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Discovering Earth's Oldest Rocks · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_01: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:14
  SPEAKER_01: Are you happy to be recording?
• 0:17
  SPEAKER_02: Well, I'm always happy to be recording.
• 0:19
  SPEAKER_02: What are you talking about?
• 0:20
  SPEAKER_02: I got my radio voice on.
• 0:21
  SPEAKER_02: You hear that?
• 0:21
  SPEAKER_01: Your radio voice is on, Christopher Ballhores.
• 0:24
  SPEAKER_01: The radio voice is dialed in here.
• 0:27
  SPEAKER_01: Oh.
• 0:28
  SPEAKER_02: I don't know about that.
• 0:29
  SPEAKER_01: How are you doing?
• 0:30
  SPEAKER_01: Chris, I'm uh chomping at the bit here.
• 0:32
  SPEAKER_01: Well, yes, you are.
• 0:34
  SPEAKER_01: This is uh this is an episode.
• 0:36
  SPEAKER_01: This is an episode or two, probably two, most likely, because we're probably gonna break Jesse.
• 0:43
  SPEAKER_02: This is definitely two episodes.
• 0:45
  SPEAKER_02: All right, yeah, you're just so everyone's clear.
• 0:47
  SPEAKER_02: This is the first of two.
• 0:49
  SPEAKER_01: Of two, okay, yeah.
• 0:50
  SPEAKER_01: What really happened?
• 0:51
  SPEAKER_01: This stemmed from a listener question.
• 0:53
  SPEAKER_01: Mark sent us a listener question, well, several suggestions, kind of on uh Earth's oldest materials, Earth's oldest rocks, and was kind of asking about this and and asked about the Acosta Nice, which rang a bunch of alarm bells in my brain.
• 1:07
  SPEAKER_01: And Chris, you probably were like, Oh god, Mark, why did you ask about the Acosta Niceses?
• 1:12
  SPEAKER_01: Because Jesse is just gonna go nuts on this one.
• 1:17
  SPEAKER_02: He yeah, what he actually named the Acosta Nice in his question, right?
• 1:22
  SPEAKER_02: He he framed that as a part of his question, and yeah, I did roll my ass.
• 1:26
  SPEAKER_01: Yeah, you were like, Oh, great, here we go.
• 1:29
  SPEAKER_02: Yep, yeah.
• 1:30
  SPEAKER_02: I'm like, oh my gosh, he really did that.
• 1:32
  SPEAKER_02: He opened the floodgates.
• 1:33
  SPEAKER_01: It's open your timer, count down to when Jesse calls me if he's seen this email.
• 1:39
  SPEAKER_02: That's right.
• 1:40
  SPEAKER_02: That's right.
• 1:41
  SPEAKER_01: So I did my PhD on the Acostanysis.
• 1:43
  SPEAKER_01: So that's why like this is Well, hold on, Jesse.
• 1:46
  SPEAKER_02: Hold on.
• 1:46
  SPEAKER_02: Sorry to interrupt you, but let's back up.
• 1:48
  SPEAKER_02: What are we doing in this two-part thing?
• 1:50
  SPEAKER_02: Yeah, what are we talking about here?
• 1:52
  SPEAKER_01: So if you're listening to this in the podcast, um, you're gonna get two-part series here basically on the acostinysis.
• 1:58
  SPEAKER_02: And we're kind of gonna break them apart into some not really the acostanysis, though.
• 2:02
  SPEAKER_02: This is about the earth's oldest rocks, which happens to surround or is surrounded by the acostanis.
• 2:09
  SPEAKER_01: That's right.
• 2:09
  SPEAKER_01: That that's a great point.
• 2:10
  SPEAKER_01: So these are well, we'll talk about that.
• 2:13
  SPEAKER_01: This is debatable whether these are actually Earth's oldest rocks or not.
• 2:16
  SPEAKER_01: There are other rocks that people suggest are super old, and we'll get into that in later episodes.
• 2:22
  SPEAKER_01: So this is kind of a if you're listening to this in the podcast, this is a two-parter on the acostanysis, kind of two parts because I'm gonna go on and on and on about these because I did my PhD on this part of the world, the Acostanysis.
• 2:34
  SPEAKER_01: Um, if you're listening to this on the app, this is one chapter in a audiobook on Earth's oldest materials, really.
• 2:42
  SPEAKER_01: So we've talked about Earth's oldest minerals, and we're talking about Earth's oldest rocks, kind of where they are globally, what they look like in different locations.
• 2:49
  SPEAKER_01: So on the audiobook, you're gonna get images.
• 2:52
  SPEAKER_01: On the podcast, you're not gonna get the images, so you gotta go to the CampGeo app to get access to the images and a little bit of extra content there in our Earth's oldest rocks book there that we have on the app.
• 3:02
  SPEAKER_01: So that's the outline.
• 3:05
  SPEAKER_01: Okay, I'm gonna stop talking, Chris, because I gotta save my voice.
• 3:08
  SPEAKER_01: I gotta save my vocal cords here, or there's a lot more talking to be done.
• 3:12
  SPEAKER_02: Well, I'm gonna be the moderator, so I think we're gonna be okay in this.
• 3:16
  SPEAKER_02: Okay, all right.
• 3:16
  SPEAKER_02: But I think Jesse, like, I have some things to interject here that during the course of these two episodes that you perhaps don't know.
• 3:26
  SPEAKER_01: I Chris, you know what?
• 3:27
  SPEAKER_01: I was thinking about this as I was kind of putting this together.
• 3:30
  SPEAKER_01: I don't know.
• 3:31
  SPEAKER_01: And you know, we've had many a Crisple His front porch, sit and chat with a beer in our hand about geology and rocks.
• 3:38
  SPEAKER_01: I don't think we've gone this deep into this topic before.
• 3:42
  SPEAKER_01: I don't think we've talked in this much detail.
• 3:44
  SPEAKER_01: So this is kind of new territory for you and I a little bit.
• 3:47
  SPEAKER_02: I think so too.
• 3:48
  SPEAKER_02: And there are gonna be some things that uh perhaps I'm gonna bring into this episode that you don't know about me.
• 3:56
  SPEAKER_01: Totally.
• 3:56
  SPEAKER_02: I so I think it's gonna be interesting.
• 3:58
  SPEAKER_01: It'll it'll be fun.
• 3:59
  SPEAKER_01: An adventure with Chris and Jesse.
• 4:01
  SPEAKER_01: So that's right.
• 4:03
  SPEAKER_01: Buckle up your seats, kids.
• 4:04
  SPEAKER_01: We're getting into the big yellow parts and we're driving down the road.
• 4:08
  SPEAKER_02: Oh man, speaking of which, speak can I say this?
• 4:11
  SPEAKER_02: I don't like I don't know.
• 4:12
  SPEAKER_02: I yeah, yeah.
• 4:13
  SPEAKER_02: Chris Bullheise was in the news.
• 4:15
  SPEAKER_02: Well, hold on.
• 4:16
  SPEAKER_02: I don't want to date this episode really, but you know, this is really on the heels of the total solar eclipse that ran through the belly of the United States.
• 4:26
  SPEAKER_02: And this is what Thursday now, and I took a hundred and two people, most of which were students, down to Ohio to view the eclipse in totality, and it was amazing.
• 4:40
  SPEAKER_02: It was really a cool experience.
• 4:43
  SPEAKER_02: Um, no, that doesn't do it justice.
• 4:44
  SPEAKER_02: This was amazing.
• 4:45
  SPEAKER_02: It was just it's one of these things that is like a once-in-a-lifetime opportunity for a lot of the people.
• 4:52
  SPEAKER_02: This is not my first totality, but it will be the first and the last for a lot of the people that I took there.
• 4:57
  SPEAKER_02: Really?
• 4:58
  SPEAKER_01: I mean, so cool.
• 4:59
  SPEAKER_01: And uh, you know, you had a little nice little write-up and a little video in the uh local news too.
• 5:03
  SPEAKER_01: It was great.
• 5:03
  SPEAKER_01: I mean I did.
• 5:04
  SPEAKER_01: I mean, it was excellent, got a lot of traction, so that was excellent.
