Clue in ancient limestone sheds light on Early Jurassic mass extinction

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Scientists have uncovered an important clue in Italian limestone that helps explain a mass extinction of marine life that happened millions of years ago.

This discovery may offer warnings about how oxygen depletion and climate change could impact today’s oceans.

Michael A. Kipp, an assistant professor of earth and climate science at Duke University, explains, “Events like this in Earth’s past are the best comparisons we have for what might happen in the next decades and centuries.”

Kipp coauthored a study published in the Proceedings of the National Academy of Sciences.

The study measures the loss of oxygen in oceans that led to the extinction of marine species 183 million years ago during the Jurassic Period. At that time, marine reptiles like ichthyosaurs and plesiosaurs thrived in the oceans.

During this period, volcanic activity in what is now South Africa released an estimated 20,500 gigatons of carbon dioxide (CO2) over 500,000 years. This massive release of CO2 warmed the oceans, causing them to lose oxygen. As a result, many marine species suffocated and went extinct.

“It’s a comparison, but not a perfect one, for predicting future oxygen loss in oceans due to human-made carbon emissions and the impact on marine ecosystems and biodiversity,” says coauthor Mariano Remírez, an assistant research professor at George Mason University.

The researchers studied limestone sediment containing chemicals from the time of the volcanic eruptions. This allowed them to estimate the changes in oxygen levels in ancient oceans. They found that at one point, up to 8% of the ancient global seafloor completely lost oxygen, an area roughly three times the size of the United States.

Since the Industrial Revolution in the 18th and 19th centuries, human activity has released CO2 emissions equivalent to 12% of what was released during the Jurassic volcanism. However, Kipp points out that today’s rapid rate of atmospheric CO2 release is unprecedented in history, making it difficult to predict when another mass extinction might occur or how severe it might be.

“We’ve never seen anything this severe,” Kipp says. “Even the most rapid CO2-emitting events in history aren’t fast enough to perfectly compare to what we’re experiencing today. We’re disrupting the system faster than ever before.”

Kipp adds, “We have at least quantified the marine oxygen loss during this event, which will help refine our predictions of what might happen in the future.”

The research offers valuable insights and emphasizes the importance of understanding past events to better prepare for future changes in our oceans.