Short Wave

Why Some Species Survive Mass Extinctions

November 5, 2025

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  • The Permian-Triassic mass extinction, or The Great Dying, was triggered by massive volcanic eruptions in the Siberian Traps, leading to global warming and ocean deoxygenation. 
  • Bivalves survived the Great Dying better than their cousins, brachiopods, because bivalves were superior at coping with high temperatures and the presence of sulfide (euxinia), even though brachiopods handled low oxygen better. 
  • Understanding the synergistic effects of multiple stressors (temperature, oxygen, sulfide) during past mass extinctions, as studied by researchers like Kemi Ashing-Giwa, is crucial for informing efforts to curb modern anthropogenic climate change impacts on ecosystems. 

Segments

Introduction to Mass Extinction
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(00:00:51)
  • Key Takeaway: The Great Dying was caused by massive volcanic activity in the Siberian Traps 251.9 million years ago, leading to global warming and ocean deoxygenation.
  • Summary: The episode of Short Wave focuses on the Permian-Triassic mass extinction, known as The Great Dying, which occurred 251.9 million years ago. This event was initiated by continental-scale volcanic eruptions in the Siberian Traps, Russia. These eruptions released greenhouse gases, causing global temperature increases and a drop in ocean oxygen levels.
Bivalves Versus Brachiopods
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(00:01:56)
  • Key Takeaway: Bivalves survived the end-Permian extinction far better than their shell-bearing, filter-feeding cousins, brachiopods, prompting research into differential survival mechanisms.
  • Summary: The end-Permian extinction was the largest loss of animal diversity in Earth’s history, wiping out the vast majority of species. Marine filter feeders like bivalves (clams) survived relatively well, while brachiopods, which share similar traits, nearly went extinct. The central mystery is understanding why bivalves succeeded where brachiopods failed under the extreme environmental pressures.
Investigating Survival Factors
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(00:04:17)
  • Key Takeaway: Bivalves possess ‘advanced gills’ that allow better oxygenation at higher temperatures, contrasting with brachiopods’ slight advantage in low-oxygen conditions without heat stress.
  • Summary: Theories for differential survival include tolerance to high temperatures or low oxygen, or differences in food quality. Experimental data suggests that while brachiopods handle low oxygen slightly better, bivalves’ gill structure allows them to oxygenate more effectively when temperatures rise.
Sulfide Toxicity Experiments
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(00:05:54)
  • Key Takeaway: Bivalves demonstrated significantly higher tolerance to sulfide (H2S) compared to brachiopods, suggesting sulfide toxicity was a major factor in the extinction.
  • Summary: Research focused on the impact of sulfide, a chemical produced by bacteria in anoxic (no oxygen) environments, on both groups. Experiments showed that bivalves were much better at dealing with sulfide than brachiopods. Sulfide production spiked because the deoxygenation caused by warming favored sulfide-producing microbes.
Combined Stressor Results
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(00:09:13)
  • Key Takeaway: Bivalves survived much better than brachiopods when exposed to high temperatures combined with sulfide, confirming that synergistic stressors dictated survival.
  • Summary: Experiments testing anoxia (no oxygen) and euxinia (sulfide plus no oxygen) across temperatures revealed that at low temperatures, brachiopods fared better in anoxic settings. However, at higher temperatures when sulfide was present, bivalves survived significantly better, indicating their superior ability to handle combined stressors.
Modern Climate Change Relevance
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(00:10:15)
  • Key Takeaway: The interconnected effects of changing temperature, oxygen, and chemical factors during The Great Dying serve as a warning that modern climate change impacts are compounded and extremely tricky to manage.
  • Summary: Lessons from this mass extinction show that climate change impacts are not isolated; the combined effects of multiple environmental changes are far worse than individual factors. This complexity underscores the need to limit human impact on the climate because ecosystems are highly interlinked. The survival of ancient lineages like brachiopods is now threatened by current anthropogenic climate change.
Host’s Dual Career
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(00:11:59)
  • Key Takeaway: The guest balances her scientific research with writing science fiction, finding that each discipline inspires and maintains excitement for the other.
  • Summary: The guest, Kemi Ashing-Giwa, is also a best-selling science fiction author alongside her PhD studies. She finds that writing science fiction helps maintain her constant excitement for science, preventing burnout from the nitty-gritty of lab work. Conversely, her scientific findings inspire her fiction writing.