Over a quarter of a billion years ago, at the end of the Permian, the resilience of life has been put to the ultimate test. Nine out of ten marine species perished – along with nearly three-quarters of land-based species – in what is now called The Great Dying.
The smoking gun is a period of intense volcanic activity in what is modern Siberia, projecting materials into the atmosphere hundreds of thousands of years before ecological catastrophe.
Now, chemists have discovered what appears to be the bullet: traces of an isotope of nickel that altered the chemistry of the planet’s oceans, triggering a domino effect that would eventually suffocate animals all over the world.
Building a record on the mother of all extinctions is a forensic exercise on an epic scale. There is no shortage of evidence, from the litany of fossils to the vast patches of igneous rock deposited in a series of cataclysmic eruptions about half a billion years ago.
It tells an all-too-familiar story of global climate change caused by volcanic eruptions, raising temperatures and deprive the oceans of their oxygen. On earth, the story was just as dark. Plants have resisted change good enough, but over a period of hundreds of thousands of years, land animals gradually died out.
Understanding the details is where it all gets a little messy. Was it global warming due to an increase in greenhouse gases? Ozone-depleting compounds digging a hole in the atmosphere? Massive poisoning of the oceans?
An important clue can be found in the geology of Meishan, a prefecture in China’s Zhejiang Province. For decades, this band of compressed rock served as a marker defining the end of the Permian and the beginning of the Triassic.
In the midst of the sediments that make up this critical layer of history, along with other similar layers around the world, is a unusual concentration of nickel.
“Nickel is an essential trace metal for many organisms, but an increase in the abundance of nickel would have led to an unusual increase in the productivity of methanogens, the microorganisms that produce methane,” he added. said geochemist Laura Wasylenki of Northern Arizona University.
Aerosols spewed out by volcanoes are certainly a source of the metal, but other more localized environmental factors should be ruled out before final claims can be made.
Wasylenki and his team analyzed black shale samples taken from the Canadian Arctic, representing oxygenated and oxygen-depleted deposits deposited during the late Permian mass extinction.
The concentrations of a specific isotope of nickel as well as the total amount of the element were plotted over a long period during the extinction, then compared to the predictions of several explanatory models.
As the amounts of the isotope barely changed on the horizon of the extinction event, the total nickel concentration plummeted, indicating uptake of the nutrient by an explosion of nickel-hungry microbes.
Their rapid growth in low oxygen conditions – and belching of large amounts of methane – would be bad news in every way, not only by contributing to greenhouse gases, but by avidly removing organic carbon from the environment, fueling a food web that would suck all available oxygen from the depths of the ocean.
“Our data provide a direct link between the global dispersion of [nickel]- rich aerosols, changes in ocean chemistry and mass extinction “, said Wasylenki.
It wasn’t a slow death either. Changes in ocean chemistry are believed to have occurred over hundreds of thousands of years, a timeline reflected in other studies.
Studying nickel isotopes to better understand fluctuations in chemistry in the distant past is a relatively new tool in the geologist’s box, but could potentially be used to solve the mystery of other ancient events.
While there is no closed file in science, the story behind one of the most catastrophic events in all of biology is slowly becoming clear.
“Prior to this study, the link between basaltic volcanism from Siberian trap flooding, marine anoxia, and mass extinction was rather vague, but we now have evidence for a specific destruction mechanism,” said Wasylenki.
This research was published in Nature Communication.