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Asteroids and Extinctions: Excerpt from Interview with Dr. Ian Miller (Geoshort) · PlanetGeo: The Geology Podcast

• 0:02
  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, so today's Geo Short is an excerpt from our interview with Dr.
• 0:18
  SPEAKER_00: Ian Miller, who is the director of Earth and Space Sciences and a curator of Paleobiology and Geology at the Denver Museum of Nature and Science.
• 0:27
  SPEAKER_00: In today's Geo Short, we talk about mass extinctions and the fossil record, and in the full interview coming out next week, we have just an amazing conversation with Ian about all things fossils and in particular some mass extinction events, where a large portion of life on Earth died in the geologic record.
• 0:45
  SPEAKER_00: So enjoy the Geo Short and tune in next week for the full interview with Dr.
• 0:49
  SPEAKER_00: Ian Miller.
• 0:52
  SPEAKER_00: So I have a couple a couple things.
• 0:53
  SPEAKER_00: First of all, you mentioned that the five mass extinction events in Earth history, or at least since multicellular life came around, and the N-Cretaceous is the most recent one.
• 1:04
  SPEAKER_00: I'm curious how the N-Cretaceous one that you've described really well compares to the other four.
• 1:10
  SPEAKER_00: Are they all the same?
• 1:11
  SPEAKER_00: Are they different?
• 1:12
  SPEAKER_00: Uh you know, kind of put this into context for us.
• 1:15
  SPEAKER_03: Absolutely.
• 1:16
  SPEAKER_03: Yeah.
• 1:16
  SPEAKER_03: So these they all have different causes, it turns out.
• 1:19
  SPEAKER_03: And so the mother of all extinctions is this one 252 million years ago.
• 1:24
  SPEAKER_03: And that one seems to be caused by massive volcanism.
• 1:27
  SPEAKER_03: Um and all the environmental effects from it.
• 1:30
  SPEAKER_03: And it plays out over like 60,000 years.
• 1:33
  SPEAKER_03: Takes a long time for things to go awry.
• 1:37
  SPEAKER_03: And in the case of the the most recent mass extinction, this dinosaur killing one, it's a moment in Earth's history.
• 1:46
  SPEAKER_03: And so that there's pretty different dynamics there.
• 1:49
  SPEAKER_00: So I have a follow-up question to that, because I'm familiar with you know a little bit of a back and forth in the literature about the controversy maybe between a mass extinction that is caused by a big volcanic eruption for a long period of time and a singular event like a meteorite impact.
• 2:05
  SPEAKER_00: I think the Ann Cretaceous, there used to be at least a fair bit of debate, and there might still be, about the Deccan traps in India being a potential cause.
• 2:13
  SPEAKER_00: You know, I've seen talks where people say, oh, here's all the mass extinction events.
• 2:16
  SPEAKER_00: And here, conveniently, there are lots of huge, volumetrically huge volcanic eruptions that take a hundred thousand years, but they're massive volumetric outflows at that same period of time, from a paleontologist's view.
• 2:30
  SPEAKER_00: How do you begin to work out how long an extinction event takes?
• 2:33
  SPEAKER_00: Because that's really the difference, as far as I can tell, between these two models.
• 2:36
  SPEAKER_03: You hit the nail right on the head, right?
• 2:37
  SPEAKER_03: And so this debate still carries on.
• 2:40
  SPEAKER_03: Was it a volcano or was it an asteroid for the dinosaur killing event?
• 2:45
  SPEAKER_03: And we know there's no debate now anymore whether or not an enormous asteroid hit us at that moment.
• 2:52
  SPEAKER_03: We're still trying to figure out the timing of the volcanic eruptions in India, but they seem to have been kicking off a few hundred thousand years before the extinction of the dinosaurs and then persisted for a couple of million years afterwards.
• 3:07
  SPEAKER_00: Oh, okay.
• 3:08
  SPEAKER_03: And so it also turns out that it looks like about 70% of the eruptions are after the boundary.
• 3:14
  SPEAKER_03: Uh, they do seem to be having a pretty significant effect on the world's ecosystems, but not an extinction level event.
• 3:21
  SPEAKER_03: Uh so the two could have conspired to set the ecosystem up before disaster, and then this, you know, this sort of a one-two punch.
• 3:30
  SPEAKER_03: And a lot of people like to think about it that way now.
• 3:33
  SPEAKER_03: I've actually come to the idea that the volcanoes are as much the creator as they are the destroyer.
• 3:39
  SPEAKER_03: So they're causing a lot of global warming, which seems to be linked to diversification of plants at different points in the record.
• 3:47
  SPEAKER_03: So we've actually sort of pushed this idea forward recently, and and it's, you know, there's still two camps, I'll put it that way.
• 3:56
  SPEAKER_03: Yeah, yeah, yeah.
• 3:56
  SPEAKER_03: For sure.
• 3:57
  SPEAKER_02: So hey, this question is for Jesse or Ian or both.
• 4:02
  SPEAKER_02: Can you paint a picture of what these volcanic eruptions look like?
• 4:05
  SPEAKER_02: Because I think people are are envisioning these massive super volcanic eruptions like Yellowstone.
