The Science of Elevation - Hypsometry

In this episode, we delve into the fascinating concept of hypsometry and its applications in understanding Earth's topography. We start with a light-hearted email from a listener, but quickly transition into discussing the principles of hypsometric curves. We break down how these curves provide insights into the distribution and stability of Earth's crust, oceanic and continental. Through our conversation, we explore the role of plate tectonics and erosion in shaping the Earth's surface, making this complex scientific topic accessible and engaging, even touching on classroom applications and educational tools.

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Transcript

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SPEAKER_01 0:02

Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. Good old mom coming through again.

SPEAKER_00 0:15

Is it a good day when we get an email from Joyce? Chris, have you read the email from Joyce? No, she said one's on the way. Oh, she did. Okay, so texted me and said, Hey, Chris, I've I've got um an a question for Jesse or something like that, right? Is that is that what it is?

SPEAKER_01 0:33

I don't know if it's not really a question, it's a comment. It's Joyce's word of the day, which is a theme I would love to continue on with. Because what was one we had one word of the day which was feldzbar. Was it feldspar or something like that? Or anorthocyte. She had some word that she really enjoyed that was a mineral from way, I mean years ago. You don't remember this?

SPEAKER_00 0:51

No, I don't remember, but she is she does make a lot of comments about words that we use, and she's she's enthralled by this new vocabulary.

SPEAKER_01 0:59

Like she good, good. We're introducing her to a whole new world of geology vocabulary. This one's not, so Joyce's word of the day is bedraggled.

SPEAKER_00 1:10

Bedragled. How does that fit into was it like a a recent episode that we had?

SPEAKER_01 1:14

Yeah, yeah. So she says bedraggled is an adjective and it's of a person or person's appearance. Messy, dirty, and often wet. Jesse's description of Chris being under the weather. I think when you were sick a while back, I called you and I said we had bedraggled Chris. Wait a minute, you actually used the word? I use bedraggled. I said we have a bedraggled Chris with us or something along those lines. And messy, dirty, and often wet. That just fits you. It fit you perfectly.

SPEAKER_00 1:45

Was mom Bullheis offended that you referred to her youngest as bedraggled? No, no. She ends with, I just love that. So I think it's a compliment. I have to let it compliment my mom, apparently. I don't know. I'll find out. I'll find out. I'm gonna see her later today, I think. So Okay, ask her if it's a compliment.

SPEAKER_01 2:04

I like this. Joyce's word of the day. We and tell her we need more words of the day. Send in her word of the day emails more frequently because they're always a delight.

SPEAKER_00 2:11

Okay. Well, I'm really trying to think of that word that we used that she was so impressed by.

SPEAKER_01 2:16

My memory is terrible, but it was not a geologic word. It was just a No, I think it was a geologic word. I think it was uh I think we were talking about anorthite or I'm not sure plagiarist or something. Some some Felsbar composition. I could be way off.

SPEAKER_00 2:29

I don't know. I can't keep up with my mom's wonderings about what we talk about. I I they get they get shoved to the way back in my head sometimes.

SPEAKER_01 2:37

Of course, of course, of course. Well, have they had any good comments when you go over there on Fridays recently about the pod? I just have to wake her up. Oh, okay. Yeah.

SPEAKER_00 2:46

Like or or I'll just start talking about what we're talking about and I'll wake her up that way and kind of bring her back into the world. Bring her back into the fold. Yeah, that's good. That's good.

SPEAKER_01 2:56

Well, hey, we got one regular listener. It's Joyce. Love it. Yes. So good. Well, Chris, today we're talking about a big fancy word that's actually really basic. I'm curious your thought, your thoughts on this. Is the word hypsometry needed? Do you think? Um, so uh no.

SPEAKER_00 3:15

Short answer is no. I agree. Hypsometry or hypsometric curve. I I did not know. I had to look this up actually. The root, what does hypso mean? And I didn't know. I didn't know the root either. Yeah. So think about that, our listeners, please, just for a quick second. What does hypso mean?

SPEAKER_01 3:34

Yeah, if you can take a guess, because this is a really fundamental, this is something you learn in every intro level class. Not this curve, but you learn the underlying principle. And then the fancy scientists over here, we have to add some complex word to it and add metric. So we're measuring something, but a hypso is aloft or high or height or something to that effect. So it's it's height, it's aloft, it's high. So it's a completely unnecessary term, right, Chris? Do you you You guys doctored this up real good? We did. We made it, we have to make it inscrutable to the average person who doesn't know all these words. I mean, it's ridiculous. So hypsometry, but this is a really, really I love this concept. Basically, it's the crustal distributions. It's think about Earth, let's take all the oceans away. And if we had a map, we don't actually need a map. All we need is a elevation distribution. So, like how much area, how much percent of Earth's surface is between zero and one kilometer above sea level? How much of Earth's surface is between zero and one kilometer beneath Earth's sea level, etc. etc. for all the elevations. How much of the earth's surface is more than six kilometers above sea level or more than five kilometers? Like it's a distribution.

