One of Earth’s most catastrophic extinction events may have begun much earlier than scientists realized.
New research, published in Nature Communications Earth & Environment, suggests that oceans started losing oxygen nearly 8 million years before the end-Triassic mass extinction, a global crisis that eliminated roughly 60 percent of species and permanently reshaped life on Earth.
While researchers have known that massive volcanic eruptions helped trigger the extinction around 201 million years ago, the new study indicates that marine ecosystems may have been under stress for millions of years before the final collapse.
The discovery could help scientists better understand how environmental crises unfold and what modern oceans might face as climate change continues to alter marine ecosystems.
Ancient Rocks Hold Clues to Ocean Oxygen Loss
Scientists have long connected the end-Triassic extinction to immense volcanic eruptions that occurred as the supercontinent Pangaea began to break apart. Those eruptions released enormous amounts of greenhouse gases into the atmosphere, warming the planet and triggering a cascade of environmental changes.
As temperatures rose, weathering of rocks accelerated, sending more nutrients into the oceans and increasing ocean acidification. At the same time, warmer seawater became less capable of holding dissolved oxygen.
This combination was devastating, as more acid and less oxygen is “kind of like a one-two punch,” said geochemist Ben Gill in a press release. “It wouldn’t have been a very happy place to be.”
Although all of this is well-known in the scientific community, researchers still face a major puzzle. Previous evidence for widespread oxygen loss in the oceans came from only a handful of locations, making it difficult to determine how extensive the problem was or when it truly began.
“It’s a 200-million-year-old cold case,” said first author Kayla McCabe.
Adding to the mystery were more recent studies hinting that environmental deterioration may have started well before the extinction event itself.
Read More: About 34 Million Years Ago, Earth’s Most Powerful Ocean Current Emerged and Reshaped the Climate
How Researchers Solved the Ancient Ocean Oxygen Puzzle
To investigate this mystery, researchers traveled to one of the most remote geological archives on Earth: Grotto Creek in Alaska’s Wrangell-St. Elias National Park.
Field expeditions in 2017, 2019, and 2022 brought the team to the isolated site, which can only be reached by small aircraft. There, they examined sedimentary rock layers that formed before, during, and after the extinction event.
These rocks act like a natural timeline, preserving chemical clues about conditions in ancient oceans. By analyzing the geochemistry of the sediments, the team reconstructed oxygen levels through time.
What they found was unexpected — oxygen concentrations in shallow marine environments began declining approximately 8 million years before the end-Triassic extinction. That early oxygen loss likely placed significant stress on marine ecosystems long before species began disappearing on a massive scale.
The situation worsened dramatically as the extinction approached. The researchers found evidence that deoxygenation intensified during the crisis itself, becoming a major factor in widespread species losses across the oceans.
Exactly what triggered this earlier decline remains unclear.
“There’s evidence of another volcanic province that roughly lines up with this time interval. But we’re in the very beginning of trying to understand what happened,” explained Gill.
What This Discovery Means for Future Climate Research
Although scientists are still working to identify the cause of the early oxygen decline, the study offers an important lesson about how environmental crises can develop.
Rather than occurring suddenly, major extinction events may unfold over millions of years, with ecosystems experiencing prolonged periods of stress before reaching a tipping point.
That insight is particularly relevant today, with modern oceans already experiencing both acidification and declining oxygen levels as global temperatures rise. Regions such as the Chesapeake Bay have become well-known examples of modern marine “dead zones” where oxygen levels drop low enough to threaten aquatic life.
“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,” concluded Gill.
Read More: 9-Million-Year-Old Ancient Whale Graveyard May Trace Back to Explosive Volcanoes
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in Nature Communications Earth & Environment: Deoxygenation in the equatorial Panthalassan Ocean predated the end-Triassic mass extinction
