We make a lot of assumptions in science. Or rather hypotheses. (Non-scientists often confuse these with "facts").
But the evidence definitely points to an association between an asteroid hid at Chicxulub and the extinction of most of the larger land animals at the time.
So, what if we could prove it? Well, we can't, but we might soon have more information - scientists from the University of Texas at Austin have plans.
Expensive plans. It's called a core sample, and they plan on taking one of the Chicxulub impactor - which is buried 5,000 feet below the sea floor. They might be able to work out, for example, what it was made of.
This is going to be next year, so we'll have to wait a good while for the results, but they might have implications for asteroid defense. I, for one, am rather interested.