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Why Continents Exist: Bowen's Reaction Series · 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.
• 0:30
  SPEAKER_00: Okay.
• 0:31
  SPEAKER_00: Let's do it.
• 0:32
  SPEAKER_00: Let's do it.
• 0:33
  SPEAKER_00: You excited?
• 0:34
  SPEAKER_00: I am excited.
• 0:35
  SPEAKER_00: How about you?
• 0:36
  SPEAKER_01: Yeah, let's do it.
• 0:37
  SPEAKER_00: This is a fun one.
• 0:38
  SPEAKER_00: I mean, they're all fun, but this is uh particularly near and dear to our hearts, right?
• 0:43
  SPEAKER_00: So, Chris, why do we have continents on Earth?
• 0:47
  SPEAKER_00: Why do we have why do we have continents?
• 0:49
  SPEAKER_00: Did you just ask that question?
• 0:51
  SPEAKER_00: Why do we have continents?
• 0:52
  SPEAKER_01: I mean, it's kind of an interesting question, right?
• 0:55
  SPEAKER_01: Well, yeah, it actually is.
• 0:57
  SPEAKER_01: If you think about it, you know, you look at the other planets in the solar system, and you know, they don't have continents in the way that we do.
• 1:05
  SPEAKER_01: We have continents and we have oceanic crust, and they're vastly different, and that makes Earth kind of unique.
• 1:11
  SPEAKER_00: Yeah, that's right.
• 1:12
  SPEAKER_00: Very unique.
• 1:13
  SPEAKER_00: I mean, why we have continents is a is a sort of a complicated and and sort of multidimensional question.
• 1:18
  SPEAKER_00: But what we're talking about today is really the some of the details of why we have continents.
• 1:23
  SPEAKER_00: And it's just a cool story of how continents get made, they sort of get distilled from the interior of the earth, right?
• 1:30
  SPEAKER_00: So we're gonna get into this.
• 1:31
  SPEAKER_00: And so what are we focusing on today?
• 1:34
  SPEAKER_01: So we're gonna focus on what's called Bowen's reaction series.
• 1:37
  SPEAKER_01: And so in geology, this is you take an intro-level geology class, and you're going to be exposed to to this thing called Bowen's Reaction Series.
• 1:47
  SPEAKER_01: And it's one of my favorite things to teach because you know what this is all about makes a ton of geology make sense.
• 1:55
  SPEAKER_01: You know, what we see around us, the core of mountain chains and so on.
• 2:00
  SPEAKER_01: It there's just so much that can be explained using this phenomenon.
• 2:04
  SPEAKER_01: But before we do that, let's uh do some introductions.
• 2:08
  SPEAKER_00: Yeah.
• 2:08
  SPEAKER_00: So no, you start, man.
• 2:11
  SPEAKER_01: Age before beauty.
• 2:12
  SPEAKER_01: Yeah.
• 2:14
  SPEAKER_01: You are Dr.
• 2:15
  SPEAKER_01: Jesse Rymink.
• 2:16
  SPEAKER_01: You are one of my former students back back in the day uh from Hudsonville, Michigan.
• 2:22
  SPEAKER_01: And uh you went on to get your PhD in geology and now work as a professor of geoscience at Penn State University.
• 2:30
  SPEAKER_00: Yeah, that's right.
• 2:31
  SPEAKER_00: And you're Chris Boyce, as you said, my former teacher.
• 2:34
  SPEAKER_00: You you are a high school teacher in Michigan, you are a nationally recognized earth science teacher, you teach geology, you teach earth science at the ninth grade level, you teach astronomy classes, you teach field courses, and yeah, I learned the basics, and I remember you teaching me about Bowen's reaction series in class.
• 2:52
  SPEAKER_00: That's right.
• 2:52
  SPEAKER_00: Uh, you know, and it's hung with me ever since.
• 2:54
  SPEAKER_00: So today we get the pleasure on Planet Geo of going into Bowen's Reaction Series, which is near and dear to my heart as well, because it's, you know, in the heart of some of my research interests.
• 3:04
  SPEAKER_01: So back when you were doing your postdoc at the Carnegie Institute, Jenny and I actually came out to visit you and you showed us around the campus there, and uh you took me into this room that had one of the vessels that these experiments were conducted in, one of Bowen's actual reactors or vessel, I guess.
• 3:24
  SPEAKER_01: That was really, really cool for me to see.
• 3:27
  SPEAKER_00: Bowen's reaction series is named for Norman Bowen, this guy who did these experiments back in the day.
• 3:33
  SPEAKER_00: And what he did was really cool.
• 3:34
  SPEAKER_00: We're gonna get into some details of what the experiments are, but he's basically forming rocks in his lab, and so they have these sort of tabletop-sized vessels that would get to really high temperature and would melt rocks.
• 3:46
  SPEAKER_00: And so I was amazed when I showed up and that they were actually right there, right?
• 3:50
  SPEAKER_00: Like the vessels that were used is super cool.
• 3:53
  SPEAKER_00: When I walked in and saw it, it was almost like there was a halo, like this, this you know, like I never thought in my entire life I'm actually gonna see one of these things because it's uh it's almost like the holy grail of and you know, the other thing that's interesting is you know, my my friends and colleagues, many of them worked in that lab, and you know, that lab was also a mess.
• 4:13
  SPEAKER_00: You would think of a scientific lab, right, as being like this really clean, uh, you know, very organized place.
• 4:19
  SPEAKER_00: No, every science lab I've ever been in is a complete disaster, and this was no different.
