forehead starts to throb a little bit more

Chris Bolhuis: I was like, what do you mean you know about plate tectonics? Like what do you know about plate tectonics? Well, we know what subduction zones are, and we know about, you know, convergent boundaries and divergent boundaries, and that other one that starts with a T, you know, and just stuff like this. I'm like, Okay, well what, what else do you know about plate Teton? And I wasn't getting much beyond that. And then I'm like, Okay, you know, you guys. You got the of plate tectonics You got all the buzzwords. But then I just started asking them questions because plate tectonics is the unifying theory of geology. Well, what does it unify? knowing about divergent boundaries and convergent boundaries, that doesn't unify a whole lot. It's,

Jesse Reimink: me, let me interject here before you get too wound up, because what you sent me. Yeah, no. You sent me a list of like 15 questions that you had given to your students that were like, Prove to me, you know, plate tectonics and these questions are not easy. Uh, they're not super specific either, but they are unifying. So at, at first I was like, Chris, come on man. Uh, I, I don't get it. But you hooked me with that. What you just said right there was how you kind of hooked me saying this is unifying theory. And we have to link plate tectonics to all these other parts of the earth's system. Rocks and minerals and atmosphere and oceans and all these other things. Link it together, plate tectonics, links, all those things. And that was the hook into kind of this thing, right? Like what we're. Introing today, this is gonna be a series of sort of questions about plate tectonics, misconceptions that you come across in the classroom. Deeper kind of thought-provoking questions about plate tectonics that are linked together in a series in, uh, we don't know how long this series might be

Chris Bolhuis: that's right. We don't know how long it's gonna be. I wrote these questions on my lunch period.

Jesse Reimink: fuming. Mad

Chris Bolhuis: No, I wasn't. I don't get mad. I was just a little taken aback, you know? I was shocked actually, cuz I don't remember ever having this experience before. So I wrote 'em on my lunch hour and then my, my next class comes in and I get the same reactions. So I had these questions prepared. I'm like, Okay, well here you go. If you know everything about plate tectonics, prove it. Put it on paper, let me know, and then we can just move on. I will go to other stuff. I'm good to go. But you have to show me that you really know plate tectonics because this is the thing. This has me fired up. this is Geology man, and that's where it came from. I'm glad you said that. I was able to at least convince you the hook and so on. Now the thing. About this though, is that I know where I want to go with these questions, but I don't know where you want to go with this. And so I'm really looking forward to it from that perspective because you come at things from a very different point of view than I do, as you should. I mean, we live in really, really different worlds. So that's gonna be a kind of a fun thing I think, to go through this series. They're not all my questions. I want everybody to understand that. The doctor in the house has added his

Jesse Reimink: So the really sort of weird questions that are really hard to understand, those are But what we're gonna do here, Chris, we've kind of broken these apart into rough categories, I guess some of them are about the rocks that plate tectonics forms, which we're gonna lead into today, at least start today. Some of them are about how earth is unique compared to other planetary bodies and how plate tectonics drives that uniqueness. We've got other things like magnetism and how powerful that was to figure out plate tectonics at the beginning, and also how it's useful for understanding the earth. interior structure of the Earth. Those are just a couple of, kind of the general categories of questions about plate tectonics that, again, unify our understanding of our planet by talking about plate tectonics. And we'll probably have some on, you know, climate notions and the driving forces and how plate tectonics interacts with that type of thing. So it's gonna

Chris Bolhuis: It's really endless

Jesse Reimink: so let's dive into the first part, but before we get to that, let's just plug Camp Geo, our conversational textbook, if you like Planet Geo, if you like this podcast, but you wanna learn the basics of geoscience. In a very structured manner with the key images that you need to have integrated within the audio content, but decoupled from it. Go to Camp Geo. Go to that link in your show notes. Chris. We're about halfway through building that class and more content is being posted frequently. go there, let us know what you think about it. , we are really excited that that's out there and, um, excited to get people using it and, uh, get some feedback on it. So let us know.

