The cataclysmic extinctions that scoured Earth 200 million years ago might have been easier to trigger than expected, with potentially troubling contemporary implications.
Rather than 600,000 years of volcanic activity choking Earth’s atmosphere with carbon dioxide, just a few thousand years apparently sufficed to raise ocean temperatures so that potent greenhouse gases trapped in seafloor mud came bubbling up.
Most of everything alive on Earth was soon wiped out. Another half-million years of vulcanism were just icing on the cake. The immediate question: What lessons, if any, can be drawn?
“Scientists have been worried about the current release of methane from seafloors. What this study shows is that it already happened in the past,” said paleoecologist Micha Ruhl of Utrecht University, whose findings are published July 21 in Science. “It could happen again. It’s only the boundary conditions that we don’t know.”
In what scientists call the end-Triassic mass extinction, at least half of all living species simply disappear from the fossil record. The die-off didn’t merely cause ecological disruption. It was so sudden and profound that planetary chemical cycles went haywire for the next several million years.
The leading explanation for the extinction invokes extended, climate-altering volcanic activity caused by splitting continental plates, but earlier research by Ruhl suggested a more nuanced and jarring narrative.
By calculating how changes in ancient sediment composition corresponded to natural cycles in Earth’s distance to the Sun, he could study the end-Triassic’s onset in fine-grained chronological detail. Ruhl found that limestone – the geological remains of corals and shellfish – vanish within the first 20,000 years. Similar terrestrial disruption can be inferred from changes in fossilized plant spores. The end-Triassic extinction must have occurred
far more suddenly than believed.
In the latest study, Ruhl’s team examined chemical traces left by dying plants on the shores of the Tethys Sea, a body of water that separated the ancient continents of Laurasia and Gondwana. Today those shores are sedimentary layers in the Austrian Alps.
The researchers concentrated on changes to carbon isotopes, or subtly different elemental formations that betray whether carbon in plants came from carbon dioxide or methane. At 201.4 million years ago, in that narrow 20,000 year window of their updated end-Triassic cataclysm, they found a rise in CO2 followed by a tremendous spike of methane.
“A small release of CO2 from volcanoes triggered a small change in the global climate, raising land and ocean temperatures. That led to the release of methane from the seafloor,” said Ruhl.
Methane, familiar to most people as the main component of natural gas fuels, is a greenhouse gas less common than carbon dioxide in the atmosphere but far more potent. Most of Earth’s supply is contained in soils and seabeds.
Scientists have raised the possibility that rising global temperatures could release trapped methane into the atmosphere, further raising temperatures and releasing more methane in a feedback loop of warming and planetary disruption. That’s apparently what happened during the end-Triassic extinction.
According to paleobiologist Jessica Whiteside of Brown University, a leading researcher on end-Triassic vulcanism, more evidence is needed before Ruhl’s interpretations are conclusively supported. It’s possible that the new study reflects localized rather than planetary patterns.