• 4:23
  SPEAKER_01: So, again, just finishing off what you started talking about with what he actually did.
• 4:28
  SPEAKER_01: So we'll run this down in greater detail.
• 4:30
  SPEAKER_01: But basically, he took rocks and ground them down to a powder, put them in these vessels, heated them up to the point where they were completely molten.
• 4:40
  SPEAKER_01: So he created this the a lava and then cooled this liquid off, and he did this at various stages where he would he'd cool it off to a certain temperature and then quench it in water to stop the reaction, and then he would, you know, re-melt it and and cool it back down at to a different cooler temperature and then quench it in water.
• 5:00
  SPEAKER_01: And so he did this at various stages.
• 5:02
  SPEAKER_00: I mean, it's really what we call cook and look, which is really just cook the rock, look what's inside, see what's happening.
• 5:09
  SPEAKER_00: And this is a way to look at magmas in the lab.
• 5:12
  SPEAKER_00: He's really generating magma and then looking at it in the lab, and you're quenching it to kind of get this window into what the high temperatures look like.
• 5:19
  SPEAKER_00: And the temperatures we're dealing with are like 1300 degrees centigrade, where most rocks will be totally melted by that point, down to about 600 or 700 degrees centigrade, which most rocks will be fully crystallized at that temperature.
• 5:32
  SPEAKER_00: So these are the temperatures we're kind of dealing with.
• 5:34
  SPEAKER_01: All right, so let's go ahead then and uh transition to what did he see?
• 5:40
  SPEAKER_00: What these experiments show is that minerals form at different temperatures, and different minerals form at different temperatures.
• 5:50
  SPEAKER_00: So remember that rocks are made up of a bunch of different minerals.
• 5:54
  SPEAKER_00: Each of those minerals are made up of a bunch of different elements, and the elements combined in different proportions bond in such a way that they form a unique chemical structure that makes different minerals.
• 6:05
  SPEAKER_00: So elements make up minerals, minerals make up rocks.
• 6:08
  SPEAKER_00: And so what what these experiments were doing was sort of looking at which minerals occurred at which temperatures in a magma.
• 6:17
  SPEAKER_01: The minerals that we're talking about are what we call in geology the silicate minerals, minerals like olivine, horn blend, biotite, muscovite, quartz, and potassium feldspar.
• 6:30
  SPEAKER_00: Yeah, and and really to kind of bring it back to the elements that make up the minerals that then make up the rock, the dark minerals usually have a lot of iron and magnesium in them.
• 6:40
  SPEAKER_00: They all have silica, back to the term silicates.
• 6:42
  SPEAKER_00: They all have a lot of silica in them, they have a lot of oxygen in them, but they vary in the proportions of these things.
• 6:49
  SPEAKER_00: So many of them have iron, magnesium, aluminum, silica, potassium, oxygen, but the proportions of those elements really change which minerals are forming, right?
• 7:00
  SPEAKER_00: So olivine has a lot of iron, a lot of magnesium, not a lot of silica, although it has some, whereas quartz is all silica, no iron and magnesium.
• 7:08
  SPEAKER_00: So when you look at the minerals in a granite countertop, the darker minerals typically have a lot of iron and magnesium.
• 7:15
  SPEAKER_00: The lighter colored ones typically don't have much iron and magnesium in them.
• 7:18
  SPEAKER_00: That's kind of a general rule of thumb.
• 7:20
  SPEAKER_01: And another thing to think about too, when you look at those minerals, and you don't have to like point at them and know what they are, but when you look at the different colors in a granite countertop, for instance, or just in a chunk of granite sitting in front of you, each one of those minerals has their own melting point.
• 7:36
  SPEAKER_01: So what I'm trying to say is that when rock doesn't have a sp a set melting point, the temperature at which it turns into lava, the minerals within that rock have their own melting points.
• 7:50
  SPEAKER_00: Right.
• 7:50
  SPEAKER_00: And that right there is the key to Bowen's reaction series.
• 7:54
  SPEAKER_00: He deciphered if you work from high temperature to low temperature, those different minerals that we went through olivine, pyroxene, amphibole, biotite, plagioclase, potassium, feldspar, those minerals they all have a different stability range.
• 8:08
  SPEAKER_00: They are all formed at different temperature ranges as you go from 1300 degrees centigrade when almost all the rock is melted, to 700 degrees centigrade when almost all the rock is solid.
• 8:20
  SPEAKER_00: Those minerals that I listed, those all crystallize at different temperature steps, and that's a really consistent phenomenon.
• 8:27
  SPEAKER_00: So if you take a rock and heat it up, certain minerals will start to melt because they become unstable.
• 8:33
  SPEAKER_00: If you take a magma and cool it down, certain minerals will start to form because they become stable at higher temperature than other ones.
• 8:40
  SPEAKER_00: So this is really what the process is.
• 8:42
  SPEAKER_00: So, Chris, what with a little quiz?
• 8:44
  SPEAKER_00: What is the series in Bowen's reaction series?
• 8:47
  SPEAKER_00: What's the order of crystallization from high temperature to low temperature?
• 8:50
  SPEAKER_00: Okay.
• 8:51
  SPEAKER_01: So you need to think of this, envision a Y.
• 8:55
  SPEAKER_01: Okay, got a Y.
• 8:57
  SPEAKER_01: At the top of the Y represents high temperature.
• 9:00
  SPEAKER_01: And as you go down to where they intersect and it forms then the bottom of the Y, that represents low temperature.
• 9:08
  SPEAKER_01: Okay, got it.
