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Forming Earth's Ocean - Office Hours · 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.
• 0:18
  SPEAKER_00: You're a funny guy.
• 0:19
  SPEAKER_00: I like that.
• 0:20
  SPEAKER_00: That made me laugh.
• 0:21
  SPEAKER_00: I need a pick-me-up.
• 0:22
  SPEAKER_00: Of all days, I uh need a pick-me-up today.
• 0:24
  SPEAKER_00: Yeah.
• 0:25
  SPEAKER_00: I am recording.
• 0:26
  SPEAKER_00: Are you recording?
• 0:26
  SPEAKER_00: I'm recording, yeah.
• 0:28
  SPEAKER_00: Now I am.
• 0:28
  SPEAKER_00: Okay.
• 0:29
  SPEAKER_00: Hold on.
• 0:29
  SPEAKER_00: Let me play with my microphone.
• 0:31
  SPEAKER_00: What's the um can I do that?
• 0:33
  SPEAKER_01: Yeah, tap tap.
• 0:34
  SPEAKER_01: Squiggle your beard against your microphone.
• 0:36
  SPEAKER_01: That's always the best.
• 0:38
  SPEAKER_01: Really uh just an appealing sound.
• 0:41
  SPEAKER_00: I can see why it would be.
• 0:43
  SPEAKER_00: Yeah.
• 0:43
  SPEAKER_00: All right.
• 0:44
  SPEAKER_00: Hey doc.
• 0:44
  SPEAKER_00: How you doing, man?
• 0:46
  SPEAKER_00: Uh the good doctor's in the house.
• 0:48
  SPEAKER_00: Joyce, the good doctor's here.
• 0:50
  SPEAKER_00: Uh oh, this will be a good test.
• 0:52
  SPEAKER_00: I'll see if she's actually listening.
• 0:53
  SPEAKER_00: If she's listening.
• 0:54
  SPEAKER_00: It's too early for her to be napping.
• 0:56
  SPEAKER_00: All right.
• 0:57
  SPEAKER_00: You know, because usually, so I go to my parents' house on Fridays as often as I can to just visit, have a beer, sit on their practice deck, you know.
• 1:08
  SPEAKER_00: Yeah, after I'm done with cross-country practice, I'll go over there.
• 1:10
  SPEAKER_00: Jenny's not home yet, so I got a little bit of time.
• 1:13
  SPEAKER_00: And more often than not, when I walk in, my mom is sleeping listening to us.
• 1:23
  SPEAKER_01: That's great.
• 1:24
  SPEAKER_01: We are just great to go to sleep to.
• 1:27
  SPEAKER_00: Yes.
• 1:28
  SPEAKER_00: Oh, you know what Jenny has started doing?
• 1:30
  SPEAKER_00: This is I can't believe this.
• 1:32
  SPEAKER_00: So she's really into audiobooks, right?
• 1:36
  SPEAKER_00: She loves that.
• 1:36
  SPEAKER_00: And I love it when we travel.
• 1:38
  SPEAKER_00: It's such a good thing.
• 1:39
  SPEAKER_00: You know, I listen to a lot of podcasts.
• 1:41
  SPEAKER_00: And then we'll also get into like a an audiobook.
• 1:45
  SPEAKER_00: Like uh one of the most recent ones we did was the one by Matthew McConaughey, Green Lights.
• 1:50
  SPEAKER_01: Oh, okay.
• 1:50
  SPEAKER_00: I haven't uh really I loved it.
• 1:53
  SPEAKER_00: It was so good.
• 1:54
  SPEAKER_00: Anyway, so Jenny now is going to sleep.
• 1:57
  SPEAKER_00: She'll set her timer on her audiobook.
• 2:00
  SPEAKER_00: So she'll put it by her uh shoulders.
• 2:02
  SPEAKER_00: Blaring by the pillow.
• 2:04
  SPEAKER_01: Yes.
• 2:04
  SPEAKER_00: So here I am.
• 2:05
  SPEAKER_00: Here I am.
• 2:06
  SPEAKER_00: I'm trying to go to sleep, right?
• 2:07
  SPEAKER_00: And she's got her audiobook, so she can doze off listening to that.
• 2:10
  SPEAKER_01: Very familiar with this problem.
• 2:12
  SPEAKER_01: Are you really like, oh yes, gotta go upstairs, gotta find the freaking phone that's making so much noise, blaring whatever, and turn it off so I can go to sleep.
• 2:20
  SPEAKER_01: Yeah.
• 2:21
  SPEAKER_00: Okay.
• 2:21
  SPEAKER_00: I thought this was a me problem.
• 2:23
  SPEAKER_01: No, no, no.
• 2:24
  SPEAKER_01: This is uh I think it's a it's a common problem.
• 2:27
  SPEAKER_01: We need to keep some like headphones up in this place or something.
• 2:31
  unknown: That's crazy.
• 2:32
  SPEAKER_01: I was talking to our neighbors actually, and uh he does this, so it's the inverse problem.
• 2:36
  SPEAKER_01: He his wife's like, yeah, he's always falling asleep with this thing, Blair, just playing from his phone.
• 2:42
  SPEAKER_00: Yeah, like wait a minute, how is this okay?
• 2:44
  SPEAKER_00: How you know I'm trying to go to sleep, and it's wild.
• 2:48
  SPEAKER_00: You got this this guy talking in a funny accent about a book that I know nothing about.
• 2:52
  SPEAKER_00: I mean, what and then you you're just so distracted, your mind starts to think about this book that you're not even into, and that's the way my mind just kind of flits about it.
• 3:00
  SPEAKER_01: So, Chris, on this episode, we're gonna have one person who better not fall asleep because this is a question that was raised from a listener.
