Researchers at the University of Texas at Austin have determined that the 10-mile-wide subsurface Ames impact crater was formed during a meteor impact 100 million years later than previously believed, linking its formation to a violent extinction event that wiped out much of Earth’s marine life 372 million years ago.
The researchers said the zircon crystal radiometric approach used to date the Ames crater’s formation could help scientists date other ancient meteor impact sites or add supplementary information to previously dated impact formations.
Ames Impact Crater Previously Dated to the Ordovician Meteor Event
According to a statement, the impact crater that the researchers examined is buried beneath several layers of sedimentary strata. Dubbed the Ames impact structure, it is also a major producer of oil and gas.
Because it lies near a series of ancient meteor strikes across the North American continent that occurred roughly 467.5 million years ago, called the Ordovician Meteor event, scientists assumed Ames was a similar age. The researchers note that the frequency of impacts around this time has caused some to suggest that Earth may have once supported a Saturn-like ring of asteroid debris.
Before now, the site had been dated only from fossilized teeth of an ancient eel-like creature called a conodont discovered within the site’s rock. Since that date matched the Ordovician date, researchers considered the case closed.
Still, the research team behind the new effort said the conodont remains could have been “jumbled around” during a much later impact, creating the false correlation.
Zircon Crystals Reveal Violent Extinction Event 100 Million Years Later
Instead of relying on fossilized teeth, Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, and colleagues employed a technique that examines the structure of zircon crystals found embedded in rocks at the site to determine when they formed.
Stockli said radiometric zircon U-Pb dating is the most accurate way to date events like major asteroid impacts in Earth’s history, since zircon microstructures can record the shock pressures of such violent events.
“These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes,” Stockli explained.
After a zircon is impacted with an extreme force, it recrystallizes in what the team described as “a very specific way.” With some assistance from NASA, the researchers imaged the crystals collected from the Ames crater using cathodoluminescence and electron backscatter diffraction.
As hoped, the tests revealed that the zircon crystals were formed around 370 million years ago when a meteorite impacted the Ames area. The researchers said this date proves that the impact event that caused the now underground crater “could not have been part of the Ordovician Meteor Event.”
Instead, the new date, which is 100 million years later than the previously suspected event, lines up with the Frasnian-Famennian mass extinction event, which occurred about 372 million years ago. Like the impact that contributed to the extinction of the dinosaurs, this event wiped out much of Earth’s marine life.
“No matter what technique we used, it was coming back to this younger signal,” explained the study’s lead author, Elizabeth Catlos, an associate professor at UT’s Department of Earth and Planetary Sciences.
“This is Where This Impact Belongs”
When discussing the significance of the findings, Catlos said the result takes “a major pawn out of the Ordovician Meteor Event” and places it into the Frasnian-Famennian event.
“This is where this impact belongs,” she said.
The researcher also noted the value of more accurate dating for mass extinction events or other large-scale events that can deform zircon crystals. Stockli echoed the sentiment, noting that the process could help date other sites and bring the Earth’s violent ancient past into clearer focus.
“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,” they explained.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.