AUSTIN, Texas — In a scientific revision that challenges long-held assumptions about North America’s geological timeline, researchers at The University of Texas at Austin have upended the history of one of the continent’s most prominent subterranean features. A team of geoscientists has conclusively redated the Ames impact structure—a massive, ring-shaped meteor crater buried deep beneath the rolling terrain of Major County, Oklahoma.
For decades, the Ames crater was celebrated by both academic geologists and the petroleum industry as a textbook example of a Middle Ordovician impact, slotted neatly into a cluster of events dating back approximately 467.5 million years. However, new high-precision radiometric dating of microscopic crystals recovered from the site has revealed an astonishing truth: the meteorite struck Earth roughly 370 million years ago, during the Late Devonian epoch.
This dramatic chronological shift strips the Ames structure of its status as a key piece of the "Ordovician Meteor Event"—a period so heavily peppered with impacts that some scientists once hypothesized Earth briefly sported a ring of asteroid debris akin to Saturn’s. Instead, the newly established timeline places the Oklahoma impact dangerously close to the Frasnian-Famennian mass extinction, a catastrophic global biotic crisis that eradicated a substantial fraction of all marine species.
Published in the journal Meteoritics & Planetary Science, the study not only resolves a decades-old geological mystery but also underscores the necessity of moving beyond biological dating methods when mapping the chronology of violent planetary events.
Main Facts: The Discovery and Its Implications
Buried hundreds of feet beneath the surface town of Ames, Oklahoma, lies an impact structure spanning roughly 8 to 10 miles in diameter. Discovered and extensively studied due to its immense economic value as a prolific oil and gas producer, the crater has long been a fixture of geological literature.
The core findings of the UT Austin study can be summarized as follows:
- The Age Revision: The Ames impact structure formed approximately 370 million years ago, making it nearly 100 million years younger than the previously accepted date of 467.5 million years.
- The Geological Epoch: The impact occurred during the Late Devonian period, shifting it from the Middle Ordovician epoch.
- The Methodology: Researchers utilized Uranium-Lead (U-Pb) dating of zircon crystals extracted from impact-altered granite, combined with advanced imaging techniques to verify shock metamorphism.
- The Extinction Link: The revised timeline aligns the Ames impact remarkably close to the Frasnian-Famennian mass extinction event (circa 372 million years ago), a major turning point in the history of marine life.
- The Death of a Hypothesis: By removing Ames from the Ordovician cluster, the study weakens the hypothesis that Earth was orbited by an ancient ring of asteroid debris during that earlier era.
Lead author Elizabeth Catlos, an associate professor in UT’s Department of Earth and Planetary Sciences, encapsulated the magnitude of the shift with a vivid metaphor: "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.’"
Chronology: How the Ames Crater Was Misunderstood for Decades
To understand how the scientific community arrived at a date nearly 100 million years off the mark, one must examine how the Ames crater was initially investigated.
When geologists first began analyzing the crater—which features a distinct inner uplifted granite core surrounded by a deep trough and an outer rim—they faced a significant hurdle: the impact site is entirely sealed beneath younger layers of sedimentary rock. Direct observation of the impact event was impossible, forcing researchers to rely on indirect proxies to estimate its age.
The Biological Trap
Historically, researchers relied on biostratigraphy—the dating of rock strata using fossilized flora and fauna. In the case of the Ames structure, scientists recovered tiny, microscopic teeth belonging to conodonts, an extinct group of jawless, eel-like chordates.
The conodont fossils found within the impact-affected rocks clearly belonged to species that thrived during the Ordovician period. Consequently, geoscientists concluded that the meteorite must have struck during that same era, as the impact breccias and disrupted strata appeared intimately associated with Ordovician life forms.
However, as Catlos and her team demonstrated, fossils can be deeply misleading messengers. The conodont teeth recovered from the Ames core were likely millions of years old at the time of the impact. When the hyper-velocity meteorite smashed into the Oklahoma basement rock, the titanic forces involved churned up preexisting, older sedimentary layers, scooping up ancient fossils and redepositing them into the chaotic debris field of the crater while miraculously keeping them intact.
For years, this geological recycling fooled researchers into reading the age of the swallowed fossils as the age of the cataclysm itself.
The Turning Point: Accessing the Core
The modern re-evaluation began with Andrew Parisi, a former graduate student at UT’s Jackson School of Geosciences. Recognizing anomalies in the historical data, Parisi traveled to the Oklahoma Geological Survey to secure a precious rock core extracted directly from the Ames structure.
Working alongside the research team, Parisi undertook the arduous task of separating microscopic accessory minerals from the granite basement rock—specifically, crystals of zircon. Tragically, Parisi passed away in 2018 before the project reached completion, but his foundational extraction work laid the groundwork for the breakthroughs that followed. Co-author Michael Brookfield also passed away prior to publication, making the final paper a bittersweet milestone for the research group.
Supporting Data: Unlocking the Secrets of Zircon
To bypass the deceptive biological clock of the conodont fossils, the UT Austin team turned to one of the most reliable chronometers in the geological sciences: zircon ($ZrSiO_4$).
Uranium-Lead Radiometric Dating
Zircon is a mineral renowned for its durability and its unique chemical composition. When zircon crystals form in magma, they naturally incorporate trace amounts of uranium while systematically excluding lead. Over millions of years, the unstable radioactive isotopes of uranium decay at a constant, well-understood rate into stable isotopes of lead.
