Oomis: The scientists call it Pangaea or something like that. And no, it did not exist post-Mabul. I once did hear a theory that the Mabul is what broke it up.
But to answer your question, the Passuk in Shvi’i says that Hashem spread the people out all over the world after Migdal Bavel. So HKBH himself put people in these far-flung places. And, of course, he moved animals and a functioning ecosystem there with them.