Earth's Oldest Fragments
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[00:00:00]
got radio, Chris.
Chris Bolhuis: I guess this is the best I can do today, Jesse. So,
Dr. Jesse Reimink: we have not full, not a hundred percent Chris right now? Or what, what does that mean?
Chris Bolhuis: no, it doesn't mean that at all. Um, it's just sometimes I wish I had a better radio voice. I've got [00:00:30] this radio face to go with it, you know, but I don't have, I need this more of a baritone kind of thing
Dr. Jesse Reimink: I think, I don't know, man. I think
got a good radio voice. You have a commanding presence.
You've got a, you've got some authority that conveys through that voice. I like it. I could
listen to Chris Bolhuis at 2. 30 AM while driving across the country.
And he wouldn't put me to sleep necessarily.
I don't
think.
Chris Bolhuis: tell you I tell you what, I put my mom to sleep. Every time I go over there on Friday afternoon, she's listening to our podcast and she's sleeping. I'm starting to think she stages it [00:01:00] this way
Dr. Jesse Reimink: Yeah, She might do. Any new words from Joyce? Any update from Joyce recently?
Chris Bolhuis: oh no. But they just listened to the episode where we were ripping on my dad's, um, the way he talks in his strong diaphragm.
Dr. Jesse Reimink: What were the repercussions about that
Chris Bolhuis: So I, I asked my mom, cause my dad hadn't joined us yet. And I said, is he, is he mad at all? And she said, Oh no, we laughed our butts off about that. And you know, they were
fine.
Dr. Jesse Reimink: good. Alright. I mean, that's the good thing about the Bolhuis family, the Bolhuis clan, is you're [00:01:30] pretty good spirited giving each other a hard time.
Chris Bolhuis: Yeah, we, we try not to take each other too seriously, you know, or take ourselves too seriously.
Dr. Jesse Reimink: right. So
it's, uh, it's good fun over there, Bolhuis clan. Yeah.
Chris Bolhuis: thing too, totally off topic, but we're interviewing for new teachers and you, you said something about a presence and it is really interesting when you have people that you've never met before, they're interviewing for a job.
it's just so interesting when people walk into a room and some people [00:02:00] have that immediate presence about them. And some people just don't, I, I haven't been a part of interviews for quite a while. It's been a long time. And I was just reminded of that. Like it was soon as somebody walks in a room, they, some of them, they just have that presence and then others don't, I don't know what to, it's an interesting thing to think about
and what
Dr. Jesse Reimink: know,
Chris Bolhuis: that.
Dr. Jesse Reimink: I, I think for me, this is my opinion, which, because we, there's a lot of conversation in let's say higher ed, about the value of advanced degrees, like what is the value of a master's [00:02:30] and a PhD?
And this is one thing that I think is really valuable, because when you're presen I mean, you know, Chris, when you're presenting, as a teacher, you're presenting all the time, so you kind of have to, to be good at it, you have to either develop that skill set, that presence, or you're kind of, you know,
You you've developed it earlier in life or something. But is one thing that in graduate school, I think you kind of have to build and you, become good at is yeah, that presence, you walk up there, you're presenting your work, your thesis, or you're, you
know, you're giving a talk somewhere you have [00:03:00] to have it. And you work really hard at those soft skills at developing those.
So I think it is something that you can learn. I certainly didn't have it early on. And I've
developed,
Chris Bolhuis: now?
Dr. Jesse Reimink: think so. I think in a classroom, I have developed a bit of a presence or at least, and I think it's that confidence, I don't know, for me, it
was that confidence, like building up confidence so that I could, I knew that I could answer any question that
was thrown at me, or at least deflect confidently,
right? It was a little bit of internal [00:03:30] confidence that had to be built up to, to get to that level. I don't know. What do you think
Chris Bolhuis: I think it is confidence. It's really hard to put your, put your thumb on what that is. Some people just automatically command a room and I don't really know what that is. And that's so it's hard to. To develop something that I can't even really quantify. I don't even really know what a presence is other than it's, it's a good way to describe it, but I still don't know what it is,
Dr. Jesse Reimink: it's so interesting to watch. I've seen this, you know, several times in, [00:04:00] including in my own development is watching a student go through graduate school and you see them develop the presence. We actually had one of our, one of the graduate students in our group just defended her, her PhD and did an amazing job at it.
