About 66 million years ago, a 12 km-wide asteroid hit Earth at 43,000 km/h, killing dinosaurs and creating Mexico's Chicxulub crater. Measuring 180 km across and 20 km deep, the crater has been buried by sediment over millions of years, with its rim visible as sinkholes. So far, researchers have only recovered a sesame-seed-sized piece of the asteroid off Hawaii.