This is a damn good thread Sesto. Nicely done. Actually answering questions with legitimate, thoughtful answers. Kudos to you. OT: I was wondering: since most models of the cosmos and life on earth at some point assume a supernova to make the heavier materials on earth, plus get the molecular cloud stirring so it eventually accretes into a solar system; are any astronomers now actively looking for a progenitor supernova remnant? Or remnants? In that, relatively close by neutron stars which might explain where precisely our atoms and molecules come from? Or since it would have happened at least 4.6 billion years ago, do they assume such systems would be so far away or out of our progenitor nebula by now that they assume they won't find them? I would think that in order to substantiate the model, concrete evidence, and an idea of where we actually came from would be necessary.