Chris Bolhuis: I think it's very exciting, so I can't wait to get feedback from everyone out there. Jesse, before we start, we need to do a cheers here, so grab your whiskey. Cheers to you,

Jesse Reimink: Cheers to you, man. Here we go. All right, so we're gonna start with my favorite type of rocks, which are igneous rocks. And Chris, the first question on our list here is, how does plate tectonics generate the rock basalt?

Chris Bolhuis: Yes it is.

Jesse Reimink: pause, .That is the first question. Where do we go from there?

Chris Bolhuis: So my approach to this question, and I want you to jump in and interject, like just interrupt. Okay. But my approach to how does plate tectonics generate the rock basalt? Plate tectonics begins at divergent boundaries. Running through the middle of oceans. You have these mid ocean ridges, and you have this atheist fear that is rising up. Convectively below.

Jesse Reimink: Athena Sphere is the plastic, the hot plastic type of the mantle. It's the deeper part of the mantle. It is the non plate tectonic part of the mantle, the part of the mantle that convex and moves around, but it is solid. That's the Athena sphere is the word you're saying there. Sorry, Chris. Go

Chris Bolhuis: Yeah, it's rock that. Solid, but it's soft because it's like right at or right near its melting point. The pressures and temperatures are just right to allow this layer to behave that way. So as the asthenosphere rises up underneath the lithosphere, the. It Convectively cools. In other words, thee reaches the base of the lithosphere, which is the cold, crunchy in brittle the. It rises up below that cools and the lithosphere is pushed apart by this kind of convective flow. Anyway, you have this esteem fear rising up. Well, the esteem fear is a part of the. Upper part of the mantle. Well, that's ultra mafic rock. It's mostly prite. Allic means super rich in iron and magnesium. Well, as this rises up, It partially melts due to the reduction in pressure. Remember, it's right at its melting point. So if you lower the pressure, some of the minerals are gonna melt. Well, what happens then is you take an ultramafic parent rock that is partially melting and we're essentially gonna distill it. We're gonna create material. Then magma that's gonna be mafic. In other words, it's gonna be a little bit more on the fsic side than the parent material.

Jesse Reimink: me just interject I really quick, Chris, and set the stage. Ultra Mafic is one end member of composition. It's rich in magnesium and iron low in silica. Felsic is the other end member of composition that we find on earth. It is high in silica, high in aluminum, potassium, sodium, low in magnesium and iron, and there's a gradient in between there. Maich and intermediate are gradients between FALs It goes ultra May intermediate felsic. Those are the four categories of composition that we're talking about here. So you're exactly right. As this thing upwells, as the mantle, the ultraman mantle rises up. The important point is that it decompresses, It gets to a lower pressure environment faster than it can cool down because if it cooled at the same, Then it would actually never melt, but it rises up faster than it can cool down. It's still extremely slow, but it rises up faster than it can cool down, which means it melts and partially melting. We're talking like seven to 15% melt, maybe 20 or 25 in some rare instances, but we're talking about that amount of melting. So seven to 15% of the ultra mantle is melting in the melt. The magma is may. Which ends up being basalt the rock in the question, how does plate tectonics generate basalt?

Chris Bolhuis: And that's super important Basalt, because it's the most common rock on the surface of the earth. You know the earth is 70 to 75% oceans. The ocean floor is made up of 99% basalt, and it's created by this divergence, which is plate tectonics. If we didn't have the divergence, we wouldn't have the decompression melting. The decompression melting takes. ultramafic parent generates a maik magma and then he erupts out cools and hardens and forms the rock basalt. To me the most abundant rock on the surface of the earth. It being, you know what it is? Basalt makes it important just by. And it's there because of plate tectonics. What do you think?

