More than 300 million years after a massive asteroid collided with Earth, scientists have found the planet's 118-mile-long scars. Experts say two huge underground domes in the Earth's crust, about 19 miles beneath central Australia's Warburton Basin, are evidence of the largest and most powerful asteroid impact ever found, reports Discovery. They were left behind after an asteroid broke into two pieces, each at least 6.2 miles wide, just before hitting Earth at least 300 million years ago. The easternmost mark was found in 2013 when geothermal drilling revealed rock that had been turned to glass—evidence of an incredible blow, the Guardian reports. A second scar showed "similar seismic and magnetic signatures," including bulges of iron and magnesium thrust into the crust from the Earth's mantle, though surface evidence of the impact has vanished over millions of years, reports Popular Science.
Just one of the asteroid pieces would have been similar in size to the one that caused the Chicxulub crater in Mexico's Yucatán Peninsula, which finished off the dinosaurs 66 million years ago. The newly discovered impact area, stretching 250 miles, "would have been curtains for many life species on the planet at the time," researcher Andrew Glikson explains. But "it's a mystery—we can't find an extinction event that matches these collisions." Scientists say sediment debris that might have been flung up by the blow, as with the Chicxulub impact, is missing from rock layers from the period, which leads Glikson to believe "the impact could be older than 300 million years." Rocks around the impact zone are as old as 600 million years. "Large impacts like these may have had a far more significant role in the Earth's evolution than previously thought," Glikson adds. (Read about how we might survive an asteroid hit.)