A New Twist On The Cause Of The Earth's Greatest Extinction Event

The Dragon Cliffs in Arctic Canada contain records of vast periods of Earth's history, including the largest extinction event in the planet's history. Nickel isotope ratios in rocks deposited at that time offer a hint as to how that event occurred. Image Credit: Arctic23 - Flickr, CC BY 2.0

New evidence has provided confirmation for the idea that immense volcanic eruptions caused the end-Permian mass extinction, but offers a novel twist as to the connection. A paper in Nature Communications reveals the eruptions were accompanied by an increase in nickel abundance, which altered the balance of life-forms on the planet, eventually sending the atmosphere's composition haywire.

Mass extinctions are measured by the proportion of species that go extinct during them. On this basis, the end-Permian, also known as the Permian-Triassic event, exceeded the dinosaur-killing end of the Cretaceous, as well as all but the worst projections for the Anthropocene extinction event. Approximately 90 percent of marine lifeforms and three-quarters of land-dwellers died out.

The event coincided with the eruption of a vast volcanic province in Siberia. Although few paleontologists considered this likely to be a coincidence, the connection has not been clear. Volcanic eruptions on this scale can be locally devastating and can change the global atmosphere, leading to extinction events, but other eruptions of similar size have killed a far smaller proportion of species.

Dr Laura Wasylenki of Northern Arizona University and co-authors have found what she considers to be the missing link in the form of nickel isotopes deposited in sedimentary rocks of the period. Wasylenki found 252 million-year-old Arctic Canadian rocks from the Sverdrup Basin have the highest proportion of light nickel isotopes ever measured in sedimentary rocks.

With all the world's continents united into Pangea at the time, Sverdrup was quite close to the Siberian traps. She concluded the Siberian volcanoes spat our immense quantities of lighter nickel isotopes, which eventually found its way into these rocks as they were laid down.

Nickel is not toxic enough to have directly killed many living things and is indeed required in trace quantities for the survival of many living things.

Hence, Wasylenki thinks the effect of nickel was in the other direction, causing immense blooms of methane-producing microorganisms. “Increased methane would have been tremendously harmful to all oxygen-dependent life,” she said in a statement. So much methane would have cooked the planet, as well as reducing oxygen abundance, making it hard to breathe.

“Our data provide a direct link between global dispersion of Ni-rich aerosols, ocean chemistry changes and the mass extinction event," Wasylenki continued.

The 300,000-year delay between the start of the eruptions and the extinction event has been another longstanding puzzle. The indirectness of the process Wasylenki proposes might help explain this.

Signs of nickel's involvement have been found before. In Meishan, South China, a spike in nickel abundance coincides with rocks recording the extinction event. Meanwhile, the Tunguska Basin, where the volcanoes were, holds immense nickel-sulphide or deposits part of which could have been released into the atmosphere during the eruptions. These deposits are possibly; “The only known occurrence of a flood basalt-associated magmatic sulphide system that was shallow enough to degas,” the paper says.

It took three million years for marine ecosystems to recover.


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