Short Wave - Why Some Species Survive Mass Extinctions

Episode Date: November 5, 2025

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 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 [e-mail] 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.See 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

Hey, shortwavers, I have a free and quick favor to ask. Right now on the app or platform where you're listening, could you leave us a rating or a review? Because it really helps new listeners find our show. And we read what people write, like this listener who recently said, quote, bite-sized pieces of fascinating science news. It's now one of my go-toes as a source of interesting non-political news. Feedback like this helps us figure out what you like and what you don't. So leave us a review and keep listening.

to Shortwave. All right, onto the show. You're listening to Shortwave from NPR. Hey, Shortwavers, producer Burley-McCoy guest hosting today with an episode about a mysterious mass extinction. So 251.9 million years ago, there are these volcanoes that erupt and they pump all these greenhouse gases into the atmosphere. This is Kemi Ashing-Giwa. She's a paleo-physiology 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 a whole continent, in what is now the Siberian traps in Russia. 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. This mass extinction, Earth's

third, is known as the Great Dying, though the official name is the Permian Trident. or the N-Permian mass extinction. The N-Permian is the largest loss of animal diversity in Earth's history. 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. Bivalves are essentially like clams. Which there are a lot of on earth, relatively. Which is why when you go to a seafood restaurant, there are muscles up the wazoo.

Less triumphant, the tale of their distant cousins, the brachio pods. They both have shells. They're both filter feeders. But brachio pods almost no one is heard of because they almost all went extinct at the end Permian. And the mystery is, why did bivalves do so good when brachio pods almost went extinct? We want to know how climate change impacts species on the scale of planets. Because, Kemi says, the conditions that led to the world's life. largest mass extinction, those volcanoes that erupted some 250 million years ago and spewed greenhouse gases into an ancient sky. Those greenhouse gases is actually similar to anthropogenic climate change. 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 Shortwave, the science podcast from NPR. Okay, Kemi, can you live? Can me, can you live? out the possibilities of why some species in this epic mass extinction called the Great Dying die out while a handful lived. That is the question. So at the end Permian, Bivalves beat out their distantly related cousins, brachio pods. 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 vivalves are better at dealing with low oxygen. People have talked about, you know, competition and food availability and the quality of this food. And so there are all these theories, but there's not as much quantitative data. And so that's where ecophysiologists and paleophysiologists come in. we're trying to collect data, quantitative data, to support these theories. Okay, and what have you learned from that data? Like, what are bivalves better at that brachio pods aren't or vice versa?

So brachyopods are better at dealing with low oxygen, but then when you increase the temperature, the, let's say the quote unquote advanced gills of the bivalve let them oxygen themselves better, and they went out in the end. So just to restate that, brachio pods 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 brachio pods. And what I saw in this study was that bivalves are much, much better at dealing with sulfide than brachio pods. are. And this could help explain potentially how bivalves were able to win out in the end. Okay. So your experiments are specifically looking at how clams versus brachio pods respond to sulfide. What is sulfide? Yes. Where did it come from? And what's it doing to them? Okay. So sulfide is H2S. It is this chemical that is produced by bacteria. in noxic settings. No oxygen. No oxygen. Yeah. So essentially, when the end permeant happened,

greenhouse gases resulted in this huge spike in temperature. It resulted in this huge decrease in oxygen. And these microbes that produce sulfide love an oxia. They love it when there's no oxygen. And so this deoxygenation happened. These microbes that produced 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. I see. Okay. So what made you want to go this route?

All the other things that could have been this kill switch. Why did you pick sulfide? 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, these synergistic effects between all of these different factors.

And I think that's important to investigate and interesting to study. Yeah. And so are you looking at sulfide with other things? Yeah. Are you like, okay. So with the study, I was looking at the impact of sulfide or the impact of eucinias, that's sulfide with no oxygen. I was looking at the impacts of anoxia, which is just no oxygen at all. No oxygen. No oxygen. Yeah. And I was looking at these effects on the species at a range of temperatures. 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 a Brachyopon. Pretty much with these experiments, I collected a bunch of bivalves and brachio pods, and then I put some into a eucynic 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 months at these different temperatures. And then what did you learn from your experiments? Yes. What I ended up seeing overall was that at the low temperatures in anoxic settings, brachio pods end up beating out bivalves. But then at higher temperatures, when you added sulfide, bivalves ended up surviving much, much better. And this indicates that bivalves are better able to deal with these added stressors that mass extinctions like the end permian presented animals with. Okay.

So at low temperatures, brachio pods, good, high temperatures, sulfur, bad. Bracobot's bad. Okay, got it. And so then how does this work help us solve the mystery of what happened during the end-permient mass extinction? So the experiments indicate that bivalves are better able to deal with these stressors, which helps explain why they did so well post-extinction. And why most people haven't heard of brachio-pods. Right, because I got their butts kicked.

The winner's right history. Yeah. The clams, the clams. The clams, yeah. Now, how could all of this together, your experiments, what you know from other researchers, help the species of today? Yeah. So mass extinctions provide a lot of critical information about how climate change, changes in temperature, changes in oxygen, changes in things like sulfide. how those changes impact 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 brachyopods have been around for a really, really long time. 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. Kemi, thank you so much for chatting with me today. Thank you so much. for having me. This episode was produced by Hamachin and edited by our showrunner Rebecca Ramirez.

Tyler Jones checked the facts and Jimmy Keely was our audio engineer. Beth Donovan is our vice president of podcasting. I'm Birdley McCoy. Thanks for listening to Shortwave from NPR. Aside from pursuing a science PhD, you are also a best-selling 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? 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 that I love to, I think, bolster my excitement for science.