• 3:07
  SPEAKER_00: That's right.
• 3:07
  SPEAKER_00: Kathy, you better not fall asleep.
• 3:09
  SPEAKER_01: You can't fall asleep during this one because we are addressing the question.
• 3:13
  SPEAKER_01: And the question was really around well, essentially what came first, oceans or atmospheres.
• 3:19
  SPEAKER_01: But I think really the question was kind of uh there's a few questions kind of around how did oceans come to be was maybe a uh a simpler way to phrase it.
• 3:27
  SPEAKER_01: So how did we get our oceans?
• 3:28
  SPEAKER_01: And I think, Chris, the structure of what we're gonna talk about is probably something along the lines of just a general history of oceans on Earth, like what we know about the oceans, what we kind of don't know about the oceans, perhaps, and how they formed.
• 3:40
  SPEAKER_01: Is that accurate uh sort of description?
• 3:42
  SPEAKER_00: But and then in the end, and this is gonna be more like your realm, Jesse, but she also wants to know the role of plate tectonics in oceans in terms of like did they have a part in you know getting plate tectonics going, I guess.
• 3:56
  SPEAKER_01: Yeah, for sure.
• 3:57
  SPEAKER_01: It's just such an interesting question and such a deep question.
• 4:00
  SPEAKER_01: I mean, we could go for our we hey, we could start a new series on on just this topic.
• 4:06
  SPEAKER_01: It's so deep that it's so rich, I so I I suppose, with information or or sort of so many different uh rabbit holes we could go down or big paths that we could go down as well.
• 4:15
  SPEAKER_01: So I don't know, Chris.
• 4:16
  SPEAKER_01: I have a hard time thinking about where to start this kind of conversation.
• 4:19
  SPEAKER_01: In your mind, when you read this question or these questions, uh, what did you think?
• 4:23
  SPEAKER_01: Where did you think, oh, we got to start here?
• 4:25
  SPEAKER_00: Um, I guess my mind automatically went, this is the way my mind operates.
• 4:31
  SPEAKER_00: I I want to just answer the overarching.
• 4:33
  SPEAKER_01: Stump grinding service.
• 4:34
  SPEAKER_01: Is that what you were thinking about?
• 4:36
  SPEAKER_00: That's that's right.
• 4:37
  SPEAKER_00: I automatically am like, what comes first?
• 4:40
  SPEAKER_00: Right.
• 4:40
  SPEAKER_00: And and so that's kind of where my mind went, but that's not a really good way to frame an episode.
• 4:45
  SPEAKER_00: And but the atmosphere has to come first because the atmosphere gave birth to the oceans.
• 4:50
  SPEAKER_00: And so we're gonna kind of walk through that process of early Earth in the sense of the world.
• 4:55
  SPEAKER_01: Yeah, and I think that's a good, a good way to start.
• 4:57
  SPEAKER_01: Like go from go back in the beginning and and then sort of walk forward.
• 5:01
  SPEAKER_01: And the important concept here is remember Earth was super hot.
• 5:04
  SPEAKER_01: Earth was a magma ocean where the entire outer part of the planet, the rocky part of the planet, was liquid.
• 5:10
  SPEAKER_01: So it was this magma ocean, just as the name implies, which is super hot, and it's hard to imagine an ocean sitting right on top of that, right?
• 5:19
  SPEAKER_01: On top of liquid magma, it would be evaporated.
• 5:22
  SPEAKER_01: It would be in the gas phase at that point.
• 5:24
  SPEAKER_01: So the earth is really hot to start with, so unlikely to have a nice calm ocean, you know, right on top of a magma ocean planet.
• 5:33
  SPEAKER_00: Yeah, right, because that would be similar to like putting maybe a pat of butter on a hot skillet, right?
• 5:38
  SPEAKER_00: I mean, it's just not gonna work, it's gonna boil off.
• 5:40
  SPEAKER_01: And so that's exactly so.
• 5:42
  SPEAKER_00: Let's get to just some stats.
• 5:46
  SPEAKER_00: Okay, and then we're gonna talk about maybe what's inside the earth and use that as a launching pad to talk about how that is thought to have led to the formation of the atmosphere, or at least how it changed the atmosphere.
• 5:58
  SPEAKER_00: Okay.
• 5:59
  SPEAKER_00: So, first of all, oceans they make up 71% of the entire surface area of our planet.
• 6:05
  SPEAKER_00: Okay, so that's a lot, right?
• 6:07
  SPEAKER_00: But they make up 97.2% of all the water on our planet.
• 6:12
  SPEAKER_00: So that's what makes this such a good question, right?
• 6:16
  SPEAKER_00: Because this is very, very important.
• 6:18
  SPEAKER_01: The oceans are it when it comes to water.
• 6:20
  SPEAKER_01: I mean, we talk about glaciers, water vapor is super important, climate's super important, but as far as volumetrically, it's the oceans.
• 6:27
  SPEAKER_01: They dominate the water budget of the surface part of the earth.
• 6:30
  SPEAKER_01: Now, there's a really open question, and we'll kind of come back to this at the end of the episode, I think, where we talk about the history of the oceans, but we know there's water, we've talked about this before.
• 6:38
  SPEAKER_01: We know there's water down in sort of trapped in minerals, bound up in minerals in the interior of the earth.
• 6:45
  SPEAKER_01: And we know this from a bunch of different pieces of evidence.
• 6:47
  SPEAKER_01: We talked about diamonds, there's inclusions in diamonds that are from the mantle transition zone, so four to six hundred kilometers deep in the earth, and we know that there's some amount of water down there.
• 6:57
  SPEAKER_01: We don't know how much, and some of the calculations would suggest you could put like six oceans worth of water down there.
