Final answer:
The heavier elements that make up 2% of our solar nebula come from stellar evolution (supernovas). When massive stars exhaust their nuclear fuel, they die in a supernova explosion where heavier elements are synthesized and ejected into interstellar space.
Step-by-step explanation:
The heavier elements that make up 2% of our solar nebula come from stellar evolution (supernovas). In stars with masses higher than about 8 solar masses, nuclear reactions involving carbon, oxygen, and still heavier elements can build up nuclei as heavy as iron.
When massive stars finally exhaust their nuclear fuel, they most often die in a spectacular explosion called a supernova. Heavier elements are synthesized in the stunning violence of these explosions and are subsequently ejected into interstellar space where they can be used to form new stars.