Methane-spewing microbes — not volcanoes or asteroids — triggered a global catastrophe 252 million years ago that wiped out nearly all life on Earth, according to a new theory put forward by scientists.
The mass extinction represented the worst of five such catastrophic events thought to have occurred during the history of the planet, with more than 90 percent of marine species and 70 percent of land vertebrate species wiped out. The scale of this extinction dwarfs the calamity that doomed the dinosaurs 65 million years ago, thought to have been triggered by a six-mile-wide asteroid smacking the planet.
Microbes known as Methanosarcina multiplied on a massive and sudden scale in the ocean, spewing methane into the atmosphere and causing dramatic changes in the chemistry of the seas and the Earth's climate, according to the theory, put forth Monday by scientists at the Massachusetts Institute of Technology and colleagues in China.
The resulting burst in methane produced effects similar to those predicted by current models of global climate change: a sudden, extreme rise in temperatures, combined with acidification of the oceans.
"I would say that the end-Permian extinction is the closest animal life has ever come to being totally wiped out, and it may have come pretty close," said MIT biologist Greg Fournier, one of the researchers.
"Many, if not most, of the surviving groups of organisms barely hung on, with only a few species making it through, many probably by chance," he added.
On land, most species were killed off, except for a handful of lineages, including ancestors of modern mammals.
Methanosarcina grew in a frenzy in the seas, disgorging huge quantities of methane into the atmosphere, they said. This dramatically heated up the climate and fundamentally altered the chemistry of the oceans by driving up acidity, causing unlivable conditions for many species, they added.
Asteroids and volcanic eruptions have been blamed for the mass extinction, but researchers instead pointed to microbes.
Geochemical evidence showed an exponential increase of carbon dioxide in the oceans at the time of the Permian extinction. At the same time, genetic evidence shows a change in Methanosarcina that allowed it to produce methane from an accumulation of carbon dioxide in the water.
Finally, sediments show a sudden increase in the amount of nickel deposited at the time. Though volcanic eruptions on their own could not explain why the die-off happened so quickly, they probably released extra nickel into the environment, which fed the microbes, said Fournier.
"A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease," he said. "Instead, we see the opposite — a rapid, continuing increase. That suggests a microbial expansion."
Microbes can increase carbon production exponentially, which might explain the speed and scale of the extinction, he said.
The research — funded by NASA, the National Science Foundation, the Natural Science Foundation of China and the National Basic Research Program of China — appears in the journal Proceedings of the National Academy of Sciences.
The first dinosaurs appeared 20 million years after the Permian extinction.
"Land vertebrates took as long as 30 million years to reach the same levels of biodiversity as before the extinction, and afterward life in the oceans and on land was radically changed, dominated by very different groups of animals," Fournier said.
Al Jazeera and wire services