User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-66.177.180.197-20121213223148/@comment-5881112-20121223093657

From what I understand, it can be spelled either way, interchangeably. In The Lost Hero it is spelled Gaea. In The Son of Neptune it is spelled Gaia. In Mark of Athena it is spelled both ways.