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Earth's Oldest Stuff · PlanetGeo: The Geology Podcast

0:01
SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
0:16
SPEAKER_01: Why do you always do this?
0:17
SPEAKER_01: Every time, every time you hit the button.
0:19
SPEAKER_01: I know.
0:20
SPEAKER_01: You just get this happy grin on your voice.
0:23
SPEAKER_00: Well, first of all, because I'm excited to be recording Planet Geo with my good buddy Chris Boyce.
0:28
SPEAKER_00: But also, I don't know.
0:30
SPEAKER_00: I always get a good comment or a good story out of you on the intro.
0:33
SPEAKER_00: Like you always I'm thinking back to when you got really pissed at me about taking more control.
0:38
SPEAKER_00: This new software we use where I get to press the button to record and I'm taking control of the podcast away from you.
0:46
SPEAKER_00: So that's what I was giggling about right now.
0:48
SPEAKER_01: Slowly diminishing my role in this, you know, like it's bit by bit.
0:52
SPEAKER_01: And you know what?
0:53
SPEAKER_01: I'm gonna do pretty soon.
0:54
SPEAKER_01: I'll I'll just be your little sidekick.
0:56
SPEAKER_01: And if you ever call me, hey, my little sidekick, Chris, here.
0:59
SPEAKER_00: Yeah, yeah, yeah.
0:59
SPEAKER_00: Chris, the coup can come in.
1:01
SPEAKER_01: Then we're done.
1:01
SPEAKER_01: I'm gonna break up with you.
1:02
SPEAKER_00: I think what I might do, Chris, is I might take all the audio content because you know I do do some of the editing around here.
1:08
SPEAKER_00: I might take all your audio content and I might make an AI version of Chris Bullheis, and then I'll just record episodes with the AI version of Chris.
1:16
SPEAKER_01: Oh, that's such a good idea.
1:17
SPEAKER_00: Such a good idea.
1:18
SPEAKER_01: Hey, it'll be a whole lot less work for me, and then I'll get at least some of the credit.
1:22
SPEAKER_01: Yeah, yeah.
1:23
SPEAKER_00: You could get royalties on it, probably, or something.
1:25
SPEAKER_00: Yeah, right.
1:25
SPEAKER_00: I think that would be a funny exercise.
1:27
SPEAKER_00: If we could figure out how to do that, that would be very funny to like test just to try it out, see what it's like recording.
1:33
SPEAKER_01: Yeah, well, so maybe our listeners don't know this.
1:36
SPEAKER_01: You and I always we end up saying, hey, we're gonna quick knock this episode out.
1:41
SPEAKER_01: It's gonna take like 30 to 45 minutes, whatever, you know, whatever this episode entails.
1:45
SPEAKER_01: And then you and I sit here and just talk at least a half hour.
1:51
SPEAKER_01: That's what you're saying, is that I I come up with these little things that bring you joy, I guess.
1:56
SPEAKER_00: You always you usually come in hot in some way.
1:59
SPEAKER_00: Usually it's a good hot, and sometimes it's like a vent hot where you gotta vent about something, which also makes me laugh.
2:05
SPEAKER_00: So either way, you're late making me laugh.
2:07
SPEAKER_00: I don't I don't vent a lot, do I?
2:09
SPEAKER_00: Well, sometimes you got a little rant that you gotta get off your chest, and those make me giggle too.
2:13
SPEAKER_00: It's just a good giggle session for me.
2:15
SPEAKER_00: I like it.
2:16
SPEAKER_00: Yeah.
2:16
SPEAKER_00: Well, what do you got for me today?
2:18
SPEAKER_00: I I'm hoping that you got something for me.
2:21
SPEAKER_01: Uh well, I did get a phone call from my dad.
2:24
SPEAKER_00: Oh, yes.
2:24
SPEAKER_00: Was Joyce on the line?
2:26
SPEAKER_01: No, Joyce was not on the line.
2:27
SPEAKER_01: They they can't do that.
2:28
SPEAKER_01: They can't they can't do two people on the line.
2:31
SPEAKER_01: I just I love my parents so much and they know this.
2:35
SPEAKER_01: So I hope uh Dave, don't be offended.
2:38
SPEAKER_01: Okay, dad, Dave.
2:39
SPEAKER_01: It's weird for me to call him Dave.
2:41
SPEAKER_01: Don't be offended, Dave, but he calls me today, Jesse, and and I missed his call.
2:46
SPEAKER_01: And so I said, Hey dad, I saw the default.
2:51
SPEAKER_00: Did they leave a voicemail or is it just a I don't know.
2:53
SPEAKER_01: I didn't because you know I don't check it.
2:54
SPEAKER_01: I see I've got a missed call, and then I just like hit it right, you know, call right back, right?
2:59
SPEAKER_01: And he's like, Hi, Chris.
3:01
SPEAKER_01: Um, this is the way my dad talks.
3:02
SPEAKER_01: He my dad, I think, has the strongest.
3:05
SPEAKER_01: He is very intense, he has the strongest diaphragm on the planet, I think, because he talks from his diaphragm.
3:11
SPEAKER_01: He's like, Hey, Chris, um, sorry about that.
3:13
SPEAKER_01: That was a butt dial.
3:14
SPEAKER_01: I have a big butt, and uh butt dial.
3:17
SPEAKER_01: So anyway, so good.
3:19
SPEAKER_01: Um, then before, you know, because we we small talked for a little bit, he's like, I just listened to a couple of your more recent episodes.
3:25
SPEAKER_01: Man, you and Jesse just do such a good job together.
3:31
SPEAKER_00: That's a great bonus impression, right there.
3:34
SPEAKER_00: That is it really is a good day to that's that's very accurate.
3:39
SPEAKER_01: Here's the deal, Jesse, is that my dad has never heard me do this impression.
3:43
SPEAKER_01: So when he looks into this episode, he's gonna it's gonna be the first time that he's heard my impression of him.
3:51
SPEAKER_01: And then on Fridays, when I go over there, it'll it'll be a couple weeks or however long when we release this, whatever.
3:57
SPEAKER_01: And then I'm gonna I'm gonna hear about it.
3:59
SPEAKER_01: I know I am.
4:00
SPEAKER_01: So I hope I get a laugh instead of Chris, that's just not okay.
