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Petrification - Rerelease · 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.
0:13
SPEAKER_00: Okay, here's the last episode in our re-release holiday series for season five of the Planet Geo podcast.
0:19
SPEAKER_00: Today we're talking about petrification, which is a really cool phenomenon that controls the production of a lot of really cool collectors' rocks.
0:27
SPEAKER_00: I mean, we see petrified wood everywhere at any rock shop you go into and a lot of gem and mineral shows.
0:32
SPEAKER_00: It's a really cool phenomenon, really interesting science behind it.
0:35
SPEAKER_00: Today we are discussing that, and like I said, last in our re-release series.
0:39
SPEAKER_00: So starting next week, we got season six of the Planet Geo Podcast, slightly modified version.
0:44
SPEAKER_00: We're gonna have deep dives with Dr.
0:46
SPEAKER_00: Rachel Phillips.
0:46
SPEAKER_00: We're gonna have uh interviews with top geoscientists and geoscience entrepreneurs, which I'm particularly excited about.
0:52
SPEAKER_00: Chris will be involved in a lot of these episodes, as will my good buddy Josh Davies, who's uh we go way back to graduate school days.
0:59
SPEAKER_00: So we'll be covering a bunch of content with those three people.
1:01
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1:04
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1:04
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1:09
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1:12
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1:17
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1:20
SPEAKER_00: There's a bunch of stuff.
1:21
SPEAKER_00: Uh, if you're running out of Planet Geo Episodes, head over there.
1:23
SPEAKER_00: First link in your show notes.
1:24
SPEAKER_00: Okay.
1:25
SPEAKER_00: Petrification.
1:27
SPEAKER_00: Chris, today, petrification is kind of our thing.
1:30
SPEAKER_00: Petrified wood is what everybody thinks about.
1:33
SPEAKER_00: Have you ever purchased?
1:34
SPEAKER_00: I know you know you and I don't like to buy our rocks.
1:36
SPEAKER_00: We like to collect them.
1:38
SPEAKER_00: Have you ever purchased a piece of petrified wood from anywhere?
1:41
SPEAKER_02: I have not.
1:42
SPEAKER_02: I I can't remember, Jesse, the last time that I bought a rock.
1:46
SPEAKER_02: Actually, I can.
1:47
SPEAKER_02: Actually, I can.
1:48
SPEAKER_02: My favorite mineral, I think, has got to be malachite.
1:51
SPEAKER_02: I just love the color of it.
1:52
SPEAKER_02: It's this beautiful green, it's copper oxide.
1:56
SPEAKER_02: And actually, one of my professors went to the Tucson mineral show and I gave him a hundred bucks or something like that.
2:03
SPEAKER_02: I'm like, get me something nice.
2:04
SPEAKER_02: And so he comes back with this big chunk of malachite because he knows I love it.
2:07
SPEAKER_02: So that's one of the only, and the last rock or mineral that I ever bought was that.
2:12
SPEAKER_00: Wow.
2:13
SPEAKER_00: Well, I I don't know.
2:15
SPEAKER_00: I don't think I've ever collected petrified wood.
2:18
SPEAKER_00: Certainly haven't bought any of it.
2:20
SPEAKER_00: So I don't even know if I have any petrified wood in my collection uh at all, which is maybe a bit of a shame.
2:26
SPEAKER_00: We should rectify that since we're doing an episode on the stuff, right?
2:30
SPEAKER_02: I know, but it it's kind of a sticky thing, right?
2:32
SPEAKER_02: Uh, because we've talked about collecting like in national forests, which you can almost always do, but you can't collect fossils in a petrified forest, and this counts as that.
2:44
SPEAKER_02: And so collecting is really um, you know, you really need to do your homework before you go about doing something because you don't want to do something wrong.
2:52
SPEAKER_00: No, that's right.
2:53
SPEAKER_00: I mean, fossils like I mean, for the most part, you can really only collect in privately owned places where you kind of pay to collect.
2:59
SPEAKER_00: Like you and I collected some fossils from I forget which shale formation what it was, but where you kind of is a green river, so you're splitting open little pieces of wafers of shale and looking for fossils inside.
3:10
SPEAKER_00: Places like that are where you can legally collect fossils, but they're often kind of a pay-to-play sort of place.
3:15
SPEAKER_00: But Chris, the word petrified, I think it's a good time.
3:20
SPEAKER_00: There's all these words like geology, we have so many stupid names.
3:23
SPEAKER_00: And your mom, your mom, Joyce has brought up many times how an E via email, I don't know, you do you tend to ignore the emails from your mother, but I read them all the time.
3:33
SPEAKER_00: And uh, she's brought up how our pronunciation is like all over the place a little bit.
3:38
SPEAKER_00: She often sides with you when you get into pronunciation debates, like it's very irritating.
