When Continents Became Stable
[00:00:00]
what's, what is the cold intro, Dr.
Dr. Jesse Reimink: It's a cold open. It's a,
Chris Bolhuis: Cold. Oh, cold open. Sorry. Sorry.
Dr. Jesse Reimink: 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 [00:00:30] why I was giggling to myself? Do you, do you, can you hazard a guess?
Chris Bolhuis: Hmm. I have, I have no idea why it's been a good few days, but I don't know why you'd be
Dr. Jesse Reimink: I was giggling to myself because a couple days ago, I called you and I had a little bit of what I thought was cranky Chris on the phone. So,
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.
I'm just upsetting. [00:01:00] Uncomfortable. I was dying. You were just like, no, I'm not cranky. I'm just uncomfortable.
Chris Bolhuis: I 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.
Dr. Jesse Reimink: Yeah,
Chris Bolhuis: anybody that knows me knows I love food so much. And I made something really good. And it was a spicy sausage lentil soup
Dr. Jesse Reimink: oh, that's, that sounds good.
Chris Bolhuis: it [00:01:30] was good. And it was, it was, Oh, 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. And then I went back and I'm like, well, I'm still kind of hungry. So
Dr. Jesse Reimink: So
you made
Chris Bolhuis: filled another one up and when I demolished it, yeah, it was not a good life decision
right there.
Dr. Jesse Reimink: no, no. That's right.
Chris Bolhuis: not a, yeah, well you're so yeah. Jesse, come on now.
You don't cranky Chris. is he really a thing? I get cranky Jesse
Dr. Jesse Reimink: let's get Jenny out. [00:02:00] 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
you're, you're rarely like low That 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.
Chris Bolhuis: Yes, I do allow myself I don't, I was going to say luxury, but it's not really luxury. I do get worked
up. I, I, I, I
happens. Yeah.
So you get emotional, [00:02:30] Chris, sometimes.
Dr. Jesse Reimink: Yeah, yeah, yeah. That's right. That's right. You know, just depending, is it the positive emotions or the negative emotions, but I'm pretty sure looking at you, I got the positive emotion, Chris, on the
line right now.
Chris Bolhuis: you 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.
Dr. Jesse Reimink: Yeah. Co authored.
Chris Bolhuis: And yeah, coauthored, I'm sorry. I'm not using proper terminology there for Dr. Reimink.
Dr. Jesse Reimink: The doctor is in the
house [00:03:00] for this episode.
Chris Bolhuis: Yeah. And I'm going to apologize to all of our listeners outright for that.
But, we're going to talk about this paper. Jesse. because this was, well, let me ask you, Where is this to be published?
Dr. Jesse Reimink: yeah, so this is published in Nature, um, which is the big dog, I guess, I mean, this
Chris Bolhuis: That's the top tier, right? That's a big, wow. That's a big
Dr. Jesse Reimink: when you think of scientific publications, Nature and Science are the, they're the really the [00:03:30] oldest ones. They're short papers. They're interdisciplinary. you know, it, 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, 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 our Yellowstone National Park audiobook is going to be [00:04:00] available in the bookstores in Yellowstone National Park.
We're partnering with Yellowstone Forever to, have them displayed in Yellowstone National Park and sort of been approved by the National Park Service. And so, that's a really exciting development for us on the Camp Geo app.
Chris Bolhuis: that was not enthusiastic enough, Jesse, because that is so awesome. I've been on cloud nine for the last three
days. You
Dr. Jesse Reimink: we, we, we've had a good, we've had a
good little run here. Yeah, we've had a
good little run, and we're just super [00:04:30] excited. Yellowstone Forever is gonna partner with us on this, and, uh, it's great. super excited about this.
