Researchers say that mercury buried in ancient rock provides the strongest evidence yet that volcanoes caused the greatest mass extinction in the history of the Earth.
The extinction 252 million years ago was so dramatic and widespread that scientists call it "the Great Death". The catastrophe killed more than 95 percent of life on Earth over hundreds of thousands of years.
Paleontologists at the University of Cincinnati and the Chinese University of Geosciences said they found an increase in mercury in the geological record in nearly a dozen sites around the world, providing persuasive evidence that volcanic eruptions were to blame. this world cataclysm.
The study was published this month in the journal. Communications of nature.
The eruptions ignited vast deposits of coal, releasing mercury vapor into the atmosphere. Eventually, it rained down to marine sediments around the planet, creating an elemental signature of a catastrophe that would herald the age of the dinosaurs.
"Volcanic activities, including volcanic gas emissions and combustion of organic matter, released abundant mercury to the surface of the Earth," said lead author Jun Shen, an associate professor at the China University of Geosciences.
The mass extinction occurred in what scientists call the Permian-Triassic boundary. The mass extinction killed a large part of terrestrial and marine life before the rise of the dinosaurs. Some were prehistoric monsters in their own right, like the fierce gorgonopsids that looked like a cross between a saber-toothed tiger and a Komodo dragon.
The eruptions occurred in a volcanic system called the Siberian Traps in what is now the center of Russia. Many of the eruptions occurred not in cone-shaped volcanoes, but through huge fissures in the ground. The eruptions were frequent and lasting and their fury extended over a period of hundreds of thousands of years.
"Typically, when large explosive volcanic eruptions occur, a large amount of mercury is released into the atmosphere," said Thomas Algeo, professor of geology at the UC McMicken College of Arts and Sciences.
"Mercury is a relatively new indicator for researchers, and it has become a hot topic for investigating volcanic influences at major events in Earth's history," said Algeo.
Researchers use the sharp fossilized teeth of lamprey-like creatures called conodonts to date the rock in which the mercury was deposited. Like most other creatures on the planet, the conodonts were decimated by the catastrophe.
The eruptions propelled up to 3 million cubic kilometers of ash into the air during this prolonged period. To put that in perspective, the eruption of Mount St. Helens in Washington in 1980 sent only 1 cubic kilometer of ash into the atmosphere, even though car windshield ashes fell as far away as Oklahoma.
In fact, said Algeo, the eruptions of the Siberian Traps threw so much material into the air, especially greenhouse gases, that they heated the planet by an average of about 10 degrees Celsius.
The warming climate probably would have been one of the biggest culprits of the mass extinction, he said. But acid rain would have spoiled many bodies of water and increased the acidity of the global oceans. And the warmer water would have had more dead zones due to the lack of dissolved oxygen.
"We often scratch our heads about exactly what was most harmful, creatures adapted to colder environments would have no luck," said Algeo. "So my guess is that the temperature change would be killer number 1. The effects will be exacerbated by acidification and other toxins in the environment."
Stretching for a prolonged period, the eruption after the eruption prevented the Earth's food chain from recovering.
"It's not necessarily intensity but duration that matters," Algeo said. "The longer it went on, the more pressure was exerted on the environment."
Similarly, the Earth took a long time to recover from the disaster because continuing disturbances continued to eradicate biodiversity, he said.
Earth has witnessed five known mass extinctions in its 4.5 billion years.
The scientists used another elemental signature, iridium, to identify the possible cause of the global mass extinction that killed dinosaurs 65 million years ago. They believe that a huge meteor hit what is now Mexico.
The plume resulting from superheated earth blown into the atmosphere rained material containing iridium found in the geological record of the entire world.
Shen said the mercury signature provides convincing evidence that the eruptions of the Siberian traps were responsible for the catastrophe. Now researchers are trying to pinpoint the extent of the eruptions and what environmental effects in particular were most responsible for the mass death, particularly of terrestrial animals and plants.
Shen said that the Permian extinction could shed light on how today's global warming could lead to the next mass extinction. If global warming, in fact, was responsible for the death of the Permian, what does warming predict for humans and wildlife today?
"The release of carbon in the atmosphere by humans is similar to the situation in the Late Permian, where Siberian eruptions released abundant carbon," said Shen.
Algeo said it is cause for concern.
"Most biologists believe that we are on the cusp of another mass extinction, the sixth largest, and I share that opinion," said Algeo. "What we should learn is that this will be a serious matter that will harm human interests, so we should work to minimize the damage."
People who live in marginal environments, such as arid deserts, will suffer first. This will lead to more climate refugees around the world.
"We are likely to see more mass hunger and migration in the most affected places, it is a global problem and one that we must recognize and deal with proactively, it is much easier to address these problems before they reach a crisis."