Chemical traces preserved in ancient rocks indicate that marine environments were deteriorating long before the catastrophe that wiped out vast numbers of species at the end of the Triassic period, around 201 million years ago.
Early Earth. Image credit: Peter Sawyer / Smithsonian Institution.
“The latest Triassic contains one of the most severe mass extinctions in the history of the planet, the end-Triassic mass extinction, that occurred just before the Triassic-Jurassic boundary (201 million years ago),” said Virginia Tech geologist Kayla McCabe and colleagues.
“This event resulted in an ~ 60% loss of marine invertebrates on the generic level and coincided with many paleoenvironmental disturbances.”
“Large-scale volcanism from the Central Atlantic magmatic province has been hypothesized to have driven the environmental changes that led to the end-Triassic mass extinction.”
“These include climatic warming, ocean acidification, and deoxygenation, among others.”
In their new research, McCabe and co-authors turned to the rock record.
In 2017, 2019, and 2022, they traveled to Grotto Creek in Alaska’s Wrangell-St. Elias National Park, a remote site accessible only by small aircraft.
There, they compared sedimentary rock layers deposited before, during, and after the extinction.
The rock layers preserve a record of environmental conditions in the ancient Panthalassan Ocean.
Flipping back through time revealed that oxygen levels in shallow ocean waters began to decline about 8 million years before the end-Triassic mass extinction.
That early loss of oxygen likely stressed marine ecosystems long before the main extinction event.
Geochemical analyses show that oxygen loss intensified during the extinction itself and became a major driver of species loss.
Benggwigwishingasuchus eremicarminis on the Panthalassan Ocean coast. Image credit: Jorge Gonzalez.
“There’s evidence of another volcanic province that roughly lines up with this time interval,” said Virginia Tech geochemist Ben Gill.
“But we’re in the very beginning of trying to understand what happened.”
“We may not yet know the cause, but we know how it played out.”
“Which means we have a rough guide for the future, as our oceans are again undergoing acidification and deoxygenation — including in the Chesapeake Bay.”
“Earth has run this experiment in the past. We have evidence that the climate gets warmer, and then all these other knock-on effects come afterwards.”
“It gives us some sense of what we can expect to happen.”
The findings were published in the journal Nature Communications Earth & Environment.
_____
K.E. McCabe et al. 2026. Deoxygenation in the equatorial Panthalassan Ocean predated the end-Triassic mass extinction. Commun Earth Environ 7, 460; doi: 10.1038/s43247-026-03362-w
