So I did some more research, and this idea of “Terra Australis” goes as far back as Aristotle, who posited that there should be a southern landmass to counterbalance the weight of the northern continents. Ptolemy even thought there was a zone occupied by “monstrosities” (http://www.geographicus.com/blog/rare-and-antique-maps/terra-australia-terra-de-quir-and-the-great-southern-continent/)
I don’t think we gave the early-modern Europeans enough credit in class today, saying that the Indians ‘should not exist’. The concept of an foreign, undiscovered continent was pondered by the early Greeks and others.
Maybe the real distinction lies between an other-worldly continent and an other-worldly people, with the latter being far more incomprehensible. Or maybe the concept is just so mind-blowing that we can’t ever really understand how Columbus felt when he discovered the ‘new’ people.