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Eruptions and Extinctions - The Geology of the Gettysburg Sill
In this episode of Planet Geo, hosts delve into the geological significance of the Gettysburg Sill and its role in the Battle of Gettysburg. They explore the connection between diabase formations and ...
Eruptions and Extinctions - The Geology of the Gettysburg Sill
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The database was instrumental in the battle. It set the stage for the topography.
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It's a large reason why the Union forces think could defend this position, this fish hook that
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they had in Gettysburg. We'll talk about that. Welcome to Planet Geo, the podcast where we talked
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about our amazing planet, how it works, and why it matters to you.
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The good doctors in the house. Hey, it's air professor director to you. I haven't gotten a full
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title out of you, you know, recently. What's up with that? No, well, not getting any respect
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around here. You only get that when we're face to face. And we're in front of your postdoc
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students or something like that. And even that's only like once, maybe in a very,
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very murky way. Did I drop any overeducated comments when I was, I don't think I did. I
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didn't. I was good. You, yeah, you were good. You were well behaved. You were well behaved.
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Maybe in front of a test, I did, but not your little minions, you know, not not to not everybody
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else. There's only like one huge piece to do to mine there. And then the rest were above me
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in the pay grade. It was, it was good to see Jesse, grappling Jesse is a fun.
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I'm just a couple of minutes above me
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in the original structure.
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A few, oh my gosh, okay.
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Well, today, Chris, this is chapter five.
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Is it part five?
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Is that right?
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Yeah.
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Yes, yes.
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I gotta give you a little bit of a hard time here.
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Why?
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Am I allowed to do that?
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Yeah, apps up.
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Yeah.
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I don't ask me to make it.
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Please, but take me down.
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Take me down.
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We were putting this together and we were debating
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about what topics deserve standalone episodes
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in our deep dive on the geology of the battle
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at Gattysburg.
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Yep.
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And 100%.
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You know, to me, this one stood out as a very clear
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single episode, like no doubt we can do an episode
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on the Diabase.
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And you were kind of hemmed in hot a little bit.
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You were easy to convince, but initially,
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you were like, I don't know.
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I don't see if there's one there.
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How do you feel now after we've gone through
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and scripted it all right?
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Write this down and take note.
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Write this down and you can timestamp and date stamp this,
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but I was 100% wrong.
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Okay.
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All right.
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And my need to be persuaded.
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I think because the story really,
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the geologic significance in the battle is easy.
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Diabase is easy, but then the importance
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of this large igneous province,
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that was something that I needed to dive deeper into.
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And then the story came, it revealed itself,
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and it's like, oh, yeah, I was wrong.
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And once again,
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one of the things that I, I think there's a leg,
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you know, this points out the leg.
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So what do we, let me just summarize what we're going to talk
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about today here real quick.
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We're talking about the Diabase.
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The Diabase was instrumental in the battle.
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It set the stage for the topography.
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It's a large reason why the Union forces,
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I think could defend this position,
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this fish hook that they had in Gettysburg.
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We'll talk about that.
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But these Diabase strikes,
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we're going to talk about them.
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The sill in the dike,
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these are part of a huge igneous event.
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That probably, quote unquote, probably,
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I emphasize probably,
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probably caused the entrassic mass extinction event.
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And so that whole story,
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and this is one of the things that I find,
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I don't know if it's frustrating,
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because I understood why it's happening,
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but the literature on the Geltj of Gettysburg
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is not updated with the geological story
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of the Rossville dike,
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and the broader regional significance
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of the Yorkevins sill.
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You don't find that stuff written about
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on the literature on the geology
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of the battle at Gettysburg yet.
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Right, that's a good point.
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Cross talk.
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Like, do you think you'll learn?
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That's where I was like,
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I needed to be convinced,
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because the geology was pretty straightforward.
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From the geology related to the battle
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of the history of Gettysburg,
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and that was pretty straightforward.
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And I'm like, I don't think there's an episode there.
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I think this is like, let's roll this into something else.
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Right, you know, it comes down to the Confederates
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are trying to kick the Union forces
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off of this high ground sill.
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That's what the whole thing came down to.
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I'm like, where is it, Jesse?
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Where's the story here?
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What am I missing?
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And then you find it.
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And I think that this is like a really interesting topic.
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And I'm looking forward to it.
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I really am.
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So you were right.
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I was wrong.
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That doesn't happen very often.
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And you'll get a signed contract coming to you there
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pretty soon to that statement signed effect.
