The mystery of Earth's greatest mass extinction, an event so catastrophic it's known as the 'Great Dying,' has finally been unraveled by a team of scientists led by Stanford. Their findings, published in the Proceedings of the National Academy of Sciences, offer a chilling glimpse into the past and a cautionary tale for our present.
Unraveling the Great Dying
Some 252 million years ago, an extinction event wiped out an astonishing 96% of marine species and 70% of land animals. The devastation was selective, favoring certain groups over others. Before this event, the ancient seafloors were dominated by brachiopods, sea lilies, and other bottom-dwelling creatures for nearly 280 million years. Yet, after the catastrophe, these once-dominant groups were almost entirely eliminated, while mollusks, clams, and snails fared better, with only about half of their species disappearing.
A Cautionary Tale for Modern Oceans
The study's lead author, Jose Andres Marquez, explains that their research aimed to understand why we collect shells of clams and snails at the beach rather than brachiopods. The answer lies in metabolism. Species with metabolisms less adaptable to warmer, oxygen-poor waters suffered the highest extinction rates. This scenario was triggered by massive volcanic eruptions, releasing vast amounts of carbon dioxide and methane into the atmosphere, leading to dramatic planetary warming.
Implications for Today's Climate
The environmental conditions preceding the Great Dying resemble the relatively cool, oxygen-rich oceans of pre-industrial times. Associate Professor Erik Anders Sperling, the study's senior author, warns that understanding how Earth responded to this ancient climate crisis could provide insights into our future.
The Role of Metabolism in Survival
During the Paleozoic era, many marine animals were slow-moving, bottom-dwelling filter feeders, including brachiopods and crinoids. In contrast, the marine animals that flourished after the extinction were generally more active, requiring faster metabolisms to support movement and predatory lifestyles. Bivalves, for instance, have greater energy demands due to their larger bodies and muscular 'foot,' which allows them to burrow and crawl.
Recreating the Ancient Ocean Crisis
Building upon a 2018 study, the researchers filled knowledge gaps by conducting extensive fieldwork and laboratory experiments. They measured the oxygen consumption of various marine animals under different water temperatures, revealing that Paleozoic animals could survive in lower oxygen conditions but struggled to meet their increased oxygen demands as temperatures rose.
Acidification vs. Warming and Oxygen Loss
While ocean acidification, caused by carbon dioxide, made shell formation more difficult, the researchers argue that warming and oxygen depletion were the primary drivers of the mass extinction.
Lessons for Today's Oceans
The Stanford team plans to expand their research to better understand how these stressors interact in today's oceans, which are experiencing increasing warming, oxygen loss, and acidification. The bad news, according to Sperling, is that we're on track for Permian-Triassic levels of warming in worst-case scenarios. The good news, however, is that we still have the power to change course and mitigate these impacts.