• 5:08
  SPEAKER_01: You know, like we talked about with um with John Douglas actually, you know, teachers who go above and beyond, like Crisple Heist does all the time, they're valued and they they should be, you know, and it's it's an exceptional thing to do.
• 5:18
  SPEAKER_01: To this was not an easy thing to organize for you, right?
• 5:22
  SPEAKER_01: This was a stressful thing.
• 5:24
  SPEAKER_01: I called you the night before, you were stressed about it, you know, you didn't know where to go, what the weather's gonna be like.
• 5:28
  SPEAKER_01: Do we have spots?
• 5:29
  SPEAKER_01: Are we sure we have a spot to like get off and get a hundred people off the buses?
• 5:32
  SPEAKER_01: And that's no small feat and uh takes effort, and you didn't need to do it, and uh, but everybody's better for it.
• 5:38
  SPEAKER_02: So I'm glad I did it.
• 5:40
  SPEAKER_02: It it turned out perfect, everything worked out perfectly, but yeah, you're right.
• 5:45
  SPEAKER_02: The day before we left, I'm I'm I had a place to go, and I'm I'm thinking, well, maybe we need to change because the weather is better in Indiana, maybe, than it is in Ohio.
• 5:55
  SPEAKER_02: So the logistics was just it was a bit of a nightmare, and I lost a lot of sleep.
• 5:59
  SPEAKER_02: So, but I feel rested now.
• 6:01
  SPEAKER_02: I it's been a couple days, so you've got to rescue Chris.
• 6:03
  SPEAKER_02: That's good.
• 6:04
  SPEAKER_02: He's he's relaxed and rested and enthusiastic, though.
• 6:08
  SPEAKER_02: Put his feet up a little bit.
• 6:10
  SPEAKER_02: Today, Jesse, can I lead this off?
• 6:12
  SPEAKER_02: Like we're gonna talk about uh the Earth's oldest rocks, but we're gonna do this in a couple sections, and this is just part one of two.
• 6:21
  SPEAKER_02: And I want to start this whole thing by talking about the discovery phase of Earth's oldest rocks, which uh leads to your research area.
• 6:32
  SPEAKER_02: So there's some debate that surrounds this actually, right?
• 6:37
  SPEAKER_02: And this goes all the way back to the 1980s, uh, which basically back then we were, you know, we didn't have the technology that we have now.
• 6:46
  SPEAKER_02: So basically, we just uh recognized that these rocks were older than most of the other rocks.
• 6:55
  SPEAKER_01: So, Chris, let me just interrupt you real quick and point to image number one because we're gonna talk about this.
• 6:59
  SPEAKER_01: And this is one of the photos that I've taken during my field work.
• 7:02
  SPEAKER_01: Image number one, it's this really what we're talking about here is a complicated suite of gneisses, what are called gneisses, G-N-E-I-S-S-E-S, right?
• 7:10
  SPEAKER_01: This is the word for high-grade metamorphic rocks.
• 7:13
  SPEAKER_01: We've talked about this in the CampGo content on the Camp Geo app.
• 7:16
  SPEAKER_01: Really deformed stuff.
• 7:17
  SPEAKER_01: Image number one is what we're talking about.
• 7:19
  SPEAKER_01: But Chris, let me kind of turn it back to you here and ask you a question.
• 7:23
  SPEAKER_01: How do geologists just generally, if you just have two rocks, how do you tell which one's older?
• 7:29
  SPEAKER_01: Like, what is a sort of a general way that we do that?
• 7:32
  SPEAKER_02: Well, regarding a gneiss or a schist, which are intensely like regionally metamorphosed rocks, those were rocks that existed beforehand.
• 7:42
  SPEAKER_02: Like, let's say that those were shallow marine sedimentary rocks.
• 7:47
  SPEAKER_02: They existed and then an event happened, and that event then formed the rocks that we're looking at.
• 7:54
  SPEAKER_02: When we look at metamorphic rocks, we know that there were older rocks that existed before that.
• 8:00
  SPEAKER_02: Does that answer your question?
• 8:02
  SPEAKER_01: That's exactly right.
• 8:03
  SPEAKER_01: And that's exactly what these geologists in the late 70s were really doing.
• 8:08
  SPEAKER_01: They didn't have the modern suite of analytical techniques that we have today, or modern suite of geochronological techniques.
• 8:15
  SPEAKER_01: So they were just walking around the rocks and they noticed, hey, these Acosta Nice rocks, these have been deformed many, many times.
• 8:22
  SPEAKER_01: We can see that like there's five different folding events in here, and that's different from other rocks nearby, which had maybe one folding event in them.
• 8:30
  SPEAKER_02: Now, you are dealing with the rocks in your research and the rocks that it were really talking about in the early 80s that said, well, these are really old, and they're older than most of the other rocks that we've ever seen.
• 8:41
  SPEAKER_02: These are gneisses, which you just alluded to.
• 8:44
  SPEAKER_02: Jesse, my question is, is this an event or is this a sequence of events?
• 8:51
  SPEAKER_02: Because a gneiss is one of the most intensely metamorphosed rocks.
• 8:55
  SPEAKER_02: Yeah.
• 8:56
  SPEAKER_02: So how tortured are they?
• 8:59
  SPEAKER_02: Let me ask it that way.
• 9:00
  SPEAKER_01: That's a great question.
• 9:01
  SPEAKER_01: These particular rocks, the acosta gneisses, are very tortured.
• 9:04
  SPEAKER_01: So they formed, many of them formed, you know, four billion years ago, 3.8 billion years ago.
• 9:09
  SPEAKER_01: We'll talk about that.
• 9:10
  SPEAKER_01: But we know now, with modern tools, we have identified at least five or six what we call high-grade metamorphic events.
• 9:18
  SPEAKER_01: So deformation events that cause the minerals to be overprinted, caused folding and faulting and all of these things.
• 9:24
  SPEAKER_01: So we know there's multiple five or six different events of sort of forming these kind of gneisses.
• 9:30
  SPEAKER_01: And the most recent one was 1.9 billion years ago.
• 9:32
  SPEAKER_01: So these have a very tortured history.
• 9:35
  SPEAKER_02: Okay.
• 9:35
  SPEAKER_02: Can you give me what kind of time frame are we talking about in terms of this series of tortures that happened to this rock?
• 9:45
  SPEAKER_02: Was this related to one event that lasted a long time?
• 9:49
  SPEAKER_02: Or are these punctuated by Yeah?
• 9:52
  SPEAKER_01: This is such a good question, Chris.
• 9:53
  SPEAKER_01: And we're we're kind of jumping ahead here.
• 9:55
  SPEAKER_01: This is what we know now.
• 9:56
  SPEAKER_01: This is not what we knew at the discovery time, but what we know now.
• 10:00
  SPEAKER_01: What we know now is four billion years ago was the kind of formation event.
• 10:04
  SPEAKER_01: Okay.
• 10:05
  SPEAKER_01: Then 3.8 billion years ago, more rocks were added to it, but also the four billion-year-old rocks were reset, were overprinted.
• 10:12
  SPEAKER_01: Then again at 3.6 billion years ago, then again at 3.4 billion years ago, then again at 2.9 billion years ago, then again at 1.9 billion years ago.
• 10:21
  SPEAKER_01: So those numbers, and this is where Chris, I'm curious what you think about this, because I'm describing numbers like three or two or something, but we're talking about hundreds of millions of years in between those events.
• 10:33
  SPEAKER_01: So these are discrete events that are literally hundreds of millions of years apart.
• 10:38
  SPEAKER_01: So they're kind of punctuated, but we're talking about a time period of two billion years where they experienced five or six metamorphic events in that two billion year window.
• 10:47
  SPEAKER_01: So the rocks are really tortured in part because they're very old.
• 10:50
  SPEAKER_02: So, did you have a question for me in that?
• 10:52
  SPEAKER_02: Like, what's your question?
• 10:54
  SPEAKER_02: No, I'm curious what your thoughts are.
• 10:55
  SPEAKER_01: Like, what are your I don't know, how does that resonate?