• 4:10
  SPEAKER_02: Is that what we're talking about?
• 4:11
  SPEAKER_03: Yeah, so that's a great question.
• 4:13
  SPEAKER_03: They are eruptive, so they are like spewing tons and tons of lava, but think of it more like oozing molten rock onto the surface in mass amounts.
• 4:22
  SPEAKER_03: So, unlike a Yellowstone that's incredibly explosive that shoots this column of ash straight up into the sky, they're more like Hawaii.
• 4:30
  SPEAKER_03: But Hawaii on a huge scale, right?
• 4:33
  SPEAKER_03: I mean, now you're talking like you know, covering multiple states of volcanoes just spewing, continuously spewing lava, right?
• 4:41
  SPEAKER_02: So it's not the lava that the problem is, it's the gases that are associated with the lava that's being spewed out.
• 4:47
  SPEAKER_03: Absolutely right.
• 4:48
  SPEAKER_03: Yeah.
• 4:49
  SPEAKER_03: So yeah, it's the chemistry of the whatever gas that's belching into the atmosphere.
• 4:53
  SPEAKER_03: And it's doing a number of different types of gases.
• 4:57
  SPEAKER_03: And we actually look for the fingerprints of the volcanoes all the way over here, a half a world away, with the mercury that comes out of the volcanoes.
• 5:05
  SPEAKER_03: And so we can sample the rocks and see the mercury seems to tie to these massive eruptions.
• 5:11
  SPEAKER_00: I've also seen some proposals that it's not actually the volcanic eruptions that the basalt spewing out of the surface or the gases coming out of the volcano.
• 5:18
  SPEAKER_00: Instead, it's igneous rocks intruding into sediments, which causes the sediments to degas volumetrically massive amounts of toxic gas into the atmosphere.
• 5:28
  SPEAKER_00: So it's not, you know, there's a lot of uh details in the weeds here.
• 5:32
  SPEAKER_00: Yes, yeah, yeah, right, exactly.
• 5:34
  SPEAKER_00: Yeah, I'd imagine, I mean, this kind of leads nicely into my next question, but I'd imagine that trying to figure out a mass extinction event from the fossil record on the order of a few tens of thousands of years is really difficult.
• 5:47
  SPEAKER_00: You're dealing with such a small timescale to kind of uh figure out what the cause is.
• 5:51
  SPEAKER_00: Is that true, Ian?
• 5:52
  SPEAKER_03: It it it is.
• 5:53
  SPEAKER_03: So it's right, our resolution as we go back further in time sort of gets lower and lower.
• 5:59
  SPEAKER_03: So the best precision that we have when dating rocks and sort of trying to resolve these problems 66 million years ago is about 15 to 20,000 years.
• 6:10
  SPEAKER_03: So all of modern human civilization has played out in 12,000 years, right?
• 6:15
  SPEAKER_03: And we couldn't even resolve that in the rock record.
• 6:18
  SPEAKER_00: It's an amazing thing.
• 6:20
  SPEAKER_00: So, okay, all right.
• 6:21
  SPEAKER_00: So I want to step back and get a little bit more philosophical because I I study the early Earth, you know, so I'm going back in time where we have extremely limited amounts of samples.
• 6:29
  SPEAKER_00: We have five rocks, you know, on Earth that are present from more than 3.8 billion years ago.
• 6:35
  SPEAKER_00: So I I think a lot about Earth from a data limited perspective.
• 6:40
  SPEAKER_00: And I'm curious, the fossil record, you know, must be this.
• 6:44
  SPEAKER_00: It's it's a biased record in some way.
• 6:46
  SPEAKER_00: So I I will I have two kind of one basic question and one philosophical question is first of all, how are fossils formed?
• 6:51
  SPEAKER_00: And the second is how do you approach evaluating the fossil record when there's probably this bias layered on top of it?
• 6:59
  SPEAKER_00: Like, how do you think about coming to conclusions from this data set?
• 7:03
  SPEAKER_03: Yeah, so um, well, first of all, there's a whole science of how fossils are formed, and it's called taphonomy.
• 7:09
  SPEAKER_03: And there are many people who just do this, they just study the process by which something ends up becoming a fossil.
• 7:17
  SPEAKER_03: And we see it in the modern, you know, as what comes out of the rock.
• 7:21
  SPEAKER_03: And it's it's always an imperfect sort of sample of that ancient world, right?
• 7:27
  SPEAKER_03: So you can the data that you get from the fossils, you've really got to think about that in its in the context of the fact that it's an imperfect sample of that ancient world.
• 7:35
  SPEAKER_00: So is the fossil the mechanism of fossil formation?
• 7:38
  SPEAKER_00: We're taking like a piece of bone or a tooth or something like that, and it's turning into rock, right?
• 7:43
  SPEAKER_00: I mean, can you describe at a very basic level, or very simplified level, that process for us, real quick?
• 7:48
  SPEAKER_03: Yeah, so it it turns out that you actually get sometimes fossils that are the original material.
• 7:53
  SPEAKER_03: So in the case of a plant, you can get a tree that gets squished in the rocks, and you actually get the carbon of the tree.