SPEAKER_00 4:47

That's right. And it's expressed as a percentage, really, of like, all right, here's the earth, here's the surface of the earth. What percent of it is just above sea level, just below sea level, really, really far below sea level, and then really, really high above sea level. So as you said earlier, you would come across this in any intro-level geology course or geoscience course. We think of it as a passive continental margin. This would be the trailing edge of a continent, basically, where you have this continental shelf, just really, really flat area, just above sea level and just a little bit below sea level. And then you get this continental slope where it dives down toward the deep ocean basin where you have this transition, the continental rise, and then finally the abyssal plane. So every geology course is gonna show this very idealized profile of the earth, and then this hypsometric curve just adds in the high, high elevations and the really low elevations like the deep sea trenches. So it's a little bit different. Take on a basic concept.

SPEAKER_01 5:53

You nailed it here. The curve itself. So this is a curve that is database, but it looks exactly like a profile of a continent, a continent transitioning to an ocean. Let's build this a minute because and and let me back out of this. Why are we talking about this? To me, this is an entire lecture that I give in my intro level class. And Chris, I'd be curious to know how you how you aggregate these concepts or how you talk about these concepts. But I spend an entire lecture on this because it's really, really cool to me that you can look at just the distribution of elevations on Earth, and we can infer as geologists, and people have done this back in the day, you can infer a ton about our planet just from that. Some really, really important first principles. So the kind of thought exercise here is what happens if we fly our spaceship into another solar system and we look at planets, and all we have is like lidar, or all we can actually measure is the surface, the topography of the planet. What can we tell about that planet from just topography? That's kind of the thought exercise. So we're turning that on Earth. What can we tell about Earth from just the topography of Earth? And there's actually some really amazing stuff that we can tell, I think. So that's why I spend the entire lecture on this. Chris, how do you how do you get these concepts across? I'm guessing you don't talk about the hypsymetric curve because it's like useless for high school students to know that word.

SPEAKER_00 7:09

You know, I talk a lot about the profile of the earth and like the continent margins and then leading into the deep ocean. It's just classic, it's an important process, it's an important thing to learn. So hold on a second. You actually do a whole lecture. Do you use the term hypsometry or hypsometric?

SPEAKER_01 7:25

I I do. How long have you been doing this? Uh this is my third year doing it, I think. Okay. It was one of these things. I was reading some papers and I was working on this. I started working on the idea of when continents emerged above sea level, which this hypsometry is kind of you know really deep involved in that. So I started like reading papers about this curve, and it's a really basic concept, but it's used a lot, and so then I was like, oh, I could probably use this as a way to explain a bunch of features of Earth, and and it actually was used in early plate tectonic theory to derive plate tectonics. So I don't know.

SPEAKER_00 8:00

I don't know if it lands totally well or not, but I think because I'm actually going to use this now, because I'm looking at the hypsymetric curve for Earth right now, and basically you already described it, but it it shows the elevation, whether it's above sea level, at sea level, or below sea level. It shows the elevation on the y-axis, and it shows the percentage of earth that is represented by that on the x-axis, and so you get this kind of longitudinal profile.

SPEAKER_01 8:27

Let's build this a minute because I think it's really important just to visualize so the listener can visualize. And this is gonna be a little bit hard to do, but that's exactly the chart. You have elevation on the y-axis, and we're gonna go percent of Earth's surface on the x-axis, and we're gonna go from zero to a hundred percent. We're just gonna we're gonna compile this. So it's basically a it's a total curve. We'll add up to 100% by the end. So what we do is we say, okay, Chris, how much of Earth's surface is above, let's say, four kilometers above sea level? Let's start high and go low. So how much of Earth's surface is between four and six or seven kilometers above sea level? And the answer is like, what, a couple percent?

SPEAKER_00 9:04

Yeah, it's so I would say maybe um looking at the curve, I would say maybe five percent of the earth is above two kilometers.

SPEAKER_01 9:12

So really high mountains, there's a very few percent. So we're gonna go from like an intersection with the y-axis is at like seven kilometers. It's gonna steeply go down to start. So by the time we're on the x-axis, about five percent, we're down to like two or four on the y-axis. We're dropping down, down and to the right. Then, Chris, we hit continental interiors, which are kind of what, let's say one kilometer to sea level. What percentage of Earth surface is that kind of like one to two kilometers to sea level area?

SPEAKER_00 9:42

So I would say maybe from 15% to to sea level, you said?