3:42
SPEAKER_00: Joyce is always on Chris's side, no matter what.
3:45
SPEAKER_00: But the reason I'm bringing this up is because we have a lot of weird words.
3:49
SPEAKER_00: Yeah, I can tell.
3:50
SPEAKER_00: I mean, she's your son and you're her you're the goal.
3:54
SPEAKER_00: That's not the reason.
3:55
SPEAKER_02: No, no, it's not because because I don't say things like methane and subsidence.
4:00
SPEAKER_02: I don't use the yeah, so she sides with me because I'm on the right side.
4:04
SPEAKER_02: That's our correct.
4:06
SPEAKER_00: Okay, I see.
4:06
SPEAKER_00: I see.
4:08
SPEAKER_00: Well, uh, all that to say, like we we have words that are weird, like geology is full of words that are weird, whereas biology often has this like Latin root to words, like especially in medicine or biology, words kind of make sense.
4:19
SPEAKER_00: Petrified or petrification is one of them that makes sense.
4:22
SPEAKER_00: There is a root to it, right?
4:24
SPEAKER_00: And so it kind of made the word makes sense a little bit.
4:26
SPEAKER_02: That's right.
4:27
SPEAKER_02: I I always go back to one of the first classes that anyone, well, actually, they're kind of changing this, and that's a whole different discussion.
4:34
SPEAKER_02: But the class petrology is kind of going away.
4:37
SPEAKER_02: Now they're like combining mineralogy and petrology and calling it like rocks and minerals or something like that.
4:42
SPEAKER_02: That's what we have here.
4:43
SPEAKER_02: That's right.
4:44
SPEAKER_02: And you and I, though, both went through this older kind of school where we took traditional mineralogy, and then the next part of that succession was probably petrology.
4:54
SPEAKER_02: And so petro, the root word of that petro means rocks.
4:58
SPEAKER_02: And so petrified, you can think of it as petrophide, if you will, if that helps.
5:03
SPEAKER_02: But and then, of course, um, it's called petrified wood, so it's rock and wood.
5:09
SPEAKER_00: And so it was once alive.
5:11
SPEAKER_00: And it it's like people often confuse petro with petroleum, is is what people think of, but petroleum is named because of the rock, because petro means rock.
5:22
SPEAKER_00: So petroleum is named such because it comes from rocks, and so petro, like you said, is is the base word rock.
5:28
SPEAKER_00: So petrified is to turn into a rock.
5:30
SPEAKER_00: I think you were going there.
5:31
SPEAKER_00: Sorry for interrupting with the the petroleum thing, but no, that's right.
5:34
SPEAKER_02: But Jesse, you I want to throw this back to you because you I think we need to paint the picture of what is the difference between then petrified wood and a fossil.
5:44
SPEAKER_00: Yeah, it's relatively simple.
5:45
SPEAKER_00: I mean, fossils can be a whole bunch of things.
5:48
SPEAKER_00: Fossils are uh the broader category here, and petrification or petrified objects are a subset of fossils, so they're a type of fossil.
5:57
SPEAKER_00: I mean, think of fossils.
5:58
SPEAKER_00: Fossils can be actually organic pieces of organic matter.
6:02
SPEAKER_00: They can also be trace fossils.
6:04
SPEAKER_00: We have things called trace fossils, which are like worm burrows where the worm is not preserved, but their burrow is preserved, and so those are all fossils.
6:11
SPEAKER_02: That's right.
6:11
SPEAKER_02: And those are some of my favorite.
6:13
SPEAKER_02: I do have a a fairly substantial amount of rock, sedimentary rock, that has these trace fossils in it.
6:19
SPEAKER_02: And then these are from like filter feeders and burrowing organisms, so and they leave these really cool traces behind on the surface of the rock.
6:28
SPEAKER_02: So I'm a I'm a big fan of that.
6:30
SPEAKER_00: Yeah.
6:31
SPEAKER_00: That's a side note.
6:31
SPEAKER_02: You got me excited.
6:33
SPEAKER_00: Uh let's not go into those.
6:34
SPEAKER_00: I think I've said this before trace fossils do not excite me very much, but they're not uh they don't do it for me, you know?
6:41
SPEAKER_00: They don't do it for me.
6:42
SPEAKER_00: But petrification and petrified stuff always looks really cool.
6:45
SPEAKER_00: And so the reason for talking about petrification now is kind of twofold, Chris.
6:50
SPEAKER_00: Like you you were just out west and looking at these beautiful petrified forests, which is a good opportunity to point to our Yellowstone National Park geology course, which we now have on the Camp Geo app as well, that you can download, you can purchase, and you can get access to all of our stuff.
7:04
SPEAKER_00: But we have basically a whole episode dedicated to these petrified forests in Yellowstone, which are just an amazing, amazing scientific story.
7:12
SPEAKER_00: And petrified objects are sort of a hot topic in geochronology as well.
