How the world of the end-Triassic extinction was similar to today--and how it differed

The end-Triassic extinction, which happened 201 million years ago, was Earth's third most severe extinction event since the dawn of animal life. Like today, CO₂ rise and global warming were present, but the similarities don't end there. As with today, it was a time of wildfires, deforestation, downpours, erosion, ocean acidification, marine dead zones, vanishing coral reefs, sea-level rise, and even insect plagues. There was also pollution by mercury, sulfur dioxide, halocarbons, and methane--and possibly even a damaged ozone layer.

"Something very violent occurred 201 million years ago, with great similarity in terms of CO₂ with what we see is happening now," said Dr. Manfredo Capriolo of the University of Oslo. That would seem to make it a good model to understand what's going on now. But there are glaring differences--most notably the lack of humans.

Instead of the human pollution of today, the end-Triassic saw massive volcanic eruptions that emitted prodigious amounts of greenhouse gases and pollutants. There were other differences as well. During the Triassic, there was just one continent, called "Pangea," and the climate started warmer and ice-free, with CO₂ levels much higher than those of today. Dinosaurs had yet to dominate the planet, and there was no grass or flowers.

Most importantly, the scale of the destruction facing the world in the end-Triassic was larger, and the amount of time involved was longer than what is envisaged for our future. So as scientists find echoes of the past that resonate today, we also need to be cautious about how those lessons apply to us.

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A pattern, if we can find it

The end-Triassic was not a one-off event.

With the exception of the dinosaur-ending asteroid impact at the end of the Cretaceous, the end-Triassic fits a loose pattern documented in 15 or so other extinctions through geological time, like the end-Permian and Ocean Anoxic Events in the Jurassic and Cretaceous.

The pattern in all these extinctions includes huge emissions of CO₂ originating from volcanic phenomena called "large igneous provinces." These resulted in climate change, sea-level rise, oxygen-starved dead zones in the oceans, and ocean acidification. Reefs disappeared, and marine species went extinct. In some cases, including the end-Permian and end-Triassic extinctions, the ocean changes happened in concert with changes on land, with forests disappearing, ferns taking over, and land animals going extinct.

This repetition shows that the Earth follows a certain logic--one where past environmental crises are stress tests we can use to reverse-engineer how our planet works.

But figuring out the chain of causes and effects in these narrow slices of Earth's vast, broken geological record is like trying to solve a murder. "We know who died and where, but we don't know how or why," as Professor Bas van de Schootbrugge of Utrecht University put it.

Timing is everything

We know the extinction happened at the end of the Triassic simply because many fossil species found in Triassic rocks don't last into the Jurassic--and we've known this since the 18^th century. "In Greece, you lose all the big fossils--it's very striking. They're just gone from one second to the next, from one bed to the next. They're all gone," said van de Schootbrugge. "In Italy, you see corals disappear."

Half of marine biodiversity was lost. Coral reefs disappeared before returning later in the Jurassic. Many groups of spiral-shelled ammonites were lost, as were many species of clam-like mollusks. Creatures called "conulariids," which resembled ice cream cones, disappeared entirely, as did eel-like creatures called conodonts. Several groups of dolphin-like ichthyosaurs also died out.

The gap between the final Triassic fossils and the first Jurassic fossils spans about 140,000 years, depending on the species. This doesn't mean the extinction actually lasted that long. But since it's rare for a creature to become a fossil after it dies--and rarer still for a human to find it--it's very likely that species lived long past their last fossilized representative. This means the fossil gap provides only a broad-brush picture, and we need far more detail to understand how exactly the mass extinction happened.

"It's super important that we get the timing right, what things happened when, and in what order," said Professor Sofie Lindstrom of the University of Copenhagen.