  Following Loeb (2001), we explore the imprint of the resonant 6708A line
opacity of neutral lithium on the temperature and polarization anisotropies of
the cosmic microwave background (CMB) at observed wavelengths of 250-350 micron
(0.9-1.2 THz). We show that if lithium recombines in the redshift range of
z=400-500 as expected, then the standard CMB anisotropies would be
significantly modified in this wavelength band. The modified polarization
signal could be comparable to the expected polarization anisotropies of the
far-infrared background on sub-degree angular scales (l>100). Detection of the
predicted signal can be used to infer the primordial abundance of lithium, and
to probe structure in the Universe at z~500.