• 10:57
  SPEAKER_01: Because when we talk about metamorphism, when we talk about you know metamorphic rocks in the Grand Canyon, at the base of the Grand Canyon, the basement, nice is there in our Grand Canyon chapter.
• 11:05
  SPEAKER_01: You know, we talk about they formed and then they were metamorphosed, and then they're now in the basement stuff.
• 11:10
  SPEAKER_02: Well, I'm gonna answer your question.
• 11:11
  SPEAKER_02: I don't know if this is exactly what you're asking, but here's here's my take on what you just said.
• 11:16
  SPEAKER_02: What are what are my thoughts, right?
• 11:18
  SPEAKER_02: My thoughts are you're throwing around numbers like 1.9 or 1.8, 1.7.
• 11:24
  SPEAKER_02: Those are small increments, right?
• 11:26
  SPEAKER_02: But that time span that you went through is like 250 million years.
• 11:32
  SPEAKER_02: So if I take that to all right, let's look at where we are now and let's go back 250 million years ago, well, this is when Pangee was being ripped apart.
• 11:43
  SPEAKER_01: Yeah, yeah.
• 11:48
  SPEAKER_02: There's a lot that happens within that time span.
• 11:51
  SPEAKER_02: So geologists throw about these numbers all the time.
• 11:54
  SPEAKER_02: Oh, it's 1.8, it was 1.7, as if those are close numbers.
• 12:00
  SPEAKER_02: But when you talk about 1.9 billion years compared to 1.7 billion years, that is not on any stretch of the imagination, close proximity time-wise.
• 12:14
  SPEAKER_02: Like that's a long period of time that happened in between, you know.
• 12:18
  SPEAKER_02: So those are my thoughts.
• 12:19
  SPEAKER_01: I guess that's exactly what I was like.
• 12:22
  SPEAKER_01: I was wondering if you were wondering, I guess, because people who study the early earth, like myself, we kind of bandy around these things, and we forget actually that the difference between 4.0 and 3.6 is basically all of animal life on earth.
• 12:35
  SPEAKER_01: You know, that that is like all of the phenaries, effectively.
• 12:38
  SPEAKER_01: And I'm just kind of saying, Oh, yeah, there's a couple metamorphic events in this rock's history.
• 12:42
  SPEAKER_01: So we can't forget that point that these rocks are very old and very tortured.
• 12:47
  SPEAKER_01: Multiple 5, 6, 7, 8 pretty high grade metamorphic events that happened to them.
• 12:52
  SPEAKER_01: So back to the story.
• 12:54
  SPEAKER_01: The geologists were mapping this area and they walked across and they said, Oh, these look different.
• 12:59
  SPEAKER_01: These are really metamorphosis.
• 13:01
  SPEAKER_01: These have seen five metamorphic events, and the other ones, those ones over there, you know, 100 kilometers that way, they're tortured, but they've only been tortured once or maybe twice.
• 13:11
  SPEAKER_01: And so therefore, these Acosta ones are most likely really old.
• 13:14
  SPEAKER_01: They didn't really know how old, but most likely old.
• 13:17
  SPEAKER_02: A question then, for let's say beginning students that are looking at their gneisses in their hand samples, right, that they have in lap, are most of these gnacy hand samples that young students have in their hands, do they represent multiple tortured events?
• 13:34
  SPEAKER_02: Is that like a blanket statement?
• 13:36
  SPEAKER_01: That is such a good question.
• 13:39
  SPEAKER_01: My guess would be probably not, because most, you know, if you go to go out west and you'd look in uh Idaho or all the way up into the British Columbia, you're gonna be able to get it.
• 13:49
  SPEAKER_02: Go into the Tetons or something.
• 13:51
  SPEAKER_01: You have these metamorphic core complexes that are exposed.
• 13:54
  SPEAKER_01: And often the roots, those roots are they've been really intensely deformed, maybe once.
• 14:00
  SPEAKER_01: The Tetons are different, they've experienced probably two metamorphic events, serious ones, maybe three.
• 14:06
  SPEAKER_01: You kind of have to be in the interior of a continent where there are old rocks to kind of see multiple deformation.
• 14:12
  SPEAKER_01: I mean, most of the adiron.
• 14:14
  SPEAKER_02: Right, because the Tetons was at the time was closer to like an active margin, right?
• 14:19
  SPEAKER_02: To the west coast, the leading edge of North America at that time.
• 14:22
  SPEAKER_02: So different than the Acosta Nice, which is in the critonic setting, which is the stable interior part of a continent.
• 14:29
  SPEAKER_01: And so that's what makes this maybe different, right?
• 14:32
  SPEAKER_01: That's exactly right.
• 14:33
  SPEAKER_01: Exactly right.
• 14:33
  SPEAKER_01: Very well said.
• 14:34
  SPEAKER_01: So the debate here is kind of like who discovered this.
• 14:38
  SPEAKER_01: I mean, these were found during mapping campaigns by the Geological Survey of Canada and a geologist called Sam Bowering, who is a profess a geochronologist really, who who was at various universities but ended his career at MIT, was the one who kind of first published on the geochronology, and he was part of those mapping campaigns.
• 14:55
  SPEAKER_02: So, Jesse, I want to interject a second because I know exactly who you're talking about.
• 14:59
  SPEAKER_02: In 1994, I did my field camp at the University of New Mexico, and this was a 12-week long field course, and we did New Mexico, northern New Mexico, Taos Region, Southwest Colorado.
• 15:13
  SPEAKER_02: We were all over that area, right?
• 15:15
  SPEAKER_02: And it was amazing.
• 15:17
  SPEAKER_02: It was one of the best geologic experiences in my life.
• 15:20
  SPEAKER_01: But and Chris, let me just back this was capstone before your senior year or after your senior year or something like that.
• 15:26
  SPEAKER_02: No, I had already graduated.
• 15:27
  SPEAKER_02: Yes, I had already graduated, and this was like the last thing that I had to do.
• 15:32
  SPEAKER_02: And in the last six weeks of the course, the lead professor at that time, because they had they brought in several professors to take sections of the field course, Carl Carlstrom, who's still at UNM, I think anyway, uh brought in a friend of his named Sam Bowery, who was a professor at MIT.
• 15:53
  SPEAKER_02: And so I spent several weeks with him and made somewhat of an impression on him because we were doing a mapping project in southwest Colorado, very complicated area.
• 16:07
  SPEAKER_02: And he, in Sam's way, and I think you know him personally, right?
• 16:12
  SPEAKER_02: You or you did know him because he passed away, but yeah, I knew him.
• 16:15
  SPEAKER_01: I mean, only a little bit, one of his students and I collaborated quite uh a lot, but I I didn't know him very well.
• 16:21
  SPEAKER_02: For whatever reason, we had a connection and uh made somewhat of an impression on him, and he in an informal way offered me to go to pursue a graduate degree.
• 16:34
  SPEAKER_01: Yes.
• 16:35
  SPEAKER_01: So cool.
• 16:35
  SPEAKER_01: Oh wow, that's amazing.
• 16:37
  SPEAKER_02: Yeah.
• 16:38
  SPEAKER_01: His lab, I mean, in that what'd you say, 94?
• 16:41
  SPEAKER_01: Is that what you said?
• 16:42
  SPEAKER_02: 94.
• 16:42
  SPEAKER_02: Yeah.
• 16:42
  SPEAKER_01: 94.
• 16:43
  SPEAKER_01: So his lab, I mean, really, he was at MIT, so like obviously a very high profile, you know, very successful uh sort of academic environment.
• 16:51
  SPEAKER_01: His lab at the time, that time they had this was actually he first published his first paper on Acosta in 1989.
• 16:58
  SPEAKER_01: So he's kind of working on these samples, presumably in his lab at that time.
• 17:01
  SPEAKER_01: And then in the in the mid-2000s, like the early 2000s, he had a series of advances that they made in geochronology that really took uranium-bled geochronology and pushed it forward by a massive step function.
• 17:13
  SPEAKER_01: Like that lab was pumping out amazing papers very soon after you would have potentially gone there.
• 17:19
  SPEAKER_02: So So can I ask you, would that have been legitimate?
