The researchers found Hg enrichments in sedimentary rocks deposited in North America and southern China 445-443 million years ago. Hg enrichments are products of multiple phases of a large igneous province volcanism. This, they say, could have led to the environmental changes that caused the disappearance of many marine animal species.

Every so often, the slate is wiped clean on the Earth. The “mass extinction” events that come close to wiping out life on the planet have been triggered by various natural phenomena. The most famous is the fifth and most recent such event, believed to have been triggered by an asteroid walloping the Earth and essentially wiping out the dinosaurs approximately 65 million years ago.

Most of the others remain mysteries over the last half billion years ago. But a new study contends that the first mass extinction event approximately 440 million years ago was caused by volcanoes, according to a new study published by the Geological Society of America.

“A volcanic trigger could explain the apparent rapidity of the Hirnantian glacial expansion and temperature decline,” write the authors. “It may also explain the severity of the first pulse of mass extinction, because marine taxa would have had little opportunity to adapt or migrate to more favorable environments.”

This first mass extinction came at the end of the Ordovician Period, and wiped out approximately 80 percent of the species on the Earth. These fauna included corals, trilobites, sea scorpions, jawless fish and other early life forms. The flora included the “land invasion of vascular plants.”

The scientists, from Amherst College and Tohoku University in Japan, analyzed sedimentary rock samples from North America and China.

The mercury found in the layers of the rock in both locations indicated that heavy volcanic activity marked the end of the period.

The mercury corresponds to huge amounts of sulfates in the atmosphere, which caused massive global cooling and killed much of the sea life.

The third and fourth are also believed to have caused by massive volcanic eruptions.

The team is proceeding to investigate the cause of the second mass extinction, they add.

Ordovician-Silurian marine fossils from the museum of Tohoku University. Photo: Kunio Kaiho