PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
When Continents Became Stable
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Today we really go into the weeds.
Jesse and a colleague just published a paper in the journal Nature that proposes a new model for how continents became stable. Stable continents have all the granite at the surface, which contains all the heat producing elements like U and Th and K - elements that decay away.
Today, we discuss that paper in detail, and along the way learn a bit about the early Earth, what we know and don't know!
Here is a link to the paper, which is open access and can be downloaded by anyone without paying.
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Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
SPEAKER_01What is the cold intro, Dr. Ramick? It's a cold open.
SPEAKER_00It's a it's a cold it's a cold open. Sorry. Sorry. I've got something for it, Chris. I was um this afternoon. I knew we were sitting down to record. So this afternoon, I really started giggling. And do you know why I was giggling to myself? Do you can you hazard a guess?
SPEAKER_01I have I have no idea why. It's been a good few days, but I don't know why you'd be giggling.
SPEAKER_00I was giggling to myself because a couple days ago I called you and I I had a little bit of what I thought was cranky Chris on the phone. So about 15 minutes into the call, I was like, dude, are you a little cranky tonight? And you go, No. Uh I ate too much at dinner and I'm just upset and uncomfortable. I was dying. You were just like, no, I'm not cranky, I'm just uncomfortable.
SPEAKER_01I ate too much. I felt bloated, and I don't like that. It's it's a horrible feeling. But I Jesse, I love food. It's just anybody that knows me knows I love food so much. And I made something really good, and it was a spicy sausage lentil soup.
SPEAKER_00Oh, that's that sounds good.
SPEAKER_01It was good, and it was and I had a bowl of it, right? And I then I'm like, oh man, I ate it really fast, and that's the mistake.
SPEAKER_00That's the mistake.
SPEAKER_01And then I I went back and I'm like, well, I'm I'm still kind of hungry. So you have majors of another. Oh, I demolished it. Yeah. It was not a good life decision, right there. No, no, no, that's right. Not a yeah, well, you so yeah, Jesse, come on now. You don't cranky Chris, is he really a thing? Yeah. I mean, uh I get cranky Jesse every once in a while.
SPEAKER_00Let's get Jenny out. Let's get Jenny, bring Jenny down here and let's ask her if Cranky Chris is a thing or not. Every once in a while. Or I don't know if crank cranky, you're not I get worked up, Chris, sometimes. Yeah, you're rarely like low. That's fair. You're rarely like low. You're like either worked up in a positive way or let's say a negative way.
SPEAKER_01Yes. I do allow myself I don't, I was gonna say luxury, but it's not really a luxury. I do get worked up. Yeah, and that's fine. I I I happens, yeah. So I mean everybody emotional, Chris, sometimes. Yeah, yeah, yeah.
SPEAKER_00That's right. That's right. It's you know, just depending, is it the positive emotions or the the negative emotions? But I'm pretty sure looking at you, I got the positive emotion, Chris, on the line right now.
SPEAKER_01You do, you have the positive Chris because Jesse, today, oh, this is exciting. Today, our topic is about a paper that you wrote. You co-wrote. Okay.
SPEAKER_00Yeah, co-author.
SPEAKER_01And yeah, co-authored. I'm sorry, I'm not using proper terminology there for Dr. Rymanck.
SPEAKER_00The doctor is in the house for this episode.
SPEAKER_01Yeah, and I'm gonna apologize to all of our listeners outright for that. But um we're gonna talk about this paper, Jesse, because uh this was uh well, uh let me ask you, where is this going to be published?
SPEAKER_00Yeah, so this is published in Nature, um, which is the big dog, I guess. I mean, this is the big top tier, right?
SPEAKER_01That's a big wow, that's a big deal.
SPEAKER_00When you think of scientific publications, nature and science are the they're the really the oldest ones. They're short papers, they're interdisciplinary. You know, it doesn't there are good and bad papers published in nature and science all the time, but it is it is nice to get published in nature. It means it's sort of uh a topic, you're writing a paper on a topic that is important to a wide range of fields. So well, Chris, one other note though it's been a good couple months, I'll be honest. We had this nature paper accepted that we'll talk about, but we also found out recently that uh our Yellowstone National Park audiobook is going to be available in the bookstores in Yellowstone National Park. We're partnering with Yellowstone Forever to have them displayed in Yellowstone National Park and and uh sort of been approved by the National Park Service. And so that's a really exciting development for us on the Camp Geo app.
SPEAKER_01That was not enthusiastic enough, Jesse, because that is so awesome. I've been on Cloud Nine for the last three days. Yeah, yeah. It's been great. We've had a good we've had a good little run here.