4:04
SPEAKER_01: You don't do that to your dad.
4:07
SPEAKER_00: I mean, it's pretty good.
4:09
SPEAKER_00: That I it's pretty accurate.
4:11
SPEAKER_01: Yeah, because you know my dad.
4:13
SPEAKER_01: You know how he is.
4:14
SPEAKER_01: It's great.
4:14
SPEAKER_00: Oh, totally.
4:15
SPEAKER_00: And I mean, it's pretty good.
4:16
SPEAKER_00: You got him nailed.
4:16
SPEAKER_00: You got him nailed at least.
4:18
SPEAKER_00: At least a caricature version of him.
4:19
SPEAKER_00: You got him nailed.
4:21
SPEAKER_00: So that's a good one.
4:23
SPEAKER_01: Yeah.
4:24
SPEAKER_01: All right.
4:24
SPEAKER_01: Well, Jesse, it's time we gotta get down to business too, right?
4:28
SPEAKER_00: But let me just say, that's why when we hit record, I usually have a giggle.
4:32
SPEAKER_00: That right there is just a perfect example of it because oh man, brings me a lot.
4:37
SPEAKER_01: I usually bring something.
4:38
SPEAKER_01: Yeah, I do, yeah.
4:40
SPEAKER_01: I think about it.
4:40
SPEAKER_01: I'm like, all right, what can I bring Jesse?
4:42
SPEAKER_01: I gotta I have to make Jesse happy.
4:45
SPEAKER_00: Um, and so I don't think AI Chris would be able to do that at a as consistently as you do.
4:51
SPEAKER_00: So so you you'll you'll we'll keep you around for a little bit.
4:54
SPEAKER_00: We'll keep Chris Pullheist, the real one for a little bit.
4:56
SPEAKER_01: I appreciate that.
4:57
SPEAKER_01: I thank you so much.
4:59
SPEAKER_01: Yeah, oh great one.
5:00
SPEAKER_01: So uh Jesse, what do we got going today?
5:03
SPEAKER_01: I like that.
5:03
SPEAKER_00: Oh, great one.
5:04
SPEAKER_00: Um, so today we got a listener question a while ago, came from Mark, and Mark was asking a couple questions about Earth's oldest rocks.
5:14
SPEAKER_00: And I got excited.
5:16
SPEAKER_00: You probably rolled your eyes and thought, oh my goodness, Jesse's gonna be a little bit much about this, which I probably am.
5:23
SPEAKER_01: Well, no, you know what I thought?
5:24
SPEAKER_01: I'm like, you know, he's not gonna want to do a one-off on this, he's gonna want to turn this into a whole series.
5:29
SPEAKER_00: Yeah, which is exactly what Jesse was right.
5:31
SPEAKER_00: Yep, I called you and was like, hey, this is great.
5:34
SPEAKER_00: Let's do a series on this.
5:35
SPEAKER_00: We can make an audiobook out of it, we can add some images.
5:37
SPEAKER_00: You know, I've got tons of photos of these locations and these types of minerals and rocks.
5:41
SPEAKER_00: So, you know, this is near and dear.
5:43
SPEAKER_00: This is my research wheelhouse, Earth's oldest stuff.
5:46
SPEAKER_00: This episode that we're gonna record is a pretty well, we're gonna try and keep it brief, but it's just an intro, an overview of what are the oldest materials we have of Earth, and then it's gonna serve as an intro into a series of podcast episodes that we will then put together with images in an audiobook on the CampGeo app in the future.
6:05
SPEAKER_00: And we're kind of working on that in the background right now as one of the many things we're working on.
6:09
SPEAKER_00: But this episode is is gonna be the leado, the intro episode in the podcast.
6:14
SPEAKER_00: All right.
6:14
SPEAKER_00: So how do you question for you?
6:17
SPEAKER_00: Go ahead.
6:18
SPEAKER_00: How much do you talk about this type of stuff in your classes, in your geology classes?
6:24
SPEAKER_00: Because I I was surprised when I started teaching at Penn State, you know, I inherited this class, this physical geology class, the one we talk about.
6:30
SPEAKER_01: Yes, the same class I teach.
6:32
SPEAKER_00: Same class you teach.
6:33
SPEAKER_00: I inherited a class with a slide deck and all that stuff that was kind of pre-made that you you know you inherit these and over the first year you make it your own, right?
6:40
SPEAKER_00: As you when you inherit a class like this.
6:42
SPEAKER_00: But I was surprised about how much content was covered in this class about formation of the solar system, Earth's oldest materials.
6:49
SPEAKER_00: I mean, it wasn't just one slide, it was maybe even a whole lecture, a whole class period, which kind of surprised me to the amount.
6:56
SPEAKER_00: So, how much do you cover?
6:58
SPEAKER_00: And has that changed over the course of your career?
7:00
SPEAKER_01: Well, yeah, it absolutely has.
7:02
SPEAKER_01: Thanks for asking that because it our relationship has changed it.
7:06
SPEAKER_01: And it's an interesting question because I teach my my two favorite things are astronomy and geology.
7:12
SPEAKER_01: And so I do have a lot of overlap with students that take both, or they'll take one their junior year and one their senior year, you know, that kind of thing.
7:21
SPEAKER_01: But geology and astronomy, yeah.
7:23
SPEAKER_00: Real quick, is there a consistent order?
7:24
SPEAKER_00: Do they take geology, then astronomy typically, or the inverse?
7:27
SPEAKER_00: Almost always.
7:28
SPEAKER_00: Oh, right.
7:28
SPEAKER_01: Almost always, but they can do it the other way.
7:30
SPEAKER_01: Okay.
7:30
SPEAKER_00: Got it.
7:31
SPEAKER_01: And then I have maybe a dozen students this year that are taking both right now.
7:35
SPEAKER_00: Okay.
7:35
SPEAKER_00: Oh wow.
7:36
SPEAKER_00: Wow.
7:36
SPEAKER_00: They're going to be able to do that.
7:37
SPEAKER_01: So they have they have the they drew the short straw, they have me twice.
7:40
SPEAKER_01: They've got a lot of cruise boys coming into their daily life.
7:43
SPEAKER_01: They got a lot of it.
