Scientists Identify Cause of Earth’s Largest Mass Extinction

A groundbreaking study led by Stanford researchers sheds new light on the physiological factors that dictated which marine organisms survived the Permian–Triassic extinction event roughly 252 million years ago. Known as the “Great Dying,” this cataclysmic episode eradicated about 96% of marine species and drastically reshaped ocean life, but the reasons behind the selective survival of some groups remained elusive—until now.

Published on July 6 in the Proceedings of the National Academy of Sciences, the study pioneers a comprehensive comparison of the metabolic responses of ancient Paleozoic fauna and their modern counterparts to shifting ocean conditions. Utilizing novel experimental data, the researchers tracked oxygen consumption rates in various marine animal groups under warming and deoxygenated water, emulating the harsh environments triggered by volcanic gas emissions in the Permian seas.

Their findings pinpoint a fundamental metabolic dichotomy: the slow-moving, filter-feeding species like brachiopods and crinoids, which thrived prior to the extinction, had metabolisms highly sensitive to increased temperatures and decreased oxygen levels. In contrast, modern fauna—including mollusks such as clams and snails, echinoderms like sea urchins, and fish—displayed more efficient oxygen utilization and resilience under warming scenarios thanks to their active, mobile lifestyles.

This discrepancy explains the dramatic transition in dominance from Paleozoic fauna to today’s marine life. Brachiopods, once prevalent, now number only around 400 species, while bivalves boast tens of thousands. Their muscle-rich bodies and enhanced respiratory systems allowed modern groups to meet heightened oxygen demands during stressful climate shifts, unlike their ancient counterparts whose metabolisms could not keep pace, accelerating their decline.

The implications resonate beyond paleontology—this historic extinction was driven primarily by rapid ocean warming and deoxygenation caused by massive volcanic CO2 and methane emissions. Laboratory simulations confirm these physical stressors as the key drivers of selective extinction, with ocean acidification playing a secondary role.

Researchers caution that today’s oceans face eerily similar threats due to anthropogenic climate change. Projected temperature rises and depleting oxygen levels could imperil contemporary marine organisms, echoing ancient extinction dynamics but on a much faster timescale. Nonetheless, there remains opportunity to mitigate these trends through decisive action.

“This study dramatically clarifies why certain marine animals perished while others endured the greatest extinction event in Earth’s history,” said senior author Erik Sperling. “It underscores the urgent need to understand species’ physiological limits in the face of global warming—a lesson from deep time that could shape the future of ocean biodiversity.”

By decoding the evolutionary and metabolic parameters that shaped past extinctions, this research offers a powerful framework to predict biological responses under ongoing climate change, emphasizing the fragility and resilience of marine ecosystems confronting an uncertain future.