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So I put it on record.
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It's there.
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It's on our podcast.
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It's on our channel.
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It's out there for real.
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Yeah.
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Okay, so this episode's a beast.
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I mean, we could, we're going to avoid lots of rabbit holes
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in lots of weeds.
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And that's partly intentionally, I think, Chris,
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because this is part of a topic
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that is a huge topic in your sciences and the geosciences,
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which is the relationship between large,
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igneous events, large, intrusive and extrusive events,
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what we call large, igneous provinces, LIPs, so lips,
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the correlation between those things
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and mass extinction events.
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And there is some correlation.
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There's probably some causation as well.
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But that's a big scientific debate.
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And it depends which one you're looking at,
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which pair you're looking at, you know, the timing.
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And so that's a whole series.
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I think that that we should definitely take it,
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take it dive into at some point.
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But we're going to kind of avoid some of those little rabbit holes
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as we go down and focus on.
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Maybe we will, maybe we won't, Jesse.
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We're going to get, we're going to get into the,
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well, let's get into this right, you know, like soon here.
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But I'm just going to say that you, you know,
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you just scolded me before we jumped on here.
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And, and so we're going to bring that into the discussion today,
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I think.
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I can't help myself.
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We have a scolding voice.
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We do.
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We have.
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All right.
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So Chris, let's go to start out.
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Can you give us, can you just review what is the,
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the sort of battlefield significance of the York Haven?
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Okay.
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Sure.
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And the Rossville dive.
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I said, I just want to emphasize, we saw this in the field.
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Like the field trip video, we saw this in multiple locations,
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little round top, doubles then, the weathering features were spectacular.
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So there's weathering differences that matter.
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But at a broader scale, set the stage and maybe look at this image number one here.
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Sure.
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Yeah.
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If you're looking at this image, so you have three dash lines on this little
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gift here, you have McPherson's Ridge on the northwest.
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You have Seminary Ridge right next to that, a little bit to the southeast of it.
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And then you have Semitary Ridge with the fish hook dashed in blue there.
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So McPherson's Ridge is just, it's a sedimentary anomaly with a little bit
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more resistant rock.
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And then you get to the Seminary Ridge, which is the Confederate and Warfield Ridge.
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Also, that's where the Confederates kind of positioned themselves during the three
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days.
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That's the Rossville Dyke.
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That's a Diabase Dyke.
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And then you have Semitary Ridge down there in the southeast, the fish hook there in blue.
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And that is the York Haven Diabase Sill.
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And so that just, that kind of like sets the stage.
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So all three of those are high grounds created by the resistance of each of those rock types
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that are involved.
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So the Confederates were sitting on the Rossville Dyke Ridge.
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And that was their strong point, their starting point.
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And the union was sitting on kind of this, this layer of hills that is within the York
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Haven Sill.
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And that was another high ground.
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And in between them, we had the sediments from the, the Gettysburg formation, which we've
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talked about before.
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The Gettysburg Basin.
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Yeah, that's right.
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And so if, you know, so this is a, we're zooming in now on this thing.
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If you want all the other episodes, there's two more coming out yet still that are published
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on our app right now.
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If you want access to those, early access to those, you can download them in the camp
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to your mobile app, first link in your show notes.
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We've also kind of covered a lot of this regional geology.
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We're going to show some figures and we're going to start to kind of be building this
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geological story now.
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And these, these sills and Dykes cross cut the sediments.
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So they're younger, but it's unclear how much, or you know, we're kind of estimating
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how much younger and geocrinology plays a big role here.
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So it does.
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And so, you know, everybody buckle in because Dr. Rhyming is going to go off on this.
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But the York Haven die base, you said this, you've said this many times to me personally
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that it's been really precisely dated.
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And so has the Rossville Dyke, which is slightly younger.
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So just to put timestamps on this, we're looking at the York Haven die base sill.
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Would you please find again?
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Let me interrupt, girl.
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Yes.
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And let me interrupt before you do that real quick, two quick points.
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First of all, York Haven die base.
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That's the, the regional name for the sill that some people, when you're in Gettysburg,
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they'll call it the Gettysburg sill.
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So you'll see it online things that are the Gettysburg sill.
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We're talking about the York Haven die base.
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So those are one and the same.
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The Rossville Dykes, a series of Dykes are younger than that.
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And you can see in this map image that they're clearly cross-cutting.
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You can see this nice ridge, the, the Warsville Dykes.
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Which is so nice.