SPEAKER_01 9:49

Yeah, to sea level. Or let's say take it all the way past sea level. Take yeah, take it all the way past sea level.

SPEAKER_00 9:55

So yeah, yeah, plus me to forty plus percent. Okay, yeah.

SPEAKER_01 10:01

So that's like that's like 25% of Earth's surface is kind of between one kilometer above sea level to one kilometer below sea level, roughly somewhere in there. So our curve goes it steeply goes down. When it hits like 10-15%, it flattens out because a large percentage of Earth's surface is right at that narrow interval between one and minus one kilometers relative to sea level. So the curve flattens out, then we hit the edge of the continental shelf, and we get to this sort of transition towards the abyssal plane, which is how much of Earth's surface is between minus one kilometer and minus four kilometers. There's not much that's in that transition area.

SPEAKER_00 10:42

Less than 10%, yeah.

SPEAKER_01 10:43

Less than 10%, yeah, like five, seven percent. And so our curve now is going to steeply drop again. And once it hits about minus four, four kilometers below sea level, we hit the abyssal plane, which I mean you could just look at a map of Earth. There's a lot of of the ocean basin that's that area, right? I mean, I don't know, I'm looking at this chart, it's like 50% probably of Earth's surface.

SPEAKER_00 11:06

50 plus percent is deep ocean. Yes.

SPEAKER_01 11:09

So that curve again kind of flatlines for a long time and goes until we're far to the right on our x-axis. We flatline far to the right on our x-axis. Now the question is how much is really deep, deep trenches? The deep trenches, again, a couple percent, five, yeah, so very small percent, uh yeah, probably less than five percent.

SPEAKER_00 11:29

Yep. When we're talking about things like the Tonga Trench or the Mariana Trench, these deep ocean trenches, yes.

SPEAKER_01 11:36

How much area is that it's not much on Earth, right? We need we can look at a map and determine that. So our curve again plunges down until it hits 100% on the x-axis and like minus 11, minus 12 kilometers on the y-axis. So our curve, let me just summarize that. It's like starts at the top left at the y-axis, dives down quickly, then flatlines in the continental interiors, then dives down again pretty quickly till we hit the ocean floor depth. And the ocean floor depth flatlines for about 50% of the x-axis until we get close to 100, and then it dives down again really deep where the trenches are.

SPEAKER_00 12:09

So, Jesse, my plan now, uh as you've been rambling on here forever, I I I formulated a plan. Okay, go ahead. So I I wanted to.

SPEAKER_01 12:19

Well, I'm trying to paint a beautiful visual for the listener.

SPEAKER_00 12:22

My mind is elsewhere then at that point. Sorry. Um, and so was everybody else's, I think. But anyway, uh sorry, Dr. Rybank.

SPEAKER_01 12:30

I mean, it's quite all right. And guess what? So were my students last week, Tuesday.

SPEAKER_00 12:35

What here's what I think I'm gonna do, Jesse is I'm gonna use the hypsymetric curve. I'm gonna give it to them. They're gonna get into their lab groups, and I'm gonna have them think about this without me talking about it.

SPEAKER_01 12:46

I'm gonna have you-that's a great idea, Chris. Do a lab on this. That's a great idea.

SPEAKER_00 12:50

Exactly, exactly. Like what you just did of breaking down the percentages of the different segments of Earth. We have the mountains, we have the plains, we have the broad continental shelf.

SPEAKER_01 13:02

Okay, this is a really good lab exercise that I want to know either how it goes, or if I keep teaching the intro-level class that I currently teach, you know, revising our labs would be good and adding a lab in like this where so are you thinking you look at a map and actually derive this curve, like make up this curve by looking at the topographic map of Earth? And then No, I wasn't thinking that.

SPEAKER_00 13:25

I was thinking about looking at the hypsometric curve, something that I've really never used before, and saying, all right, well, let's first get the breakdowns. What do we have here? They're gonna be able to derive, well, we have mountains, we have this really broad plane that is just above sea level or just a little tiny bit below sea level. Oh, I like that. Then we have this deep dive to the deep ocean basin, right? And and so they're gonna come up with we've got mountains, we've got this broad shelf, we have the rise, we have the abyssal plane, and then we have these deep trenches, and then assign percentages to that, right? So that's a start, okay? Just interpret the graph. Then what I want to do is all right, well, what kind of inferences can we make then from this data? This is real data. Like, what can we can we make inferences about the small percentages? And let's have our listeners start thinking about that a second. If we have a smaller, this is where we're going.