Jesse Reimink: I like that. I think that's where it's interesting here is that's how a lot of basalt is formed. There is basalt formed in different environments that are not this kind of upwelling thing. We have mantle plumes that form basalt subduction zones, which we'll talk about in the next question. It appears also form some decent amount of basal, but I think basalt's really interesting as well. A basalt occurs on other planets as well that do not have plate tectonics, but they're typically variations on basalt. So the basalt that we're talking about here is kind of particular to earth in some geochemical indications that are two in the weeds for this to really talk about here. But, this basalt is a really interesting variety of basalt that is formed at mid Ocean Ridge settings. Again, just The plates are spreading apart. It's divergent, the pulling apart of the plate stuff up wells to fill the spot that the plate's left behind and it melts and forms new plates. So it's this kind of cycle that forms oceanic crust.

Chris Bolhuis: That's right. And if you look at the Atlantic Ocean, if you look at a map of the Atlantic Ocean and you see in the middle of the ocean, this kind of S-shaped ridge running through it, the mid-Atlantic Ridge, that's where we're talking about every ocean in the world has. Something similar to this. This is just strikingly obvious because that S-shaped ridge follows the contour of the continents that are on the east and the west of it. You know, Africa and South America being the very striking example of this, you. That's where this process begins,

Jesse Reimink: yes, that's exactly right, and I think you hit it right on the head there at the end. This is the first stage. This is the important. Part of the process. Because our second question here, how is Andy produced at a subduction zone is the second question. How is Ando site, which is an intermediate volcanic rock? So this, and Aite is an intermediate rock type. It's in between May and Felsic Compositionally, and it's a volcanic rock, so it came out of a volcano. So how is Andesite produced at a subduction zone? And this is the part of the story. The basalt that we just talked about, it was being birthed at these mid ocean ridge places, often in the middle of an ocean or somewhere in the ocean subduction zone is where it goes to die. . The basalt or the oceanic crust. This is where it's dying. Is that where you're going with this question, Chris? Is that the kind of where we're headed?

Chris Bolhuis: Yeah. And again, one other thing about Basalt that's super important in this process is that it is a high density rock. and that's why basalt then in a subduction zone, which is what you just said, where the plate goes to die, it's where it's gonna dive down beneath another plate. Basaltic Crust is the one that's involved in this because of its high density and acidic plates don't. Abduct continental crust or granite crust that does not abduct. It's gonna be oceanic basalt that is involved in subduction due to its density. So I wanna pass this off to you actually, Jesse, cuz I want to hear your take on this. Um, I feel like you're the expert here on this process, so, Go ahead and lead us into how Plate Tectonics forms the rock and a site, which by the way, and a site is named after the Andes Mountains,

Jesse Reimink: That really helps sort of categorize the rock and put it into a plate tectonics context, because the Andes are a classic subduction zone system, One of the classic ones on Earth. What's happening is the oceanic plate, in this case, the Pacific plate. If you imagine South America, you're looking on the west side. There's all the mountains there, all this huge mountain chain down the west side of South America the oceanic plate to the west of South America is diving down underneath of the continent of South America. Well, let's go back to that basalt, the mid ocean ridge setting. What happened to that stuff in the meantime? It got formed at the East Pacific rise. That's a mid ocean ridge setting. New basalt is formed, erupted under the ocean. It's been sitting under the ocean for a long time. It's picked up water. Carrying water molecules and liquid water, but it has picked it up in the minerals. , the rocks at the surface have been altered. They're forming clays. They're forming a whole bunch of different hydris minerals that have water in their structure. So now this oceanic plate, this basalt, is waterlogged. It's a waterlogged plate. When it hits South America and it dives down, it's more dense. It starts to dive down. And on the modern. Which is a qualifier that I think we'll get to at some point in this plate. Tectonics, you know, sort of path we're taking. Uh, and

Chris Bolhuis: Uh, you're to integrate that in,

Jesse Reimink: I know I wanna talk about old rocks. I wanna talk about old rocks, but I won't, I'll hold back. But on the modern Earth, what happens is that plate dives down in the mantle as it dives down. It goes up in pressure, first of all, but it also goes up in tempera. Gets heated up by the mantle around it, but it stays pretty cold for how deep it's diving down. It goes up in pressure a lot faster than it heats up. So as it goes up in pressure, it reaches a point where those hydrated minerals, the water logged part of the basalt gets squeezed out. They're no longer stable. The water in their structure gets kind of ringed out of the rock itself. Right? And so you

Chris Bolhuis: It's kind of like ringing out a sponge. That's kind of how I describe it. Now, I know that when you pick up a water log saturated sponge, you're literally ringing out liquid water, and that's not what you're referring to, but the analogy still works. It's getting heated. It's getting squeezed, and the water that's in the mineral structures now is getting squeezed, right?

