Study reshapes understanding of late-Devonian mass extinction

Diverse and rich in marine life, Earth’s Devonian era, which occurred more than 370 million years ago, saw the emergence of the first seed plants, which spread as vast forests across the continents of Gondwana and Laurussia.

However, a mass extinction event near the end of this era has long been debated. Some scientists say the Late Devonian mass extinction was caused by large-scale volcanic eruptions, causing global cooling. Others argue that a massive deoxygenation event caused by the expansion of land plants was to blame.

A study recently published in the journal Earth and Environment Communications conducted by IUPUI researchers, now posits that both factors played a role and calls attention to the environmental tipping points the planet faces today.

The study is co-authored by IUPUI School of Science faculty Gabriel Filippelli and William Gilhooly III. The lead author is Matthew Smart, an assistant professor of oceanography at the United States Naval Academy, who was a graduate student in Filippelli’s lab at the time of the study.

This work is the first to unify two competing theories of Late Devonian extinction into a comprehensive cause-and-effect scenario. Essentially, the group concluded that both events – mass volcanism and deoxygenation caused by land plants releasing excess nutrients into the oceans – had to occur for the mass extinction to take place.

“The key to solving this puzzle was identifying and integrating the timing and magnitude of the geochemical signals we determined using a sophisticated global model,” Filippelli said. “This modeling effort revealed that the magnitude of nutrient events we were observing based on geochemical records could drive significant marine extinction events, but the duration of these events required both factors – root evolution trees and volcanism – to maintain toxic marine conditions. to organisms.”

With experts in sedimentology, paleontology, geochemistry, biogeochemistry and mathematical modeling, the group literally dug deep to geochemically analyze hundreds of samples scattered across different continents. These include samples from Ymer Island in eastern Greenland, home to some of the oldest rock samples on the planet.

“The process was highly interdisciplinary,” Gilhooly said. “This combined expertise created a rigorous approach to collecting the samples, correlating the sequences over time, acquiring the chemical data, and using geochemical models to test working hypotheses about the relative influences of biotic (plants) and chemical (volcanoes) triggers ) of mass extinction. Our analyzes demonstrate that the influences are much more mixed than an “either one or the other” scenario.

Filippelli and Gilhooly said the study’s findings give researchers a lot to think about. During the Devonian era, new biological findings on land had negative effects on life in the ocean. Today, Gilhooly noted, activities such as fertilizer runoff flowing into the ocean, combined with heating from burning fossil fuels, reduce ocean oxygen levels. The previous outcome of this similar scenario in the Late Devonian had catastrophic consequences, he said.

“Throughout Earth’s history, there have been a series of biological innovations and geological events that have completely reshaped biological diversity and environmental conditions in the ocean and on land,” Gilhooly said .

“During the Devonian era, a new biological strategy on land negatively impacted life in the ocean. It’s a sobering observation when placed in the context of modern global and climate change driven by human activities. We have much to learn. Earth’s history that can help us think about strategies and actions to avoid future tipping points.”