• 17:23
  SPEAKER_02: Can you see that happening or not?
• 17:25
  SPEAKER_01: Uh, you doing a PhD?
• 17:27
  SPEAKER_02: Well, like I'm I'm asking, like, was his offer because he was pretty persistent.
• 17:32
  SPEAKER_01: You know, I can tell you for a fact, you don't offer that without having meaning behind it.
• 17:38
  SPEAKER_01: That's a no-joke thing.
• 17:39
  SPEAKER_01: I mean, you don't you don't say, Oh, you should come to a grad school with me unless at least I don't, and I don't think many people do.
• 17:45
  SPEAKER_01: You don't offer that flippantly.
• 17:47
  SPEAKER_02: So yeah, so this was an interesting thing because it was a this was a pivotal moment in my life.
• 17:53
  SPEAKER_02: Yeah, I didn't have ready contact with Jenny because I was out in the field and you know, cell phones weren't weren't really around then at the time.
• 18:00
  SPEAKER_02: You know, that uh they were just beginning to have a beeper commander, a pager.
• 18:04
  SPEAKER_02: No, beeper, but I was out in the field, like it was I had to wait three weeks to get back to Albuquerque, and I'm like, Jenny, this just happened and I don't know what to do because I already had a job offer in Portland.
• 18:17
  SPEAKER_01: Well that must have been a difficult decision, or like at least a lengthy conversation.
• 18:22
  SPEAKER_02: It was, but here's the thing is Jenny was doing her student teaching, she had it all arranged to do it in Oregon.
• 18:29
  SPEAKER_02: We had so much invested in that direction.
• 18:33
  SPEAKER_02: That was my trajectory.
• 18:35
  SPEAKER_02: It was a very um tempting moment.
• 18:37
  SPEAKER_02: I don't think you and I have talked about that before, have we?
• 18:39
  SPEAKER_01: Only like offhand.
• 18:40
  SPEAKER_01: You mentioned that you knew Sam Bowering and that he said you should come to grad school.
• 18:44
  SPEAKER_01: I thought he was at Washington University when that had happened, but he was already at MIT at that point.
• 18:48
  SPEAKER_01: So it was at MIT.
• 18:49
  SPEAKER_01: Yeah, yeah.
• 18:49
  SPEAKER_01: I mean, well, you know, this is so interesting how these little one-off things, but the I I uh you don't so that's interesting because this was been very soon after he'd sort of first published on the Acostanises, which is around 89, and then he'd kind of been, you know, sort of working on them in the lab.
• 19:04
  SPEAKER_01: And really, there's a uh several technique developments that kind of got us to the point of being able to date these rocks.
• 19:10
  SPEAKER_01: And this is, I think Chris is going to be an interesting part of the discussion.
• 19:14
  SPEAKER_01: So, image number two in your stack, if you're on the book here, image number two shows a piece of equipment that for me is one of the more impressive pieces of equipment.
• 19:24
  SPEAKER_01: This is what's called an ion microprobe.
• 19:26
  SPEAKER_01: And an ion microprobe can analyze mineral grains, the width of hair, so tiny, tiny sand grains.
• 19:35
  SPEAKER_01: They can put tiny, tiny spots on tiny, tiny sand grains and get really good geochronology, uranium-lead isotope ratios out of it.
• 19:43
  SPEAKER_01: So you can basically image these grains and use an ion microprobe to measure the age of them and isotopic compositions.
• 19:50
  SPEAKER_01: And this is an image of one.
• 19:51
  SPEAKER_01: This is one of the early ones, and this thing takes up a whole room, Chris.
• 19:55
  SPEAKER_02: Like, this is where does it start, Jesse?
• 19:57
  SPEAKER_02: Like, where do they send the ions through and where do they count the ions on the back end?
• 20:01
  SPEAKER_02: Is it on the right or the left?
• 20:04
  SPEAKER_01: They vary uh depending on which you know brand or make or model of instrument.
• 20:07
  SPEAKER_01: But in this particular one, which is called the shrimp two, the ion beam starts on the right, so the sample will be loaded into a little chamber on the right there, and then basically you're you're taking an ion beam that's either oxygen or cesium ions, and you're hammering your sample with it, what's called sputtering.
• 20:25
  SPEAKER_01: It just kind of kicks off atoms from the top surface layer, and those atoms then get funneled through the magnet, is the big orange thing or big yellow thing in the back, and uh and then there's a detector on the farm.
• 20:35
  SPEAKER_02: Wait, so hold on.
• 20:36
  SPEAKER_02: The magnet is not the horseshoe thing, the silver thing in the corner.
• 20:41
  SPEAKER_01: The magnet is inside of that box that's labeled shrimp two.
• 20:44
  SPEAKER_01: The big curve thing is what's called an electrostatic analyzer, which just filters not for mass but for energy.
• 20:50
  SPEAKER_01: So it's just curved electric plates.
• 20:52
  SPEAKER_01: So it's a way to get higher sensitivity out of these things.
• 20:55
  SPEAKER_02: So because my thought was that the magnet would be there because that's going to affect the degree of bend of the ion.
• 21:02
  SPEAKER_02: Does that make sense?
• 21:03
  SPEAKER_01: Yeah, that's right.
• 21:04
  SPEAKER_01: So basically, what happens is you send these ions, your charged particles, they're flying really fast.
• 21:09
  SPEAKER_01: But when it comes off the sample, there's a bunch of different ones, bunch of different speeds, a bunch of different velocities of ions that come off.
• 21:14
  SPEAKER_01: And you want one velocity.
• 21:16
  SPEAKER_01: So you have to they put it through this sort of racetrack of electric fields that filters out some of the high energy ones and the low energy ones and filters for a particular energy.
• 21:25
  SPEAKER_01: So, anyway, these techniques, we really kind of developed these techniques called ion microprobes and a couple other technique developments in the the late 80s, early 90s that allowed geochronology to do what's called in- situ work.
• 21:38
  SPEAKER_01: So to be able to take an individual sand grain, in this case a zircon, and blast little parts of it, tiny, tiny little fragments, and get reliable ages out of that.
• 21:47
  SPEAKER_01: And this this technique transformed our understanding of the early earth because it allowed us to date parts of mineral grains that preserved a record of a really old record, basically.
• 21:59
  SPEAKER_02: What do you mean?
• 22:00
  SPEAKER_02: In situ?
• 22:01
  SPEAKER_02: What do you mean specifically when you say that?
• 22:04
  SPEAKER_01: So in situ means, in this case, means, and maybe this is a good time to turn to image number three if you're listening to this in the book.
• 22:11
  SPEAKER_01: Image number three is an image of a Nacasta zircon grain, a 4.02 billion year old zircon grain.
• 22:17
  SPEAKER_01: And this GIF just shows you know which parts are old and which parts are younger.
• 22:21
  SPEAKER_01: But the center part of this grain is old.
• 22:23
  SPEAKER_01: So those little, there's these little circles, tiny little squares and circles on the grain.
• 22:28
  SPEAKER_01: So in situ means I image the grain and I can put my spots on the grain without destroying the grain itself.
• 22:34
  SPEAKER_01: Previous techniques, you had to dissolve the whole grain, so you kind of lost that spatial resolution.
• 22:40
  SPEAKER_02: Oh, you lost this spatial component.
• 22:42
  SPEAKER_02: That makes sense.
• 22:44
  SPEAKER_02: So you're taking the zircon in its original state, and you're dating from rim through to the core of that zircon grain, the age.
• 22:55
  SPEAKER_01: That's exactly right.
• 22:56
  SPEAKER_01: You can sort of look at the outer part, the inner part, any metamorphic rims.
• 23:00
  SPEAKER_01: And and we talked about these rocks are super deformed, they've been metamorphosed multiple times.
• 23:05
  SPEAKER_01: The mineral grains record that.
• 23:07
  SPEAKER_02: Yeah.
• 23:07
  SPEAKER_02: So, Jesse, why is it that the rim of the zircon?