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It's just so nice to have this clear cross-cutting relationship.
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Beautiful.
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To, to like timestamp things relative to each other.
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Yes.
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Exactly.
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And Chris, so the Rossville to me, but just real quick, one thing that stood out to me,
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just about the general topography, especially when we were, when we were standing on the ridges,
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the first one we were looking at cemetery ridge and then we went up into the tower
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and we were looking out over the landscape.
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And we were kind of trying to figure out that was seminary ridge, actually.
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I'm sorry, that's what, sorry, those are two very simpler words that,
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I just get flopped in my head.
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Yes, seminary ridge.
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We're up in the tower, looking over the landscape in that part of the world,
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all the little knobs.
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It took us a while to kind of figure this out, but there's a bunch of little knobs.
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Some of them are little ski hills and stuff like this, but all those little
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nobily things, little nobily hills, those are all in the York Haven database.
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Almost all of those weird little ridges and little round top and cemetery hill.
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Those are all very similar little nobles.
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So there's a very different weathering feature to them.
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They don't have long linear ridges necessarily to them.
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So anyway, that, that struck me.
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Anyway, we're talking about your problem.
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I think, I think you're right.
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I, I, I 100% backed that up.
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These are subtleties that you can see on the battlefield,
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but the geology makes it make sense.
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You know, like, when I looked at it just strictly from a historical standpoint
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for the last two decades, that didn't really make a lot of sense to me
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until I dove into this.
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You know, those little nuances of the topography is what I'm talking about.
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So geologists the best.
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Let's put some timestamps on this.
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The York Haven database, still or the Gettysburg still locally.
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201.48 million years old.
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And that's with an uncertainty of 0.031 million years.
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So, you know, that's, that's, you're talking 200 plus million years old,
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but these, these numbers matter.
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And I think we're going to get into this here in a little bit, right?
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So, Chris, I don't know how you, we talk a lot about how these numbers are hard
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to wrap your head around, especially when it's 201 point, you know, something
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201 million, 480,000 years old.
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That's that.
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And the precision on that is 31,000 years.
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So that means plus or minus 31,000 years on the York Haven.
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So that's, that is just mind boggling that we're going back 201 million years.
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And we're saying we know that age plus or minus 31,000 years.
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It never ceases to astound me how great, especially Zirca and Uranium led to your
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chronology is these days.
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Okay.
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Yeah.
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All right.
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Dr.
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Ramin, hold on a second.
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So the Rossville dikes, which are younger because, and they have to,
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I'm going to put the cross cut to your cave here.
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Yep.
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So the Rossville dikes cross cut the York Haven, so they have to be younger.
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And the Uranium to lead geochronology backs this up.
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So you have 201 point 31,000,000 years old.
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So slightly younger.
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We're talking on the order of, you get the uncertainties in here, but 150,000
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years younger plus or minus, you have to throw the answer.
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And there's no, we're kind of broadly 150,000 years younger.
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Yeah.
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Right.
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So that's what we're talking about.
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That's, I think that's cool.
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That it has to be younger because of crosscutting relations.
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But then the geochronology, people like you bear this out.
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The numbers support the observations.
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And that's, that's a cool thing.
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And it's cool to stand there, you know, stand on cemetery ridge or seminary ridge
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and look across the field and see the other one and say, you know, that's 150,000
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years younger older.
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That's a, that's a tractable amount of time you can kind of say it's not insignificant.
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I understand that amount of time.
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It's a big amount of time, but I kind of can grasp it, right?
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And it's a really interesting feature of that landscape.
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So yeah.
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That's right.
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And so as you said, that age, those that we, people don't just date these things
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really precisely for the hell of it.
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There's a reason why they go to great lengths to get that uncertainty down to
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the story.
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One thousand years or 34,000 years, like you, you have to work really, really hard
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to get that level of precision.
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I mean, this is a years long project to do that.
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And so I got a question.
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And there's a reason for that.
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Yeah.
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Sorry.
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I have a question for you then because, you know, like the literature is a little
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bit all over the place with, with these numbers.
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You'll see variation in the 201 point, you know, the decimals, the hundreds or
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tens of thousands of years, right?
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But those numbers matter.
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Why is there so much variance?
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And it's very frustrating from my standpoint, because I'm looking at this and,
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and you're trying in your head as you're reading all this stuff to try to keep
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the numbers straight because there's a very important piece of this puzzle that
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we have yet to talk about.
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And you're trying to keep it straight because it has to work.
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Yeah.
