  WMAP's detection of high electron-scattering optical depth suggests
substantial star formation at high redshift z~17 +/- 5. On the other hand, the
recovered sigma_8 ~ 0.84 +/-0.04 disfavors a cluster Sunyaev-Zeldovich (SZ)
origin for the observed small-scale-CMB fluctuation excess, which generally
requires sigma_8 ~ 1.1. Here we consider the effects of high-redshift star
formation on the CMB. We derive a fairly model-independent relation between the
electron scattering optical depth and the number of ionizing photons emitted
per baryon, and use this to calibrate the amount of high-redshift supernova
activity. The resulting supernova remnants Compton cool against the CMB
creating a Compton-y distortion y ~ few x 10^-6, within observational bounds.
However they also create small-scale SZ fluctuations, which could be comparable
with SZ fluctuations from unresolved galaxy clusters. This raises the exciting
possibility that we have already detected signatures of the first stars not
just once, but twice, in the CMB.