Chris Bolhuis: Okay. Jesse, can we get down to this a minute? So the title of your co
authored
Dr. Jesse Reimink: um, uh, hold on. I'm, I'm putting on my emotional, armor right now. Cause I, I get the sense I'm going to get a lot of crap here this episode
Chris Bolhuis: so I don't know. yeah, you might, you might, but I, I do have to be careful because you did coauthor it and I don't want to offend your coauthor in the least bit. I maybe only [00:05:00] want to offend you a little
bit, but
Dr. Jesse Reimink: Andy Smy is quite hard to offend, so don't
Chris Bolhuis: okay, that's good to know. That's good to know. All right, Jesse.
So the title of your paper. Alright, Jesse. This paper then is released in nature.
Dr. Jesse Reimink: that's right.
Chris Bolhuis: Right now, as we release this episode, this is, this is a paper that is
Dr. Jesse Reimink: Yeah, that's right. And 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
Chris Bolhuis: Yeah. I hate that when I don't get open
Dr. Jesse Reimink: I know. [00:05:30]
Chris Bolhuis: you know.
Yeah. Okay. Awesome. So the title of the paper, Jesse is everybody ready? It is called sub aerial weathering drove stabilization of continents. Okay.
Dr. Jesse Reimink: And everybody goes wild and the crowd goes
Chris Bolhuis: That's it's crazy. Okay. Let me read it again. Just for impact. Sub aerial weathering drove stabilization of continents.
Okay. Can, can we talk about this a minute?
Okay. Go
Dr. Jesse Reimink: I [00:06:00] 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? Cause 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
Chris Bolhuis: okay. Can I answer your question with another question then, which is why is this important? An important question to answer.
Dr. Jesse Reimink: Oh, yeah. [00:06:30] Okay. We probably need to do a bit of Archean geology background here a little bit to, to kind of understand. 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, yeah. Understanding the continents is a really important, thing to understand when we compare our planet to [00:07:00] other planetary bodies.
Chris Bolhuis: yeah, 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
Dr. Jesse Reimink: That's right. And so, 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 bit of an open question.
Chris Bolhuis: Okay, so are you saying then, let me re ask the, I don't know if I want to re ask the [00:07:30] question, but are you saying that the purpose of this paper then is to answer the question about why Earth is unique?
Dr. Jesse Reimink: Kind of, yes. I mean, it is really, it's certainly related, intimately related to that topic. Why is earth
a unique planet? Why is earth different from Venus?
Chris Bolhuis: don't you think you need help with title work then, Jesse? Like, I don't know, like, I don't know. [00:08:00] I think I came up with a, maybe a more interesting, I don't know, I would not have gotten what you said, which I, by the way, 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
Dr. Jesse Reimink: Now, so this is, it's a difficult thing, right? Because,
well, there's some nuance to it because like, okay, I, we [00:08:30] 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, toe 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
Chris Bolhuis: I know
Dr. Jesse Reimink: I'm
not good at paper titles, so, there's people who are better at [00:09:00] this, but it is a hard one, I think, for most people,
Chris Bolhuis: That's a really interesting comment I find that amazing. because I think that this title what you're really. Trying to
Dr. Jesse Reimink: I, 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.
Chris Bolhuis: So if I go back to, and I think everybody, if you did [00:09:30] not listen to our episode on how to read a scientific paper,
go
Dr. Jesse Reimink: a fun one, Chris. That was a
Chris Bolhuis: it was fun and we got some really good responses, you 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 sit down for an hour and slug it out with this article that Jesse and, and his co author wrote.
So, but can I read the first
sentence? [00:10:00] Okay. Well, the, okay. So again, again, the title is suburb. Sub Aerial 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. I think it's an awesome title. I think it's catchy and I think it's [00:10:30] intellectual enough for, the circles you run in.
Dr. Jesse Reimink: I totally agree. It's a, I love that intro sentence. I'm glad it, I'm glad you liked it too.
Chris Bolhuis: I do.
Dr. Jesse Reimink: In that, in 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 [00:11:00] suggesting here.
Chris Bolhuis: All right. Let's get into that in a minute. So can we, I'm going to have you set the stage for this because you then go into very quickly into cratons
and. I'm going to 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?
