Schematic illustration of early chemical enrichment and galaxy evolution under the two-phase formation scenario. In the early Universe (top left), metal-free stars, including both massive Pop III stars (large stars) and less massive ones (smaller stars), form from pristine gas. Pop III stars end as PISNe (orange bursts), while lower-mass metal-free stars produce CCSNe (blue bursts). The stars that form from this enriched material inherit the colour of the enriching SN type. They populate an early compact massive galaxy, or ‘red nugget’ (pink background), with high [Si/Mg]. In normal massive galaxies, a second phase brings mergers and accretion, together with additional enrichment by CCSNe and SNe Ia (blue and green bursts), significantly diluting [Si/Mg]; they then evolve into massive ETGs (greenish background). In contrast, relic galaxies like NGC 1277 do not experience significant mergers over the second phase, passively evolving with only minor additional enrichment (the lighter pink background exemplifies such a minimal dilution). The bottom-middle tracks show the schematic [Si/Mg] evolution for each formation pathway.