  I show that neutral lithium couples strongly to the cosmic microwave
background (CMB) through its 6708A resonant transition after it recombines at
z~500. At observed wavelengths of <335 micron, the CMB anisotropies are
significantly altered since the optical depth for resonant scattering by
neutral lithium is substantial, of order 0.5. The scattering would suppress the
original anisotropies, but will generate strong new anisotropies in the CMB
temperature and polarization on sub-degree scales (l>100). Observations at
different wavelengths in this spectral regime can probe different thin slices
of the early universe. The anisotropy noise contributed by continuum radiation
from foreground far--infrared sources could be taken out by subtracting maps at
slightly different wavelengths. Detection of the above effects can be used to
study structure at z<500 and to constrain the primordial abundance and
recombination history of lithium.

Astrophysics