The difference between magnatic and true will have to wait - not half such fun.
One for the mythbusters if they haven't done it already, or any competent mathematician who can find the numbers. I have heard it said that there is a significant chance that in any day you breathe air that has been circulated so comprehensively by the world's meteorological systems to the extent that any breath might contain a molecule from Nelson's dying breath, or one of Henry VIII's belches (or worse) or Nefertiti's sneeze or a dinosaur's bellow. Presumably, the further back in time the more likely. So what are the chances that a molecule in the air I'm breathing now was once breathed by a slave building the Sphinx?
Or in similar mode, the human body is mostly water, which is circulated in the same way - what chance any part of me was once in the bilge of Leif Ericsson's Viking ship on the Greenland coast? Or of the puddle that Raleigh spread his cloak over for Elizabeth 1? Or even part of Raleigh before she had him shortened by a head for being presumptuous?