SPEAKER_01 14:17

This is the point, and this is where we're both sitting up straight in our chair. I mean, this is this is where we're going with this entire episode. So, yeah, I like this idea. This is great. So, do you envision taking student? I mean, how much I'll be curious about this, and and we can use this for the podcast too. How much help do you think students are gonna need to get to the inferences that we're gonna talk about here that you and I have talked about and we're gonna cover? Like, do you think your students are gonna need a lot of help? No, I don't. No? Okay. No, I don't they're gonna need some help. Let me ask another a second question. When do you envision over the course of the course doing this? In the beginning, at the end? Like, how much information do they need? I guess those are two related questions.

SPEAKER_00 14:57

Okay. It won't be right at the beginning because they're gonna need some background information. You know, they're gonna need to know the types of crust that we have on Earth. We have two types of crust, we have oceanic crust, we have continental crust. So I want to already have talked about that. And no, I don't think I will have already discussed the longitudinal profile of a passive continental margin, of the continental shelf, slope, rise, and abyssal plane. I won't have done, I won't do that yet. So, kind of in between those two things is I want to introduce the hypsymmetric curve.

SPEAKER_01 15:27

Gotcha. Okay.

SPEAKER_00 15:28

So I think what they're gonna need, my they're pretty quick. My students are pretty quick. And so they're not gonna need a lot of help. They're gonna be able to do that. Well, they're well trained. Yeah, they're gonna get to they're gonna be able to deduce all right, we got mountains, we got this broad plane, and so on. They're gonna get the five basic areas that I'm looking at on this hypsymetric curve and assign percentages to it, they'll be fine with that. They don't need any help. Yeah, then what kind of inferences they'll need a little nudge. And so I'm gonna maybe give them keywords about maybe like, all right, think about stability. What is stable and what's not stable based upon the percentages?

SPEAKER_01 16:04

I like this a lot, Chris. I want to know how this goes for sure. And if you're listening to this podcast and you're a teacher and you want to know how this goes too, send us an email and you want to use something like this, because I love this idea, and I want to use it, I couldn't use it this semester, but next year I could certainly we could revise the labs and and the there's aspects we have labs that are kind of old, and I would love to revise a few of them and do something like this would be would be kind of very thought-provoking and cool. So yeah, okay.

SPEAKER_00 16:33

All right, so it's gonna be a minute because I don't get my geology students until November. No, that's perfect. So right now I'm I'm teaching astronomy, so I'll get my geology students in November. Then it'll take us a little bit to get that far, and then I'm gonna definitely do this.

SPEAKER_01 16:48

In the new year or something like that. I like that idea a lot, a lab on this. Okay, so let's walk the listener through this lab to the end goal is to get to these really, really amazingly basic but really important inferences. So the first thing that we can do, Chris, for me, this is the one that stands out to me. Again, we're pretending we're like from outside the solar system coming in, and all we can do is map the earth in topography. So we've got a lidar thing that goes around, and that's about it. What stands out is the flat parts of the curve. And the flat parts here mean that there's a lot of crust that's very similar elevation to a lot of other crusts. So the continental interiors, that plus one to minus one kilometer elevation, there's like, wait, what we say, 25, 30 percent of Earth is that? That's all one thing. And then the other flat part is the abyssal plane, minus four to minus six kilometers below sea level. That's like 50% of Earth's surface. So those two things stand out. And what what basic inference can we say with that?

SPEAKER_00 17:46

Well, if I'm gonna nudge him and I'm gonna say, all right, let's think about stability then. Well, because there's such a big percentage of those two types of crust. When you look at the curve or when you look at that longitudinal profile of a passive margin, the part that is just above at and just below sea level, it looks thicker. Right? And so, and they will they'll know this. You know, my freshmen know this that the continental crust is thicker, it's more buoyant, it's less dense, and this curve clearly shows that. And then the other kind of crust is the oceanic crust, and that's the deep part of the ocean, that's the abyssal plane. It's much thinner, it's denser, and it is the antithesis of buoyant. You know, it's a with plate tectonics, that's what's involved in subduction and and so on. So those two things.

SPEAKER_01 18:36

Exactly. We have two plateaus, they're different elevations, and what we can infer from that is we have two different types of crust on Earth, which is very basic, very first principles thing. We have two types of crust, one of them's thicker or more buoyant, it's actually both. One of them's thinner or more dense, it's actually both. We have oceanic crust and continental crust, and you know, we wouldn't need to name them that. We wouldn't need to know that one of them is below the ocean floor and one of them's at near the surface to understand that there's two types of crust, one's thicker, more buoyant, one's thinner, more dense. Like that's a really fundamental thing about Earth that we have on Earth that is pretty unique to Earth that we can look at and figure out from the hypsymmetric curve.

SPEAKER_00 19:14

That begs the question then, since there's so much of it, does that mean Earth has this bimodal crust that you just described? Are both types of crust then stable?

