Final answer:
The asteroid impact at the end of the Cretaceous period left behind a layer of rock that is particularly rich in the rare metal iridium, providing evidence of the impact and its link to a mass extinction event.
Step-by-step explanation:
The asteroid impact that occurred at the end of the Cretaceous period left a worldwide layer of rock that is rich in iridium. This rare metal, along with other elements, is relatively abundant in asteroids and comets but exceedingly rare in Earth's crust. The sediment layer that contains this iridium also includes various minerals indicative of the high temperatures and pressures from the impact.
This layer provides evidence of the cataclysmic event, which is believed to be associated with a mass extinction, marking the transition from the Cretaceous to the Paleogene period. Such an impact would have released immense amounts of dust and material, enriching the sediments that settled afterward with extraterrestrial iridium.