Ancient Rocks Provide Insight into How Volcanoes Caused The Mother of All Extinctions
Over a quarter of a billion years ago, near the end of the Permian, the ultimate test of life’s survival occurred. Nine out of 10 marine species perished – as did approximately three-quarters of terrestrial species – during what is now known as The Great Dying.
The smoking gun is a time of strong volcanic activity in what is now modern-day Siberia, which blasted particles into the sky hundreds of thousands of years before the ecological disaster.
Now, experts have discovered what appears to be the bullet: traces of a nickel isotope that altered the chemistry of the planet’s waters, unleashing a cascade effect that suffocated species everywhere.
Constructing a case for the mother of all extinctions is a massive forensics endeavor. There is much evidence, ranging from a plethora of fossils to massive plates of igneous rock deposited in a sequence of cataclysmic eruptions around half a billion years ago.
It depicts an all-too-familiar scenario of global climate change caused by volcanic eruptions, which send temperatures skyrocketing and deplete the oxygen in the seas. On land, the story was as depressing. Plants adapted well to the changes, while terrestrial creatures steadily dwindled over hundreds of thousands of years.
The details are when things get a little sticky. Was it global warming caused by an increase in greenhouse gas levels? Are ozone-depleting chemicals tearing a hole in the ozone layer? Oceans being poisoned in mass?
The geology of Meishan, a prefecture in China’s Zhejiang Province, provides an important insight. For decades, this compacted strip of rock served as the de facto boundary between the Permian and the Triassic.
The sediments that comprise this key layer of history, as well as other similar layers found throughout the world, have an exceptional concentration of nickel.
“Nickel is an essential trace metal for many organisms, but an increase in nickel abundance would have driven an unusual surge in productivity of methanogens, microorganisms that produce methane gas,” explains Northern Arizona University geochemist Laura Wasylenki.
While volcanic aerosols are undoubtedly a source of the metal, other, more localized environmental factors must be ruled out before any definitive claims can be made.
Wasylenki and her colleagues investigated samples of black shale from Arctic Canada, which included both oxygenated and oxygen-depleted layers formed during the end-Permian mass extinction.
Concentrations of a particular nickel isotope and the element’s total abundance were tracked over a lengthy period during the extinction and then compared to the predictions of numerous explanatory hypotheses.
While the isotope’s abundance remained constant at the extinction event’s horizon, the total concentration of nickel decreased, indicating an uptake of the nutrient by an explosion of nickel-hungry microorganisms.
Their rapid growth in low oxygen environments – and subsequent belching of copious amounts of methane – would be disastrous for the environment, not only contributing greenhouse gases but also greedily stripping organic carbon from the environment, feeding a food web that would suck up all available oxygen from the ocean’s depths.
“Our data provide a direct link between global dispersion of [nickel]-rich aerosols, ocean chemistry changes, and the mass extinction event,” Wasylenki explains.
It was also not a slow death. Ocean chemistry changes would have occurred over hundreds of thousands of years, a period reflected in previous studies.
While studying nickel isotopes to gain a better understanding of chemical variations in the distant past is a relatively new technique in the geologist’s toolbox, it has the potential to help unravel the riddle of other ancient events.
While there is no such thing as a closed case in science, the story of one of biology’s most disastrous occurrences is gradually becoming obvious.
“Prior to this study, the connection between Siberian Traps flood basalt volcanism, marine anoxia, and mass extinction was rather vague, but now we have evidence of a specific kill mechanism,” Wasylenki explains.
Nature Communications published this research.