Well, the old saw is that the Mayan people were such good astronomers, and ancient good astronomers are so good at prophesy (but somehow missed the factors that ended their empire) that they have, honestly, really, cross-your-heart-and-hope-to-die predicted the world's ending this December. So, what could go wrong?
Archaeology, that's what. Guys and gals digging around in the remains of old, dead civilizations who find stuff just layin' around, that's what.
You know, things like old calendars. Mayan calendars that don't end this December but go on for about another five thousand years! Actually, they didn't find calendars, but they found the tables that Mayan astronomers used to calculate stuff - like calendars, and when the king's birthday falls into which god's period of influence - tables that tracked the orbits of the planets, like Venus, for about seven thousand years after when the tables were painted on the walls.
Not bad for folks without computers, huh?
From the Washington Post.