How does an invisible underwater crater prove an asteroid killed the dinosaurs?

A team of scientists recently set off to drill a 1,500m-deep hole into the seabed off the coast of Mexico. Their goal is to learn more about the asteroid impact some 66m years ago that many scientists believe killed the dinosaurs. But how do we know that this now-invisible crater, measuring some 180km across, is responsible for such devastation to life across the globe?