Jesse Reimink: Exactly. And that water is an extremely powerful molecule. I mean, water might, There's a strong case we made that water's the most important molecule on earth because what that water does is when you put it in the mantle, that prototype that we talked about, the prototype that melted as it got risen up in mid Ocean Ridge settings. That prototype, if you add water to that thing, it melts, boom instantly, almost instantly. It melts. because it partially melts, not the whole thing. It partially melts. You add water to it, all of a sudden the minerals in there are very unhappy. They break down and start to melt, and we do this again, 15 to 10, 15, 20% partial melting when you add water to this thing. And now we have magma from the mantle. Is less dense and rises up and it hits the base of the crust. If you partially melt the mantle ultra maik, you get basalt maik. That's first distillation step. Now we've got all that magma, that basaltic magma underneath of the thick South American continental crust, and the way we get Andesite out the top is that basalt. Sits there and crystallizes partially, so it kind of partially crystallizes. It melts some of the continental crust. It's very hot, 1500 degrees centigrade when it hits the crust, which melts a lot of the crust and it integrates a lot of that crustal composition. And it becomes this blended composition between Maik and Felsic, which is and a site. And that's what we get out of the volcanic chain. The stuff that erupts out onto the surface is, and a site. Did I get close to what you're

Chris Bolhuis: Jesse, that was really well put. I loved that explanation. Well done. I just, Paint a picture for where the water's getting driven off. So imagine this subducting plate diving down beneath a continental plate, diving down beneath the west coast of South America at let's say a 45 degree angle. So this is gonna be well under that continental. Fairly deep down where it gets enough heat and enough pressure. So this is not a SU process. The water's getting driven off fairly deep beneath that continental plate , so then that will rise up into the mantle, the water will, that's what causes the partial melting, which then rises up further. And does this kind of blending that you just described,

Jesse Reimink: So ANDAs site is, I said before we were talking about basalt, that basalt is found on other planetary bodies, which it is. Most of the Martian crust is basalt of some variety. It's basically basalt. A lot of the moon is basalt. And Aite is extremely rare on other planets if it's found at all. There's been a series of papers the last five years that are documenting Endo site like rocks on other planets. But they're tiny, tiny volumes. Like there is very little Endo site on any other planet. And the reason is because Endo site is really one of these unique plate tectonic features. Like it's fairly hard to produce and a site, at least how we understand it, in any other tectonic environment apart from plate tectonics, like plate tectonics equals and a site,

Chris Bolhuis: that This distillation process that you described only happens when plate tectonics is an active process. is that a fair

Jesse Reimink: absolutely, and, and you know what we're talking about here. This subduction zone system. It's not a one and done thing. This is a conveyor belt. This oceanic plate that we're describing, we've just described how basalt is formed at a administrative ridge setting. It's pulled apart. It's moved over, and then it's, dives down beneath continent. That's a conveyor belt so we can produce shitloads of by This process like this produces a lot of rocks. For a long time. I mean, subduction zone systems operate on the West Coast of the United States. It operated for about 180 million years. Pretty much constantly producing end aite and the intrusive equivalence of andesite, diorites and gabbros and granite, DIYs and tonite. So, It produces a ton of this stuff because it's this conveyor belt. It's just constantly bringing new, waterlogged basalt to the subduction of squeezing it out, ringing it out, melting the mantle, adding new stuff to the continent. It's a really, really volumetrically dominant process.

