Ocean collapse triggered ancient wildfires, research suggests

Ocean collapse triggered ancient wildfires, research suggests Gaby Clark Scientific Editor Robert Egan Associate Editor Research led by the University of Alabama found that widespread wildfires during one of Earth's ancient environmental crises did not trigger an ocean collapse but were a consequence of it. The study, published in Science Advances in April, revisits the Late Devonian period, when large parts of the coastal ocean became oxygen-depleted, disrupting marine ecosystems on a global scale. This period is considered one of the five great extinction events in Earth's history. Some have proposed that wildfires, also evidenced in the geological record, might have caused the massive die-off of marine life. In theory, wildfire can mobilize nutrients from terrestrial ecosystems into coastal waters. The new findings point to a different sequence. Timing reshapes the story By analyzing chemical signals preserved in sedimentary records from a shale deposit in Tennessee, the research team reconstructed the sequence of environmental changes for the first time. The study draws in part on fossil biomarkers—organic molecules derived from past organisms and preserved in rocks—to trace processes across land and ocean systems. These molecular fingerprints reveal a clear pattern: Indicators of marine anoxia (oxygen-depleted conditions) appear first, followed by signals of terrestrial wildfire activity. This sequence provides strong evidence that ocean deoxygenation preceded widespread burning on land. "In the past, there has been no direct evidence," said Dr. Yuehan Lu, the UA researcher who led the study. This is primarily because of uncertainties in age dating. Earlier reconstructions of the sequence relied on samples collected from varying geographic locations or at less precise temporal resolutions. Lu's team sampled at one location at an exceptionally high temporal resolution, so they finally had enough detail to confirm the sequence of events. Oxygen fuels fire beyond the mass extinction interval The study links the rise of wildfires to a long-term shift in Earth's carbon cycle. When these marine anoxic events and the mass extinctions of ocean life happen, organic material sinks to the ocean floor. The carbon in those life forms is buried instead of being released into the atmosphere. In a normal cycle, this carbon would eventually bind with atmospheric oxygen to create carbon dioxide. When it is instead buried under ocean sediment, the amount of oxygen in the atmosphere is thrown out of balance. Elevated oxygen levels increase vegetation flammability and promote more frequent, intense fires. Wildfire activity thus rose—not as a trigger, but as a response to marine anoxia. The research also shows that this response is delayed and nonlinear. Importantly, this oxygen-driven increase in wildfire activity persisted beyond the mass extinction itself, suggesting a long-lasting shift in atmospheric conditions. Why it matters today Although these events occurred about 370 million years ago, the study offers insights into how tightly coupled Earth's systems are. Changes in ocean chemistry, atmospheric composition and terrestrial ecosystems can reinforce one another over long timescales. As modern climate change alters carbon cycling and wildfire regimes, understanding these deep-time feedbacks will help scientists anticipate future environmental responses. Publication details Man Lu et al, Massive wildfires followed oceanic anoxic events during the Late Devonian Frasnian-Famennian mass extinction, Science Advances (2026). DOI: 10.1126/sciadv.ady4534 Journal information: Science Advances Provided by University of Alabama in Tuscaloosa