Final answer:
Iridium is a good chemical marker of the Chicxulub impact. The impact released a large amount of iridium into the atmosphere, which settled and formed a sediment layer. This layer can be identified by the high concentration of iridium and other cosmic components.
Step-by-step explanation:
A good chemical marker of the Chicxulub impact is iridium. Iridium is a rare metal that is relatively abundant in asteroids and comets but exceedingly rare in Earth's crust. The impact of the asteroid or comet that created the Chicxulub crater released a large amount of iridium into the atmosphere, which settled and formed a sediment layer. This layer can be identified by the high concentration of iridium and other elements that are characteristic of cosmic components.