Chris Bolhuis: And we have this same process going on in the northwestern part of the United States in Cascadia, where we have from Northern California, Oregon, Washington, and up into Canada, where the Wanda Fuka plate is diving down subducting beneath that part of North America doing this same process that you just described. . It's generating massive amounts of these rocks in particular, and a site. So the same rocks that you're banging around on Mount St. Helens or Mount Rainier or you know, Cascadia Volcanoes, Jefferson and Hood, and so on. They're the same ones that you would see down in South America, along the west Coast too. Same mechanism, same process. We have it.

Jesse Reimink: I just wanna touch, on that again, is that we can go back in the rock record and see the presence of these types of settings because we can see these exact types of rocks, Andys, that look exactly like modern. Andys going back, there's huge. Pulses of this 1.9 billion years ago. There is, and a site in the related intrusive rocks all over the globe found in these belts of 1.9 GA rocks that look a lot like modern seduction zone systems. , and so this has been going on for a long time on earth and really constructed the continental crust. This is how the continental crust was really made. That second distillation step is what gets you from mantle

Chris Bolhuis: So I. Sorry to interrupt. I want to ask you, where is this? 1.9? You said ga, which is billion year old acidic rock. Where? Where is this?

Jesse Reimink: This is kind of all over actually. The base of the Grand Canyon, the fish new shift. There are OIDs that are kind of similar ages of that, that are what we call calc lin, which is the endo site type. It's the category of rocks that includes endo site. there's a whole bunch up in northern Canada, huge belts. One's called the Wopmay Orogen. They're all called Orogenies because they're subduction zone systems that ended with Continental collision. They're kind of all over. If you look at a map, a geological map of any continent, there will be 1.9 ga belts all over the place. it's a really interesting thing,

Chris Bolhuis: That is really interesting. That's, That's awesome. All right. Hey, way to go. My young sage. Nice job. See, I knew I was right. Can you just say it please?

Jesse Reimink: Not yet. Not yet. We're we're not there. Maybe when we get to episode six, you'll get a, You were right outta me, But I will

Chris Bolhuis: All right.

Jesse Reimink: having fun. So

Chris Bolhuis: Let's move to the last question for today in this episode. How does plate tectonics explain the formation of granite? Now, granite is the second most abundant rock. On the surface of the planet. So you have oceanic crust, which is primarily made up of basalt. You have continental crust, which is while it's often covered with a real thin veneer skin, kind of like sedimentary rock and other kinds of things. But below that is granite. So continental crust is typified by granite, making it the second most abundant rock on the surface of the earth.

Jesse Reimink: I think, let me just modify that slightly, Chris, what you just said. If you take the average of the continents, the bulk average of the continents is and is and acidic, right? You know this, but it's usually because The idea is that there's a lot of endocyte in the continental crust for sure. Sure. But we have. And deeper down in the continents. The base of the continents, most people would argue are maik or basalt. So we have this like two layered structure of continents. We have granite up top and basalt down below. there's some debate about that structure of the continents. But if you average mafic andels, like you get intermediate, So the average continental crust, if you take a global average, it might be an acidic, but there's a lot of granite, and the granite is usually the upper half of the continental crust. Continental crust is, you know, between 45 and 75 kilometers thick. So the upper tens of kilometers beneath your feet, if you're listening to this, if you're not sitting on an island somewhere, some beautiful island in Hawaii, if you're sitting on a continent listening to this, the upper, I don't know, 20 kilometers beneath your feet, is usually mostly granite.

Chris Bolhuis: That's good. Good point. Way to get doctory on me, but that's good. I love it. I,

Jesse Reimink: bit in the weeds, but.

