Researchers at The University of Texas at Austin have revised the timeline of the Ames impact structure in Oklahoma, dating the massive underground meteor crater to approximately 370 million years ago during the Late Devonian. This finding places the impact roughly 100 million years younger than its long-assumed Ordovician period assignment.
The Shift in Oklahoma Geologic History
Beneath the town of Ames, Oklahoma, lies a meteor impact structure spanning 14 to 16 kilometers wide, hidden beneath layers of sediment. For years, scientists linked the Ames crater to a cluster of impacts across North America dating back roughly 467.5 million years, an era known as the Ordovician Meteor Event. That clustering inspired hypotheses that Earth may have once possessed a Saturn-like ring of asteroid debris. New uranium-lead dating of zircon crystals extracted from impact-altered basement granite changes that picture entirely. The team at The University of Texas at Austin determined the meteorite struck about 370 million years ago during the Late Devonian.
No matter what technique we used, it was coming back to this younger signal,
said lead author Elizabeth Catlos, associate professor at UT’s Department of Earth and Planetary Sciences.
Why Conodont Fossils Misled Researchers for Decades
Prior to this updated geochronology, researchers relied on biological evidence to date the Ames crater. Scientists had recovered teeth from conodonts, which are tiny, eel-like ancient marine animals, preserved in the surrounding rock. Those fossils pointed to an Ordovician age between roughly 478 million and 458 million years. However, the new analysis reveals those fossils were likely already millions of years old when the asteroid struck. The cataclysmic impact churned up older material, mixing ancient fossils into younger impact deposits while preserving them intact.
To verify the true age, the research team focused on zircon crystals, which naturally incorporate uranium during formation while accumulating lead through radioactive decay. Using advanced analytical techniques including cathodoluminescence and electron backscatter diffraction in collaboration with NASA, the team confirmed that the zircons recorded the intense pressures of a high-velocity impact. While most zircons preserved older basement granite signatures dating back about 1.4 billion years, a younger group produced a weighted mean age of 369.7 million years, with an uncertainty of 5.9 million years.
Connecting an Ancient Crater to a Mass Extinction Event
Moving the Ames impact structure out of the Ordovician and into the Late Devonian aligns its formation closely with the Frasnian-Famennian mass extinction event. That biological crisis occurred about 372 million years ago and wiped out a large proportion of marine life on Earth. Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, noted that zircon U-Pb dating provides accurate ways to determine when events occurred deep in Earth’s past.
These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes,
Stockli stated. 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.
By removing Ames from the Ordovician Meteor Event, researchers must reevaluate theories regarding ancient asteroid clusters and planetary debris rings. Elizabeth Catlos described the shift by noting they are taking a major pawn out of the Ordovician event and placing it into the Frasnian-Famennian event. Beyond its academic significance, the Ames structure remains economically vital as a producer of oil and gas.
