contributing factor lol, the fact is our science still sucks. It's obvious are carbon dating is failed, it will take some time for anyone to prove that though. The Yucatan crater "could" still be more then just a factor if the way we understand a extinction by an ice age caused by dust thrown up blocking the sun is flawed. We still haven't solved the most important questions, and lots of them aren't even scientific in nature. We just believe science is the best route to solve them.
Say it took 300,000 years in full for the process to happen? Geological worldwide events have known to take 700,000 liek the magmetic polar shift happening in 100 years. We don't even known why were late for this one, maybe it's gonna be different? Open up a gaping o-zone whole(they known it will open big enough ones), that would throw enough radiation to kill all of our children, and theirs?
Imo we don't really know anything.
"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"