7:16
SPEAKER_00: And so we're gonna kind of use this episode to kick off a geochronology sort of series where we're gonna go through a bunch of different things related to geochronology and we'll end this conversation talking about dating petrified fossils, basically.
7:29
SPEAKER_00: Um, so yeah, that's true.
7:31
SPEAKER_02: That's a good point.
7:32
SPEAKER_02: And and I want to, real quick, again, back talking about Yellowstone very quickly here.
7:37
SPEAKER_02: We got to see some absolutely massive redwood trees preserved in Yellowstone.
7:43
SPEAKER_02: Some of them were still upright as these like you know, 16 foot-high stumps, and some of the trees were knocked over and it were these horizontal logs.
7:53
SPEAKER_02: But it was a really, really cool thing, Jesse.
7:57
SPEAKER_02: But man, was it a punishing hike?
8:00
SPEAKER_02: It was it's been a long time since I've taken any students there, and it was they thought we were absolutely just brutally punishing them.
8:10
SPEAKER_02: I mean, it's a it was a hard hike.
8:12
SPEAKER_00: This is one that was it wasn't super long, but it was very steep.
8:15
SPEAKER_00: Is that is that right?
8:16
SPEAKER_00: Very uh high um high angle.
8:19
SPEAKER_02: And it funny, uh, because at the end of the trip, the kids do skits, and this one tent group did a skit with us on Andrew and I, and they they show us, they said, Well, we're gonna talk about the peculiar relationship between Mr.
8:33
SPEAKER_02: DeWitt and Mr.
8:34
SPEAKER_02: Bullheis, and these two kids come skipping in holding hands, and then these other kids are dragging behind them because Andrew and I were just super excited to see these trees.
8:46
SPEAKER_02: And for the most part, I think the kids were too, but it was it was a little bit tempered by the brutality of the hike.
8:53
SPEAKER_02: Um, but one kid did say to me, he said, Mr.
8:56
SPEAKER_02: Bullice, this is perhaps the best experience of my entire life.
9:00
SPEAKER_02: He was so excited about seeing these trees.
9:02
SPEAKER_02: It was just that's just a very cool thing.
9:04
SPEAKER_02: So, yeah, very cool.
9:05
SPEAKER_00: So, so Chris, why don't you give us a quick outline of what we're gonna cover, sort of bullet point the the topics we're gonna hit here as we work away through the episode, because this has the potential to get a little bit confusing, I think.
9:15
SPEAKER_00: This particular topic.
9:16
SPEAKER_00: Everything in there, every piece is relatively simple, but in combined, it could potentially you know get lost in the weeds a little bit.
9:23
SPEAKER_02: So we're gonna begin by talking about the conditions geologically that allow for petrification to happen.
9:31
SPEAKER_02: In other words, the wood doesn't rot, instead, something else happens.
9:34
SPEAKER_02: And then we're gonna get into you know the geologic conditions where this can actually occur, and we're gonna finally wrap up with how does the science work with petrification?
9:47
SPEAKER_00: And we're gonna have to keep each other out of the weeds here, I think.
9:50
SPEAKER_00: So this is gonna be an exercise in me keeping you out of the weeds and you keeping me out of the weeds.
9:54
SPEAKER_00: So are we agreed we can we'll keep each other out of the weeds this episode?
9:57
SPEAKER_00: Because there is a tendency sometimes when we want to go into the weeds, we can kind of death spiral both of us into the weeds, and I don't think that's good for anybody.
10:06
SPEAKER_00: Probably not, probably not, but it it's just a cool thing, right?
10:09
SPEAKER_00: Okay, Chris.
10:10
SPEAKER_00: So the conditions that are needed for petrification.
10:13
SPEAKER_00: So petrification happens relatively quickly on a geologic timescale, like thousands to tens of thousands of years, but pretty long on biological timescales.
10:22
SPEAKER_00: So, what conditions do we need for this to happen?
10:25
SPEAKER_02: Well, like you just said, we basically we we can't have the wood rot.
10:30
SPEAKER_02: And so what we need to have is we need to have the wood usually, almost always, needs to be buried uh in this wet sediment that is saturated with certain minerals, loaded with dissolved minerals.
10:44
SPEAKER_02: And it's almost always, we'll get into the detail later on, but it's almost always going to be silica, which is a quartz-rich, dissolved constituent to the water.
10:53
SPEAKER_02: And the other really important thing is the burial needs to be anoxic, it needs to be very little oxygen present because that's all that these decomposers need.
11:04
SPEAKER_02: Give them some air, and then they'll just eat the wood and it'll decompose and rot, and petrification can't happen then.
11:11
SPEAKER_02: So it's got to be wet, rich in minerals, and very low oxygen content.
