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We present accurate metallicity measurements for 121 damped Lya systems at0.5<z<5 including ~50 new measurements from our recently published EchelletteSpectrograph and Imager surveys. This dataset is analysed to determine theage-metallicity relation of neutral gas in the universe. Contrary to previousdatasets this sample shows statistically significant evolution in the meanmetallicity. The best linear fit rate to metallicity vs. redshift is -0.26 +/-0.07 dex corresponding to approximately a factor of 2 every Gyr at z=3. The DLAcontinue to maintain a floor in metallicity of ~1/700 solar independent ofobservational effects. This metallicity threshold limits the prevalence ofprimordial gas in high redshift galaxies and stresses the correspondencebetween damped systems and star formation (i.e. galaxy formation). This flooris significantly offset from the metallicity of the Lya forest and therefore weconsider it to be more related to active star formation within these galaxiesthan scenarios of enrichment in the very early universe. Finally, we comment onan apparent 'missing metals problem': the mean metallicity of the dampedsystems is ~10x lower than the value expected from their observed starformation history. This problem is evident in current theoretical treatments ofchemical evolution and galaxy formation; it may indicate a serious flaw in ourunderstanding of the interplay between star formation and metal production.Comment: 9 pages with 2 B&W figures. Submitted to ApJL (May 7, 2003

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