And you kind of, I mean, she was always pretty good, had a pretty good presence, but now she's like, it's a no joke presence. Like, you know, she looks into the
room and you're like, okay, this is somebody where everybody perks up their ears. Right. And
But so it's, it's really fun to watch that development over the course of a degree
program. Right. Um, I'm sure it's the same for you. Like you're on the, the maybe older end of [00:04:30] the teacher's spectrum.
You probably have seen young teachers kind of develop it maybe, or,
Chris Bolhuis: Absolutely. Yeah Yeah, for sure. you get to watch that happen. It's kind of a cool thing to see
I have a question for you, Jesse, then, when they defend and they do this successfully, it's gotta be a really intimidating environment, by the way, do you make them, when they walk out of the room, do you bring them back in and call them doctor?
Dr. Jesse Reimink: oh, of course. Yeah, yeah,
for sure. I mean, you know, at a PhD, the defense is usually a little bit more lighthearted than
the earlier tests you [00:05:00] take, like you take a test in
your second year and third year, and those are, those are more there's more risk. By the time you finish your PhD, you've written a thesis. It's just how well do you do? Like you're going to
probably pass by that point, but yeah, I mean, it's a great thing. You come in, the supervisor usually goes and gets them from the hallway. You know, you kick them out into the hallway while
the committee discusses, okay, how do we do? What, what recommendations do we have?
et cetera. And then the, you know, person goes and gets them and says, Oh, well, congratulations, doctor so and so, and everybody goes and shakes their hands, gives hugs all around, you know, it's a [00:05:30] great, it's really,
it's really nice, and then usually, have a little party, get together at that evening, or at some point,
to kind of celebrate it, and everybody's calling him doctor, it's great, I remember it,
my, um, actually, I probably have it here on the shelf, um,
Chris Bolhuis: All I see are the Harvard classics behind you.
Dr. Jesse Reimink: yeah, where did it go? Okay, this is funny, my wife has removed it from my shelf, it used to be here. well I'll have to get on it. Where'd she put it? One of my friends who's a faculty member in Alberta got me a knife and they had engraved Dr. Reimink on it,
and uh, gave it to me [00:06:00] that night. It's just so fun.
Yeah, totally
Chris Bolhuis: Well, she, she took it because she's the real doctor in the Reimink
household
Dr. Jesse Reimink: exactly right. She probably took it. Yeah, it's probably on her desk.
Chris Bolhuis: that's
Dr. Jesse Reimink: anyway,
Chris Bolhuis: earned it.
Dr. Jesse Reimink: anyway, is a cool moment. So,
Yeah.
that's interesting. Um,
Well,
I don't know how we transition, Chris. There's a, how do we transition into what we're talking about today?
Chris Bolhuis: We just jump.
Dr. Jesse Reimink: We okay, let me try one. Here we go. these rocks that we're talking about are the really the minerals. They have a
[00:06:30] presence because they've been around a long time and they've developed a presence.
Chris Bolhuis: That's good, Jesse. Nice done. Nice done. By default, these zircons have a
Dr. Jesse Reimink: You can feel when they're around, right? We're
talking about today, and this is, if you're in the podcast, this is part one of two, we're gonna have two episodes on this, but these are the oldest fragments of earth, and that's a really important qualifier. These are not the oldest rocks on earth, but they are the oldest fragments of earth that we know of.
[00:07:00] Chris, what do you think about this topic? How do you, What's your knee jerk?