11:17
SPEAKER_00: So I think the the a way to think about this is like uh you need those stuff in this case, wood, to be preserved for a long time.
11:24
SPEAKER_00: And think about walking around the forest and you see dead trees falling, or you're up in the mountains, you see dead trees falling down.
11:30
SPEAKER_00: They can be old, those can be really old on human time scales, but it's rare you'd see a thousand-year-old tree trunk laying there that hasn't decayed away, right?
11:39
SPEAKER_00: These things do decay over many, many years.
11:41
SPEAKER_00: So we need to kind of preserve those, as you said, lock them away in some place where microbes can't get to them and they can't break down, and they the organic matter can't decompose.
11:50
SPEAKER_00: And so, a couple of key areas where this can happen, lowland areas in tropical climates.
11:56
SPEAKER_00: This is like the classic place where a lot of fossils are typically made.
12:01
SPEAKER_00: So you are basically forming a shale.
12:03
SPEAKER_00: So you have rivers that flood in, you have mud and sand, burying things really rapidly, and there's enough organic matter around where there's no oxygen, it just soaks up any of the free oxygen.
12:14
SPEAKER_00: So decomposition does not happen very much.
12:17
SPEAKER_00: And this is a coal-forming environment, an ancient coal forming environment like a peatland or a wetland or a lowland.
12:23
SPEAKER_00: Another one which is really common, Chris, outwest.
12:26
SPEAKER_02: Hold on, real quick, deltas, floodplains, that's the kind of environment that you're describing there.
12:32
SPEAKER_02: So you take those kinds of geologic settings or that swampy coal forming environment, you know, and you put it in a tropical climate, and those are really, really good conditions for petrification to happen.
12:45
SPEAKER_00: Yeah, exactly.
12:46
SPEAKER_02: Back, you know, way back in the past.
12:48
SPEAKER_00: So yeah, exactly.
12:49
SPEAKER_00: And another one, which we talk about for the for the instance of Yellowstone, the petrified trees that you were just talking about, petrified wood you were talking about taking your students to, these are volcanic ash deposits.
13:00
SPEAKER_00: And volcanic ash, especially these big stratovolcanoes that we've talked about before, when ash and lah deposits get washed downhill, they can knock down all the trees and then they can bury the trees.
13:12
SPEAKER_00: And that's again a really reducing environment.
13:14
SPEAKER_00: This volcanic ash is really reducing, and so that stuff can just sit there and and does not decompose quickly.
13:22
SPEAKER_02: It is the perfect setting.
13:23
SPEAKER_02: And you mentioned this word, and again, for review's sake, lahar.
13:29
SPEAKER_02: And so you have this, it has the ability to knock over trees as it floods out of the river valley, destroys everything in its path, and it buries it quickly.
13:39
SPEAKER_02: So you have everything that you need, it seals it off from the air above.
13:43
SPEAKER_02: Also, because it's volcanic related, it's loaded with silica.
13:48
SPEAKER_02: The water is, and so that's a very common setting where these kinds of things can happen in the past.
13:55
SPEAKER_00: And I think Chris, that points to a really interesting property here is that if you bury stuff in like asphalt or in soil or something like that, think about where the oxygen would be coming from to do this decomposition.
14:05
SPEAKER_00: It's almost all coming from the atmosphere.
14:07
SPEAKER_00: When that atmospheric oxygen has to get through a bunch of rock to make its way to this organic material, this tree down buried meters below the surface, a lot of oxidation reactions happen.
14:19
SPEAKER_00: A lot of that oxygen is consumed by things like rusting, you know, turning all the iron into the rock into like hematite or something.
14:25
SPEAKER_00: Oxygen will be consumed before it reaches the tree down buried at depth.
14:30
SPEAKER_00: So as soon as you bury something, burying something quickly is a good way to lock it away and preserve it for future petrification, which brings us to hold on, my young sage, that is really well put.
14:42
SPEAKER_02: I did not know what you were gonna say.
14:44
SPEAKER_02: Uh and that's such a good point.
14:46
SPEAKER_02: That's it, you did, but it's such a good point because one of the things that we love about petrified wood are the all the colors, right?
14:53
SPEAKER_02: That are in the minerals.
14:54
SPEAKER_02: And most of those colors are a result of iron or some other metal that oxidizes and again consuming the available oxygen and preventing the decomposers from going to town on it.
15:05
SPEAKER_02: So, really, really good point.
15:07
SPEAKER_02: Well done.
15:07
SPEAKER_00: You get the Segway Award for this episode because nice segue into like, I think what we have to cover next, which is like what is petrification?
15:15
SPEAKER_00: Like, what's happening?
15:16
SPEAKER_00: Okay, we've got this thing preserved, it's preserved, it's sitting down there, it's organic material.
15:19
SPEAKER_00: What's happening?
15:20
SPEAKER_00: Well, I think most people, if you're interested in petrification or petrified wood, you've probably thought about this and you might have come to the the conclusion here.
