Mass extinction event was due to oxygen-depleted seas

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Mass extinction event was due to oxygen-depleted seas

September 01, 2019 - 11:00
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Researchers have solved the mystery of the Lau/Kozlowskii extinction which took place 420 million years ago, in which 23 percent of marine life on Earth was wiped out.

Artist's depiction of fish during the Silurian Period.

Around 420 million years ago, 23 percent of all marine animals were wiped out in a mysterious mass extinction event.

This was known as the Lau/Kozlowskii extinction, and it took place at the end of the prehistoric Silurian Period.

Throughout the years, no one has managed to uncover the cause of the devastation—there was no known meteor crash or volcanic eruptions that took place that could have caused it.

Until now.

Researchers from Florida State University (FSU) have discovered that the mass extinction was triggered by rapid and widespread depletion of oxygen in the global oceans.

They recently published their findings in the Geology journal.

In their research, the team used advanced geochemical methods including thallium isotope, manganese concentration, and sulfur isotope measurements from important sites in Latvia and Sweden to reconstruct a timeline of ocean deoxygenation with relation to the Lau/Kozlowskii extinction and subsequent changes to the global carbon cycle.

According to the press release of their findings: “Their multiproxy measurements established a clear connection between the steady creep of deoxygenated waters and the step-wise nature of the extinction event—its start in communities of deep-water organisms and eventual spread to shallow-water organisms.”

In addition, the team discovered that the extinction was likely to have been driven in part by the proliferation of sulfidic ocean conditions.

“For the first time, this research provides a mechanism to drive the observed step-wise extinction event, which first coincided with ocean deoxygenation and was followed by more severe and toxic ocean conditions with sulfide in the water column,” said FSU doctoral student Chelsie Bowman, who led the study.

Co-author Jeremy Owens, an assistant professor in the Department of Earth, Ocean and Atmospheric Science, added, “This work provides another line of evidence that initial deoxygenation in ancient oceans coincides with the start of extinction events.”

“This is important as our observations of the modern ocean suggest there is significant widespread deoxygenation which may cause greater stresses on organisms that require oxygen, and may be the initial steps towards another marine mass extinction.”

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