• 23:12
  SPEAKER_02: It makes sense that the rim of the zircon crystal here that you have on image number three is younger, but man, that's a big difference in time between the rim 3.3 billion years old to the core of it as 4.02 billion years old.
• 23:29
  SPEAKER_02: That's a massive amount of time.
• 23:30
  SPEAKER_02: Why?
• 23:31
  SPEAKER_01: So the rim is a metamorphic grown rim.
• 23:35
  SPEAKER_01: So it'll have grown during a metamorphic event.
• 23:38
  SPEAKER_01: It's like garnet.
• 23:39
  SPEAKER_01: Yeah, the metamorphism was so intense that the zircon started to be dissolved, and then some new zircon was grown on the edges of it, and that's metamorphic.
• 23:48
  SPEAKER_01: So think of a garnet zoning and garnet growth.
• 23:51
  SPEAKER_01: It's really a metamorphic mineral, the outer part of it.
• 23:53
  SPEAKER_02: So the z the rim of the zircon got melted or partially melted and metamorphosed, but it didn't reach into the core of the zircon grain.
• 24:03
  SPEAKER_01: That's exactly right.
• 24:03
  SPEAKER_01: Not into the core.
• 24:04
  SPEAKER_02: Okay, so for the listener, then when you melt something and then it crystallizes, that resets the clock on it, or at least partially resets the clock.
• 24:14
  SPEAKER_01: Yeah, it can absolutely reset the clock or partially reset it.
• 24:18
  SPEAKER_01: It depends on how intense this alteration is.
• 24:20
  SPEAKER_01: And this is usually, we think of this as fluid-grown zircon, so not actually magma.
• 24:25
  SPEAKER_01: There's not actually molten magma moving around, but it's a fluid-rich environment.
• 24:29
  SPEAKER_01: And usually in these rocks, you'll have things like amphibole.
• 24:32
  SPEAKER_01: And amphibole, when that breaks down and starts to get broken down by metamorphism, it'll release zirconium into the fluid, and then that zirconium will start building more zircon.
• 24:42
  SPEAKER_01: So you kind of have the other minerals around it are breaking down and releasing the building blocks of zircon into the fluid, and it grows new zircon around an existing one in that case.
• 24:51
  SPEAKER_01: So that's what's going on here.
• 24:54
  SPEAKER_02: So do we use this kind of I'm gonna call this zoning, if you will, in image number three.
• 25:00
  SPEAKER_02: We use the zoning then to put a number on how many events happened.
• 25:06
  SPEAKER_02: Exactly.
• 25:07
  SPEAKER_01: Is that that's exactly right of saying it?
• 25:09
  SPEAKER_01: Exactly.
• 25:09
  SPEAKER_01: So you can look at those cores, you can look at the rims.
• 25:12
  SPEAKER_01: In one rock, you can get a bunch of different ages.
• 25:14
  SPEAKER_01: And Chris, this brings up a source of debate that has been a kind of a long-standing debate about the acostinessis.
• 25:20
  SPEAKER_01: And this will become relevant in either in the the second part of the podcast or later on in this chapter, because it begs the question, what does an age of a rock mean?
• 25:29
  SPEAKER_01: So when I say a rock is some age, just any old age, a nice, a schist, some metamorphic rock is an age.
• 25:36
  SPEAKER_01: What do you think, in your view, what does that age mean?
• 25:39
  SPEAKER_01: Or how do we interpret that age?
• 25:41
  SPEAKER_01: What age am I giving, if that makes sense?
• 25:43
  SPEAKER_02: Um not really.
• 25:44
  SPEAKER_01: Like if I said this shist, there's a schist.
• 25:48
  SPEAKER_01: It originally was a shale, and then it's been metamorphosed into a schist, and the schist is 1.8 billion years old.
• 25:54
  SPEAKER_01: What event am I referring to?
• 25:57
  SPEAKER_02: You're referring to the metamorphic event, not the event that formed the rock to begin with.
• 26:04
  SPEAKER_02: In other words, not the protolith to the metamorphic rock.
• 26:08
  SPEAKER_01: Okay, great word.
• 26:09
  SPEAKER_01: Can you define the protolith?
• 26:11
  SPEAKER_01: Can you define that?
• 26:11
  SPEAKER_01: Because that's I think that's going to be an important word here.
• 26:14
  SPEAKER_02: So if you take a shale, let's say that's the protolith, and let's metamorphose the crap out of this rock, that shale can turn into a schist.
• 26:24
  SPEAKER_02: So shale is the protolith, it's the parent rock to the metamorphic rock.
• 26:30
  SPEAKER_02: So when we date the age of the metamorphic rock, we are not dating the age of the shale that the rock came from.
• 26:37
  SPEAKER_01: That's what I'm saying.
• 26:38
  SPEAKER_01: That's right.
• 26:39
  SPEAKER_01: So let me ask you another question.
• 26:41
  SPEAKER_01: What if I gave you a granite that had been metamorphosed into a gneiss and told you the age was 1.8?
• 26:47
  SPEAKER_01: What would you assume?
• 26:48
  SPEAKER_01: Would it be the same?
• 26:50
  SPEAKER_02: No, the 1.8 is the age of the event that turned the granite, the protolith, which we're not, you're not giving me the age of the granite.
• 26:58
  SPEAKER_02: You're giving me the age at which the granite turned into gneiss.
• 27:01
  SPEAKER_01: Okay.
• 27:02
  SPEAKER_01: And this is a really fundamental debate about the Acosta Nice complex.
• 27:06
  SPEAKER_01: Because when I am talking about the age of the Acosta Nice complex, when you say it's four billion years old, that age is the initial formation age.
• 27:15
  SPEAKER_01: It's not the latest metamorphic age.
• 27:18
  SPEAKER_01: The latest metamorphic event here is 1.9.
• 27:20
  SPEAKER_01: So if you were saying the what is the age of the gneisses, they're 1.9 or maybe 3.2 billion years old.
• 27:27
  SPEAKER_02: I got you.
• 27:27
  SPEAKER_02: So you are using a different tool in your toolbox then to do that.
• 27:32
  SPEAKER_01: That is exactly right.
• 27:33
  SPEAKER_02: So there are certain radiometric clocks that you use in your lab, whether it's uranium to lead, rubidium to strontium, all kinds of different tools that you can use.
• 27:45
  SPEAKER_02: And some of them are able to see through the metamorphic event and go back to the protolith.
• 27:54
  SPEAKER_02: And that's what you've done with the acosta nice.
• 27:58
  SPEAKER_02: I I'm tracking 100%.
• 27:59
  SPEAKER_01: And like I think this is a really fundamental, and I think it's an interesting question that I think you know should challenge listener to think about.
• 28:07
  SPEAKER_01: What is the age of a rock?
• 28:08
  SPEAKER_01: A metamorphic rock, what is the age of it?
• 28:10
  SPEAKER_01: Because we all we say the the acosta nice, oldest rock in the world, it's been metamorphosed multiple times, six times at least.
• 28:17
  SPEAKER_01: What does that age actually mean?
• 28:19
  SPEAKER_01: And and what I'm talking about is I'm talking about small portions of specifically zircon grains, the inner parts of zircon grains are the only parts of that rock that record the four billion year age, the primary age of the rock.
• 28:32
  SPEAKER_02: I'm sorry, but I want to interrupt you because I want to, for our listeners, let's talk about a metamorphic rock and what tool we would use for dating that metamorphic rock, and then let's take that metamorphic rock and what tool would we use to see through that event back to the protolith.
• 28:52
  SPEAKER_01: This is a nice exercise.
• 28:54
  SPEAKER_01: This is a very good exercise.
• 28:55
  SPEAKER_01: Yep.
• 28:55
  SPEAKER_02: So walk us through that without providing the answer because then we'll get to that at the end.
• 29:00
  SPEAKER_02: Does that make sense?
• 29:01
  SPEAKER_02: Just talk about the differences.
• 29:02
  SPEAKER_01: So geochronologists play this game.
• 29:04
  SPEAKER_01: You know, we say, okay, we've got a bunch of tools.
• 29:06
  SPEAKER_01: We got you said rubidium, strontium, smaramidium, uranium-lead.
