[ianburrell]

Earth after extinction-level asteroid is still more habitable than Mars.

Also, CME is coronal mass ejection and they happen all the time. One happened last month. CMEs are worse for Mars than Earth since Earth has atmosphere to protect while Mars gets the radiation directly. Carrington Event would cause power outages on Earth and possible death on surface of Mars. Like other things, Earth can prevent CME power outages. Can afford lots of preparation for cost of Mars colony.

If you are talking about gamma ray burst, then those would affect both planets. Earth has the advantage that would probably habitable and any survivors can live outside even if only using rocks. If civilization collapses on Mars, there won't be a Stone Age.

My feeling is that Mars civilization doesn't have to worry about external extinction because it would be fragile enough that won't last long. It depends on technology to survive and any interruption in that technology will cause collapse and there is no recovery. In the short term, it will be reliant on Earth and any problems on Earth will doom the colony.