The turnover of land plants in Europe 200 million years ago was driven by environmental changes triggered by massive volcanic activity, according to a study published online this week in Nature Geoscience.

The mass extinction at the boundary of the Triassic and Jurassic periods is considered to be one of the five largest extinctions, but its causes, particularly on land, have remained elusive.

Bas van de Schootbrugge and colleagues used cores of rock to reconstruct the changing ecology and environment in what is now Germany and southern Sweden. They found that as volcanic activity increased, the lush Triassic forests were replaced by a hardier assemblage of ferns, horsetails and mosses. Geochemical analyses indicated that toxic chemicals ― generated by the interaction of basalt lava and organic matter ― were deposited throughout the European region.

The authors conclude that the decline of the forests was caused by these environmental toxins, combined with climate change triggered by massive release of carbon dioxide from the volcanic activity.