• 7:04
  SPEAKER_01: So that's like potential storage, but we know there's a little bit down there, we don't know how much.
• 7:10
  SPEAKER_00: Okay, so first of all, you said the mantle transition zone, the MTZ.
• 7:14
  SPEAKER_00: This is the boundary that separates the upper mantle from the lower mantle.
• 7:19
  SPEAKER_00: This has actually garnered a lot of headlines in the research world recently because there's a recent paper that's come out that has really shined a light on the amount of potential water down in that zone, right?
• 7:33
  SPEAKER_01: Yes, now for sure.
• 7:34
  SPEAKER_00: This is though hugely variable.
• 7:37
  SPEAKER_00: I mean, this is not constrained very well at all.
• 7:39
  SPEAKER_01: So let me sort of frame this just briefly because this transition zone, what the transition part is uh referencing is it's a seismic transition zone.
• 7:48
  SPEAKER_01: So we can see with seismic waves passing through the mantle, we can see that there's some kind of boundary there because seismic waves change energy, they kind of refract at that boundary.
• 7:57
  SPEAKER_01: There's one at around 440 kilometers and one around 660 kilometers in that ballpark range.
• 8:02
  SPEAKER_01: So it's a kind of a couple hundred kilometer thick layer in the mantle where seismic waves do weird stuff.
• 8:08
  SPEAKER_01: What we know happens there is that we have a mineralological change.
• 8:13
  SPEAKER_01: So as you go down in pressure, if you take a piece of the mantle, the mantle up in the upper mantle has olivine and two different types of pyroxenes, those types of minerals in it, and those minerals undergo a transition.
• 8:24
  SPEAKER_01: They become unstable in this transition zone, they become different minerals.
• 8:28
  SPEAKER_01: Ringwidite and Wadsleite are a couple different of these high pressure phases of those minerals.
• 8:33
  SPEAKER_01: And those phases can hold water in their structure, whereas olivine and pyroxines, they don't really hold much water.
• 8:38
  SPEAKER_01: So there's this like sweet spot in the middle, this sandwich layer, where the minerals could potentially hold water.
• 8:44
  SPEAKER_01: We don't know if they do, though.
• 8:46
  SPEAKER_01: We know that like one ringwiddite we've ever measured that came up in a diamond inclusion.
• 8:51
  SPEAKER_01: We know that that had water in it, but it's like one tiny, tiny inclusion in this huge layer of earth that it's unknown.
• 8:58
  SPEAKER_00: Okay, so we need to talk about why this is important.
• 9:00
  SPEAKER_00: And that leads us into this whole discussion about the atmosphere coming first and where the atmosphere came from and how the atmosphere got changed.
• 9:08
  SPEAKER_00: So let's go back to what you started with.
• 9:11
  SPEAKER_00: You know, first of all, let's just say it outright.
• 9:13
  SPEAKER_00: The oceans formed a long time ago.
• 9:16
  SPEAKER_00: We're talking billions of years ago, like what Jesse 4.1-ish billion years ago.
• 9:24
  SPEAKER_00: There's a variance in this.
• 9:26
  SPEAKER_01: So 3.8 billion years ago, we have sedimentary rocks that formed 3.8 billion years ago.
• 9:31
  SPEAKER_01: So we know that there is rocks formed under the ocean 3.8 billion years ago.
• 9:35
  SPEAKER_01: So we know there's liquid water then.
• 9:37
  SPEAKER_01: Older than that, we have some zircons, which we can look at the oxygen isotope chemistry of the zircons, and it kind of tells us that the granites that formed the zircons interacted with water, low temperature water, probably liquid water or steam.
• 9:52
  SPEAKER_01: So that goes back to like 4.1, 4.2 billion years ago.
• 9:56
  SPEAKER_00: Now, prior to this, we know also, and this is one of your fields of study, and and looking for the oldest rocks on the earth and wind plate tectonics began.
• 10:05
  SPEAKER_00: We know that early Earth was exceedingly hot.
• 10:07
  SPEAKER_00: Like you said, it was this kind of magma ocean on the surface, right?
• 10:11
  SPEAKER_00: So what was happening due to this like magma ocean?
• 10:16
  SPEAKER_00: Well, first of all, a couple points that we need to make is that in these conditions, only water vapor could exist.
• 10:22
  SPEAKER_01: Think of how hot you have to get a rock to melt it, Chris.
• 10:24
  SPEAKER_01: You have to get 800 degrees at least up to 1200, 1500 degrees, depending on the rock type.
• 10:29
  SPEAKER_01: So water is going to be vapor at that temperature.
• 10:32
  SPEAKER_01: It's not going to be liquid water.
• 10:34
  SPEAKER_00: So a couple things then that were going on, right, is that the atmosphere, both the atmosphere and the surface had to cool down immensely.
• 10:42
  SPEAKER_00: In both the atmosphere and the surface, it would have been way too hot.
• 10:46
  SPEAKER_00: Only water vapor could exist.
• 10:48
  SPEAKER_00: So we had to cool this whole thing down to below the boiling point.
• 10:52
  SPEAKER_00: Now, that doesn't mean the boiling point was 100 degrees Celsius because there could have been different atmospheric pressures which would have changed things and so on, but the atmosphere had to cool down below the boiling point of water so that rain could happen.
• 11:09
  SPEAKER_00: Okay, now let's talk about how water would have been added to the atmosphere.
• 11:17
  SPEAKER_00: Where was this coming from?
• 11:19
  SPEAKER_01: Yeah, this is a uh a very open question.
• 11:23
  SPEAKER_01: How did Earth get its water and other quote-unquote volatile species?
• 11:29
  SPEAKER_01: And one question is where did it come from?