7:44
SPEAKER_01: So uh Jesse, I mean, in astronomy, I get into this with the meteorites and the age of the solar system and the evidence for it.
7:52
SPEAKER_01: Because again, we've talked about this before.
7:54
SPEAKER_01: This is the marriage between astronomy and geology, and they they really can't be separated.
7:59
SPEAKER_01: They they go together, they're hand in hand.
8:01
SPEAKER_01: I get into this a lot, but in geology, though, I'm also really passionate.
8:07
SPEAKER_01: I'm doing this now.
8:08
SPEAKER_01: Uh, in fact, tomorrow my students are taking their like summative exam on geologic time.
8:16
SPEAKER_01: Oh, really?
8:17
SPEAKER_01: Oh, okay.
8:17
SPEAKER_01: Timely episode then.
8:18
SPEAKER_01: Yeah.
8:19
SPEAKER_01: So, yes, I'm in it.
8:20
SPEAKER_01: I'm in it.
8:21
SPEAKER_01: So we have been talking most recently about absolute time.
8:25
SPEAKER_01: Okay.
8:25
SPEAKER_01: So you're a daily topic of conversation.
8:27
SPEAKER_01: I bring you.
8:28
SPEAKER_01: I feel like my kids they I think they feel like they know you, you know.
8:31
SPEAKER_00: I as they should, as they should.
8:34
SPEAKER_01: As they absolutely should.
8:35
SPEAKER_01: But I'm passionate about this topic, the geologic evidence for the age of the earth.
8:42
SPEAKER_01: Just the other day, I was talking to my students about you know, the comment section, the rabbit hole of of social media, you know, my frustrations with that going.
8:53
SPEAKER_01: Yeah.
8:53
SPEAKER_01: And the turn of phrase that you've used with me a lot is the toolbox.
8:58
SPEAKER_01: Geochronologists have this really diverse and expansive toolbox to use.
9:06
SPEAKER_01: And so the mis I talked a lot about the misconceptions that that surround geochronology.
9:12
SPEAKER_01: It's it's fun when you have a you know students that come up to you after class and give you a high five on their way out.
9:17
SPEAKER_01: They're like, that was awesome, you know.
9:19
SPEAKER_01: And it's just, I don't know.
9:20
SPEAKER_01: I'm passionate about it.
9:21
SPEAKER_00: That's why you do it though, right?
9:23
SPEAKER_00: Those those interactions.
9:24
SPEAKER_00: It raises the hair on your on your on your skin a little bit, you know.
9:28
SPEAKER_01: Passion is contagious, and this is something that I'm definitely into.
9:32
SPEAKER_01: So as much as you like to give me a hard time for rolling my eyes at you wanting to do this, this is something that I actually I love this stuff, and so I can't wait.
9:41
SPEAKER_01: So we need to get into this.
9:43
SPEAKER_00: That's right.
9:43
SPEAKER_00: We we will not turn down a good listener question.
9:46
SPEAKER_00: And if we if we haven't responded to your listener question, it's just because we're thinking about it, we're stewing on it.
9:51
SPEAKER_00: It's not because we think it's a bad idea.
9:53
SPEAKER_00: Um, you know, we've we've taken a uh several actually recent listener questions and are kind of making them into series.
9:59
SPEAKER_00: Um, so let's for this intro, this intro chapter, I think, Chris, the goal here, because I I need to keep myself constrained and you constrained as to what we need to cover.
10:08
SPEAKER_00: Let's just talk briefly about where the oldest rocks and materials are, what they are, where they occur, and what their ages are.
10:17
SPEAKER_00: And we're gonna go through the first maybe 700 million years of earth history, which is actually that's the Phanerozoic, you know, that that's like animal life on Earth.
10:27
SPEAKER_00: So this is no small amount of time, but what we want to convey is how how few samples we have from this first 700 million years of earth history.
10:37
SPEAKER_00: I think that's kind of the goal, and so we'll work from start to finish, maybe, or beginning to more recent.
10:42
SPEAKER_00: Is that the the the trajectory to go?
10:44
SPEAKER_01: Yeah, absolutely.
10:46
SPEAKER_01: So we're gonna try to frame this and and say, all right, well, earth is 4.568 billion years old, which by the way, I think that's impressive.
10:54
SPEAKER_01: I mean, this is very different from even when I first started teaching.
10:59
SPEAKER_01: It was like the Earth is 4.54 billion years old.
11:03
SPEAKER_01: But to take it down to three decimals, and you know, you've said this before that hey, that million years is important.
11:11
SPEAKER_01: And that's a powerful statement, and I couldn't agree more because a million years is a long, long time.
11:17
SPEAKER_01: And in geology, we just throw it around flippantly, and we probably shouldn't do that.
11:21
SPEAKER_01: So we're gonna take that 4.568 billion year old earth and we're gonna kind of reference back every now and then to let's put this on a year timescale.
11:31
SPEAKER_01: So we're talking about this is 12 a.m.
11:33
SPEAKER_01: January 1.
11:35
SPEAKER_00: They have dropped.
11:37
SPEAKER_00: Yeah, yes, yes.
11:38
SPEAKER_01: You know, everybody's kissing.
11:40
SPEAKER_01: That's right.
11:40
SPEAKER_00: That's right.
11:41
SPEAKER_00: Champagne is everywhere, that's the start.
11:43
SPEAKER_00: And let me just say a word about that, Chris.
11:45
SPEAKER_00: We made an episode, oh man, probably two years ago, on the age of the earth, and we think we called it something like Age of the Earth and How to Build a Planet.
11:52
SPEAKER_00: That's a really fun episode.
11:54
SPEAKER_00: That if you want to know more about what that 4.568 number comes from and what it means, that's a good episode to go to.
12:00
SPEAKER_00: But that's a number that comes from meteorites.
12:02
SPEAKER_00: So we don't have any record, we don't have any rocks from Earth from that time period, obviously.
12:07
SPEAKER_00: Hold on, why is that obvious?
12:09
SPEAKER_00: Why is that obvious?
12:10
SPEAKER_00: Good question.
12:11
SPEAKER_00: I mean, because we've talked about this aspect before, that very first Earth stage was violent.
12:16
SPEAKER_00: It was building a planet.
