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Magma Oceans and Triple Junctions - Listener Questions Part 2! · PlanetGeo: The Geology Podcast

• 0:03
  SPEAKER_00: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:14
  SPEAKER_00: Really, really fast.
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  SPEAKER_00: Really excited.
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  SPEAKER_00: Excited, Chris Mohawse today.
• 0:19
  SPEAKER_01: That's right.
• 0:20
  SPEAKER_01: You get fun, Chris.
• 0:21
  SPEAKER_01: Fun Chris is a good Chris.
• 0:22
  SPEAKER_01: Fun Chris.
• 0:23
  SPEAKER_00: He's got his fun pants on.
• 0:24
  SPEAKER_00: That's always exciting.
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  SPEAKER_01: Does.
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  SPEAKER_01: That's right.
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  SPEAKER_01: That's right.
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  SPEAKER_00: Exciting for everybody.
• 0:28
  SPEAKER_01: How are you doing, Jesse?
• 0:29
  SPEAKER_00: I'm great, Chris.
• 0:30
  SPEAKER_00: I'm great.
• 0:31
  SPEAKER_00: We are picking up part two of listener questions.
• 0:34
  SPEAKER_00: Last week we talked about the first two about Michigan Basin, and we talked about some hot spots and ultra-low velocity zones.
• 0:41
  SPEAKER_00: Today we're going to take a bit of a deviation and cover a few other topics from listeners.
• 0:47
  SPEAKER_01: That's right.
• 0:48
  SPEAKER_01: So we have a question from Natalie about the Mendocino triple junction, which is a really geologically very interesting, I don't know what you call it, phenomenon in the northern part of California.
• 1:06
  SPEAKER_01: So that's it's basically just open-ended.
• 1:10
  SPEAKER_01: Hey, can you educate everybody about the Mendocino triple junction area?
• 1:14
  SPEAKER_01: And that's what we're gonna do.
• 1:15
  SPEAKER_01: We're gonna tackle this one.
• 1:16
  SPEAKER_00: Exactly.
• 1:17
  SPEAKER_00: This is in Humboldt County.
• 1:18
  SPEAKER_00: So Natalie, thank you for the question.
• 1:19
  SPEAKER_00: A resident of Humboldt County, but it's north of San Francisco, and so that's kind of where we're talking, right on the coast of California, near San Francisco, north of San Francisco.
• 1:28
  SPEAKER_00: And that plays an important role here because as most people might know, probably know, the San Andreas Fault runs through San Francisco or runs very near San Francisco.
• 1:39
  SPEAKER_00: And so that comes into play here in the Mendocino triple junction.
• 1:43
  SPEAKER_00: And as the name implies, it is a triple junction, which these are amazingly interesting and complicated places around the world.
• 1:50
  SPEAKER_00: It's where three tectonic plates come together, triple junction.
• 1:54
  SPEAKER_00: So this is Mendocino triple junction, where the three plates are coming together.
• 1:58
  SPEAKER_00: What are our three?
• 1:59
  SPEAKER_01: Well, I just want to say this is you don't get this in an intro-level geology textbook.
• 2:05
  SPEAKER_01: You know, we talk about diverging plates and everything is so neat and tidy, the plates go apart, right?
• 2:10
  SPEAKER_01: A convergent boundary, they come together, a transform boundary, they slide past each other.
• 2:14
  SPEAKER_01: What the hell is a triple junction then?
• 2:16
  SPEAKER_01: Where you know this is this is not something that's typically covered, but it's super, super interesting.
• 2:22
  SPEAKER_01: This is the northern end.
• 2:25
  SPEAKER_01: This is where the San Andreas fault system ends, is at the Mendocino triple junction.
• 2:31
  SPEAKER_01: It's the northern extent of this fault system.
• 2:36
  SPEAKER_00: And it's the southern extent of the Cascadia subduction zone system.
• 2:41
  SPEAKER_00: So all the arc volcanoes we've talked about, Mount St.
• 2:43
  SPEAKER_00: Helens, Lassen Volcanic Field, all of those Shasta.
• 2:48
  SPEAKER_00: I mean, all those that run all the way up into southern British Columbia, it's the end of that system.
• 2:53
  SPEAKER_00: So right now, we're from the north.
• 2:54
  SPEAKER_00: If you travel from the north to Mendocino, you're gonna be going along a subduction zone system.
• 2:59
  SPEAKER_00: If you head from the south to the north, you're gonna be going along the San Andreas Fault system.
• 3:03
  SPEAKER_00: Where these two tectonic regimes intersect, it gets complicated.
• 3:08
  SPEAKER_00: And so, what are the plates we're dealing with here, Chris?
• 3:11
  SPEAKER_00: Like, what are we gonna talk about?
• 3:12
  SPEAKER_00: Because this is gonna be a little bit visually difficult to describe.
• 3:14
  SPEAKER_00: So we're gonna have to be really explicit about it.
• 3:16
  SPEAKER_01: Okay.
• 3:17
  SPEAKER_01: So we have the North American plate.
• 3:19
  SPEAKER_01: That's easy.
• 3:20
  SPEAKER_01: All right, so this is east of the San Andreas Fault System, and the North American plate is moving west-southwest.
• 3:27
  SPEAKER_01: Okay.
• 3:28
  SPEAKER_01: Then you so that's the one of the plate junctions.
• 3:31
  SPEAKER_01: The other plate junction is the Pacific plate, which is moving north-northwest.
