Why Some Species Survive Mass Extinctions

Around 250 million years ago, one of Earth’s largest known volcanic events set off The Great Dying: the planet’s worst mass extinction event. The eruptions spewed large amounts of greenhouse gases into the atmosphere, temperatures rose globally and oxygen in the oceans dropped. And while the vast majority of species went extinct, some survived. Scientists like paleophysiology graduate student Kemi Ashing-Giwa https://kashinggiwa.com/research/ want to know why, because lessons about the survivors of The Great Dying could inform today’s scientists on how to curb extinctions today. Interested in more Earth science? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:44Speaker 00

  You're listening to Short Wave from NPR.

• 0:49Speaker 02

  Hey, ShortWavers. Producer Burleigh McCoy guest hosting today with an episode about a mysterious mass extinction.

• 0:56Speaker 03

  So 251.9 million years ago, there are these volcanoes that erupt, and they pump all these greenhouse gases into the atmosphere.

• 1:07Speaker 02

  This is Kemi Ashingiwa. She's a paleophysiology graduate student at Stanford University. And this volcanic activity she's talking about wasn't just one or two eruptions, it was on the scale of the whole continent, in what is now the Siberian Traps in Russia.

• 1:23Speaker 03

  And as a result of this, there is global climate change. Temperatures go up, oxygen in the ocean goes down. Not everything dies, but almost everything dies.

• 1:35Speaker 02

  This mass extinction, Earth's third, is known as the Great Dying, though the official name is the Permian Triassic or the End Permian Mass Extinction.

• 1:44Speaker 03

  The End Permian is the largest loss of animal diversity in Earth's history.

• 1:49Speaker 02

  The vast majority of all species on land and at sea were wiped out, but a small percentage survive, like a class of marine filter feeders called bivalves.

• 2:00Speaker 03

  Bivalves are essentially like clams.

• 2:02Speaker 02

  Which there are a lot of on Earth, relatively.

• 2:05Speaker 03

  Which is why when you go to a seafood restaurant, there are mussels up the wazoo.

• 2:10Speaker 02

  Less triumphant, the tail of their distant cousins, the brachyopods.

• 2:15Speaker 03

  They both have shells. They're both filter feeders. But brachyopods, almost no one is heard of because they almost all went extinct at the End Permian.

• 2:26Speaker 02

  And the mystery is, why did bivalves do so good when brachypods almost went extinct?

• 2:31Speaker 03

  We want to know how climate change impacts species on the scale of planets.

• 2:37Speaker 02

  Because, Kimmy says, the conditions that led to the world's largest mass extinction? Those volcanoes that erupted some 250 million years ago and spewed greenhouse gases into an ancient sky?

• 2:49Speaker 03

  Those greenhouse gases is actually similar to anthropogenic climate change.

• 2:55Speaker 02

  Today on the show, a mass extinction mystery. How scientists are looking to descendants from the great dying for clues that may help the species of today. You're listening to Short Wave, the science podcast from NPR.

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  This message comes from Planet Visionaries. If you're looking for a dose of optimism, Planet Visionaries is the podcast you need. Host Alex Honnold sits down this season with extraordinary doers creating real climate action. It's a lineup that proves hope isn't naive. It's fuel for change. In partnership with the Rolex Perpetual Planet Initiative, this is Planet Visionaries. Listen or watch wherever you get your podcasts.

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• 4:33Speaker 02

  Okay, Kami, can you lay out the possibilities of why some species in this epic mass extinction called the Great Dying die out while a handful lived?

• 4:45Speaker 03

  Okay, that is, that is the question. So at the end Permian, bivalves beat out their distantly related cousins, brachyopods. And one of the biggest questions for this extinction is how? And people suggested all sorts of things. People have talked about, you know, maybe bivalves are better at dealing with high temperature. Maybe bivalves are better at dealing with low oxygen. People have talked about, you know, competition and food availability, availability and the quality of this food. And so there are all these theories, but there's not as much quantitative data.

• 5:26Speaker 03

  And so that's where ecosys scientists and paleophysicists come in. We're trying to collect data, quantitative data to support these theories.

• 5:36Speaker 02

  Okay, and what, what have you learned from that data? Like, what are bivalves better at that brachyopods aren't, or vice versa?

• 5:45Speaker 03

  So, brachyopods are better at dealing with low oxygen. But then when you increase the temperature, the, um, let's say the quote unquote advanced skills of the bivalve let them oxygenate themselves better and they went out in the end. So, just to restate that, brachyopods are a bit better at dealing with low oxygen, but bivalves are better at dealing with high temperatures. When it comes to my own research, I recently finished up a study looking at the impact of sulfide on bivalves and brachyopods. And what I saw in this study was that bivalves are much, much better at dealing with sulfide

• 6:30Speaker 03

  than brachyopods are. And this could help explain potentially how bivalves were able to win out in the end.

• 6:39Speaker 02

  Okay, um, so your experiments are specifically looking at how clams versus brachiopods respond to sulfide. What is sulfide?

• 6:47Speaker 03

  Yes.

• 6:48Speaker 02

  Where did it come from and what's it doing to them?

• 6:51Speaker 03

  Okay, so sulfide is H2S. It is this chemical that is produced by bacteria in anoxic settings.

