The world of the dinosaurs vanished in just a few hours when a ten-to fifteen-kilometer-wide asteroid crashed into Earth.21 The crash caused a major extinction event, during which about half of all genera disappeared. Geologists refer to this as the K/T event because it occurred at the border between the Cretaceous period (often abbreviated K, from the German word for “chalk,” Kreide) and the Tertiary period, an older name for the Cenozoic era, which began sixty-five million years ago.