• 3:37
  SPEAKER_01: Okay, so that's beneath the majority of the Pacific Ocean.
• 3:41
  SPEAKER_01: And then we have this little subplate that's involved in this triple junction called the Gorda plate.
• 3:49
  SPEAKER_01: The Gorda plate, it's a subplate of the WandaFuca plate that is largely responsible for the Cascadia subduction zone and so on.
• 3:59
  SPEAKER_01: So it's uh Jesse, like we need to paint a better picture, like in terms of where so we have the North American plate, we have the Pacific plate, and then where where do you put the Gorda?
• 4:16
  SPEAKER_00: Like Yeah, the Gorda plate.
• 4:17
  SPEAKER_00: So I think it's easiest to say, okay, the North American plate, let's just assume that's not moving for the for the time being.
• 4:23
  SPEAKER_00: It is moving, but let's assume it's not moving, because we're talking about relative plate motions anyway.
• 4:27
  SPEAKER_00: So let's keep North America where the North American continent is, coast of California, Oregon, Washington, all the way up to Vancouver Island.
• 4:34
  SPEAKER_00: Keep that stationary.
• 4:35
  SPEAKER_00: The Pacific plate down by Los Angeles, San Francisco, that thing is sliding up to the north-northwest past the North American plate.
• 4:45
  SPEAKER_00: So that's sliding up if you're looking at a map view.
• 4:48
  SPEAKER_00: Now, the Wandafuca plate is off the coast of Oregon and Washington and Vancouver Island.
• 4:52
  SPEAKER_00: It's a relatively small one, but there's a plate there that is moving to the east.
• 4:58
  SPEAKER_00: So it is colliding with the North American plate.
• 5:01
  SPEAKER_00: And it is an oceanic plate, so it subducts beneath North American continent.
• 5:05
  SPEAKER_00: And so this Wandafuca plate and the Gorda subplate to the south, those are both moving to the east.
• 5:11
  SPEAKER_00: They're moving right on this diagram.
• 5:13
  SPEAKER_00: So they're moving right into the continent, they're going underneath of the continent, but we have this Pacific plate that's coming up to the north-northwest.
• 5:21
  SPEAKER_01: It creates at this weird area, the triple junction, it creates a convergent boundary because that subplate, the Gorda plate, isn't getting out of the way of the Pacific plate fast enough.
• 5:34
  SPEAKER_01: So the Pacific plate is jamming itself up against that.
• 5:39
  SPEAKER_01: And this creates then a really geologically and tectonically active zone.
• 5:48
  SPEAKER_01: Because there's something else that's important is this triple junction is not it's not a point.
• 5:54
  SPEAKER_01: You can't pinpoint it.
• 5:55
  SPEAKER_01: It's it's this whole it's a zone, right?
• 5:58
  SPEAKER_01: Where these three plates are all touching each other.
• 6:02
  SPEAKER_01: And so it creates like really, really active areas.
• 6:05
  SPEAKER_01: Rapid uplift.
• 6:07
  SPEAKER_01: Okay, because you that's what you get when you have a convergent boundary.
• 6:10
  SPEAKER_01: This causes mountains, like the King Range.
• 6:13
  SPEAKER_01: There is a mountain range that is formed by this convergence, and it's one of the most rapidly uplifting areas, and it rivals the amount of uplift that happens right now in the Himalayas.
• 6:29
  SPEAKER_00: Oh, just such rapid uplift.
• 6:31
  SPEAKER_00: These mountains are going up quickly.
• 6:33
  SPEAKER_00: And you can see the implications of this, the geological implications of this, with stranded terraces, and so these are flat kind of benches near the coastline that are above sea level, and that's where sea level used to be.
• 6:46
  SPEAKER_00: And the reason that those are up above sea level now is not because sea level has dropped, it's because the land has moved up.
• 6:52
  SPEAKER_00: So if we get some seismic event that thrust the land up, those benches, they used to be at sea level.
• 6:59
  SPEAKER_00: That's where the ocean was eroding.
• 7:01
  SPEAKER_00: That used to be a beach, it's nice and flat there.
• 7:03
  SPEAKER_00: It gets shoved up, and then the ocean starts to erode down below that and make a new beach.
• 7:09
  SPEAKER_00: So you kind of get a cliff that then becomes a beach, and then that gets shoved up again.
• 7:13
  SPEAKER_00: So we have these terraces in this region that are due to, well, they're a clear sign of the land uplifting really rapidly.
• 7:22
  SPEAKER_01: And we call that an emergent coastline, and it does this episodically.
• 7:27
  SPEAKER_01: You'll have a violent event or series of events that causes the land area to uplift and it strands then, it leaves it stranded, the old surf zone where the waves were crashing back and forth, cutting this flat kind of terrace area, and leaves a cliff then in its place.
• 7:44
  SPEAKER_01: And then it starts to cut a new platform, and then a new event happens and it leaves that platform stranded.
• 7:50
  SPEAKER_01: And so these terraces are just a really, really cool feature, and they're a sign then of this rapid, kind of violent uplift that typifies this area.
• 8:01
  SPEAKER_00: That kind of gives us a brief introduction into the Mendocino Triple Junction region, which is a region there that's creating this rapid uplift.
• 8:09
  SPEAKER_00: Uh, Natalie had a follow-up question, though, about the rocks themselves.
• 8:12
  SPEAKER_00: And um, she's heard that these are newer rocks, that they're younger than the continent itself, and was asking, sort of, okay, is that true?