• 7:02Speaker 02

  No oxygen.

• 7:03Speaker 03

  No oxygen, yeah. So essentially, when the end permeant happened, greenhouse gases resulted in this uh huge spike in temperature. Uh, it resulted in this huge decrease in oxygen. And these microbes that produce sulfide love anoxia. They love it when there's no oxygen. And so this deoxygenation happened. These microbes that produce sulfide were living it up. They produce tons of sulfide and then you have a lot of sulfide in the ocean. And that put pressure on animals.

• 7:38Speaker 02

  I see, okay. So what made you wanna go this route? All the other things that could have been this kill switch, why did you pick sulfide?

• 7:47Speaker 03

  Um, so there's been a lot of discussion about temperature. There's been a lot of discussion about oxygen. There's been a lot of discussion about sulfide. But there's a limited number of experiments on all three of these together, or even two of them together. And I think in the labs that I'm part of, there is definitely an emphasis on, you know, the synergistic effects between all of these different factors. And I think that's important to investigate and um interesting to study, yeah.

• 8:22Speaker 02

  Um, and so are you looking at sulfide with other things?

• 8:26Speaker 03

  Yeah.

• 8:26Speaker 02

  Are you like, okay?

• 8:27Speaker 03

  Um, so with this study, um, I was looking at the impact of sulfide or the impact of eucynesis, that sulfide with no oxygen. I was looking at the impacts of anoxia, which is just no oxygen.

• 8:42Speaker 02

  No oxygen.

• 8:42Speaker 03

  No oxygen, yeah. And I was um looking at these effects on the species at a range of temperatures.

• 8:51Speaker 02

  Okay, and then briefly paint the picture of what your experiments look like, like? You don't have a clam in your left hand and like you're.

• 9:00Speaker 03

  Pretty much with these experiments, I collected a bunch of bivalves and brachypods. And then I put some into a euksinic setting, so sulfide with no oxygen. And I put some into anoxic settings, so no oxygen and no sulfide there. And I looked at their survival over a couple of months at these different temperatures.

• 9:26Speaker 02

  And then what did you learn from your experiments?

• 9:28Speaker 03

  Yes, uh, what I ended up seeing overall was that at the low temperatures in anoxic settings, uh, brachypods ended up beating out bivalves. But then at higher temperatures, when you added sulfide, bivalves ended up surviving much, much better. Uh, and this indicates that bivalves are better able to deal with these added stressors that mass extinctions like the end Permian presented animals with.

• 9:55Speaker 02

  Okay, so at low temperatures, brachypods, good. High temperatures, sulfur, bad.

• 10:04Speaker 03

  Brachypods, that, yes.

• 10:05Speaker 02

  Got it. And so then how does this work help us solve the mystery of what happened during the end Permian mass extinction?

• 10:13Speaker 03

  So the experiments indicate that bivalves are better able to deal with these stressors, um, which helps explain why they did so well post extinction.

• 10:22Speaker 02

  And why most people haven't heard of brachypods.

• 10:25Speaker 03

  Right, because they got their butts kicked.

• 10:27Speaker 02

  The winners write history.

• 10:29Speaker 03

  Yeah.

• 10:29Speaker 02

  The clams, the clams.

• 10:30Speaker 03

  The clams, yeah, yeah.

• 10:32Speaker 02

  Now, how could all of this together, your experiments, what you know from other researchers, help the species of today?

• 10:39Speaker 03

  Yeah, so mass extinctions provide a lot of critical information about how climate change, changes in temperature, changes in oxygen, um, changes in things like sulfide, uh, how those changes impact.

• 10:57Speaker 03

  Animal life and life in general. And so what we have learned from our experiments, from these various models and all of these studies, is that it's not just temperature that matters. It's not just oxygen that matters. It's not just sulfide that matters. It's all of these things together because their combined effects are so much worse. And I think it means that climate change is an extremely tricky problem, an extremely complicated problem. And we really want to limit our impact on the climate and on these ecosystems as much as possible because everything is interlinked. I think brachypods have been around for a really, really long time.

• 11:40Speaker 03

  They survived the end Permian, and it would be a real tragedy for anthropogenic climate change to be the thing that knocks them out for good.

• 11:49Speaker 02

  Kimmy, thank you so much for chatting with me today.

• 11:52Speaker 03

  Thank you so much for having me.

• 11:56Speaker 02

  This episode was produced by Hannah Chin and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts, and Jimmy Keeley was our audio engineer. Beth Donovan is our vice president of podcasting. I'm Birdley McCoy. Thanks for listening to Short Wave from NPR.

• 12:16Speaker 02

  Aside from pursuing a science PhD, you are also a bestselling sci-fi author. You've said that you get a lot of your sci-fi ideas from your science, which I get, makes sense. I'm wondering, does it ever work the other way around?

• 12:31Speaker 03

  I would say yes, absolutely. I think writing science fiction and reading and watching really good science fiction like helps me maintain this, I think, constant excitement about science and the work. I think it's easy to get lost in the nitty gritty of experiments when you've spent, you know, like 10 hours in the lab. But I definitely use science to inspire my fiction, and I definitely use the media that I love to, I think, bolster my excitement for science.

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