Chris Bolhuis: Um, well, first of all, I had never heard, we are going to talk about In these two episodes, we're going to talk about what's called the Jack Hill's zircons. Jesse, I've never heard of this before. before maybe, I don't know, three or four weeks ago, I've never heard of the Jack Hill zircons. when did you come across this in your educational career?
Cause you right away, when you went to graduate school, you started digging into earth's oldest material. So I would assume you came [00:07:30] across this pretty
Dr. Jesse Reimink: that's right. Chris. I think right away during graduate school at the start of graduate school. and it's Once you have heard of these, you'll start to see like, I'll be interested to see Chris over the next like, you know, month or two, I bet you're going to see more news articles that kind of mentioned them.
You know, these like geology news publications, a lot of publications on the Jack Hills get a lot of press because it's like, Hey, we discovered, quote unquote, discovered as we'll talk about, we'll discovered some signal about plate tectonics starting 4. 4 billion years ago, and [00:08:00] all that evidence is based on the Jack Hills.
So you'll kind of
see more of that. I guess my point is I bet some of our listeners for sure have heard of these because they pay attention to the geology news sphere and have heard of these zircon grains
Chris Bolhuis: All right. So Jesse, give us the 30 second overview then of what is it? What are the Jack Hill zircons and, and again, just kind of tie this into tectonics began on planet earth.
Dr. Jesse Reimink: Yeah, so what these are, are the oldest fragments of [00:08:30] earth and they're found, these are individual zircon grains, so they're grains of a rock, a rock is made of minerals, they were crystallized from a magma, that magma formed a rock, that rock was eroded, And these zircons are the only things that have survived, the only things that we know have survived from that rock.
And so we find these little zircon grains. Now, if you're in the app, you can go to image number two in your stack here. This is a photo of the Jack Hill's rock. The rock that contains the Jack Hill [00:09:00] zircons, it's a conglomerate. So these things now are found in a conglomerate that has sand grains in it and cobbles.
And some of those sand grains are really, really old zircons, older than 4. 2 billion year old zircons. 4.
2.
Yeah. So some of them go up to 4. 35 or 4. 38 billion years old.
Chris Bolhuis: Okay. So let me just back up a minute. I want to just make sure that we set the stage the right ways to bring everybody along. The first of all, this is a [00:09:30] gorgeous rock. I love conglomerate anyway. Um, and this is a really pretty rock. So I would just want to make sure that our listeners understand that this came from a felsic magma.
These zircon grains initially were probably a part of granite, right? Because this is. Zircons grow in that kind of magma as opposed to more of an intermediate or mafic, basaltic kind of,
Dr. Jesse Reimink: One quick modification to that, Chris, is that zircons do grow in intermediate rock. So probably not basaltic, but kind of
any other rock type. I [00:10:00] mean, not mafic or ultramafic, but any kind of
intermediate to felsic rock mostly has zircons in it. So, so yeah, I would broaden that and that'll come back in probably the second episode we have on this.
We'll talk about the debate here because there's a ton of scientific debate about these. So it could be intermediate or it could be
granitic.
Chris Bolhuis: So we're saying then is those rocks formed and especially if it was granitic, these formed quite deep inside the earth, then they have to get brought to the surface through weathering, erosion, isostasy, this kind [00:10:30] of uplift that happens with that. And then it has to get weathered out of the rock.
and carried to where it is now in Western Australia and deposited. Do we know when this conglomerate was deposited?
Dr. Jesse Reimink: Yeah, well, we'll see. Yes, mostly. It's between 3 billion and 2. 7 billion years ago. So it's a very old sediment. I mean, it's a 3 to
2. 5 billion year old sediment and part
of its material, part of the cargo that's in that sediment is really old. [00:11:00] And so Chris, this is something that I think is often, Confusing here, and you laid it out really nicely, that sequence of events, you have to have a magma that crystallizes, so the zircon grows there, that zircon is included in it's parental rock, that parental rock is exposed at the surface, it's weathered, eroded, the zircon, is the one that survives. All the quartz and feldspar and all the other stuff gets eroded out, and the zircon is the only one that survives. So, that
Chris Bolhuis: only the strong survive. That's right.