• 8:20
  SPEAKER_00: And and how do those get added to the continent?
• 8:22
  SPEAKER_00: And Natalie, that is exactly true.
• 8:25
  SPEAKER_00: Those rocks that you are living on top of right now are young.
• 8:29
  SPEAKER_00: They're new additions to the continent.
• 8:31
  SPEAKER_00: The continent, the interior of the continent, where Chris is at in Michigan, where I'm at in Pennsylvania, these are much, much older rocks.
• 8:37
  SPEAKER_00: These were added to the continent hundreds of millions or billions of years ago.
• 8:41
  SPEAKER_00: The rocks in the what is called the Franciscan complex, this is basically ancient seafloor that was scraped off onto the edge of the continent during subduction zone.
• 8:51
  SPEAKER_00: So that Wandafuca plate used to be a lot bigger, used to be in that region.
• 8:54
  SPEAKER_00: It used to be subducting down beneath this part of the North American continent.
• 8:59
  SPEAKER_00: During that subduction, this is not like a gentle dipping process.
• 9:03
  SPEAKER_00: This is two tectonic plates running into each other.
• 9:05
  SPEAKER_00: And so the top surface of that ancient sea floor, the Wandafuca plate, which has pillow basalts, it has oceanic mafic crust, it has sediments on top of it.
• 9:17
  SPEAKER_00: All of that gets scraped off at this boundary and can get accreted to the continent and added to the continent.
• 9:24
  SPEAKER_00: So we're kind of shoving a whole bunch of new rock onto the edges of the continent.
• 9:28
  SPEAKER_00: So you have lots of stuff like sediments, you have basalts, you have cherts.
• 9:32
  SPEAKER_00: So there's no wonder that there are seashells, you know, in the rocks in the creek near where you live, because this is an ancient seafloor environment that's just been scraped off onto the edge of the continent and then thrust up in this Mendocino triple junction.
• 9:45
  SPEAKER_00: So great question, Natalie.
• 9:47
  SPEAKER_00: Very interesting area to live in.
• 9:49
  SPEAKER_00: Um, you know, dare I say, one of the more interesting geological places to live.
• 9:53
  SPEAKER_00: There rocks there are very, very cool.
• 9:55
  SPEAKER_01: Very, very tectonically active, though.
• 9:57
  SPEAKER_01: It has over 80 earthquakes a year that are 3.0 and larger.
• 10:02
  SPEAKER_01: And it's had, I think it was uh back in 1992, they had a series of very large earthquakes that caused a significant amount of damage.
• 10:11
  SPEAKER_01: And and so, yeah, very gorgeous area, but also very, very tectonically active.
• 10:18
  SPEAKER_00: Yes, extremely.
• 10:20
  SPEAKER_00: So cool place, great question.
• 10:22
  SPEAKER_00: Thank you for the question, and uh, you know, keep them coming.
• 10:25
  SPEAKER_00: So, Chris, what's the next thing we're gonna cover here?
• 10:28
  SPEAKER_00: We're gonna cover a question from Valeria.
• 10:31
  SPEAKER_00: Valeria, right?
• 10:32
  SPEAKER_00: Yes, all right, let's get into it.
• 10:34
  SPEAKER_00: All right, who uh we've addressed a question from before, I believe.
• 10:37
  SPEAKER_00: But Valeria's curious, uh, really in a lot to do with the moon, I suppose.
• 10:43
  SPEAKER_00: She says that you know, the moon is moving away from the earth at a a rate, and we're gonna discuss this, but you know, the question comes up how did the moon form?
• 10:52
  SPEAKER_00: What did Earth look like during the time that the moon formed?
• 10:56
  SPEAKER_00: What was this what was this event like?
• 10:59
  SPEAKER_00: She asks, did it create a lot of earthquakes, a lot of volcanic eruptions?
• 11:03
  SPEAKER_00: So we're gonna go through how the moon formed, and we're gonna you know give a brief introduction into this and then the the currently the moon's orbit.
• 11:12
  SPEAKER_00: But suffice to say, when this collision happened, and Chris, let's set the stage for what this collision is.
• 11:17
  SPEAKER_00: But basically the moon formed by a collision of two planets, a proto-Earth and what we call Thaya, this Mars-sized impactor.
• 11:24
  SPEAKER_00: What did Earth look like like during this event?
• 11:27
  SPEAKER_01: So this was really, really early on in the formation of Earth, at the time, a proto-planet, we were destined to become a planet.
• 11:36
  SPEAKER_01: So we're sweeping out the debris in our orbit.
• 11:40
  SPEAKER_01: And then this massive impactor, roughly half the size of Earth, slams into us.
• 11:46
  SPEAKER_01: Like you said, it's it's this thing that we've we've deemed or we've called it Thaya.
• 11:51
  SPEAKER_01: Like this kind of event, the simulations, if you Google this, are really, really dramatic.
• 11:56
  SPEAKER_01: I mean, it's a little horrifying.
• 11:59
  SPEAKER_01: Um, but something like this has enough energy in it to totally resurface the planet.
• 12:06
  SPEAKER_01: You know, it melted all of the crustal rocks during this collision and flung a bunch of stuff out away from Earth.
• 12:16
  SPEAKER_00: It actually probably melted the entire planet.
• 12:19
  SPEAKER_00: So right now we have the crust, the mantle, and the core.
• 12:24
  SPEAKER_00: The crust and mantle are solid, right?