Chris Bolhuis: yeah, absolutely. But it's a hundred percent right. Alright, so. How does plate tectonics produce

Jesse Reimink: Exactly. Let me just review quickly. We hit distillation, step number one, which was ultra maik to maik. We hit distillation step number two, which was maik through water to intermediate and endo site. Now we're gonna get to distillation step number three, which is intermediate to. Felsic, we're getting to that last step, last distillation step. This is your like really high, really, really, really aggressive liquor that you've distilled. Or like maple syrup that's been super distilled to get super sugary and really distilled. Um,

Chris Bolhuis: your Ever clear

Jesse Reimink: Ever clear this is the ever clear. That's a good one. Granite is the ever clear of rocks. Um, so granite, basically we have to melt continents. That's how we get granite is either melting, continental crust, partially melting continental crust. If you partially melt andesite, you get granite or you have to take basalt and fractionate the hell out of it. Remove 80% of the mass of the magma by crystallization. In what you're left with is granite. Is that an app description, Chris?

Chris Bolhuis: Yeah, I think so. To me, I would, in terms of the formation of granite to my students, I'm gonna stay away from fractionation.

Jesse Reimink: That's.

Chris Bolhuis: At this point, because it's not as, it's not as important. Now, you correct me if I'm, Cause you're in the, this is the, the space you live in, but it's not as important of a mechanism as distilling the middle part of the continent. That part that you. corrected me on, you

Jesse Reimink: You are absolutely right. There is granite in the oceanic crust, but it's tiny volumes. I mean, it's tiny, tiny, tiny amounts because you have to do so much fractional crystallization to get to granite, so it really doesn't matter for this purpose. You're right.

Chris Bolhuis: Yeah, for our classes, our intro level classes that we teach, they're not ready for that part of it yet. I think it would just be confusing and so on. So we can just stick to, you know what, take that average composition of the Continental crust, that and a site, and let's take it one step further. Let's distill it again. Let's have magma well up underneath it, partially melt, intermediate magma. And guess what You get? There's a theme here. You partially melt intermediate, and you generate now felsic magma, which then cools and crystallizes usually inside the earth. Not becoming extrusive, stays intrusive, forming the beautiful rock granite.

Jesse Reimink: Yes. Another way that plate tectonics does this is. If you take two continents, which are like we said, on average and acidic, and you smash them together, This is what's happening in Tibet right now. The Indian continent is hitting the Asian continent, and you have two continents together. Chris, you said earlier that continents don't abduct. You're absolutely right. Continents do not go down into. What happens, one slides under the other one, when you have continent that is all of a sudden doubly thick, that stuff gets really hot and starts to melt. So there's a lot of granite being produced underneath of. Mount Everest, for instance, right now, because the continent is doubly thick and it's heated up and it's melting like mad down there. But what is it? Melting? It's melting. And a site when you partially melt and a site, you get granite. When you partially melt, Basalt plus and aite mixed together, you get granite out of it. So that's another way that plate tectonics generates granite credit.

Chris Bolhuis: a very good point. And it is the indie, the subcontinent of India that is shoving itself underneath kind of like a sliver underneath Eurasia. The reason why is because before those two continents met, India was riding on an oceanic plate, and it was just a typical ocean to continent subduction zone. At that point, when. That subduction zone brought India to Eurasia. It tried to pull it down. It's like, um, you know, if I, I grabbed your wrist and, and yanked on it, your body's gonna come with it. It tried to, to yank the subcontinent of India down with it into that subduction zone. Didn't work. But it, it shoved it underneath the Eurasian continent. And then now you're talking about, like you said, generating this really hot situation and also lower temperature minerals. They melt easier because they're more fsic,

Jesse Reimink: Absolutely. , Great, point. Felsic rocks on average melt at much lower temperatures than the mantle. You have to get to really high temperatures to melt the mantle over a thousand degrees centigrade to partially melt it. A granite will partially melt at about 700 degrees centigrade. So there's a big difference in those temperatures as to. Temperatures you can achieve within the crust and within the mantle. So that, that's a great point, Chris, that, um, you know, the dynamics of how this works and basically, not only do you have to have continents to form granite, but you have to smash continents together, to form granite to do this third distillation step really in a very general sense. So to form large volumes of granite at it, at least.