• 29:10
  SPEAKER_01: We can apply those specific elemental combinations of parent-daughter or parent product isotopes.
• 29:16
  SPEAKER_01: We can apply them to individual mineral grains, we can apply them to different minerals in the same rock, we can apply them to different rocks in the same kind of package of rocks.
• 29:24
  SPEAKER_01: And so, you know, we're dealing with a problem of scale a little bit here.
• 29:27
  SPEAKER_01: But if you look at something like rubidium-stronium, that system, ribidium is really mobile in fluids.
• 29:34
  SPEAKER_01: So any fluidy event, any metamorphic event that's moving fluids through the rock will reset that to your chronometer, the rubidium-stronium system.
• 29:42
  SPEAKER_01: If you look at smeraminodymium, it's a bit more reliable.
• 29:46
  SPEAKER_01: Like it doesn't move in fluids so much, but it moves when things are melted.
• 29:50
  SPEAKER_01: If you think about uranium lead, certain minerals have what's called a low closure temperature.
• 29:55
  SPEAKER_01: So they will be reset at 500 degrees centigrade.
• 29:58
  SPEAKER_01: Zircons won't be reset until like a thousand degrees centigrade.
• 30:01
  SPEAKER_01: Different minerals have different kinds of ranges that they're sensitive to or that they get reset at.
• 30:06
  SPEAKER_02: Or another example would be, let's say, potassium to argon.
• 30:09
  SPEAKER_02: And whereas argon's a gas, when potassium decays into argon, metamorphism can squeeze the gas out of it and reset the clock.
• 30:18
  SPEAKER_02: And so you're not going to be able to date the protolith using that tool in your toolbox.
• 30:25
  SPEAKER_02: You're only going to be able to date the time that it was squeezed and tortured.
• 30:30
  SPEAKER_01: So the age for these rocks, if you've looked at the potassium argon system, they're going to be 1.9 billion years, if not younger than that, because that's the last time that the rocks reach this temperature, 400 degrees centigrade or something like that.
• 30:43
  SPEAKER_01: So in these particular cost and ice samples, most of the minerals have a an overprint at 1.9 billion years old.
• 30:51
  SPEAKER_01: Some of them, zircon's one of them, titanite is another one, or sphenes, some people call it, uh apatite, some of them have older signatures, and zircon has the oldest, but only parts of zircon have the oldest one.
• 31:02
  SPEAKER_01: And I and many other geochronologists interpret that as the original magmatic age, because that zircon, if you go back to image number three, that zircon, the sort of tree ring growth zoning, tells us that that grew in a magma.
• 31:16
  SPEAKER_01: So that zircon grew in a magma.
• 31:18
  SPEAKER_01: That zircon is 4.02 billion years old, so therefore this rock originally grew from a magma 4.2 billion years ago and has since been reset tons of times.
• 31:28
  SPEAKER_01: But it's kind of a philosophical discussion that still exists.
• 31:31
  SPEAKER_01: Like, what is the age of the Acostanics?
• 31:33
  SPEAKER_01: Are we talking about the metamorphic age or the the original Proto-Lithigneus age?
• 31:37
  SPEAKER_02: Yeah, that's a it's I'll tell you, Jesse, this is an interesting, this is a rabbit hole in and of itself.
• 31:43
  SPEAKER_01: Totally.
• 31:44
  SPEAKER_01: Oh my goodness, yes.
• 31:45
  SPEAKER_01: Yeah.
• 31:45
  SPEAKER_02: When when you start digging into and reading about the geology of an area, right?
• 31:50
  SPEAKER_02: This is something that you have to sort out early on.
• 31:54
  SPEAKER_02: Because when you read about the geology of, let's say, the Precambrian core and they start throwing out numbers.
• 32:00
  SPEAKER_02: Well, hold on a minute.
• 32:01
  SPEAKER_02: What do those numbers represent?
• 32:02
  SPEAKER_02: They say this rock formed 2.7 billion years ago.
• 32:05
  SPEAKER_02: Well, what are we talking about?
• 32:07
  SPEAKER_02: Are we talking about the rock that we have right now in front of us, or are we talking about the protolith, right?
• 32:13
  SPEAKER_02: And this can this is something, Jesse, that I don't think that we as geologists, we don't do a good job of this.
• 32:22
  SPEAKER_02: We need to tease that out and be more specifically because it leads to confusion.
• 32:28
  SPEAKER_02: I'm just gonna say that.
• 32:29
  SPEAKER_01: I agree completely.
• 32:30
  SPEAKER_01: Massive confusion, and that confusion is really well represented in the Acosta Nice complex because this debate still kind of exists as soon as Sam Broering and others discovered the age, the really old age of these grains.
• 32:41
  SPEAKER_01: People immediately started to say, wait, hold on, that's not right.
• 32:44
  SPEAKER_01: That's not the right age.
• 32:45
  SPEAKER_01: You're talking about some invasion.
• 32:47
  SPEAKER_01: They were talking about two different things.
• 32:49
  SPEAKER_01: Yeah, exactly.
• 32:49
  SPEAKER_01: So you're kind of talking across each other, talking about two different things.
• 32:52
  SPEAKER_01: It really kind of also depends on which tool you trust the most.
• 32:56
  SPEAKER_01: And whenever a new technique is developed, not many people trust it.
• 33:00
  SPEAKER_01: The technique developers have to prove that this is a reliable technique.
• 33:03
  SPEAKER_01: So this ion microprobe technique, nobody believed it for like five years.
• 33:08
  SPEAKER_01: And so everybody said, No, that one's not right.
• 33:10
  SPEAKER_01: My Sumerium Neandimium system that I trust and have been using for 20 years is the one that's the geochronometer that's the best.
• 33:16
  SPEAKER_01: Your new ion microprobe zircon thing isn't.
• 33:19
  SPEAKER_01: And so it took a while for this to become like trusted by the community in a way.
• 33:24
  SPEAKER_01: So that's kind of sort of the debate there.
• 33:26
  SPEAKER_02: All right, so Jesse, we need to transition right now because we I love I love doing this, man.
• 33:33
  SPEAKER_02: I'll tell you, but but man, I'll tell you, these discussions are just good for the soul.
• 33:38
  SPEAKER_01: Like they are I agree when you just consider on sort of BSing about something you're passionate about and you really enjoy it.
• 33:44
  SPEAKER_01: That's kind of how I feel.
• 33:45
  SPEAKER_02: You know, you and I are on my front porch right now.
• 33:47
  SPEAKER_02: Totally, totally, and uh, we're drinking a beer, and now we're drinking a bourbon, and we're talking about this, and it's it's really good, it's good for the soul.
• 33:55
  SPEAKER_02: So let's move into you talked about the ion microprobe, and it's kind of like not accepted for a while.
• 34:03
  SPEAKER_02: Let's move into more recent work.
• 34:05
  SPEAKER_02: So there have been many, many PhD projects that have been done on the Acosta Nice.
• 34:11
  SPEAKER_02: By the way, you gave me Acosta Nice.
• 34:16
  SPEAKER_02: Did you give me good Acosta?
• 34:17
  SPEAKER_02: Oh, I gave you the best.
• 34:18
  SPEAKER_02: I need to know this.
• 34:19
  SPEAKER_02: I gave you Did you really have a good one?
• 34:21
  SPEAKER_01: That's that's the good that's the old stuff right there.
• 34:23
  SPEAKER_01: Yep, for sure.
• 34:24
  SPEAKER_02: Do you know where I put it?
• 34:25
  SPEAKER_02: Do you know where I put it?
• 34:26
  SPEAKER_01: I don't know that actually.
• 34:27
  SPEAKER_01: Where is it?
• 34:28
  SPEAKER_01: Jesse.
• 34:28
  SPEAKER_01: Is it in your classroom?
• 34:29
  SPEAKER_01: It's on my no oh the good stuff doesn't go in the classroom, the good stuff goes in the in the house?
• 34:34
  SPEAKER_02: No, no, my release my really good stuff is at my house.
• 34:38
  SPEAKER_02: Oh, that's I don't think I knew that.
• 34:41
  SPEAKER_01: That's funny.
