Around 201 million years ago, vast stretches of what is now northwestern Europe burned repeatedly. Forests that had dominated the land gave way to open fern savannahs, which in turn fed fires that raged across the landscape for tens to hundreds of thousands of years.
That picture emerges from a study published on 21 July 2026 in Nature Geoscience by an international team led by researchers from Utrecht University. The work examines one of the five major mass extinctions in the geological record, an event tied to massive volcanic releases of carbon dioxide from the Central Atlantic Magmatic Province. Those emissions drove global temperatures up by between 5 and 10 degrees Celsius.
The heat stress, combined with prolonged drought alternating with extreme precipitation, dismantled tree-dominated forests. Disturbed ground was quickly colonised by fast-spreading ferns. Once established, these plants supplied abundant fuel for fire.
Analyses of drill cores recovered from Germany, Luxembourg, Denmark and the United Kingdom show a clear interval of intense wildfire activity that coincided with the surge in fern spores. The evidence includes elevated microcharcoal, pyrolytic polycyclic aromatic hydrocarbons, and a distinctive darkening of fossil pollen and spores. Researchers call this the palynomorph dark zone.
Controlled heating experiments on modern spores confirmed that the colour change matches what would be expected from surface fires moving through fern vegetation rather than deeper burial processes. The team also developed a low-cost method known as the Palynomorph Darkness Index, which uses RGB values from ordinary light microscopy to quantify these colour shifts and track wildfire activity independently of other maturation effects.
Fire-adapted ferns sustained the cycle
Ferns did more than provide fuel. Some species appear to have acted as fire ladders, carrying flames upward, while their underground root systems allowed rapid regrowth after each blaze. This gave them a competitive edge over slower-recovering trees. The fern spike interval persisted for an estimated 40,000 to 300,000 years.
