Alvarez, et. al. the first person to put forth the hypothesis of the Chicxulub origin as the demise of the dinosaurs did extensive research worldwide to verify this result. He used the presence of a rare radioactive mineral, iridium, found at the contact zone between the end of the Cretaceous and the Tertiary. Iridium is a by-product if a high energy impact event like Chicxulub. It is found at multiple K-T contact sites.

Their are a number of geologists that are re-weighing the ultimate impact attributed to the meteor. They don't deny the event, just assert that its only one of the reasons for the dinosaurs extinction.