• 12:25
  SPEAKER_00: Even though the mantle is kind of plasticky, it's mostly solid.
• 12:28
  SPEAKER_00: This event would melt the entire planet.
• 12:30
  SPEAKER_00: So now we have what's called a magma ocean stage, which is a planet that has mostly just molten rock in it.
• 12:37
  SPEAKER_00: There's no solid mantle.
• 12:39
  SPEAKER_00: There might be some thin crust at the top, but then we have this solid inner mantle that's really hot.
• 12:45
  SPEAKER_00: It's all liquid, and that thing starts to crystallize.
• 12:48
  SPEAKER_00: And this magma ocean phase is a really uh there's a lot of research focus on magma oceans right now.
• 12:55
  SPEAKER_00: Um, because Mars probably had a magma ocean, the moon had a magma ocean phase, Earth had a magma ocean phase.
• 13:01
  SPEAKER_00: So there's a lot of like interest in magma oceans.
• 13:05
  SPEAKER_00: But suffice to say, the entire planet was reset, was melted, and then it started to cool and solidify.
• 13:12
  SPEAKER_00: Uh, potentially during this process, we formed these ultra-low velocity zones, which we talked about last week in the question from Kathy.
• 13:20
  SPEAKER_00: And so these magma ocean processes, like, could how does it the questions are like, how does it crystallize?
• 13:26
  SPEAKER_00: Does it start at the bottom and then cool and crystallize upwards?
• 13:29
  SPEAKER_00: Does it start crystallizing at the top and crystallize downwards?
• 13:32
  SPEAKER_00: Like, how does Bowen's reaction series, which we've covered in this episode, how does that work at a planetary scale?
• 13:37
  SPEAKER_00: That's a pretty unknown um field of research at the moment.
• 13:41
  SPEAKER_00: So, but anyways, suffice to say, Earth sucked to be on during this time, right, Chris?
• 13:47
  SPEAKER_00: Not a good place to be at all, for sure.
• 13:50
  SPEAKER_00: So, Chris, this earth Earth was in this magma ocean stage after this impact, but how did we get the moon?
• 13:54
  SPEAKER_00: Like, where did the moon how did the moon form?
• 13:58
  SPEAKER_01: Well, with this with an impact like this, there was a lot of material that was ejected off from Earth, and that material coalesced and became the material that would form the moon.
• 14:08
  SPEAKER_01: At the time when this happened, the moon was it began to rotate.
• 14:12
  SPEAKER_01: It was rotating very quickly, it was coalescing, it was congealing together, and it actually got into a locked rotation with Earth very soon in the formation of the moon.
• 14:25
  SPEAKER_01: So it was spinning rapidly, it rapidly slowed down and got into the locked rotation.
• 14:30
  SPEAKER_01: This is why no matter where you are on planet Earth, you look up at the moon, you're gonna see the same side of the moon.
• 14:37
  SPEAKER_01: Okay, and uh like that's a really common misconception that I come across actually quite a bit, is that if you're in the northern hemisphere, you see one side of the moon, if you're in the southern hemisphere, you see the other side of the moon.
• 14:49
  SPEAKER_01: Oh, that's a funny one.
• 14:51
  SPEAKER_00: I've never I've never had never come across that one.
• 14:53
  SPEAKER_00: That's a funny one.
• 14:53
  SPEAKER_01: I actually had a friend who went to Australia and he came back and he told me about the other side of the moon.
• 15:00
  SPEAKER_01: And like this is a weird situation to be put in, right?
• 15:03
  SPEAKER_01: Because what do you do?
• 15:04
  SPEAKER_01: Do you say, well, no, um, actually that's not possible, or do you just let ignorance be bliss and and you know it's a it's a really interesting situation to be put in.
• 15:14
  SPEAKER_00: This is where the term, you know, the dark side of the moon comes from, is the side of the moon we never see.
• 15:18
  SPEAKER_00: We only saw them when we sent satellites and spacecraft and Apollo missions around the dark side of the moon.
• 15:23
  SPEAKER_00: So, you know, the famous Pink Floyd album, The Dark Side of the Moon.
• 15:27
  SPEAKER_01: And it looks really, really different.
• 15:29
  SPEAKER_01: The dark side of the moon, the the side we don't get to see, is very, very different looking than the side that we get to see.
• 15:36
  SPEAKER_01: It's a much thicker crust, whereas the side that faces the earth is a thinner crust, which I'm sure you have like your little, you know, doctory theories about about the cooling history of the moon, but it did cool differently on the side facing Earth versus the side not facing Earth, which is how we know that it got locked in actually very quickly to Earth's rotation.
• 16:02
  SPEAKER_00: That's right.
• 16:02
  SPEAKER_00: This sort of what we call tidally locked.
• 16:04
  SPEAKER_00: So one side's always facing the planet.
• 16:06
  SPEAKER_00: And so the other question, the other part to Valeria's question was really about do we have pieces of the moon on Earth?
• 16:14
  SPEAKER_00: And the answer is yes, we do.
• 16:15
  SPEAKER_00: We have pieces from two sources, really.
• 16:17
  SPEAKER_00: The first is the Apollo missions.
• 16:20
  SPEAKER_00: Contrary to some misconceptions, we did go to the moon in the Apollo era, grab samples, they are now on Earth, and there's loads of people that study these things.
• 16:28
  SPEAKER_00: And we also have meteorites from the moon that were ejected off the moon's surface and made their way to Earth, so we can find lunar meteorites on the Earth's surface.
