Marine life became strangely uniform after Earth’s worst mass extinction

About 252 million years ago, Earth witnessed the worst biological disaster ever recorded. Known as the end-Permian mass extinction, it erased over 80% of marine life.

Scientists refer to it as the “Great Dying.” Yet what came next has its own strange legacy – a time when marine life everywhere looked the same.

This era, called the “Great Dulling,” spanned millions of years. From the tropics to polar regions, ocean life became oddly uniform.

Species that once stayed in tight local zones suddenly appeared everywhere. Scientists have puzzled over this mystery for decades.

Marine life changed after mass extinction

Stanford researchers now offer a compelling explanation. The team used fossil records and environmental data to track how marine creatures reacted after the Great Dying.

The research was focused on groups like clams, oysters, and snails – organisms that not only survived but spread globally.

Published in the journal Science Advances, the study introduces a climate model that tracks oxygen and temperature changes. It helps explain why some creatures expanded rapidly while others died out.

The findings suggest that global environmental shifts shaped who survived – and where they lived.

Studying mass extinctions in a new way

Study senior study author Jonathan Payne is the Dorrell William Kirby Professor of Earth and Planetary Sciences in the Stanford Doerr School of Sustainability.

“For us in the paleobiology field, this model is the equivalent to climate scientists getting computerized climate models to make quantitative predictions of how the world should change based on some simple mathematical representations,” said Professor Payne.

“We are now able to study big biogeographic changes of mass extinctions in a new way and get a better sense of why some animal groups made it through while others perished.”

Shockingly uniform marine communities

To reconstruct ancient oceans, scientists use fossils and chemical traces.

These markers reveal environmental shifts like temperature, acidity, and oxygen levels. Around the end of the Permian period, massive volcanic activity in modern Siberia set off global warming and ocean acidification.

These changes alone can’t explain why surviving species suddenly spread across every ocean. That mystery belongs to the Triassic period, when marine life grew boringly similar everywhere.

“If someone asked you today where you’d find kangaroos, you’d say Australia,” said Jood Al Aswad, the study’s lead author and a PhD candidate.

“But now imagine some major disaster happened, like a giant volcano erupted, and afterward you’re finding kangaroos in great numbers all over the globe – they’re all the way out in Antarctica, they’re hopping by the pyramids in Egypt, and they’re even in Stanford, California.”

Before the extinction, marine communities were highly diverse. Afterward, they became shockingly uniform. The team found that species variety across different parts of the world dropped by over half.

Homogenization on a global scale

For nearly 200 years, scientists have debated what caused this sudden sameness.

One idea is “ecological release” – when surviving species thrive because predators and competitors vanish. Another idea suggests that climate change made Earth more habitable to certain organisms everywhere. The Stanford team tested both ideas.

The researchers used geochemical data to model ancient ocean temperatures and oxygen levels. Then, they added physiological data from living marine animals – relatives of those ancient survivors – to simulate how creatures might have spread after the mass extinction.

The model showed that environmental conditions alone – higher temperatures and lower oxygen – were enough to predict where species could live. There was no need to consider missing predators or rivals.

“Our study has provided a simple environmental explanation, rather than an ecological one, for why certain survivors of the end-Permian extinction prospered and why homogenization happened on a global scale,” said Professor Payne.

Today’s crisis echoes past mass extinction

The model doesn’t just shed light on ancient history. It also helps scientists understand modern threats. Human activity is now causing another mass extinction. The model could offer insights into what life on Earth might look like in the future.

“The current biodiversity crisis is anticipated to herald changes in ecosystem composition that surpass even those seen in the earliest Triassic, which has been the greatest homogenization event to date,” the study authors wrote.

The research team now plans to apply this model to other mass extinction events, including the one that wiped out non-avian dinosaurs.

“Our model offers a great way of studying how animals respond to extreme changes in the environment,” said Al Aswad.

“With anthropogenically spurred climate change, there has been some warning that if we continue, then in the future we’re going to see taxonomic homogenization of organisms in modern oceans as well.”

The study is published in the journal Science Advances.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–