Researchers at The University of Texas at Austin have redated the buried Ames impact structure in Oklahoma to roughly 370 million years ago, placing the 10-mile-wide crater nearly 100 million years younger than previously thought and aligning its formation with the Late Devonian marine mass extinction.
University of Texas at Austin researchers have redated a 10-mile-wide buried crater in northern Oklahoma to approximately 370 million years ago.
For decades, scientists linked the Ames impact structure to a meteor bombardment during the Ordovician Period around 467 million years ago. New radiometric dating of zircon crystals extracted from impact-altered granite core samples places the collision during the Late Devonian, nearly 100 million years later.
The crater lies hidden beneath 9,000 feet of sedimentary rock near the town of Ames. It was unknown until seismic soundings revealed its circular subsurface structure in 1991.
Subsequent drilling into the fractured rock uncovered major petroleum reservoirs. Wells drilled within the crater have produced 17.4 million barrels of oil and 79.5 billion cubic feet of natural gas. Harold Hamm, then-CEO of Continental Resources, later established a local museum dedicated to the discovery.
Zircon Dating Challenges the Ordovician Timeline
Previous age estimates relied on biochronology—specifically examining the teeth of conodonts, small eel-like creatures whose fossilized remains filled the crater fill. Those fossils indicated an Ordovician origin, tying Ames to the Ordovician Meteor Event across North America.
That cluster of ancient impacts led some researchers to hypothesize that Earth was once encircled by a ring of debris resembling Saturn’s rings. The research team says this hypothesis relied on groupings of craters that the new zircon evidence calls into question by removing the Ames structure from that count.
Zircon traps uranium when it forms while systematically expelling lead, providing a reliable radiometric clock.
“No matter what technique we used, it was coming back to this younger signal.”
Elizabeth Catlos, associate professor at the University of Texas at Austin
The team imaged the grains using cathodoluminescence and electron backscatter diffraction, which uses a scanning electron microscope to study how electrons are diffracted at different angles by different atoms. A recurrence of Devonian dates across different grains and methods provided strong statistical evidence that the crater is younger than previously believed, according to the paper.
Catlos explained that the older conodont fossils recovered from the site were likely already millions of years old when the asteroid struck and simply became jumbled into the impact breccia. Andrew Parisi traveled to Oklahoma to obtain the rock core from the Oklahoma Geological Survey, extracted the zircon crystals from the material, and helped determine their ages. Co-author Michael Brookfield, an affiliated researcher at the school, passed away before the paper was published.
Ames Impact Aligns With Late Devonian Extinction
The region that is now Oklahoma was submerged beneath a shallow sea when the impact occurred 370 million years ago.
“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.’”
Elizabeth Catlos, lead author and associate professor
Researchers have pruned one of the prominent impact structures used to support theories of a Middle Ordovician debris ring by removing Ames from the Ordovician dataset. Danny Stockli, dean of the Jackson School of Geosciences at the University of Texas at Austin and a co-author of the study, emphasized the utility of the technique in establishing reliable timelines for ancient planetary catastrophes.
“These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes. 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.”
Danny Stockli, dean of the Jackson School of Geosciences at the University of Texas at Austin
