Most atoms we experience (on this planet, for simplicity) were created very long time ago in supernova explosions and the like.
The light elements (eg helium made in the Sun) and some heavy ones (nuclear reaction products) are sometimes newer. But most of the other ones are remnants of long-gone stars. Gone through countless reactions but still the same.
My question is: these atoms that are here for such a long time, can we think about them as unchanged?
Perhaps electrons are physically exchanged when creating bonds. But I wonder if nuclei of these elements ever change physically? Can we perceive atom nuclei as the very same matter that was produced by the stars eons ago?
I do realize it's hard to talk about matter on that scale. All atomic particles may better be described by quantum wave functions. But since they are the building blocks of the macroscopic matter that we know the question whether they are physically the same stuff seems valid.