SPEAKER_01 19:25

Yeah.

SPEAKER_00 19:26

Is that what inference can be made?

SPEAKER_01 19:28

I love your intro with the word stability or your your your sort of um The nudge. The nudge with stability because it's such a great one. It brings up this question. What do we think? I mean, let's think through this. Do we think that it means that they're stable? At first, I would say yes, because there's a lot of it. So either I think the two options are either you're creating a ton of it very quickly, or it's stable. It's created and it doesn't decay away and it doesn't actually change elevation much. It's kind of bobbing up and down, you know, it's very stable. And so let's work through that. Like continental crust. We're producing some, we're producing a decent amount of volcanic arcs and um at subduction zones, continental subduction zone systems, but there's arguments that we're kind of destroying continental crust too. So that one to me is more of a stability thing. So yes, I would say that answers that checks the box. There's a bunch of it, so it means it's stable over long time periods. We know that from Earth. What about oceanic crust?

SPEAKER_00 20:24

Well, it's different because in oceanic crust, is it being eroded? Does that process happen in a way that happens above sea level? And the answer's really no. No, not really. It's not. Not not really, not much anyway, not significantly, because it's underwater. But is it stable? Is it stable? And if you look at what can happen to oceanic crust or what is inevitable with oceanic crust is that it's going to, because of plate tectonics, it's going to be involved in subduction at some point during its lifespan. This is why, you know, one of the questions that Dr. Maddox loves to ask my students at on the exam is how old is oceanic crust? And and geologically, you it's hard to find oceanic crust that's older than 200 million years. Oh, yeah. And geologically, that's really young. And so why? Well, that's because it gets recycled in subduction zones event eventually. And so it's not stable.

SPEAKER_01 21:23

It's not stable. Yeah, okay. I I totally agree. It's not stable. So I don't know that we could use, we could really argue for stability based on a large amount of of these two types of crust. Now, let's come back to that because maybe we can, once we kind of put the other puzzle pieces in place that we we can figure out using this hypsymmetric curve, we might be able to get there. At least we can have a hypothesis about it. So let's move on to the next one. And Chris, I want to let's move away from the two peaks in distribution or the two large areas of Earth that are a certain distribution. Let's focus on mountains first because I think that flows nicely. How? High mountains, a small amount of very high mountains. Okay, we can tell a lot from this, but it's not, I don't think this is necessarily intuitive. The first one is certainly intuitive. Like when I ask my class, I say, okay, what do high mountains tell us? And usually it might not be the first answer, but one of the first three answers is there's stuff being pushed up. No, they often kind of get too complicated with it first, and then I need to back them up and say, no, no, no, basic stuff. They're like, oh, well, it's stuff's being pushed up. Like there's stuff going up, which you always say there's two forces on Earth, stuff that pushes stuff up and stuff that pushes stuff down. And we're gonna talk about both right now.

SPEAKER_00 22:37

But that's right. I'm just saying that because we have such a small percentage of it, means that stuff is getting shoved up, but it also means that the second force is also very much at play. The belt grinder of weathering and erosion is an active process. So if this process is going on and has been for billions of years, then if it was stable, once it's created, it's there. But this curve says that they're not, so they get knocked down.

SPEAKER_01 23:06

And so I think, Chris, I always have this discussion in my class before I talk about plate tectonics, because I want them to come at this without having plate tectonics in their mind. Because I don't think that, in my opinion, the fact that we have high mountains and we know that stuff's being pushed up does not mean plate tectonics yet. Because there are other forces that people have talked about that could potentially create high mountains. You know, there's buoyancy stuff, there's this old expanding earth kind of theories, which have been disproven now. But but on a different planet, maybe there are forces that could push stuff up to these extreme elevations that are not plate tectonics. On Earth, we know it's plate tectonics. But that last point you made, the thing about erosion, that's one that my students rarely get to because again, I haven't talked about erosion yet. I haven't talked about any of these forces. I give it near the beginning of the semester, like week two or three. But it's an important question, it's an important thing. We know there's stuff being pushed up there, so why isn't there a lot of it? Well, it means the process only just started recently on Earth, or it means erosion. It means that something is knocking it down. That to me is a really cool conclusion you can make just by looking at this curve. I I don't know. What do you what are your thoughts?

SPEAKER_00 24:15

Yeah, I think so. What we're doing is we're looking at something that is a very, very basic idea in geoscience. Uh the force that lifts things up, the force that tears things down. But we're looking at it from a data standpoint. I've never thought about it in this regard before, actually. Before you brought this to my attention, this hypsometry. Uh it's not a word that I've ever heard before. And I love it, though, actually, because this is something that maybe, like you said earlier, that we can look at Mars maybe with LIDAR or just a topographic profile, and maybe make some inferences about what's happening on this planet or what has happened on this planet before.