12:18
SPEAKER_00: That building a planet by accretion, meteorites running into each other, planetesimals running into each other, moon-sized bodies smashing into each other and gradually building up a big planet, that took 50, 60 million years by some estimate.
12:33
SPEAKER_00: The process of building Earth took a while, but we have like like solar system solids at 4.568 billion years.
12:39
SPEAKER_01: That's right.
12:40
SPEAKER_01: And and for the listeners, we if you take a rock that, let's say, cools and crystallizes for magma and nothing happens to it, that's very easy to date.
12:49
SPEAKER_01: But what you're saying is that during this early time, the first 700-ish million years of Earth's history, we were getting smacked by massive objects, many, many objects, which caused Earth was resurfaced, the whole outer shell of the planet was melted again several times.
13:09
SPEAKER_01: And what that does is it resets the clock.
13:13
SPEAKER_01: It's starting over again.
13:15
SPEAKER_01: The radiometric, the geochronology clock of that rock is reset at that time.
13:22
SPEAKER_01: So we'll never find a rock that is 4.568 billion years old on Earth because all of the surficial rocks had been resurfaced several times during that time.
13:36
SPEAKER_00: Very nice Segway Award uh nominee there, Chris, because another event that we need to talk about is the moon forming impact.
13:43
SPEAKER_00: And so the moon formed by you know Thaya, this Thaya, this this thing that we call Thaya, this Mars-sized body hitting Earth, smacking Earth, throwing a bunch of material out into orbit around Earth, which then accreted to form the moon.
13:57
SPEAKER_00: And we don't know when that happened.
13:59
SPEAKER_00: So 4.568, again, that's 12 a.m.
14:02
SPEAKER_00: January 1st, the ball is dropping.
14:04
SPEAKER_00: If we go to the moon forming impact, there's two kind of ways to think about dating that event.
14:11
SPEAKER_00: You can put a minimum age on it, and Chris, how do we how do we just generally think about that?
14:15
SPEAKER_00: Well, how would we put a really firm minimum age on the age of the moon forming impact?
14:21
SPEAKER_01: Well, we have lunar rocks, and we can date those and get a minimum age based upon those rocks because those lunar rocks are simpler than Earth rocks, because we have plate tectonics that's going on too.
14:38
SPEAKER_01: And so our rocks are continually being recycled in the rock cycle, and that doesn't happen on the moon, and it really never has.
14:49
SPEAKER_01: And so we're able to get this like minimum age.
14:53
SPEAKER_01: We just don't really know when the maximum age is.
14:58
SPEAKER_00: That's right.
14:58
SPEAKER_00: And that minimum age, so the the youngest that the moon forming impact could have occurred, we have rocks on the moon that are 4.35 billion years old.
15:08
SPEAKER_00: And in our calendar, that would be January 16th, so about half a month, right?
15:14
SPEAKER_01: That's crazy.
15:15
SPEAKER_01: That's so good.
15:16
SPEAKER_00: That's the youngest that the moon forming impact could have occurred.
15:18
SPEAKER_00: We also actually will talk about this next.
15:20
SPEAKER_00: We have mineral grains, individual mineral grains from Earth that are broadly the same age.
15:25
SPEAKER_00: That 4.38 or 4.35 billion years old.
15:29
SPEAKER_00: There are people who've made geochemical, and these get really convoluted and really hard to visualize on a podcast.
15:35
SPEAKER_00: These are kind of isotopic tracer systems and argument convoluted geochemical arguments that some people have argued that the moon forming impact could be as old as 4.55 billion years old, which would be January 2nd on our scale.
15:48
SPEAKER_00: So that's a this is kind of this is a big debate, and I think this example shows why it's a big debate.
15:54
SPEAKER_00: Like we don't know when the moon formed within half a month of you know Earth history calendar years.
15:58
SPEAKER_01: Right.
15:59
SPEAKER_01: But here's the deal, Jesse, is that the difference between 4.55 billion years and 4.35 billion years is 200 million years.
16:09
SPEAKER_01: I know.
16:09
SPEAKER_01: Let's not forget that.
16:10
SPEAKER_01: That's a lot of time.
16:12
SPEAKER_01: So, Jesse, that is the dinosaurs met their demise 65 million years ago.
16:18
SPEAKER_01: That's three times longer than that.
16:20
SPEAKER_01: It's a great- You know, so this is not an insignificant amount of time.
16:24
SPEAKER_00: And Chris, this is one thing I struggle with when I talk about this in a grad level class or upper level class when we start really talking about this content.
16:32
SPEAKER_00: Is I don't have a good way of conveying this because the numbers don't do it justice.
16:37
SPEAKER_00: If I say 4.55 and 4.35, you you, the listener out there, think of that as basically the same number, right?
16:44
SPEAKER_00: But actually it's 200 million years.
16:47
SPEAKER_00: You that was beautifully said, three times the as long as the dino when the dinosaurs used to roam the earth.
16:53
SPEAKER_01: Like that's a huge amount of time.
16:55
SPEAKER_01: But it is interesting, and I'm gonna get another Segway award here because it it is interesting.
17:01
SPEAKER_01: I feel like I need a double fist bump for that.
17:03
SPEAKER_00: You're gunning for the Segway Award here.
17:05
SPEAKER_01: The oldest zircon grains that have been found on Earth are about what 4.38-ish billion years old, right?
17:17
SPEAKER_01: So we haven't found anything older than that.
17:21
SPEAKER_01: And that kind of to me, and I I I'm not I'm not gonna know entering the research arena research arena on this, but I mean that lends credence to the younger age as opposed to the four point five five billion.
17:34
SPEAKER_00: Excellent.
17:34
SPEAKER_00: I was gonna ask you what you thought about that.
17:36
SPEAKER_00: Does the overlap or the the similarity between the oldest mineral grains we have on Earth and the oldest rocks on the moon, does that uh does that resonate with you as like convincing evidence for a younger, quote unquote younger, a January 16th moon forming impact, not a January 2nd moon forming impact?
17:53
SPEAKER_00: And you're saying yes, I think, is that right?
17:55
SPEAKER_01: It to me it does, and here's here's why, because both of them would have been molten because of this impact.
18:02
SPEAKER_01: The entire surface of the earth would have been resurfaced, it would have been entirely molten, and so you should see the oldest materials found on each of those planetary bodies should be very similar.
