The most abundant elements in the universe are hydrogen and helium, but there are also small but significant amounts of heavier elements in stars and planets and in our own bodies. Where did these heavy elements originate?

in nuclear fusion deep in the interiors of stars

Explanation:

Nuclear fusion -

It is the type of reaction, where two or more atomic nuclei of the atom merges together to release two or more different nuclei along with some subatomic particles, is referred to as a nuclear fusion reaction.

The reaction can very well be done on stars, because of very high energy.

Hence, a nuclear fusion occurs deep inside the stars.