• 11:32
  SPEAKER_01: There's a couple potential culprits, and one of them is uh rocks called carbonaceous chondrites, which have a lot of carbon in them, they have a lot of volatiles in them, and so the earth might have formed during Earth formation.
• 11:44
  SPEAKER_01: We had this episode, we what do we call it, Chris?
• 11:46
  SPEAKER_01: How to build a planet, I think was how we called it, but we sort of talked about how does a planet form?
• 11:51
  SPEAKER_01: And it's got a bunch of meteorite impacts, a lot of heat, it's this magma ocean stage that's kind of boiling off water, as you've described, and probably losing it.
• 12:01
  SPEAKER_01: So there's kind of two culprits for water, like where did the ocean water come from?
• 12:06
  SPEAKER_01: And one is it was added later by these meteorites.
• 12:09
  SPEAKER_01: So these meteorites kind of brought water in, and they after the earth kind of solidified and had a solid crust and started to cool down, these meteorites came in and added water to the system.
• 12:18
  SPEAKER_00: And this is during the heavy bombardment era, correct?
• 12:20
  SPEAKER_01: Yeah, that would it would be like the first couple hundred million years of Earth history.
• 12:24
  SPEAKER_00: Yeah, yeah, we're getting smacked a lot, not like these very sporadic, you know, meteor impacts that we have going on.
• 12:31
  SPEAKER_00: Now we were getting hit a lot.
• 12:32
  SPEAKER_01: Smacked a lot and by big ones too.
• 12:34
  SPEAKER_01: These big, they'd form like like look at the moon, there's big impact basins on the moon, and it's that size.
• 12:40
  SPEAKER_01: Big, big, big meteorites bringing this material in.
• 12:43
  SPEAKER_01: The other one is outgassing from the mantle.
• 12:45
  SPEAKER_01: If water could be trapped in this crystallizing magma ocean, as the mantle solidified, some of the minerals might soak up some water and trap it in there, and that could trap some volatiles in the mantle that then degas gradually over geologic time.
• 12:58
  SPEAKER_01: They outgas into the atmosphere and then into the ocean.
• 13:02
  SPEAKER_00: Now, let me ask you this then.
• 13:03
  SPEAKER_00: So as the water is being added to the atmosphere, and it's not just water, it's carbon dioxide, it's carbon monoxide, all these other kind of gases that we associate with volcanism today are being added to the atmosphere.
• 13:16
  SPEAKER_00: This must have affected the time that all of this took place, right?
• 13:21
  SPEAKER_00: I mean, because in other words, I would think it slowed it down.
• 13:24
  SPEAKER_01: Is that a good assumption that that the atmosphere slowed it down?
• 13:28
  SPEAKER_00: Slowed down the cooling of the planet.
• 13:31
  SPEAKER_01: Oh, absolutely.
• 13:32
  SPEAKER_01: Yeah, for sure.
• 13:33
  SPEAKER_01: This is a really interesting calculation that a few people have started doing recently is to say, okay, look at a magma ocean, study a magma ocean planet, and put together these big simulations of how it might crystallize.
• 13:44
  SPEAKER_01: Does it crystallize from the top down?
• 13:47
  SPEAKER_01: And this is an interesting question or interesting point.
• 13:49
  SPEAKER_01: Pressure, as you mentioned earlier, has a lot to do with when stuff crystallizes.
• 13:54
  SPEAKER_01: So when we think of a mantle that's 2,800 kilometers thick, that's a lot of pressure variation across this molten magma ocean.
• 14:02
  SPEAKER_01: And so we don't really know where the crystallization started.
• 14:05
  SPEAKER_01: There's suggestions that it started crystallizing on the top and then crystallized downward.
• 14:10
  SPEAKER_01: Some people would suggest the crystallization started on the bottom and works its way to the top.
• 14:14
  SPEAKER_01: Then we have these middle out and outside in type of crystallization models too.
• 14:18
  SPEAKER_01: So we don't really know.
• 14:19
  SPEAKER_01: But one thing we do know is that if you put an atmosphere around that, it's like a blanket.
• 14:24
  SPEAKER_01: You slow down the cooling of the planet, of the magma ocean stage.
• 14:29
  SPEAKER_00: It's kind of like going camping, and on a clear night, you know that it's gonna be a cold night.
• 14:33
  SPEAKER_01: Oh, yeah, yeah, yeah.
• 14:34
  SPEAKER_00: And if you don't have that blanket of cloud cover, you just lose heat more rapidly.
• 14:39
  SPEAKER_00: And the atmosphere acts as that blanket.
• 14:41
  SPEAKER_00: So we have then two sources that uh probably worked in conjunction for adding water to the atmosphere.
• 14:49
  SPEAKER_00: This degassing from what is now the mantle, and also getting smacked by these meteors and particularly massive big comets, okay, during the heavy bombardment era.
• 15:02
  SPEAKER_00: Both of those have lots of water.
• 15:03
  SPEAKER_00: So this whole thing then cools down below the boiling point, whatever that happened to be at the time, due to the pressures involved.
• 15:10
  SPEAKER_00: And it begins to rain.
• 15:13
  SPEAKER_00: And like this must have, Jesse, are there estimates on this that this must have taken millions of years?
• 15:18
  SPEAKER_01: Yeah, it's a really hard calculation to it's really it's really hard to figure out what's happening in the first like hundred million years of Earth's life.
• 15:28
  SPEAKER_01: And this is the other complicating factor of Earth, is that we have a moon, and we know the moon formed by a giant impact that basically reset the planet.
• 15:38
  SPEAKER_01: We don't know when the moon formed.
• 15:39
  SPEAKER_01: Some people would say 4.35 billion years ago is when the moon formed.