By measuring the precise ratio of uranium to lead (U-Pb dating) using advanced mass spectrometry, scientists can determine the exact moment a zircon crystal crystallized or underwent a major thermal reset.
Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, emphasized the unmatched precision of this method. "These small crystals allow us to go back in time and learn about major changes to Earth’s ancient landscapes," Stockli said. "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."
Proving Impact Shock
Finding the right age was only half the battle; the team needed absolute proof that the zircons they dated had indeed been altered by the Ames meteor strike, rather than an unrelated geological event millions of years prior.
To achieve this, the researchers partnered with NASA scientists to subject the zircon crystals to sophisticated non-destructive imaging:
- Cathodoluminescence (CL): This technique reveals internal zoning and structural damage within crystals by bombarding them with electron beams, causing them to emit light of varying colors based on trace element distribution and lattice defects.
- Electron Backscatter Diffraction (EBSD): EBSD maps crystal orientation and lattice strain at the microscale.
When a meteorite slams into the Earth’s crust, the resulting shockwave generates pressures exceeding hundreds of gigapascals and temperatures hot enough to melt rock. Zircon caught in this thermal and mechanical crossfire experiences distinct structural breakdown and recrystallization.
The NASA imaging confirmed that the Ames zircons bore the unmistakable structural scars of extreme shock metamorphism. The U-Pb dating of these unequivocally shock-modified domains consistently yielded the same younger signal: roughly 370 million years ago.
"No matter what technique we used, it was coming back to this younger signal," Catlos noted.
Official Responses and Expert Commentary
The findings have sent ripples through the geological community, prompting a re-evaluation of how impact structures are cataloged across North America. While the paper’s July publication in Meteoritics & Planetary Science generated immediate academic interest, its implications extend far beyond theoretical geology into petroleum geology and planetary science.
Reflecting on the collaborative nature of the project, the research team highlighted the contributions of other institutional figures, including Research Professor Sean Gulick and Professor Emeritus Mark Cloos, both of the Jackson School of Geosciences.
Speaking on the broader importance of the methodology, Dean Stockli pointed out that many of North America’s classic impact craters were dated decades ago using rudimentary techniques or problematic proxies like fossils and potassium-argon dating of altered whole-rock samples.
"If we can apply modern, high-resolution micro-analytical techniques like U-Pb zircon dating and electron backscatter diffraction to other legacy impact sites, we may find that Ames is not an isolated case," Stockli suggested. "Our entire database of impact timing could be due for a rigorous audit."
Industry professionals are also taking note. The Ames structure is not merely an academic curiosity; it is a world-class petroleum reservoir. The fractured granite of the central uplift and the surrounding chaotic impact breccias form exceptional traps for oil and natural gas. Understanding the precise thermal and structural history of the crater—including when it actually formed relative to regional burial and maturation histories—provides vital data for exploration and reservoir management in Oklahoma’s prolific basins.
Implications: Solving the Mass Extinction Puzzle
Beyond Oklahoma, the revision of the Ames crater’s age injects a fresh, provocative data point into one of paleontology’s most enduring debates: What drives mass extinctions?
Throughout Earth’s history, life has suffered catastrophic bottlenecks—mass extinctions that wiped out vast swathes of biodiversity, clearing the evolutionary stage for new dominant species. The causes behind these periodic die-offs are frequently divided into two camps:
- Extraterrestrial Forces: Bolide impacts (asteroids or comets) that inject massive amounts of dust, sulfur, and debris into the atmosphere, choking out sunlight and collapsing global food webs.
- Terrestrial Forces: Massive internal planetary upheavals, such as large igneous province (LIP) volcanism, which release colossal volumes of greenhouse gases, driving rapid global warming, ocean acidification, and widespread marine anoxia.
The Late Devonian period was punctuated by the Frasnian-Famennian extinction event, which unfolded roughly 372 million years ago. During this protracted crisis, warm-water marine ecosystems—particularly coral reefs and shallow-water brachiopods—suffered devastating losses, with estimates suggesting that up to 75% of all species on Earth perished.
For years, paleontologists have sought the smoking gun for the Frasnian-Famennian extinction. While intense volcanism (such as the Siberian Traps or contemporaneous LIPs) has frequently been cited, the sudden addition of a major extraterrestrial impact right on the doorstep of this extinction window changes the calculus.
By moving the Ames impact from the Middle Ordovician to the Late Devonian, researchers have provided a powerful new timestamp for a major cosmic collision occurring during a critical period of biological stress. While the Ames impact alone may not have been global enough to trigger a worldwide extinction on the scale of the Chicxulub impact that doomed the dinosaurs, it demonstrates that Earth was actively being struck by sizeable asteroids during the very epoch when marine ecosystems were collapsing.
A Call for Global Re-evaluation
As geoscientists continue to comb through legacy data and apply cutting-edge micro-analytical tools to Earth’s scarred crust, the story of our planet’s violent past continues to evolve.
The UT Austin study serves as a stark reminder that even well-established scientific consensus can rest on shaky foundations when relying on ambiguous proxies like fossilized teeth. By anchoring geological history in the unyielding atomic clocks of zircon crystals, researchers are finally drawing a sharper, more accurate map of the cosmic and terrestrial forces that shaped the modern world—proving that sometimes, to understand where life is going, we must radically revise where it has been.
