Researchers at the University of Texas at Austin have discovered that a meteor hit Ames, Oklahoma, at a different time than previously believed.Under the small town of Ames, a crater lies buried beneath layers of rock. The crater is also important today because the area is a major oil and gas-producing region. Researchers have now challenged the fossil evidence that defined its age. Scientists had previously believed the impact was about 467.5 million years old. It was therefore considered part of a group of meteor impacts across North America known as the Ordovician Meteor Event. Because there were so many impacts around the same time, scientists theorised that Earth may once have had a ring of space rocks around it, similar to Saturn’s rings during the Middle Ordovician. They believed this ring of asteroid debris may have eventually fallen towards Earth, causing many meteor impacts.The researchers at the University of Texas, however, recently discovered that the Ames impact structure is nearly 100 million years younger than previously believed. By dating zircon crystals in the rocks, scientists discovered that the meteor hit Ames about 370 million years ago, not 467 million years ago as previously thought.“No matter what technique we used, it was coming back to this younger signal,” lead author Elizabeth Catlos, associate professor at UT’s Department of Earth and Planetary Sciences, said in a statement. The research is published in the journal Meteoritics & Planetary Science.
Credit: Catlos et al.
Previously, the Ames meteor impact site was only dated biochronologically. During that time, researchers found the teeth of an ancient eel-like creature called a conodont in the rock, which existed during the older Ordovician age. But the teeth were likely millions of years old when the asteroid struck Ames and likely just got jumbled around in the mix of the impact, remaining preserved, according to Catlos.The new dating of the zircon crystals shows that the Ames meteor impact did not happen during the Ordovician Meteor Event. Instead, it happened around 370 million years ago, close to the Frasnian-Famennian mass extinction, which was about 372 million years ago, when a large amount of marine life died out on Earth.Zircon U-Pb dating is not only the most accurate way to tell when events like this occurred in Earth’s history, but microstructures in zircon can record the shock pressures of impacts, Danny Stockli, dean of the Jackson School of Geosciences and a co-author of the study, said.“These small crystals allow us to go back in time and learn about the major changes to Earth’s ancient landscapes. 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,” Stockli explained.
Credit: Catlos et al.
In order to prove that the zircons’ dates were affected by the meteor, the researchers teamed up with NASA to examine the crystals using special imaging techniques. When a meteor hits, zircon crystals change their structure in a distinctive way. Scientists can see these changes using these techniques, confirming that the crystals were affected by the impact.Having a more accurate timeline for mass extinction events and other big moments in Earth’s history is crucial for understanding how our planet works, Catlos said. The researcher explained that it is important to see whether these extinctions were driven by an extraterrestrial force such as this one, or an internal force such as a series of massive volcanic eruptions.“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,’” she said.This research was started by Andrew Parisi, a former graduate student at the Jackson School of Geosciences who graduated in 2018 and has since died. He collected the Ames rock core from the Oklahoma Geological Survey, extracted the zircon crystals, and helped date them. The co-author Michael Brookfield, an affiliated researcher at the school, also passed away before the paper was published.Research Professor Sean Gulick and Professor Emeritus Mark Cloos at the Jackson School also contributed to this research.