Dr. Jesse Reimink: what they are, first of all, is cratons are big [00:11:30] blocks of continental crust that have a thick mantle keel beneath them that are
stable. Mantle keel, like mantle keel, like a boat's keel underneath 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 plate bit above it, the continental raft at [00:12:00] the top is stable for billions of years as it gets batted around the earth by plate
tectonics.
Chris Bolhuis: Interesting. So can we talk a minute then about does that,
Dr. Jesse Reimink: Chris, 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 Craton The Canadian Shield is kind of another term for what we think of the North American Craton. If you go up to the Canadian Shield, you're walking across 2.
5 billion year old granites that look exactly the same [00:12:30] as the granites in Yosemite National Park that we talked about with Mike Akerson 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, think of it like an iceberg being blown around ocean, and it kind of bumps into other stuff, but it doesn't actually do anything, it just sits there.
Chris Bolhuis: I have so many questions based on what you just said now that I want to do my job in this episode, which is [00:13:00] keeping us on track, but a couple of 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
Dr. Jesse Reimink: Those are really, that's a really good question. The, I'll go to the second one first and 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 [00:13:30] order, like classes, second level classes.
Chris Bolhuis: Okay. And I asked that question only because today I introduced the word Craton to my students because we were doing geochronology, relative dating, and I, drew up a cross section. on the Algoma district 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. And one [00:14:00] of them involved, yeah, one of them involved a crotonic setting. And. They did not know what that was.
And so I had to introduce just today, actually, what craton and cratonic
Dr. Jesse Reimink: so you don't, you don't often do this in class or is
this not every year? Okay. And how did the
Chris Bolhuis: know. I actually, I do this, but I don't use cratonic.
Yes.
Dr. Jesse Reimink: Yeah.
Chris Bolhuis: Okay. Sorry. So I interjected, but
Dr. Jesse Reimink: examples.
Yeah. So, I refer to cratons. What [00:14:30] 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 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 San Francisco Craton, 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 [00:15:00] over. They're underlying continents, mostly.
Chris Bolhuis: Okay. And does it refer also to a specific rock type?
Dr. Jesse Reimink: No, kraton is a block of stable crust, and it can be made up of a whole bunch of different rocks.
Chris Bolhuis: do I live in Southwest Michigan? Am I a part of the North American Craton?
Dr. Jesse Reimink: you would be. I mean, 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.
Chris Bolhuis: Yeah, that's the way I describe it to my students. [00:15:30] 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.
Dr. Jesse Reimink: That's exactly right.
Chris Bolhuis: so, 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?
Dr. Jesse Reimink: so cratons sort of by [00:16:00] definition, they just bob right near sea level. Kind of, they're a little bit exposed above or a little bit below. North American cratons are 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. 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 [00:16:30] 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, we, Talked about the Grand Canyon. Uh, you know, the, the, the nice is that that's, that's basement. That's Craton. That's North American Craton, exposed at the bottom of the Grand Canyon.
It's 1. 8 billion years old. So that's a younger Craton, but we don't have anything older than 3 billion years old that, that would qualify as a Craton. So we kind of got, Earth got to sort of teenage years and cratons started forming. that's kind of the [00:17:00] question we're addressing, like why that time, what was going on that, if we go back further than that, the rocks are different,
there
Chris Bolhuis: So 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?
Dr. Jesse Reimink: That'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 as continental crust, rocks that are more like granite, they're not quite granite in the Archean, [00:17:30] 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, 4 billion year old rocks, I did my PhD on, those have been
Chris Bolhuis: Just so everybody knows, me and few of your other close friends used to just call you Acosta.
Dr. Jesse Reimink: Yeah, yeah, that's right. You wouldn't even, you wouldn't even give [00:18:00] me the dignity of calling me Mr. Acosta. It was just Acosta.
Ha ha ha ha ha. Yeah.
Chris Bolhuis: Hey, Acosta, shut
Dr. Jesse Reimink: Cause every time I'd just be rambling on about Acosta.
Um, yeah, exactly. So, if you, so, 4 billion year old rocks, they're silica rich, they're intermediate composition rocks, so 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 [00:18:30] 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 state. A stable thing. They're not part of a craton.
