Generally, although that's never going to need to happen.
If I didn't sacrifice myself to save the Earth, I would be all alone forever.
If you're living on the Earth you're gonna die either way. If you sacrafice yourself to save the earth, you're saving millions of lives, if you don't you still die and kill others.
I'm going to die sooner or later anyways, why not make myself useful, and hopefully, remembered?
If a single person had to be sacrificed to save everyone else on this planet,I would lay my life down for the cause
Earth will last longer than me, so there's no need to.
This is contingent on if the Human race and all my favorite animals get to colonize an alternate planet.
i would not save the earth as i do not see that the earth would ever fall to such a situation and if it did your "average joe" wouldn't be able to do anything.