A new study shows that the combination of volcanic activity and ocean cleansing processes has brought Earth’s ecosystems to a tipping point. Diverse and rich in marine life, Earth’s Devonian period, more than 370 million years ago, was marked by the emergence of the first seed plants that spread across vast forests on the continents of Gondwana and Laurasia.

However, the mass extinction event at the end of this period has been a matter of debate for a long time. Some scientists argue that the mass extinction during the Late Devonian period was caused by large-scale volcanic eruptions that caused global cooling. Others argue that massive deoxygenation caused by the expansion of land plants is responsible.

Latest research results

A study recently published in the journal Contact Earth and Environment The study, led by researchers at IUPUI, argues that both factors play a role and highlights the environmental milestones the planet faces today.

Filippelli and Gilhooly said the study’s findings give researchers a lot to consider. During the Devonian period, new biological influences on land negatively affected life in the ocean. Gilhooly noted that activities such as manure runoff into the ocean, combined with warming from burning fossil fuels, reduce oxygen levels in the oceans. An earlier outcome of this similar scenario in the Late Devonian had disastrous consequences, he said.

Historical lessons and contemporary implications

“Throughout Earth’s history, there have been a number of biological innovations and geological events that have completely changed biodiversity and environmental conditions in the oceans and on land,” Gilhooly said. “The new biological strategy on land during the Devonian period had a negative impact on life in the ocean. This is a sobering observation in the context of modern global and climate change resulting from human activities. We have much to learn from Earth’s history that can help us develop strategies and actions to avoid future turning points.” “

Other participants in the study included Kazumi Ozaki of the Tokyo Institute of Technology, Christopher Reinhard of the Georgia Institute of Technology, John Marshall of the University of Southampton, and Jessica Whiteside of San Diego State University.

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

Results and methodology

This study is the first to combine two competing theories of Late Devonian extinction into a comprehensive causal scenario. Essentially, the team concluded that for a mass extinction, both events would have to occur: mass volcanism and deoxygenation caused by land plants dragging excess nutrients into the oceans.

“The key to solving this puzzle was to identify and combine the timing and magnitude of the geochemical signals we identified using a complex global model,” Filippelli said. said. “These simulations showed that the nutrient abundance we observed based on the geochemical record could cause significant marine extinctions, but the duration of the events showed that both factors (tree root evolution and volcanism) were necessary to sustain marine conditions that were toxic to organisms.”

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

“The process was extremely interdisciplinary,” Gilhooly said. “This combined experience created a rigorous approach to collecting samples, correlating sequences over time, obtaining chemical data, and using geochemical models to test working hypotheses about the relative influence of biotic – plants – and chemical – volcanics – in driving the mass extinction. Our analysis , shows that the effects are much more mixed than an either-or scenario.