Volcanic eruptions have already been appointed as the main culprit of the Permian-Triassic mass extinction.

Previous research indicated that the resulting rise in atmospheric and oceanic carbon lead to the Great dying. But new findings in the journal Geology point to a large influx of mercury as a another cause likely involved in the annihilation.

The largest source of mercury on Earth are volcanic eruptions. But while the end-Permian was a period with the highest volcanic activity in Earth’s history, no one before had thought of looking into mercury as a potential contributing factor to the greatest mass-extinction in the history of our planet.

Too much to clean up

Normally algae act as the vacuum cleaners of the ocean, absorbing mercury and transporting it to the ocean floor as they die. But the estimated amount of mercury inserted into the ecosystem by the end-Permian volcanic eruptions was thirty times higher than current levels. A load so overwhelming that the natural buffering system of algae could not stop it from spreading through the entire ecosystem. With a substance as toxic as mercury such levels would have been catastrophic for the already stressed global ecosystem.

The accumulation of stress factors on the marine ecosystems eventually led to the extinction of approximately 90 per cent of all aquatic life. But the cascading events during the end-Permian mass extinction also led to anoxic marine conditions. Which may in fact have been a blessing in disguise, since the absence of oxygen in the oceans in fact made the chemical drawdown of mercury sulphides possible, that sank to the ocean floor, thereby removing mercury from the ecosystem.

The blessing of euxinic conditions

The remaining 10 per cent of ocean dwelling species encompassed all of Life’s Kingdoms which eventually, after millions of years, managed to recover. Without the anoxic period however, this might not have been possible due to remaining high levels of mercury.

While mercury levels were exceptionally high during the mass extinction event, similar levels can currently be found at certain areas on Earth. The difference however is that those areas are contaminated through human activity. The most notable of such areas are ponds near smelters, which are so highly contaminated that aquatic life is nearly impossible. But also coal-fired power plants are a source of increased mercury levels in their direct surroundings.

The research team warns about the continuing introduction of mercury into the environment through industrial emissions. They plan to take a closer look at mercury levels during other mass extinction events, to see if there is a significant rise in those periods as well and possibly to discover what the effect of rising mercury levels on the Holocene mass extinction might be.

© Jorn van Dooren | www.bitsofscience.org