SPEAKER_00Yeah, we've had a good little run, and we're just super excited. Yellowstone Forever is gonna partner with us on this, and uh it's great. Super excited about this.
SPEAKER_01Okay, Jesse, can we get down to this a minute? So the title of your co-authored paper.
SPEAKER_00Um hold on. I'm I'm putting on my emotional armor right now because I I get the sense I'm gonna get a lot of crap here this episode.
SPEAKER_01Well, and most of the So I don't know. Yeah, you might, you might, but I I do have to be careful because you did co-author it, and I don't want to offend your co-author in the least bit. I maybe only want to offend you a little bit.
SPEAKER_00Professor Andrew is quite hard to offend. So don't worry about it.
SPEAKER_01Okay, that's good to know. That's good to know. All right, Jesse. So the title of your paper, all right, Jesse. This paper then is released in nature.
SPEAKER_00That's right.
SPEAKER_01Right now, as we release this episode, this is this is a paper that is out. Yeah, that's right.
SPEAKER_00And we'll put a link in the show notes here. And this is uh we made it open access like we paid for it to be totally open access. So you don't have to, it's not behind a paywall at all.
SPEAKER_01I hate that when I don't get open access to those. I know.
SPEAKER_00So this one's open access.
SPEAKER_01Okay, awesome. So the title of the paper, Jesse, is everybody ready? Here we go. It is called Subarial Weathering Drove Stabilization of Continents. Okay.
SPEAKER_00And everybody goes wild and the crowd goes wild.
SPEAKER_01That's it's crazy. Okay, let me read it again just for impact. Subarial weathering drove stabilization of continents.
SPEAKER_00So I have a question for you, Chris.
SPEAKER_01Can we talk about this a minute? Okay, go ahead.
SPEAKER_00I mean, what do you the first time you read that, what were your thoughts? What was your knee-jerk? What was your like gut, you know, reaction? Because this is something we agonize over, right? Like as writing these things, we're like, what should we put the title as? And I'm not sure we got it right, right? We had a whole bunch of options we were picking from, but what is your reaction?
SPEAKER_01I can I answer your question with another question then, which is why is this an important question to answer?
SPEAKER_00Oh yeah, okay. We probably need to do a bit of Archean geology background here a little bit to to kind of understand this, but the but the tagline, the short tagline, and we've talked about this before. Continents are, as far as we know, singular to the planet Earth, and really a major feature of what makes Earth unique. And it's intimately linked to oceans. We've talked about that before. So understanding the continents is a really important thing to understand when we compare our planet to other planetary bodies.
SPEAKER_01Yeah, because when you compare us to the other terrestrial planets in our solar system, Mercury, Venus, Mars, they don't have continents in the way that we do. They don't have tectonics the way we do.
SPEAKER_00That's right. And so you kind of ask yourself why are continents stable? Why are they stable for billions of years? And uh, you know, there's some first order things we know about them, but it's also a a bit of an open question.
SPEAKER_01Okay, so are you saying then? Let me re-ass the I don't know if I want to re-ass the question, but are you saying that the purpose of this paper then is to answer the question about why Earth is unique?
SPEAKER_00Kind of, yes. I mean it it is real, it's certainly related, intimately related to that topic. Why is Earth a unique planet? Why is Earth different from Venus?
SPEAKER_01Don't you think you need help with title work then, Jesse?
SPEAKER_00Okay, so there's an answer to my question.
SPEAKER_01I don't know. Like uh I think I came up with a uh maybe a more interesting I don't know that I would not have gotten what you said, which I by the way, I I want to be really clear on this. I think that answering the question about what makes Earth and Earth's continent so unique is really, really important and I think very interesting. But I would not have gotten that out of that title.
SPEAKER_00No. So this is it's a difficult thing, right? Because is it a nuance? Well, there's some nuance to it because, like, okay, I we submit this paper, it goes out to other people like us, other experts in Archean geology or in granite formation who look at this and review it. So if you put a a really catchy title that's attractive to the biologists in there, some of the the reviewers might be like, that's a stupid title. So you have to you have to like tow this line between scientifically accurate and rigorous and catchy. And that's I mean, I'm not saying I'm great at it. You know, I'm not good at episode titles. I'm not good at paper titles. So you know this. There's people who are better at this, but it it is a hard one, I think, for most people.
SPEAKER_01That's a really interesting comment. I find that amazing because I think that this title hides what you're really trying to do.
SPEAKER_00I I I think that's probably right. Yep, I would agree with that. It is it is a little bit um too scientific, maybe. Uh or it could be it could be simplified and made more powerful.
SPEAKER_01So if I go back to, and I think everybody, if you did not listen to our episode on how to read a scientific paper, oh that was a fun one, Chris.
