Oklahoma's buried Ames crater is 100 million years younger than long believed

A buried meteor crater beneath the town of Ames, Oklahoma, has turned out to be nearly 100 million years younger than scientists had believed for decades, according to new research led by geologists at the University of Texas at Austin.

The Ames impact structure spans roughly 10 miles across and lies buried under about two miles of sediment, discovered originally through oil and gas drilling because its shattered, porous rock has long made it a productive petroleum reservoir — a formation long catalogued by Oklahoma's state geological survey. For years, researchers dated the crater to roughly 467 million years ago, during the Ordovician period, based on fossilized conodont teeth recovered from the impact rock.

The new study, led by Elizabeth Catlos, an associate professor in UT Austin's Department of Earth and Planetary Sciences, instead used uranium-lead dating of zircon crystals pulled from granite altered by the impact, according to the research record held in the university's own repository. The team analyzed 37 spots across multiple zircon grains and found the youngest, most reliable signals consistently pointed to a much younger age. "No matter what technique we used, it was coming back to this younger signal," Catlos said, in comments reported by ScienceDaily.

The revised estimate places the Ames impact at about 369.7 million years ago, plus or minus 6 million years — squarely within the Late Devonian period, near the Frasnian-Famennian mass extinction event roughly 372 million years ago that devastated marine ecosystems worldwide. Researchers say the fossil-based dating method used previously was likely unreliable because the conodont fossils embedded in the rock were probably already millions of years old by the time the impact occurred, making them poor markers of when the strike actually happened, as Earth.com detailed in its account of the findings.

The findings, published in the journal Meteoritics & Planetary Science, do not prove the impact triggered the extinction event, and the researchers are careful to note that dating alone cannot establish causation. The reassignment also removes Ames from a cluster of craters previously linked to the so-called Ordovician Meteor Event, a hypothesized spike in asteroid impacts roughly 465-470 million years ago. With Ames now dated to the Devonian instead, scientists say the inventory of confirmed Ordovician-age impact sites shrinks by one, a detail that matters for broader models of asteroid bombardment through Earth's history.