As a star ages, it fuses lighter elements into heavier elements. This means the abundance of heavier elements increases over time.

Here's why:

* Nuclear Fusion: Stars generate energy through nuclear fusion, where lighter elements combine to form heavier ones.

* Hydrogen to Helium: A star's primary fuel is hydrogen, which is fused into helium.

* Further Fusion: As a star ages, it may fuse helium into carbon, carbon into oxygen, and so on.

* Iron Accumulation: The process ultimately leads to the accumulation of iron, which is the most stable element in the universe and cannot be further fused to release energy.

So, in summary, older stars have a higher abundance of helium, carbon, oxygen, and other heavier elements compared to younger stars.