SPEAKER_01 24:55

I mean, it it's all hypothesis. If we if this is the only data we have, we generate hypotheses about the Earth. But a very, very solid one is that there's something knocking these mountains down. There's something pushing them up, and there's not many of them, so there's something pushing the mountains down. That's very fundamental that there's erosion going, there's some form of erosion, there's something knocking these things down. And I don't know, that to me is just such a cool leap. There's such a cool little bit of intuition, and this is the beauty of geology to me, is it's fundamentally this like very artistic storytelling science where we look at data and interpret it over long time scales. But it's like we've talked about many times the basic things about geology, like cross-cutting relations. It's not that obvious unless you've heard it, but once you've heard it, it's really cool and actually kind of obvious and incredibly powerful. This to me is kind of in that category of stuff, these 100% little bits of intuition.

SPEAKER_00 25:45

So this is something that is a like a in education, just in general, the more we can expose younger minds to this idea of looking at real data and then making inferences from it. It's a difficult thing for them to do, but it's definitely something that is emphasized on all of the standardized tests.

SPEAKER_01 26:04

Oh, is that right? Okay. This kind of like data analysis.

SPEAKER_00 26:08

Data and graph analysis is absolutely yeah.

SPEAKER_01 26:11

Oh, I didn't know that actually. I probably should have known that. But um on the standardized testing, this is like a big deal for Oh, it's huge.

SPEAKER_00 26:17

Yeah, this is so the more we can come across like really good examples of this, and the hypsometric curve is this is perfect for that kind of thought experiment. Absolutely.

SPEAKER_01 26:27

This would be cool. Yeah, this is cool. I I I if this would be fun to kind of build a lab that would that I mean you're you can go like we've talked about before into more detail than than I do in the in the college class. And so we might have to make a shorter version for my for my class or shorten the one you make in some way, shape, or form. But okay, so can we move on to the trenches?

SPEAKER_00 26:47

Yeah, the last one, the last tiny little sliver, the last aspect of the hypsymetric curve is these really, really deep sea trenches.

SPEAKER_01 26:54

We're gonna jump all the way to the right in the hypsymetric curve, you know, between 95% and 100%. So 5% averse area is like really deep trenches. And you said it before, we're talking about the Tonga trench. We're talking about these trenches that are in the ocean floor that are really, really deep. And Chris, this was used. There's a really cool, we'll talk about this in a in an upcoming episode, but there's a really cool story to this where people who were doing back in the early days of plate tectonics, like pre-plate tectonics ideas, people were doing a lot of gravity measurements, and they'd take ships and they'd have a gravitometer in the chip and they'd they'd drive around, they'd measure the gravity field. And you know, you could see mountain ranges. You probably talk about this in class. You can see mountain ranges, you can see the gravity of mountain ranges, you could see the lack of gravity. They'd drive over trenches, they could see the lack of gravity in the trench. They actually started to piece together plate tectonics because of this, or proposed plate tectonics. And this is kind of this is a bit of a leap. This is a bit of a this is certainly in the hypothesis that needs to be tested category. But okay, if we back up, number two, high mountains told us that first of all, stuff was being pushed up and they were being knocked down, and that's likely erosion. So that material, that mass has to go somewhere. And it's not too hard to understand that it probably goes into the ocean. So then where's that connection between there's erosion happening but there's a trench? How do we get to plate tectonics from there? That's like a tricky equation. Erosion plus deep trench equals plate tectonics is complicated. So, how will you like nudge your students in this direction?

SPEAKER_00 28:25

Well, again, thinking about stability, you'd think, well, maybe because there's such a small percentage of deep, deep, deep sea trenches, are they getting filled by some mechanism? Like, is the erosion from the high stuff on the continental side is that getting shoved out into the deep oceans and into the deep sea trenches and filling them, thereby removing them?

SPEAKER_01 28:45

Okay, there we go. It is, right? Like we know erosion's going out. It would fill up the trenches. That's a pretty sound interpretation, right, in your mind? Do you think like Yes, yeah.

SPEAKER_00 28:56

Because these deep sea trenches are not that far off the shoreline. They're nearer the source of the sediment. It will make its way that far for sure.

