Final answer:
In stars with higher masses, nuclear reactions can produce elements as heavy as iron. Massive stars can potentially undergo a supernova explosion, which allows for the synthesis of even heavier elements. The progressive enrichment of heavy elements in successive generations of stars explains their abundance in newer stars and on Earth.
Step-by-step explanation:
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. This process is known as nucleosynthesis. While stars with lower mass can produce carbon and some oxygen, only more massive stars can achieve the necessary conditions to create elements heavier than iron.
As these massive stars near the end of their lives, they can potentially undergo a supernova explosion. This explosion releases an enormous amount of energy and allows for the synthesis of even heavier elements.
Overall, the progressive enrichment of heavy elements in successive generations of stars explains why elements heavier than hydrogen and helium are more abundant in newer stars, and it also accounts for the presence of heavy elements on Earth and in our bodies.