Some 252 million years ago, an extinction event aptly named the "Great Dying" wiped out 96 percent of animals in the sea and 70 percent of animals on land. According to a study now published in Nature Communications, the very first victims of this tragedy were not animals, but plants.
There have been five mass extinction events in Earth's history and we may be in the midst of a sixth. Of those, the "Great Dying" (technically known as the Permian-Triassic extinction event) was the most calamitous, extinguishing almost all life from the face of the planet.
Scientists now believe the process was triggered by a series of eruptions in the Siberian Traps, a region of volcanic rock in northern Russia. This, they say, released a noxious concoction of carbon monoxide, carbon dioxide, sulfur dioxide, and methane, which, in turn, resulted in a period of intense global warming and, possibly, some vinegar-like acid rain.
It proved to be too much for many of the species inhabiting planet Earth at that time.
Now, researchers at the University of Nebraska-Lincoln think high concentrations of nickel in the Sydney Basin’s mud-rock could imply some of Australia's plant species went extinct almost 400,000 years before the majority of marine animals bit the dust.
This is “big news”, says Christopher Fielding, professor of Earth and atmospheric sciences and lead author of the paper. “People have hinted at that, but nobody's previously pinned it down. Now we have a timeline,” he said in a statement.
The team came to their conclusion after analyzing fossilized pollen and studying the chemical composition of sediment in Australia's southeastern cliffsides. They say they were surprised by the presence of nickel because there are no sources of the metal in the local vicinity.
Fielding and colleagues think it is likely the nickel arrived there thanks to lava erupted in the Siberian Traps. The process, they say, may have transformed the nickel into an aerosol, which traveled by air to its new home on the Australian continent. Apparently, similarly unexpected spikes of nickel have been found elsewhere, again pointing to a similar process of air transportation.
If this is indeed the case, it may be that this extinction of plant life then triggered an extinction of herbivore life that depended on those plants for survival, and subsequently, the carnivore species that fed on the herbivores. There would also have been other contributing factors, including the acidification of the oceans and rising global temperatures.
"So it was a combination of circumstances," Fielding added. "And that's a recurring theme through all five of the major mass extinctions in Earth's history."
The Great Dying may have exceeded the current ecological crisis, said Tracy Frank, professor and chair of Earth and atmospheric sciences, but there are similarities, particularly in terms of greenhouse gas spikes and extinctions that make it worth studying.
"Looking back at these events in Earth's history is useful because it lets us see what's possible," she added. "How has the Earth's system been perturbed in the past? What happened where? How fast were the changes? It gives us a foundation to work from – a context for what's happening now."