Why does the low metal content of globular clusters provide clues about their formation?

The low metal content of globular clusters is a critical indicator of their ancient origins and provides essential clues about the early history of the Milky Way Galaxy.12

In astronomy, elements heavier than helium are referred to as "metals." Because these heavy elements are produced within stars and subsequently dispersed into the interstellar medium through processes like supernova explosions, the concentration of metals in a star or cluster serves as a proxy for its age.13

Globular clusters contain very low levels of these heavy elements—often as little as 0.02 percent by mass, compared to approximately 2 percent in the solar neighborhood. This chemical composition indicates that these clusters formed from primordial gas before the Galaxy had been significantly enriched by the death of previous generations of stars. Consequently, their low metal content confirms that globular clusters are among the oldest objects in the Galaxy, having formed during the earliest stages of its collapse, before the material settled into the present thin disk.124