Dr. Jesse Reimink: Yeah, that's
Chris Bolhuis: Yeah. Well, if you think about that, so the Zircon grains are [00:11:30] 4. 38.
almost 4. 4 billion years old. And this Jack Hill's conglomerate. Was deposited, 1. 3 billion years later.
Dr. Jesse Reimink: Yeah.
Chris Bolhuis: I mean, a tremendous amount of time right there. I mean, that's, that's just insane to me.
Dr. Jesse Reimink: So, Chris, let me, let me interject one part about, uh, this rock. The rock's around three billion years old. It's a really, really restricted area where the old zircons are found. So like one outcrop, [00:12:00] basically, that most of the
zircons come from. There's a bunch of old zircons in there. Some go really old, up to you said 4. 38, which is the oldest one. But you know, there's a bunch of 4. 1 billion year old zircons. There's a bunch of 3. 9 billion years. So there's a huge range
of ages. They're just I
Chris Bolhuis: babies.
So now, okay, hold on, Jesse. So, first of all, why is it such a restricted area? why are they in this one spot? The truly old ones? How come?[00:12:30]
Dr. Jesse Reimink: Now, it's a really hard question to answer confidently, but let's use an analogy. If you think of a stream in the Rockies, the Rocky Mountains, or in the Alps, or whatever mountain range you want to think about, that stream is a big stream. going to be a conglomerate someday. It's got a bunch of boulders and a bunch of cobbles
and sand. Fast moving, Exactly. Think about how, let's say, gold exploration companies explore for gold. They take stream sediment samples. And so if you're at the mouth, right, out by Denver, where the big river flows out onto the [00:13:00] plains, you're going to collect some stream sediment samples.
If you find gold there, you're going to say, Oh, somewhere upstream. There's gold and you're going to work your way upstream and sample and sample and sample. You're going to sample the tributaries. You're going to sample all over the place until you find where you don't have gold anymore. Then you can rule out some part of that tributary and you're going to focus in on like where you have gold.
You could do the same thing with old zircons because. the old rocks might have only been exposed in one small tributary part of stream,
and so they're [00:13:30] only deposited in one little tributary branch, not in the big stream, or at least they're much more infrequent the Mississippi has very few really old zircon grains, but if you get to some tributary up in Minnesota, there's a lot of old zircon grains there.
So it's just really localized, like where these
Chris Bolhuis: So these zircons are a lot like a placer deposit then, uh, kind of panning for gold, you
know, they're strong, they're dense, they're chemically very, very, very stable.
Dr. Jesse Reimink: That's that. Hold on. I want to say that is a [00:14:00] really, really good analogy. They are just like a placer deposit, Think about trying to find gold nuggets somewhere. It's going to be a very restricted area that they're found. And the same thing goes for these zircons.
Chris Bolhuis: so then let me ask a follow up question to this then. Well, maybe a couple.
is this place really difficult to get to and have you ever been there?
Dr. Jesse Reimink: So no, I've never been. And yes, it's very difficult. It's very remote part of Western Australia in what's called the Yulgarn Craton. It's an old block of crust. We've talked about those before, but yeah, it's very remote. It's [00:14:30] very, hard to get to. but it's been studied a lot. And so, I've never been there. one of my PhD supervisors was there and, went there and actually gave me a rock sample from it. So I
do
Chris Bolhuis: nice. Nice.
Dr. Jesse Reimink: from it. Uh, but
it's, um, yeah.
Chris Bolhuis: have that on your desk right now.
This should be,
Dr. Jesse Reimink: office. It's because I
use it for teaching a lot. You know, my intro level class, probably the, the first lecture I give, I come and I have
the oldest rock and the oldest minerals.
And so, you know, students come up and hold them and
Chris Bolhuis: Yeah. Yeah. That's cool. [00:15:00] Absolutely. Hey, So Where did it come from? Where is the parent rock? This, this igneous pluton.