• 16:37
  SPEAKER_01: I'm gonna pick up with what you just said.
• 16:39
  SPEAKER_01: Jesse, how in the world are we possibly gonna determine that a meteorite that we found on Earth was actually something that was ejected off from the moon?
• 16:49
  SPEAKER_01: How do we know that?
• 16:50
  SPEAKER_00: Oh, that's a great question.
• 16:52
  SPEAKER_00: So we know, well, we know a lot about the moon from both orbiter data.
• 16:57
  SPEAKER_00: So these, you know, satellites that have orbited the moon and collected chemical maps of the moon.
• 17:02
  SPEAKER_00: Also, the people who went on and walked on the moon, grabbed samples, came back.
• 17:06
  SPEAKER_00: They're very different.
• 17:06
  SPEAKER_00: Those rocks are very different from Earth.
• 17:08
  SPEAKER_00: We don't see lunar rocks, rocks like on the moon, on Earth, very much at all.
• 17:15
  SPEAKER_00: So they're very different.
• 17:16
  SPEAKER_00: Okay, that's the first thing.
• 17:17
  SPEAKER_00: But then you should be asked the question how do we know it's from the moon and not from like Mars or some other planet, right?
• 17:24
  SPEAKER_00: And the moon and earth are chemically.
• 17:27
  SPEAKER_00: I just said the rocks are very different, and the rocks themselves, the mineralogical makeup is very different.
• 17:32
  SPEAKER_00: But if you look at the chemistry of any given element, the moon and the earth are very, very similar.
• 17:38
  SPEAKER_00: So if you look at, we've talked about isotopes before.
• 17:40
  SPEAKER_00: If you look at, for instance, isotopes of titanium or isotopes of chromium, the earth and moon are almost identical, indistinguishable, whereas all other meteorites, including ones from Mars, are very different.
• 17:54
  SPEAKER_00: So we can do this sort of genetic tracing of planets by looking at the isotopic composition of specific elements from the rocks that we can get back, either from Apollo missions or from meteorites.
• 18:06
  SPEAKER_00: So we can say, oh, this rock is from Mars, this rock's from the moon, this one is from the asteroid Vesta, and this one is from some other meteorite class.
• 18:16
  SPEAKER_00: We have this sort of categorization scheme that is chemical in nature, isotopic in nature.
• 18:23
  SPEAKER_01: Um, one of the things that's really cool about the moon is that because there's no atmosphere, because there's no tectonics, lunar rocks, not a lot happens to them.
• 18:34
  SPEAKER_01: They can get affected by impacts and so on.
• 18:37
  SPEAKER_01: But what I'm saying is the moon provides Earth with some of its earliest memories.
• 18:45
  SPEAKER_01: Because the formation of the moon happened really early on in Earth's formation, too.
• 18:51
  SPEAKER_01: This massive collision happened very soon.
• 18:54
  SPEAKER_01: So, our early rocks, we need the moon for these early memories because ours get recycled, they get destroyed by weather and erosion, they get destroyed or recycled by plate tectonics.
• 19:03
  SPEAKER_01: The moon doesn't have that.
• 19:06
  SPEAKER_01: And so studying these rocks becomes like really important to people like you because you're trying to reconstruct when plate tectonics began on this planet.
• 19:16
  SPEAKER_01: In order to do that, you have to understand how these things happened, you know, how the moon happened and what the impact of this impact was.
• 19:26
  SPEAKER_00: Yeah, that's absolutely right.
• 19:26
  SPEAKER_00: And the timing, too.
• 19:28
  SPEAKER_00: Like we we know it happened in the first couple hundred million years of solar system formation, but we don't really know what it could have happened 50 million years after solar system formation or 200 million years after solar system formation.
• 19:40
  SPEAKER_00: So there's some uncertainty in that as well.
• 19:42
  SPEAKER_00: Um, so Chris, does that bring us to the question about Earth's orbit and the moon's orbit?
• 19:48
  SPEAKER_01: Not yet.
• 19:49
  SPEAKER_01: How many rocks did the Apollo missions bring back?
• 19:51
  SPEAKER_01: I think that's kind of a cool thing.
• 19:53
  SPEAKER_01: We brought back 842 pounds of lunar rocks.
• 19:58
  SPEAKER_01: Now that's like a uh that would be a small load on our collecting trips, Jesse.
• 20:03
  SPEAKER_01: Yeah, that's true.
• 20:06
  SPEAKER_01: Not a ton.
• 20:06
  SPEAKER_01: My truck is sagging, but so 842 pounds.
• 20:10
  SPEAKER_01: All these rocks here that we brought back, they are in a hyper-secure like facility at the Johnson Space Center.
• 20:18
  SPEAKER_01: And then we've actually taken 15% of those rocks and we store them in an off-site facility just in case.
• 20:27
  SPEAKER_01: Okay.
• 20:27
  SPEAKER_01: And if you are one of the people that is fortunate enough, I was gonna say lucky, but luck really probably has nothing to do with it.
• 20:35
  SPEAKER_01: Fortunate enough to get it granted access to study these, the process is really rigorous, and you may get a tenth of an ounce to study.
• 20:46
  SPEAKER_00: A very, very tiny amount.
• 20:47
  SPEAKER_00: I we've we've been uh I have a PhD student who's interested in doing some lunar work, and it's such a difficult process.
