Oklahoma Ames Crater Dating Shifted by 100 Million Years
Researchers at The University of Texas at Austin have revised the geologic age of the buried Ames impact structure in Oklahoma to roughly 370 million years ago during the Late Devonian, separating the crater from the Ordovician Meteor Event nearly 100 million years earlier. Below the town of Ames, the 14- to 16-kilometer-wide crater spans miles underground and serves as a major oil and gas producer while remaining heavily covered by sedimentary strata. For decades, scientists linked the Ames structure to a widespread North American cluster of meteor impacts dated near 467.5 million years ago, fueling theories that Earth may have possessed a Saturn-like ring of asteroid debris during the Middle Ordovician.
Zircon Uranium-Lead Dating Replaces Conodont Fossils
The previous timeline relied entirely on biochronology after researchers found fossilized teeth from conodonts—extinct, eel-like marine animals—associated with the crater rocks. Lead author Elizabeth Catlos, associate professor at UT’s Department of Earth and Planetary Sciences, stated that the earlier date was misleading because the teeth were likely millions of years old before the asteroid struck and were simply churned up and mixed into the impact debris. To establish a more precise timeline, the research team extracted zircon crystals from impact-altered granite obtained from an Oklahoma Geological Survey rock core, utilizing uranium-lead geochronology to measure isotope ratios. Danny Stockli, dean of the Jackson School of Geosciences and co-author of the study, explained that microscopic structures preserved within zircon crystals record the extreme shock pressures of a collision, allowing scientists to pinpoint ancient impact dates with high precision. Analytical imaging conducted in partnership with NASA using cathodoluminescence and electron backscatter diffraction confirmed that the crystals recrystallized under the intense conditions of the meteorite strike, providing a weighted mean age of 369.7 million years with an uncertainty of 5.9 million years.
Frasnian-Famennian Mass Extinction Timing Overlaps the Revised Crater Age
Moving the Ames impact structure out of the Ordovician Period places its formation close to the Frasnian-Famennian mass extinction event, which unfolded approximately 372 million years ago and eliminated a large proportion of marine life on Earth. Researchers emphasize that while the radiometric date overlaps this biological crisis, additional samples and dating work are required to directly connect the meteorite impact to the extinction event itself. Catlos characterized the shift by stating that the research removes a major pawn from the Ordovician hypothesis and places the impact into the Devonian extinction window. The investigation originated with the late Andrew Parisi, a Jackson School graduate student who traveled to Oklahoma to retrieve the rock core and extract the zircons before his passing in 2018, alongside co-author Michael Brookfield, who also passed away prior to publication.
Did You Know? Underground Oklahoma Oil and Gas Hub
The Ames impact structure is not only a significant geologic marker but also an economically vital oil and gas producer in northern Oklahoma, with numerous active wells mapped across the buried crater rings.
Questions About the Oklahoma Ames Crater Timeline
Why were conodont fossils inaccurate for dating the Ames crater?
Conodont teeth found in the crater sediments originated from animals that lived during the older Ordovician Period, but those fossils were already millions of years old when the asteroid struck and were mixed into the impact debris during the collision.
How do zircon crystals record a meteor impact?
Under the extreme heat and pressure of a meteorite strike, zircon crystals recrystallize in a distinctive way that alters their internal structure, allowing scientists to detect the collision using NASA imaging techniques and uranium-lead isotope dating.
Who initiated the University of Texas research project on the Ames structure?
The project was started by Andrew Parisi, a graduate student at the UT Jackson School of Geosciences who obtained the rock core from the Oklahoma Geological Survey, extracted the zircons, and helped determine their ages before graduating in 2018.
Pro Tip for Geology Researchers
Combining high-resolution zircon uranium-lead dating with electron backscatter diffraction imaging provides a reliable method for distinguishing primary impact recrystallization from later hydrothermal alteration and burial heating in ancient basement rocks.
“These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes,” Stockli said.