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Earth's Oldest Sediments - The Isua Supracrustal Belt · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_01: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it worked, and why it matters to you.
• 0:14
  SPEAKER_00: How do I look?
• 0:15
  SPEAKER_00: Do I look like Jenny got me a new shirt?
• 0:19
  SPEAKER_00: As good as it's gonna get, I guess.
• 0:23
  SPEAKER_00: It's hard to improve upon this, isn't it?
• 0:27
  SPEAKER_01: Understand.
• 0:28
  SPEAKER_01: Uh it's it's something.
• 0:30
  SPEAKER_01: It's something, man.
• 0:30
  SPEAKER_01: You got something going on over there.
• 0:32
  SPEAKER_00: I do.
• 0:33
  SPEAKER_00: I know.
• 0:34
  SPEAKER_00: I know.
• 0:35
  SPEAKER_00: I've got an update on my fight club status.
• 0:38
  SPEAKER_00: I'm still holding strong.
• 0:39
  SPEAKER_00: Oh, oh yeah.
• 0:40
  SPEAKER_00: Okay.
• 0:41
  SPEAKER_00: That's good.
• 0:43
  SPEAKER_00: It's a dang good thing it's a virtual fight club, I'll tell you that.
• 0:46
  SPEAKER_00: No, yeah, yeah, yeah.
• 0:49
  SPEAKER_00: Yeah, you know, I'm thinking of I want to ask you this.
• 0:52
  SPEAKER_00: I'm thinking about changing the name of my class.
• 0:55
  SPEAKER_00: Why?
• 0:56
  SPEAKER_00: Give me the pitch.
• 0:57
  SPEAKER_00: Because um what?
• 0:59
  SPEAKER_00: Give me the pitch.
• 1:01
  SPEAKER_00: Oh, that's not what I thought you said.
• 1:03
  SPEAKER_00: Um because uh like I don't know.
• 1:05
  SPEAKER_00: I just think that that geology is is um more old school, I think, that and geoscience is more it has a bigger umbrella, I think.
• 1:14
  SPEAKER_00: Does that make sense?
• 1:15
  SPEAKER_00: What do you think?
• 1:15
  SPEAKER_01: Should I?
• 1:16
  SPEAKER_01: I think that's right.
• 1:17
  SPEAKER_01: I uh well I'm a little I don't know.
• 1:19
  SPEAKER_01: I'm of two minds about this.
• 1:21
  SPEAKER_01: First of all, our department at Penn State.
• 1:23
  SPEAKER_01: I mean, I had no say in in this.
• 1:24
  SPEAKER_01: I when I showed up, they had already changed the name to geoscience.
• 1:27
  SPEAKER_01: That had happened a long time ago.
• 1:29
  SPEAKER_01: But I think it's a good name.
• 1:30
  SPEAKER_01: I'm always a little suspicious of name changes that departments do.
• 1:35
  SPEAKER_01: And it it was, I don't know, maybe 10 years ago is a really common thing for geology departments across the US to change their name and kind of a rebranding to like Earth science departments or Earth and Planetary Science Departments is now a very popular one.
• 1:51
  SPEAKER_01: And I think it you know it makes some sense when you start hiring people who study Mars, yeah, that maybe are you know hyperspectral experts and not geologists, they're kind of like the name doesn't fit me anymore.
• 2:01
  SPEAKER_01: You know, the name doesn't fit us very well anymore.
• 2:03
  SPEAKER_01: So it makes some sense.
• 2:04
  SPEAKER_01: Um and I think you're right.
• 2:06
  SPEAKER_01: Like I think it's whatever new students associate better with like what they want out of the degree program, right?
• 2:15
  SPEAKER_01: I I'd be curious.
• 2:17
  SPEAKER_01: It was really interesting.
• 2:18
  SPEAKER_01: I was reading through Rachel.
• 2:19
  SPEAKER_01: So we talked to Rachel Phillips, and I was reading through her grant proposal.
• 2:22
  SPEAKER_01: She's putting some big grant proposal together, and a lot of her work, she's kind of coming up against this really weird statistic.
• 2:28
  SPEAKER_01: I wanted to get her on it.
• 2:30
  SPEAKER_00: We should talk to her about the misconceptions around geology and geoscience, right?
• 2:34
  SPEAKER_01: Yeah.
• 2:35
  SPEAKER_01: Geology was like the lowest.
• 2:38
  SPEAKER_01: I'm I'm probably misquoting, but like geology was among the lowest um science disciplines, STEM disciplines for what people thought were what students thought were kind of sustainable or good jobs for the environment, or like people who cared about the environment.
• 2:55
  SPEAKER_01: And that kind of shocked me because every geologist I come across and know is like, you know, they love the outdoors and love the environment.
• 3:02
  SPEAKER_01: You know, it's it's not like uh a kind of a rape and pillage mentality um in amongst geologists, but the perception is that.
• 3:08
  SPEAKER_01: So if you change it to geoscience, it might be different.
• 3:10
  SPEAKER_00: Well, she said that she said that that was she, I think she did a poll, right, of your your feelings about the word geology and what it encompasses.
• 3:19
  SPEAKER_00: And then geoscience was really quite different.
• 3:22
  SPEAKER_00: Way different.
• 3:23
  SPEAKER_00: And that's what got me kind of thinking about it.
• 3:25
  SPEAKER_00: I don't know.
• 3:25
  SPEAKER_00: I think I'm gonna do it.
• 3:27
  SPEAKER_00: I think it's a good idea.
• 3:28
  SPEAKER_00: Why not?
• 3:28
  SPEAKER_00: I'm gonna rebrand Chris's geology, geoscience class.
• 3:32
  SPEAKER_01: I'd be curious to know what the students think about that.
• 3:35
  SPEAKER_01: You you should ask your students.
• 3:36
  SPEAKER_01: I'm going to and ask them what they think about the difference between geology and geoscience.
• 3:41
  SPEAKER_00: Yeah, it's a good idea.
• 3:42
  SPEAKER_00: I gotta come up with a way to frame it.
• 3:44
  SPEAKER_00: Um I want to have them provide feedback or maybe have them like what words do you associate with geology and what do you associate with geoscience?
• 3:54
  SPEAKER_01: Yeah, right, right, right.
• 3:56
  SPEAKER_01: Gotcha.
• 3:56
  SPEAKER_01: Yeah, that's a good one.
• 3:57
  SPEAKER_01: Yeah, that'd be interesting to know.
• 3:58
  SPEAKER_01: Cool.
• 3:59
  SPEAKER_01: I'll um I'll um stay tuned.
• 4:00
  SPEAKER_01: I'll give you an update.
• 4:01
  SPEAKER_01: Stay tuned, yeah.
• 4:02
  SPEAKER_01: Give us an update.
• 4:02
  SPEAKER_01: I'd be very curious to hear that.
• 4:04
  SPEAKER_01: That's that's super interesting.
• 4:06
  SPEAKER_01: Uh okay, Chris, today.
• 4:08
  SPEAKER_01: This is chapter what are we on?
• 4:11
  SPEAKER_00: Well, I don't know.
• 4:12
  SPEAKER_00: We're on we're on our fourth or fifth uh kind of episode that surrounds Earth's oldest materials.
