Complex sentence: Raivata and Revati returned to earth, for which to them they had only left a short while ago, and they were shocked by the changes that had taken place over 27 "catur"-yugas.
Split into simpler sentences: Raivata and Revati returned to earth, which to them they had only left a short while ago. They were shocked by the changes that had taken place over 27 "catur"-yugas.