On "morality derived from space colonization"

"Morality derived from space colonization" defines as the highest "Good" the survival of humans in case of an eventual global Earth cataclysm. I believe that such goal (humanity preservation) is likely to be acceptable for many people, but why only by space colonization?

There are arguments that an event that could destroy human life on Earth is likely to happen. We don't need to go until Sun depletion, it is more likely that a big enough asteroid will fall in the next thousands of years. Even without this, life of Earth might be threatened by local events like nuclear accidents, major climate change (it happened before). Even destructive diseases might not be contained in a certain Earth region. If not this, we might also face resource depletion if the population continues to grow.

It seems reasonable that saving humanity from a global Earth cataclysm depends on... finding another planet capable to sustain human life. It's like in the saying "don't put all your eggs in the same basket". It's always good to have a backup plan.

But how can this define Morality and Ethics?