Population Migration / Travel
Marking the end of their settlement, living on the planet that gave birth to them, it is now too damage to sustain their numbers.
The decision to leave their place of birth was hard, as many felt they should keep trying to fix the damage they had done to their home, but the fact was time was the only hope they had. It would be cared for, as the debates on the topic, saw them form a society that would preserve, monitor and keep what they could from being lost to time.