We present preliminary results from a chemical evolution model that tracks the composition of elements heavier than iron in a globular cluster. The heavy elements can be used as tracers of the nucleosynthetic events that defined the formation and evolution of star clusters in the early Universe. In particular, the chemical evolution model focuses on the hypothesis that rapidly-rotating massive stars produced the heavy elements via the slow neutron-capture process and seeded the proto-cluster while the stars we see today were still forming.
We compare our model with abundances in M4 and M5, which show very different heavy element patterns even though they have the same metallicity [Fe/H] of -1.2. In these clusters, there are no star-to-star variations in the neutron-capture elements, suggesting that whatever stars produced the heavy elements did not also produce the light elements. We also compare our model to the s-rich and s-poor populations in M22.