I think that... (Spoilers for CT and CC ahead!)

[KentaRawr!]

I think that the second (SPOILER)world in chrono cross was created when Crono died in chrono trigger, this is because when you switch the clone with Crono, marle, lucca, magus, lavos, schala, and zeal would have still seen crono die! so that would mean that there would probobly be clones of marle and lucca looking for ways to revive crono running around, and then the clones and the real people would cross paths sooner or later...but this didn't happen! but marle and lucca (the ones in the past) still witnessed cronos death. so if they don't appear in the first world, there must be a second! this could either mean a second world was created right then, or a second world was already there.

^_^

[Kawaii Ryûkishi]

The second world was created when Sarah came out of nowhere and rescued Serge from drowning in the ocean.

[Doomgaze]

The game's very clear on this, yes.

[KentaRawr!]

oops...forgot about that ^_^;; but this is confusing now... x_x

[Azure Chrysanthemum]

Go to www.gamefaqs.com there's a handy chronology guide.

[KentaRawr!]

ty! ^_^