Dr. Jesse Reimink: As far as we know, destroyed. So we don't really know. And these
rocks, these three billion year old sediments and sediments, they're deformed, they're altered, they're old. So we can't really like work out where
it came from.
Chris Bolhuis: When you look at image number two, then that looks like a metaconglomerate,
right? Okay. And that's what we're looking at here. So it was, yeah, this was once a, just your [00:15:30] typical conglomeratic rock that then got subjected to massive amounts of heat and pressure and changed it into something that's a lot more durable than it, than it
was when it first formed, probably.
Dr. Jesse Reimink: if you take that Conglomerate, take that conglomerate, you crush it up, you separate out all the sand grains, all the sand pieces, you're gonna get, at most, a couple percent, up to maybe four percent, that are older than four billion years old, of the zircons.
Of the
zircons that are
Chris Bolhuis: So, okay. What are
the [00:16:00] 96 percent of them are
3. 7 or even younger
Dr. Jesse Reimink: All the way down to the depositional age, three billion years old. So there'll be 3. 1 billion year old grains in there too, and those will
Chris Bolhuis: That's hold on a second. really interesting to me. how would that be possible? How would you get zircons that form in a magma, but they're the same age or maybe a little bit older than the time in which they were deposited? How does that
Dr. Jesse Reimink: So if you think about like the Cascades, right, you know, you've got Mount Shasta, Mount St. Helens blows up and, everything about Mount St. [00:16:30] Helens
Chris Bolhuis: Can I interject, Jesse? So are you saying then that these zircons, the younger ones, would have formed from more of an intermediate kind of magma rather than plutonic, like really, really deep? So they were already exposed at the
Dr. Jesse Reimink: It's, it's really hard to tell the difference there because we're talking about, again, this goes back to what we talked about at the intro chapter of like the time scales involved here. We're talking about a billion year age difference. A lot can happen in a billion years, right?
You can have can be intruded and then exposed [00:17:00] on the surface in a couple million years. that's
not uncommon to see that happen. you don't need a long time to get You know, deep rooted rocks up to the surface. my point about the Cascades or the Andes, maybe, there's sediment being eroded off of those mountains into the ocean basin and being dumped down there, if you go sample those sediments, they're going to have the volcanic arc zircons in them that are 10, 000 years old, 50, 000 years old, you know, a million years old.
you can get sediments that [00:17:30] have zircons in them that are basically the same age as the deposition of the sediment. so these are what these kind of zircons look like. And, maybe, Chris, we can talk about, for the next couple minutes here,
Chris Bolhuis: Okay. So can I ask you that looks like it's really shocked.
Is, is that the case? Are we looking at fractured zircon
Dr. Jesse Reimink: It's fractured, but probably, that's probably not shocked. Shocked, you'll see like very parallel lines all the way through it, but zircon, you bring up a really important point, Chris. Zircon is [00:18:00] a really robust mineral, we've talked about this
before. It's really reliable. survives a whole bunch of processes, but it also has this radiation damage.
If you go back to our geochronology section, we've talked
about that a bunch in a bunch of different stuff, including the Grand Canyon audiobook. when uranium and thorium decay, they blow apart the grain structure and that causes this expansion. And so the cracking is usually expansion cracking because over time, the volume inside is getting bigger because of this decay.
And so the outside gets cracked a [00:18:30] bit.
Chris Bolhuis: in the way that this does that, Jesse, this is by alpha decay. Right. And so this is that kind of shot out of a cannon analogy. And, and is that what is destroying this kind of internal structure
Dr. Jesse Reimink: so you like, you take the cannon recoils and it
breaks the lattice right around it, there's more volume because it's a broken lattice, it's not like nicely bound together. And so if you do that a whole bunch of times over time,
and then you can get fluids that percolate in there and can expand it even further.
So yeah,
those are like typically thought [00:19:00] of as expansion cracks.
Chris Bolhuis: Jesse, what is the basic formula of a zircon crystal? Okay.
