Stanford Scientists Say They've Cracked What Made Earth's Greatest Mass Extinction So Deadly

About 252 million years ago, at the boundary between the Permian and Triassic periods, life on Earth suffered its most catastrophic collapse — an event so severe that scientists call it the "Great Dying." Now researchers at Stanford University say they have identified why the extinction was so lethal, tracing the devastation to the metabolic limits of the creatures that could not survive a rapidly warming, oxygen-starved ocean.

The extinction wiped out roughly 96 percent of marine species and about 70 percent of land animals, reshaping the course of evolution. Its ultimate trigger has long been understood: colossal volcanic eruptions in what is now Siberia pumped enormous volumes of carbon dioxide and methane into the atmosphere, driving intense global warming and draining the oceans of oxygen. What has been harder to explain is why some groups of animals perished while others endured.

In the new study, published in the Proceedings of the National Academy of Sciences and led by Stanford's Jose Andres Marquez, the team combined physiological data from both extinct and surviving species — an approach the authors describe as a first for this event. Their analysis found that "species whose metabolisms were less able to cope with warmer, oxygen-poor water suffered the highest extinction rates," offering a mechanistic link between the environmental catastrophe and the pattern of who lived and who died.

The metabolic divide helps explain one of the era's great paleontological puzzles. Bivalves such as clams and mussels survived far better than brachiopods, the shelled filter-feeders that had dominated the seafloor for some 280 million years. Active animals with higher oxygen demands, the researchers found, tended to possess more efficient gill and muscle structures that allowed them to withstand the environmental stress, while slow-moving, low-energy filter feeders could not adapt quickly enough to the changing seas.

The findings carry a pointed message for the present. "The biggest mass extinction of all time started from a world that is very similar to today," said senior author Erik Sperling, drawing a cautionary parallel between the greenhouse conditions that unfolded 252 million years ago and the warming, deoxygenating oceans of the modern era. The study suggests that as today's seas warm and lose oxygen, the animals most at risk may again be those least equipped, physiologically, to cope.

While no single study can fully reconstruct a planetary catastrophe that unfolded over thousands of years, the Stanford work adds a crucial biological dimension to a story usually told in terms of geology and chemistry. By showing how the physiology of individual animals dictated their fate, the research brings scientists closer to understanding not just what happened during the Great Dying, but why it struck with such uneven and merciless force.