In every single one of those cases, including the Cretaceous–Paleogene asteroid situation, you would be better off on earth than on mars as it is today by a mile.
Building a giant anti-asteroid system, or a mine-shaft system (a la Dr. Strangelove) would be infinitely better and cheaper solutions to the asteroid problem than MOVING TO MARS.
There have been pandemics in the past - Black Plague anyone - and we seem to have recovered fine. Earth based global warming is a joke compared to the atmoshpheric CO2 density of mars (95%!) - the fact that global warming is always brought up as a case to go to mars is proof positive that no one has really thought this stuff through.
I'm all for exploration and big shot dreams and stuff, but lets stop with the delusion that moving even one person to a completely uninhabitable place - as in almost anywhere on earth would be easier to live in, including under the ocean - 140,000,000 miles away is a practical idea.
and all that new science and technology and trade and opportunity for international collaboration.
As someone building future technology I call bullshit on the "spin-off" argument as a reason for doing something. The idea that "maybe some practical technology will come from it" is not a good reason to do anything. Using that logic we should be perpetually at war as nothing has moved technology further and faster than war.