The Ames impact crater buried beneath Oklahoma formed approximately 370 million years ago during the Late Devonian period, placing the collision nearly 100 million years later than geologists long estimated. The finding connects the massive geological scar to the Frasnian-Famennian boundary event, one of the five major mass extinctions in planetary history, rather than a previously assumed Ordovician meteor shower.
Researchers led by the University of Texas at Austin revealed the revised timeline after analyzing isotopic ratios in mineral crystals extracted from the site. The findings shift the crater out of an ancient cluster of Ordovician impacts, challenging prior models of early terrestrial asteroid rings while linking the structure to an era when an estimated 40 percent of all marine life disappeared from Earth.
University of Texas team analyzes zircon crystals from Ames
Geoscientists determined the structure’s age by conducting uranium-lead dating on microscopic zircon crystals recovered from the subterranean crater rock. The measurements yielded a weighted average age of 369.7 ± 5.9 million years, directly anchoring the blast in the Late Devonian rather than the Ordovician period 467.5 million years ago. Zircon crystals, which are silicate minerals, exclude lead during their formation while incorporating uranium and thorium; over geological time, radioactive uranium isotopes decay into lead at stable rates, allowing scientists to calculate the exact timing of high-pressure impact events.
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The mineralogical investigation relied on collaboration between University of Texas researchers and specialists at the NASA Johnson Space Center, who used cathodoluminescence alongside electron backscatter diffraction to image and map crystal shock deformation. Cathodoluminescence bombards rock specimens with electrons to stimulate photon emission at distinctive wavelengths based on composition, while electron backscatter diffraction utilizes a scanning electron microscope to measure how crystalline lattices scatter electron beams. Lead author Elizabeth J. Catlos, an associate professor in the Department of Earth and Planetary Sciences at the University of Texas at Austin, noted that every experimental method confirmed the younger chronological signal.
“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’,” said Catlos. “No matter what technique we used, it was coming back to this younger signal.”
Dimensions, depth and historical data of the Ames structure
The impact site exhibits significant subterranean dimensions and plays an unusual role in energy production, as detailed in the publication in the journal Meteoritics & Planetary Science and municipal geological surveys:
- 16 kilometers (10 miles): the approximate diameter of the circular impact structure.
- 2.7 kilometers (9,000 feet): the depth of sedimentary rock burying the structure under Ames, Oklahoma.
- January 1, 1991: the year when exploration teams first discovered the crater using seismic readings.
- 17.4 million barrels: the cumulative volume of crude oil extracted from fractured reservoir rock inside the crater since 1991.
- 79.5 billion cubic feet (2.25 billion cubic meters): the volume of natural gas produced from crater wells over the same period.
Fossil evidence and the Ordovician ring hypothesis
The earlier estimate of roughly 467 million years relied on biostratigraphy, a dating method that matches rock layers with the fossil record. Geologists previously identified fossil teeth belonging to conodonts, an extinct group of eel-like primitive vertebrates, inside the crater fill. Because these specific conodont species flourished during the Middle Ordovician, scientists assumed the impact occurred during that window, grouping Ames with nearly two dozen equatorial craters attributed to the Ordovician Meteor Event.
Catlos and her team demonstrated that the conodont fossils were already tens of millions of years old when the meteorite arrived, having existed in preexisting rock layers that were violently jumbled, shattered, and redeposited during the Devonian explosion. The reassignment of Ames undercuts empirical support for the hypothesis that Earth possessed a debris ring similar to Saturn’s during the Middle Ordovician, as that model relied heavily on the clustering of impacts within 30 degrees of the paleoequator.
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Late Devonian environmental crisis and future research
When the projectile struck approximately 370 million years ago, shallow ocean waters covered what is now Oklahoma. Marine sedimentation gradually deposited 2.7 kilometers of layered stone over the blast site, while deep underground fractures provided pathways for migrating petroleum and gas deposits. The revised date aligns the collision with the Frasnian-Famennian boundary extinction around 372 million years ago, an ecological catastrophe marked by widespread oceanic anoxia, extreme volcanic pulses, and devastating losses across marine communities.
Co-author Danny Stockli, dean of the Jackson School of Geosciences at the University of Texas at Austin, emphasized that isotopic analysis of shocked minerals should be expanded across North America to correct historical timelines. Research co-authors Andrew F. Parisi and Michael E. Brookfield contributed to the data collection prior to passing away before the study’s formal publication. Scientists have not yet confirmed whether the 16-kilometer Ames blast served as an active global driver of Devonian ecological collapse or represented a localized collision coinciding chronologically with broader terrestrial phenomena such as oceanic anoxia and intense volcanism.