SPEAKER_01 29:04

So the sediment would fill these up if they were stagnant. So therefore, the fact that the trench exists means what? That you have two forces going on there as well. Exactly. Oh, it's so good. You're actively creating the trench, too. It's an active process of creating the trench. So because it's so cool. I I found the I find this so cool. The fact that the trench exists means because there's erosion, that we're dumping stuff into the ocean basin, the fact that the trench exists and that it's so freaking deep, six kilometers of trench below the abyssal plane, the fact that it exists means that it has to be actively being produced. It's like mountains. The fact that they exist means they have to be actively being pushed up because they otherwise they'd be destroyed. The earth wants to be flat everywhere. The processes want to make it flat. This is where the plate tectonics theory, one of the ways that it originated, is like, oh, wait, there has to be an active process creating a trench. What's a good one? A good active process creating a trench is this oceanic plate diving down into the mantle. That's a pretty good way to keep a trench active over long time period. So that's certainly a hypothesis. If this is the only data we have, but it's a sound one, when we get more data, like it's it's a it's the simplest explanation for keeping a trench active for a long time. So I love that one because you were kind of building this. We're saying we have two types of crust on Earth. We have mountains that are going up. We also can tell that they're being knocked down because there's not many mountains. So because there's stuff being knocked down, that stuff's going into the oceans. We know it's going into the oceans. So therefore, because we have trenches, they would be filled up if the trench wasn't being actively created. So the trench is being actively created. So we can look at this curve and say, we live on an active planet. It's a pretty good bet that there's erosion and plate tectonics going on, all from the hypsymmetric curve.

SPEAKER_00 30:52

And you know, it's really this is an interesting thing because I think all of our listeners know that we live on an active planet. They knew that before this episode, but this is just looking at it from a different standpoint than I think many and most, maybe yeah, most people have ever thought about it.

SPEAKER_01 31:10

And I would bet I wanted to kind of end with this, but you kind of answered it already. Because I know that some of the textbooks have this hypsymetric curve, you know, in it and talk about it, but it doesn't, it doesn't feel to me that it it takes it's not fundamental. Whereas I've kind of structured my lectures a little bit around it being kind of a fundamental process. And I keep alluding back to the hypsymmetric curve throughout the rest of the course a little bit just because it's kind of a this fundamental thing, especially when I get to play tectonics. Do you think I mean okay, you've answered it because you you want to make a lab. So I was gonna ask, like, do you think this is a useful like teaching tool? But you've kind of already answered that. But that's interesting, it comes from this data-driven standpoint that that students there's an emphasis on getting students to like read and understand and infer stuff from data. That's a really I hadn't thought about that before. So kind of with that, I want to ask you a question about this to back to the stability thing. I could see a way that we end here with there's deep trenches, therefore there's plate tectonics, and what we mean is that oceanic crust is likely diving down into the mantle. So there's the oceanic crust is diving down into the mantle. Can we bring that back to the stability question? Do you think students would be able to make that connection to bring it back to stability where we talked about stability in the beginning?

SPEAKER_00 32:25

So, what you're asking is, do you think that they will be able to deduce that the deep sea trenches are not stable?

SPEAKER_01 32:31

Or that oceanic crust is not stable, whereas cottonal crust is. The high mountains get knocked down to continental crust level. The ocean floor gets subducted down trenches. I think we can make a hypothesis link. If you really think about this for a long time, I think you might get there. My question is like, could students get there to back to the stability thing and say oceanic crust is not stable, but continental crust is stable.

SPEAKER_00 32:54

I don't think right at the outset, but what I envision happening is they're gonna then put the they're gonna identify the different parts of Earth based on the hypsymmetric curve. Then they're gonna assign percentages to it, then they're gonna start thinking about what's stable and what's not stable. And they're probably going to say that oceanic crust looks like it's stable. I would I would expect them to get to that, but then we're gonna have a class discussion about that. And so just by asking more questions, kind of like what you and I did walking down from the Tetons 20 year plus years ago, yeah, yeah, yeah. Is they're going to be able to deduce that no, it's not without me answering it. I'm just gonna ask them other questions because they do have a fundamental background in geoscience already, because they took you know my class as a freshman, they're just earth science. Yeah, yeah, yeah. Totally.

SPEAKER_01 33:45

Okay.

SPEAKER_00 33:46

They'll be able to get there.

SPEAKER_01 33:47

Yeah. I mean, that's impressive. That's very cool. I'm so interested to know how this goes.

SPEAKER_00 33:53

And uh I, you know, we we keep talking about this, but when I think about what I just said to you, Jesse, I think I am so proud of the school that I'm a part of that I work for, in that we provide a really good background in geoscience. And then with electives, you know, thrown into that, like my geology course and and then astronomy, there's a lot of planetary geology that goes into a class like that. Also, it's so unusual, I think, for a public school to have that deep of options.