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That's right.
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Okay.
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The short answer is that techniques improve through time.
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So all literature then.
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All right.
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So older literature, the long answer is that there are different techniques at
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play.
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And so in even within one category of techniques, Zircon, Uranium, Lead Data,
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there's data treatment differences at play.
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So for instance, the first point, older literature, much of the older
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literature on these things are, we're argon, argon to your chronology, which
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just is inherently less precise.
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We don't have the dual decay system.
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It's not as well.
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I mean, it works really well, but the uncertainties are 10 times bigger than
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these Zircon, Uranium, Lead uncertainties that we get here.
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So there is just a bloodshimmer, right?
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Not a chisel.
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And then that's fair.
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The difference is a lot of the differences are, yeah, it's those differences.
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Then in a frame versus a finished carpenter, right?
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Exactly.
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Yeah, exactly right.
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Exactly right.
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Different tools in your toolbox.
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The small corrections, which are, I think, more frustrating or could be
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more frustrating.
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Like, for instance, there's some, some literature, some of the early literature
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early early in the latest phase of, of Zircon, Uranium, Lead,
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your chronology from like 2013 or something like that.
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That type of data, it's Zircon, Uranium, Lead Data, and then a recent paper
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came out and summarized a bunch of that.
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And there are little corrections that you do for things like what is the
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thorium uranium ratio of the magma?
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That's a little input parameter into the cascading data reduction.
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Yeah.
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Well, can I just talk about that a second real quick, Jesse, because thorium is
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a part of the decay series to get you down to lead.
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And so that's what you're referring to is all these daughter isotopes that
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happen along the way also have to be taken into account, right?
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That's right.
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That's what you're referring to.
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So in this time scale, it's not going to change your age from 201,000 to 202,000,
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but it can change you that the tens of thousands of years, maybe 100,000 year.
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If you change that thorium uranium ratio, and we know the limits of it,
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it's just kind of picking which value.
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And so people will go and take older data from the literature and recalibrate it
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using a different thorium uranium ratio and get a slightly different number,
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for instance.
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So and there's valid reasons for doing that.
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And there's debate about exactly which process you should use, which one's correct.
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Okay.
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Well, Jesse, it does.
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I think that's helpful.
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Let's move on.
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So let's talk about the York Haven and Diabase stills in the larger context then.
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Let's let's move to that.
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So these are a part of this.
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We're ready for an acronym.
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We've got to give people ready for an acronym coming at us.
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So it's a, it's a, well, there are a couple acronyms involved in this.
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I mean, it's an LIT.
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Yeah, lip, right?
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It's a large, agnus province.
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But this one specifically, this massive event that happened is part of what's called camp,
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not the camp that I love deer near and dear to my heart, the group camp.
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You can see a mp.
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Okay.
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I love them.
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But this is just CAMP.
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So this is the central Atlantic magnetic province.
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And so name tells you a lot, Chris.
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And this is a,
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so the central Atlantic magnetic problem.
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This is a lip, a large agnus province.
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These sills and dikes are part of that.
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The York Haven, Diabase, the Rossville or excuse me, the York Haven,
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so the Rossville Dike, these are part of the central Atlantic magnetic province.
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And this is a map, this image number three here.
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This is a map that just I pulled in a bunch of the data points that people have analyzed samples from.
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And you can find these things all have been on the east coast of North America all the way up into Newfoundland.
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You can find them down into South America, into the Amazon.
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You can find these things very similar age, similar composition, et cetera.
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You can find them in Africa and up in Europe as well.
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mainland Europe.
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So you can find these things.
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And that's kind of important because if you zipper up the Atlantic Ocean,
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then these data points are connected.
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They're close together.
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It, it, there's a, this is not random.
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This is a pattern.
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That's established here.
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In that time, 201, we talked about this couple of episodes ago in the classic rift basin,
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the sediments to Gettysburg, you know, formation.
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These were formed in kind of a rifting environment, a stretching environment.
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And so it makes sense that these basalt flows and these die-based intrusions go along with.
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Oh, good point.
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Good point.
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So we are talking about the Rossville Dikes and the York Haven die-based sills.
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Those are intrusive things.
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Those are intrusive bodies.
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But equally important, maybe more important.
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I don't know.
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You can weigh in on this, but you also have extras.
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If you have flood basalts that are involved in the space.
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The head image number four here, Chris.
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And this is an image from some of the famous flows in Morocco.
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And I've just highlighted with a gift here where the basalt flow is in this sequence.
