What Killed the Dinosaurs?

What I found the most surprising about this article is that there is a possibility that mass extinction took place before an asteroid impact. For the most part, I've only been acquainted with the well-known theory that an asteroid impact caused devastation that wiped out most species. This is the first time I've heard about the gradual acidifying of the oceans doing this same thing. I believe a combination of the two theories killed the dinosaurs. There is overwhelming evidence that Chicxulub caused widespread extinction in North America and possibly South America, as well as overwhelming evidence that the Deccan eruptions caused this in Europe and elsewhere. At this point, it is impossible to rule out either event as the culprit. Something that stood out to me is the sentence that stated that the Alvarez duo "discover[ed] lots of iridium in places worldwide". This being such a crucial pointer to the Chicxulub theory, I would have expected a more specific explanation rather than such a general statement that lacks exact amounts and places.