• 9:09
  SPEAKER_00: Come with you.
• 9:10
  SPEAKER_01: So, all right, the minerals that we're talking about are the common, what we call in geology, the silicate minerals, uh, minerals like olivine.
• 9:19
  SPEAKER_01: And olivine uh is, you know, it tends to be this olive green color, various shades, you know, light green or dark green, but it's called olivine because of its color.
• 9:28
  SPEAKER_01: Um, then there's a mineral called pyroxine, and then you get into minerals that more people have heard about, minerals like uh the amphiboles, which the most common mineral in that group is is hornblend, biotite, muscovite, quartz, and uh potassium feldspar.
• 9:47
  SPEAKER_01: If you look at it like a granite countertop, or you know, everybody has seen granite before, and you look in granite, those are the minerals that you're gonna see.
• 9:55
  SPEAKER_01: Now, typically, you're gonna see obviously the quartzes, um, they tend to be, you know, white or shades of gray in a in a granite.
• 10:04
  SPEAKER_01: That's pretty typical.
• 10:06
  SPEAKER_01: The pink color in a granite that's common usually comes from the potassium feldspar in there, and then you get these like flat flecks of black mineral, like horn blend and biotite.
• 10:17
  SPEAKER_01: Those are the two common minerals that we see in a granite.
• 10:20
  SPEAKER_01: Okay, so go to one side of the Y.
• 10:23
  SPEAKER_01: Let's say the left.
• 10:24
  SPEAKER_00: Left side.
• 10:25
  SPEAKER_00: Okay, I'm at the top of the left side of the Y.
• 10:27
  SPEAKER_01: Okay.
• 10:28
  SPEAKER_01: The left side is the we're what we're gonna call the discontinuous series of Bowen's reaction series.
• 10:34
  SPEAKER_01: Okay, and it's where you go from one mineral to another as it cools off.
• 10:38
  SPEAKER_01: So as we work from top down on the Y on the left side of it, you go from olivine to pyrixine to amphibole, which the most common mineral there is horn blend, to biotite mica.
• 10:53
  SPEAKER_00: And this is going from high temperature to low temperature, is that right?
• 10:56
  SPEAKER_00: From on the left side of the Y.
• 10:57
  SPEAKER_01: That's going from high temperature to low temperature.
• 10:59
  SPEAKER_01: Okay.
• 11:00
  SPEAKER_01: That's the discontinuous series because it changes from one mineral to another.
• 11:04
  SPEAKER_00: And that means that olivine is only stable at high temperature, and pyroxene is stable at slightly less high temperature, amphibole, lower temperature, etc.
• 11:14
  SPEAKER_00: These are stability bands.
• 11:15
  SPEAKER_00: We're the minerals where the particular blend of elements that make up that mineral structure, where it's stable, meaning it's in a solid form, it's not a liquid.
• 11:25
  SPEAKER_01: Yep.
• 11:25
  SPEAKER_01: You go to the other side of the Y, okay, the top, the right side.
• 11:30
  SPEAKER_01: Now that's called the continuous series, and it's continuous because it's one mineral, but the mineral is changing composition as it cools off.
• 11:38
  SPEAKER_01: So that's the plagioclase feldspar side of the reaction.
• 11:42
  SPEAKER_01: And it changes from calcium-rich plagioclase down to as it cools off, it changes to sodium rich.
• 11:49
  SPEAKER_01: Now, if you think about this, the I guess the way that I see this is kind of like building a brick wall.
• 11:56
  SPEAKER_01: Okay.
• 11:57
  SPEAKER_00: All right, an analogy here.
• 11:58
  SPEAKER_00: Let's see if it's a good one.
• 11:59
  SPEAKER_00: Yep.
• 12:00
  SPEAKER_01: Analogy time.
• 12:01
  SPEAKER_01: If you build a brick wall and you start with white cinder blocks, let's say.
• 12:07
  SPEAKER_01: Okay, you just start building the wall.
• 12:10
  SPEAKER_01: And the white cinder blocks represent then the calcium-rich plagioclase felds bar.
• 12:16
  SPEAKER_01: As it cools off, though, sodium, the element sodium replaces calcium in the plagiuclase feldspar.
• 12:25
  SPEAKER_01: So uh if you're building this wall out of white cinder blocks, what I'm saying is you have to take now a block that is a different color, let's say red, and you take the a white block out and put a red block in, and then put the white block somewhere else on the wall.
• 12:42
  SPEAKER_01: Okay, so it's changing its chemical composition as it cools off.
• 12:47
  SPEAKER_01: In the end, you're gonna end up with a wall that's red and white, but it didn't start out that way.
• 12:54
  SPEAKER_01: It started out as all white, and then the red kind of transitioned in the higher you built the wall.
• 13:00
  SPEAKER_00: Right, exactly.
• 13:01
  SPEAKER_00: And so this in the red bricks in this analogy, that was a great analogy, by the way, Chris.
• 13:05
  SPEAKER_00: When you put a red brick in there, it changes the thermodynamic properties of the wall so that at high temperature you might have less red bricks, and at low temperature, you might need more red bricks for it to be stable.
• 13:17
  SPEAKER_00: So this is why this continuous reaction series exists, is because plugging in different bricks changes the structure, the sti changes the stability of the mineral structure or the thermodynamic properties of that structure.
• 13:29
  SPEAKER_01: Right.
• 13:30
  SPEAKER_01: So it's called the continuous series because it's changing the composition, but it's still the same mineral.