• 34:41
  SPEAKER_01: That's great.
• 34:42
  SPEAKER_02: So no, it's on my fireplace mantle.
• 34:45
  SPEAKER_02: Oh no.
• 34:46
  SPEAKER_02: The the rock wall behind my fireplace on the main floor.
• 34:49
  SPEAKER_02: I have the Acosta that you gave me.
• 34:51
  SPEAKER_02: So it's in the rock wall.
• 34:52
  SPEAKER_02: It's in the rock wall, so it's never going to be a good thing.
• 34:54
  SPEAKER_02: You guys can't ever move.
• 34:56
  SPEAKER_02: Nope.
• 34:56
  SPEAKER_02: I'm not ever moving from my house anyway.
• 34:58
  SPEAKER_02: So yeah, anyway.
• 34:59
  SPEAKER_02: Okay.
• 35:00
  SPEAKER_02: So let's talk about some notable stuff.
• 35:02
  SPEAKER_02: Yeah.
• 35:03
  SPEAKER_02: Okay.
• 35:03
  SPEAKER_01: So we're kind of fast forward a little bit.
• 35:05
  SPEAKER_01: We left off in kind of the late 80s, early 90s.
• 35:08
  SPEAKER_01: People have kind of refined the age of these things, you know, started at 3.96, then it got to actually this is an important one.
• 35:14
  SPEAKER_01: You'll see the 3.96 billion year old number.
• 35:17
  SPEAKER_01: You'll see that in some museums.
• 35:18
  SPEAKER_01: That's the original age, like in 1989 age, that has since been updated in 1999.
• 35:24
  SPEAKER_01: And then in my PhD work, it got updated to 4.02 billion years old.
• 35:28
  SPEAKER_01: Which Chris, it's I know it sounds like a small difference, but it's like 50 million years.
• 35:32
  SPEAKER_02: No, no, it's not.
• 35:33
  SPEAKER_02: We've already covered this ground, it's not insignificant, because as you said, you know what?
• 35:39
  SPEAKER_02: Those million years matter.
• 35:41
  SPEAKER_02: Yeah, okay.
• 35:42
  SPEAKER_02: Like you said this when we touched off our series on geochronology, like, and that's an impressive thing to say.
• 35:48
  SPEAKER_02: I get that, I relate to that, but but Jesse, like, this is annoying to me.
• 35:53
  SPEAKER_02: Also, talking about the confusion, we are not good at updating numbers.
• 35:59
  SPEAKER_01: I know it's yeah, I don't know what to do about it because I've gone to museums and I've said, Oh, yeah, look at that rock, that's must be an acostiness.
• 36:06
  SPEAKER_01: Look at the thing.
• 36:06
  SPEAKER_01: Yeah, acostiness, 3.96 billion years old.
• 36:08
  SPEAKER_01: It's like, guys, yeah, that age has been updated since 1999.
• 36:12
  SPEAKER_01: You know, there's a better number for that.
• 36:14
  SPEAKER_01: And it's a little bit of a bad thing.
• 36:16
  SPEAKER_02: But here me too, because let's say that you decide I'm going to the Grand Canyon.
• 36:21
  SPEAKER_02: I want to learn about the geology of the Grand Canyon before I go there.
• 36:25
  SPEAKER_02: And you start looking into the literature, and they start getting into the numbers of the ages of the rocks, and you see right away massive discrepancies of the numbers that are thrown out.
• 36:36
  SPEAKER_02: And it's very, very irritating.
• 36:38
  SPEAKER_02: It should not be this way.
• 36:40
  SPEAKER_02: We need to do better.
• 36:42
  SPEAKER_01: There needs to be Wikipedia for ages in your chronology where the things are kind of open sourced and community updated things.
• 36:48
  SPEAKER_01: It's just, it's really hard.
• 36:50
  SPEAKER_01: Anyway, we've got a whole that's that's a whole separate thing.
• 36:52
  SPEAKER_02: I know it is a whole separate thing.
• 36:54
  SPEAKER_02: All right, let's go.
• 36:55
  SPEAKER_01: Let me skip forward here.
• 36:55
  SPEAKER_01: So that age was kind of updated in the late 90s, early 2000s.
• 36:59
  SPEAKER_01: Then there's a bunch of PhD work that kind of kicked off in the sort of mid-2000s.
• 37:04
  SPEAKER_01: And there's several I mean, there's been dozens of PhD projects done on the Acosta Nice.
• 37:08
  SPEAKER_01: I'll highlight a couple here, and I think we'll end part one at the end of this little section here.
• 37:13
  SPEAKER_01: We're gonna go up to when I started my PhD.
• 37:16
  SPEAKER_01: Like, what did we know about the Acosta Nice up until that point?
• 37:19
  SPEAKER_01: And there's some really great work done by a Japanese group.
• 37:21
  SPEAKER_01: Soyoshi Azuka was kind of the lead person who was doing their PhD on this place, and he did a really impressive job mapping this area, and so went across and sort of mapped.
• 37:31
  SPEAKER_01: We're talking about maybe a 30 square kilometer area in the center of the Acosta Nice region that he did some mapping on and really showed that there's quite variable strain.
• 37:42
  SPEAKER_01: And what I mean by strain is like how deformed are the rocks.
• 37:44
  SPEAKER_01: And so image number four here shows what are called flaggy gneisses.
• 37:49
  SPEAKER_01: And Chris, I I love this term.
• 37:51
  SPEAKER_01: The term is flaggy gneisses because it looks like kind of an American flag or stripes on a flag, you know.
• 37:56
  SPEAKER_01: These are really just these rocks are toothpaste, except they have been smooshed straight.
• 38:02
  SPEAKER_01: And this little gif shows that there's this really nice tight fold.
• 38:05
  SPEAKER_01: That's actually my PhD supervisor in the background there, Tom Chaco, looking at these boats.
• 38:08
  SPEAKER_02: Oh, that's not you?
• 38:10
  SPEAKER_01: It's not me.
• 38:10
  SPEAKER_01: No, that's that's Chaco.
• 38:12
  SPEAKER_01: Okay, but this is flaggy nices.
• 38:15
  SPEAKER_01: And I think if you've walked across deformed stuff, you've seen some.
• 38:18
  SPEAKER_01: They're just each layer is centimeter thick at most, they're just stretched into oblivion.
• 38:23
  SPEAKER_01: That's the the sort of flaggy nices.
• 38:26
  SPEAKER_01: So Izuka, Tsyoshi Izuka, did this map and showed that there's some really deformed stuff on the west side and some less deformed stuff on the east side.
• 38:35
  SPEAKER_01: And image number five in the book here shows some less deformed rocks.
• 38:39
  SPEAKER_01: These are obviously not flaggy gneisses.
• 38:41
  SPEAKER_01: There's like beautiful cross-cutting relationships.
• 38:44
  SPEAKER_01: Chris, this reminds me of the outcrop that you taught me about cross-cutting relations on up in the upper peninsula, Michigan, where you can kind of trace out the little white veins as they're cutting across things and work out the time frames of them.
• 38:54
  SPEAKER_01: Whereas in that previous image, the flaggy gneisses, like all cross-cutting relationships are lost, they've just been stretched into oblivion.
• 39:01
  SPEAKER_01: So really nice PhD that kind of did this mapping project on this.
• 39:06
  SPEAKER_02: Very, very cool.
• 39:07
  SPEAKER_02: I have a question that I want to ask you.
• 39:09
  SPEAKER_02: Let's say that that image number four, the flaggy gneiss.
• 39:13
  SPEAKER_02: Let's say that we compare a gneiss to granite.
• 39:18
  SPEAKER_02: And so we have like kind of gneiss and granite next to each other.
• 39:23
  SPEAKER_02: There's a contact between them, and we're going to shove this up to form mountains.
• 39:28
  SPEAKER_02: Which one is going to be more resistant to erosion?
• 39:31
  SPEAKER_01: Oh, that is such a good question.
• 39:33
  SPEAKER_01: Granite, probably, in part, because gneiss is going to have well, granite's going to be kind of homogeneous.