SPEAKER_00That was a fun one like a year ago.
SPEAKER_01You know, online about that. You know, we got good emails about it. Go back and listen to that episode if you haven't, or it's been a long time, and then maybe listen to this or maybe sit down for an hour and slug it out with this article that Jesse and and his uh co-author wrote. So, but can I read the first sentence?
SPEAKER_00Yeah, yeah.
SPEAKER_01Okay. Well the armor on it. So again, again, the title is Subarial Weathering Drove Stabilization of Continents. And the summary paragraph intro sentence is Earth's silica-rich continental crust is unique among the terrestrial planets and is critical for planetary habitability. That one sentence is the title to me. And I think it's an awesome title. I think it's catchy, and I think it's intellectual enough for the circles you run in.
SPEAKER_00I I totally agree. It's a I I love that intro sentence. I'm glad it I'm glad you liked it too.
SPEAKER_01I do.
SPEAKER_00And that part introduces why this is an important topic. Why should we as a field, why are there thousands of people working to understand the history of the continents? That sentence is kind of a summary of that. What it doesn't do is it doesn't summarize our proposal or summarize the new features of what we're suggesting here.
SPEAKER_01All right, let's get into that in a minute. So can we I'm gonna have you set the stage for this because you then go into very quickly into cratons, and I'm gonna have you introduce to our listeners because some of them, I'm sure, know what a craton is, and I'm sure some of them do not. So what is a craton and why is that an important aspect of your discussion?
SPEAKER_00What they are, first of all, is cratons are big blocks of continental crust that have a thick mantle keel beneath them that are stagnant. Mantle what? Mantle keel, like mantle keel, like a boat's keel underneath of it, you know, like a sailboat has this big keel. We refer to them as keels because we think of them as stabilizing the mantle root, the mantle lithosphere. So this is part of the tectonic plate. It's really thick, it's 250 kilometers thick, and it helps make sure that that continental bit above it, the continental raft at the top, is stable for billions of years as it gets batted around the earth by plate tectonics.
SPEAKER_01Interesting. So can we talk a minute then about how does it Chris?
SPEAKER_00I'm I missed out one key point. It's stable, meaning like not much has happened to it, hardly anything. If you if we go up to the North American Kraton, the Canadian Shield is kind of another term for what we think of the North American Kraton. If you go up to the Canadian Shield, you're walking across 2.5 billion year old granites that look exactly the same as the granites in Yosemite National Park that we talked about with Mike Ackerstone that are 90 million years old. And literally nothing has happened to them. They've been right near the surface of the earth for that long. That's just like a tectonically stable tract of crust that has just got you think of it like an iceberg being blown around the ocean and it kind of bumps into other stuff, but it doesn't actually do anything, it just sits there.
SPEAKER_01I have so many questions based on what you just said now that I want to do my job in this episode, which is keeping us on track. But a couple questions. What are some other examples of cratons? And do you use the word craton in your intro? Do you introduce your students to the cratonic or cratons?
SPEAKER_00Those are really that's a really good question. This I'll I'll go the second one first. And the I I do kind of only because I'm talking about my research. I don't teach it in the intro level as a thing they need to know in intro geology. It's definitely second level, second order, second order like classes, second level classes.
SPEAKER_01Okay, and I asked that question only because today I introduced the word Kraton to my students because we were doing geochronology relative dating, and I drew up a cross section on the Algoma district in in Canada, and all I did was I made statements about the rock types that I had drawn in the cross section, and I asked my students to say whether they were probable or not probable statements. Oh, interesting. And one of them involved, yeah, one of them involved a cratonic setting, and they did not know what that was. And so I had to introduce just today actually what craton and cratonic meant.
SPEAKER_00So you you don't you don't often do this in class, or is this not every year? Okay.
SPEAKER_01And how did the students no, I actually I do this, but I don't use cratonic, yes.
SPEAKER_00Okay, gotcha. Yeah, yeah.
SPEAKER_01Okay, sorry. So I interjected, but examples.
SPEAKER_00Examples, yeah. So I refer to cratons. What I often mean when I'm talking about cratons is Archean cratons, so blocks that are older than two and a half billion years old. And there's like five in North America, probably eight in North America, and they're all kind of aggregated together to make the Canadian Shield. Another one, there's a couple in South America. There's the Sao Francisco Kraton, and there's a couple of them that are amalgamated together to make the interior of South America. There's a really famous one, several famous ones in Australia, a bunch in Africa. Yeah. So they're all over. They're underlying continents mostly.
SPEAKER_01Okay. And does it refer also to a specific rock type?
SPEAKER_00No. Kraton is a block of stable crust and it can be made up of a whole bunch of different rocks.