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And it's pretty thick, right?
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This is a pretty, pretty voluminous basalt flow package.
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And just the aerial extent here is enormous.
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Camp basalts, sills and dikes have been formed.
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Ben found over 10 million square kilometers in landmass area reconstructed.
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So this is a huge area where this stuff is found.
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The volume erupted is not huge on the scale of large,
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igneous provinces, but it's still a ton, two to four million cubic kilometers of basalt erupted onto the surface.
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And some of these dikes are huge, 500 kilometers long and 30 meters wide.
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Like these are, these are monsters.
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These are monsters.
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Well, even even the York Haven, Diabase,
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Sill is on the order of 330 meters thick to 600 plus meters thick.
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You may be even 700 meters thick.
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So you know, that's, these are massive intrusions.
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These are really big ones.
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And some famous ones that people might have heard as the preckness flows up in New Jersey,
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the North mountain basalt in Nova Scotia.
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These are geological names that people might know if they've looked into this or they've,
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thought about large,
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igneous provinces and mass extinction events before.
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And so it's a lip.
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I particularly like that acronym.
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It's a lip.
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It's a large igneous province.
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There are intrusive and extras of parts to that.
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And that's going to be really important in the story of teasing a part
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how this may have or may not have influenced a mass extinction event at the end of the Jurassic.
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So that leads us to, you know, kind of parsing out these igneous events.
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And there were different phases that were involved.
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And we know this in part.
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And this kind of leads us down to the discussion now of Chris getting scolded by Dr.
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Rimec here.
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I was your first.
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He's scolding by Dr. Rimec.
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What's that?
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My first are you kidding me?
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This.
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So in the literature, you will read about these pulses that happen, these events that happen,
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maybe four of them over a 600,000 year time span.
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It's whatever.
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That's not important.
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But you'll read about the titanium levels, low titanium, high titanium.
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And I kind of went down a rabbit hole with it, you know, because the titanium levels
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in and of themselves is not important other than, okay, these magma's had different
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evolutions.
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They they had different sources.
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They were there were different times that this happened.
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But then maybe the link of low titanium to a lot of outgassing of carbon dioxide
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and sulfur dioxide, that's the whole I went down and kind of like I just said that low
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titanium kind of coincides with a lot of this, these really important gases that kind of
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set the thermostat for the planet.
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And you scolded me and said, you need to back off on this because, you know, there's
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debate involved here.
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So, well, what's the takeaway Jesse?
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I mean, you know, my, I think my take on it, at least, is that the titanium is important
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in that it's different flavors.
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It's a way that chemically that patrologists, people who study these things can chemically
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fingerprint these things.
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I say, oh, this one's high titanium and is what I court normative has high titanium
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concentrations in the rock, like the rock has more titanium than the other flavor, which
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has low titanium.
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And those tell us something about the patrology, how that basalt or dye base got to be in
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all the processes that happened before that.
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And there is a correlation between the high titanium and the low titanium and the agents,
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like there's this sort of general theme.
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But I think it's kind of, I think it gets a little complicated in trying to match those
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up across this huge area.
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Understatement of the day, it gets kind of complicated.
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Kind of complicated.
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It does.
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My sense was just, this is a rabbit hole that we could, that we don't need to go into
spk_0
to explain the story here.
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Now, I would love to go down.
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I think this deserves many episodes in some series about the link between lips and large
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and massive extinction.
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Yeah, I agree.
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Because it's really a key point.
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And there's some really interesting stuff in there or the debate.
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Well, let's see, maybe.
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That's fair.
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It's fair and I'm duly scolded.
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We're talking about the end-trastic extinction.
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So that's been dated at 201.36 million years ago.
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And so it's like it coincides with these igniast intrusions that we're talking about.
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And it coincides with these flood basalts.
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It's kind of like right in the middle of them.
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The ETE, the end-trastic extinction event is kind of straddled by these intrusions and
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extrusions.
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And so is it causal?
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Is it causal?
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That's the key.
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Yeah.
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We see this coincidence between them.
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And is it caused by the same process?
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And so let's skip ahead here to the fifth image, which I like this fossil reconstruction
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here.
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But what is the end-trastic extinction?
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Okay.
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Let's just run through some numbers.
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We lost trastic amonites, devastated corals in the oceans.
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25 to 30% of the general were lost in the oceans.
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So a big extinction event in the oceans.
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On land, huge turnover in vertebrates, we lost 95% of the megaflora, 42% of the tetrapods,
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which went extinct.
