The Guardia royal family passed down Schala's pendant as an heirloom for all of its history. However, in Magus's flashback, Schala is clearly seen trapped in the Ocean Palace Incident after the three Gurus and Janus are gated to various eras. How did the Pendant originally make it to the outside world?
During Crono's time traveling, Schala used the Pendant's power to transport his two teammates and Magus out of the Ocean Palace. Now, provided that the Pendant retained the same amount of power in the Lavos Timeline in the original incident, she would have been able to transport three other individuals out. She may have simply used the Pendant to remove herself, Queen Zeal, and perhaps another person out of the palace. This would allow the Pendant to exist on the outside world and find its way to Last Village; additionally, this would prevent Queen Zeal from staying behind and raising the palace as the Black Omen.
From: Theory (Objects)