Scientists say that mercury buried in old stone gives the strongest evidence that volcanoes caused the greatest mass extinction in the history of the earth.
The extermination 252 million years ago was so dramatic and widespread that scientists call it "the great dying." The catastrophe killed more than 95 percent of life on earth for hundreds of thousands of years.
Paleontologists at the University of Cincinnati and China's University of Earth Sciences said they found a nail in mercury in the geological record of nearly a dozen sites around the world, providing compelling evidence that volcanic eruptions would blame this global catastrophe.
The study was published this month in the journal Nature Communications .
The outbreaks ignited coal deposits, releasing mercury vapor high into the atmosphere. Eventually it rained down into the marine sediment around the world, creating an elementary signature of a disaster that would mean the age of dinosaurs.
"Volcanic activities, including the release of volcanic gases and the combustion of organic matter, released abundant mercury to the surface of the earth," said senior author Jun Shen, a professor at the University of China's Geosciences University.
Mass extinction occurred at which researchers call the Permian-Triassic Boundary. Mass extinction killed much of the terrestrial and marine life before the emergence of dinosaurs. Some were prehistoric monsters in themselves, like the grymonopsides that looked like a cross between a saber-toothed tiger and a Komodo dragon.
Outbreaks occurred in a volcanic system called Siberian traps in what is now central Russia. Many of the eruptions did not occur in cone-shaped volcanoes but through gaping cracks in the ground. The outbreaks were frequent and prolonged and their fury stretched over hundreds of thousands of years.
"When you have large explosive volcanic eruptions, a lot of mercury is released into the atmosphere," said Thomas Algeo, a professor of geology at UC's McMicken College of Arts and Sciences.
"Mercury is a relatively new indicator for researchers. It has become a hot topic to investigate volcanic influences on major events in Earth's history," Algeo says. [1
The outbreaks drove as much as 3 million cubic meters of ash high up in the air during this longer period. To put it in perspective, the 1980 outbreak of Mount St. Helens in Washington only 1 cubic kilometer ash in the atmosphere, although ash fell on the car window as far away as Oklahoma.
In fact, Algeo said outbreaks of Siberian traps spewed so much material into the air, especially greenhouse gases, that it warmed the planet by an average of about 10 degrees Celsius.
The heat climate would probably have been one of the greatest sins of mass extinction, he said. But acid rain would have destroyed many water bodies and increased the acidity of the global oceans. And the warmer water would have had more dead zones from lack of dissolved oxygen.
"We have often left the scraping head about what was most harmful. Creatures that were adapted to colder environments would have been unlucky" Algeo said. "So my guess is that temperature change would be the No. 1 killer. The effects would be aggravated by acidification and other toxins in the environment."
Stretching over a long period of time prevented outbreaks after the outbreak of the Earth's food chain to recover.  "It's not necessarily the intensity but how long it is," said Algeo. "The longer this went on, the more pressure was on the environment."
Likewise, the earth was slow to recover from the disaster, as the ongoing disturbances continued to wipe out biodiversity, he said.
Earth has witnessed five known mass extinctions over its 4.5 billion years.
Researchers used another elementary signature – iridium – to determine the probable cause of global mass extinction that obliterated the dinosaurs 65 million years ago. They believe that a huge meteor hit what is now Mexico.
The resulting plum of superheated soil blown into the atmosphere rained down material containing iridium contained in the geological record around the world.
Shen said the mercury signature provides convincing evidence that outbreaks of Siberian traps were responsible for the disaster. Now, researchers are trying to reduce the extent of the outbreak and what environmental effects were particularly responsible for the mass reduction, especially for ground animals and plants.
Shen said that the opportunity could highlight how global warming today can lead to the next mass extinction. If global warming was actually responsible for Permian death, what warming gives rise to humans and wildlife today?
"Emissions of coal into the atmosphere of humans resemble the situation in the late perm, where abundant coal was released by the Siberian outbreaks," Shen said.
Algeo said it's worrying.
"A majority of biologists believe we are facing another mass extinction – the sixth major. I also share that view," says Algeo. "What we should learn is that this will be serious business that will harm human interests so that we should work to minimize the damage. "
People living in marginal environments like dry deserts will suffer first. It will lead to more climate refugees around the world.
" We will probably see more famine and mass migration in the most difficult places. It is a global issue and one that we should recognize and proactively manage. It is much easier to deal with these problems before they reach a crisis. "