• 13:36
  SPEAKER_01: It's plagioclase feldspar.
• 13:38
  SPEAKER_01: Okay.
• 13:38
  SPEAKER_01: So now then we're at the stem of the Y.
• 13:42
  SPEAKER_01: Okay.
• 13:42
  SPEAKER_01: Where the where they meet.
• 13:43
  SPEAKER_01: Yep, right at the junction.
• 13:45
  SPEAKER_01: Okay, now we get into the low temperature minerals, and the minerals we're talking about are minerals that I think are familiar to almost everyone: quartz, potassium feldspar, and muscovite.
• 13:55
  SPEAKER_01: Okay.
• 13:56
  SPEAKER_01: Muscovite is this transparent mineral that peels into sheets like uh almost like paper.
• 14:03
  SPEAKER_01: Right.
• 14:03
  SPEAKER_01: Okay, and biotite is just like that.
• 14:05
  SPEAKER_01: Biotite's on the discontinuous side of the reaction.
• 14:08
  SPEAKER_01: Biotite is just like that, peels into thin sheets, but it tends to be black.
• 14:13
  SPEAKER_01: So biotite is black, rich in iron and magnesium.
• 14:17
  SPEAKER_01: Muscovite doesn't have much iron and magnesium in it.
• 14:20
  SPEAKER_01: It's clear, transparent in color.
• 14:22
  SPEAKER_00: So right.
• 14:23
  SPEAKER_00: And so let's kind of step back now.
• 14:25
  SPEAKER_00: So this is the reaction.
• 14:26
  SPEAKER_00: So Bowen, the people doing these experiments, melting rocks, cooling them down, quenching them, looking at them, they saw this reaction series.
• 14:34
  SPEAKER_00: They saw with temperature, different minerals are forming and different minerals are actually being redissolved as well.
• 14:40
  SPEAKER_00: So what's the point?
• 14:41
  SPEAKER_00: Why does this matter?
• 14:42
  SPEAKER_01: Yeah, this is all right.
• 14:44
  SPEAKER_01: Let's get into this because you know, let's this is the good part about it, right?
• 14:47
  SPEAKER_00: Yeah, exactly.
• 14:48
  SPEAKER_00: How do we see this represented on the surface of the earth?
• 14:50
  SPEAKER_01: Yeah, what this really gives us is an order of crystallization.
• 14:56
  SPEAKER_01: Okay, the order in which minerals crystallize out of a magma.
• 15:00
  SPEAKER_01: Now, what happens then is as these minerals crystallize out, it can change the it changes the composition of the remaining liquid, of the remaining magma.
• 15:10
  SPEAKER_01: Okay, so it gives us this order.
• 15:11
  SPEAKER_01: But you know what?
• 15:12
  SPEAKER_01: Equally as important, it gives us the order in which minerals melt, which explains a ton.
• 15:18
  SPEAKER_00: Let me back up here because this is a little bit of a complicated topic, and it gets to our distillation point at the beginning, which is let's take this magma.
• 15:27
  SPEAKER_00: The magma is at high temperature, 1300 degrees C, it's all melted.
• 15:32
  SPEAKER_00: You drop it down a little bit, olivine starts to crystallize.
• 15:35
  SPEAKER_00: So olivine mineral grains are forming and they're sitting in this magma.
• 15:39
  SPEAKER_00: Now, olivine, the mineral, the mineral grain, is actually more dense than the magma.
• 15:44
  SPEAKER_00: So it can settle out, it can drop out and fall to the bottom of the magma chamber.
• 15:50
  SPEAKER_00: What does that do?
• 15:51
  SPEAKER_00: Well, that changes the composition of the rest of the liquid that's left behind, the rest of the magma, because iron and magnesium occur in high proportion in olivine.
• 16:00
  SPEAKER_00: So olivine is removing a lot of magnesium and a lot of iron from the magma chamber, which means that the rest of the magma left behind has to be higher in proportion in the other elements.
• 16:12
  SPEAKER_00: It is depleted in magnesium and iron relative to everything else.
• 16:15
  SPEAKER_00: So this is the distillation step.
• 16:18
  SPEAKER_00: This is the enrichment in the earth of silica, aluminum, potassium, things that occur in the low temperature minerals that you just described at the bottom of this Y, below the junction, at the main post of the Y, those low temperature minerals are enriched in the earth at the surface because they are stable at lower temperatures.
• 16:42
  SPEAKER_00: And Bowen's reaction series explains this perfectly.
• 16:45
  SPEAKER_00: Yeah, but why is that important?
• 16:47
  SPEAKER_00: It's important because those low temperature minerals, those ones that are rich in silica, aluminum, sodium, potassium, those minerals are less dense, and so they kind of quote unquote float.
• 16:59
  SPEAKER_00: They float the continents above the mantle.
• 17:02
  SPEAKER_00: So the continents are above sea level in part because they are much less dense than the rest of the earth, and they're less dense because Bowen's reaction series has differentiated, has has distilled these elements from the rest of the earth via this process that we're talking about.
• 17:21
  SPEAKER_00: So the reason we have continents is because Bowen's reaction series is a property of how magmas cool down on Earth.
• 17:30
  SPEAKER_01: Okay.
• 17:31
  SPEAKER_01: So applications.
• 17:33
  SPEAKER_01: What do we see?
• 17:34
  SPEAKER_01: What does this make help make sense of?
• 17:36
  SPEAKER_01: Let's look we've talked a lot on this podcast about Yellowstone.
• 17:40
  SPEAKER_01: Okay.
