A dinosaur-killer sized asteroid strike would still leave earth far, far more habitable than mars is (there would at least be air and water) as would essentially any other conceivable natural or cosmic disaster.

I hadn't really thought about that before. But I still think the sudden, cataclysm still could render humans extinct on Earth even if Mars is a more difficult climate. Mars dwellers would have had a great deal of time to prepare for that environment. On Earth, it would be suddenly thrust upon them. This is also assuming that the Mars colony was at a point where it could exist without supplies from Earth.

I thought so too, until I read this New Yorker article [1].

It’s about a site in the Hell Creek formation that seems to show, in incredible detail, what happened in the first hour after the Chicxulub strike a couple thousand miles away.

It reset my ideas about Earth’s habitability after the impact.

[1] https://www.newyorker.com/magazine/2019/04/08/the-day-the-di...

(AFAIK, not paywalled unless you’ve used up your monthly quota of free NY articles)

you're just making the single point bigger

This could be said for any expansion, until your single point becomes "everything that is".

It so happens, that the Sun's expansion will eventually consume most of the planets in the galaxy; of course, it will also be so cold long before that point humans won't be alive.

> It so happens, that the Sun's expansion will eventually consume most of the planets in the galaxy; of course, it will also be so cold long before that point humans won't be alive.

In the galaxy or solar system?

I can see Arcturus right now and the galaxy still seems to exist so I'm gonna guess b)

By a minimum of about 33.9 million miles, yes.