SPEAKER_01Do I live in Southwest Michigan? Am I a part of the North American Kraton?
SPEAKER_00Yes, you would be. I mean, be basically you're part of the Kraton if you're sort of roughly near sea level, which is you know within a kilometer of sea level, and you not much has happened recently.
SPEAKER_01Yeah, that's the way I describe it to my students. I when I talk about a craton, I say, look, I'm in the middle of a continent. I'm in the stable interior portion of a continent where not a lot is happening.
SPEAKER_00That's exactly right.
SPEAKER_01So, Jesse, my second question then is you described the Canadian Shield, which is a lot of granite and it, you know, it's a really, really old basement rocks. Describe how that forms and how that gets exposed at the surface.
SPEAKER_00So cratons, sort of by definition, they just bob right near sea level. Kind of they're a little bit exposed above or a little bit below. North American Kraton's a great example of this, like where you're in Michigan. You're sitting on sediments and it kind of bobbed up and down. Now it's above sea level. If sea level rises, it's a little bit below sea level. That's what cratons do. But the relevant point here is that cratons started forming 2.8 billion years ago, roughly. There's a whole bunch of cratons that formed and stabilized, had their final stabilization around 2.8 to 2.5 billion years ago. We don't have cratons that are older than that. We have cratons that are younger than that. The rocks at the base of the Grand Canyon. That's interesting about the Grand Canyon. Uh, you know, the the the gneisses that that's that's basement, that's craton, that's North American Kraton exposed at the bottom of the Grand Canyon, it's 1.8 billion years old. So that's a younger Kraton, but we don't have anything older than three billion years old that that would qualify as a Kraton. So we kind of got Earth got to sort of teenage years and Kraton started forming. That's kind of the question we're addressing. Like, why that time? What was going on? That if we go back further than that, the the rocks are different. There was less than a little bit.
SPEAKER_01Well, can we tease this out a second? Can we tease this out? Like, how do we ever get rocks then that are older than this?
SPEAKER_00That's a great question. Uh this is my uh opinion or take on this is that as soon as you make silica-rich cotton, you know, continental crust, what we think of is continental crust, rocks that are more like granite, they're not quite granite in the Archean, but they're they're intermediate in composition, let's say tonalites, andesites, that kind of composition. Those kind of float, they're less dense, so they float up a little bit, and then they kind of bop around and they remain in the continental crust package, but they're not stable. They would get metamorphosed. So if we go back to the Acosta nice complex, four billion-year-old rocks I did my PhD on, those have been metamorphosis.
SPEAKER_01So everybody knows me and a few of your other close friends used to just call you Acosta.
SPEAKER_00Yeah, yeah, that's right. You wouldn't even you wouldn't even give me the digging of calling me Mr. Acosta. It was just Acosta.
SPEAKER_01No, absolutely not. Just hey, Acosta, shut up.
SPEAKER_00Because every time I'd just be rambling on about Acosta.
SPEAKER_01So good.
SPEAKER_00Yeah, exactly.
SPEAKER_01All right, sorry, go ahead. Carry on.
SPEAKER_00Four billion-year-old rocks. They're silica rich, they're intermediate composition rocks, so they they they sort of float up. But they were metamorphosed 3.8 billion years ago, 3.5 billion years ago, 3.2 billion years ago, 2.9 billion years ago, 1.9 billion years ago. So they've been metamorphosed a whole bunch of times and deformed and turned into gneisses and stuff like that. So they've not been in a stable, a stable thing. They they're not part of a craton. A craton is like this block of crust that nothing happens to it. It just It's too buoyant that it's too far away from all this stuff. Exactly. And it has this big keel beneath it that kind of it provides this, it's like a bumper, buffers that don't allow tectonics to manipulate the rocks above.
SPEAKER_01You get the segue word because that was my next question. How does the continent develop this keel?
SPEAKER_00Oh, that is such a great question. We don't know. We don't know. What we do know is cratons started forming, or they started being preserved because a craton is a stable block of crust. They started stabilizing 2.8 billion years ago, roughly. We don't get many samples of the keel beneath the continents. Really, the only way is these Kimberlyte volcanic deposits that bring up diamonds, they bring up pieces of the mantle. And they're very small, it's not a representative selection of the keel. My opinion on this, and we've done some work from ancient diamonds on this, is that it was sort of plate tectonic-like processes that kind of thrust. If you take the oceanic crust and it's subducting, and you kind of shove it underneath of a continent, and then you break it off and you shove another layer under and you shove another layer, you can kind of stack what's called stacking. You stack these things together and it gets thick, and then it can become cool enough to stabilize because you're taking cold oceanic plate and shoving it down there, and it's kind of it cools down and stabilizes. That's one idea that's not necessarily the right idea. There's a lot of debate about this. Mantle plumes could do it.