• 17:40
  SPEAKER_01: Yellowstone is a hot spot.
• 17:42
  SPEAKER_01: There's a hot spot underneath continental crust.
• 17:45
  SPEAKER_01: So you have this body of super, super hot rock and some magma in there, and we talked about what a magma chamber looks like in a previous episode.
• 17:54
  SPEAKER_01: But what happens then is it's sitting in continental crust and it's melting some of those rocks that it's sitting in, right?
• 18:05
  SPEAKER_01: But what minerals is the magma gonna melt preferentially?
• 18:09
  SPEAKER_00: Right.
• 18:10
  SPEAKER_00: So this is a key point that Bowen's reaction series works the opposite direction as well.
• 18:16
  SPEAKER_00: So if you take that Y and you flip it upside down, now we're going from top to bottom, now we're going from low temperature to high temperature, we are heating things up.
• 18:25
  SPEAKER_00: And as we heat things up, we do not melt all the minerals in each rock at the same proportion at the same time.
• 18:32
  SPEAKER_00: We melt specific minerals at lower temperature, and it takes more temperature to melt the other minerals.
• 18:38
  SPEAKER_00: So what this means is you get quartz and feldspar and muscovite, those melt first.
• 18:44
  SPEAKER_00: Those minerals that are at the base of that Y, they melt first.
• 18:47
  SPEAKER_01: And that's really important because, first of all, you have a lot of quartz and a lot of feldspar and a lot of mica in continental crust.
• 18:54
  SPEAKER_01: So this hotspot is preferentially melting those and changing the composition of the hotspot itself.
• 19:02
  SPEAKER_01: But those minerals that have now melted, that liquid is less dense.
• 19:07
  SPEAKER_01: It floats, it's like a buoy.
• 19:09
  SPEAKER_01: It floats to the top of the chamber.
• 19:10
  SPEAKER_01: Okay.
• 19:11
  SPEAKER_01: Now that's why Yellowstone behaves the way it behaves, because it's made up of a predominance of really low temperature, what we call felsic minerals, light colored minerals.
• 19:23
  SPEAKER_01: And those minerals have a very high viscosity.
• 19:26
  SPEAKER_01: In other words, the magma is sticky, it's thick, it's gooey.
• 19:31
  SPEAKER_01: And that kind of magma is the recipe for violent volcanic eruptions.
• 19:37
  SPEAKER_01: Now, the other famous hotspot, there are more, but another famous hotspot is Hawaii.
• 19:42
  SPEAKER_01: But this hotspot sits within or below, but the magma chambers are within oceanic crust.
• 19:49
  SPEAKER_01: Now, Jesse, oceanic crust, what's the deal with that?
• 19:52
  SPEAKER_01: What what's the difference?
• 19:54
  SPEAKER_00: Much more iron and magnesium, much less silica, so it's much thinner and much more dense.
• 20:00
  SPEAKER_01: So these minerals are getting incorporated into the magma that makes up the hotspot, right?
• 20:06
  SPEAKER_01: But the difference is because they're richer in iron and magnesium, it's less rich in silica.
• 20:13
  SPEAKER_01: That's what gets incorporated into the hotspot, into the magma chamber.
• 20:17
  SPEAKER_01: It's less sticky, it's less viscous.
• 20:20
  SPEAKER_01: And so it's runnier, more fluid.
• 20:23
  SPEAKER_01: And so those kinds of volcanic eruptions tend to be more frequent and they tend to be less violent because it's not as sticky and gooey and the kind of thing that you get with Yellowstone.
• 20:34
  SPEAKER_00: That's right.
• 20:34
  SPEAKER_00: So Bowen's reaction series explains everything from why we have continents to why certain types of volcanoes in certain locations have big explosive eruptions, and other types of volcanoes in other places have small, runny eruptions that can do damage, but don't do the globally catastrophic damage that a place like Yellowstone might.
• 20:53
  SPEAKER_00: Yes.
• 20:54
  SPEAKER_00: So this is the story of Bowen's reaction series, and it's a really fundamental principle of basically how the Earth works.
• 21:01
  SPEAKER_00: And Bowen's reactions, the vessels that we saw that they were using, Chris, these things are, you know, it's basically just taking this vessel that you can heat up to really high temperature, but that's at atmospheric pressure.
• 21:14
  SPEAKER_00: So they're doing these experiments at the pressure of the surface of the earth.
• 21:19
  SPEAKER_00: So one atmosphere, one bar of pressure.
• 21:22
  SPEAKER_00: That was back in the 20s or the the early 1900s.
• 21:26
  SPEAKER_00: That's what the techniques were capable of at that time.
• 21:29
  SPEAKER_00: Now we have, and we saw these things, Chris, we have these huge experimental contraptions really that can generate really, really high pressures.
• 21:38
  SPEAKER_00: And so in the lab, I don't do this work, but other people do.
• 21:42
  SPEAKER_00: In the lab, people can generate pressures that are equivalent to thousands of kilometers down deep in the earth.
• 21:49
  SPEAKER_00: That's crazy.
• 21:50
  SPEAKER_00: And so, with this like technological development of being able to generate pressure and temperature at the same time, we recognized that Bowen's reaction series was just based.
• 22:00
  SPEAKER_00: On temperature, so he was mapping out the the mineral stability based on temperature.
• 22:04
  SPEAKER_00: Pressure is an additional influence, and pressure changes some of these things a little bit and changes the composition of the mineral stable, but the general rules still apply.
• 22:13
  SPEAKER_00: And water, for instance, can change the composition.
