Researchers at The University of Texas at Austin have discovered that the buried Ames impact structure in Oklahoma is nearly 100 million years younger than previously believed. By dating zircon crystals from the site, scientists determined the meteorite struck about 370 million years ago, moving its timeline from the Ordovician period to the Late Devonian.
A meteor impact structure spans miles deep beneath the surface of the small town of Ames, Oklahoma. While sedimentary strata now cover the crater, the site holds major economic value as an active oil and gas producer as well as a scientific landmark. For decades, geologists grouped the Ames crater with a cluster of North American impacts centered around 467.5 million years ago, an era known as the Ordovician Meteor Event.
That widespread clustering of ancient craters previously inspired researchers to theorize that Earth might have been encircled by a Saturn-like ring of asteroid debris during the Middle Ordovician. New radioisotopic evidence removes the Oklahoma crater from that celestial hypothesis entirely.
Dating Zircon Crystals With Uranium-Lead
Investigators studied zircon mineral grains extracted from granite samples altered by the original impact to establish a more precise timeline. Zircon is especially valuable for geochronology because the mineral traps uranium as it forms, allowing lead to accumulate predictably through radioactive decay over millions of years.
Most of the extracted crystals preserved much older crystallization ages reaching back roughly 1.4 billion years to the region’s original basement granite. However, a younger population of zircons produced a weighted mean age of 369.7 million years, with an uncertainty of about 5.9 million years, pointing to a major Late Devonian heating and recrystallization event.
The team collaborated with NASA to analyze the samples using cathodoluminescence imaging and electron backscatter diffraction to confirm that the crystals recorded the actual meteorite collision rather than later thermal resetting. These techniques revealed the distinctive microstructures and fine shock-pressure fractures that occur when extreme impact conditions force zircon to recrystallize.
How Conodont Fossils Misled Earlier Researchers
The age of the Ames crater rested entirely on biological evidence before this geochronological revision. Previous investigators recovered fossilized teeth from conodonts—tiny, eel-like marine animals that thrived during the Ordovician period—within the impact’s associated rock layers.
Catlos explained that those teeth were likely already millions of years old by the time the asteroid arrived. The violent collision churned up older subsurface material and jumbled the ancient microfossils into the newly formed impact breccia while leaving them physically preserved.
The research findings were published in July in the journal Meteoritics & Planetary Science. The project itself was initiated by Andrew Parisi, who traveled to the Oklahoma Geological Survey to secure the core samples, extract the zircon crystals, and assist with initial dating. Co-author Michael Brookfield, an affiliated researcher at the institution, also passed away prior to publication.
Linking the Crater to Ancient Mass Extinction
Placing the Ames crater in the Late Devonian aligns its formation squarely with the Frasnian-Famennian mass extinction event, a devastating biotic crisis that occurred roughly 372 million years ago and wiped out a massive percentage of marine life on Earth.
While the 9-mile-wide crater was far too small to trigger global extinction on its own, researchers emphasize that establishing precise timings is essential for understanding whether planetary die-offs stem from extraterrestrial impacts or interior forces such as massive continental volcanic activity.
The research team hopes to apply similar radiometric dating and microstructural imaging techniques to additional impact structures across North America to build a more accurate chronology of Earth’s geological history, building on past efforts that once linked the crater to the Ordovician Meteor Event 467.5 million years ago.