Thanks, Zaperking. Your post helped a lot... however I got one more question... If they really did split in 1010, then what's the 'Lucca' ghost talking about...
"As Schala fell through the
time gate in this condition,
she heard your crying
echoing through time...
That is when her story and
yours began to intertwine...
It is also when the past and
the future began to intersect,
and when the world became
divided into two..."
It's a reference, like an idea which is explaining how the whole of CC began from an outsiders point of view. SPOILERS BELOW!
Schala was gated, and fell through time. At this point, the Time Crash had already happened, and El Nido had already been built. Serge was born, and one day, was bitten by a panther. He was going to die, and started crying. His crys echoed through time, and Schala heard it. This was when it all began, which led him to being the Chrono Trigger/Arbiter.
As Schala tried making contact with his dimension to save him, her interfernce resulted in a mighty storm engulfing the Sea of Eden. Chronopolis blackedout, and Schala guided Miguel, Wazuki and Serge to Chronopolis. Wazuki heard Schala's calls through the flame "Bring him to me.. The child. Bring him to me" and took him into the Frozen Flame room, where he was healed by Schala. That very instant, Serge was registered as "The Arbiter" thanks to the Prometheus Circuit (a rouge file built by Lucca inside FATE's hardware). After that, nobody could reach the flame, and the only person who did have the power is Serge. Wazuki seeing the flame brought the images of Serge almost dying back, and he went crazy. Miguel was held hostage in Chronopolis, and Wazuki and Serge barily escaped and got back to Arni. There, Wazuki dumped Serge at Marge's house and ran away.
And then the reason the dimension split is that Wazuki was made into Lynx (because cats/Lynx's are Serge's fear) by FATE as a bio-organic interface. Wazuki's soul was pretty much.. destroyed. Anyway, FATE needed the flame bad, and decided to kill Serge. So one day when he was fishing, Lynx came and killed Serge, hoping that the lock would open up. Nope. And it didn't. Then in 1015AD, Lucca was taken by Lynx to open it (with Harle's help), but she didn't want to do it, and probably was killed.
Then sometime in the future, Kid travels back in time to save Serge. He is saved, and the dimension split (my theory was that she used her pendant on him, so one version of him died, whilst one version was sent back into the immediate past). Yeah so anyway, that's how the dimension split, I guess. Feel free to correct anything that I said.
Oh yeah, and history repeats itself again. So in 1015AD in another world, Lucca is kidnaped and presumed killed for not helping FATE out. In Home World, she's not killed and Kid stays on the mainland, or just doesn't exist most likely.