• 4:21
  SPEAKER_01: This is this is number six, actually.
• 4:24
  SPEAKER_01: Um, we've done five of these already.
• 4:26
  unknown: Yeah.
• 4:27
  SPEAKER_01: This is number six.
• 4:28
  SPEAKER_01: Um and so we're ripping through these things.
• 4:32
  SPEAKER_01: This is the we're gonna talk about the issue greenstone belt.
• 4:35
  SPEAKER_01: That's I-S-U-A greenstone belt.
• 4:38
  SPEAKER_01: This is up there, it's probably more famous than Acosta, uh, as uh a location.
• 4:46
  SPEAKER_00: No, no, a little bit.
• 4:48
  SPEAKER_00: I I think so.
• 4:49
  SPEAKER_01: It's really interesting.
• 4:50
  SPEAKER_01: This is they're all so different, Chris.
• 4:52
  SPEAKER_01: All these locations that have old rocks.
• 4:55
  SPEAKER_01: Issue was kind of one of the first.
• 4:57
  SPEAKER_01: It was discovered in the 70s or 80s, this hints of old rocks, and it's been studied since then.
• 5:02
  SPEAKER_01: Uh, I mean, there have been so many papers published on this stuff.
• 5:05
  SPEAKER_01: These rocks here, they've been the focal point of a lot of research.
• 5:09
  SPEAKER_01: And you'll hear it called different things, and we'll kind of the point here is just to give a really high-level overview.
• 5:15
  SPEAKER_01: I'm not an expert on these rocks.
• 5:17
  SPEAKER_01: I know old rocks, and I pay attention to this literature.
• 5:19
  SPEAKER_01: I've not read every single paper on Issua.
• 5:21
  SPEAKER_01: It's just that would be a like a really hard task.
• 5:25
  SPEAKER_01: There's been so many papers published on these rocks, but there's some commonalities between these rocks and other ones that we can get into.
• 5:33
  SPEAKER_01: And this is going to be a pretty high-level overview of the geology of this suite of rocks.
• 5:39
  SPEAKER_01: So this is southwest Greenland.
• 5:41
  SPEAKER_00: Real quick, uh, pronunciation-wise, are you saying issua or ishua?
• 5:46
  SPEAKER_00: Because I've always said issua, but I I I feel like I'm getting an SH sound.
• 5:50
  SPEAKER_01: No, I think it's issua, issua or ishua.
• 5:52
  SPEAKER_01: Some you'll hear it pronounced differently, but I would say isua.
• 5:55
  SPEAKER_00: Yeah, issua makes the and just for perspective, image number one here uh shows the location of where this is found, where this rock suite is found.
• 6:05
  SPEAKER_00: It's Nook, right?
• 6:06
  SPEAKER_00: Is what it's Nook, yeah.
• 6:08
  SPEAKER_01: I think some people give it a harder U, but yeah, Nook.
• 6:10
  SPEAKER_01: Um down there near this this region, this this village.
• 6:13
  SPEAKER_01: Um, and this has been discovered, you know, a long time ago.
• 6:18
  SPEAKER_01: The history of these discovery things is is always kind of interesting.
• 6:21
  SPEAKER_01: But um, you know, it's it's mapping before the a the days of really, really quick geochronology that we have now.
• 6:28
  SPEAKER_01: So, you know, getting a date from a rock was a really difficult thing.
• 6:32
  SPEAKER_01: Uh, hints of these old rocks.
• 6:34
  SPEAKER_01: First thing, Chris, uh, this is going to be chapter six in our Earth's oldest rocks visual podcast series.
• 6:39
  SPEAKER_01: So you can get the images here in audio form on the app.
• 6:42
  SPEAKER_01: Go to the Camp Geo Mobile app.
• 6:44
  SPEAKER_01: First link in your show notes.
• 6:45
  SPEAKER_01: So what we've got here, yeah, southwest Greenland.
• 6:47
  SPEAKER_01: You'll hear this referred to as Southwest Greenland rocks, you'll hear this referred to as the Issua Supercrustal Belt, the Issua Greenstone Belt.
• 6:54
  SPEAKER_01: There's many names that kind of relate to different parts of this, but it's an area along the coast that's not covered by the Greenland ice sheet.
• 7:02
  SPEAKER_01: Old rocks down there in the south.
• 7:04
  SPEAKER_00: Yeah, do we have any idea how extensive this greenstone belt is?
• 7:08
  SPEAKER_01: Yeah, actually, so I'm going to skip ahead to this image number two here, real quick.
• 7:12
  SPEAKER_01: And image number two is a map that this is a very, very simplified map.
• 7:17
  SPEAKER_01: So I I took the base geological map, which is more complicated, and I super simplified it.
• 7:22
  SPEAKER_01: All we're showing here in these different frames is kind of the as we zoom in to the rocks here.
• 7:28
  SPEAKER_01: First of all, you have ocean with fjords, and then you have yellow land, and then you I've also shown where the extent of the ice sheet is.
• 7:36
  SPEAKER_01: Um, and so the ice sheet is is is shown there as well.
• 7:39
  SPEAKER_01: The orange rocks are an old series of rocks that's called the Itzok Nice complex, and that's kind of you can think of that like the Acosta gneiss complex.
• 7:49
  SPEAKER_01: These are old metamorphosed igneous rocks that are like 3.7, 3.8 billion years old.
• 7:56
  SPEAKER_01: Um, and they're really deformed, they're altered, but they're map, you can map them out and it's kind of disaggregated.
• 8:01
  SPEAKER_01: You can see this, it's kind of broken up, it's not a continuous exposure, it's exposed in kind of bits and bops everywhere in this area in a big linear belt.
• 8:09
  SPEAKER_01: And then I'll just note that the issua greenstone belt, the old rocks, what these are are these are an inclusion in the Itzok Nice complex.
• 8:19
  SPEAKER_01: And Chris, what do we know about inclusions in rocks?
• 8:23
  SPEAKER_01: Uh how do we think about inclusions?
• 8:25
  SPEAKER_00: Yeah, that's a it's a basic principle in geology, the that the inclusions are older than the rock that they're in.
• 8:32
  SPEAKER_00: You know, they so this is the oldest of the old, basically.
• 8:36
  SPEAKER_01: That's exactly right.
• 8:37
  SPEAKER_01: So if this if this Itzok Nice complex is 3.7, 3.8 billion years old, the oldest components in there, and it cross-cuts the issue of greenstone belt rocks, the issue of rocks are an inclusion in it, then issua greenstone belt, the issue of supercrustal belt must be older.
• 8:54
  SPEAKER_01: So they're these are kind of rocks that we can put a minimum age on.
• 8:58
  SPEAKER_01: We we don't necessarily have a maximum age that's uh that I know of that's very clearly defined.
• 9:03
  SPEAKER_01: Um, but they're they're like 3.85, 3.9 billion year old rocks.
• 9:07
  SPEAKER_00: Okay.
• 9:08
  SPEAKER_00: Hey, uh, so it looks like all indications are that it does continue under the ice sheet, right?
• 9:13
  SPEAKER_00: We just don't know how the extent of of this, like from a lateral standpoint, right?
• 9:18
  SPEAKER_01: Yeah, I uh that's a good one.
• 9:20
  SPEAKER_01: I I don't I don't know exactly where this ends.
