Rapid changes in marine oxygen levels may have played a significant role in Earth’s first mass extinction, according to a new study by researchers at Florida State University.
About 443 million years ago, life on Earth was undergoing the Upper Ordovician Mass Extinction, or LOME, which 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 persistent low oxygen conditions 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 previously documented patterns of this mass extinction coincided with an initial rapid decrease in marine oxygen levels followed by a rapid increase in oxygen. Their work is published online in the journal Scientists progress.
“Paleontologists noted that there were several groups of organisms, such as graptolites and brachiopods, that began to decline very early in this mass extinction interval, but we didn’t really have strong evidence of an environmental or climate signature to link this onset decline of these groups to a particular mechanism,” said co-author Seth Young, associate professor in the Department of Earth, Ocean, and Atmospheric Sciences. This article can directly link this early phase of extinction to oxygen changes. We see a marked change in the isotopes of thallium at the same time as these organisms begin their steady decline in the main phase of the mass extinction event.”
This decrease in oxygen was immediately followed by an increase. This rapid change in oxygen coincided with the traditional first mass extinction disappearance and major ice sheet growth over the former South Pole.
“The turbulence of oxygen levels in ocean waters is really what seems to have been quite problematic for organisms that lived in the Upper Ordovician at that time, which might have been adapted to cope with low oxygen conditions. oxygen at the start or vice versa,” Young said. “The fact that oxygen levels in the oceans next to continents alternate on short geologic time scales (a few hundred thousand years) really seemed to wreak havoc on these marine ecosystems.”
The Late Ordovician extinction was one of five major mass extinctions in Earth’s history and the only one scientists are sure of occurred under what are called “icebox” conditions. in which extensive ice caps are present on the Earth’s surface. The Earth is currently experiencing ice cold conditions and a loss of biodiversity, making this ancient mass extinction an important analogue of current conditions, while trying to understand Earth’s future as our climate continues to warm and that the ice caps are receding.
Previous research on the environmental conditions surrounding LOME has used evidence found in limestones from more oxygenated environments, but this study used shales that were deposited in deeper, oxygen-poor waters, which record different geochemical signatures , allowing researchers to draw conclusions about global marine conditions. , rather than for local conditions.
“The discovery of the initial expansion of low oxygen conditions globally and the coincidence with the early phases of marine animal declines help paint a clearer picture of what was happening with this extinction event,” said lead author Nevin Kozik, a visiting assistant professor at Occidental College and a former FSU doctoral student.
The co-authors of this paper were PhD student Sean Newby and Associate Professor Jeremy Owens of FSU; former FSU Postdoctoral Fellow and current Assistant Professor at College of Charleston Theodore Them; Mu Liu and Daizhao Chen of the Chinese Academy of Sciences; Emma Hammarlund of Lund University; and David Bond of the University of Hull.
Nevin P. Kozik et al, Rapid Marine Oxygen Variability: Driving the Late Ordovician Mass Extinction, Scientists progress (2022). DOI: 10.1126/sciadv.abn8345
Provided by Florida State University
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