In 1991, an oil company discovered a giant crater buried under Ames, Oklahoma. Subsequent investigations led researchers to propose the meteor responsible for the structure belonged to the many meteors that struck North America some 470 million years ago. New dating, however, challenges this account—while proposing an entirely different context for this enigmatic crater.
According to a recently published study in Meteoritics & Planetary Science, researchers dated zircon crystals from the site and found that the Ames crater likely formed about 370 million years ago, during the Late Devonian. That represents a whopping 100-million-year gap with the Ordovician meteor event, when Earth saw a large increase in meteor events roughly 467 million years ago. Importantly, this now temporally places the Ames crater within another significant period in geological history: the Frasnian–Famennian mass extinction, which drastically reshaped Earth’s marine ecosystems.
“No matter what technique we used, it was coming back to this younger signal,” Elizabeth Catlos, the study’s lead author and an Earth scientist at the University of Texas at Austin, said in a statement. “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.’”
Truly impactful
A giant rock from space smashing into Earth brings about a number of changes to the local environment. To take the Ordovician meteor event as an example, scientists have proposed that the huge flux of chondrites from this period contributed heavily to biodiversification on Earth. A more recent study also strengthened the link between the ice age and this event, which would have generated so much dust that Earth experienced global cooling.
Meanwhile, the Ames crater is among the largest impact structures associated with the Ordovician event with a diameter of roughly 9 miles (15 kilometers), according to the study. As a result, it has been an integral part of theories about the full implications of the Ordovician meteors on Earth’s geological history. Despite its importance, however, scientists had yet to collect high-precision data on the crater’s geochronologic history, the team pointed out in the paper.
A renewed perspective
For the latest study, the researchers studied zircon samples from the site using a number of different techniques, including uranium-lead dating, which revealed both the age of the crater and the shock pressure left behind by the meteor. Then, the team collaborated with NASA to confirm that the zircon crystals were indeed affected by the meteor impact.
According to the paper, there was a “recurrence of Devonian dates” across different grains and methods, which provides strong statistical evidence for the Ames crater being younger than previously believed. It’s possible that the younger zircon dates come from “later tectonic events,” but this is less likely as the crater is mostly isolated from major and minor faults in Oklahoma, the team added in the study.
Equally consequential
Now, the renewed dates now place the Ames crater in another significant period from Earth’s geological history, namely the Frasnian-Famennian mass extinction event. This period, which scientists have called the “most devastating biotic crisis” at the time, led to huge portions of marine life going extinct. To be clear, this particular meteor, which produced a crater 9 miles wide, was far too small to drive global extinction on its own (but given the timing, it probably added some insult to injury). The precise triggers for this extinction event remain unclear, although a major theory concerns large-scale volcanism.
In that sense, the latest findings may offer new insights into this particular mystery. As Catlos added in the statement, having a more accurate timeline for Earth’s major extinction events teaches us how our planet operates—especially if the competing theories involve volcanic eruptions and extraterrestrial forces.