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So kind of, I don't know how to think about this, Chris.
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I'm not a paleontology expert.
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But I've thought about it like these kind of crocodile terrifying, big landcrumbs.
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Rocketile things became less important.
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And this extinction event set the stage for dinosaurs and really for mammals eventually
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to kind of take over and radiate.
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Is that, I don't know if that's accurate, like, or if that's a perfect framing of it?
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Well, I think it is.
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It's adequate for what we're doing here.
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You know, we saw on the plum run bridge, we saw dinosaur footprints in the Heidelersburg
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remember, which is older than this extinction event.
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So the dinosaurs were around, but they were different.
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They weren't very big at this point.
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And it kind of just set the stage for them to fill a niche, this biological niche, you
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know, and also the mammals that were around as well.
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And so this kind of extinction event, I think it was important from that kind of historical
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standpoint is it kind of just set the stage for them.
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Okay, sure.
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That's the stage.
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Yeah.
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That's how I feel about it.
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I like this image because it's a fight a sore, which is plant lizard, which I don't know.
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If I was naming this thing, I wouldn't think this thing looks like a plant lizard to me.
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You know, definitely not to walk around eating plants.
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I don't think I must say I'm kind of happy that the, uh, and drastic extinction occurred
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here because I don't want these things to walk around.
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This is not good.
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Um, so, all right, Jesse, let's talk about the timing of the entriassic extinction.
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How does that number happen?
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Okay.
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Maybe Chris, let's, I don't know how to do this.
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Maybe we set the stage again and, and give a little bit of a historical background.
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So like, there's this coincidence between the entriassic extinction event, which you
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see in the sediments, you have to see that in sediments, especially ocean sediments are
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the best ones for pinning down an extinction event because those are the ones where there's
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higher fossilization rate.
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That's where the, yeah, that's where the posses are going to be put.
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Yep.
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Yeah.
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In an ocean basin on land, you know, there are fossils in there, but they're, they're
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less regularly preserved.
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It's, it's more random distribution of fossils, let's say.
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So, okay, people notice this extinction event here.
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They noticed that there's basalt and sills that brought the correlate.
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Like I said, a lot of the early geochronology, the argon geochronology and some of the astronomical
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tuning stuff was, of course, a coarse thing.
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That's it.
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Yeah.
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There's a correlation here.
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Maybe it caused it.
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Some ideas about why it caused it.
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Later geochronology, especially we started to really hone the zircon uranium lead geochronology.
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That started to notice that data started to show that a lot of the basalts post data
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at the extinction event or probably post data at the extinction event.
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Just by a little bit.
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Just by a little bit.
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And that's important because if, if that's important because if the basalt happened
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after the extinction, this large igneous province, you know, then that couldn't have been
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causal.
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Well, Chris, what is, let me ask you a question.
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What is the easy explanation, the easy cause, the easy causal relationship between a large
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igneous province and a mass extinction event?
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Like, what's the, oh, gassing.
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Okay, perfect.
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See, outgassing a bunch of CO2, sulfur dioxide, mercury, and you kind of change climate, poison.
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If these, okay, let's take this a little bit of chemistry and geochemistry here.
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If you take these igneous intrusions and you inject them into hydrocarbons and...
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Hold on, hold on, no, no, no, Chris, hold that story.
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Hold that.
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I want to talk about the extrusive thing, I mean, because that comes later.
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The extrusive thing, if we were thinking, oh, if a large igneous province caused a mass
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extinction, outgassing CO2, then we'd say, oh, the basalts are the outgassing.
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They represent the outgassing.
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They represent magma-megensway to the surface, right?
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So the fact that a lot of these basalts and even things like the Rossville Dykes are
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after the extinction kind of brought this into question.
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However, more data and different data, especially focused on the intrusive rocks, has shown
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that these intrusive relationships, or these intrusive magmatic rocks, especially down
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in South America, I'll go back to this, down in South America, especially predate the extinction
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event.
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They're slightly older.
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So they're old enough to be a little bit before the extinction event.
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So okay, Chris, this begs the question, then, then, what's the process?
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What's the link we have again, this correlation, but what's the causation theory behind this?
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Can I talk now about that?
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Yes, I want you to please, please, go.
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All right.
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Well, if you take these really massive intrusions, and you inject them or squirt them into
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hydrocarbons, like petroleum and natural gas filled rocks, these sedimentary rocks, or
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you inject them into carbonates, you're going to get two gases in abundance that are going
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to be outgassed into the atmosphere, then.
