Credit
Sarah Leibovitz
A study led by Stanford University has provided the clearest explanation yet for how the “Great Dying”, the Permian–Triassic mass extinction, permanently restructured ocean life
Published in the Proceedings of the National Academy of Sciences, the research confirms that a catastrophic injection of volcanic carbon dioxide triggered global warming and ocean deoxygenation, selectively wiping out marine species with vulnerable, slow-moving metabolisms.
Mass extinction and the Great Marine Turnover
About 252 million years ago, the Permian–Triassic extinction wiped out 96% of marine species and 70% of land animals. However, the destruction was not random.
Before the event, the Earth’s seafloors had been dominated for 280 million years by the Palaeozoic fauna: mostly immobile, slow-metabolising filter-feeders like brachiopods (which resemble clams but have very little meat) and crinoids (sea lilies). The mass extinction decimated these groups, wiping out nearly all brachiopods.
Conversely, the Modern fauna, consisting of more active, mobile, or predatory organisms like bivalves (true clams, oysters, and mussels), snails, urchins, and fish, fared much better, losing only about half their species. Following the Great Dying, these faster-metabolising groups took over the vacant ecological niches and have dominated global oceans ever since.
Testing the metabolic hypothesis
While a 2018 study established that ocean warming and oxygen loss drove the extinction, its data relied heavily on modern commercial species like fish and crustaceans. To determine exactly why the Palaeozoic fauna died while modern groups survived, the Stanford team spent years collecting representative living specimens from both lineages, sourcing brachiopods from locations like the San Juan Islands.
The researchers placed the animals into specialised chambers to measure their exact oxygen consumption under shifting temperatures, revealing a critical physiological flaw in the ancient body plans:
The Palaeozoic flaw:
Animals like brachiopods have low baseline metabolic demands and can survive in stagnant, low-oxygen water that would suffocate modern species. However, when water temperatures rise, their slow metabolisms cannot adapt efficiently. Their oxygen requirements spike drastically with heat, but because they lack complex muscular systems and high-capacity gills, they cannot draw in enough oxygen to keep pace. They effectively suffocate as the temperature increases.
The modern advantage:
Mobile, athletic animals like bivalves and fish require much more oxygen at a minimum. However, because their active lifestyles require robust muscular networks and highly efficient gills, they possess the physiological “headroom” to cope when environmental stress forces their oxygen demands upward.
While ocean acidification (caused by carbon dioxide dissolving into seawater) also played a role by making shell growth more difficult, the metabolic experiments demonstrate that warming and oxygen loss were the primary killers.
A modern climate warning
The Stanford team notes that the global climate preceding the Great Dying closely mirrors the baseline climate Earth has experienced for the past tens of millions of years—a baseline now being rapidly destabilised by human fossil fuel emissions.
During the Permian-Triassic transition, massive volcanic activity drove global ocean temperatures up by 8°C to 12°C over thousands of years. Today, human activities are on track to drive temperatures up by 1.5°C to 4°C by the year 2100—a change occurring over a span of just one or two centuries rather than millennia.
The researchers warn that current worst-case emission pathways are tracking toward Permian-Triassic levels of environmental stress. Understanding how ancient marine metabolisms collapsed under sudden carbon injections provides a direct preview of which modern marine families are most vulnerable to current global warming and expanding ocean dead zones.
