The primordial deuterium-to-hydrogen (D/H) ratio, measured from absorption systems in the spectra of distant quasars and inferred from Big Bang Nucleosynthesis calculations, exhibits scatter and apparent evolution with redshift that is difficult to reconcile with a single, uniform early-universe nucleosynthesis scenario in Lambda-CDM. The variation in measured D/H ratios across different systems, combined with uncertainties in stellar processing of deuterium, suggests either systematic observational errors, time-dependent nucleosynthesis conditions, or non-standard early-universe physics (Cooke et al. 2014; Pettini & Conan Doyle 2000).