A new study led by researchers from Florida State University shows that rapid changes in marine oxygen levels may have played a significant role in driving the planet’s first mass extinction.
About 443 million years ago, life on Earth was going through the Late Ordovician mass extinction, or LOME, that wiped out about 85% of marine species. Scientists have long studied this mass extinction and continue to investigate its possible causes, such as reduced habitat loss in a rapidly cooling world or conditions of persistently low oxygen in the oceans.
By measuring isotopes of the element thallium—which shows particular sensitivity to changes in oxygen in the ancient marine environment—the research team found that the previously documented patterns of this mass extinction coincided with a rapid initial drop in marine oxygen levels followed by a rapid decline. An increase in oxygen. Their work has been published online in the journal Science advances.
“Paleontologists have noticed that several groups of organisms, such as Graptolites and brachiopods, began to decline very early in this period of mass extinction, but we really didn’t have any good evidence of an ecological or climate signature to correlate that early,” the author said. “These clusters back down to a specific mechanism,” co-author Seth Young, associate professor in the Department of Earth, Ocean and Atmospheric Sciences, added. “This paper can directly relate that early phase of the extinction to changes in oxygen. We see a significant change in thallium isotopes at the same time that these organisms begin their steady descent into the main stage of the mass extinction event.”
This decrease in oxygen was immediately followed by an increase. This rapid shift in oxygen coincided with the first classical mass extinction and significant growth of ice sheets over the ancient Antarctic.
“The disturbance in oxygen levels in ocean waters is really what appears to have been a major problem for organisms living in the late Ordovician period at the time, which may have been adapted to deal with initially lower oxygen conditions or vice versa,” Young said. “The fact that oxygen levels in the oceans adjacent to the continents change back and forth over short geological timescales (a few hundred thousand years) seems to be detrimental to these marine ecosystems.”
The late Ordovician extinction was one of five major mass extinctions in Earth’s history, and the only one scientists are confident it happened in so-called “ice house” conditions, in which there are widespread ice sheets on the Earth’s surface. Earth is currently experiencing ice house conditions and biodiversity loss, making this ancient mass extinction an important analogue to current conditions, along with trying to understand Earth’s future as our climate continues to warm and ice sheets retreat.
Previous research into the environmental conditions surrounding the LOME used evidence in limestone from more oxygenated places, but this study used shales deposited in deeper, anoxic waters, which record different geochemical markers, allowing researchers to draw conclusions about global marine conditions. , and not to local conditions.
“The discovery of the initial expansion of low-oxygen conditions globally coinciding with early stages of decline in marine animals helps paint a clearer picture of what was going on with this extinction event,” said lead author Neven Kozik. Visiting Assistant Professor at Occidental College and former PhD student at Virginia State University.
The co-authors of this paper are doctoral student Sean Newby and assistant professor Jeremy Owens from Florida State University. former postdoctoral scholar at FSU and current assistant professor at Theodore College of Charleston; Mu Liu and Daizhao Chen from the Chinese Academy of Sciences; Emma Hammerlund of Lund University; and David Bond from the University of Hull.
This research was supported by the National Science Foundation, the American Chemical Society, the Sloan Research Foundation, and the Geological Society of America.