• 9:23
  SPEAKER_01: I've not been to this region, so I don't know exactly where the ice sheet you know ends.
• 9:26
  SPEAKER_01: There are almost certainly old things exposed up underneath of the ice sheet, and there's been one study actually, I'd have to revisit it, haven't read it in a couple years, but there's been one study where they took stream sediment samples and looked at the detrital zircons that were being eroded from under the ice sheet.
• 9:43
  SPEAKER_01: I mean, we talked about eskers before, and I think eskers are like a really interesting exploration tool.
• 9:47
  SPEAKER_01: And um, this was kind of doing that in the modern setting.
• 9:50
  SPEAKER_01: So they got they got some old ages from up under the ice sheet.
• 9:53
  SPEAKER_01: So there's old stuff up there, Archean, Mesoarchean, Palearchean, these old rocks, but not clear that it's older than the Issue Supercrustal package.
• 10:02
  SPEAKER_01: So yeah.
• 10:03
  SPEAKER_01: So just let me Chris, let me run through that that that those names again because they get confusing.
• 10:08
  SPEAKER_01: So what we're focusing on here is the isua supra crustal belt, or also called the isua greenstone belt.
• 10:14
  SPEAKER_01: That's the the super old stuff that people focus on a lot.
• 10:17
  SPEAKER_01: The broader complex, the Itzok Nice complex, those are metamorphosed igneous rocks that are you know comparable to Acosta, except younger.
• 10:27
  SPEAKER_01: So they're like 3.8, 3.7 billion years old.
• 10:30
  SPEAKER_01: And then this whole region is kind of southwest Greenland, uh, it's part of the North Atlantic Craton, the Nane province.
• 10:36
  SPEAKER_01: So you hear different words that kind of refer to different packages within here.
• 10:39
  SPEAKER_01: But the point is that there are old gneisses, and the issua supra crustal belt is a inclusion in those old gneisses, and that means it's older.
• 10:49
  SPEAKER_00: So hey, I think Jesse, let's uh let's back out of this a second before we get into the specifics of the Issua and why this is so important and so you know, so extensively studied.
• 10:59
  SPEAKER_00: Let's talk about greenstones in general, you know, because geologically the greenstone we call them greenstone belts quite often.
• 11:07
  SPEAKER_00: Um, they're not they're not that uncommon, right?
• 11:10
  SPEAKER_00: And they're almost always old.
• 11:12
  SPEAKER_00: A lot of them are really old within the pre-Cambrian.
• 11:15
  SPEAKER_01: Yeah, yeah.
• 11:16
  SPEAKER_01: So, Chris, I mean, I remember you you describing greenstone.
• 11:20
  SPEAKER_01: Um, and I did you have an alternate word?
• 11:23
  SPEAKER_01: Did you used to have an alternate word for greenstone?
• 11:25
  SPEAKER_01: Yeah, what is it?
• 11:26
  SPEAKER_01: Remind me what that is again.
• 11:27
  SPEAKER_00: I just called it a meta basalt.
• 11:29
  SPEAKER_00: Yeah.
• 11:29
  SPEAKER_01: Yeah, okay, okay.
• 11:30
  SPEAKER_01: Yeah, yeah.
• 11:31
  SPEAKER_00: That's it's it's okay.
• 11:32
  SPEAKER_00: It's like, you know, it makes more sense to my students, you know.
• 11:36
  SPEAKER_00: Yeah, I know for sure.
• 11:37
  SPEAKER_00: So young.
• 11:38
  SPEAKER_01: That's all it is.
• 11:39
  SPEAKER_01: I mean, that that's simply what it is.
• 11:41
  SPEAKER_01: So basically, I remember going back to the menards, the famous what used to be the outcrop behind the menards.
• 11:49
  SPEAKER_01: Oh ticked off.
• 11:50
  SPEAKER_01: Regular listeners of the podcast will have heard of this one before.
• 11:53
  SPEAKER_01: Uh, but yes, the these these things occur in a lot of different places.
• 11:57
  SPEAKER_01: And the ones we went to, uh, where was that, Chris?
• 12:01
  SPEAKER_01: In the UP?
• 12:02
  SPEAKER_00: In Marquette County.
• 12:04
  SPEAKER_00: And so this is on the Lake Superior side of the Upper Peninsula, basically, for the for those that aren't you know all that familiar with what we call the UP in Michigan, the Upper Peninsula.
• 12:15
  SPEAKER_00: Um, yeah, I I yeah, it's just they were beautiful, Jesse.
• 12:18
  SPEAKER_00: I mean, you know, you're hard pressed to find like more striking and like really, really good looking pillow basalts, meta basalts.
• 12:28
  SPEAKER_00: You get just it's like this perfect area to just sit and talk about a lot of like really important geology concepts, you know?
• 12:36
  SPEAKER_00: It's just there's so much there.
• 12:38
  SPEAKER_00: It's really cool.
• 12:39
  SPEAKER_00: Dynamited it for to make room for a bigger lumber yard.
• 12:43
  SPEAKER_00: It was so mad.
• 12:44
  SPEAKER_01: Bummer, bummer.
• 12:46
  SPEAKER_01: Um, the thing about these is that they're everywhere, and so yeah, up up there, it's around Ishpaming, right?
• 12:52
  SPEAKER_01: It's a it's a uh a package of metamorphosed basalts.
• 12:56
  SPEAKER_01: We call them greenstones.
• 12:57
  SPEAKER_01: That's kind of the shorthand for them, in especially in Archean geology.
• 13:00
  SPEAKER_01: Those ones, Chris, up there are 2.7 billion years old, which is a really common age for greenstones globally.
• 13:07
  SPEAKER_00: Um, why is 2.7 the number?
• 13:11
  SPEAKER_00: We've talked about this a little bit before, I think.
• 13:14
  SPEAKER_00: In we talked about like the evolution of continents and so on, right?
• 13:17
  SPEAKER_00: You get a lot of ages that that kind of fit in that that timestamp.
• 13:21
  SPEAKER_00: Yeah.
• 13:22
  SPEAKER_01: So this is a big peak.
• 13:24
  SPEAKER_01: Well, it depends who you ask, but this is this is as as usual, as with everything, especially when we go back in time.
• 13:30
  SPEAKER_00: Yeah, but we're asking you, the the the resident doctor in the house.
• 13:34
  SPEAKER_00: Okay, I'm asking you.
• 13:35
  SPEAKER_00: I don't care about it.
• 13:36
  SPEAKER_00: I don't care about everything.
• 13:37
  SPEAKER_01: What we do know what we okay, fair enough.
• 13:40
  SPEAKER_01: What we do know is that at around 2.7 billion years old, we start to have a lot of rocks preserved on Earth for the first time.
• 13:47
  SPEAKER_01: Like we have a lot of areas that have stable cratons are forming or being stabilized around that time period.
• 13:55
  SPEAKER_01: And so you could argue that that's a crustal formation age, that actually crust is being formed in a large volume at 2.7 billion years old, or you could argue that it's a preservational thing, that there's some processes that are creating a preservational bias for that time period.
• 14:10
  SPEAKER_01: And there's those are two sides of kind of the same coin, but the point is that cratons stabilized these big blocks of continental crust that stabilized and became um basically they don't get deformed for billions of years after that.
