Scientists have found telltale evidence that an asteroid twice as large as any previously known smashed into Earth about 300 million years ago. Previously, the largest asteroid impact was believed to have occurred 66 million years ago, when a massive space rock hit what is now the Yucatan Peninsula in Mexico, causing such havoc that it led to the extinction of the dinosaurs.
But scientists conducting geothermal drilling below the surface of Central Australia recently discovered two vast underground scars of an even more massive asteroid, which broke in two and blasted into Earth from 300 million to 600 million years ago. Testing revealed that the two impact zones—now 19 miles below the surface—were actually caused by the same meteorite.
At more than 250 miles wide, the combined size of the craters suggests that the asteroid was some 12 miles wide—perhaps double the size of the dinosaur-killing asteroid—before it broke in two. The double punch should have raised so much dust that it darkened the skies for years and wiped out most living things, but scientists have no evidence of that. “It’s a mystery,” says lead researcher Andrew Glikson. “We can’t find an extinction event that matches these collisions.”