• 22:15
  SPEAKER_00: So the quote unquote experimentalists, the people who melt rocks in the lab, have mapped out the way that Bowen's reaction series behaves or the way that minerals behave across a wide range of different control.
• 22:30
  SPEAKER_00: What am I trying to say here?
• 22:32
  SPEAKER_01: I don't know.
• 22:32
  SPEAKER_01: You're being a huge nerd right now.
• 22:34
  SPEAKER_01: Am I being too much?
• 22:36
  SPEAKER_01: Enormous Okay.
• 22:37
  SPEAKER_01: Enormous nerd.
• 22:38
  SPEAKER_01: Do I need to shut up?
• 22:39
  SPEAKER_01: I've lost people.
• 22:40
  unknown: I don't know.
• 22:40
  SPEAKER_01: I I'm sorry, I drifted off there for a little bit.
• 22:42
  SPEAKER_01: Um if you're falling, I mean if you're falling asleep, then Oh my gosh.
• 22:46
  SPEAKER_01: Okay, then I need to stop.
• 22:47
  SPEAKER_00: Um wow.
• 22:49
  SPEAKER_00: Yeah.
• 22:49
  SPEAKER_00: Well, anyways, all right, all right, all right, anyways, anyways.
• 22:52
  SPEAKER_00: All right, hold on.
• 22:52
  SPEAKER_00: I I want to take this in a different direction.
• 22:54
  SPEAKER_00: The only point I want to just wrap it up by saying that it's more complicated.
• 22:57
  SPEAKER_00: It is, yes.
• 22:58
  SPEAKER_00: There you go.
• 22:59
  SPEAKER_00: Wow.
• 23:00
  SPEAKER_00: Look at you go.
• 23:01
  SPEAKER_01: But the general rules apply.
• 23:03
  SPEAKER_00: Okay, I'll leave it.
• 23:04
  SPEAKER_01: Okay, wow.
• 23:04
  SPEAKER_01: Hey, it's more complicated.
• 23:06
  SPEAKER_01: Okay, guys.
• 23:06
  SPEAKER_01: That's what the takeaway is with this.
• 23:08
  SPEAKER_01: Yeah.
• 23:09
  SPEAKER_01: So listen.
• 23:10
  SPEAKER_01: Um how does Bowens then explain the most common rock in the world is basalt.
• 23:16
  SPEAKER_01: Yep.
• 23:17
  SPEAKER_01: Okay, because the basalt is what makes up the ocean.
• 23:20
  SPEAKER_00: This is the really dark colored rock, very fine grained, can't really see any mineral grains in it very easily.
• 23:25
  SPEAKER_01: Right.
• 23:25
  SPEAKER_01: So, how is oceanic floor, oceanic crust created?
• 23:28
  SPEAKER_01: Well, this happens at what are if you go back to our plate tectonics episode, and you know, we talk about spreading centers or these divergent boundaries.
• 23:36
  SPEAKER_01: And what happens is this part of the mantle rises up.
• 23:40
  SPEAKER_01: And to touch on what you just said, you know, the pressure aspect of this, as it rises up, it's super hot.
• 23:46
  SPEAKER_01: It's flowing like this really kind of not really a liquid, not really a solid kind of material.
• 23:52
  SPEAKER_01: But with a lower pressure, certain minerals melt, and that's where you take into account Bowens, right?
• 23:58
  SPEAKER_01: So the mantle is what we call ultra mafic.
• 24:01
  SPEAKER_01: It's super rich in iron and magnesium.
• 24:04
  SPEAKER_01: Okay.
• 24:04
  SPEAKER_01: But if you partially melt that, you're gonna generate then a magma that is a little bit more felsic than what you started with.
• 24:13
  SPEAKER_01: And so you generate then this mafic material which forms basalt, and that pours out you know at spreading centers at the bottom of oceans and so on.
• 24:22
  SPEAKER_00: So that's distillation step number one on Earth.
• 24:25
  SPEAKER_01: Right.
• 24:26
  SPEAKER_01: Yep.
• 24:26
  SPEAKER_01: So how do you get then another common rock is intermediate in composition?
• 24:31
  SPEAKER_01: In other words, it's not mafic, it's not felsic, it's not dark colored, it's not light colored, it's somewhere in between.
• 24:36
  SPEAKER_00: It's kind of the salt and pepper look to it.
• 24:39
  SPEAKER_00: Yeah.
• 24:40
  SPEAKER_01: Yeah.
• 24:40
  SPEAKER_01: And this is the the common, well, the extrusive version of it is called andesite.
• 24:45
  SPEAKER_01: Okay, this is what makes up most of what the Cascades are in the Pacific Northwest or the Andes Mountains in South America.
• 24:53
  SPEAKER_01: They're made up of andesite.
• 24:55
  SPEAKER_01: So how do you get andesite then?
• 24:58
  SPEAKER_01: How does this happen in the distillation process?
• 25:01
  SPEAKER_00: Yeah, so the distillation process here is again it's melting the mantle, but it's melting the mantle with water present.
• 25:07
  SPEAKER_00: So adding water into the mix, again, this comes back to it, it's more complicated.
• 25:11
  SPEAKER_00: When you add water into the mix, you can do a lot more melting.
• 25:14
  SPEAKER_00: A lot more melting leads to more distillation, and that column of magma now that's above the subduction zone, that column of magma gets distilled even further by Bowen's reaction series because things like olivine or amphibol or garnet in some places actually form at the deep roots underneath of those volcanoes, and those are removing more iron, removing more magnesium, that's increasing aluminum, increasing silica, increasing sodium in the magma that's left behind, the residual magma, and that's what's erupted out onto the surface.