18:15
SPEAKER_00: Yeah, that's exactly, that's exactly right.
18:18
SPEAKER_00: Yep.
18:18
SPEAKER_01: And so we haven't found a 4.55 billion year old grain, which is amazing to be to say that, right?
18:28
SPEAKER_01: We haven't found a little zircon grain in a detrital sedimentary rock that is close to that age, 4.55 billion billion years.
18:37
SPEAKER_00: Two notes here exactly on that topic is that we have found 4.5 billion year old zircon grains, mineral grains from Mars.
18:44
SPEAKER_00: We don't have a lot of pieces of Mars, but we do have a single piece that has a very old zircon grain in it, that's 4.5.
18:51
SPEAKER_00: So Mars doesn't have a moon and didn't have this moon forming impact, and there are samples from that age, right?
18:56
SPEAKER_00: So we might expect to find some that age.
18:59
SPEAKER_00: And the second point, let me just say the second point here is that it kind of this discussion, the difference between 4.55 being January 2nd, 4.35 being January 16th, I think it highlights why researchers spend a ton of time and argue a lot about trying to find even little fragments of mineral grains that are older than 4.35 or 4.38.
19:22
SPEAKER_00: And there's a recent paper published from the lunar zircons where they found a core of a zircon that might be 4.42 billion years old.
19:29
SPEAKER_00: So, like it that's a big deal.
19:31
SPEAKER_00: That's a big difference, actually.
19:33
SPEAKER_00: And so it's important.
19:35
SPEAKER_00: What might seem like a really minor niche scientific debate actually is a big deal when we're talking about this time scale.
19:41
SPEAKER_01: Yeah, I have a lot of thoughts swirling around in my mind about that possibility of an older grain on the moon.
19:47
SPEAKER_01: Well, look, here's my thought, right?
19:49
SPEAKER_01: Or my one of my main thoughts that's kind of whirling around, is that couldn't that have been something that was brought to the surface later from deeper down, which could be older, you know, because it's a really good question.
20:04
SPEAKER_00: And I think my answer is gonna be probably not, although certainly not, definitely not, I guess, if that makes sense.
20:10
SPEAKER_00: The people who model who like try and understand what are the physics that created the moon, like what did this impact look like?
20:18
SPEAKER_00: What happened?
20:19
SPEAKER_00: How did the debris that got scattered out around the earth, how did that coalesce into the moon?
20:23
SPEAKER_00: There's a whole bunch of different models.
20:25
SPEAKER_00: Many of them are really hot.
20:28
SPEAKER_00: There's good evidence that the moon was a magma ocean body for a long time.
20:33
SPEAKER_00: There's good evidence for that.
20:34
SPEAKER_00: So probably the moon was totally reset, like all the material was totally melted when the moon formed, so we wouldn't have any mineral grains preserved from before the moon.
20:43
SPEAKER_00: So therefore, the oldest grain is the youngest age for the impact event.
20:48
SPEAKER_00: But there are ways out of that argument, too.
20:51
SPEAKER_00: So yeah, it's not like a perfectly 100%.
20:54
SPEAKER_01: This is like mental gymnastics for me, and it's uh I I like this.
20:58
SPEAKER_01: Um well, okay, Jesse, then let's talk about the oldest fragments on Earth.
21:03
SPEAKER_01: And basically, what we're talking about are these exceedingly rare little tiny zircon grains in a sediment.
21:12
SPEAKER_01: So, in other words, these are clastic or these are detridal grains that were weathered out of a rock, let's say a grant, probably a granite, right?
21:24
SPEAKER_01: They were eroded, transported in probably an ocean basin, and so like as a sandy shale or a sandstone, something like this.
21:34
SPEAKER_01: So they're not found in the original host rock in which they formed.
21:38
SPEAKER_01: Can we talk about that real quick in terms of why are they found in detrital grains or or these fragments of pieces of rock, not the original rock that they came from?
21:49
SPEAKER_00: It's a very good question.
21:50
SPEAKER_00: Well, this is the mineral zircon, so it's really robust.
21:53
SPEAKER_00: It's robust to chemical and physical alt.
21:55
SPEAKER_00: It's super tough, both physically and chemically, which means that it ends up in.
22:00
SPEAKER_00: Sand.
22:00
SPEAKER_00: If you go to beach sand, you're probably if you scoop it.
22:03
SPEAKER_00: It's a lot like quartz.
22:04
SPEAKER_00: It's a lot like quartz.
22:05
SPEAKER_00: You're going to find this mineral in that sand, most likely.
22:08
SPEAKER_00: So it can survive a bunch of sedimentary cycles, whereas the rock gets broken down.
22:12
SPEAKER_00: So if you have a granite, the granite is going to crystallize maybe half a percent or less than that of the granite is zircon.
22:19
SPEAKER_00: Most of those minerals, 99.9% of the minerals in the rock, are going to break down, but zircon won't.
22:25
SPEAKER_00: So zircon will survive and it can survive multiple sedimentary cycles.
22:29
SPEAKER_01: Only the strong survives.
22:31
SPEAKER_00: Only it is the strongest of the strong when it comes to sand.
22:34
SPEAKER_00: And so that's one really good reason for that.
22:37
SPEAKER_00: But it's also a downside because uh a single mineral grain cannot preserve as much information as a whole rock could.
22:45
SPEAKER_00: So there's a ton of debate about these zircons.
22:47
SPEAKER_00: And you'll hear these referred to colloquially as the Jack Hills zircons or Australian detrital zircons.
22:54
SPEAKER_00: Like they're different names for them, but they come from the Jack Hills region of Australia.
22:59
SPEAKER_00: There's like a outcrop that has a bunch of these grains in it, and it's actually in a conglomerate, kind of a coarse grain conglomerate that's been metamorphosed.
23:07
SPEAKER_00: But the conglomerate age is about 2.7 or 2.8 billion years old, but it has over 4 billion year old zircon grains in it, and those zircon grains, one of them goes up to 4.38 billion years old.
23:19
SPEAKER_00: So we'll have a whole discussion about these grains later on, but I think that's probably enough for now is to say that the oldest pieces of earth are detrital mineral grains found in a much younger sediment.
23:31
SPEAKER_00: That again, Chris, is is about January 16th, January 17th, something like that, ballpark.