• 20:55
  SPEAKER_00: You have to prove that your lab is excellent and clean, and you can do the analyses, you have to really go to great lengths to show that you're not gonna screw up the lunar sample if they give it to you.
• 21:05
  SPEAKER_00: And then you have to have this clear like chain of ownership about every lunar sample, like who touched it, who held it, or this really excellent record keeping.
• 21:12
  SPEAKER_00: I mean, it all makes sense.
• 21:13
  SPEAKER_00: These are really valuable pieces of rock.
• 21:15
  SPEAKER_00: But yeah, it's an arduous process, which you know we we've been debating.
• 21:20
  SPEAKER_00: Okay, is it worth it to go through this process to look at some of the moon or rocks?
• 21:24
  SPEAKER_00: But anyway, very, very cool, very you know, important.
• 21:28
  SPEAKER_00: And hopefully we're gonna get some more soon, you know.
• 21:30
  SPEAKER_00: Hopefully in the near future we'll get some more samples returned from the moon.
• 21:33
  SPEAKER_00: So this brings us to Earth's rotation a bit.
• 21:36
  SPEAKER_00: And as Valeria, as you mentioned, the moon is receding from Earth at a you know, a decent clip.
• 21:43
  SPEAKER_00: I mean, it's not tiny.
• 21:44
  SPEAKER_00: It's I mean it is tiny, but it's not really, really small.
• 21:48
  SPEAKER_00: Yeah, it's like the rate of continental plates drifting around, right?
• 21:51
  SPEAKER_00: That's a couple centimeters per year, right, Chris?
• 21:54
  SPEAKER_01: It is.
• 21:54
  SPEAKER_01: It it actually is.
• 21:55
  SPEAKER_01: It's like thirty eight point two millimeters per year.
• 21:59
  unknown: Okay.
• 22:00
  SPEAKER_01: Well, the moon is 384,000 kilometers from the Earth.
• 22:04
  SPEAKER_01: So when you put it in perspective, like it's not a lot, but then when you compound this with geologic time, that's one of the beauties of geology.
• 22:14
  SPEAKER_01: Or just like deep time in general, is holy cow, yeah, 38 millimeters a year adds up to a lot in the long run.
• 22:23
  SPEAKER_00: You know, that's right.
• 22:24
  SPEAKER_01: It just puts scale in perspective.
• 22:26
  SPEAKER_01: I love that.
• 22:28
  SPEAKER_00: Here's the question about the Earth-Moon distance, right?
• 22:31
  SPEAKER_00: There's a big question about the history of that distance because it's moving away now.
• 22:36
  SPEAKER_00: We know that really well.
• 22:37
  SPEAKER_00: If you back calculate, if you say, oh, the moon is moving away at you know, what is it, 3.8 centimeters per year?
• 22:44
  SPEAKER_01: 38.2, yep.
• 22:45
  SPEAKER_01: 38.
• 22:45
  SPEAKER_01: Millimeters per year.
• 22:46
  SPEAKER_00: 38.2 millimeters per year.
• 22:48
  SPEAKER_00: If it's moving away at that rate.
• 22:49
  SPEAKER_00: Now, let's backcalculate.
• 22:51
  SPEAKER_00: Let's go back in time, and how would that evolution have changed?
• 22:55
  SPEAKER_00: So if you take that rate and you just go backwards in time, it would mean that the moon was literally at the Earth's surface 1.5 billion years ago.
• 23:04
  SPEAKER_00: That's the rate here.
• 23:06
  SPEAKER_00: And so we know geologically that cannot be true.
• 23:09
  SPEAKER_00: We know that the moon was not right next to the earth one and a half billion years ago.
• 23:15
  SPEAKER_00: So we know that this rate is not constant.
• 23:17
  SPEAKER_00: Like, you know, the moon didn't form and then just start migrating away from Earth.
• 23:20
  SPEAKER_00: We know that this rate has been changing since the moon formed 4.4 billion years ago.
• 23:25
  SPEAKER_00: The question is how much?
• 23:26
  SPEAKER_00: And you know, this is a pretty active research area.
• 23:29
  SPEAKER_00: There's some pretty good ideas that about two and a half billion years ago, the moon was about three-quarters of the distance it is today.
• 23:39
  SPEAKER_00: So that rate has changed over time, and maybe it maybe it kind of goes in and out a little bit, or it has been slowing or speeding up its rate of leaving Earth or moving away from Earth.
• 23:51
  SPEAKER_00: But we have to go back in time and put these like points in time to say what was the Earth-Moon distance back in time.
• 23:57
  SPEAKER_00: The oldest one we have, the oldest reliable measurement is about 2.3, 2.5 billion years ago, and the uncertainties on that three-quarter of the distance is pretty large.
• 24:05
  SPEAKER_00: So we still don't know a lot really far back in time.
• 24:09
  SPEAKER_01: But we also know that as the moon recedes or retreats from Earth, it's removing energy from the earth and it slows the rotation by 2.3 milliseconds per century.
• 24:24
  SPEAKER_01: So that seems like a ridiculously small amount.
• 24:29
  SPEAKER_01: But what that means is if you go back to the age of the dinosaurs, that uh we were actually rotating faster then than we are today.
• 24:38
  SPEAKER_01: And so our days were on the order of maybe 22 hours per day.
• 24:44
  SPEAKER_01: So we had more days per year.
• 24:48
  SPEAKER_01: This will continue, the moon will continue to remove energy as it recedes away from Earth until it slows Earth's rotation down enough where we're also tidally locked with the moon.