15:28
SPEAKER_00: It's turning it into a rock.
15:29
SPEAKER_00: So we have to get rock into that biological structure of, in this case, a tree.
15:34
SPEAKER_00: And there's a couple common categories of stuff.
15:37
SPEAKER_00: Really, there's it's quartz is the main one, so SiO2, varieties of SiO2, and then also pyrite.
15:44
SPEAKER_00: So pyrite does this as well.
15:45
SPEAKER_00: So if we we go back to our two settings, the sort of floodplain deposit where there's lots of organic material, river mouth in a tropical climate where lots of organic material is just piling up, that's where you'll often get pyritization happening.
15:59
SPEAKER_00: And these volcanic ash deposits where trees are getting knocked down and buried, this is often where we get the silicification or silica being added in.
16:09
SPEAKER_00: And so, Chris, what are the the types of minerals that can do this petrification?
16:13
SPEAKER_02: Yeah, we're gonna stick to for the sake of staying out of the weeds, to just the silicification for the most part.
16:19
SPEAKER_02: And so there are two kinds of common mineralization that you get.
16:24
SPEAKER_00: One is called Chalcedney, or Chalcedney is Do we need a pronunciation competition here with Joyce?
16:31
SPEAKER_00: Because Chalcedney or Chalcedony, is Chalcedony another valid.
16:36
SPEAKER_02: No, but you don't call it Chalcedony, do you?
16:39
SPEAKER_02: You don't, do you?
16:39
SPEAKER_02: Please tell me about it.
16:40
SPEAKER_00: I've also heard it called Chalcedney, Chalcedony, Chalcedney, Chalcedony.
16:46
SPEAKER_00: Okay.
16:46
SPEAKER_00: How do you say it?
16:47
SPEAKER_02: Uh uh I say Chalcedney, don't you?
16:49
SPEAKER_00: Chalcedney.
16:50
SPEAKER_00: Okay.
16:50
SPEAKER_00: Ooh, the emphasis on the E there, huh?
16:52
SPEAKER_00: Okay.
16:52
SPEAKER_00: That's good.
16:53
SPEAKER_00: We'll we'll see what Joyce thinks about that.
16:55
SPEAKER_00: Who's right?
16:55
SPEAKER_00: Of course she's gonna come back with Chris's right.
16:58
SPEAKER_00: My son is right.
16:59
unknown: Chal Sedney.
17:02
SPEAKER_02: Well, you know, we can simplify the whole thing.
17:04
SPEAKER_02: And a lot of people that are into this a lot, they call they just call it agatized wood, you know.
17:08
SPEAKER_02: And we did an episode a long time ago on how agates form.
17:12
SPEAKER_02: Agates are highly sought after because they're beautiful, they tend to happen in geodes and so on.
17:17
SPEAKER_02: And the agates are almost always made up of this microcrystalline flavor of quartz, which is called Chalcedony.
17:24
SPEAKER_02: There's another beautiful variance on this, which is called opal or opalized wood.
17:30
SPEAKER_02: And this is a non-crystalline form of silica.
17:33
SPEAKER_02: And the difference is between this and Chalcedony is it usually has water as a part of its chemical formula.
17:39
SPEAKER_02: So that changes some of the properties of it, but it's absolutely, or at least it can be, gorgeous stuff.
17:46
SPEAKER_00: I mean, oh opal is extremely beautiful stuff.
17:49
SPEAKER_00: And as you said before, the color variations in petrified wood or in most petrified organic pieces all come from oxidized manganese, oxidized iron, elements like that that get in there in very trace amounts.
18:02
SPEAKER_00: I mean, you would not really detect these unless you're using our lab at Bent State and like analyzing them with a laser system or something.
18:08
SPEAKER_00: You can detect the concentrations, but they're really small amounts.
18:10
SPEAKER_00: They're not really building minerals in there, they're just incorporated into the crystal structure as kind of impurities.
18:16
SPEAKER_00: And I think we often think of petrification as petrified wood, and that's what we're kind of framing this conversation around.
18:24
SPEAKER_00: But this petrification process always occurs in pyrite, and there's a big um industry of collecting these sort of pyretized ammonite fossils and pyritized fossils that are in black shales.
18:35
SPEAKER_00: So if you think of a black, black shale bed, there's a lot of iron in there, and when these things decay, they kind of release sulfur and iron plus sulfur, you can get pyrite.
18:44
SPEAKER_00: And the pyrite can kind of take over um and petrify the you know, the the fossil creature that's buried in the shale.
18:52
SPEAKER_00: We usually don't get trees down there that are pyrotized, but we get a lot of other sort of uh marine organisms that are that are then pyratized and will form these beautiful fossils that are basically it's a hunk of pyrite in the shape of like an ammonite fossil or something.