23:36
SPEAKER_01: Yes.
23:36
SPEAKER_01: Okay, so I don't know if you contradict yourself with this, because we know that some of the oldest rocks on Earth are 4.25 billion years old, but that's up for some debate though.
23:50
SPEAKER_01: So how does that rock outcrop that we find in Quebec compare to the Jack Hill stuff in Australia?
23:58
SPEAKER_00: So the this is from what's called the Nuvoagatuck greenstone belt up in Quebec, northern Quebec, on the shores of Hudson Bay.
24:06
SPEAKER_00: Don't ask me to spell it.
24:07
SPEAKER_00: Um it's a guy, it's a word I misspell all the time, and Microsoft Word has no idea when I take this in a Jesse.
24:13
SPEAKER_01: I'm sorry to interrupt because you're in a flow, I can tell, but can you really quick say what a greenstone is?
24:17
SPEAKER_00: I feel like that has to be a part of like Yep, great, great, great question.
24:20
SPEAKER_00: This is a metamorphosis.
24:22
SPEAKER_01: We have this up in the upper peninsula in Michigan, and and it's a very important rock.
24:26
SPEAKER_00: Very important.
24:26
SPEAKER_00: It's metamorphosed basalt.
24:28
SPEAKER_00: It's basalt, or in this case, ultramafic rock, that was erupted under the seafloor, was hydrated by that water, and then was metamorphosed.
24:36
SPEAKER_00: So it doesn't look like a basalt now, but it it's a green basalt.
24:40
SPEAKER_01: Kinda does.
24:40
SPEAKER_01: It's got a it's got a smearing of chloride on it.
24:43
SPEAKER_01: Exactly.
24:43
SPEAKER_01: That's the first really super old rock I took you to when you were students of mine.
24:47
SPEAKER_00: That's right, up there in the mid-continent rift.
24:50
SPEAKER_00: So these rocks in northern Quebec, they are the rocks themselves are argued to be 4.25 billion years old.
24:56
SPEAKER_00: And there's definitely some debate on this.
24:59
SPEAKER_00: It gets into the details of some pretty deep isotopic arguments that we'll cover in the episode that we talk about these particular rocks.
25:07
SPEAKER_00: We'll go through that, that the logic there.
25:09
SPEAKER_00: But suffice to say that there's a big amount of debate about this.
25:11
SPEAKER_00: The rocks are at least the youngest they are is 3.8 billion years old, but there's a significant group of people who argue that they're 4.25 billion years old.
25:21
SPEAKER_00: I myself, I'm about three-quarters convinced that they are 4.25 billion years old.
25:28
SPEAKER_00: There's multiple ways to explain.
25:29
SPEAKER_00: They really are.
25:30
SPEAKER_01: That's amazing.
25:31
SPEAKER_01: So have you seen them?
25:32
SPEAKER_01: Like, have you been to this outcome?
25:34
SPEAKER_00: I haven't been up there, but my former postdoc supervisor is one of the people who worked a lot on these.
25:38
SPEAKER_00: And so I have samples of them uh in my office at work, actually.
25:41
SPEAKER_01: But it's funny because I don't seem to have one.
25:44
SPEAKER_00: I yeah, okay.
25:46
SPEAKER_00: That's fair.
25:46
SPEAKER_00: Fair point.
25:47
SPEAKER_00: Fair point.
25:48
SPEAKER_01: I don't seem to have one of those samples.
25:50
SPEAKER_01: Or you're hoarding.
25:51
SPEAKER_01: Fair point.
25:51
SPEAKER_01: Fair point.
25:52
SPEAKER_00: And that is fair point.
25:54
SPEAKER_00: We need to remedy that.
25:54
SPEAKER_00: I'll work on that.
25:55
SPEAKER_00: I'll work on that, definitely.
25:56
SPEAKER_01: All right, please do.
25:57
SPEAKER_01: All right, so these are originally mafic rocks that got metamorphosed into um what I call a metabasalt often.
26:04
SPEAKER_01: That's right.
26:05
SPEAKER_01: Or greenstone.
26:06
SPEAKER_01: Okay.
26:06
SPEAKER_01: This would be at 4.25 billion years old.
26:09
SPEAKER_01: That'd be January 25.
26:11
SPEAKER_00: So we're almost at the end of January.
26:12
SPEAKER_00: Let me just say one real quick thing, Chris.
26:14
SPEAKER_00: The difference we've moved into talking not about individual mineral grains, but the rock itself.
26:19
SPEAKER_00: Like you pick up a rock, all the minerals in that rock are old.
26:24
SPEAKER_00: As opposed to you pick up a rock and just one mineral grain in that rock is super old.
26:28
SPEAKER_00: So that's the distinction here.
26:29
SPEAKER_00: Sorry.
26:30
SPEAKER_01: Good point.
26:30
SPEAKER_00: January 25th.
26:31
SPEAKER_01: So we know for sure, though, and this is you, this is your like research.
26:37
SPEAKER_01: This is your wheelhouse, that we have rocks that are 4.02 billion years old.
26:44
SPEAKER_01: And this is the Acosta dice up in the northern Northwest Territories of Canada.
26:48
SPEAKER_01: They have these zircons in them, and these have been really well established, right?
26:53
SPEAKER_01: They've been dated at 4.02.
26:56
SPEAKER_01: Real quick, Jesse, what's the range?
26:58
SPEAKER_01: 4.02 to what have you found in these zircon grains?
27:02
SPEAKER_00: Yeah, that's a good good question.
27:04
SPEAKER_00: There's a bunch of grains.
27:05
SPEAKER_00: Any igneous portion of a zircon grain will be 4.02 billion years old.
27:09
SPEAKER_00: There will be metamorphic zones.
27:11
SPEAKER_00: So some of them some of the outer rims have the the rock has experienced multiple metamorphic events, which we will talk about in a later episode when we talk about it.
27:19
SPEAKER_01: Which means basically that it gets reset, right?
27:21
SPEAKER_00: Exactly.
27:22
SPEAKER_00: Yep.
27:22
SPEAKER_00: You get new mineral growth, kind of a shell of new growth on the outside.
27:26
SPEAKER_00: That stuff is 3.3 billion years old, all the way down to 2.9 billion years old.