• 14:24
  SPEAKER_01: And so all the rocks that are in that region get preserved, and a lot of them are these 2.7 billion-year-old metabasalts.
• 14:30
  SPEAKER_01: But the important thing here, and this image number three here shows this really well is the pillowed aspect of these.
• 14:35
  SPEAKER_01: And Chris, pillows are one of the coolest phenomena out there.
• 14:40
  SPEAKER_01: They're just as far as a what you could, you know, a geologically observable phenomenon, like look at the rocks, you think, holy crap, this is a beautiful feature, and it tells you stuff about the rock.
• 14:51
  SPEAKER_00: So, yeah, let's talk about that a second.
• 14:52
  SPEAKER_00: But before we talk about pillows, Jesse, and what that means, let's get into the detail on that.
• 14:58
  SPEAKER_00: Why not, right?
• 14:59
  SPEAKER_00: But I want to ask you this though.
• 15:01
  SPEAKER_00: When we talk about a meta basalt and the age of it being 2.7 billion years, are we talking about the origin of the basalt?
• 15:08
  SPEAKER_00: Are we talking about the metamorphism that so are we looking at the the rock that it turned into, or are we talking about the original volcanic rocks that then got metamorphosed?
• 15:20
  SPEAKER_01: It's a really good question.
• 15:21
  SPEAKER_01: Usually, in almost all cases, we're talking about the original formation age of the rock.
• 15:27
  SPEAKER_01: So 2.7 is the eruptive age of these pillow basalts, of these metabasalts, of these greenstone belts.
• 15:34
  SPEAKER_01: And um so the formation age, and then they're metamorphosed, but they're usually not metamorphosed that much.
• 15:40
  SPEAKER_01: And here's the key for the green stone part is that these are metamorphosed to pretty low grade.
• 15:45
  SPEAKER_01: It's like it's a it's chlorite, is the main mineral.
• 15:48
  SPEAKER_01: So you take a lot of the basaltic minerals, your typical basaltic minerals, you turn the feldspar into sort of serasitize it a little bit, but it's still feldspar.
• 15:55
  SPEAKER_01: And you you take a lot of the amphiboles and turn them into chlorite and a couple other low-grade minerals like that.
• 16:01
  SPEAKER_00: Chlorite is this kind of like various shades of green.
• 16:04
  SPEAKER_00: It's a beautiful rock because I uh you get this greenish black.
• 16:07
  SPEAKER_00: And it to me, Jesse, it always kind of looks like a a smearing of green over top of the black.
• 16:14
  SPEAKER_00: That's exactly right.
• 16:15
  SPEAKER_01: And so this it's a low-grade metamorphic event.
• 16:19
  SPEAKER_01: It it's it's definitely in it.
• 16:21
  SPEAKER_01: We call this a green schist facies metamorphism because it creates this green rock.
• 16:26
  SPEAKER_01: Um, and it's a lot of chloride.
• 16:28
  SPEAKER_01: So this is like low temperature, hydrothermal, couple hundred degrees centigrade, variable pressure.
• 16:34
  SPEAKER_01: This could have happened, you know, at a mid-ocean ridge setting, kind of, maybe a little bit higher grade than that, but but it's that's what's happening here.
• 16:42
  SPEAKER_00: So, what else indicates that this would be a mid-ocean ridge kind of setting where you would get this is the fact that you have pillow basalts.
• 16:50
  SPEAKER_00: You know, and that's what I love about pillow basalts or pillow lavas is the story that is locked up in that rock, you can get so much information just from almost a cursory, just a short glance at it.
• 17:05
  SPEAKER_00: Because the only way to get these pillow structures is to have lava that erupts out onto either an ocean bottom, so a mid-ocean ridge, or you know, you can get this in lakes, you know, in more of kind of this niche setting.
• 17:19
  SPEAKER_00: But you have to have lava that's erupting into water.
• 17:22
  SPEAKER_00: What you have then is you get this very fast cooled, almost like a rind is how I refer to it, like a watermelon rind, if you will.
• 17:31
  SPEAKER_00: You know, you get this like inch or so shell around this rounded structure, but the lava that is underneath that cracks the rind, and a new you know, lava pillow squirts out and and the process just repeats again and again and again.
• 17:48
  SPEAKER_01: Um beautiful rocks, but I that rind character, the rind description is really good because you get this really rapidly cooling rind, and then you know, a little bit in you get coarsening of the rock in as you go into the pillows.
• 18:00
  SPEAKER_01: And the key feature here is that these are basalts erupted into water.
• 18:08
  SPEAKER_01: That's the key observation.
• 18:10
  SPEAKER_01: And a lot of these things in that 2.7 billion year old age interval, a lot of those pillow basalts erupt through older gneisses, and so they're erupting through what used to be kind of a continent-like thing, but they're still underwater.
• 18:27
  SPEAKER_01: And so that old gneiss package was submerged beneath sea level, these basalts erupted into it, and sometimes these can be really thick.
• 18:34
  SPEAKER_01: In the 2.7 billion-year-old rocks, these are really thick, they can get to kilometers thick packages of basalts, they're really important for economic uh resources, huge amounts of gold in these areas, lots of other metals that we mine from these regions, so they're very they're good targets for exploration.
• 18:51
  SPEAKER_01: And this is what gives the term there's a very classic term for Archean blocks of crust that are called granite greenstone belts.
• 18:59
  SPEAKER_01: And the granite is these granite intrusions.
• 19:01
  SPEAKER_01: We've talked about earth distilling itself and and melting, and then the greenstone belts kind of surround the granite.
• 19:07
  SPEAKER_01: The granite kind of intrudes through the greenstone belts, which is a later event.
• 19:10
  SPEAKER_01: That's very common of that's very typical Archean geology in Kratons globally.
• 19:15
  SPEAKER_01: That's not we're well, that is kind of what we're talking about here.
• 19:18
  SPEAKER_01: Just Ischua is a very much much older version of this.
• 19:22
  SPEAKER_00: It's 3.9 billion years old, uh at least that's amazing to me for this reason, really, is that first of all, that's a staggering number that we have rocks that are that old, and but that's what we're talking about, Earth's oldest materials.
• 19:36
  SPEAKER_00: But Jesse, this means then that because you have pillows, that you also had oceans at this time.
• 19:44
  SPEAKER_00: Right?
• 19:44
  SPEAKER_00: And and that's that's uh I don't know, let that sink in a minute, right?
• 19:50
  SPEAKER_01: Yeah, it's so cool.
• 19:51
  SPEAKER_00: We had oceans on this planet that are really, really, really old.
• 19:56
  SPEAKER_01: Yeah, really old.
• 19:57
  SPEAKER_01: Really old, unbelievably old.
• 19:59
  SPEAKER_01: And if we refer back to our uh two episodes on the Jack Hill zircons, those little zircons contain isotopic evidence for oceans going back even further than that.
• 20:11
  SPEAKER_01: So we've had oceans for a long time.
• 20:13
  SPEAKER_01: We keep kind of pushing the limits of these things, going back and back.
• 20:17
  SPEAKER_01: The more rock record we get, the more observations we kind of get that there was surface water.
• 20:22
  SPEAKER_01: There's we'll talk about this in this this episode here.