19:05
SPEAKER_00: They're really spectacular.
19:06
SPEAKER_02: Yeah, and and for our listeners, pyrite is fool's gold.
19:09
SPEAKER_00: Fool's gold, exactly right.
19:10
SPEAKER_02: So it's absolutely stunning.
19:12
SPEAKER_02: It's gorgeous stuff because who doesn't like fools gold, right?
19:15
SPEAKER_00: So it's just a sort of a note about another chemical reaction that can take place in the other setting that we that we talked about.
19:21
SPEAKER_00: But I think we can move into like actually the mechanisms for this.
19:24
SPEAKER_00: How do we get this quartz or opal or pyrite into the wood or the ammonite or whatever is being fossilized, being petrified?
19:33
SPEAKER_02: Right.
19:33
SPEAKER_02: There are two ways that this happens, and actually both of them are almost always at play within the process.
19:41
SPEAKER_02: First of all, there is replacement where the actual wood fibers and the cellular structure of the wood is replaced by the minerals.
19:50
SPEAKER_02: And this is kind of an interesting thing.
19:52
SPEAKER_02: So as the wood kind of slowly decays, and we I know that we said that decay has to be minimized, and it is minimized, but it's still occurring, right?
20:02
SPEAKER_02: Some of the molecules that make up those cellular walls of the wood are actually replaced by silica, by this microcrystalline variety of quartz or this non-crystalline variety of opal, you know.
20:15
SPEAKER_02: And and so what this does then, this is really a cool thing.
20:18
SPEAKER_02: It keeps the template of the cellular structure of the wood intact.
20:23
SPEAKER_02: And that's really cool because that means that we can look at this cellular structure, the way the the cell walls are put together, the way they interlock with each other, and so on.
20:33
SPEAKER_02: We can identify this species of wood.
20:35
SPEAKER_02: And that's a that's a very cool thing.
20:38
SPEAKER_02: And and I'm sure you have a lot to say about that.
20:40
SPEAKER_02: We're not going to today because this is more like in your field of you would come across research articles and so on like this.
20:46
SPEAKER_00: Well, yeah, this this sort of micro replacement of like C and H bonds with silica bonds.
20:51
SPEAKER_00: But anyways, that the replacement happens, it's it's rare to not find replacement having occurred.
20:56
SPEAKER_02: That's right.
20:56
SPEAKER_02: And and it's kind of cool too, Jesse, is that some of the wood can still be intact even after millions of years.
21:03
SPEAKER_02: So not all of the wood needs to be or is even necessarily going to be replaced.
21:10
SPEAKER_02: But the other thing that happens is called permineralization.
21:14
SPEAKER_02: And this is basically just where wood fibers and cellular structures of wood is very, very porous.
21:20
SPEAKER_02: So silicification, which is the most common type of perminalization, is when silica-rich water precipitates silica, deposits silica within the cell walls and also between them.
21:34
SPEAKER_02: It's not replacing the wood, it's just like filling everything up.
21:38
SPEAKER_02: All the spaces between get filled up with this microcrystalline variety of quartz.
21:42
SPEAKER_02: And that's called permineralization.
21:44
SPEAKER_00: And I think let me interrupt you right there, Chris.
21:46
SPEAKER_00: I want to just visualize this for people.
21:48
SPEAKER_00: Think about how trees respire.
21:50
SPEAKER_00: Like, how do trees get water up to their leaves?
21:52
SPEAKER_00: They're sucking water up from down below, and it's you know, this force of evaporation is pulling water up through the trunk.
21:58
SPEAKER_00: Well, a dead tree is very porous.
22:00
SPEAKER_00: There's water that can flow through this thing.
22:02
SPEAKER_00: And when you have, especially like a lava flow or an ash flow, that is really, really fine-grained rock that is very, very easy to dissolve.
22:10
SPEAKER_00: And silica is really easy to dissolve.
22:12
SPEAKER_00: So rain water comes in, that water starts to pick up silica, hits the tree trunk, and it's not going to decompose it, but it's loaded with silica.
22:21
SPEAKER_00: And that silica will flow through the tree and then can be precipitated in there.
22:25
SPEAKER_00: Again, because go back to our episode on the geology of uranium where we talked about these redox gradients where it'll be oxidizing fluid, it'll hit another rock, and it'll turn reducing right away and dump it out.
22:36
SPEAKER_00: That's what's happening here.
22:37
SPEAKER_00: This oxidized water that can pick up silica, hits the tree trunk, gets sucked up the tree trunk, and then it becomes reducing and dumps out that silica right there.
22:45
SPEAKER_00: So it's all these sort of little fine-scale changes in the in the um chemistry of the water that are doing this process.
22:52
SPEAKER_02: If you think about like a paper towel and you take a corner of a paper towel and you dip it in water, and you'll see water soak up into the paper towel, that's what dead trees do.
