Research findings published in the journal Proceedings of the National Academy of Sciences suggest that the Permian-Triassic extinction, the earth’s largest and known as the Great Dying, may have been caused by microbes. Their spewing of methane into the atmosphere killed about 90 percent of marine species and 70 percent of land vertebrates 252 million years ago.
Geological evidence shows there was lethally high global warming and ocean acidification at the time. One leading suggested cause is the then highly active Siberian volcanoes which put out enough lava to cover the United States entire landmass. The Siberian Traps may have fueled the growth of methane-producing microbes. The theory is other microbes converted the methane into massive carbon-dioxide levels that acidified oceans as the CO2 dissolved in the sea and turned into carbonic acid. In the sea, trilobites and sea scorpions who had existed for hundreds of millions of years vanished. CO2 formation also used up the atmosphere’s oxygen and killed the living including forests of conifers and tree ferns and the large amphibians and reptiles roaming them.
The three lines of evidence are, “First, we show that geochemical signals indicate superexponential growth of the marine inorganic carbon reservoir, coincident with the extinction and consistent with the expansion of a new microbial metabolic pathway. Second, we show that the efficient acetoclastic pathway in Methanosarcina emerged at a time statistically indistinguishable from the extinction. Finally, we show that nickel concentrations in South China sediments increased sharply at the extinction.”
The researchers found the high concentrations of nickel in the oceans attributed to the cataclysmic volcanic eruptions. Nickel is an element which facilitates the growth of Methanosarcina, members of a kingdom of single-celled organisms called archaea. They are distinct from bacteria and lack a nucleus and other usual cell structures. The oceans’ oxygen-starved conditions prevented normal microbial break down of the large quantities of organic matter’s carbon accumulated in ocean sediments, leaving a stockpile of acetate.
The Methanosarcina flourished as they used a newly evolved ability to break down acetate. They produced huge amounts of methane which would then be converted into CO2 by other microbes. The extinction was not a sudden die-off like from an asteroid impact, but unfolded over tens of thousands of years.
Microbes can have positive effects on earth depending on which chemicals they consume or release. One such example is the ‘great oxygenation event’ 2.5 billion years ago when they created oxygen-rich environments that resulted in complex animal evolution. The bacteria engaged in photosynthesis giving out huge amounts of oxygen into the Earth’s atmosphere that allowed the later appearance of animals.
One of the researchers, MIT biologist Greg Fournier said, “As small as an individual microorganism is, their sheer abundance and ubiquity make for a huge cumulative impact. On a geochemical level, they really do run the planet. “
One very tiny microbe species may have changed Earth drastically 252 million years ago and it could happen again.