SPEAKER_01 34:29

And it speaks, you know, it speaks to two things. You know, it's it's 90% you, and it's 10% your administrators, like allowing this freedom and flexibility to navigate. And you know, I I went through Hudson Public Schools, and the science department was great then, and I it's been great for a long time. I mean, your dad was a great biology teacher there, my dad is a great biology teacher there. The science department has been very, very good in many different fields, and geology is you know, one of the big dogs that barks there, I think, now. And you produce big dog. We have but but you know, to brag for you, you produce, or Hudsonville produces, I forget what the long-term average is, like seven or eight geology majors who end up going on into geoscience, and usually that is a college geoscience degree in some way, shape, or form, and be either teachers or researchers or professionals in the industry, various industries. That's a high number for especially for the state of Michigan. That's a very high number.

SPEAKER_00 35:23

And I would not say, I want to push back on one thing though. It's not 90% me, because I'm only one of four people that teach freshmen, all the freshmen that come through our school.

SPEAKER_01 35:33

Oh, yeah. Uh okay.

SPEAKER_00 35:34

That's they, you know, they actually do the most of it because I teach these other electives to it's for the upper classmen. I teach geology and and astronomy. And so I'm not.

SPEAKER_01 35:45

No, that that's totally fair. And the summer science thing, you you know, you've done that for a long time, but you're half of that team always. And I was more speaking of the upper level stuff, you know, like you you got to create astronomy, you created the geology thing. Yes, and somebody's gonna inherit that, but and and hopefully keep running with it. But um someone's gotta start it. So yeah, right. Yeah, that's the I I was referring to the upper level stuff a bit, but yeah, okay.

SPEAKER_00 36:07

All right. I just want to like I don't want to slight anybody. I I work with amazing people and uh we do a really I'm just proud of it because I when I think about what my geology students are gonna be able to do with this hypsymmetric curve, I think they're gonna do a lot with it because they already have a really good background in geoscience. So I I will be able to hit this early on without having talked about a lot of these concepts in my geology class.

SPEAKER_01 36:31

Well, I think again, I think that, you know, okay, somebody sitting there listening is probably Joyce is probably like, what the heck are we talking about here? Why are we talking about this? And to bring it back for Joyce, I I hope the term of the day for Joyce is hypsometry. That's H-Y-P-S-O, M-E-T-R-Y, hypsometry. And it's a completely unnecessary term for the vast majority. So why we make an episode about it? It's a cool, I think it's an amazing bit of intuition, of geological intuition, that you can piece together these really fundamental things about a planet, our Earth, because of this curve. And so, although it's a useless term, I think the term is valuable because it describes the data that we would use to get to these inferences, and it kind of aggregates all sorts of ideas about the Earth, really basic ideas from like different parts of an intro-level class. I mean, you talk about erosion until the weathering and erosion chapter, and there'd be one chapter on plate tectonics, and there'd be one chapter on the oceans and stuff, but linking them all together, the hypsymmetric curve, the value of it is that it links them all together in this really fundamental way, I think. So that's why we did an episode on it. Which is tedious episode.

SPEAKER_00 37:41

No, I don't think so at all. It's some fun, actually. Uh, for me, uh anyway. You and I had fun talking about this. Yeah, yeah.

SPEAKER_01 37:45

Joyce isn't asleep, but that's okay that's good. That's normal.

SPEAKER_00 37:48

She always is. Um, I think maybe it could have been called the elevation curve or something like that. Just much simpler. A topographic curve. I mean something simpler.

SPEAKER_01 37:57

But hey, we gotta get it, we gotta get Latin with it and hip symmetric, you know? It's so good. Well, I don't know, Chris, what do you think about a wrap?

SPEAKER_00 38:06

I have it is, but I have not gotten my merch yet. I or I ordered merch and I haven't gotten my hat and shirt yet.

SPEAKER_01 38:12

I'm sure it's on the way. The white glove delivery service is coming. Maybe they're knocking the door behind you.

SPEAKER_00 38:21

Oh gotta be patient, man. It's coming. All right. I'm not a patient person, I'll tell you that. I know I know you're not.

SPEAKER_01 38:28

No, we'll uh we'll have to record with our Planet Geo hats on next time. Yes. Yeah, I can't wait. Plenge a hat, Plan Geo shirt. On that note, there's a couple ways to support us. You can go to our website, plangeocast.com. We have merch now. There's uh a hat, a shirt. We're gonna be adding some stuff to it as well, a couple different varieties of a hat with the Planet Geo logo. So that's one way to support us. Another way is download our mobile app. First link in your show notes. We have a ton of visual podcast series. The main one is this course that Chris and I teach. I teach at the college level, and Chris teaches basically it's college level to high schoolers. We have most of that entire course in visual podcast series there for free. You can also buy audiobooks, and some of them are podcast plus images, and some of them are standalone audiobooks on the geology of the amazing national parks that our country has to offer. You can send us an email, plangeocast at gmail.com. You can also follow us on all the social medias at PlanGeocast. Cheers.