Orbit speeds similar at a given radius. Wide ranges of orbital speeds. No Blue M-S stars Random elliptical orbits in all directions. Supernova explosions enrich the interstellar medium with metals. The next generation of stars form out of the metal-enriched interstellar gas.
Successive generations get more metal rich.
Higher Metal Content in Later Generations. Chemical Evolution only affects populations . Fusion occurs in the deep interiors of stars. Except for CNO elements, surface composition remains effectively unchanged over a stars life. Once a star forms, its chemical composition is mostly fixed for life.