• 8:00
  SPEAKER_03: It looks like a pancake when it comes out of the hill, but we see them all the time.
• 8:03
  SPEAKER_03: So you're actually seeing the carbon from the original tree.
• 8:06
  SPEAKER_03: But sometimes those trees might be petrified, and this is often the case in vertebrate fossils, where on a on a molecular level, you're actually exchanging the chemistry of the original organism with uh essentially silica and making a rock out of it.
• 8:23
  SPEAKER_03: So in the case of trees, you petrify trees and you get this beautiful, colorful, petrified wood in the end, and it might even have cellular detail if you cut it and look at it underneath a microscope.
• 8:35
  SPEAKER_03: But it's not the tree anymore.
• 8:37
  SPEAKER_03: It's been replaced at the uh molecular level.
• 8:40
  SPEAKER_03: The carbon has been replaced by silica.
• 8:42
  SPEAKER_03: It's very complicated, as I should, you know.
• 8:44
  SPEAKER_03: So many things are replaced by different kinds of chemicals.
• 8:48
  SPEAKER_03: But what's also interesting is that you also don't get the whole organism usually, right?
• 8:53
  SPEAKER_03: That's you know, we often think of like a dinosaur beautifully preserved from its nose to the tip of its tail.
• 8:58
  SPEAKER_03: But the truth is we're looking at these animals through their teeth, through little isolated bones, you know, fingers, vertebrae, and for plants, we might have their seeds or their pollen or their leaves.
• 9:10
  SPEAKER_03: And so we have to reconstruct these ancient worlds from just the sort of parts that have fallen apart and become part of the fossil record.
• 9:17
  SPEAKER_00: Okay.
• 9:18
  SPEAKER_00: Oh, interesting.
• 9:18
  SPEAKER_00: So then back to the fossil record in interpreting it.
• 9:21
  SPEAKER_00: You know, the place that we were talking about, uh Coral Bluffs, this is maybe a location that's exceptional only for its preservation, not for what was going on in the time.
• 9:31
  SPEAKER_00: Like presumably, all these mammals were all over the place.
• 9:33
  SPEAKER_00: They just got preserved in this area.
• 9:35
  SPEAKER_00: Is that is that an accurate description or not?
• 9:37
  SPEAKER_03: That's completely accurate, right?
• 9:39
  SPEAKER_03: It's a window that is given to us through this sort of special chemistry of the rocks that allow us to see this life that was everywhere, right?
• 9:48
  SPEAKER_03: And it's just getting preserved in this moment.
• 9:50
  SPEAKER_03: So it's sort of no, that's a that's a very accurate description.
• 9:54
  SPEAKER_00: So I guess that's kind of similar to the earlier thing a little bit.
• 9:57
  SPEAKER_00: You work with what you have, not with what you don't have.
• 9:59
  SPEAKER_00: Because if you don't have it, it doesn't really mean anything.
• 10:02
  SPEAKER_00: You know, the the fact that it's not preserved is meaningless.
• 10:04
  SPEAKER_03: Uh yeah, I feel like I'm shooting in the dark most of the time, right?
• 10:08
  SPEAKER_03: So yeah, yeah.
• 10:09
  SPEAKER_03: It's uh it's not that we're completely making things up, but we have but we we do have uh limited.
• 10:17
  SPEAKER_01: We're gonna edit that part out.
• 10:21
  SPEAKER_01: Jesse, that's all he does, is just shoots in the dark.
• 10:24
  SPEAKER_01: He has no idea what the hell's going on.
• 10:27
  SPEAKER_00: So no, that's really interesting.
• 10:30
  SPEAKER_00: I mean, I think the interpreting the rock record, which is very biased, and we know it's biased, you know, we kind of have to think about our approach to understanding that, um, which is a fun exercise in some ways.
• 10:42
  SPEAKER_00: It makes it makes locations like you're describing really valuable.
• 10:46
  SPEAKER_03: Yeah, I mean, it's it's and I'm sure this is the case in the early Earth as well.
• 10:50
  SPEAKER_03: You just get these exceptional sort of windows and into the history, right?
• 10:53
  SPEAKER_03: And they don't occur everywhere.
• 10:55
  SPEAKER_03: And and when you have one, it just opens up a new data set.
• 10:58
  SPEAKER_03: And in the case of this one, we've we've got people all over the world working on these fossils now, just because nobody really had access to this information before.
• 11:06
  SPEAKER_03: So it becomes a treasure trove that goes well beyond us, right?
• 11:10
  SPEAKER_03: We happen to be the discoverers of it, but you know, science is taking advantage of it now, and it's it'll it'll generate all kinds of ideas well beyond what our brains can come up with.
• 11:20
  SPEAKER_00: All right, thanks for listening.
• 11:21
  SPEAKER_00: And as a reminder, you can tune in to the full interview with Dr.
• 11:24
  SPEAKER_00: Ian Miller next week, Thursday on Planet Geo.
• 11:28
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• 11:31
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• 11:33
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• 11:37
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• 11:41
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• 11:44
  SPEAKER_00: Take care.