Dr. Jesse Reimink: it's zirconium Zr, Zirconium, Silica, Si, and Oxygen. So it's ZrSiO4 is the basic formula. So it's a silicate mineral. It's zirconium silicate mineral.
Chris Bolhuis: Okay. And then you're, what is uranium? How does uranium incorporate into the structure
then
Dr. Jesse Reimink: it'll, go in because uranium can
be for, yeah, zirconium or silicon site depending. Um,
and so it'll, it'll substitute in, um, in
Chris Bolhuis: Okay.
Dr. Jesse Reimink: And the [00:19:30] same for thorium as well.
Chris Bolhuis: Okay. Yep. Yep. Okay. Oh, interesting. So you're saying that you do have initial thorium that is a part of the internal crystal structure as
Dr. Jesse Reimink: That's right, and it's not
commonly, it's not as much, and it's not as commonly used in Zircon, but it is there for sure, like
in measurable amounts, and you have a whole bunch of other, you know, rare earth elements,
you have all sorts of interesting stuff in the Zircon,
which we'll come back to in the later episode, um,
Chris Bolhuis: Right. I just want to, [00:20:00] right. I just want to say for the listeners, the reason why I asked that question is because that's what uranium decays into is thorium is the daughter isotope for uranium 235.
Dr. Jesse Reimink: Yeah, there's two different chains. So the, there's uranium decays to both decay to thorium, and then the thorium also decays separately. So there's thorium 2 32 that decays to, 2 0 8 lead.
Chris Bolhuis: Right. And so it's an important question because, Jesse, as the geochronologist has to account for how much initial daughter isotope, how much initial thorium was in [00:20:30] the crystal structure in order to get an accurate age date on these zircon crystals.
Dr. Jesse Reimink: exactly right. so Chris, maybe let's round out this particular episode by talking so the jackals gons. Let's back up the jackals Gons. We've talked about where they're found, we've talked about what rock they're in. maybe we end this. by saying what we, we as a scientific community generally agree upon, and then there's a whole, I mean the whole basically next episode is going to be like what we don't agree upon
because there's all sorts of different [00:21:00] ideas about these zircon grains. But Chris, let me ask maybe what you think about this, like why would you think there's so much debate or so little consensus about these grains?
Chris Bolhuis: okay. I don't know. So let me just. Say what my thoughts are and, you can, let me just start with this that, you know, it's interesting that, you say that these things were deposited, 3 billion years ago, 0 to 2. 7 billion years ago. Right? And that, that means that we obviously had running [00:21:30] water well before then.
that's a really interesting thing to think about that. planet earth had running water billions of years
ago.
I, I dunno, I just, I find that to be an amazing thing. so I guess the, why is this important? That's what I'm thinking about. Why is the Jack Hills important?
And well, if we had Zircon, then we have the kind of magma that is important in making continents.
and so it's super important for that because in order to have [00:22:00] continents in the way that we think about them today, have to have plate tectonics. You have a, you have to have a mechanism to differentiate this magma to kind of distill it out enough to get this kind of magma.
Right? I guess that's why it's important. I don't really know why it's so controversial though. I don't know.
Dr. Jesse Reimink: yeah, so you're exactly right on both points about the water and the potential for plate tectonics the difficulty or the reason in my view this is there's a bunch of reasons why it's [00:22:30] contentious but one of the reasons is because we're dealing with only zircon grains like we don't have a rock to look at we don't have all the other minerals we're looking at zircons and zircons We usually look at the zircons try and see if they are recording the magma they came from properly or accurately.
Like are is an individual mineral really recording the signatures that are tied up in a rock really well or not? Are there some signatures that they don't record very well? So, kind of think of [00:23:00] zircon as this beautiful little capsule for age. And maybe chemistry, we don't have a rock as the point.
We're dealing with individual mineral grains, really. And really you, you look at image number three and those are four different zircon grains that have four different histories. They're from four different rocks. We can't really interpret them together. You can't say, Oh, I saw this signal over here and this signal over here.