• 25:46
  SPEAKER_00: Now, Chris, that's the intermediate composition.
• 25:49
  SPEAKER_00: Now, what about the other end member, the really felsic stuff, the stuff we think of as rhyolite, the really light-colored rocks, granite and rhyolite?
• 25:57
  SPEAKER_00: Where and how do those form?
• 25:59
  SPEAKER_01: So granite is what makes up continents.
• 26:03
  SPEAKER_01: Okay, and so this is what makes up the bedrock of most continental land masses.
• 26:09
  SPEAKER_01: They may be covered with sedimentary rocks and um the boring stuff coating on top of it.
• 26:14
  SPEAKER_01: But yeah, granite is what makes up the continental crust.
• 26:18
  SPEAKER_01: Okay.
• 26:19
  SPEAKER_01: So what setting geologically forms, distills it down to granite?
• 26:24
  SPEAKER_01: Give me the quick and dirty version.
• 26:26
  SPEAKER_00: The other contribution to Bowen, which is not really the reaction series, but it's related to it, is if we just think of the bottom part of the Y, granite is made of quartz and feldspar mainly.
• 26:36
  SPEAKER_00: A little bit of muskweight, a little bit of biotite, maybe.
• 26:38
  SPEAKER_00: But those minerals at the bottom of the Y, those melt at the lowest temperatures.
• 26:43
  SPEAKER_00: And no parts of the rock melt before those minerals melt.
• 26:46
  SPEAKER_00: So if you're going to heat up the crust, if you're gonna heat up the earth in some way, you're not gonna melt it until you get quartz and feldspar.
• 26:55
  SPEAKER_00: And once it does form quartz and feldspar, then you've melted it and then it starts to cool off and you can move that stuff up higher.
• 27:01
  SPEAKER_00: So basically, what this means is that anytime you heat up the crust, whether you're smashing two continents together and they're getting hot that way, or whether you are putting a big plume underneath of the continents and you're heating it up that way with extra heat from below, basically the melting that goes on, you form this granite material.
• 27:22
  SPEAKER_00: And so just melting the crust, you're always gonna form granite.
• 27:25
  SPEAKER_01: So then why does it all collect together?
• 27:28
  SPEAKER_01: Why do we have the continents then?
• 27:30
  SPEAKER_00: Because as soon as you get to, and it depends on which composition we're dealing with, but as soon as you get to a certain percent of melt in a system, so think of a rock, think picture your granite countertop.
• 27:41
  SPEAKER_00: If you heat that up to about 600 degrees centigrade, you're gonna get a little bit of melt to form.
• 27:46
  SPEAKER_00: The quartz and the felt spar are gonna start to form.
• 27:49
  SPEAKER_00: As soon as you get about 10% of that rock melted, round about 10, maybe 15%, then there's enough melt in there that it can kind of flow in the rock.
• 27:59
  SPEAKER_00: There's enough porosity and permeability that the melt can kind of aggregate together.
• 28:03
  SPEAKER_00: Before that, it's disconnected little blobs.
• 28:05
  SPEAKER_00: After that, it kind of, as you said, Chris, it's buoyant.
• 28:08
  SPEAKER_00: So it can kind of aggregate together and sort of move upwards vertically due to gravity.
• 28:13
  SPEAKER_01: That makes sense.
• 28:14
  SPEAKER_01: That makes sense.
• 28:14
  SPEAKER_01: Good job, Jesse.
• 28:15
  SPEAKER_01: I actually gonna give you some credit on that.
• 28:17
  SPEAKER_01: That was nice.
• 28:18
  SPEAKER_00: I'll take it when I can get it.
• 28:19
  SPEAKER_00: I don't get much of that around here, but I'll take it when I can get it.
• 28:21
  SPEAKER_00: All right, Chris, last point.
• 28:23
  SPEAKER_00: Owen's reaction series relates to weathering.
• 28:25
  SPEAKER_00: This is interesting in why.
• 28:27
  SPEAKER_01: Okay.
• 28:27
  SPEAKER_01: Minerals are stable.
• 28:29
  SPEAKER_01: They're most stable when they exist at under the conditions in which they form.
• 28:34
  SPEAKER_01: So olivine begins crystallizing at 1300 degrees Celsius.
• 28:39
  SPEAKER_01: That means that olivine then is most stable at that temperature and at the pressure in which it formed.
• 28:45
  SPEAKER_01: Well, now put olivine at the surface of the earth where it's 50 degrees out.
• 28:51
  SPEAKER_01: That's a long ways.
• 28:52
  SPEAKER_01: That's Fahrenheit.
• 28:53
  SPEAKER_01: That's a long ways away from 1300 degrees centigrade.
• 28:56
  SPEAKER_01: And that means then that olivine is the least stable because at the surface of the earth, it's existing in conditions that are a long way away from where it formed.
• 29:06
  SPEAKER_01: Quartz and Feldspar, they're much closer to the conditions in which it formed, 600 degrees Celsius.
• 29:14
  SPEAKER_01: That's closer to what exists at the surface.
• 29:16
  SPEAKER_01: So they're much more stable.
• 29:18
  SPEAKER_01: So Bowen's reaction series doesn't just give us an order in which minerals crystallize or melt.
• 29:23
  SPEAKER_01: It also gives us an order of stability.
