The underground impact structure, known as Ames crater, is located in northern Oklahoma and is named after a small town that sits above the submerged crater. At around 10 miles (16 kilometers) wide, it is the fourth-largest impact structure in the U.S.
Until now, researchers thought Ames crater dated to the Ordovician meteor event around 467 million years ago. During this period, an unusually high number of large space rocks smashed into Earth, likely due to the fragmentation of a single parent body somewhere in space. Scientists found fossils of marine animals in and around the crater that date to around the time of that event.
There are no visible signs of the Ames crater today. However, scientists have been able to map out its size and shape using ground-penetrating radar. This circle represents the rough outline of the the submerged structure. (Image credit: EarthExplorer/USGS/Landsat with annotations Harry Baker)
"No matter what technique we used, it was coming back to this younger signal," study first author Elizabeth Catlos, a geologist and planetary scientist at the University of Texas at Austin, said in a statement.
Analyzing zircon crystals is now one of the primary methods of dating ancient meteor craters, and the technique has led to several other impact dates being revised. For example, in July, researchers in Australia revealed that the North Pole Dome crater was around 500 million years younger than initial studies predicted, and in 2025, experts found that the impact that birthed Scotland's Stac Fada Member structure happened around 200 million years later than earlier research estimated.
The internal structure of zircon crystals preserves evidence of being exposed to extreme conditions, such as high temperature and pressure, making them ideal for exploring ancient impacts. This photo, captured during a completely unrelated study, shows one such crystal under an electron microscope. (Image credit: Emmanuel Roquette via Wikimedia)
"These small crystals allow us to go back in time and learn about the major changes to Earth's ancient landscapes," study co-author Danny Stockli, a geologist and dean of the Jackson School of Geosciences at the University of Texas at Austin, said in the statement. "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."
"This is where the impact belongs"
During the Frasnian-Famennian event, which began around 372 million years ago and lasted for several million years, as much as half of all marine life went extinct as Earth's oceans were depleted of oxygen. The die-off, which was most likely triggered by global cooling due to increased levels of volcanic activity, is often cited as one of the five major extinction events in Earth's history.
RELATED STORIESThe researchers emphasized that the Ames impact was not the cause of the Frasnian-Famennian event. However, they noted that the fallout from the impact, which would have injected huge clouds of dust into the air, may have contributed to the atmospheric cooling effect in the region.
"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,'" Catlos said.
The new study was dedicated to co-authors Andrew Parisi and Michael Brookfield, who sadly died before it was published.
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