A craton is like this block of crust that nothing happens to it. It just,
Chris Bolhuis: It's too buoyant that it's too far away from all this
Dr. Jesse Reimink: 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.
Chris Bolhuis: You get the segue word because [00:19:00] that was my next question. does the continent develop this keel?
Dr. Jesse Reimink: Oh,
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 kimberlite [00:19:30] 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 on, and you shove another layer, you can kind of stack, what's called stacking, you stack these [00:20:00] things together and it gets thick, and then it can be cut.
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 maybe do
this. Yeah. Mantle plumes are, some people argue mantle plumes do this, but
the cr,
Chris Bolhuis: a mantle plume guy, you know, so
Dr. Jesse Reimink: we talk about Yellowstone all the time.
Chris Bolhuis: right. I
mean, you put kids to sleep all the
time. Talk about what is the magma chamber? [00:20:30] So, all right. Um, so, um, Okay. So Jesse, can you just take, please, 30 seconds. And, and tidy this up for us.
Dr. Jesse Reimink: Okay.
So,
Chris Bolhuis: I, then I want to move on.
Dr. Jesse Reimink: so to answer the question, we do have rocks older than 3 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.
Chris Bolhuis: Okay. Jesse, let's. [00:21:00] Continue on with your paper, then, What are the takeaways? Like, I don't know, I would say, like, give me, give us three takeaways for the purpose of this paper. Or,
your findings, actually, I think is what I want to ask.
Dr. Jesse Reimink: So could I do one 30 second framing? I think we need
Chris Bolhuis: Yeah,
Dr. Jesse Reimink: piece of information that kind of frames this.
Chris Bolhuis: take me off on another rabbit hole,
Dr. Jesse Reimink: okay, So what do you need to [00:21:30] stabilize continental crust?
Chris Bolhuis: Buoyancy.
Dr. Jesse Reimink: 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, and 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 [00:22:00] you have to remove, you have to take all the uranium, thorium, and potassium and move it right near the surface. End. 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, thorium, 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, thorium, 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 [00:22:30] block of crust down because there's no heat being produced deep down.
down deep, or there's less heat being produced down deep. So Archean cratons have loads, like, shitloads of granite at the surface. there's granite everywhere in Archean cratons because of this magmatic event that removed all the heat from the the deeper parts and put it up to the top. Okay.
Chris Bolhuis: That's the answer to my Other question from a long time ago then, right? In terms of why
Dr. Jesse Reimink: Yeah,[00:23:00]
Chris Bolhuis: so much granite exposed in the Canadian
Dr. Jesse Reimink: that, that's, is exactly why. so to frame it, people have debated what did this process, what, what would do all this melting? People have said mantle plumes. You put a mantle plume underneath of like a protocontinent, 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, thorium, potassium up near the surface, and you cool down that block of crust. So there's a [00:23:30] bunch of different ways to do it. And what so I don't know if you have other questions, or you want me to sort of add some conclusions to this, but or what our sort of thesis is here.
But
Chris Bolhuis: I do have a question and I guess 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, [00:24:00] okay, so they melt the stuff near the surface or at the surface that doesn't form granite then because granite is intrusive and it's, it's deeper and slower and, So
those are the two questions that I mainly
Dr. Jesse Reimink: maybe I don't think I Explain this quite well. the granite at the surface, it used to be a kilometer deep or three kilometers deep like it. So, 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 [00:24:30] 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, 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, 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 [00:25:00] then all that uranium, thorium, potassium is locked up there, and when it decays over the next 3 billion years, all the heat is just lost to the atmosphere very quickly.
instead of being
trapped in the earth.
Chris Bolhuis: and the important thing with that too, is that it has a lid,
which is, which is yes. Okay. That makes sense. Okay. I get you. so you set the stage
takeaway from your research.