• 29:27
  SPEAKER_01: You know, the top of the Y being the least stable, the bottom of the Y, cooler temperatures, more stable.
• 29:35
  SPEAKER_01: So yeah, that's kind of a cool thing, too.
• 29:37
  SPEAKER_00: Yeah, absolutely.
• 29:38
  SPEAKER_00: Very cool thing.
• 29:39
  SPEAKER_00: And then the field, uh the areas that I've done field work, you know, you can often see where the dark colored rocks, which have a lot of olivine and pyroxine in them, those things weather out really quickly.
• 29:48
  SPEAKER_00: So they form valleys.
• 29:49
  SPEAKER_00: And the ridges are the more felsic rocks, the ones with a lot of the light-colored minerals in them, quartz and feldsparth, because those are more resistant to weather.
• 29:57
  SPEAKER_01: Not only that, when you see basalt in the field, it's often covered with a rusty brown color.
• 30:03
  SPEAKER_01: It's oxidizing, it's chemical weathering, it's changing.
• 30:06
  SPEAKER_01: And that's very common.
• 30:07
  SPEAKER_01: That's why in the field, like if you want to get a good look at what basalt looks like, you need to take your rock hammer out, bust it in half, and get a fresh break, because then you're gonna see what the rock looks like on the inside because the outside of it is changing.
• 30:20
  SPEAKER_00: Yeah, and you usually got to fight through all that damn biology, too.
• 30:23
  SPEAKER_00: That's in the way.
• 30:24
  SPEAKER_00: I mean, stupid soil and dirt and freaking trees growing on it.
• 30:29
  SPEAKER_00: Oh my goodness.
• 30:30
  SPEAKER_00: Right on.
• 30:31
  SPEAKER_00: All right, man.
• 30:32
  SPEAKER_00: That is Bowen's reaction series.
• 30:35
  SPEAKER_00: All right.
• 30:35
  SPEAKER_00: I mean, what do you think?
• 30:37
  SPEAKER_00: Does it answer the questions then?
• 30:39
  SPEAKER_00: I think so.
• 30:39
  SPEAKER_00: This is why we have continents.
• 30:41
  SPEAKER_00: We have continents because of Bowen's reaction series in part.
• 30:44
  SPEAKER_00: I mean, what a cool story.
• 30:45
  SPEAKER_00: It's amazing.
• 30:46
  SPEAKER_01: It is a cool story, and I got to see one of those vessels.
• 30:48
  SPEAKER_01: It was like the holy grail.
• 30:49
  SPEAKER_00: Oh man, amazing.
• 30:50
  SPEAKER_01: Walked into the room and it started to glow.
• 30:53
  SPEAKER_00: That's right.
• 30:54
  SPEAKER_00: That's kind of how I at least in your mind.
• 30:56
  SPEAKER_00: I don't I wonder if Jenny felt the same way.
• 30:57
  SPEAKER_00: We should ask her.
• 30:59
  SPEAKER_00: No, she doesn't even remember it.
• 31:01
  SPEAKER_00: She thought it was quite a messy room that she was walking into, actually.
• 31:04
  SPEAKER_01: Yeah, that was really interesting too.
• 31:05
  SPEAKER_01: You're right.
• 31:06
  SPEAKER_01: Those labs were not all that clean.
• 31:08
  SPEAKER_01: No.
• 31:09
  SPEAKER_01: You know, you you you showed me that was so cool too.
• 31:12
  SPEAKER_01: Some of the devices that they built themselves, these scientists, these researchers, to replicate pressures deep inside the earth.
• 31:20
  SPEAKER_01: So cool.
• 31:21
  SPEAKER_00: Amazing.
• 31:22
  SPEAKER_00: It's amazing.
• 31:22
  SPEAKER_00: Some of the uh some of the some of the finest machinist work of the day was making those because you have to be so precisely made.
• 31:30
  SPEAKER_00: It's unbelievable.
• 31:31
  SPEAKER_00: Yeah.
• 31:31
  SPEAKER_00: So cool.
• 31:32
  SPEAKER_00: All right.
• 31:32
  SPEAKER_00: Well, anyway, hey, I think that's a wrap then, Jesse.
• 31:35
  SPEAKER_00: That's a wrap.
• 31:36
  SPEAKER_00: Hey, before we end the episode, though, we have a new website, right, Chris?
• 31:39
  SPEAKER_00: We do.
• 31:40
  SPEAKER_00: We do.
• 31:41
  SPEAKER_00: So you can go to planetgeocast.com.
• 31:44
  SPEAKER_00: That's our new website.
• 31:45
  SPEAKER_00: You can see all of our episodes there.
• 31:47
  SPEAKER_00: You can learn a little bit about us, and you can pay attention to stuff we got coming up, which we're really excited about, and there'll be more on the way.
• 31:54
  SPEAKER_00: That's right.
• 31:55
  SPEAKER_00: All right, hit us up social media or at planetgeocast and send us an email, planetgeocast at gmail.com, or visit our website.
• 32:01
  SPEAKER_00: There's a contact us form there as well, planetgeocast.com.
• 32:05
  SPEAKER_01: And if you have a lingering question about Bowen's Reaction Series after listening to this episode, please send us an email and we will address that question in our next episode.
• 32:15
  SPEAKER_00: That's right.
• 32:16
  SPEAKER_00: Hit us up.
• 32:17
  SPEAKER_00: Take care, everybody.
• 32:17
  SPEAKER_00: All right.
• 32:18
  SPEAKER_00: Have a good week.
• 32:19
  SPEAKER_00: Peace.