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They're going to be basically liberated from the rocks, and that's carbon dioxide and
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sulfates.
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Okay.
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And both of those are greenhouse gases.
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So if you get a lot of that in a short period of time, which is what they think happened,
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this early stage that predates the ETE, the extinction event, then that could have been
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the driver of the extinction that is observed in the sedimentary rock record.
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Which is such a cool, um, I'm biased.
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I must say I'm biased because one of the people involved in this work is a friend of mine
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from graduate school, but it's such a cool theory or such a cool process.
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It's like, okay, it's not what we thought.
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It's not the normal thing that we thought.
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It's not the simple explanation.
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It's actually more complicated than that.
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And it's to cause a mass extinction, you might need basalt, basaltic magma, injecting
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into carbonates, these rock types that contain all the stuff that send mercury, that this
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volatileization, that's right.
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And mercury.
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Hold on.
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Let's talk about that a second.
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Because if you do this, what I just talked about, injecting these sedimentary rocks with this
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massive amount of magma, another thing that's going to be released is mercury.
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And you just alluded to that.
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And, and that also gets liberated.
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And so what we find in the sedimentary rocks that happen after these intrusions in these
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shallow basins is a spike in mercury that lends credibility to the idea that they're
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that that it did indeed happen before the extinction event.
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These gases were put into the atmosphere, liberated and put into the air before and maybe
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driving the extinction then.
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And then, but it makes sense too that that this would continue after the extinction.
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You know, so it happened before, during and after because this large igneous province
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spanned a pretty significant amount of time.
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We're talking to 600,000 years, you know, ish plus or minus.
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The extinction event probably didn't take that long.
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Well, yeah, but it wasn't, it, it also wasn't like an instant in time, right?
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It's, you know, things are 40,000 to 100,000 year estimates for the, the length of the extinction
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event.
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And the question, you might be sitting there listening to us thinking, well, why is this
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so hard?
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It seems like it's been nailed, right?
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Like, why is this seems simple now?
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It's not because think about how would you, I find this fun to kind of think about.
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Like, how would you identify an extinction event if you wanted to put your finger on it?
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How would you identify it?
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Well, you'd have to say, okay, what is the fossil that represents the next phase?
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What's the best fossil that represents the Jurassic?
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And I'd have to find that fossil somewhere and say, okay, that's the beginning of the
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Jurassic.
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Okay, then go back and say, well, what fossil do we not find, you know, after the Jurassic,
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what, what goes away, what dies out and find a fossil from that?
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That's a Jurassic one.
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But then you've just got a bracket.
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You've got a bracket in time.
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And you don't actually know if there's an extinction, if there's some preservation bias
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in there, if there's an extinction event, or if that bracket is actually the time that
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it took for the extinction event to happen.
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And so there's all exact time lags in it.
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And then could I either wait up to second?
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Yeah, absolutely.
spk_0
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So bracketing an extinction event is exactly, that's the correct way to put this because
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sedimentary rocks are really difficult to put an exact time stamp on because they're
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made of detrital grains, which means that if there's any zircon in the sediment, you're
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not dating when the sediment was deposited, which is what we want to know.
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You're dating when those detrital grains formed.
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So it had to be formed, get weathered out, eroded, and then deposited and lithified into
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rock.
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You know, so they're just really hard to do.
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They're hard to date this way.
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So you need other things.
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You need the fossils like ash is important, right?
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Because this is a great point and this is ash is super important and why is ash important?
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Well, because you can find zircon in it and it's a distinct event, you know, the volcanic
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eruption happened.
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Sediment in the ash came in and the zircons came from the volcano.
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So we can date that really precisely.
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And if we can date a bunch of ash layers in a sedimentary sequence, then we get, we
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can get an age model through that sediment.
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We can figure out deposition rate through that sediment.
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And that's really valuable.
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But the problem with these large, igneous provinces is that we don't have a lot of ash.
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This is basaltic eruption.
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This stuff doesn't create huge volcanic eruptions that sends ash everywhere.
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And so a continent that's extending produces, that's kind of breaking apart, produces a lot
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of basalt that basalt is preserved on land, not in the oceans.
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So the ocean sediments are better at capturing the extinction event.
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The land sediments are better at capturing the basaltic lava's, but the two don't often
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correlate and they're kind of hard to match up in different ways.
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So it's just a complicated, I mean, we don't need to get any more in the weeds.