• 20:24
  SPEAKER_01: There might be evidence for life in these rocks.
• 20:27
  SPEAKER_01: So there's really, really uh the more rocks we have, the the more evidence we can accrue to tell us about how the planet looked back in time.
• 20:35
  SPEAKER_01: And these, Chris, are really interesting because you talked about water, you know, water being around.
• 20:40
  SPEAKER_01: The next package of rocks, or or really, if this was just a greenstone belt, it wouldn't have received as much focus as it has over the last 50 years, this issues supra crustal belt.
• 20:51
  SPEAKER_01: But the supra crustal is above the crust.
• 20:55
  SPEAKER_01: I mean, that's kind of what that means.
• 20:56
  SPEAKER_01: It's above, sits on top of the crust.
• 20:58
  SPEAKER_01: So usually these are volcanic rocks that are erupted onto the surface and sediments that are interspersed.
• 21:04
  SPEAKER_01: And this, just like the ones you took me to in high school up in up in Ishboming, there, we have banded iron formations layered in amongst the greenstone layers in this supra crustal package.
• 21:17
  SPEAKER_00: Yeah, it's a geologic mess, Jesse, to try to work this out just in terms of the principles and geology of you know, relative dating, just doing that.
• 21:27
  SPEAKER_00: I mean, I that was one of the things that we did when when I took you up there as a young student, is you know, we went to this beach and had to work out this this beach is a part of that greenstone belt that you know runs through the UP.
• 21:39
  SPEAKER_00: And working out the geology, it's a it's just a great mental gymnastics exercise to uh to apply these just awesome principles.
• 21:48
  SPEAKER_00: But Jesse, like I I want to ask you about this because you have this this package, uh a suite of rocks that includes volcanic rocks, uh basalts, uh sediments, uh, and gneisses.
• 22:00
  SPEAKER_00: All of it's super old, but how how did the the sediments themselves, the sedimentary rocks, were they metamorphosed to in Isuwa?
• 22:09
  SPEAKER_00: Are they they're not still just sedimentary rocks?
• 22:13
  SPEAKER_01: No, no, these things will have been metamorphosed as well, and these things get these things get metamorphosed.
• 22:20
  SPEAKER_01: This is what makes them complicated, and this is what makes them difficult, and this is where all the scientific debate comes from.
• 22:26
  SPEAKER_01: That is so frustrating at times because we do we have a lot of ideas, we don't necessarily know for sure a lot of stuff, and that's frustrating, right?
• 22:36
  SPEAKER_01: I I I I I get frustrated by that.
• 22:38
  SPEAKER_01: It is frustrated hard and fast things, but they've been metamorphosed multiple times.
• 22:43
  SPEAKER_00: What are the debates about that that kind of surround the isua?
• 22:47
  SPEAKER_01: Yeah, so most of them the ones will highlight, there's many debates, but the ones will highlight the ones that I think most people who who might listen to this podcast may have heard of are ones surrounding evidence for life.
• 23:01
  SPEAKER_01: And so just imagine a scenario.
• 23:03
  SPEAKER_01: This is the I'm gonna try, I'm gonna paint a very kind of simplistic picture of how this stuff formed.
• 23:09
  SPEAKER_01: We have a setting that's in a shallow ocean environment.
• 23:14
  SPEAKER_01: You have basaltic eruptions happening that are putting these basalts under the surface, pillow basalts are forming, but in between the time when the pillow basalt, the volcanic eruptions are forming and the basalt is flowing out onto the surface, in between that you're gonna have deposition.
• 23:29
  SPEAKER_01: And so we have these banded iron formations, chemical precipitates.
• 23:33
  SPEAKER_01: Speaks to a very, very different world, the the banded iron formation, the fact that these are being deposited, and there's debate about how those actually form, but it's a it's a very different ocean chemistry that's dropping these things out, and so then you have another basalt eruption that covers up the banded iron formations, and then after that quiets down, then you have more banded iron formation getting deposited or more chemical sediments getting deposited.
• 23:57
  SPEAKER_01: Maybe there's a little volcanic arc that pokes its head up above the the surface nearby, and there's some sort of graywacky like sediment that that gets washes that sediment down in thin layers of graywacky type you know, uh let's explain sediment.
• 24:13
  SPEAKER_00: Maybe a lot of maybe some listeners haven't heard of what graywacky is.
• 24:17
  SPEAKER_00: So we call it graywacky or sometimes just a wacky sandstone.
• 24:21
  SPEAKER_00: And this is a poorly sorted sandstone that you get in kind of very niche settings in geology.
• 24:28
  SPEAKER_00: It's not a super common rock at all.
• 24:30
  SPEAKER_00: Um, in fact, I I decided to remove it out of my set of rocks that I have my geology students um identify as well.
• 24:38
  SPEAKER_00: Oh, really?
• 24:38
  SPEAKER_00: Okay.
• 24:38
  SPEAKER_00: Yeah, I did.
• 24:39
  SPEAKER_00: I took it out because it's just it's so niche and and they were never getting tested on it, and so I just removed it just to make it a little simpler and faster.
• 24:47
  SPEAKER_00: But you know, you get this like in turbidity currents and and things like this that that sometimes rip down continental slopes, or as you said, where you'd have this sediment washed off these arcs, maybe, and you get rapid deposition, and that's really the only sorting that you get is the heavy stuff, you know, settles right away, and then the finer grain stuff takes a little bit longer to settle, and that's really the extent of the sorting because in the in this erosion process.
• 25:13
  SPEAKER_01: So, yeah, that's right.
• 25:14
  SPEAKER_01: And and so these things are they're actually the these types of wacky type rocks are more common in the early earth than they are today, or at least proportionally, they're proportionally more common, and the various arguments about that, but but either immature continents, you don't have huge Mississippi-style drainage basins forming, you have more island arcs popping up and getting eroded down, or you know, it's a preservation thing that these are more likely to be preserved, whereas uh huge pure quartz uh quartz aeronites are more likely to be eroded.
• 25:49
  SPEAKER_01: Well, and it's proportional.
• 25:50
  SPEAKER_01: We just don't have that many rocks with which to assess this.
• 25:52
  SPEAKER_01: So that of the things we see, they're proportionally more, but we don't know if that actually is statistically meaningful either.
• 26:00
  SPEAKER_00: So the back to the controversy uh with with life and whether or not that's what's doing this, right?
• 26:07
  SPEAKER_01: So there's uh there's a couple different there's basically two different pieces of evidence that people have well, there's more than that, but two main ones that people have argued are evidence for life in these sediments.
• 26:18
  SPEAKER_01: Because you think this sediment thing is happening, the ocean's there, this might contain a record of early life.
• 26:23
  SPEAKER_01: And if we're looking for old life, we're gonna find it here, not in rocks like Acosta, because Acosta has almost all igneous rocks.
• 26:31
  SPEAKER_01: There's no sediments in there, there's no surface basalts that we know of, there's no really clear pillow basalts in Acosta.
• 26:38
  SPEAKER_01: So here is the place you would go to look for life, for signs of ancient life, because there's that these rocks were formed in that near surface environment, and some of them are precipitated right from the ocean or have interacted with the ocean.
• 26:50
  SPEAKER_01: So we've got a couple different rock types here.