SPEAKER_01There's a lot of debate on this. Okay.
SPEAKER_00Yeah, mantle plumes are some people argue mantle plumes do this.
SPEAKER_01But you're a mantle plume guy, you know, so Yeah, we talk about Yellowstone all the time. Right. I mean, you put kids to sleep all the time, talking about chambers. So hanging out about that. Oh, so okay, so Jesse, can you just take please 30 seconds and tidy this up for us? Okay.
SPEAKER_00Okay, because then I then I want to move on. So to answer the question, we do have rocks older than three billion years old, but those rocks were not a part of a craton. They were stable because they're buoyant, so they kept in the crust, but they got bombarded a whole bunch, they got overprinted a whole bunch, whereas a craton is something that doesn't get metamorphosed or doesn't get deformed.
SPEAKER_01Okay, Jesse, let's uh continue on with your paper then. What are the takeaways? Like, I don't know, I would say like what give me give us three takeaways for the purpose of this paper, or your findings, actually, I think is what I want to ask.
SPEAKER_00So could I do one 30-second framing? What I think we need one more piece of information that kind of frames it.
SPEAKER_01That might take me off on another rabbit hole, but okay, go ahead.
SPEAKER_00So, what do you need to stabilize cottonal crust? Buoyancy. You need buoyancy, absolutely true. But what you also need is you need to get all the heat close to the surface. The thing has to be cold. You need to have a really thick and cool package of crust. And Chris, we've talked about this a bunch. Rocks have radioactive elements. When uranium, thorium, potassium decay, they release and produce heat. If you have that stuff down below, the thermal conductivity rocks don't conduct heat, so that heat kind of gets trapped down there deep. So you You have to remove, you have to take all the uranium, thora, and potassium and move it right near the surface. And what that means is you have to melt the crust. The best way to do that is to melt stuff deep down. All the uranium, thor, and potassium goes into the melt, the melt migrates up, maybe erupts out onto the surface as a volcano, and you have all your heat producing elements, what we call heat producing elements, uranium, thorough, and potassium, at the surface. So all the heat, the internal heat engine is at the surface, which means it can cool off and it can cool that whole block of crust down because there's no heat being produced down deep, or there's less heat being produced down deep. So Archean Kratons have loads, like shitloads of granite at the surface. There's granite everywhere in Archean Kratons because of this magmatic event that removed all the heat from the the deeper parts and put it up to the top.
SPEAKER_01That's the answer to my other question from a long time ago, then, right? In terms of why there's so much granite exposed in the Canadian sheet.
SPEAKER_00That is exactly why. So to frame it, people have debated what did this process, what would do all this melting? People have said mantle plumes. You put a mantle plume underneath of like a proto-continent and you melt the heck out of it, you move all that granite to the surface, you could stabilize it. A subduction zone is a great place to melt stuff. You're melting things, you're moving uranium, thorough, and potassium up near the surface, and you cool down that block of crust. So there's a bunch of different ways to do it. And what so I I don't know if you have other questions or you want me to sort of add some conclusions to this, but um or what our sort of thesis is here.
SPEAKER_01But I mean, I I I do have a question, and I guess the it's trying to best frame this. Why why would this happen where it happens? You know, what concentrates these radioactive elements that then rise up with the magma, and then and then the other thing, Jesse, is that okay, so they melt this stuff near the surface or at the surface. That doesn't form granite then, because granite is intrusive and it's it's deeper, it's slower. And so those are the two questions that I mainly have.
SPEAKER_00Maybe I I I don't think I explained this quite well. W the granite at the surface, it used to be a kilometer deep or three kilometers deep. So but near surface, not not 20 kilometers deep, but three kilometers deep. You need to mobilize the the heat-producing elements and get them up to the surface. The way to do that is if you have a rock deep down 30 kilometers deep in the lower crust, and let's say it's a sediment that has a bunch of uranium, thorium, and potassium, how do you get that uranium, thorium, potassium up to the surface? Really, the only way is to make a melt to melt that rock, and the magma that's formed loves uranium, thorium, potassium. What's left behind hates uranium, thorium, and potassium. So the melt gets enriched in uranium, thorium, potassium, and then the melt travels, migrates up like magmas do, to the near surface area. And then all that uranium, thorium, potassium is locked up there, and when it decays over the next three billion years, all the heat is just lost to the atmosphere very quickly instead of being trapped in the earth.
SPEAKER_01And the important thing with that too is that it has a lid. It has a lid, which is that's exactly right. Yes, yep, yep, exactly. That makes sense. Okay, I get you. So you set the stage, takeaway from your research.
