About 252 million years ago, the Permian-Triassic crisis, widely regarded as the most severe mass extinction in the fossil record, transformed life on Earth. Estimates vary with the groups counted and the quality of the fossil record, but losses are commonly described as exceeding 90% of marine life and reaching roughly 70% of terrestrial species. The devastation was not uniform: while some groups vanished almost entirely, others survived and later diversified. New research from Stanford University offers an explanation for this uneven impact, pointing to physiological and metabolic traits that influenced which marine organisms endured.
Published in PNAS, the study combines laboratory experiments with modeling to simulate how ancient organisms responded to rising temperatures and declining ocean oxygen. Its results suggest that survival depended in part on organisms’ capacity to meet their oxygen needs as conditions changed. Paleozoic fauna, including brachiopods and crinoids, were adapted to low-oxygen conditions but could not meet the increased oxygen demand associated with warmer temperatures. In contrast, groups such as mollusks and echinoderms, despite greater oxygen requirements, had body structures and muscular capacity that helped them withstand the stresses.
Before the extinction, seafloor communities were dominated by animals characteristic of the Paleozoic. Afterward, ecological relationships shifted as surviving groups spread into newly available habitats. The study’s simulations closely matched fossil-record patterns: groups most sensitive to warming and oxygen loss lost more suitable habitat and suffered higher extinction rates, while more resilient lineages survived and expanded. Ocean acidification was another stress, though the study’s findings indicate that temperature and oxygen changes were more decisive for the groups it examined.
The leading explanation for the crisis links prolonged eruptions of the Siberian Traps to the release of carbon dioxide and methane, driving greenhouse warming. Warmer seawater holds less dissolved oxygen, while changes in ocean circulation and the spread of oxygen-poor waters further reduced habitable environments. Acidification and, in some regions, sulfide-rich conditions added other pressures. These stresses did not necessarily unfold at the same time or with equal intensity everywhere, helping explain why impacts differed among regions and lineages.
The ecological recovery was also uneven. During the Triassic, surviving bony fish diversified, with changes to jaws and teeth accompanied by changes in fins, supporting new feeding and movement strategies. That expansion illustrates how lineages that survive an extinction can occupy ecological opportunities left by groups that disappeared, reshaping marine ecosystems in the process.
Although the Permian-Triassic event occurred hundreds of millions of years ago, the study draws attention to parallels with current trends. Human-driven emissions are warming the oceans and contributing to oxygen loss, conditions that were among the stresses associated with the ancient crisis. The researchers’ projections suggest that comparable levels of warming could be reached if emissions continue unchecked, while the trajectory remains subject to human choices.
Understanding how past life responded to catastrophic environmental shifts is not just academic. As recent disasters, such as the deadly wildfire in Almería that forced mass evacuations and tragic losses, detailed in this report on the Los Gallardos fire, have shown, the interplay between environmental change and survival remains a pressing issue. The Stanford study underscores the importance of physiological ability to recover as today’s oceans continue to warm and lose oxygen.
The Permian-Triassic extinction, often called the “Great Dying,” remains a stark reminder of how rapidly life on Earth can be transformed. Its aftermath shows that survival depends on the scale of environmental change and the biological traits of individual groups. Survivors can then go on to reshape ecosystems.