And therefore, one plus one equals two here. You have to go one, is one is one is one. Like you can't really combine the signals too well.
Chris Bolhuis: I get that. but the other [00:23:30] thing is, is that, you know, zircons don't or very rarely form in mafic
magma.
and so you say we don't have a rock, but we do know that.
Dr. Jesse Reimink: Exactly. So that's one of, that's the first order thing that we can all, basically everybody agrees upon. These probably, most people would say these did not form in mafic rocks. These are from, as you said, intermediate to felsic rocks. So we kind of have a whole category of rocks that look like the modern continental crust or look like some things on the moon or Mars, [00:24:00] these are probably representing or intermediate rocks.
that's one thing everybody mostly agrees upon. So, that's one. The second thing The other thing that we can broadly agree upon is what you said before, Chris, that these things have indications of water. And you said, okay, yeah, the sediment the conglomerate was laid down in water 3 billion years ago.
We know that for sure. These zircons, the oxygen in them has a signature of [00:24:30] water in them. Not water in the zircon, but the oxygen isotopes. basically tell us that there was water, liquid water, on the surface of the earth 4. 3 billion years ago. And I think most people, that's widely agreed upon. So we
probably had liquid water on the surface of the earth 4.
billion years ago. And I don't know if it's important to get into the details of oxygen isotopes, but what do you think?
Chris Bolhuis: I mean, we have an image, so we might as well at least talk about it. so [00:25:00] Jesse, when you talk about oxygen isotopes, there are three isotopes of oxygen. There's O16, which is the vast majority of all the oxygen that exists naturally on earth. And then you have O17 and O18. And we're talking about the atomic mass of the oxygen isotope.
So three different isotopes, they each have eight protons in them. They just have slightly different masses and they get a little bit heavier. So, I talk about this when I talk about climate and climate change and some of the evidence for climate change, because, you know, it's really kind of a cool thing when you talk about these [00:25:30] layers that get deposited, because you get water trapped in seafloor sediment, right?
the way that our atmosphere circulates is it's basically driven by what happens at the equator. It's really warm there and there's just an abundance of water. So you have a lot of evaporation. And that water. That evaporates out of the ocean, makes its way to the poles. It makes its way up to Greenland.
It makes its way up to Antarctica. Well, Greenland and Antarctica, they're like two to three mile thick time machines, because they trap, you know, this, ice, they should be [00:26:00] trapping water. And the oldest stuff is on the bottom of the glaciers. And the youngest stuff fell as snow yesterday.
What they do though, is they provide this record of how climate has fluctuated over
time. Based upon the dominance of, well, do we have heavy water in, the ice or do we have light water? Because during ice ages, heavy water preferentially condenses and not very much of it makes its way up to the ice caps.
And so during ice [00:26:30] ages, the ice is loaded with light water isotopes, which means the ocean sediment is richer in heavy water isotopes.
Dr. Jesse Reimink: Chris, that's basically the same way we use oxygen isotopes in Zircon. And so, remember that Zircon, Z R S I O 4, it's got, a bunch of oxygen in it, it's 50 percent oxygen. those oxygen atoms in isotopes came from a magma. And so we're using Zircon to trace the magma, the original magma composition. Now the way this works, it's exactly the same way as you [00:27:00] described. We have two different reservoirs of oxygen on earth. the ocean is our standard. So we call that zero by definition. The ocean is zero. When we look at the ratio of 18 to 16 in the ocean, it's zero. The mantle, the rocks in the mantle are about plus five, a little bit above plus five.
They're plus 5. 5, 5. 3. And so if you look at image number four, if you're in the book, you can see a plot here that shows oxygen isotopes on the left in isotope composition versus. Age. [00:27:30] And this is from my PhD work, but it's a plot that's just showing oxygen isotopes. The gray band there is a vertical gray band.
