More:
The iridium - "the iridium occurs in a layer just above the last Cretaceous microfossils," this probably means the solution to the impact in a probably 11,000 years after the extinction. -
http://mygeologypage.ucdavis.edu/cowen/~GEL107/KT.html
A probably: I see you understand that the impact is previous, later dead dinosaurs and later probably 1000 years later the iridium take land. This is near impossible, how any species survive the impact?
If would dead by the impact the iridium would to be at same level, the take of land would be like much 1 - 2 years later and probably less.
In that subjectiv study not find other probably layers with more iridium, asteroids impact near every time. And also not study (maybe they make this study, I have not find) if the layers correspond all at same time.
But may occur all at same time, we know that in a difference of + or - 11,000 years maximun a good asteriod impact.
The proof of the iridium for me is: the dinousaus extinct, then later in a time until 11,000 years or less have impact the asteroid, and without extinction effects, the animals in few number after o into that bad period of dead not are extincted.
In all form, the populations in time before the extinction are decreasing, probably in exctintion danger, but not only the dinosaurs, all the species, the dinosaurs extinct and other but not all.
False is to say that the extinction of the dinosaurs is by impact later that already the scientist with their subjectiv studies discover is false, but continue say that is true.