Solving the World's Greatest Murder Mystery

Photo: Permian-triassic boundary, Meishan, China. The band of calcium-, carbon- and nickel-rich limestone deposits are the remains of fossilized marine shell creatures, which died in massive numbers after a major volcanic event deposited ash the MIT researchers tested and dated. Shuzhong Shen, 2014

One of science's deepest mysteries appears to have been solved: 252-million-year-old fossils show that at the close of the Permian Era, nearly 90 percent of all species on the planet were abruptly destroyed in a mysterious planet-wide disaster that scientists call the Great Dying. This was by far the worst extinction event in Earth's history.

After decades of ingenious detective work, combining genetic analysis, biochemistry and geochemistry, in 2014, a team of MIT researchers, with the support of NASA, the National Science Foundation, the Natural Science Foundation of China, and the National Basic Research Program of China concluded that the global killer came in the form of microbes. A species of methane-producing archaea named Methanosarcina bloomed explosively across the planet's oceans, spewing great clouds of toxic methane gas into the atmosphere, dramatically altering the climate and the ocean's chemistry. Methanosarcina's sudden, explosive spread seems to have been due to its ability to harvest carbon and nickel, emitted by the era's massive volcanism.

MIT geophysics professor Daniel Rothman, along with a team of six other MIT and Chinese scientists discovered three key pieces of evidence: a massive Permian ocean-wide carbon dioxide increase, coupled with genetic changes in Methanosarcina that permitted it to produce methane after extracting organic carbon from sea water. The third key piece of evidence used to build their case is a sudden massive buildup of nickel deposits at the time.

The carbon deposits indicate a significant increase in carbon dioxide and methane when the mass extinction occurred. Previously, researchers believed these gases had been produced by the Siberian traps, a huge volcanic rock formation created by the largest and longest-lasting eruptions in Earth’s surviving geological history. However, Rothman's team proved these eruptions weren't nearly enough to create all the carbon found in the sediments.

What's more, changes in carbon deposits over time run counter to typical volcanic behavior, according to Gregory Fournier: “A rapid initial injection of carbon dioxide from a volcano would be followed by a gradual decrease. Instead, we see the opposite: a rapid, continuing increase. That suggests a microbial expansion. The growth of microbial populations is among the few phenomena capable of increasing carbon production exponentially, or even faster. Genomic analysis shows that Methanosarcina had used gene transfer from another microbe to evolve a particularly rapid method of producing methane at the end of the Permian Era.

The final piece in the puzzle was the discovery of massive nickel deposits from the Siberian Trap eruptions just the right mineral nutrients to support the explosive spread of the newly-evolved killer microbes. The sudden, massive increase in methane resulted in the same sort of ocean acidification projected to result from human-produced climate change. Such oceanic acidity is deadly to marine creatures with calcium shells - and they were all but completely destroyed at the close of the Permian Age.

Source: Ancient whodunit may be solved: The microbes did it! Methane-producing microbes may be responsible for the largest mass extinction in Earth’s history. News release, David L. Chandler, MIT, March 31, 2014

Note: this is one of a number of updates to my book The Path Book I: Origins