• 39:41
  SPEAKER_01: It's quartz, feldspar, maybe some biotite.
• 39:44
  SPEAKER_01: Those are not very erodable minerals, and it's really well put together.
• 39:48
  SPEAKER_02: It's it's interlocking.
• 39:50
  SPEAKER_02: The crystals all grow like a jigsaw puzzle into each other till they can't grow anymore.
• 39:55
  SPEAKER_02: And metamorphism kind of distorts that whole thing and separates them all out.
• 40:02
  SPEAKER_01: That's exactly right.
• 40:03
  SPEAKER_02: And so we often this is just something that I just wanted to throw in for our listeners because it's something that when you look at mountains like the Tetons, let's say, many of the high peaks are granite, not the gneiss that makes up the bulk of the Teton range, because the granite is more resistant to erosion.
• 40:24
  SPEAKER_02: It's just that like I don't know, it's just one of these things that fits in geologic, like common sense kind of thing.
• 40:31
  SPEAKER_01: That is such a great point, and I just want to build on that because the opposite here, when we have these gneisses, if you go to image number four, when we have these gneisses, these things are really strained into oblivion.
• 40:41
  SPEAKER_01: There's a bunch of different compositions in there.
• 40:42
  SPEAKER_01: There's mafic, little mafic parts, there's little felsic parts, there's little intermediate parts.
• 40:47
  SPEAKER_01: Some of those will be easily weatherable.
• 40:49
  SPEAKER_01: And actually, the deformation itself, the strain itself, just having a fabric in the rock makes it easier to break down because fluid can kind of percolate in through cracks and kind of exploit that weakness.
• 41:00
  SPEAKER_01: I mean, I just realized this the other day.
• 41:02
  SPEAKER_01: I was looking at the local geological map in my house in York, and I live on this kind of big sloping hill that goes down towards kind of the level of the city down below.
• 41:11
  SPEAKER_01: I live on a fault, a little fault that has a bunch of quartz veins running through it.
• 41:15
  SPEAKER_01: So if you're just walking around in hilly terrain and there's a gully there, odds are there's some sort of geological feature that controls even little gullies.
• 41:23
  SPEAKER_01: I mean, so they these you they're usually little fault veins or little areas where where their rock has been deformed because it makes it much more easily erodible, basically.
• 41:32
  SPEAKER_02: Can I interject a really bad geology pun here?
• 41:35
  SPEAKER_01: No, I hate puns, but yes, you may.
• 41:37
  SPEAKER_02: I know, but you just said you lived on a fault.
• 41:39
  SPEAKER_02: But Jesse, geologists all have their faults, but they're stress-related.
• 41:47
  SPEAKER_01: That's a good one.
• 41:48
  SPEAKER_01: Actually, I was wearing my shirt that has no you don't like this.
• 41:51
  SPEAKER_01: No, that's it.
• 41:52
  SPEAKER_01: That's a good one.
• 41:53
  SPEAKER_01: I was wearing, um, I was wearing my shirt the other day that it's like bright colors.
• 41:58
  SPEAKER_01: You know, my wife gets me these silly geology bun ones for my birthday because she knows I hate it, so she tortures me.
• 42:03
  SPEAKER_01: But this one is um what was he saying?
• 42:06
  SPEAKER_01: It's not my fault, metamorphically speaking, or something like that.
• 42:10
  SPEAKER_01: Yeah, something metamorphically speaking.
• 42:13
  SPEAKER_01: I love it.
• 42:13
  SPEAKER_01: It's quite funny, but it's a very bright shirt in my uh anyway.
• 42:16
  SPEAKER_01: I got comments about it.
• 42:17
  SPEAKER_02: You know, metaphorically exactly, yeah, exactly.
• 42:20
  SPEAKER_02: Yeah, yeah, that's awesome.
• 42:21
  SPEAKER_02: All right, so Jesse, let's wrap this up real quick.
• 42:24
  SPEAKER_02: So to end this part of our part one of two K is the Acosta Nice.
• 42:32
  SPEAKER_02: If you go back to the Protolith, you strongly feel that the Acosta Nice is not 3.9 or 3.96 billion years old, that it is 4.02 billion years old.
• 42:48
  SPEAKER_01: Yes, certain parts of it.
• 42:49
  SPEAKER_01: Yep, certain rocks within it.
• 42:51
  SPEAKER_01: But there's also let's add a little fuel to the confusion fire here, because the Suyoshazuka, this excellent Japanese PhD student who who did a PhD project there, also found a not 4.02, but 4.2 zircon core.
• 43:07
  SPEAKER_01: One single core of a zircon in a rock that was 3.9 billion years old.
• 43:13
  SPEAKER_01: So the entire rock, all the zircons in this rock are 3.9 billion years old.
• 43:16
  SPEAKER_01: They grew in a magma.
• 43:18
  SPEAKER_01: There's one little core that's 4.2.
• 43:21
  SPEAKER_01: And that is a term we call xenochrystic, foreign crystal, xenochrystic, much like xenolith.
• 43:29
  SPEAKER_01: We've talked about xenolith before, Chris, like a foreign rock that's intruded in a younger magma.
• 43:34
  SPEAKER_01: This is the same thing.
• 43:34
  SPEAKER_01: It's a 4.2, not O2, 4.2 billion-year-old zircon core.
• 43:40
  SPEAKER_01: So what it tells us is that there used to be 4.2 billion-year-old rocks in the area.
• 43:45
  SPEAKER_02: Somehow this mineral escaped.
• 43:47
  SPEAKER_01: It escaped, yeah, exactly.
• 43:49
  SPEAKER_02: Resurfacing events.
• 43:51
  SPEAKER_02: Because this is at a time when Earth was in the heavy bombardment era.
• 43:56
  SPEAKER_02: We were getting smacked, and some of these were resurfacing, these events were big enough to resurface our entire planet, which means a total reset of the clock, of the radiometric clock.
• 44:09
  SPEAKER_02: So is that right?
• 44:10
  SPEAKER_02: Like this was perhaps deep enough to escape that.
• 44:13
  SPEAKER_01: Yeah, and this is deep enough or or it didn't get hit randomly.
• 44:17
  SPEAKER_01: One spot of the earth didn't get hit by a big impact.
• 44:20
  SPEAKER_01: But this 4.2, what it tells us is that this Acosta nice area used to have 4.2 billion year old rocks around.
• 44:28
  SPEAKER_01: We haven't found any yet, and we'll come back to this in the second part because we'll we'll kind of talk about where we're at now and what's coming, the future work or future questions are.
• 44:36
  SPEAKER_01: But there is evidence for 4.2 billion year old rocks in this area.
• 44:40
  SPEAKER_01: We just haven't found them yet.
• 44:41
  SPEAKER_01: We haven't found the actual rocks.
• 44:43
  SPEAKER_01: We have the signatures that they used to exist, but we don't see them anymore.
• 44:46
  SPEAKER_01: And this sample is funnily enough, it's kind of from a boulder.
• 44:50
  SPEAKER_01: Uh it doesn't really matter because it's just a random, you know, it's a it's an old zircon that's we lost the context because it's a core, a xenocrystrap.
• 44:57
  SPEAKER_02: It's not a it's not in place, it's not in place.
• 44:59
  SPEAKER_01: So who cares that it's from a boulder, but it is sampled from a boulder.
• 45:02
  SPEAKER_01: It's kind of a funny story there.
• 45:03
  SPEAKER_01: Yeah, we're funny people though.
• 45:04
  SPEAKER_01: We care about details like that.
• 45:06
  SPEAKER_01: That's exactly right.
• 45:06
  SPEAKER_01: So okay, Chris, we're almost an hour into this beast.
• 45:09
  SPEAKER_01: I simply cut it there.
• 45:10
  SPEAKER_02: Jesse, how did that happen?
• 45:12
  SPEAKER_01: For part one, let's cut it off there, and we'll pick up part two with where we're at when my PhD kind of started.
• 45:18
  SPEAKER_01: How about that?
• 45:19
  SPEAKER_01: Okay, let's do it.
• 45:20
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• 45:29
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• 45:43
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• 45:45
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• 45:46
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