SPEAKER_00The takeaway here is we've proposed another model, and I think in some ways a better model for how this could have happened. What was special about three to two point eight to two point five billion years ago? Why did cratons start to form then? And I think we provide a perhaps better model. Like we think mantle plumes have been happening since the beginning of Earth. So if mantle plumes are forming cratons, why did cratons only start forming 2.8 billion years ago? Why'd it take that long?
SPEAKER_01And what we Jesse, can I hold on? Let me interject a second. Can you really quick give a couple examples? Well-known examples of mantle plumes to paint a picture for everybody. Sure.
SPEAKER_00Well-known examples of mantle plumes are Iceland, has a mantle plume underneath it, also has a mid-ocean ridge, so tons of melting. That's Iceland's kind of a proto-continent. Hawaii is a mantle plume, Yellowstone is a mantle plume, and there's loads of melting going on in Yellowstone. So you can envision this scenario, like why this might be happening. Mantle plumes aren't necessarily a great way to form cratons, though, because they they melt everything. Like mantle plumes come up to the surface, they're huge. They like erase the root. There's they don't flip.
SPEAKER_01And they express themselves differently on the surface.
SPEAKER_00Yeah, it's exactly right. Exactly right. So back to the question, we're trying to answer the question of what was unique about Earth 2.8 to 2.5 billion years ago where all these cratons formed in this interval. And what we did is we looked around and said, well, what else was happening on Earth at that time? And there's pretty good evidence that prior to about 3 billion years, so before 3 billion years ago, the Earth was a water world, which means the continents that were there were mostly submerged below sea level. So they were subaqueous below sea level level, not subarial, exposed to the atmosphere. And if you look at the old rocks, the the rocks that are older than three billion years old, they're really intermediate rocks. They're like andesites, they're not granites. They're a lot more like andesites, they're not not that much granite around.
SPEAKER_01So they're very part about that is they're not as buoyant.
SPEAKER_00They're not as buoyant, they're different composition. They have less uranium, thorium, potassium in them. You also don't have sediments. There's not a lot of sediment on Earth prior to three billion years ago. Like those old rock terrains.
SPEAKER_01So why would there not be sediment if you had a water world?
SPEAKER_00Exactly. So that is a great question. I hope the listener is thinking about that a minute. Why would you not produce sediment? What do you need to produce sediment? Well, you need rock above sea level. Erosion isn't happening below sea level. You're not breaking minerals down. I mean, a little bit you are, but weathering under the ocean is just you form a little weathering rind on the rock. You don't actually break down rock and remove it with rivers or glaciers and put it out in the ocean, and then you have fresh rock exposed. So weathering and erosion is very much a process that happens when rocks are exposed to the atmosphere, not just to the ocean. So if continents are submerged below sea level, you don't form a lot of sediments. There are some sediments. Like you can imagine if all the continents are below sea level. If you raise sea level a kilometer, a lot of the continents are going to be underneath the water. What's going to poke above? It's going to be active volcanoes. Japan. Volcanoes poke up and then they get eroded down really quickly. That's not a huge volume of stuff. You produce lots of localized, yep. Very localized. And we that that did happen, but you didn't have like Mississippi River type drainage, Amazon, Nile River, weathering continents. So what we said is we made that observation that we said, okay, maybe this is important for melting the continents. What happens if you try and melt continents without sediments versus what happens if you try and melt continents with sediments? And it's a dramatic difference, especially when you go back in time, because two and a half billion years ago, there was a lot more uranium, a lot more thorium, a lot more potassium than there is today. So the heat blanket, the radioactive heating was a lot higher. So sediments have a ton of radioactive elements in them. They're really good at concentrating uranium, thorium, potassium, especially shales. So what we propose is continents raise above sea level for some reason, they start to form sediments, those sediments get thrust down deep in the earth, and they start to melt the continents because you've got all this radioactivity 30 kilometers deep, which melts everything, and that's a good way to form a thick, stable cratonic block of crust.
SPEAKER_01How did the sediments get thrust down 30 kilometers?
SPEAKER_00You would have to have something like plate tectonics to do that. And in my opinion, not everybody agrees with this, but my opinion is we have great evidence for subduction back then. So to me, that that is a an easy one. Like we think subduction was going on then, so you just add sediments to a subduction zone system and the sediments go down, but they get pushed deep underneath of the crust there. Yeah. And then they melt that crust.
SPEAKER_01That is now I think for everybody, if it I mean, my mom is undoubtedly asleep right now.
SPEAKER_00However, yeah, this is a good nap episode for Joyce. Yep.