• 26:53
  SPEAKER_01: There's these bandanir formations, first of all.
• 26:55
  SPEAKER_01: There are some quartzites with like calc silicate schists.
• 26:59
  SPEAKER_01: Those are kind of the gray wacky or wacky stone type things that are gonna get metamorphosed together.
• 27:03
  SPEAKER_01: So we have these calciate shifts, and we also have these quartz-rich rocks that are banded together with carbonates.
• 27:12
  SPEAKER_01: So these kind of carbonate-rich things, these quartz-rich things, they've all been metamorphosed a lot.
• 27:17
  SPEAKER_01: So there's a lot of discussion about what these things sort of actually are or actually represent.
• 27:22
  SPEAKER_01: Some of them contain graphite layers.
• 27:24
  SPEAKER_01: So image number four here, I'll skip ahead to this biff.
• 27:27
  SPEAKER_01: This is a graphitic bif.
• 27:29
  SPEAKER_01: So there are like there's a lot of graphite in these things, and graphite's carbon, and carbon is essential to life.
• 27:36
  SPEAKER_01: So it's interesting to figure out what these things might be, right?
• 27:40
  SPEAKER_01: This is if you're looking for old life, you're gonna go look at these things because there's carbon in these rocks, there's graphite.
• 27:46
  SPEAKER_01: We're wondering what are these things, right?
• 27:47
  SPEAKER_00: And you know, yeah, because Jesse, I don't think the debate is still settled on in terms of how biffs are laid down, these alternating layers where it's really iron-rich, and then you know, then you have silicate minerals and then uh back to iron and so on.
• 27:59
  SPEAKER_00: They keep flip-flopping back and forth, whether these were aided by photosynthetic organisms that were you know providing the free oxygen that allowed iron to precipitate, right?
• 28:10
  SPEAKER_00: But that's not the only evidence for life, um, because there's also these carbonate rocks that have a lot of magnesium and calcium carbonate in them, uh, like a dola stone, if you will, or a dolomite that has stromatolites in it, or what we believe to be stromatolites, you know, and that's another piece to yeah.
• 28:32
  SPEAKER_01: And there's okay, this is my reading of you know this literature at the moment.
• 28:37
  SPEAKER_01: So, first of all, the the the back to the graphite thing, real quick.
• 28:39
  SPEAKER_01: There are graphite layers.
• 28:41
  SPEAKER_01: You can use the carbon isotope composition, and so carbon has a couple different isotopes.
• 28:47
  SPEAKER_01: The ones we care about here are 12 and 13, different number of neutrons in the nucleus, and life has a very, very, very prolific at fractionating these isotopes at selecting one over the other.
• 28:59
  SPEAKER_01: And so if you look at the carbon isotope composition of the graphite, either in these bandanformation layers, or actually as a graph, little graphite piece or a little carbonate-rich, or excuse me, excuse me, carbon-rich inclusion in, let's say, an apatite grain, you can measure the carbon isotope composition of that, and a lot of these come up very low, minus 15, minus 25, minus 30, really low, which on the modern Earth, we would say, oh, that's clear evidence for life because life is really good at making low carbon isotope values here.
• 29:30
  SPEAKER_00: Okay, so hold on.
• 29:32
  SPEAKER_00: Let's let's make sure that we double-click on that.
• 29:34
  SPEAKER_00: When you say that you're looking at carbon 13 to carbon 12, life prefers what?
• 29:40
  SPEAKER_01: Well, there's a couple different reaction pathways that will make it light, make it low, make it have more 12 over 13, which in our nomenclature just means it drives the value down because we're talking about a normalized value here.
• 29:53
  SPEAKER_01: So it just makes it negative, very negative.
• 29:56
  SPEAKER_01: So so Chris, people what people have done have have looked with you know, huge mass what are big mass spectrometers to make little tiny spots on on these these carbon-rich grains, huge room, room-filling mass spectrometers, measure tiny little pieces of of carbon, measure the carbonized soap composition, um, and see what it is.
• 30:14
  SPEAKER_01: And and there's an argument to be made that this is life, that this is this carbonized soap composition on the modern earth.
• 30:21
  SPEAKER_01: We'd have kind of no problem interpreting it as life.
• 30:23
  SPEAKER_01: However, when we go back in time, there's more debate because we don't actually know if there's life around 3.8 billion years ago.
• 30:28
  SPEAKER_01: So, to my reading, this is still contested space.
• 30:32
  SPEAKER_01: Some people would say, yes, the simplest explanation is that these carbon isotope values in these rocks are indicative of life.
• 30:40
  SPEAKER_01: The nail's not in the coffin yet.
• 30:42
  SPEAKER_01: There's other people who would say that's not clear evidence for life.
• 30:45
  SPEAKER_01: It's a possible explanation for these values, but you can generate low carbon isotope values with metamorphic fluids and more complicated pathways, more complicated stories.
• 30:54
  SPEAKER_01: So it's an open question what these carbon isotope values actually mean, or at least it's a challenged idea.
• 31:00
  SPEAKER_01: The stromatolite thing.
• 31:02
  SPEAKER_01: So if we go down to these stromatolites, you you said you you mentioned it that they we have these like magnesium and carbonate-rich layers, magnesium and iron carbonate-rich layers.
• 31:12
  SPEAKER_01: This is what a stromatolite looks like.
• 31:13
  SPEAKER_01: We you can envision this, Chris.
• 31:15
  SPEAKER_01: Like you you see stromatolites on the the backside of the Tetons, is that right?
• 31:20
  SPEAKER_01: Oh, yeah, for sure.
• 31:22
  SPEAKER_00: They're they're beautiful.
• 31:23
  SPEAKER_00: Yeah, absolutely.
• 31:25
  SPEAKER_00: Uh Glacier National Park, too.
• 31:27
  SPEAKER_01: Yeah.
• 31:27
  SPEAKER_01: Uh in the Hell on the Limestone.
• 31:29
  SPEAKER_00: Oh, yeah.
• 31:29
  SPEAKER_00: Oh, it's and they're you have the these different colonies, you know, with the way they stack up, is sometimes they look like cabbage heads and different types of stromatolites will look like stacked construction cones.
• 31:41
  SPEAKER_00: And you know, you get these like beautiful, intricate patterns in the rock.
• 31:45
  SPEAKER_00: Uh these are Earth's oldest known fossils.
• 31:48
  SPEAKER_00: They're just blue-green spectacles, photosynthetic algae, but they're yeah, these kind of algal mats growing on top of each other, creating these layers.
• 31:55
  SPEAKER_01: And and there are people who've argued that they see structures that are stromatolites, again, in these sediments that are interlayered with the mafic volcanic rocks, with the metabasalt package, the greenstone package, they're interlayered in there.
• 32:10
  SPEAKER_01: There are people who would argue that these are stromatolites.
• 32:14
  SPEAKER_01: That's been proposed relatively recently, like in the in the 2010s.
• 32:18
  SPEAKER_01: Um, and then there's been a bunch of work that also argues that this is just very complicated metamorphic deformation.
• 32:26
  SPEAKER_01: And so you could imagine, and I want to kind of visualize this a minute, like if you have a package of metamorphosed of basalts with pillows in them, you have sediments layering in between them, the sediments are kind of draping off of the basalt flows.
