Researchers at The University of Texas at Austin have revised a key piece of Oklahoma’s geologic history, redating the Ames impact structure beneath the state to roughly 370 million years ago during the Late Devonian period. The finding separates the crater from a cluster of North American meteor strikes previously tied to the Ordovician Meteor Event nearly 100 million years earlier.
Granite Alteration Reveals a Younger Ames Crater
Beneath the town of Ames, Oklahoma, a meteor impact structure stretches for miles underground. Layers of sediment now cover the crater, but the geological feature remains a major producer of oil and gas. For years, scientists classified the site as part of the Ordovician Meteor Event, a cluster of major North American impacts dated to roughly 467.5 million years ago. That cluster previously led some researchers to propose that Earth was once surrounded by a Saturn-like ring of asteroid debris during the Middle Ordovician period.
New work from University of Texas researchers shows that the Ames impact does not belong to that episode. By dating zircon crystals extracted from granite altered by the meteor strike, the team determined that the collision occurred about 370 million years ago. That places the crater nearly 100 million years younger than previously believed, landing it close to the Frasnian-Famennian mass extinction event that wiped out a large proportion of marine life about 372 million years ago.
No matter what technique we used, it was coming back to this younger signal,
said lead author Elizabeth Catlos, associate professor at UT’s Department of Earth and Planetary Sciences. The research was published in July in Meteoritics & Planetary Science.
Zircon Crystals Correct the Geologic Timeline
Before the new study, researchers had only dated the Ames impact using biological evidence. Scientists previously recovered teeth from an ancient eel-like animal called a conodont preserved in the rock, originating from organisms that lived during the older Ordovician period. Catlos explained that those teeth were likely already millions of years old when the asteroid struck. The impact churned up older material and mixed the fossils into younger rocks while keeping them intact.
To establish an accurate timeline, the research team turned to zircon U-Pb dating, which Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, described as one of the most reliable methods for dating deep geologic history. Zircon crystals retain microscopic structures created by intense impact pressures. These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes,
Stockli said.
To verify that the zircons recorded the impact, the team worked with NASA to image the crystals using cathodoluminescence and electron backscatter diffraction. Extreme impact conditions cause zircon to recrystallize in a distinct pattern, which these imaging techniques can detect. The project was initiated by former Jackson School of Geosciences graduate student Andrew Parisi, who traveled to Oklahoma to obtain the rock core from the Oklahoma Geological Survey, extract the zircon crystals, and help determine their ages before his passing in 2018. Co-author Michael Brookfield also passed away before the publication of the paper.
Frequently Asked Questions About the Ames Crater Study
How did researchers confirm the new age of the Ames impact structure?
The research team dated zircon crystals extracted from granite altered by the meteor strike using uranium-lead dating. They also worked with NASA to image the crystals with cathodoluminescence and electron backscatter diffraction to confirm the grains recorded the shock of a collision.
Why did previous studies date the crater to the Ordovician period?
Earlier estimates relied on conodont fossils—teeth from an ancient eel-like organism—found in the rock layers. Researchers now conclude those fossils were already millions of years old when the asteroid struck and were simply churned up and mixed into the rock during the impact.
What major extinction event aligns with the revised timeline?
The new date of roughly 370 million years ago places the Ames impact close to the Frasnian-Famennian mass extinction event, which occurred about 372 million years ago and eliminated a large portion of marine life on Earth.
Where was the research published?
The findings were published in July in the journal Meteoritics & Planetary Science.
Related reading