The finding, published in July in the journal Meteoritics & Planetary Science, is more than a local correction to Oklahoma’s geological timeline. It removes a major data point from the growing body of evidence used to argue that Earth once possessed a transient, Saturn-like ring of asteroid debris during the Middle Ordovician, and it simultaneously inserts the Ames crater into the timeframe of one of the most severe mass extinctions in the planet’s history, the Frasnian-Famennian event, which unfolded about 372 million years ago and devastated marine ecosystems worldwide. The realignment of a single crater, in other words, touches two of the most debated questions in Earth science: how often large extraterrestrial objects struck the ancient continents, and what role those strikes may have played in driving biological crises.

The Ames impact structure has long been an object of both scientific curiosity and commercial importance. Although it is entirely hidden from view at the surface, buried beneath layers of younger sedimentary rock, its circular geometry and shocked minerals were identified through subsurface drilling, and the fractured, brecciated rocks at its center turned out to be prolific reservoirs for oil and gas. That economic role is what ultimately made the crater accessible to science: boreholes drilled by energy companies penetrated the structure and recovered core samples of the deformed rocks, which were archived by the Oklahoma Geological Survey. It was from one of these archived cores that the new study’s raw material was drawn, a reminder that the samples collected for industrial purposes can, decades later, become the evidence that rewrites textbooks.

The previous age assignment rested on a fundamentally different and considerably less precise dating method. Researchers had relied on biochronology, the practice of assigning ages to rocks based on the fossils they contain. In the Ames rocks, that fossil evidence consisted of the teeth of conodonts, an extinct group of eel-like jawless vertebrates whose tiny, tooth-like elements are abundant in marine sediments and serve as classic index fossils for Paleozoic strata. The conodont elements recovered from the impact-related rocks pointed to an Ordovician age, and that assignment was accepted and repeated. The problem, as the new study makes clear, is that an impact crater is one of the worst possible environments for preserving a clean fossil record. The violence of the collision excavates, mixes, and redeposits enormous volumes of older rock, incorporating fragments and fossils that were already ancient at the moment of impact.

Lead author Elizabeth Catlos, an associate professor in UT’s Department of Earth and Planetary Sciences, explained that the conodont teeth were likely already millions of years old when the asteroid struck, and were simply jumbled into the chaotic breccia produced by the event, where they remained preserved and misleading. The zircon crystals, by contrast, offer a direct and internally testable clock. Zircon is a zirconium silicate mineral that incorporates uranium atoms into its crystal lattice when it forms while almost completely excluding lead. Because uranium decays to lead at precisely known rates, measuring the ratio of parent uranium to daughter lead isotopes in a zircon yields the time since the crystal crystallized or, in the case of an impact, since shock heating reset the isotopic system. This uranium-lead method, applied to zircon, is widely regarded as the most accurate chronometer available for events deep in Earth’s history.

Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, emphasized that zircon U-Pb dating not only pins down the timing of such events with unmatched precision, but that the microstructures preserved within the crystals can also record the shock pressures they experienced. When a zircon is subjected to the extreme transient pressures of a meteorite impact, on the order of many gigapascals, its internal crystal structure deforms and recrystallizes in characteristic ways. Those deformation features act as a fingerprint, allowing researchers to distinguish grains that genuinely experienced the impact from older detrital grains that were merely swept along in the target rocks. Stockli noted that these small crystals allow scientists to travel back in time and reconstruct major changes to Earth’s ancient landscapes, and he expressed the hope that similar work could be extended to more impact sites across the continent to build a more accurate timeline of major impacts.

Establishing that the dated zircons had in fact been shocked by the Ames impact, rather than simply being young crystals that happened to be in the wrong place, required independent confirmation of their impact history. To achieve this, the research team partnered with NASA to image the crystals using two complementary microscopic techniques: cathodoluminescence, which reveals internal growth zoning and recrystallization textures by detecting the light emitted when an electron beam excites the crystal, and electron backscatter diffraction, which maps the crystallographic orientation of the lattice at fine scales and exposes the characteristic deformation patterns produced by shock. Together, these methods demonstrated that the zircons had recrystallized in the specific manner associated with impact shock, tying the young radiometric ages directly to the crater-forming event rather than to any unrelated geological process.

Catlos reported that no matter which technique the team applied, the results kept converging on the same younger signal, a consistency that left little room for the old Ordovician assignment to survive. The implications radiate outward in two directions. First, the Ames crater can no longer be counted among the cluster of North American impact sites whose ages center on 467.5 million years ago, a cluster so striking that researchers have theorized Earth may have been encircled by a ring of asteroid debris, perhaps the remnants of a large asteroid broken apart by tidal forces as it passed within the Roche limit, with fragments subsequently raining down over millions of years. Removing Ames from that population weakens one of its supporting examples. Second, the new date of roughly 370 million years ago places the impact squarely within the interval of the Frasnian-Famennian extinction, also known as the Late Devonian or Hangenberg-adjacent Kellwasser crisis, which eliminated a huge percentage of marine life, including many reef-building organisms, in two closely spaced pulses.

Whether the Ames impact had any causal connection to that extinction remains an open question, and the authors are careful not to overclaim. But Catlos argued that precise timelines are essential precisely because the stakes of the question are so high. It matters, she said, whether mass extinctions were driven by extraterrestrial forces such as impacts, or by internal forces such as the series of massive volcanic eruptions that are implicated in several other biological crises. Distinguishing between these drivers requires knowing exactly when impacts occurred relative to extinction pulses, and a crater whose age is wrong by 100 million years is worse than no data at all. With this research, she said, the team is essentially taking a major pawn out of the Ordovician Meteor Event and placing it into the Frasnian-Famennian event, declaring that this is where the impact belongs.

The study also carries a human story. The research was instigated by Andrew Parisi, a former graduate student at the Jackson School of Geosciences who graduated in 2018 and passed away before the work reached publication. It was Parisi who traveled to Oklahoma to collect the Ames rock core from the Oklahoma Geological Survey, extracted the zircons from the impact-shocked granite, and helped to date them, laying the analytical foundation on which the final result was built. Co-author Michael Brookfield, an affiliated researcher at the school, also died before the paper appeared. Research Professor Sean Gulick and Professor Emeritus Mark Cloos, both of the Jackson School, contributed to the research as well. The authors declared no competing interests. For now, the crater beneath Ames keeps producing, both hydrocarbons for the present and, thanks to a handful of microscopic zircon crystals, a sharply revised window onto one of the most turbulent moments in the history of life on Earth.

Subject of Research: Radiometric dating of the Ames impact crater in Oklahoma and its revised age relative to ancient meteor events and mass extinctions

Article Title: Meteor hit Oklahoma 100 million years later than previously thought

Article References: Meteor hit Oklahoma 100 million years later than previously thought. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Ames crater, Oklahoma, meteor impact, zircon dating, U-Pb geochronology, Ordovician Meteor Event, Late Devonian, Frasnian-Famennian extinction, mass extinction, impact crater, conodonts, University of Texas at Austin