• 15:44
  SPEAKER_01: Some people would say 4.55 billion years ago, and that's 200 million years age difference.
• 15:50
  SPEAKER_01: So you we could have had this planet that got started and had an ocean and had all these things happening to it, and then all of a sudden it got smacked by the moon forming impact and completely reset itself again into a magma ocean stage, and then you had to start this process over.
• 16:04
  SPEAKER_01: So we really don't have very a very good idea of what was going on in that first, let's say, 200 million years of Earth.
• 16:13
  SPEAKER_01: It's really tricky to figure out because the models get really complicated and there's feedback loops in these things.
• 16:18
  SPEAKER_00: Right.
• 16:18
  SPEAKER_00: But it is safe to say that we had to fill the ocean basins, and the ocean basins were filled from condensation and precipitation from the early formed atmosphere.
• 16:29
  SPEAKER_01: Exactly.
• 16:29
  SPEAKER_01: So as the you can imagine this, as you put a let's guys imagine a magma ocean, a ball of magma, and you've got a water vapor atmosphere around that.
• 16:38
  SPEAKER_01: What happens pretty quickly is you're losing, oh, the atmosphere is losing heat to space pretty quickly.
• 16:43
  SPEAKER_01: And so you're forming pretty soon that it gets cool enough where you'll have a crust, like a solid thin layer.
• 16:52
  SPEAKER_01: And I always think of a lava or pohoihoy lava, you know, this really ropey kind of lava texture where if a uh a lava flow is flowing, you rarely see just pure magma or pure lava.
• 17:05
  SPEAKER_01: Like you don't often see that.
• 17:06
  SPEAKER_01: It often has a little crust on top of it.
• 17:08
  SPEAKER_01: That crust forms really quickly.
• 17:10
  SPEAKER_01: Yeah, this so this thin skin that would happen on a planetary scale, too.
• 17:13
  SPEAKER_01: So you'd have this thin skin, and that can start to cool down, then the atmosphere cools down, and as soon as you get below condensation point of water, then you start to precipitate or and depart and condense that water into oceans, then.
• 17:26
  SPEAKER_00: And we didn't have continents at the time, and so right.
• 17:29
  SPEAKER_01: Well, depends who you ask on that.
• 17:31
  SPEAKER_01: But yes, in my opinion, continents are uh we didn't have huge amounts of continents, certainly not 4.5 billion years ago.
• 17:39
  SPEAKER_01: Some people would argue 4.4 billion years ago, we've got continents.
• 17:42
  SPEAKER_00: But uh, so are we looking for then in the near future for Dr.
• 17:47
  SPEAKER_00: Rymank to find a 4.4 billion year old zircon crystal?
• 17:51
  SPEAKER_00: Is that what we're is that what you're saying right there?
• 17:52
  SPEAKER_01: That would be very good.
• 17:54
  SPEAKER_00: We'll see you on the tonight show then, right?
• 17:56
  SPEAKER_00: Yeah, that's right.
• 17:58
  SPEAKER_01: Yes, exactly.
• 18:00
  SPEAKER_01: I don't think that's gonna happen because I I'm not um I don't really think continents were a huge component of the the Hadian Earth, but some people would argue with that.
• 18:09
  SPEAKER_01: So Okay.
• 18:10
  SPEAKER_00: So there's also something else that's important to note is that Earth is a little bit different from other nearby planets in that you know, we're big enough to hold on to the vast majority of its water.
• 18:23
  SPEAKER_01: Ooh, what do you mean by big enough, Chris?
• 18:25
  SPEAKER_01: Well phrased.
• 18:26
  SPEAKER_00: You know, we're heavy enough to gravitationally hold on to the H2O.
• 18:31
  SPEAKER_00: Most of it, anyway.
• 18:32
  SPEAKER_00: There's very little of it that has been lost to space.
• 18:34
  SPEAKER_00: Obviously, you have some chemical reactions where you know some of the hydrogen has been dissociated from the oxygen and and therefore lost and so on.
• 18:42
  SPEAKER_00: But over time, our water cycle is pretty well kept intact.
• 18:47
  SPEAKER_01: Yes.
• 18:48
  SPEAKER_00: I don't know, you look at Mars uh and the evidence is so vast that there was a lot of flowing water on the surface of Mars at some time.
• 18:56
  SPEAKER_00: Um I'll eat my desk if that's not a correct statement.
• 18:59
  SPEAKER_00: I mean, it I feel that confident.
• 19:01
  SPEAKER_00: I mean, but it's gone, right?
• 19:03
  SPEAKER_00: And the same thing is true of Venus.
• 19:05
  SPEAKER_00: The water is gone.
• 19:06
  SPEAKER_00: I know there are different things at play here.
• 19:08
  SPEAKER_00: Earth is really in this perfect zone, and it's also the perfect size to retain this stuff that we're talking about here.
• 19:18
  SPEAKER_01: There's two important points to that.
• 19:19
  SPEAKER_01: First of all, we're big enough to hold on to water molecules, water vapor, and other sort of heavier molecules will not get blown away by the sun's radiation or by cosmic rays.
• 19:30
  SPEAKER_01: Our gravity holds on to that stuff, but we're not too near the sun that everything boils off, that the entire oceans boil off, and then we're done.
• 19:38
  SPEAKER_01: So we're kind of that's what we mean by the sweet spot.
• 19:40
  SPEAKER_01: This uh there's different ways to define the quote unquote habitable zone, but we're like far enough away, but close enough and big enough.
• 19:46
  SPEAKER_01: That's kind of the calculation you we sort of need to do to think about this thing.
• 19:50
  SPEAKER_01: But to your point, yes, we have really good evidence for oceans being on Earth.
