How does the heavy-element content in extremely old nebulae, like those in globular clusters, typically compare to newer nebulae?

Answer

Lower by a factor of about 50

When observing extremely old nebulae, astronomers find a very low heavy-element content, sometimes lower by a factor of about 50 compared to newer nebulae, while maintaining a relatively normal abundance of helium.

How does the heavy-element content in extremely old nebulae, like those in globular clusters, typically compare to newer nebulae?
SpaceastronomycompositionstarsElementsstellar nebula