3.3. Spectral Evolution
We should also comment on the spectral properties of high-redshift quasars, which look surprisingly like their low-redshift counterparts. The emission-line spectra of the first quasars discovered at z 5 (e.g., Schneider, Schmidt, & Gunn 1991; Fan et al. 1999) show C, N, O, and Si lines in the strengths normally seen at low redshifts. The Dietrich et al. (2002) compilation of spectra covering 0.5 < z < 5 shows remarkably little evolution with redshift. While it is dangerous to jump to conclusions about abundances based on the appearance of strong emission lines, their lack of evolution is consistent with more detailed analyses. Put another way, we have no evidence for chemical evolution in quasar spectra, except that, if anything, some abundances were higher at high redshifts (Hamann & Ferland 1999).