User blog comment:ImperiexSeed/Supernatural Mysteries/@comment-3481504-20130307031256/@comment-3481504-20130307174027

You don't need to insult me, FTWinchester, by providing an alternative that you and I both know is implausible. There couldn't have been a single proper Bone of a Righteous Mortal Washed in the Three Bloods of the Fallen in space, mainly because there's not Man (bone), not a Fallen Angel's blood contracted from a vessel (blood #1), not a King of Hell (not blood #2), and not an Alpha (bone #3).

I don't at all agree with the "proto-Earth", or the Purgatory being the first Earth, theory.

They posed a threat to anything that walketh (ha ha) or lives--Seraphs, Angels, Cherubs, demons, Deities, monsters--, that there is the reason why God incarcerated them in the confines of Purgatory. Then again, Death did say, "He locked them away.... (that's not the full quote, but this snippet is relevant to this)", so I guess, it's possible Purgatory acted as a initial Earth, and simply sealed it, when they became too aggressive and destructive.

When referring to the baseline, Death uses the word "petri dish", implicating an experiment of sorts. So yeah, maybe Purgatory was God's "proto-Earth."