The aftermath of Earth's worst mass extinction: 250-million-year-old rocks from Svalbard hold traces of wildfires

Futura reports that an international research team has found chemical traces of wildfires in shale from Spitsbergen, the largest island of the Norwegian Arctic archipelago Svalbard. The rocks formed in the Early Triassic, around 250 million years ago, while life was recovering from the end-Permian extinction. The study appeared in Communications Earth & Environment. Its results challenge the view that wildfire activity collapsed completely after that extinction.

The Permian-Triassic mass extinction took place about 252 million years ago and is also called the Great Dying. It is the most severe extinction known, with intense warming, disturbed oceans and failing ecosystems on sea and land. Eruptions in what is now Siberia are regarded as the principal driver. Deposits from roughly the five million years afterwards hold very little fossil charcoal, the usual marker of ancient fires. This is called the Early Triassic charcoal gap. Proposed explanations were oxygen too low for burning, too little surviving vegetation to fuel fires, or fires that left no recognisable trace.

The team studied approximately 30 sediment samples. They searched for polycyclic aromatic hydrocarbons (PAHs), compounds produced when material such as plants burns incompletely. PAHs can persist for very long periods even after larger charcoal pieces are gone. The samples contained significant concentrations, with a rise in layers younger than the Smithian-Spathian stage boundary. Because coal burning, volcanic activity and reworked older organic material can also produce PAHs, the researchers compared the relative amounts of different molecules. The pattern pointed mainly to burning vegetation. Some PAHs travel far through the atmosphere before settling in the sea, so the finding does not show that fires burned at the Svalbard site itself.

The researchers also ran climate and vegetation simulations, using BIOME4 and the MIT General Circulation Model. These suggest that temperature, rainfall and plant communities could have shaped how often and where fires occurred. Futura notes that the study does not establish how many fires occurred, how large they were or whether they became more frequent everywhere. The evidence comes from one geological record.

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