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It's just a point to say this is a problem.
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Well, actually, I'm going to get a little bit more into the weeds.
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I have a question for you.
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Perfect.
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So going back to the mercury issue, is it enough mercury to, because mercury is a toxin,
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it's a neurotoxin, and not just to us, to just a lot of forms of life, was the mass extinction,
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then also maybe a kill shot that involved carbon dioxide, outgassing, sulfate outgassing,
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and an abundance of this neurotoxin that was liberated too.
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Could that have had something to do with it?
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I mean, it's certainly possible.
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I think the mercury thing to my knowledge is, you know, people focused on mercury for
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a while, but it's kind of a blossoming field.
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I mean, we have a new faculty member on our staff here who is a mercury expert in mercury
spk_0
in these large, these provinces.
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And there's a lot of new research coming out on mercury specifically.
spk_0
People are kind of focusing in on it.
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It's a big, it's a growing field, I would say, because you're highlighting the importance
spk_0
of why, like, is it enough?
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Is it the thing, or is it, in order to do a mass extinction, do you need one thing, or
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do you need a whole bunch of little things?
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Yeah.
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Yeah.
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Okay.
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Great question.
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Yeah.
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All right, Jesse.
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Well, let's begin to wrap this episode up.
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Why did you put back in this last image here showing, you know, we used this in previous
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episodes too.
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So let's bring this full circle.
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This is our timeline image that just shows back to the Gettysburg basin, how these things
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are preserved.
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And we have, you know, 230 million years ago, this thing starts as just a stratigraphic
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column that goes up from 230 to about 190 million years.
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We have the sedimentary rocks on the bottom, the new Oxford formation, which we don't
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see in the Gettysburg battlefield.
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Then we see the Gettysburg formation, the Heidelersburg member, which are very important
spk_0
features.
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And then right at the Jurassic, Jurassic boundary, we have probably two, it's certainly too
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thick on this, but you have to make it thick enough to represent some amount of time here
spk_0
to see it.
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But the Yorkhaven sill and the Rossville dykes, just to kind of bring this back in and highlight
spk_0
that the Rossville dyke post-Aixx extinction event, the Yorkhaven sill kind of overlaps
spk_0
maybe a little bit depending upon which of these small number changes you see, which
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reference you're looking at.
spk_0
But they are related, this event, the related to this central Atlantic, magnetic province
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event, the camp event, which to my reading, Chris, I think it's a pretty, I would say,
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the working model is that it did cause the entrassic mass extinction by exactly the
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process you described.
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These intrusions, especially in South America and Africa, intruded into the sediments that
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helped outgast the sediments, which created this climate perturbation that ended up inducing
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an entrassic mass extinction event that took several tens of thousands of years to
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kind of play out.
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I don't know, is that a good wrap up?
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It's a good story, Jesse.
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It's a good story.
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I think the end of the incursions.
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You know, what we haven't talked about at all is any of the weathering features, but I
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feel like we covered that pretty well in our field trip episode talking about the cool
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from the other end.
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Yeah, the edges, weather slower than the middle part of it and so on.
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Yeah, that is our field trip episode.
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Yeah.
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Field trip episode.
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It's just kind of nice to, when we were walking around the field trip, we looked, I mean,
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walk around in Devils Den or on Little Roundup and thinking, you know, this rock had something
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to do with a mass extinction event 200 and 1 million years ago.
spk_0
It's a fun thing to think about.
spk_0
It's a somber thing and you just saw some dinosaur footprints down the hill and now you're
spk_0
standing on the dive base that probably caused the extinction of those creatures that left
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those footprints.
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Geology is powerful.
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It all comes down to geology.
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Geology wins.
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I love that.
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Geology wins.
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Yeah.
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All right.
spk_0
Well, hey, that's a wrap on this episode.
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We've got a couple more coming at you later.
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If you want early access to those, download the campfire mobile app first link in your show
spk_0
notes.
spk_0
We have a Gettysburg Geology Visual Podcast series there.
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You can get early access to that.
spk_0
Follow us on all social media's wrap plan.
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We have a contact us link on our website, plan.
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Geocast.com.
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Cheers.
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Peace.
Topics Covered
Diabase significance
Gettysburg geology
Union forces defense
topography of Gettysburg
igneous province
mass extinction events
Rossville Dike
York Haven Diabase
battlefield geology
sedimentary anomalies
geological significance
large igneous events
geosciences discussion
historical geology
geological story of Gettysburg