I've always felt that one of the biggest mysteries in FFVII was the origin of the Black Materia. Materia and Magic is the knowledge of the Ancients using the power of the planet. So how in gods name did an anti-planet spell wind up on aplanet that for most of the game's history that we know of, was run by the peaceful planet loving Cetra? It's like a hippie convent having an atomic bomb in their backyard, how did it get there and who the hell made it, and why? It's always been one of the few elements of VII's plot that kind of nags me. I have a theory myself but I'm curious to know what others think first.