  The notion that dust might have formed the cosmic microwave background (CMB)
has been strongly refuted on the strength of four decades of observation and
analysis, in favour of recombination at a redshift z ~ 1080. But tension with
the data is growing in several other areas, including measurements of the
Hubble constant H(z) and the BAO scale, which directly or indirectly impact the
physics at the surface of last scattering (LSS). The R_h=ct universe resolves
at least some of this tension. We show in this paper that---if the BAO scale is
in fact equal to the acoustic horizon---the redshift of the LSS in this
cosmology is z_cmb ~ 16, placing it within the era of Pop III star formation,
prior to the epoch of reionization at 15 > z > 6. Quite remarkably, the
measured values of z_cmb and H_0 = H(0) in this model are sufficient to argue
that the CMB temperature today ought to be ~ 3 K, so H_0 and the baryon to
photon ratio are not independent free parameters. This scenario might have
resulted from rethermalization of the CMB photons by dust, presumably supplied
to the interstellar medium by the ejecta of Pop III stars. Dust
rethermalization may therefore yet resurface as a relevant ingredient in the
R_h=ct universe. Upcoming high sensitivity instruments should be able to
readily distinguish between the recombination and dust scenarios by either (i)
detecting recombination lines at z ~ 1080, or (ii) establishing a robust
frequency-dependent variation of the CMB power spectrum at the level of ~ 2-4%
across the sampled frequency range.