• 19:55
  SPEAKER_01: Basically, as old as we have a rock record or a mineral record, we see evidence for oceans.
• 20:00
  SPEAKER_01: So back to 4.3, 4.2 billion years ago, we have evidence for liquid water on the surface of the earth.
• 20:07
  SPEAKER_01: Now, there is something that has changed in earth history, and this kind of comes full circle back to this mantle transition zone water.
• 20:14
  SPEAKER_01: You might be thinking, why did we talk about that before?
• 20:18
  SPEAKER_01: Because I think that there's a maybe not a complete consensus, but there's a big section of the research community that thinks that the early Earth was a water world, meaning continents were not emerged, emerged above sea level.
• 20:32
  SPEAKER_01: If we had continents, they were below sea level, and we might not have had many continents, so that's why they were below sea level.
• 20:38
  SPEAKER_01: But basically, Earth was probably a water world, or at least dominantly a water world for that sort of three billion years and older time period.
• 20:47
  SPEAKER_01: So it brings up many questions that we don't have answers to.
• 20:50
  SPEAKER_01: Like one hypothesis would be we used to have more water on the surface, and oh and continents were there, they were just flooded, and then that water got soaked up by this mantle transition zone through something like plate tectonics, bringing water down and then this transition zone kind of soaking it up like a sponge.
• 21:06
  SPEAKER_01: That's one model.
• 21:07
  SPEAKER_01: Other ones are oh, continents just grew, and so when you grow a continent, it it pokes its head above sea level.
• 21:12
  SPEAKER_00: For my thought, why we began talking about the transition zone of the mantle is also it proves the amount of water that's inside the earth.
• 21:23
  SPEAKER_00: It gives a source for degassing of our early planet.
• 21:27
  SPEAKER_01: Yeah, it it could.
• 21:28
  SPEAKER_01: It could give that source exactly.
• 21:30
  SPEAKER_01: Like we don't know how much water's down there, but it is a potential reservoir.
• 21:33
  SPEAKER_01: Like it's somewhere you could point and say, oh, look, there could have been, and there could still be water in there.
• 21:38
  SPEAKER_01: It could have been there, outgassed, and then is regassing in is being sort of pushed down with subduction now.
• 21:45
  SPEAKER_01: That's one possibility.
• 21:47
  SPEAKER_00: Which is still the case today.
• 21:48
  SPEAKER_00: If you think about magma chambers beneath active volcanic areas, the majority of the gas that's dissolved in magma is H2O.
• 21:56
  SPEAKER_00: You know, as much as 75%.
• 21:58
  SPEAKER_00: You know, that's a lot.
• 22:00
  SPEAKER_01: Yeah, you might be thinking, like, wait a minute, how does water get all the way down into the mantle, that far down in the mantle?
• 22:07
  SPEAKER_01: And y you're right, Chris, that a lot of the water that goes down comes back up in arc volcanoes, like all that gas coming out of Mount St.
• 22:15
  SPEAKER_01: Helens or any of those stratovolcanoes, they're always steaming.
• 22:19
  SPEAKER_01: No matter what they're steaming.
• 22:20
  SPEAKER_01: And a lot of that's groundwater, but some of it's magmatic water.
• 22:22
  SPEAKER_01: That water ultimately was sourced from the oceanic plate going down, and it drives off all the volatiles as it goes down, or at least most of the volatiles, but really cold subduction zones can actually take some water down further.
• 22:35
  SPEAKER_01: They can kind of go past the subduction zone and make it into the deeper mantle.
• 22:40
  SPEAKER_01: These minerals, certain minerals can bring them down really deep.
• 22:43
  SPEAKER_00: So to be clear, are you referring to the waterlogged plate on top of the subduction zone that gets brought deep down?
• 22:51
  SPEAKER_00: So when you say cold subduction zones, you're talking about subduction, subducting plates that are old and cold, right?
• 22:58
  SPEAKER_01: Exactly, yeah.
• 22:59
  SPEAKER_01: And what we mean is old, cold, oceanic crust.
• 23:02
  SPEAKER_01: So an oceanic plate that's really far away from the mid-ocean ridge that it was formed in.
• 23:08
  SPEAKER_01: That will be really cold as it dives down into the mantle.
• 23:12
  SPEAKER_01: It takes a while to heat up, and some of those minerals can hold on to their water longer and make it past this kind of subduction zone.
• 23:19
  SPEAKER_01: Think of the subduction zone like squeezing out the sponge, and some cold stuff will be really waterlogged.
• 23:25
  SPEAKER_01: The squeezing action won't really wring it out completely.
• 23:28
  SPEAKER_01: So there'll be little bits of water that make it down into the mantle.
• 23:31
  SPEAKER_01: Could envision scenarios where the water is being soaked up by the mantle through time, you can imagine water being outgassed over time from the mantle to the oceans, and and so we get into a sort of armwavy space here where we don't really understand the full history of our oceans.
• 23:46
  SPEAKER_00: Yeah, good point.
• 23:47
  SPEAKER_00: Just to come back to what you were saying about old and cold.
• 23:50
  SPEAKER_00: I use this in my intro-level geology class when we talk about convergent boundaries and you talk about like an ocean-to-ocean convergent boundary.
• 23:58
  SPEAKER_00: Well, yeah, everyone knows oceanic crust in a convergent boundary is going to be the one to subduct, but when you have two oceanic crusts, which one goes?
• 24:06
  SPEAKER_00: And I just say, well, the one that is older and colder.
• 24:09
  SPEAKER_00: It's just a, you know, it's a basic concept.
• 24:11
  SPEAKER_00: It's the one that is furthest away from the mid-ocean ridge, furthest away from that heat source.
• 24:16
  SPEAKER_00: It's older, it's colder, and therefore it's denser, and that's the one that dives down.
