The question might be too open-ended. Maybe some constraints might help with creating interesting discussion. How long ago did the old civilization go away? Ho

The question might be too open-ended. Maybe some constraints might help with creating interesting discussion. How long ago did the old civilization go away? How many people are still around? Are there many remains of the old civilization? Did the former civilization prepare for this event and tried to leave seeds for a new civilization? If any, which ones?