Cosmological density of metals as a function of redshift. Red hexagons show the measurements from this work based on the [C II] luminosity densities at z ≈ 5 and ≈7, converted to Ω_Z, ISM. The other symbols represent the metal densities inferred by various approaches, color-coded as a function of the distinct gas phases they are probing from the compilation of Péroux & Howk (2020), including results from Sanders et al. (2023a) and with the purple triangle denoting the lower bound derived from O I absorption at z ≈ 6 in sub-DLAs by Becker et al. (2011). The solid black line shows the expected yield of metals from star formation, assuming Ω_Z(z) = yΩ_⋆(z), with y = 0.033 being the integrated yield of the stellar population and Ω_⋆(z) is the stellar mass density quantified by Walter et al. (2020). These measurements suggest that metals mostly reside in the ISM of galaxies at z ≳ 3.