27:31
SPEAKER_00: And they're it's a babe.
27:32
SPEAKER_00: Yeah, exactly.
27:33
SPEAKER_00: Super young, boring.
27:34
SPEAKER_00: But the zircons in them, there's very little debate that these rocks, the rocks themselves, were initially a magma.
27:41
SPEAKER_00: That magma crystallized 4.02 billion years ago.
27:44
SPEAKER_00: And these are the Acostanises, and this would be February 12th.
27:48
SPEAKER_00: So we jumped ahead into February now, February 12th on our geological time scale.
27:52
SPEAKER_00: So, and for a long time, up until about 2005, these were the oldest rocks in the world, without a doubt.
27:59
SPEAKER_00: And then in 2008, the debate about these Nuvoaga took these metabasalts, this greenstone belt package kind of came on the scene.
28:06
SPEAKER_00: So for a long time, we had no rocks for the first month and a half of Earth history, and now we maybe have one from the first month and a half, and we have some mineral grains.
28:17
SPEAKER_01: Yeah, by the way, this 4.02 billion years old would be February 12.
28:23
SPEAKER_01: Wow.
28:24
SPEAKER_01: It's it's pretty much.
28:26
SPEAKER_01: So, Jesse, what are the oldest sediments that we have on Earth?
28:33
SPEAKER_00: So this goes back, it's a really good question.
28:36
SPEAKER_00: We don't have many sediments from the early earth.
28:38
SPEAKER_00: Let's say that out front.
28:39
SPEAKER_00: And we talked about this in previous episodes most recently.
28:42
SPEAKER_00: But the oldest sediments that we know for sure are sedimentary rocks are 3.8 billion years old.
28:47
SPEAKER_01: And these are Yeah, because hold on, hold on.
28:49
SPEAKER_01: I'm sorry, I gotta interrupt because I think we need to make the point.
28:52
SPEAKER_01: We're not talking about the grains in the sediment, we're talking about the rock itself.
28:58
SPEAKER_01: Okay, because earlier we said that we found zircon grains that are 4.38 billion years old.
29:05
SPEAKER_01: That's the grain in the rock that doesn't speak to when the rock was laid down.
29:09
SPEAKER_01: Now we're talking about the rock itself.
29:12
SPEAKER_01: Exactly.
29:12
SPEAKER_00: That's a really important distinction.
29:14
SPEAKER_00: That's amazing, Jesse.
29:15
SPEAKER_00: Really important distinction.
29:16
SPEAKER_00: So 3.8, these are in southwest Greenland.
29:18
SPEAKER_00: They're called the Issua Supra Crustal Belt.
29:22
SPEAKER_00: You'll see that word isua or southwest Greenland.
29:24
SPEAKER_00: It's a pretty large expanse of 3.8 billion year old rocks.
29:27
SPEAKER_00: It was discovered in the 80s, so it's been studied by many, many, many people.
29:31
SPEAKER_00: It's a very famous location.
29:34
SPEAKER_00: So these are water-lane sediments, some green stones, uh, some basalts in there.
29:39
SPEAKER_00: We've got some banded iron formations and little thin packages of like, you know, schists or shaley kind of stuff.
29:46
SPEAKER_01: That's an important thing that you just said that you just kind of glossed over, is that we had water on our planet 3.8 billion years ago.
29:56
SPEAKER_01: Jesse, that's not a small thing.
29:58
SPEAKER_01: You know, that's a it's a huge I feel like I have to just let that sink in for a little bit.
30:05
SPEAKER_01: Like that's amazing.
30:06
SPEAKER_00: And this is this is the beauty of geology, I think, Chris, because this is uniformitarianism at its best.
30:13
SPEAKER_00: It's it's look at that rock.
30:15
SPEAKER_00: That's a sediment, that's a that's a banded iron formation that we know is a water, something that is deposited in water.
30:22
SPEAKER_00: That's a shale, that's a meta wacky gray wacky that we know is deposited in deep water environments.
30:28
SPEAKER_00: We see it, we can date it, it's 3.8 billion years ago.
30:31
SPEAKER_00: Therefore, the 3.8 billion year old Earth had large enough bodies of water to do that.
30:37
SPEAKER_00: That's the power of geology.
30:39
SPEAKER_00: That's the rocks telling you a story, a beautiful story, and a really important one.
30:43
SPEAKER_01: So a gray wacky for the listeners is a very, very poorly sorted sandstone.
30:51
SPEAKER_01: This is often deposited on continental slopes at the base of the continent slope in a turbidity current, something like this.
30:58
SPEAKER_01: So it's it's a sandstone-ish.
31:01
SPEAKER_00: That's exactly right.
31:02
SPEAKER_01: It's not what we typically think of.
31:04
SPEAKER_00: And people think these particular rocks are deposited in the ocean on the flanks of a volcano.
31:10
SPEAKER_00: So kind of, you know, think of Japan off the coast of Japan or off the coast, off the west coast of the U.S.
31:16
SPEAKER_00: where the cascades are erupting out and that they're just being eroded full scale into the ocean basin there.
31:21
SPEAKER_00: That's kind of what we think about for these sediments.
31:24
SPEAKER_00: So those are, again, 3.8 billion years old, and that's February 26th on our time scale.
31:30
SPEAKER_00: So we've gone through the first two months, and we have a few locations with old zircons, and then we have maybe three locations with old rocks that old.
31:40
SPEAKER_00: So not a lot, let's put it that way.
31:42
SPEAKER_00: That's crazy.
31:43
SPEAKER_01: Yeah, and I want to touch on this actually, Jesse, to finish off this episode because we're we're nearing the end, and this is a good place to like stop this.
31:51
SPEAKER_01: But I have touched a rock that is 4.02 billion years old, but I only touched that because that you gave it to me.
32:01
SPEAKER_01: Okay, and it's one of my favorite rocks because the Acosta Nice.
32:06
SPEAKER_00: I'd be so offended if it wasn't.
32:08
SPEAKER_01: Like, oh my gosh.
32:10
SPEAKER_01: But here's the deal, Jesse, is you and I, you know, we put together this book on the Grand Canyon.
32:15
SPEAKER_01: We put together a Yellowstone book.
32:16
SPEAKER_01: We're working right now on a on a Teton book, an audio visual book.
