[Fitzcarraldo]

Or cross-contamination between planets? There was a lot of asteroid impact activity in the pre-cambrian.

[Aracelis]

That's on my mind too, but I think it will be a long time before that question is settled...plus the question of "who" might have contaminated "who". (Ok, my grammer stinks...I'm a geologist. We're used to simply grunting in the field.)