The Earth's Devonian era, unfolding over 370 million years ago, marked a period of remarkable diversity and abundant sea life. During this epoch, the first seed-bearing plants emerged, sprawling into expansive forests across the ancient continents of Gondwana and Laurussia.
Despite this flourishing ecosystem, the Late Devonian era witnessed a contentious mass extinction event, sparking debates among scientists. Some contend that large-scale volcanic eruptions, inducing global cooling, were the culprits, while others attribute the event to a mass deoxygenation caused by the proliferation of land plants.
In a groundbreaking study published in the journal Communications Earth & Environment, researchers at IUPUI propose a reconciling perspective, suggesting that both factors played a role in this pivotal event. The study, led by Matthew Smart, an assistant professor of oceanography at the U.S. Naval Academy and a former graduate student in Gabriel Filippelli's lab at IUPUI, unifies these two competing theories into a comprehensive cause-and-effect scenario.
The research, co-authored by Filippelli and William Gilhooly III from the School of Science at IUPUI, is the first to assert that both mass volcanism and deoxygenation induced by land plants collaboratively contributed to the Late Devonian mass extinction.
“The key to resolving this puzzle was identifying and integrating the timing and magnitude of the geochemical signals we determined using a sophisticated global model,” explained Filippelli. “This modeling effort revealed that the magnitude of nutrient events we were seeing based on the geochemical records could drive substantial marine extinction events, but the duration of the events required both factors—tree root evolution and volcanism—to sustain the marine conditions that were toxic to organisms.”
The interdisciplinary nature of the study involved experts in sedimentology, paleontology, geochemistry, biogeochemistry, and mathematical modeling. The team conducted extensive geochemical analyses on hundreds of samples from various continents, including the oldest rock samples on Earth from Ymer Island in eastern Greenland.
Gilhooly emphasized the mixed influences of both biotic (plants) and abiotic (volcanoes) factors, challenging the conventional either-or scenario. The study's conclusion, drawing parallels between the Devonian era and present-day scenarios, prompts reflection on the potential consequences of human-induced activities like fertilizer runoff and fossil fuel combustion, which are impacting ocean oxygen levels.
“As we observe Earth's history, there have been numerous biological innovations and geological events reshaping biodiversity and environmental conditions,” noted Gilhooly. “The Devonian era teaches us valuable lessons about how changes on land can have profound effects on ocean life. Applying these insights to modern challenges, driven by human activities, can inform strategies to avert future environmental tipping points.”
Source: Indiana University