That's the mantle field in the ocean would be at zero down below off the chart here. So. We have those two reservoirs when we talk about rocks and zircons. Ocean is zero, mantle, all rocks start in the mantle and it's 5.
Chris Bolhuis: And what you're talking about though, when you say that is that it has a much higher ratio of oxygen 18,
Dr. Jesse Reimink: That's right. There's more 18, [00:28:00] there's more 18 in the mantle proportionally, than there is in the ocean. So
what happens, Chris? So the, the, your point's a really good one. If you just take those two things and you mix them together, you take 5. 5 and you mix it with zero, you're gonna get something in between. that only happens at high temperatures. So if you have really high temperature, like boiling water, and it interacts with rock, it's going to mix, just straight mixing. But you said, beautifully said, that bonds with 18 in [00:28:30] it are more stable. So if water interacts with rock at low temperatures, like below 100 degrees centigrade, Low temperatures. The 18 is going to go into the rock, the altered rock now. So altered oceanic crust, the top layer has higher than 5. 5 because it has more 18 in it. So Sediments have like 20 plus 20 on this plot. So anything above the mantle field means you had low temperature water. on earth and that interacted [00:29:00] with rock and then melted to form the rock we see today or the zircon we see today
Chris Bolhuis: the takeaway is we're able to determine something about where the conditions in which that zircon grain formed.
Dr. Jesse Reimink: And you, And to bring it full circle, you said, can use this, it's a temperature proxy. You use it for ancient paleo temperature. This, we're using it for ancient water rock interaction temperature. Was it high temperature or low temperature? Same kind
of thing. But either way, it's outside the mantle field.
The only way to do that is to have water on the [00:29:30] surface of the earth. So, That's one thing almost everybody agrees upon. We need low temperature, meaning liquid water on the surface of the earth. And that signal is imparted into these zircon grains. So that's something we, we kind of agree upon. The last thing we agree upon, and this will go back to an episode we recorded on neodymium. I think it was the making magnets or something like
that.
We talked about using this as a tracer. And there's other, Elements in the zircon. One of them is hafnium and [00:30:00] basically it's a radiogenic isotope. We use it as a tracer in the same way neodymium is.
We don't need to get into the details, but these tracers tell us that there were older rocks that were melted to form The Jack Hill zircon crystallizing rocks. So there's something older out there that could be older basalt, it could be older felsic crust, but it wasn't just coming out of the mantle.
These weren't mantle derived zircons, they came from some pre existing crust, either mafic or felsic, that's even older than 4. [00:30:30] 2 billion years old, or 4. 3. So that's
the other thing that most people kind of agree upon.
Chris Bolhuis: All right. Well, Jesse, then I think that that's a good place to stop. What's coming next is going to be what we don't agree on, but I think most importantly is I want to talk about why, are we just arguing semantics? Are these small things that are be, you know, I want to talk about why there's so much disagreement in this.
And, and cause that's, what's interesting to me.
so,
Dr. Jesse Reimink: I agree. And we'll talk maybe just [00:31:00] a little bit. We'll tell the, the brief story of the discovery of these things, which is, kind of an interesting thing then. Yeah, you're totally right. We'll get into the debate. And are these scientists just too in the weeds? That's kind of the question.
That'll come in the next part here. So I think,
uh, what do you think Chris, is that a wrap here for
the part one of the Jack kills? We're not too in the
weeds yet.
Chris Bolhuis: Not yet.
Dr. Jesse Reimink: No, we'll get there next time. Hey, that's Rep if you are listening on the podcast. Thank you. We appreciate it. You can download the Camp Geo app and you can get all the content, including the Jack Hill [00:31:30] Zircons here in our Earth's Oldest Rocks book.
the first link in your show notes is the app. You can go to our website, planet geo cast.com and click on the link to support us there. We always appreciate that. Send us an email, planet ucast@gmail.com and follow us on all the social medias. We're at Planet ucast
Chris Bolhuis: Cheers.
Dr. Jesse Reimink: Peace.
