Ancient volcanoes poisoned ferns for millions of years

Millions of years ago, the end-Triassic period was marked by a cataclysmic mass extinction event during which massive volcanoes reshaped Earth’s climate and its life forms. A recent study from an international team of researchers highlights how ancient volcanoes and climate change caused lasting impacts on ecosystems and ferns.

Malformed ferns

The researchers examined sediments from Germany and uncovered a wealth of fossilized pollen and spores from ancient plants. Shockingly, they found a large number of fern spores with unusual deformities. These weren’t minor imperfections; the spores were distorted in strange ways, suggesting major problems during their growth.

“The sheer number and variety of malformations were astounding,” said Remco Bos, a PhD candidate at Utrecht University and lead author of the study. “It’s a clear sign that these ferns were under immense stress.”

And this wasn’t an isolated event. Similar patterns of deformed fern spores have been discovered in Denmark and Sweden. This suggests that vast regions across Europe were once filled with these struggling ferns.

Resilient ferns

Ferns are remarkably resilient plants. They are known to quickly take root in areas ravaged by natural disasters like fires or volcanic eruptions. The end-Triassic extinction, caused by massive volcanic activity, would have destroyed huge portions of forests. In this devastated landscape, ferns seized their chance and flourished, replacing trees in a significant change to the ecosystem.

However, while ferns managed to survive the immediate extinction event, their challenges were far from over. The lack of forests had a negative impact on ferns, exposing them to new dangers.

Volcanos and fern deformities

Volcanoes release numerous harmful substances, including mercury, a highly toxic element. Mercury is particularly dangerous because it can transform into a gas and be carried by winds over vast distances, contaminating areas far from the eruption site.

The research team carefully analyzed the sediment layers and discovered surges in mercury levels that directly matched the periods when deformed ferns spores were most abundant. This strong correlation provides compelling evidence that mercury poisoning was responsible for the ferns’ abnormalities.

Surprisingly, the damage wasn’t limited to the immediate aftermath of the volcanic eruptions. Scientists discovered four additional periods of elevated mercury levels and fern deformities spanning an astonishing 1.3 to 2 million years after the extinction event. This reveals a much longer and more complex environmental crisis.

Climate cycle due to volcanoes and ferns

The presence of repeated mercury spikes long after the volcanic activity subsided raises the question: what was the ongoing source of this toxic pollution? The answer involves a long-term astronomical cycle. Every 405,000 years, subtle changes in Earth’s orbit cause it to move slightly closer to the sun. This results in a periodic increase in the amount of solar radiation reaching Earth.

In the aftermath of the extinction, the planet was already experiencing abnormally high temperatures. This cyclical boost in sunlight likely caused recurring episodes of forest death. Forests that decayed or burned released the mercury they had absorbed during the volcanic era back into the environment. Rain and erosion then carried this mercury, along with mercury trapped in the soil, into waterways and surrounding landscapes.

Ferns, with their ability to thrive in disturbed environments, were able to recolonize these devastated areas. However, their resilience couldn’t protect them from the renewed waves of mercury poisoning.

Significance of volcano eruptions and fern mass extinction

“This echoes what we see with present-day mercury pollution,” said Dr. Tomas Navratil, a co-author on the study. “Forest soils can act as long-term reservoirs for mercury, which can be remobilized during hotter periods, poisoning ecosystems long after the initial contamination.”

The end-Triassic extinction serves as a powerful reminder of how climate change and pollution can become intertwined, creating devastating environmental crises. Mass extinction events, often portrayed as sudden catastrophes, are far more complex. They trigger long and unpredictable environmental disruptions that play out over extended periods.

In the case of the end-Triassic extinction, the initial volcanic eruptions caused a dramatic shift in the planet’s climate. However, the environmental consequences unfolded over millions of years. Mercury contamination from the eruptions lingered in the environment, poisoning ecosystems long after the immediate extinction event. Furthermore, natural climate cycles interacted with this pollution, creating repeated waves of ecological damage.

Earth’s resilience eventually allowed it to recover from this mass extinction. Life, however, took millions of years to return to a semblance of normality. This extended period of environmental instability highlights the profound impact that mass extinction events can have on the trajectory of life on our planet.

The study is published in the journal Nature Communications.

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