Walk along a beach today, and the shells beneath your feet tell the story of Earth's deadliest mass extinction. Instead of the brachiopods that once dominated ancient seafloors, you're far more likely to find shells from clams and snails, which are groups that survived the catastrophic event and continue to thrive today.
A new study from Stanford University and published in the Proceedings of the National Academy of Sciences concludes that an animal's metabolism largely determined whether it survived the Permian–Triassic mass extinction about 252 million years ago, when roughly 96 percent of marine species and 70 percent of land animals disappeared.
The findings strengthen evidence that rising temperatures and widespread oxygen loss in the oceans drove what is often called the Great Dying.
"The biggest mass extinction of all time started from a world that is very similar to today in having a relatively cool, relatively well-oxygenated ocean, and then there was a giant injection of carbon dioxide into the Earth system,” said study senior author Erik Anders Sperling, associate professor of Earth and planetary sciences at Stanford, in a press release. “Understanding how Earth and Earth’s biota responded back then could inform us of what’s to come."
Read More: Poop of the Ocean’s Tiniest Organisms Could Combat Climate Change
Survival Came Down to Metabolism
The Great Dying was triggered by massive volcanic eruptions that released enormous amounts of carbon dioxide and methane, warming the planet and leaving much of the ocean warm and oxygen-depleted.
The new study found that animals least able to tolerate those conditions suffered the highest extinction rates.
"Our findings show that, across different organism groups, extinctions happened at much higher rates for those more vulnerable to increases in water temperature and decreases in oxygen availability," said lead author Jose Andres Marquez in the statement.
Before the extinction, ancient seafloors were dominated by slow-moving, filter-feeding animals such as brachiopods and sea lilies. Afterward, oceans increasingly belonged to more active creatures, including fish, clams, snails, sea urchins, and other animals with higher-energy lifestyles.
Today, only about 400 brachiopod species remain, while bivalves, including clams, oysters, and mussels, number between 10,000 and 15,000 species.
"This study is really the final nail in the coffin for what caused the Permian–Triassic mass extinction," said Sperling.
Why Some Animals Survived
The research builds on a 2018 study that linked the Great Dying to warming oceans and declining oxygen levels. This time, however, researchers gathered physiological data from animal groups that resembled those that dominated the oceans before the extinction, including living brachiopods collected in Washington state's San Juan Islands.
Laboratory experiments showed that these ancient-style animals can survive in lower-oxygen water than many modern marine species. But as temperatures rise, their slow metabolisms struggle to keep up with increasing oxygen demands. More modern groups, by comparison, are better equipped to meet those demands thanks to body plans adapted for greater activity.
The findings suggest that while ocean acidification likely added to the environmental stress, warming and oxygen loss were the primary drivers of the mass extinction.
A Warning for Today's Oceans
The researchers plan to study additional marine groups to better understand how warming, oxygen loss, and acidification interact as oceans continue to change.
Although today's extinction risks differ from those 252 million years ago, the study highlights how rapidly changing ocean conditions can reshape life on Earth.
"The bad news is, we are on track for Permian-Triassic levels of warming in worst-case scenario projections," said Sperling. Temperatures rose by an estimated 8 to 12 degrees Celsius over thousands of years during the Great Dying, while global temperatures are projected to increase by 1.5 to 4 degrees Celsius above pre-industrial levels by 2100.
"But the good news is, we're still at the point where we can change things and do something about it."
Read More: A Life Oasis Protected Plants During the Permian Mass Extinction Event
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in PNAS: Differences in physiological tolerance to global warming caused the Permian–Triassic transition between the Paleozoic and Modern faunas
