@everickert So basically, how many supernovae contributed the elements which are right now inside you? Or me? Or any of us?
I’ve left this idea to smoulder in the back of my mind for about 24 hours now (sorry for the delay), and unfortunately, I can only conclude that there’s no possible way of knowing. Which is a pity, because it’s a very interesting question.
The minimum is one. Stars which are massive enough to explode as supernovae are the Universe’s only real way of creating iron in any significant quantity. Our blood contains a lot of iron (as does our planet), so at least one supernova must have contributed.
The maximum? Well… I can estimate it. But only with some wild speculation, some horrifically inaccurate estimates, and some completely uncertain assumptions. So…
The first stars in the Universe formed during the epoch of reionisation, around 150 million to one billion years after the Big Bang. Those first stars are quite mysterious. We know nothing about them. They would have been made entirely from Hydrogen, Helium, and a pinch of Lithium. They must have been very massive, and would have burned out very quickly and produced the first supernovae ever. None remain in the Universe today, and none have ever been identified by astronomers. As such, we know nothing about how many there were. That part is impossible to even guess at. This was, after all, before the galaxies had even formed.
In the remaining 13.65 billion years, a lot of supernovae must have exploded. In our galaxy today, they explode at a rate of about 20000 every million years. Assuming that this has never varied, that gives a total of 2730000000 supernovae in our galaxy since reionisation. 2.73 billion supernovae is actually a gross underestimate. Various cosmic events would have caused bursts of star formation and subsequent flurries of supernovae. Events such as our galaxy devouring smaller galaxies, or colliding with drifting intergalactic gas clouds.
Some may argue that we should discount the past 4.6(ish) billion years, because after the Sun formed, less supernova material would have ended up in the solar system – though there’s a lot of evidence to suggest that supernova debris has landed on Earth in the past.
Even so, discounting those years still gives 1.81 billion supernovae. A human being weighing 70 kg contains about 7E27 (that’s 7,000,000,000,000,000,000,000,000,000) atoms. Of those, there are about 4.5E22 Iron atoms. While unlikely, this does mean that it’s possible for at least one Iron atom from each of those supernovae to be in your body right now.
Even if only 0.0001% of those supernovae contributed any atoms to your body, that means that there are atoms from over 1000 supernovae in your blood right now.
Short answer: I genuinely have no idea how many atoms from supernovae any of us contains, but chances are it’s quite a few.