Past as Prelude? –“How Life on Earth Nearly Ended 250 Million Years Ago”

 

NASA Earth from Space

 

The mass extinction brought about at the end of the 50-million-year-long Permian period, brought about the end the entire Paleozoic era, in progress since the dawn of animal life. The Paleozoic, with its ancient seas filled with trilobites, brachiopods, and strange reefs, was as starkly different from the age to come as the age of dinosaurs is from our world today.

In the terrifying aftermath of the Permian, reefs were replaced with piles of microbial slime, the stromatolites, uninspiring mounds of muck from the dreary eons before complex life writes Peter Brannen in The Ends of the World. “They had mostly disappeared since their heyday, but in the wake of the worst mass extinction ever, the oceans were as empty as they had been since the bacterial age.

“Perhaps most disturbing,” continues Brannen, “is that, although the Paleozoic era had lasted for hundreds of millions of years—encompassing the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods—it ended (in geological terms) in what was almost a subliminal time frame. Investigating Chinese rocks that record the mass extinction in the Permian ocean, legendary MIT geochronologist Sam Bowring found that the entire nightmare took place over a breathtakingly short period of fewer than 60,000 years. The End-Permian mass extinction marked the end of one venerable planet and, after a harrowing convalescence, the beginning of another.”

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Meanwhile, tucked into the Paleozoic, roughly 430 million years ago, during the intermezzo of Earth’s Silurian Period, global oceans were experiencing changes that would seem eerily familiar today. Melting polar ice sheets meant sea levels were steadily rising, and ocean oxygen was falling fast around the world.

At around the same time, a global die-off known among scientists as the Ireviken extinction event devastated scores of ancient species. Eighty percent of conodonts, which resembled small eels, were wiped out, along with half of all trilobites, which scuttled along the seafloor like their distant, modern-day relative the horseshoe crab.

Now, a Florida State University team of researchers has uncovered conclusive evidence linking the period’s sea level rise and ocean oxygen depletion to the widespread decimation of marine species. Their work highlights a dramatic story about the urgent threat posed by reduced oxygen conditions to the rich tapestry of ocean life.

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Although other researchers had produced reams of data on the Ireviken event, none had been able to definitively establish a link between the mass extinction and the chemical and climatic changes in the oceans. “The connection between these changes in the carbon cycle and the marine extinction event had always been a mystery,” said lead author Seth Young, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science.

To address this old and obstinate question, Young and his co-authors deployed new and innovative strategies. They developed an advanced multiproxy experimental approach using stable carbon isotopes, stable sulfur isotopes and iodine geochemical signatures to produce detailed, first-of-their-kind measurements for local and global marine oxygen fluctuation during the Ireviken event.

“Those are three separate, independent geochemical proxies, but when you combine them together you have a very powerful data set to unravel phenomena from local to global scales,” Young said. “That’s the utility and uniqueness of combining these proxies.”

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Young and his team applied their multiproxy approach to samples from two geologically important field sites in Nevada and Tennessee, both of which were submerged under ancient oceans during the time of the extinction event. After analyzing their samples at the FSU-based National High Magnetic Field Laboratory, the connections between changes in ocean oxygen levels and mass extinction of marine organisms became clear.

The experiments revealed significant global oxygen depletion contemporaneous with the Ireviken event. Compounded with the rising sea level, which brought deoxygenated waters into shallower and more habitable areas, the reduced oxygen conditions were more than enough to play a central role in the mass extinction. This was the first direct evidence of a credible link between expansive oxygen loss and the Ireviken extinction event.

But, Young found, that oxygen loss wasn’t universal. Only about 8 percent or less of the global oceans experienced significantly reducing conditions with very little to no oxygen and high levels of toxic sulfide, suggesting that these conditions didn’t need to advance to whole-ocean scale to have an outsized, destructive effect.

“Our study finds that you don’t necessarily need the entire ocean to be reducing to generate these kind of geochemical signatures and to provide a kill mechanism for this significant extinction event,” Young said.
Today, like 430 million years ago, sea level is on the rise and ocean oxygen is hemorrhaging at an alarming rate. As parallels continue to emerge between today’s changes and past calamities, peering into the Earth’s distant past could be a critical tool in preparing for the future.

“There are common threads with other climatic and extinction events throughout Earth’s history, and future work will continue to help us understand the similarities and differences of these events to constrain future climate predictions,” said co-author Jeremy Owens, an assistant professor in FSU’s Department of Earth, Ocean and Atmospheric Science who has worked on other extinction events in the Jurassic and Cretaceous periods.

“I think it’s important to see how these events played out all the way from extinction interval through recovery period, how severe they were and their connections to the ancient environment along the way,” added Young. “That could help us figure out what’s in store for our future and how we can potentially mitigate some of the negative outcomes.”

The prospect of ocean acidification in the next few decades according to Peter Brannen and MIT’s Daniel Rothman, could be truly world-changing. “Though the funhouse numbers of the End-Permian dwarf the total amount of carbon we could ever hope to inject into the system,” writes Brannen, this doesn’t rescue humanity.”

“It’s the pace of carbon dioxide emissions,” Brannen concludes, “not the absolute volume, it turns out, that’s everything. This is the reason why—despite the Hieronymus Bosch–like conditions that prevailed on earth 252 million years ago—Stanford University’s Jonathan Payne and his colleague, paleobiologist Matthew Clapham at UC Santa Cruz could publish—with a straight face—a paper with the title “End-Permian Mass Extinction in the Oceans: An Ancient Analog for the Twenty-First Century?

Image at the top of the page shows Earth as seen from orbit, filmed in space by an IMAX camera aboard a NASA space shuttle mission in December 1988.

The Daily Galaxy via Peter Brannen, The Ends of  the World and  Florida State University