23:02
SPEAKER_00: Yeah.
23:02
SPEAKER_02: And so if they're soaking up this silica-rich water, then it will silicify.
23:07
SPEAKER_02: It's going to deposit that mineral in the pore spaces and between the cell walls and so on.
23:14
SPEAKER_02: And that process is called permineralization.
23:16
SPEAKER_00: So I think Chris, let me uh just just summarize this again real quick.
23:20
SPEAKER_00: And then I want to make a little bit of a point about this petrified wood.
23:23
SPEAKER_00: So, I mean, we've talked about what petrification requires, and it's sort of you need this quick burial or it needs to be isolated from decay.
23:31
SPEAKER_00: We talked about what type of stuff replaces what does the petrifying, what type of minerals, and that's chalcedony, opal can happen with pyrite as well.
23:39
SPEAKER_00: And then we talked about how does that happen, how does it become a rock?
23:42
SPEAKER_00: And we have these replacement and perminalization processes that do this.
23:46
SPEAKER_00: And petrified wood, you know, we talked about how it's rare.
23:49
SPEAKER_00: It is pretty rare, but you can find it in many sedimentary layers all over the western United States, so much so that I didn't actually know this.
23:56
SPEAKER_00: And I know I've been to Petrified Forest National Park, but there's an entire house built out of petrified wood.
24:04
SPEAKER_00: It's called the Agate House.
24:05
SPEAKER_00: It's been restored, but this was built thousands of years ago entirely out of petrified wood.
24:09
SPEAKER_00: Because if you're in that landscape, you have this big wood pieces, petrified wood pieces that are really solid.
24:16
SPEAKER_00: Once you make that thing, it speaks to the durability of petrified wood.
24:19
SPEAKER_00: Once you make this thing petrified, it's just quartz.
24:22
SPEAKER_00: And quartz is really, really durable when it's in that solid phase.
24:26
SPEAKER_00: So I thought this was kind of interesting.
24:28
SPEAKER_00: And there were hundreds of these structures constructed by the Pueblos a thousand years ago in this region.
24:33
SPEAKER_00: So it it is a useful.
24:35
SPEAKER_00: Um past societies found these things useful, and we find them very beautiful and um treasure petrified wood in many ways.
24:43
SPEAKER_02: Um, I did not know that either.
24:44
SPEAKER_02: That's a really interesting um point.
24:46
SPEAKER_02: I want to round out this episode, Jesse, by talking about kind of like how this whole thing started.
24:52
SPEAKER_02: We're gonna do a series on geochronology, and you're the expert in the room on geochronology.
24:57
SPEAKER_02: So the question is can we use uh the methods that maybe you employ in your lab to date the age of a petrified piece of wood?
25:08
SPEAKER_00: Yeah, uh, this is a great question, and it's a really good intro into geochronology, I think, into our series, and we've touched on a lot of these topics before.
25:17
SPEAKER_00: One way to think about this is to make a good geochronometer or uh a clock, a geological clock, you need something, a substance that takes up a radioactive element.
25:28
SPEAKER_00: Uranium's radioactive, potassium's radioactive, you need something that takes up one of those elements.
25:33
SPEAKER_00: We've talked about quartz.
25:35
SPEAKER_00: Quartz is really bad at taking up radioactive elements.
25:39
SPEAKER_00: Like it really only wants silicon oxygen.
25:41
SPEAKER_00: It doesn't really take up too much else, you know.
25:43
SPEAKER_00: So there's not much uranium.
25:45
SPEAKER_02: Those atoms are they're probably too oddly shaped, right?
25:48
SPEAKER_02: They don't fit in the crystal structure, they're too big probably to fit in the crystal structure lattice of uh quartz crystal.
25:55
SPEAKER_00: Exactly.
25:55
SPEAKER_00: And so quartz is not a great chronometer there uh as far as from this uh radioactive decay chronometers.
26:02
SPEAKER_00: And so if we sort of broaden this out from petrification, we can broaden the the question to sort of fossilization.
26:10
SPEAKER_00: And there when I was a student, when I was a PhD student, there's a paper that came out in I think it was 2011 or something like that, that that proposed that we could date dinosaur bones, the fossilization process of dinosaur bones, of forming dinosaur bones.
26:24
SPEAKER_00: And the reason was very much similar to our geology of uranium episode where uranium was flowing through, it was getting picked up, being oxidized in the six plus state, and then when it hit the bone, it got dumped out and turned into uranium-4 plus.
26:37
SPEAKER_00: So basically, during fossilization, the bone that is now a fossil would have been enriched in uranium.
26:43
SPEAKER_00: Then that starts the clock.
26:44
SPEAKER_00: That's kind of you know tipping the sand dial on edge is starting the clock, pushing a bunch of uranium into it.