Dr. Jesse Reimink: The takeaway here is we've proposed another model, and I think in some ways a better model, [00:25:30] for how this could have happened. was special about 3 to 2. 8 to 2. 5 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 did it take that long? in
Chris Bolhuis: Jesse, can I hold on? Let me interject a second. Can you really quick give a couple examples, well known [00:26:00] examples of mantle plumes to paint a picture for
Dr. Jesse Reimink: sure. well known examples of mantle plumes are Iceland has a mantle plume, underneath it also has a mid ocean ridge, so there's 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. [00:26:30] There's they don't
form a
root.
Chris Bolhuis: differently on the surface.
Dr. Jesse Reimink: that'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 [00:27:00] means the continents that were there were mostly submerged below sea level. So they were sub aqueous below sea level, not sub aerial exposed to the atmosphere. And if you look at the old rocks, 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. And there's very little sediment.
Chris Bolhuis: they're not as buoyant.
Dr. Jesse Reimink: not as buoyant, they're different composition. They have [00:27:30] less uranium, thorium, potassium in them.
You also don't have sediments. There's not a lot of sediment on earth prior to 3 billion years ago.
Like those
Chris Bolhuis: Okay. Hold on.
Dr. Jesse Reimink: terrains.
Chris Bolhuis: So why there not be sediment if you had a water world?
Dr. Jesse Reimink: 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 [00:28:00] 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 [00:28:30] imagine 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 sediment.
Very low class, and 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 and we [00:29:00] 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 [00:29:30] concentrating uranium, thorium, potassium, especially shales. so what we propose is continents raised 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, block of crust.
Chris Bolhuis: did the sediments get thrust down 30 [00:30:00] kilometers?
Dr. Jesse Reimink: You 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 then.
So to me, that, that is a, an easy one. Like we think subduction was going on then. So you just add subduction zone system and the sediments go down they get pushed deep
underneath of the crust there.
Yeah.
Chris Bolhuis: All right. That is Now, I think for everybody, if you, I mean, my mom is undoubtedly [00:30:30] asleep right now. However,
the, the title,
Dr. Jesse Reimink: nap episode for Joyce. Yep.
Chris Bolhuis: But the title now makes complete sense. And I think to people that have been tracking, that it does, it makes complete sense now. that sub aerial 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 [00:31:00] melting that took
Dr. Jesse Reimink: exactly. and so if you'd allow me, Chris, am I allowed to say two little things here?
Chris Bolhuis: Keep it
Dr. Jesse Reimink: 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, have less uranium, thorium, potassium because a lot of it's decayed away. compared to 3 billion years ago. So this process would be a more powerful process back in time. So it would explain why formed 3 to 2. 5 billion years ago, [00:31:30] 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 [00:32:00] 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, [00:32:30] but we need to go
test it. Kind of like Mike Akerson.
We talked about Mike Akerson'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.
Chris Bolhuis: Are you going to present this at GSA or AGU
Dr. Jesse Reimink: Yeah. Uh, I think Andy Smy coauthor, my co-author is he's gonna present it at the Goldman 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 'cause it's something that we, we, we [00:33:00] think needs to be tested by a bunch of people, a bunch of different lab groups, not just us, other people.
Chris Bolhuis: so would you be nervous standing up in front of a group of scientists, your peers and presenting
Dr. Jesse Reimink: I gave, I gave about 75% of this talk of this idea at a conference. about a year and a half ago, I was very nervous. Um, it was,
Received, yeah, especially
when it's something that's new that hasn't been like reviewed and you don't know what the response is going to be. I would say I had a couple of [00:33:30] nice comments, a couple of people said that's really interesting, really cool.
And then a couple of 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. So
Chris Bolhuis: Yeah, I've seen these things go sideways. So
that's why I've asked. Um,
Dr. Jesse Reimink: exactly,
Chris Bolhuis: so Jesse, maybe we're ready to wrap this up, but I want to
like, I
want to ask one final question. Maybe. Yeah, I know. I know. I know.
um, I guess. [00:34:00] I want to know where this idea came from.
Dr. Jesse Reimink: Oh, uh, this is good. It came from a conversation over a couple of beers in my living room.