• 24:20
  SPEAKER_00: So yeah, exactly.
• 24:22
  SPEAKER_01: For sure.
• 24:22
  SPEAKER_01: Yeah, it's a great one.
• 24:23
  SPEAKER_01: I was just talking about this the other uh yesterday in class.
• 24:25
  SPEAKER_01: Actually, we went over subduction zones and and uh we're just talking about the angle of subduction and how it's related to the coldness of the slab and these sort of first principles.
• 24:34
  SPEAKER_01: So well, we've brought up a lot of questions, I think, that we don't know the answers to, but we've answered the fundamental question.
• 24:41
  SPEAKER_01: And the point here is that the oceans, the history of the oceans, is really, really interesting.
• 24:45
  SPEAKER_01: I mean, Chris, we talked about bandit iron formations and how ocean chemistry was completely different way back in time because we were depositing precipitating silica in these bandit iron formations, and we we don't form those in the modern earth.
• 24:56
  SPEAKER_01: So ocean chemistry has changed a ton too.
• 24:59
  SPEAKER_01: So gosh.
• 25:00
  SPEAKER_00: Well, think about this early atmosphere, right?
• 25:02
  SPEAKER_00: Getting pumped and loaded with water, but it had no oxygen.
• 25:05
  SPEAKER_01: And it was probably had a lot more CO2 than we have today.
• 25:07
  SPEAKER_01: Like I really the earth has changed a lot over time, even though the oceans have remained present for basically all of our geologic record.
• 25:17
  SPEAKER_01: The question is, is how does it change?
• 25:18
  SPEAKER_01: It changed chemistry, it changed volume, like all those things we don't really know, but we know it was there.
• 25:23
  SPEAKER_01: I think that's uh that's kind of a summary.
• 25:27
  SPEAKER_00: Well, I don't know if that was a summary or not.
• 25:30
  SPEAKER_00: I don't know.
• 25:31
  SPEAKER_01: It's true, it's true.
• 25:32
  SPEAKER_01: I mean, it's one of these things I think probably I I sort of think non-geologists might look at us and be like, why don't you know this yet?
• 25:40
  SPEAKER_01: Like this seems like a really first order thing to like know the history of the oceans.
• 25:45
  SPEAKER_00: I I understand that.
• 25:46
  SPEAKER_00: However, we are talking about stuff that's very, very old.
• 25:50
  SPEAKER_00: And in geology, we often get into this trap.
• 25:53
  SPEAKER_00: I think it's a trap when we throw around these really massive numbers.
• 25:57
  SPEAKER_00: We're saying, ah, it's 3.8 billion years old, or it's 4.1 billion years old.
• 26:01
  SPEAKER_00: Holy crap, that's ridiculous.
• 26:03
  SPEAKER_00: You know, we just we throw these around without actually really wrapping our minds around it sometimes.
• 26:09
  SPEAKER_00: And when you talk about stuff that's this old, there's so little evidence, it's scant.
• 26:15
  SPEAKER_00: And so for us to to know a ton about that, I think is that's a massive bar to overcome.
• 26:23
  SPEAKER_00: It's just the sheer age, you know.
• 26:25
  SPEAKER_01: Yeah, and I do we do tend to throw around these numbers.
• 26:27
  SPEAKER_01: You know, we take 3.8 billion with a ton of zeros and we turn it into 3.8, and it feels smaller to us, right?
• 26:34
  SPEAKER_01: But yeah, it's a it's a I mean, heck, I don't even know what a million looks like, really.
• 26:38
  SPEAKER_01: I mean, I've never seen a million of something in one spot, I don't think.
• 26:41
  SPEAKER_01: So I don't really know what that looks like, let alone a billion.
• 26:44
  SPEAKER_01: I I just can't conceive of it, you know, mentally.
• 26:46
  SPEAKER_01: My schema is.
• 26:48
  SPEAKER_00: I mean, it's hard.
• 26:49
  SPEAKER_00: Every once in a while, every once in a while, if if the conditions are just right, sometimes your mind can begin to untangle it a little bit, and then my stomach gets all uneasy and I get unsettled, and it then I don't feel good.
• 27:01
  SPEAKER_00: I feel like I almost have to throw up, you know.
• 27:03
  SPEAKER_01: I know, I know, I agree completely.
• 27:04
  SPEAKER_01: Like there's every once in a while, I remember there was this one time, I think it was like the third, second year, maybe that I was doing field work up in the Acostanized complex, where sitting on the four billion-year-old outcrop, right?
• 27:15
  SPEAKER_01: And sitting there, and we were having lunch or something, and the person I was in the field with had wandered off, and I was just sitting there, and it kind of dawned on me I could kind of grasp four billion years, like not really, I wasn't even close to grasping it, but I could kind of like see it a little bit or start to feel it, and it it's so unsettling.
• 27:33
  SPEAKER_01: I was like, I don't I don't want to think about that too deeply.
• 27:35
  SPEAKER_01: Like, yeah, it gets really unsettling.
• 27:38
  SPEAKER_00: It does, it really scratches the brain, you know.
• 27:40
  SPEAKER_00: Totally.
• 27:41
  SPEAKER_01: Oh man, very unsettling feeling.
• 27:44
  SPEAKER_01: Yeah.
• 27:45
  SPEAKER_01: Oh man, but it's something, you know, we we you're right, we have to deal with as geologists.
• 27:49
  SPEAKER_01: We have to kind of I think we have to get better at communicating things like that.
• 27:52
  SPEAKER_01: That it is uh awe-inspiring, but it's also something we can be a little we can trivialize a little bit.
• 27:57
  SPEAKER_00: Yeah, I'm guilty of it.