Chris Bolhuis: And none of that happens without the movement of tectonic plates. So these rocks are directly tied to plate tectonics. This diversity of rocks is tied to plate tectonics. You know, I think to wrap up, Jesse, this episode, cause I think we're there. There is a theme, right? If you partially melt ultra mafic, you get mafic, you partially melt may. You get intermediate and you partially melt intermediate, and you get fell sick. And then of course, those corresponding rock types.

Jesse Reimink: And that's a process that happens on earth because of plate tectonics on other planetary bodies. We'll talk about this in another, episode on this theme, but on other planetary bodies, you get basalt, but you don't get that second and third distillation step, at least not in large volumes that you get on earth. You don't get 30% of the surface of the earth covered in continents. Again, seduction zones. This is conveyor belt. It's great at this, creating this second distillation step. So plate tectonics is why we have continents.

Chris Bolhuis: and we haven't gotten to formation. how does sedimentary rocks tie into plate tectonics? How do metamorphic rocks tie into plate tectonics? So we have to add to this diverse list. You know,

Jesse Reimink: We actually, uh, had those on the list for this episode and, uh, we're not gonna get there. . Let's cut it off at that and we'll come back to those because again, like you said before, this is the unifying theory. We're gonna talk about how all this stuff is unified by plate tectonics, all the different parts of the Earth system, and we've covered the one category of, of rocks, the igneous rocks. We have sedimentary metamorphic to go. We have all sorts of other stuff to hit under the unifying theory.

Chris Bolhuis: But the one thing that is important to me that I wanna drive home is that I think all too often students think of these rocks as standalone things. Oh, okay. There's granite, there's basalt, there's andesite and this other, all this other rich array of rocks, right? Without understanding what they really mean. Do you know what I mean by that? it's this like skin level understanding of it, but plate tectonics takes it deeper.

Jesse Reimink: It's the difference between, and, and this is something I've, I try and drive home in my class, via some of the questions and I think you've gotten a little exposure to this during Camp Geo. When I ask you the questions at the end of each episode of Camp Geo, I tend to ask questions that are not just regurgitate the definition to me kind of questions. It's put it in context and interpret. Like if you go out there and you see an end. What does that tell you? Like, I wanna know, do you know what that is? And it's difficult because you have to have, like we've talked about this before, the physical geology class or the intro to geology class that you teach and that I teach, that's a difficult class to teach because in order to get all these concepts, you kind of have to have all the names, you have to know all the definitions, and you have to have this linking, this idea, this tectonic framework to link them all together. In order to do this really complicated interpretation step. , and that's one of the difficulties of teaching this class. And one of the difficulties that we went through going through this camp Geo, , conversational textbook that we built. So, I think this is kind of a similar exercise in some ways, is

Chris Bolhuis: Well, yeah, I think you're right. By the way, the questions at the end of each Camp Geo episode, that is my absolute favorite part cuz I never know what you're gonna ask me. And then sometimes you just come up with ridiculous stuff. Like it's just

Jesse Reimink: yeah, sometimes they're a little bit out there. I think sometimes they're okay and sometimes they're great and sometimes they're complete garbage. But you you gotta throw it against the

Chris Bolhuis: They give me a, they give a glimpse into how your mind works and sometimes I really don't want to know

Jesse Reimink: scary place. It's a scary

Chris Bolhuis: Dr. Jesse works

Jesse Reimink: Imagine being here all the time. Oh man,

Chris Bolhuis: No, that's, That's tough. It'd be tough. I feel bad for Tess.

Jesse Reimink: Yeah. Oh man. Well, Chris, I think that's a wrap. We should wrap it up here on, on the part one and, uh, you know, we're gonna keep coming back to this, maybe not all in consecutive order, we'll bounce around, but we'll come back to this theme more and more in the next, , couple months here. So with that, you can follow us on all the social medias. We're at Planet Geo Cast. Go to our. Planet Geo cast.com. There you can subscribe, you can follow us, you can learn about us, you can support us. , follow the links in the show notes and share planet Geo with your friends.

Chris Bolhuis: That's right. Thanks for listening. Cheers.