SPEAKER_01But the title now makes complete sense. And I think to people that have been tracking that it does, it makes complete sense now that subarial weathering drove the stabilization of the continents because we had these sediments that were being driven down in subduction zones, rich in these radioactive elements and causing melting that took place.
SPEAKER_00Exactly. And so if you'd allow me, Chris, am I allowed to say two little things here? Yeah, keep it tight. Okay, keep it tight. So uh thing number one is that this process would be more important back in time because there's more radioactivity back in time. Sediments today, they have less uranium, thorough, and potassium because a lot of it's decayed away compared to three billion years ago. So this process would be a more powerful process back in time. So it would explain why cratons formed three to two point five billion years ago, but they aren't really forming that much now, or they're not forming by this process today. There's a big difference between Earth as a teenager and Earth today because of radioactivity. And the second point I want to make is that this paper, well, my postdoc supervisor, Rick Carlson, who's a very, very, very highly regarded scientist in the early Earth Planetary Science community, really top-flight scientist, he always described nature papers as the best nature paper was a good idea that might even be right. Which, you know, it means it's like one of those interesting ideas, but it's certainly unproven, and you know, it could be wrong. And I would put this paper that we've written is very much in that category. Like it is it's a new idea. There's a little bit of evidence, there's like hints of evidence backing this up, but it certainly needs to be tested. We have to go out and test this. It's provocative, but untest like not untested. It's a good story, it makes sense now, but we need to go test it. Kind of like Mike Eckerson, we talked about Mike Eckerson's nature paper on granite formation. It's the same as that. There's good evidence for this proposal, but we really need to go test it more.
SPEAKER_01Are you gonna present this at GSA or AGU?
SPEAKER_00Yeah, uh I think Andy Smai, co-author, my co-author is he's gonna present it at the Goldschmidt Conference, which is the geochemistry conference, and um the other conferences are not till the fall. So we'll we'll yeah, we'll we'll be presenting this around at conferences for sure. Just because it's something that we we we think needs to be tested by a bunch of people, a bunch of different lab groups, not just us, other people.
SPEAKER_01So would you be nervous standing up in front of a group of scientists, your peers, and presenting this?
SPEAKER_00I gave I gave about 75% of this talk, uh of this idea at a conference about a year and a half ago. I was very nervous. Um, it was risky.
SPEAKER_01It's always a nerve-wracking thing, anyway.
SPEAKER_00Especially when it's something that's new that hasn't been like reviewed and you don't know what the response is gonna be. I would say I had a couple nice comments, a couple people said that's really interesting, really cool. And then a couple people were like, Yeah, you know, in my part of Australia or Canada, I don't think there's good evidence for that. So, you know, you haven't considered some things, which is which is good. Like that, you know, that's the conversation you kind of want to have.
SPEAKER_01So yeah, I've seen these things go sideways, so that's why I've asked.
SPEAKER_00Yeah, no, exactly. Exactly.
SPEAKER_01So, Jesse, maybe we're ready to wrap this up, but I want to like I want to finish maybe.
SPEAKER_00Yeah, I don't know. No, no, I'm kidding.
SPEAKER_01Um, I guess I want to know where this idea came from.
SPEAKER_00Oh, uh this is good. It came from a a conversation over a couple beers in my living room. Really? It was just you know with who? With Andy Was it with Andy? With Andy Smile, yeah, really and and uh another colleague, and we were just kind of talking shop, you know, talking about research. How's your research going? What are you thinking about? You know, this kind of thing. And so it's really it's really fun that way because it's just a conversation with colleagues that ends up, you know, you kind of have these conversations. It's like you and I, Chris. We were talking about we were circling like the Camp Geo thing, you know, making audiobooks with images. We didn't come up with that idea out of thin air. We talked about a problem for a long time. We kind of went back and forth. You wanted to do a course in the podcast, you wanted this podcast to be like a course. I didn't really want that. We went back and forth. Then we're like, we need images, maybe we don't need images. How do we make it work? And then it kind of hit. We're like, wait, we need to build an app for this. Like it was very much like that. Uh very casual conversation where you're just kind of batting around ideas, and then somebody says something, and you're like, oh wait, that might be interesting.
SPEAKER_01That is interesting.
SPEAKER_00How long was this process then? What's that? How long was this process? Oh boy, probably about two years, year and a half, two years. It just takes a while. But you know what? These ideas, sometimes those ideas happen, and then you go and you like set you look at the literature and it's like, oh wait, somebody did that in the 80s. It was a good idea. I just didn't know somebody'd already done it or whatever. Or maybe you realize, wait, that was a terrible idea, and here's why. But this one, it kind of was like, no, wait, this might be a good idea, and we kept going deeper and deeper. And so, but like I said, it could be wrong. I and I think you know, I was excited to do this as a podcast episode in large part because I love talking about this, but I also think it's a good way to introduce the early earth. I think it's something that many people don't know, even really good practicing geologists don't really have a full grasp of how different the early earth was compared to our modern planet and how little we know about the early earth. Like we don't know what was going on 2.8 billion years ago, which is Earth was a teenager, like we didn't understand that. That is kind of crazy, right?
