An extinction event is defined as a widespread and rapid decline in Earth’s biodiversity. A sharp change in the diversity and abundance of multicellular organisms is indicative of such an event. It occurs when the rate of extinction exceeds the rate of speciation and the rate of background extinction.
According to new research from Florida State University, a decline in the element molybdenum across the planet’s oceans preceded a significant extinction event about 183 million years ago. The decrease may have contributed to the mass extinction, which killed up to 90% of oceanic species, and it implies that much more organic carbon was buried in the extinction event than previously estimated. The findings have been published in AGU Advances.
“This research tells us more about what was happening with molybdenum during this extinction event, but we also take it a step further,” said Jeremy Owens, an associate professor in FSU’s Department of Earth, Ocean and Atmospheric Science and a paper co-author. “Our findings help us understand how much carbon was cycling through the system, and it’s much larger than previously thought – potentially on the scale of modern atmospheric and oceanic increases due to human activities.”
The uniqueness of the study sites has allowed us to take a deep look into how the chemistry of the global ocean changed over millions of years, which reconciles much of the current scientific debates that are focused on the local versus global aspects of this time interval.
Theodore Them
Previous research showed decreases in molybdenum during the main phase of the ancient mass extinction, but it was unclear how widespread the decrease was, how early it started or how long it lasted.
To find answers, the scientists examined rocks from three locations in Alberta, Canada, that were once part of a massive ocean that surrounded the ancient continent of Pangea. Because the site was linked to the global ocean, the researchers were able to infer conditions from all over the world rather than just one basin.
They discovered new estimates for the beginning and duration of molybdenum drawdown, as well as the first phase of deoxygenation. Their research revealed that the decline began about one million years before the extinction and lasted about two million years in total, which is much longer than scientists had previously estimated.
The decrease in molybdenum also implies a massive increase in organic carbon burial in the ocean, which could be several times greater than previously calculated. Those calculations were based on estimates of the amount of carbon dioxide released by volcanic activity, implying that the amount of carbon dioxide released by volcanoes was actually much higher, which would be required to balance global carbon reservoirs.
Carbon dioxide is being added to the Earth’s system at an increasing rate, just as it was 183 million years ago, which may reduce marine trace metals such as molybdenum, which many organisms rely on for survival as the oceans lose oxygen and bury more organic carbon. Following the ancient extinction event, global conditions gradually improved, but it took hundreds of thousands of years.
“The uniqueness of the study sites has allowed us to take a deep look into how the chemistry of the global ocean changed over millions of years, which reconciles much of the current scientific debates that are focused on the local versus global aspects of this time interval,” said Theodore Them, a former postdoctoral fellow at FSU who is now an assistant professor at the College of Charleston.
