FunkMonkey,
The terraforming and renaming story is told by Thea (II, ch. 10).
The presumed Xanthic Continent is a bit more dicey. The Xanthic Lands are a group of a couple hundred (or more) islands in the ocean to the west of the Commonwealth (V, ch. 46). The people there speak the Xanthic tongue and are xanthoderms (yellow skinned). The only named island we know is "Blue Flower Island" (V, ch. 46). The people are a bit more primitive than folks in the Commonwealth, such that they have little food security and periodic food riots. Call that fact one.
Fact two. Jonas and Hethor talking some kinda foreign language(s). Jonas talking about an Asian-sounding name being common in a place now sunk under the sea back when he was young. Seems like some Asian spacefaring group was topdog on Urth back when Jonas and Hethor first went up and away.
Fact three. Cyriaca's tale of the Library (III, ch. 6). Rise and long decline of the First Empire.
Speculation puts these three together: Jonas and Hethor come from the time of the First Empire (Cyriaca's tale), which then suggests that the First Empire was created by Asians (since Jonas and Hethor have Asian tongues, as it were), and the Xanthic Lands (populated by what to our eyes appear to be Asians) are the fallen remnants of that particular civilization. That someplace important sank while they were gone could also go towards explaining how they couldn't find a port to land (as Jonas says about the crashlanding).
(Must remember to intercorrelate Cyriaca's tale with Tale of the Boy Called Frog . . . )
=mantis=