Really? It
was just, you know,
with Andy Smott, with
Andy?
Smott. Yeah. 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 was really, it was 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, when [00:34:30] we were talking about, we were circling like the Camp Geo thing, you know, making audio books 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, 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 and we
were like, wait, we need to build an app for this. Like, you know, it was very much like that, uh, very casual conversation where you're just kind of [00:35:00] batting around ideas and then somebody says something and you're like, oh wait, that might be interesting.
and that happens a lot. What's that?
Chris Bolhuis: How long was this process?
Dr. Jesse Reimink: 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 had 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 [00:35:30] 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, cause 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 [00:36:00] is, Earth
was a teenager.
Like we didn't understand that. That is, it's kind of crazy. Right. So
Chris Bolhuis: yeah, it is, because we throw around big numbers all the time, and sometimes we uh, get into a little funk with it, we maybe throw them around a little too
Dr. Jesse Reimink: that's right. I
Chris Bolhuis: do know
what was going on, and
Dr. Jesse Reimink: that's a really good word. Flippantly. That's a good way to describe it For
sure. For sure.
Cool.
Well,
Chris Bolhuis: next?
Dr. Jesse Reimink: well, we're going to go test this. What we need to do is one of the beauties of, of this paper, one thing I'm really [00:36:30] excited about is that it's really good science in 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 that, how they would form.
So we're going to go look for those. We're going to go I mean, hopefully we're going to write some proposals to kind of have students funded to go do work in South Africa and [00:37:00] up in Canada and look at the minerals in detail. And so, yeah.
Chris Bolhuis: So the most interesting thing you said this whole episode is that last sentence
about, we're going to go look, there should be sediments buried in the cratons. I, you know, like, that's really
interesting.
Dr. Jesse Reimink: one outcome. I mean, if this model is accurate at all, they should be there.
That's what this model predicts.
Chris Bolhuis: then? When are you, when are you going to look? Okay.
Dr. Jesse Reimink: done some like literature review at the moment to kind of see what rocks do we know of. we're going to write a proposal. That is [00:37:30] going to go in South Africa in the, what's called the Capval Craton, big meteorite impact, the Vredefort impact structure, meteorite impact hit, huge impact, and it tilted the crust, so basically we have, uh, there's a tilted
crustal section 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 [00:38:00] 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
Chris Bolhuis: Really cool.
Yeah.
No kidding.
Dr. Jesse Reimink: hopefully, uh, so if anybody from NSF is listening, you should fund this proposal.
Chris Bolhuis: Time frame.
Dr. Jesse Reimink: you know, ideally the shortest it would be is submit the proposal here in a couple months, here back in six months that it's funded, try and go [00:38:30] like next summer, next fall, maybe, to go do some field work.
Yeah, a 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.
Chris Bolhuis: [00:39:00] very very interesting. Dr.
Dr. Jesse Reimink: Well, thank,
thank you
thanks for supporting
Chris Bolhuis: ripped on you in my class today.
So,
uh, yeah. I said, I just talked about how you like to be called doctor and how I don't like to call you doctor. And then I'm like, you know, doesn't really deserve
it.
And
Dr. Jesse Reimink: it's true, Did you
tell them that you like to be called doctor by some of our listeners?
Chris Bolhuis: no,
Dr. Jesse Reimink: didn't say that? Oh, well you
Chris Bolhuis: didn't say that I'm not gonna
Dr. Jesse Reimink: Well when I zoom in with your class sometime soon, I'll uh, I'll tell them that you [00:39:30] like to be called doctor too every once in a while.
Chris Bolhuis: okay. All right. All right.
Dr. Jesse Reimink: Shoot. All right.
Hey, well, thanks, Chris. Thanks for humoring me. This was a, 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.
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We also have several audio books for sale as well there that you can buy. Visual audio books. So, you know, listen to Chris and I talk about Yellowstone or the Grand Canyons with all the images you need to learn really deeply. So, head there. you have any questions, send us an email planetgeocast at gmail.
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Chris Bolhuis: Cheers. [00:40:30]
