The fern that cooled the planet
The Arctic Ocean is covered by freshwater fern for 800,000 years
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Drilling on the Lomonosov Ridge revealed in 2004 an eight-metre layer of Azolla remains in Eocene sediments. The fern doubles its biomass in two days under favourable conditions. Estimates of the carbon burial vary widely, but the event coincides with atmospheric CO₂ beginning its long fall from around 3,500 ppm towards modern levels — the start of the cooling that ends in the ice ages. Whether Azolla was cause or symptom is contested, but it is one of the cleanest examples of a single species altering the planet's carbon budget.
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The Arctic Ocean was then a warm, almost enclosed basin with fresh water on top. A small floating fern grew there so densely that it covered the entire sea — and did so for nearly a million years. When it died and sank, it took enormous quantities of carbon to the bottom.
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Part of Terra Saga — the story of Earth on a timeline. terrasaga.org