In regards to the second part, I’d point out that earth isnt a closed system, and small amounts of new matter are constantly ending up on earth. Think things like meteors (if i remember correctly, a few dozen tons of them fall on earth daily) the very thin traces of gas in space (it’s not a actually a perfect vacuum) and certain types of cosmic radiation that happen to consist of atoms. As such, I’d imagine it’s unlikely we’d ever get every atom on earth having once been part of one.