• 27:58
  SPEAKER_00: I'm sure you are, especially you are, because you deal with old stuff all the time.
• 28:02
  SPEAKER_01: Including my podcast partner.
• 28:04
  SPEAKER_01: Oh stop.
• 28:08
  SPEAKER_00: That was all right.
• 28:09
  SPEAKER_00: That was a good one.
• 28:10
  SPEAKER_00: I'm proud of myself.
• 28:11
  SPEAKER_00: That was all right.
• 28:12
  SPEAKER_00: I got you.
• 28:13
  SPEAKER_00: That was good.
• 28:13
  SPEAKER_00: That was good.
• 28:14
  SPEAKER_00: Um is there anything that you want to add or we should add about oceans and tectonics?
• 28:21
  SPEAKER_01: Um yes and no.
• 28:24
  SPEAKER_01: I think it's it's kind of um again, something we don't have a great answer to.
• 28:28
  SPEAKER_01: We think it's important.
• 28:29
  SPEAKER_01: We think like the hydration of the plates, you can imagine it kind of lubricates plate tectonics and it helps drive a lot of things.
• 28:36
  SPEAKER_01: So we definitely think it's it's quite important that an ocean helps plate tectonics continue and helps sort of fertilize the planet for plate tectonics.
• 28:46
  SPEAKER_01: So yeah, they're probably intimately linked for sure.
• 28:48
  SPEAKER_00: Okay.
• 28:49
  SPEAKER_00: But I would you can straighten this out if you you know if I'm wrong or off base here, but I think too that oceans preceded what we know of as plate tectonics.
• 28:59
  SPEAKER_00: I mean, the oceans came first.
• 29:01
  SPEAKER_01: It's a great question.
• 29:02
  SPEAKER_01: My opinion, yes.
• 29:03
  SPEAKER_01: My opinion would be.
• 29:29
  SPEAKER_00: Okay.
• 29:29
  SPEAKER_00: Question for you then to follow up on this.
• 29:31
  SPEAKER_00: Uh, so are you uh shifting a little bit in your career uh away from like answering that big overarching question and looking at different things because of your interests, or this is just kind of a feeling that I get.
• 29:45
  SPEAKER_01: Yeah, I would say that's accurate.
• 29:46
  SPEAKER_01: Maybe, well, it's hard.
• 29:48
  SPEAKER_01: Um, I don't want to study one suite of rocks for the rest of my career, right?
• 29:53
  SPEAKER_01: That's sort of an unhealthy situation to be in.
• 29:56
  SPEAKER_01: And unless I go out and manage to find some other old rock location, it's hard to just say I'm gonna continue studying the early earth, right?
• 30:04
  SPEAKER_01: It's super interesting to me, but I don't want it to be my whole research initiative and agenda.
• 30:08
  SPEAKER_01: So I'd like it to be, you know, a quarter of my research sort of profile, and then I'm sort of developing the other ones for sure.
• 30:15
  SPEAKER_01: So I'm getting into this critical minerals type thing, and yeah, there's different avenues to to go, but you don't want to I don't want to be just on like a single track.
• 30:24
  SPEAKER_00: So this is definitely, Jesse, a Crisple Hoist front porch beer in hand conversation.
• 30:30
  SPEAKER_01: Definitely absolutely.
• 30:32
  SPEAKER_01: We gotta sit on the rocking chairs, have a couple beers, talk it through.
• 30:36
  SPEAKER_01: Absolutely.
• 30:37
  SPEAKER_01: I look forward to it.
• 30:38
  SPEAKER_00: All right, all right, man.
• 30:40
  SPEAKER_00: Well, Kathy, I hope we did it justice.
• 30:43
  SPEAKER_00: Um I think that's a wrap.
• 30:45
  SPEAKER_01: I think it's a wrap.
• 30:45
  SPEAKER_01: It's as good as we can do for now, at least.
• 30:48
  SPEAKER_01: That's right.
• 30:48
  SPEAKER_01: That's right.
• 30:49
  SPEAKER_01: Right?
• 30:50
  SPEAKER_01: Uh, you can find us now on our mobile app, both on iOS and Android.
• 30:54
  SPEAKER_01: Just type in Camp Geo into the app store and you'll find us there.
• 30:57
  SPEAKER_01: You can download it.
• 30:58
  SPEAKER_01: You can listen to all of our Camp Geo stuff.
• 31:01
  SPEAKER_01: You can download all the images and audio files and listen offline.
• 31:04
  SPEAKER_01: That's a key feature there.
• 31:05
  SPEAKER_01: And you can also purchase access to our Yellowstone geological guide to Yellowstone National Park in the same way.
• 31:11
  SPEAKER_01: And again, download content offline.
• 31:13
  SPEAKER_01: You can also head to our website, that's planetgeocast.com.
• 31:16
  SPEAKER_01: There you can subscribe, like, follow us, and support us.
• 31:19
  SPEAKER_01: We really appreciate that.
• 31:20
  SPEAKER_01: And lastly, Chris, send us an email, planetgeocast at gmail.com.
• 31:23
  SPEAKER_01: We've been getting a bunch of them, a bunch of good questions.
• 31:25
  SPEAKER_01: And we like answering them.
• 31:26
  SPEAKER_01: Like, you know, things like this come up and we're like, hey, that's an episode right there.
• 31:29
  SPEAKER_01: Let's put together uh some talking points and just uh walk through it because it's super interesting topic.
• 31:34
  SPEAKER_01: So keep sending those our way.
• 31:36
  SPEAKER_01: We love it.
• 31:36
  SPEAKER_01: Yeah.
• 31:37
  SPEAKER_01: Cheers.
• 31:37
  SPEAKER_01: Peace.