Ancient teeth told the wrong story

Why was the date wrong for so long? The Ames site had previously been dated only biochronologically — using fossils as time markers. Researchers had found teeth of a conodont, an ancient eel-like creature, in the rock, and those teeth pointed to the older Ordovician age. But the teeth were likely already millions of years old when the asteroid struck, Catlos explained, and were probably jumbled into the impact debris and preserved there, giving a misleading signal.

The new date carries real weight. At about 370 million years old, the Ames impact no longer fits the Ordovician Meteor Event at all. Instead, it lines up closely with the Frasnian-Famennian mass extinction, which occurred roughly 372 million years ago and wiped out a huge percentage of marine life on Earth.

That timing raises an obvious question: did a meteor contribute to that extinction? The study establishes the new date, but does not by itself prove a causal link — a distinction researchers will need to explore with further work.

Crystals that remember the shock

To make sure the zircons they dated were actually part of the impact and not random minerals, the team worked with NASA to image the crystals using cathodoluminescence and electron backscatter diffraction — techniques that reveal a crystal's internal structure at very fine scale. When a meteor impact hits zircon, the mineral recrystallizes in a very specific, recognizable way, and those microstructures preserve a record of the shock pressures involved.

Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, said zircon uranium-lead dating is the most accurate way to pin down when events like this occurred, and that the crystals carry even more information besides the date.

"These small crystals allow us to go back in time and learn about the major changes to Earth's ancient landscapes," Stockli said. "It would be great to do this for more of the meteor impact sites across the continent so we could get a more accurate timeline for these major events."

Why the timeline matters

Catlos said a more accurate timeline for mass extinctions and other pivotal moments in Earth's history is crucial for understanding how the planet works. The cause matters: whether an extinction was driven by an extraterrestrial force, like a meteor impact, or by something inside the Earth, such as a series of massive volcanic eruptions, tells very different stories about how life responds to catastrophe.

"With this research, we're basically taking a major pawn out of the Ordovician Meteor Event and dumping it into the Frasnian-Famennian event, and saying, 'This is where this impact belongs,'" she said.

The project began with former Jackson School of Geosciences graduate student Andrew Parisi, who graduated in 2018 and has since passed away. He traveled to Oklahoma to collect the Ames rock core from the Oklahoma Geological Survey, extracted the zircons and helped date them. Co-author Michael Brookfield, an affiliated researcher at the school, also died before the paper was published. Research Professor Sean Gulick and Professor Emeritus Mark Cloos at the Jackson School also contributed to the research.

One revision to one crater under one small town may sound modest. But as more impact sites across North America get re-examined with the same rigorous crystal clocks, the timeline of Earth's most violent chapters — and the role of meteors in its worst extinctions — may keep shifting.