32:22
SPEAKER_01: None of those rocks are older than 2.7 billion years old, or older than 2.68 billion years old.
32:31
SPEAKER_01: None of them are.
32:32
SPEAKER_00: I mean, they're all like what, born in May or June or something on our time scale, right?
32:37
SPEAKER_00: The time frame this is really rare.
32:40
SPEAKER_00: The time frames involved in the early earth are not to be trifled with.
32:44
SPEAKER_00: Like we throw around numbers with the second decimal place, and it's that's the 10 million year spot.
32:51
SPEAKER_00: Like that we have to be careful and to remember that there are massive amounts of time involved here.
32:56
SPEAKER_00: And so this is a hard calculation to do really accurately.
33:00
SPEAKER_00: So I'm gonna I'm gonna temper this with like that.
33:02
SPEAKER_00: This is a rough estimate, but if you randomly landed on Earth today and you landed on a continent, and you said, I'm gonna grab a rock from the continent randomly, you would probably have less than a one in a million chance of grabbing one of these rocks, a rock that's this old.
33:18
SPEAKER_00: Actually, probably far less than a one in a million chance of grabbing a 3.8 or older rock.
33:23
SPEAKER_01: Ooh, hey.
33:25
SPEAKER_01: This is, I think, a good way to end the episode, Jesse, is with a question to our listeners.
33:31
SPEAKER_01: If you were going to go and find an old rock, the oldest rock, okay, where would you go?
33:39
SPEAKER_01: Would you go to the oceanic floor, the oceanic crust?
33:46
SPEAKER_01: Would you go to the edge of a continent?
33:51
SPEAKER_01: Or would you go to the interior part of a continent?
33:56
SPEAKER_01: Three choices.
33:58
SPEAKER_01: Ocean floor, edge of a continent, or middle of a continent.
34:05
SPEAKER_00: Okay, while our listener is thinking about that, what do you think?
34:09
SPEAKER_00: Is that a good question?
34:11
SPEAKER_00: It's a great question.
34:12
SPEAKER_00: And do you ask your students this?
34:14
SPEAKER_01: I don't, because this idea just popped into my head.
34:16
SPEAKER_01: See, I'm a genius.
34:18
SPEAKER_00: So piece of evidence number three, that Chris is a genius.
34:24
SPEAKER_00: Uh so tomorrow, try to ask your students this tomorrow, and I want to hear what you get back because this is actually an unbelievable, it's not even about the Earth's oldest rocks, it's about how does the earth work.
34:34
SPEAKER_00: This is a question, really fundamental question about how the earth works.
34:38
SPEAKER_00: So the correct answer should be that you go to the interior of continents, because the interior is the oldest part.
34:45
SPEAKER_00: All the young stuff, all the new events are happening on the margins of the continents.
34:50
SPEAKER_00: So new volcanoes are popping off on the edges of the ring of fire in all the edges of the continents.
34:56
SPEAKER_00: The interiors are usually where the old rocks are.
34:59
SPEAKER_00: And those interior, what we call cratons, which we'll get into later, those usually have pretty low relief.
35:06
SPEAKER_00: So they're they're like the Midwest, Chris, or they're like the Canadian Shield.
35:09
SPEAKER_00: They're really close to sea level, they don't have a lot of mountain building activity, they've been insulated from tectonic reworking for billions of years, which allows you to preserve these signals.
35:20
SPEAKER_00: Whereas if you go to the moon and you say, hey, find me an old rock, uh, you're you're probably gonna go to lunar highlands, but they're everywhere.
35:27
SPEAKER_00: Like you you can kind of pick a spot, you're gonna have some chance of finding old stuff mostly.
35:32
SPEAKER_01: That's right.
35:32
SPEAKER_01: But Jesse, real quick, it just popped into my head too.
35:36
SPEAKER_01: You talk about going to the moon, right?
35:37
SPEAKER_01: When you look at the moon and you see areas that are not heavily cratered, that means those areas are young.
35:45
SPEAKER_01: Those areas have been covered with more recent lava flows and after the heavy bombardment era, and so they're not pockmarked with all these impact craters.
35:56
SPEAKER_01: So the oldest parts of the moons are the areas that are heavily, heavily, heavily impacted.
36:00
SPEAKER_00: Exactly.
36:01
SPEAKER_00: So, Chris, that's a really, really great question to ask.
36:04
SPEAKER_00: And and uh it's actually the answer tells you a lot about just really first principles of how the earth works and plate tectonics and um and sort of where you might find old stuff.
36:14
SPEAKER_00: So, okay, Chris, I think that's a wrap.
36:17
SPEAKER_00: Thanks, Mark, for the excellent question.
36:19
SPEAKER_00: You've spawned a whole bunch of discussion and event and a series of podcasts here that'll be part of an audio book that you can buy on the Camp Geo app.
36:27
SPEAKER_00: That's our app.
36:28
SPEAKER_00: It's the first link in your show notes.
36:30
SPEAKER_00: It's one of the main ways to support us, is head to the Camp Geo app.
36:33
SPEAKER_00: There we have audio visual content for basically the entire class that Chris, you and I teach, the intro-level geology class that's there for free.
36:41
SPEAKER_00: We have old podcast episodes arranged in a kind of a convenient order for you as well.
36:46
SPEAKER_00: And you can also purchase access to audiobooks on the geology of Yellowstone, the geology of the Grand Canyon, and the Grand Tetons and Mammoth Cave National Park, and a few on Earth's climate as well.
36:57
SPEAKER_00: So head there.
36:57
SPEAKER_00: That's one way to support us.
36:58
SPEAKER_00: The other way to support us is go to our website, planetgeocast.com.
37:01
SPEAKER_00: There's a link.
37:02
SPEAKER_00: You can support us there.
37:03
SPEAKER_00: You can also send us an email with any of your questions.
37:06
SPEAKER_00: We love getting listener questions.
37:07
SPEAKER_00: And follow us on all the social medias.
37:08
SPEAKER_00: We're at Planet Geocast.
37:10
SPEAKER_00: We love hearing from people in any avenue that you choose.
37:13
SPEAKER_00: So thanks for listening.
37:14
SPEAKER_00: Cheers.
37:15
SPEAKER_00: Peace.