You'll have to visit Sadda after fighting the Vampire in Terra Cavern to get the Earth Rod. All it does is open B4 of that dungeon, allowing you to reach Lich and restore the Crystal of Earth. Key Item or glorified quest flag? You decide!
You'll have to visit Sarda after fighting the VAMPIRE in the Earth Cave to get the ROD. It unlocks the path to B4 of that dungeon, allowing you to reach LICH and restore the ORB of Earth.