FSU researchers note that in ancient times, mass extinctions were preceded by depletion of the crucial trace element

FSU researchers note that in ancient times, mass extinctions were preceded by depletion of the crucial trace element

Image: The research group taking samples.
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Credit: Photo by Ben Gil/Virginia Tech

A decline in the element molybdenum in the planet’s oceans preceded a major extinction event about 183 million years ago, new research from Florida State University shows.

The decline may have contributed to the mass extinction that killed up to 90% of species in the oceans, and suggests much more organic carbon was buried in the extinction than previously thought. The work is published in AGU progress.

“This research tells us more about what happened to molybdenum during this extinction event, but we’re taking it a step further,” said Jeremy Owens, associate professor in FSU’s Department of Earth, Ocean and Atmospheric Science and co-author of the publication. “Our results help us understand how much carbon was circulating through the system, and it is much larger than previously thought – possibly on the order of modern atmospheric and oceanic increases due to human activity.”

Previous research showed a depletion of molybdenum during the main phase of the ancient mass extinction event, but it was unclear how widespread the depletion was, how early it started, or how long it lasted.

To answer these questions, the researchers analyzed rocks from three locations in Alberta, Canada, that were part of a vast ocean surrounding the ancient continent of Pangea. Because the site was connected to this global ocean, researchers were able to infer conditions around the world rather than just in a single basin.

They found new estimates for the start and duration of molybdenum mining and the initial phase of deoxygenation. Their research showed that the decline preceded the onset of the extinctions by about a million years and lasted about two million years in total, much longer than scientists previously thought.

The decline in molybdenum also implies a massive increase in ocean organic carbon deposits, which may have been many times larger than previous calculations. These calculations were based on estimates of carbon dioxide release from volcanic activity, implying that carbon dioxide release from volcanoes was actually much higher, which would be necessary to offset global carbon stocks.

Just as it was 183 million years ago, more and more carbon dioxide is being added to the Earth system today, which could reduce marine trace metals like molybdenum that many organisms depend on for survival as the oceans lose oxygen and bury more organic carbon. After the ancient extinction event, global conditions gradually became more habitable, but this process took hundreds of thousands of years.

“The uniqueness of the study sites has allowed us to take an in-depth look at how global ocean chemistry has changed over millions of years, reconciling much of the current scientific debate focused on the local and global aspects of that time interval,” said Theodore Them, a former postdoctoral fellow at FSU who is now an assistant professor at the College of Charleston.

Researchers from the California Institute of Technology, Western Michigan University, the University of Utrecht, and Virginia Polytechnic Institute and State University co-authored this study.

This research was supported by grants from the National Science Foundation, NASA, and the Sloan Foundation.

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