• 24:59
  SPEAKER_01: So the if you were on the moon, you would always see the same side of the earth, like how we see the same side of the moon.
• 25:07
  SPEAKER_01: And that'll happen.
• 25:08
  SPEAKER_01: You know, there's a ton of variability in this, of course, because it may not be the same as as time goes on.
• 25:14
  SPEAKER_01: In about 50 billion years, we'll be tidally locked.
• 25:17
  SPEAKER_01: We will orbit each other once every 47 days.
• 25:21
  SPEAKER_01: So we have a little ways.
• 25:23
  SPEAKER_00: Little ways.
• 25:23
  SPEAKER_00: 50 billion years, that's you know, what is that?
• 25:26
  SPEAKER_00: 10 times the lifetime of the solar system at the moment.
• 25:29
  SPEAKER_00: So that's a ways in the future.
• 25:31
  SPEAKER_00: Well, so this is such an interesting question.
• 25:33
  SPEAKER_00: Um, great question, Valeria.
• 25:35
  SPEAKER_00: This is such an interesting your topic.
• 25:37
  SPEAKER_00: How did the moon form?
• 25:38
  SPEAKER_00: What's the relationship to it?
• 25:39
  SPEAKER_00: Both from the present day, like you know, why is the moon moving away from us and what's the future of that?
• 25:45
  SPEAKER_00: And what was it back in time?
• 25:46
  SPEAKER_00: But and how did the moon form?
• 25:47
  SPEAKER_00: Very interesting questions.
• 25:49
  SPEAKER_00: Chris, one last one to wrap up here.
• 25:51
  SPEAKER_00: This is a question from Chelsea.
• 25:53
  SPEAKER_00: And uh Chelsea says that I just learned about a place called Rainbow Mountain in Peru and would love to hear a podcast about it.
• 25:59
  SPEAKER_00: So we had to do some looking.
• 26:01
  SPEAKER_00: I've I actually have seen pictures of this now that I looked it up, right?
• 26:04
  SPEAKER_00: What Rainbow Mountain in Peru.
• 26:06
  SPEAKER_00: It's also known as Vinicunca, and it's a place in Peru that is quite a popular tourist destination, actually, and very it seems Instagrammable, perhaps.
• 26:18
  SPEAKER_01: Uh absolutely.
• 26:20
  SPEAKER_01: Look, if you haven't ever seen this, then stop, push, pause, and Google image it.
• 26:26
  SPEAKER_01: It is so unbelievably beautifully colored.
• 26:30
  SPEAKER_01: Um, yeah, they're like, I don't know, is it's like six or seven different vibrant colors, okay?
• 26:36
  SPEAKER_01: And it's all sedimentary rocks.
• 26:38
  SPEAKER_01: Isn't there a place in China that has this too, Jesse?
• 26:42
  SPEAKER_00: Yeah, yeah, I think so.
• 26:43
  SPEAKER_00: These things are not uncommon.
• 26:45
  SPEAKER_00: Chris, you and I, we've actually collected rocks like this in the Black Hills of South Dakota.
• 26:50
  SPEAKER_00: I mean, it's not quite the same scale.
• 26:52
  SPEAKER_00: The unk Papa sandstone, which you and I love collecting, famous for its uh you know, housing rattlesnakes in the area that we were looking for.
• 27:01
  SPEAKER_00: But these are sedimentary layers that in the in the unk Papa sandstone in the Black Hills, South Dakota, they're really finely layered.
• 27:08
  SPEAKER_00: So they're like a centimeter, a millimeter scale layering of these same colors: pinks, purples, lavenders, whites, like really, really beautiful colors in sedimentary rocks.
• 27:18
  SPEAKER_00: This rainbow mountain or Vinicunka is that except expanded.
• 27:22
  SPEAKER_00: The layers are meters, tens of meters, and the rocks are tilted, so they're kind of striped along the mountainside.
• 27:29
  SPEAKER_00: And what forms this coloring?
• 27:32
  SPEAKER_00: This in general, coloration in sedimentary rocks are not uncommon.
• 27:36
  SPEAKER_01: Right.
• 27:36
  SPEAKER_01: So you have really you have pink, purple, and really vibrant red, which are like most of these rocks are clays and carbonates, there is a mixture of them, but they've been oxidized with like iron oxidized, various degrees of iron oxidation that turned those rocks those vibrant colors.
• 28:01
  SPEAKER_01: Then you also have in the mix of all this, you have these bright white colors.
• 28:06
  SPEAKER_01: And what usually happens when you have white colors?
• 28:09
  SPEAKER_01: Like what is the white?
• 28:10
  SPEAKER_00: The white is usually just a really clean quartz sandstone.
• 28:13
  SPEAKER_00: So quartz is usually kind of whitish.
• 28:16
  SPEAKER_00: And uh, if you just have a whole bunch of it, it's hard to chemically alter quartz.
• 28:21
  SPEAKER_00: And so you can't really rust quartz, you can't really oxidize it or reduce it, and so quartz just remains this white color.
• 28:27
  SPEAKER_00: So that's usually the white layers.
• 28:28
  SPEAKER_00: You also have green layers in here, which are really stunning.
• 28:30
  SPEAKER_00: And those are iron-rich sediments that have the same kind of clay minerals in them that you were talking about, but this iron is reduced, it's in a reduced form.
• 28:38
  SPEAKER_00: So it's not oxidized, it doesn't have more oxygen attached to it.