26:50
SPEAKER_00: And then over time that has decayed.
26:52
SPEAKER_00: That was not, I would say, widely accepted.
26:54
SPEAKER_00: I think it's still sort of debatable how well you can date dinosaur bones, just dating the bone material or the fossil bone material.
27:03
SPEAKER_00: There have been recently in the last year or two some uh tests using appetite.
27:08
SPEAKER_00: And appetite's like the mineral in our teeth, right?
27:11
SPEAKER_00: And so appetite can form during this fossilization process.
27:16
SPEAKER_00: During this mineralization process, this replacement or permineralization process, you can get tiny little appetite grains that with the the sort of micro-sampling techniques, we can go in and date those individual appetites.
27:27
SPEAKER_00: And appetite's a good one for uranium-led geochrinology.
27:30
SPEAKER_00: So I would say there's hope, but it's not entirely clear that it's really reliable at the moment.
27:36
SPEAKER_02: Okay.
27:37
SPEAKER_00: But it begs the question, Chris, how do we get the dates of the fossil forests in Yellowstone National Park?
27:42
SPEAKER_00: Like, how do we know when these things were fossilized or when these things were were sort of destroyed?
27:48
SPEAKER_02: I would assume then that we have to bracket it between like what's below it and what's above it, where we can date the actual rocks themselves that are in place, and then you kind of get this.
27:58
SPEAKER_02: Uh is that right?
27:59
SPEAKER_02: Is that that's kind of how it's done, right?
28:01
SPEAKER_00: Exactly.
28:01
SPEAKER_00: Yep, that's exactly what we were looking at.
28:02
SPEAKER_00: I mean, if you have a big ash fall, big lahar flow goes through, that lah is a rock that is formed in that moment, and it's pretty easy to date these ash falls.
28:12
SPEAKER_00: So we just extract some zircons from we can get ages of the rock that killed the trees, and then the assumption is that the the petrification process happened a few tens of thousands of years after that, like pretty soon after that.
28:25
SPEAKER_00: So, yeah, that's how we go about dating that.
28:27
SPEAKER_00: So there's kind of two processes, but it's a good intro.
28:30
SPEAKER_00: You know, I think starting out with where the process doesn't work is perhaps a good intro into the broad topic of geochronology and where it does work in different places where it does work.
28:41
SPEAKER_02: So I remember reading the paper that you talked about with the dinosaurs, because I think that was done by somebody out of the University of Alberta, wasn't it?
28:49
SPEAKER_00: It was uh in part, yeah, done at the University of Alberta, yeah.
28:51
SPEAKER_02: So I didn't I knew that it was it was just happening, and uh and I didn't really know how it ended up.
28:56
SPEAKER_02: And so that's kind of where our discussion came from then with hey Jesse, well, I was just out there, I'd looked at these awesome gigantic redwoods.
29:05
SPEAKER_02: Redwoods would never grow in a climate like Yellowstone today.
29:08
SPEAKER_02: Yeah.
29:09
SPEAKER_02: Um and so this is this speaks to a time that was vastly different than it is now.
29:14
SPEAKER_02: How do we know when we put a number on it and say these trees are 43 to 46 million years old?
29:19
SPEAKER_02: How do we know that?
29:20
SPEAKER_02: And and that's kind of that's where this whole thing came from.
29:23
SPEAKER_00: I think it's a good uh a good start.
29:24
SPEAKER_00: A good start to a uh a series on geochronology and also a good standalone episode.
29:29
SPEAKER_00: I mean, who doesn't like petrified wood?
29:30
SPEAKER_00: It is freaking beautiful stuff.
29:32
SPEAKER_00: Beautiful stuff.
29:33
SPEAKER_00: And I mean, it's just so cool to pick it up and think this used to be a tree millions of years ago.
29:38
SPEAKER_00: This was a tree, now it's a rock.
29:39
SPEAKER_00: I'm holding it in my hand.
29:40
SPEAKER_00: I mean, it totally cool.
29:41
SPEAKER_02: And it's a lot heavier than the tree was.
29:44
SPEAKER_02: You know, the petrified wood is heavy stuff.
29:47
SPEAKER_02: Yes, um, but that ought to make sense.
29:49
SPEAKER_02: That ought to make sense because the wood is so porous.
29:51
SPEAKER_02: We talked about that, and that porosity is replaced by no porosity because it's filled in with quartz usually.
29:58
SPEAKER_00: Absolutely, absolutely.
30:00
SPEAKER_00: Hey, this was a fun episode.
30:01
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30:05
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30:06
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30:08
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30:10
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30:14
SPEAKER_00: If you want to learn about Yellowstone and these beautiful petrified wood forests that we were just talking about, you can head over to geodotampcourses.com or the first link in your show notes.
30:23
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30:30
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30:36
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30:41
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30:42
SPEAKER_00: Peace.