Earth’s Biggest Mass Extinction Reveals Chilling Parallels to Today’s World : ScienceAlert

For the first 280 million years of animal life on Earth, slow-living creatures such as clam-like brachiopods and crinoid sea lilies dominated seafloor ecosystems.

Then, suddenly, things changed.

The planet warmed due to enormous amounts of greenhouse gases unleashed into the atmosphere by massive volcanic eruptions, triggering the Great Dying that ended the Permian period.

It’s the largest mass extinction in Earth’s history so far. And, in many ways, it was eerily similar to the kind of climate change we’re experiencing today, with rapidly warming seas starving for oxygen.

New research led by Stanford University scientists has now uncovered a strong link between the extinction of what were dominant marine groups and the deadly heat and low-oxygen conditions that plagued end-Permian oceans.

Before the Great Dying, the seafloor was home to many different creatures, some of which are still around today, and others that we know only from fossils.

Earth scientist Jose Andres Marquez and his colleagues have now figured out what made the difference between those species that survived this catastrophic climate change event and those that didn’t.

“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,” Marquez says.

“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.”

Essentially, the slow metabolisms of Paleozoic fauna made them particularly vulnerable to these drastic changes, compared to the species that survived: what the researchers call ‘modern’ fauna, like molluscs, fish, starfish, and sea urchins.

The researchers demonstrated this by comparing the tolerance of 38 different species under the heat and low-oxygen conditions of the Permian-Triassic extinction event.

They included 9 species of Paleozoic fauna (some of the few that did actually survive past the Great Dying) and 29 species of modern fauna.

For some of those species, Marquez and team conducted experiments to collect new data on the limits of their tolerance, while for others, they used data from prior studies.

Bringing all that data together revealed that Paleozoic fauna tended to be far more sensitive to temperature and oxygen levels than modern fauna.

“The aerobic metabolisms of the Paleozoic fauna are more rapidly
limited by oxygen as water temperatures increase (or their biogeographic ranges are more rapidly limited by oxygen as temperatures increase) compared to their modern faunal counterparts,” the authors explain in their paper.

Interestingly, Paleozoic fauna were better able to tolerate low oxygen (hypoxia) so long as they were in a resting state. In an active state, this advantage disappeared.

Looking at only two factors, oxygen and temperature, the researchers don’t rule out that other environmental stressors, such as ocean acidification, may also have contributed to the intolerable conditions of the Great Dying.

Nevertheless, the findings paint a pretty clear picture.

“The bad news is, we are on track for Permian-Triassic levels of warming in worst-case scenario projections,” says Stanford earth scientist Erik Sperling.

“But the good news is, we’re still at the point where we can change things and do something about it.”

When the Great Dying occurred, temperatures increased by 8-12 °C (46-54 °F) across thousands of years.

In the present day, across just a few hundred years of emissions, temperatures are projected to rise 1.5-4 °C above pre-industrial levels by 2100.

The big difference is we’re the ones releasing those emissions into the atmosphere. We can’t stop a volcano from erupting, but we can stop burning fossil fuels.

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“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,” Sperling says.

“Understanding how Earth and Earth’s biota responded back then could inform us of what’s to come.”

The research was published in Proceedings of the National Academy of Sciences.

This article was fact-checked and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.