Researchers identify what caused Earth’s biggest mass extinction

Around 252 million years ago, Earth experienced the most catastrophic extinction event in its history. Known as the Permian–Triassic mass extinction, or the Great Dying, it wiped out an estimated 96% of marine species and around 70% of land animals, permanently reshaping life on the planet.

Image used for illustrative purposes/NASA/Unsplash

Now, researchers from Stanford University say they have uncovered the strongest evidence yet explaining why some marine animals survived while others disappeared forever.

Published in the journal Proceedings of the National Academy of Sciences, the study found that rising ocean temperatures and declining oxygen levels were the primary drivers behind the mass extinction. The research also helps explain why modern oceans are dominated by shellfish, fish and starfish rather than brachiopods – clam-like animals that once ruled the seafloor.

The scientists discovered that marine animals with slower metabolisms were particularly vulnerable to warmer, oxygen-poor waters. These conditions developed after massive volcanic eruptions released enormous quantities of carbon dioxide and methane into the atmosphere, dramatically altering Earth’s climate.

“With this study, we essentially wanted to solve the mystery of why, when you go to the beach, you collect the shells of clams and snails rather than those of brachiopods,” said lead author Jose Andres Marquez, formerly of Stanford University.

The findings reveal that groups unable to cope with warmer, less oxygenated oceans experienced far higher extinction rates than more adaptable species.

Before the Great Dying, slow-moving, filter-feeding creatures such as brachiopods and sea lilies dominated the ocean floor. After the extinction, more active animals with faster metabolisms – including bivalves, snails, fish, sea stars and sea urchins – flourished and eventually became the dominant marine life seen today.

The research builds on previous work linking the extinction to widespread ocean warming and oxygen depletion but expands the evidence by examining ancient animal groups that were hardest hit, rather than relying only on modern marine species.

Researchers conducted fieldwork and laboratory experiments to compare how ancient and modern marine animals respond to warming water. They found that while ancient species could tolerate lower oxygen levels under cooler conditions, their metabolisms struggled as temperatures rose, making them far more susceptible to extinction.

The study also found that although ocean acidification likely played a role, warming and oxygen loss were by far the most significant factors driving the collapse of marine ecosystems.

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Beyond solving a long-standing scientific mystery, the findings also carry a warning for the future.

According to the researchers, Earth’s oceans before the Great Dying were relatively cool and well oxygenated, much like they have been for millions of years before modern industrialisation. The rapid increase in greenhouse gases then triggered dramatic warming – a process with concerning parallels to today’s human-driven climate change.

“The biggest mass extinction of all time started from a world that is very similar to today,” said senior author Erik Sperling. “Understanding how Earth and Earth’s biota responded then could inform us of what’s to come.”

While temperatures during the Great Dying rose by an estimated 8–12°C over thousands of years, scientists note that current warming is occurring much faster. Under the highest emissions scenarios, global temperatures could rise between 1.5°C and 4°C above pre-industrial levels by the end of this century.

The researchers stress that, unlike 252 million years ago, humanity still has the opportunity to reduce emissions and avoid the worst outcomes for today’s marine ecosystems.

SOURCE: EurekAlert