• 32:38
  SPEAKER_01: Like, imagine the picture in your mind, you know, a mid-ocean ridge setting or basaltic eruption, a volcanic flow top under the ocean, and then sediments getting laid down on top of that.
• 32:50
  SPEAKER_01: It's not a beautifully clean boundary, it's not beautifully flat, it's going to be wavy and deformed.
• 32:55
  SPEAKER_01: Then you take that thing and you metamorphose it and you stress it over a couple billion years a couple different times.
• 33:01
  SPEAKER_01: The basalt is going to deform differently than the sediments do.
• 33:06
  SPEAKER_01: The way that the stress gets partitioned into deformation in the rock dramatically differs between these things and it gets really complicated very quickly.
• 33:15
  SPEAKER_01: And so I think that the stromatolite argument is not well accepted.
• 33:21
  SPEAKER_01: To my reading, it's not uh a well-accepted argument, more widely disputed.
• 33:26
  SPEAKER_01: Whereas the carbon isotopes in the graphite layers are more, I don't know, 50-50, or or perhaps a little bit more of a consensus view that that might be life.
• 33:34
  SPEAKER_01: The stromatolites is is an interesting discussion.
• 33:38
  SPEAKER_01: It goes back to kind of how you interpret structures in really complicated rocks.
• 33:41
  SPEAKER_01: You can imagine how this is this is difficult.
• 33:44
  SPEAKER_01: Like it can be frustrating to for you know to hear, oh, it's controversial.
• 33:49
  SPEAKER_01: It's like, we don't know.
• 33:50
  SPEAKER_01: But that that points to difficulty.
• 33:52
  SPEAKER_01: I think when that happens, I think you can think we're really pushing the limits.
• 33:57
  SPEAKER_01: This is cool because we're pushing the limits scientifically here.
• 34:00
  SPEAKER_01: It's controversial because it's hard.
• 34:03
  SPEAKER_01: It's hard to go to these rocks and figure out is there life there or not?
• 34:07
  SPEAKER_01: That's a big question.
• 34:08
  SPEAKER_01: Was there life 3.8 billion years ago?
• 34:10
  SPEAKER_01: Like when was the first time that we have evidence for life on Earth?
• 34:13
  SPEAKER_01: Is a really important question.
• 34:15
  SPEAKER_01: And so, of course, there's a lot of debate about this because we're we're pushing the limits.
• 34:20
  SPEAKER_01: We're not just sticking to the easy interpretations, we're going out there on a limb and saying this might be the where it is.
• 34:26
  SPEAKER_01: We're looking for scarce, scant evidence and trying to piece the story together.
• 34:32
  SPEAKER_00: Um I understand that it's so interesting when I look at all of this, the whole Isuwa complex, if you will.
• 34:41
  SPEAKER_00: It's so similar to what you see in the upper peninsula of Michigan.
• 34:45
  SPEAKER_00: You know, I mean, every single thing.
• 34:47
  SPEAKER_00: You have these the meta basalts that are you have pillow lavas, you have banded iron formation that is world-class banded iron, it's so beautiful.
• 34:57
  SPEAKER_00: And you have also stromatolite within the Kona Dolostone.
• 35:01
  SPEAKER_00: Um I don't think I took you there because uh you know it's a it's a quarry now.
• 35:06
  SPEAKER_00: And um, but I have taken classes there, but they they charge us to go in.
• 35:10
  SPEAKER_00: I think when the last time I went, it was like 150 bucks, and they let us you know go in and collect whatever we want.
• 35:16
  SPEAKER_00: It's a beautiful rock, it's a it's a churty dola stone, it's got a lot of pink minerals in it, it's just gorgeous, and it has these intricate stromatolites within it as well.
• 35:26
  SPEAKER_00: And so it's just like it's so striking that every single thing that we're looking at here with the issues is something that you you know you see in the great state of Michigan too in the upper peninsula, yeah.
• 35:35
  SPEAKER_00: The greenstone belts.
• 35:36
  SPEAKER_01: This is the amazing thing about the Archean world, is that we get a lot of these.
• 35:41
  SPEAKER_01: 2.7 billion years old, there's a bunch of greenstone belts, much like the ones up in up in Ishwing that you go to.
• 35:47
  SPEAKER_01: There's a bunch of those around the world.
• 35:49
  SPEAKER_01: What's spectacular about Ishua, and actually the one we're going to talk about next chapter too, when we talk about the Nuva Agatak greenstone belt, is not that they're spectacularly unique rocks, it's that they're old.
• 36:02
  SPEAKER_01: And if you think about the rocks that are here, we have metamorphosed basalt, we have sediments.
• 36:08
  SPEAKER_01: Both of those are really hard to date.
• 36:11
  SPEAKER_01: Really hard to date with traditional, they don't crystallize zircon.
• 36:15
  SPEAKER_01: It's not like you can extract zircons out of the basalt and date them.
• 36:18
  SPEAKER_01: I mean, you can because there's metamorphic ones in there, but they give you young ages.
• 36:22
  SPEAKER_01: You don't know what that means.
• 36:22
  SPEAKER_01: It's a metamorphic age.
• 36:24
  SPEAKER_01: Clearly, you don't know the crystallization age still or the eruption age.
• 36:27
  SPEAKER_00: What do you what you mean is you're not going back through the metamorphism to the original.
• 36:32
  SPEAKER_00: Exactly.
• 36:32
  SPEAKER_01: And these rocks have been metamorphosed a bunch of times, so they get comp they get more complicated every time you metamorphose them and you erase more of the initial signature.
• 36:41
  SPEAKER_01: So it's just shock like I just want to frame how cool this is is that we have water lane sediments and basalts that were erupted under the ocean that we know are at least 3.8 billion years old, and in those rocks, there are hints or potential indications of life in the carbon isotopes or in the stromatolites.
• 37:04
  SPEAKER_01: Maybe there's a lot of debate, but we're really we're pushing the limits, we're seeing through four or five metamorphic events to see that these were not only laid down in the ocean, but see what kind of chemistry there was, with the bandanimer formations, the different types of sedimentary rocks that are being deposited, and then we're having a debate about you know whether there's signs of life in this.
• 37:22
  SPEAKER_01: So we're like we're really far along in the geological interpretation of these rocks, given that they're so old.
• 37:28
  SPEAKER_01: It's just a it's impressive.
• 37:30
  SPEAKER_01: I think it's impressive that these things get discovered.
• 37:33
  SPEAKER_01: And there's a reason people study them so much, right?
• 37:35
  SPEAKER_00: That's right.
• 37:36
  SPEAKER_00: And that's why this is such an important suite of rocks, is that there's so much to learn from it.
• 37:42
  SPEAKER_00: Was there life at this point?
• 37:43
  SPEAKER_00: We you know, if we can establish the age of these rocks pretty well, and and you feel very good about that, right?
• 37:49
  SPEAKER_01: Three billion years old.
• 37:51
  SPEAKER_01: Yep.
• 37:52
  SPEAKER_01: 3.8, the the sediments, you know, there's not debate in that, right?
• 37:56
  SPEAKER_01: There's not a lot of things.
• 37:57
  SPEAKER_01: There's not a lot of debate.
• 37:58
  SPEAKER_01: Yep, that's right.
