Chris O'Donnell has all the info over at his blog, but here's a synopsis:
400 or so years ago, a bishop somewhere determined that the Earth was created on October 23, 4004 BC. Wrote a whole book about it, too! A book that many, many confused people refer to as a "history" book, one that's recommended for all homeschoolers! I can't resist quoting COD:
Well, we do read a lot of fantasy in this house. I guess it fits into the fantasy collection. Although I find Tolkien’s account of Middle Earth history to be far more believable.
And there you have it! Although now I'm confused about Earth Day which is in April. Maybe it's the Earth's half-birthday celebration? I think the greedy Earth just wants more presents, if that's the case.