WASHINGTON (CBSDC) – Professionals and amateurs looking for evidence of meteor strikes on Earth often come up empty.
Plate tectonics and natural erosion usually erases all traces of craters.
There are only about 185 known impact craters on our planet. By contrast, the moon has more than 100,000.
But new technology is making it easier for geologists to find evidence of ancient impacts that is much easier and far more accurate than scouring satellite photos and maps.
“Google Earth images are not good enough to identify an impact structure,” noted planetary geologist Christian Köeberl told Live Science.
Scientists can measure shocked minerals, deformed rocks, and structural features to see if they match other craters.
The clues suggest that three sites in the U.S. are strong candidates for impact craters from space rocks that slammed into the Earth 470 million years ago, during the Ordovician Period.
The enigmatic structures are found in Wisconsin, Kentucky, and Tennessee.
Researchers have found traces of minerals shattered or heated by the impact.
Though no one has yet found the smoking guns in crater research: shatter cones, finely fractured rocks that form when shock waves travel through the ground.
But even without the smoking gun, Emily Zawacki, an undergraduate at Lawrence University in Appleton, is convinced that a meteor strike is the best way to explain a formation at Brussels Hill in Wisconsin.
The hill is perfectly round and peppered with fractured sandstone that would lie much deeper in the ground if it had not been disturbed.
The rock fragments are arranged in such a way that they appear to radiate from the center of the hill and tilt inward.
“This is a highly disturbed area in otherwise flat-lying stratigraphy,” Zawacki said. “It very clearly is anomalous and we feel a meteoritic impact best explains it.”
The other two sites also display anomalous features that suggest an impact.
The findings will be presented next month at the Geological Society of America’s annual meeting in Vancouver, British Columbia.