SPEAKER_01So we throw around big numbers all the time, yeah. And sometimes we uh get into a little funk with that. We maybe throw them around a little too flippantly.
SPEAKER_00That's right.
SPEAKER_01We really do know what was going on, and that's a really good word, flippantly.
SPEAKER_00It's a good way to describe it for sure, for sure.
unknownCool.
SPEAKER_00All right, what's next? Well, we're gonna go test this. What we need to do is one of the beauties of this paper, one thing I'm really excited about is that it's really good science and that it's a hypothesis that outlines how it should be tested. And if this model is true, there should be a bunch of sediment preserved in the roots of cratons. And so we need to go look for that. And there's very specific predictions that you can make based on what those should look like now, because the model suggested how it forms. So we're gonna go look for those. We're gonna go. I mean, hopefully, we're gonna write some proposals to kind of have students funded to go do work in South Africa and up in Canada and look at the minerals in detail, and so yeah.
SPEAKER_01So the most interesting thing you said this whole episode is that last sentence about we're gonna go look. There should be sediments buried in the cratons. I you know, like, yeah, that's really interesting.
SPEAKER_00That's one outcome. Well, I mean, if this model is is accurate at all, that they should be there. That's what they're doing.
SPEAKER_01So when does it start then? When are you when are you gonna go look?
SPEAKER_00Well, we've done some like literature review at the moment to kind of see what rocks do we know of. We're gonna write a proposal that is gonna go in South Africa in the what's called the Kapval Kraton. There's a big meteorite impact, the Vreda Ford impact structure. Meteorite impact hit, huge impact, and it tilted the crust. So basically, we have uh there's a tilted crust. So you have exposed rock then. Exactly. We get there is exposed crust from from deep, you know, 30 kilometer deep crust gets brought up to the surface, but you don't know how biased that is. Was that just a really squishy bit that got brought up? In the Alps, there's a there's some lower crust that's been exposed. This is a meteorite impact and it just tilted it. So you're getting like an unfiltered view, unbiased view of the Archean lower crustal package. So we go look for sediments in that package, which will be fun. Really cool. Yeah, yeah. So hopefully hopefully, uh, so if anybody from NSF is listening, you should fund this proposal. Time frame? You know, ideally the shortest it would be is submit the proposal here in a couple months, hear back in six months that it's funded, try and go like next summer, next fall, maybe to go to a year and a half, yeah, year and a half before we even get started, and that would be collecting the samples. And this is probably like PhD project level, so results coming online two or three years from now, kind of thing. So, but hopefully there will be other people who have these rocks in hand who read our paper and say, wait, I can test that with my rocks I have in the lab, let me go look. That would be a quicker way to do it. We kind of have to go chase funding, so which takes a lot longer.
SPEAKER_01Very, very interesting, Dr. Ryman. Well, I see I called you doctor.
SPEAKER_00Thanks for supporting.
SPEAKER_01I ripped on you in my class today.
SPEAKER_00So yeah, what'd you say?
SPEAKER_01Yeah. I said I just talked about how you like to be called doctor. Oh, yeah, and how I don't like to call you doctor, and then I'm like, you know, he doesn't really deserve it.
SPEAKER_00And so did you tell them that you like to be called doctor by some of our listeners? No, you didn't say that. No, that's uh I didn't say that.
SPEAKER_01No, I'm not gonna do that.
SPEAKER_00Well, when I zoom in with your class sometime soon, I'll uh I'll tell them that you like to be called doctor too every once in a while.
SPEAKER_02Okay.
SPEAKER_00All right, all right. All right, hey. Well, thanks, Chris. Thanks for humoring me. This was uh this was a fun episode for me. I hope it was fun for you, and I hope it was fun for the listener. You can find out more about us, go to planetgeocast.com. You can support us. There's two ways to support us, and we appreciate both of them. Go to planetgeocast.com, there's a support us link there to help us, you know, keep the show on the road. You can also go to the first link in our show notes, which is the Camp Geo app. You can download our mobile app, you can listen to a whole bunch of content regarding basically the intro to geosciences, the Camp Geo content. We also have several audiobooks for sale as well there that you can buy visual audiobooks. So listen to Chris and I talk about Yellowstone and the Grand Canyons with all the images you need to learn really deeply. So head there. If you have any questions, send us an email, planetgeocast at gl.com. Cheers.