• 37:59
  SPEAKER_01: They're they're in that range, 3.9 billion years old.
• 38:02
  SPEAKER_01: Yep.
• 38:02
  SPEAKER_00: Then if knowing that age, then then if we can answer these other questions, those are really important things to know.
• 38:09
  SPEAKER_00: Was there life at this point?
• 38:11
  SPEAKER_00: What was the ocean like at this point?
• 38:13
  SPEAKER_00: And and who knows where it goes from there, right?
• 38:15
  SPEAKER_00: We atmospheric indications and and it's just uh so much to learn from this suite of rocks.
• 38:24
  SPEAKER_01: Suite of rocks, yeah.
• 38:25
  SPEAKER_01: And so I Chris, so maybe it'll just end as a lead-in to the next episode or kind of a cliffhanger for the next episode, which we're gonna talk about, another package of supra crustal rocks, kind of very similar rock types, except the age has been suggested to be 4.25 billion years old.
• 38:42
  SPEAKER_01: There's debate about that age, but it's another one we got to talk about because it's it's very similar to Ishua, it could be the same age as Isua, or it could be 300 million years older than Isua.
• 38:51
  SPEAKER_01: And so the age is the debate here.
• 38:55
  SPEAKER_01: When you get to these rocks that are this old, there's different ways you can kind of calculate the age.
• 38:59
  SPEAKER_01: We're gonna talk about the age debate on what might be the oldest rocks on Earth, than the Nuve Agatuck supercrustal belt up in um Quebec.
• 39:09
  SPEAKER_01: But it's you kind of have to think, these are these are the it's kind of the same type of thing.
• 39:13
  SPEAKER_01: It's basalts, it's banded iron formations, it's some chemical sediments interlayered together in this complicated package of rocks.
• 39:20
  SPEAKER_01: That's a very similar story across most of the Archean when we get this record.
• 39:25
  SPEAKER_00: Okay.
• 39:25
  SPEAKER_00: Hey, quick question then.
• 39:28
  SPEAKER_00: So with we learn different things studying the issua than we learn when we study the Acasta, right?
• 39:36
  SPEAKER_00: We're looking at different questions.
• 39:38
  SPEAKER_01: Different processes, yep, exactly.
• 39:40
  SPEAKER_01: Yeah, yeah, for sure, for sure.
• 39:41
  SPEAKER_01: In Ishua, because these rocks are formed in the near surface environment with oceans around and water around, we're looking at surface processes.
• 39:50
  SPEAKER_01: We're looking at maybe there's life, we're looking at what's the climate, we're looking at what's the ocean chemistry, that kind of process.
• 39:55
  SPEAKER_01: In Acosta, it's much more, these are igneous rocks, magmas that crystallized.
• 40:01
  SPEAKER_01: It's much more kind of how did continents form.
• 40:04
  SPEAKER_01: So that's kind of like how did the continent crust form?
• 40:07
  SPEAKER_01: Here we're looking at what was going on between the the serve in the surface environment, the near surface environment in the ocean.
• 40:13
  SPEAKER_01: And so what you can do is if you find, and this is very common across all the old rock locations, if you find older stuff, you can just take the same suite of tools that we've applied, the same kind of scientific methods, that same toolbox, and you do it again, except older.
• 40:27
  SPEAKER_01: So when Acosta was found, we just not we, I wasn't around, but the scientific community just took the same suite of tools they'd been using at other locations and used it on Acosta now.
• 40:37
  SPEAKER_01: When the Jack Hill zircons that they developed, there's all sorts of tools, techniques.
• 40:41
  SPEAKER_01: The geochemist toolbox is really, really big for the old zircons.
• 40:45
  SPEAKER_01: When you find a new suite of zircons, which have just been discovered in um in South Africa, you can just take that same toolkit and apply it to those new samples.
• 40:54
  SPEAKER_01: So finding new samples is you do kind of do two things.
• 40:57
  SPEAKER_01: You find new samples and you develop the toolbox.
• 41:00
  SPEAKER_01: And those are two different sort of strategies to take when studying these old rocks.
• 41:04
  SPEAKER_01: So yeah.
• 41:05
  SPEAKER_01: But you're you're totally right.
• 41:06
  SPEAKER_01: The toolbox is focused on what did this what did the ocean chemistry look like?
• 41:10
  SPEAKER_01: What was their life at this time?
• 41:12
  SPEAKER_01: Those types of questions for sure.
• 41:13
  SPEAKER_00: Yeah.
• 41:14
  SPEAKER_00: You know what we need to do at the end, Jesse, when we wrap this up, is we need to have a final image where we have uh like a chart of the Acosta, the Jack Hills, the Isuwa, and so on.
• 41:27
  SPEAKER_00: And what are the important questions that each of those understanding those rocks, you know what that what that can be like?
• 41:35
  SPEAKER_01: Yeah, yeah, yeah.
• 41:35
  SPEAKER_01: I like that idea.
• 41:36
  SPEAKER_01: That's a nice one.
• 41:37
  SPEAKER_01: Yeah.
• 41:37
  SPEAKER_01: Okay.
• 41:38
  SPEAKER_01: Put it put a put a uh what's your phrase?
• 41:41
  SPEAKER_01: Put a pin in it.
• 41:41
  SPEAKER_01: Put a pin in that one, Chris.
• 41:43
  SPEAKER_01: We'll come back to it.
• 41:44
  SPEAKER_01: I didn't know that was my phrase.
• 41:46
  SPEAKER_00: Apparently, apparently I have phrases now, Jesse.
• 41:49
  SPEAKER_01: You do you do have a lot of phrases.
• 41:50
  SPEAKER_01: Yeah.
• 41:52
  SPEAKER_01: Mr.
• 41:52
  SPEAKER_01: Smudge over there has a lot of phrases.
• 41:56
  SPEAKER_00: Okay.
• 41:56
  SPEAKER_00: All right.
• 41:57
  SPEAKER_00: That is not okay.
• 41:58
  SPEAKER_00: That's not a name that's gonna stick, Mr.
• 42:01
  SPEAKER_00: Smudge.
• 42:02
  SPEAKER_00: Jesse thinks I smudge everything with my dirty fingers.
• 42:05
  SPEAKER_00: You do.
• 42:06
  SPEAKER_01: You're just a smudge factor over there, smudging everything you touch.
• 42:09
  SPEAKER_01: Um, all right, Chris.
• 42:10
  SPEAKER_01: Hey, I think that's a wrap.
• 42:11
  SPEAKER_01: You can find this with all the images that we talked about on our Camp Geo Mobile app, the Earth's oldest rocks visual podcast series there.
• 42:18
  SPEAKER_01: It's available there.
• 42:19
  SPEAKER_01: Um, with the previous five episodes that we've talked about, other old rock locations, including Akas and the Jack Tills.
• 42:25
  SPEAKER_01: And we've got more coming this way.
• 42:27
  SPEAKER_01: So um, yeah, stay tuned.
• 42:28
  SPEAKER_01: You can follow us on all the social media, we're at Planet GeoCast.
• 42:30
  SPEAKER_01: Send us an email, planetgeocast at gmail.com.
• 42:32
  SPEAKER_01: Visit our website, planetgeocast.com.
• 42:34
  SPEAKER_01: Cheers.