• 28:43
  SPEAKER_00: It just means that the iron is usually forms a green mineral, um, or greenish minerals, has a greenish hue.
• 28:50
  SPEAKER_01: So, yeah, the irons can't combine with oxygen to form a various like form of rust.
• 28:55
  SPEAKER_01: Instead, it forms with silicates to form some of these really common minerals that have this greenish hue.
• 29:02
  SPEAKER_01: Like you said, too.
• 29:03
  SPEAKER_01: I love, love the green.
• 29:05
  SPEAKER_01: I think the green is probably my favorite color of all of them.
• 29:08
  SPEAKER_01: And then you have these the bright, bright yellows.
• 29:12
  SPEAKER_01: So the yellows usually indicate that there are minerals in that rock that have sulfur-bearing minerals, so they form what we call in in mineralogy a sulfide, and it turns them like this just bright, bright yellow color.
• 29:28
  SPEAKER_01: So there we have that, Jesse, but we still haven't gotten to what they look like.
• 29:33
  SPEAKER_01: So imagine these vertically stacked layers, they're all flat, right?
• 29:37
  SPEAKER_01: When did the colors happen?
• 29:39
  SPEAKER_01: When did they turn the colors that they turned?
• 29:42
  SPEAKER_00: Well, it's a combination of both during deposition.
• 29:44
  SPEAKER_00: So think of the reduced ones.
• 29:46
  SPEAKER_00: In order to have reduced sediments, usually you have to have an environment that is a reduced environment, bottom of a lake or a bottom of a water where oxygen can't get down to the bottom layer and oxygen isn't percolating through the water to get there.
• 30:01
  SPEAKER_00: The reddish ones, the rusted ones, those are usually surface depositions.
• 30:04
  SPEAKER_00: So these are ones that expose to the atmosphere.
• 30:07
  SPEAKER_00: These are sediments in stream beds or coastal plains.
• 30:10
  SPEAKER_00: And so some of these colors, most of them are probably formed during deposition.
• 30:15
  SPEAKER_00: There are some of these minerals that we've talked about that will be formed after deposition, during this diagenesis process, the forming of the rock itself.
• 30:24
  SPEAKER_00: So taking a loose sediment and making it into a rock, there's a lot of fluids around, you're forming new minerals.
• 30:30
  SPEAKER_00: So some of them, like the sulfur-bearing ones, like lemonite, which is uh an iron hydroxide, those can form during this lithification or diagenesis process, making the sediment into a rock.
• 30:42
  SPEAKER_00: So a combination of both.
• 30:44
  SPEAKER_01: But you don't get the striping with where we're at right now.
• 30:49
  SPEAKER_01: We have flat sedimentary rocks in this area.
• 30:51
  SPEAKER_01: If you haven't Googled image it, do it.
• 30:53
  SPEAKER_01: It's beautifully striped with these vibrant colors.
• 30:56
  SPEAKER_01: So, how do you get this striping that shows up in areas like this?
• 31:01
  SPEAKER_00: Yeah, well, we need to take those flat rock layers, we need to turn them on our side.
• 31:04
  SPEAKER_00: And it's really just as simple as that.
• 31:06
  SPEAKER_00: In the Black Hills, where we've looked at the Unkpapa sandstone, most places it's pretty flat, but in some places it's tipped up, tipped up on edge.
• 31:12
  SPEAKER_00: And so you would see this striping pattern diving down into the ground.
• 31:16
  SPEAKER_00: This is just done at a much larger scale in Peru, where these sediments are tilted up and they sort of dive down this beautiful purple and pink and white and green striping is diving down into the mountainside.
• 31:30
  SPEAKER_00: It's just because those rock layers were tilted during the formation of the mountain range.
• 31:34
  SPEAKER_00: And these things are in uh Peruvian mountains, and so that makes sense that the rocks are folded and tipped up.
• 31:41
  SPEAKER_01: Coming back to plate tectonics, once again, the world revolves around plate tectonics, doesn't it?
• 31:47
  SPEAKER_00: Uh it makes it that makes the world interesting.
• 31:49
  SPEAKER_00: That is absolutely true.
• 31:51
  SPEAKER_00: So, Chelsea, great question.
• 31:53
  SPEAKER_00: Very cool area.
• 31:54
  SPEAKER_00: Uh, hopefully you've been there.
• 31:55
  SPEAKER_00: That would be really cool.
• 31:56
  SPEAKER_00: I I have not, I would say, but um maybe we put it on the bucket list, Chris.
• 32:01
  SPEAKER_00: Beautiful striped sedimentary rocks.
• 32:05
  SPEAKER_00: That's right.
• 32:06
  SPEAKER_00: Let's go.
• 32:06
  SPEAKER_00: Very cool.
• 32:07
  SPEAKER_00: All right.
• 32:07
  SPEAKER_00: Hey, thanks for the questions.
• 32:08
  SPEAKER_00: Natalie, Valeria, and Chelsea.
• 32:10
  SPEAKER_00: We really appreciate those.
• 32:11
  SPEAKER_00: Keep reaching out.
• 32:12
  SPEAKER_00: We love questions, and uh stay tuned.
• 32:14
  SPEAKER_00: We've got some really great episodes coming up in the next few weeks.
• 32:17
  SPEAKER_00: That's right.
• 32:18
  SPEAKER_00: Cheers.
• 32:18
  SPEAKER_00: Take care.