  In the redshift range 100<(1+z)<137, the cosmic microwave background (CMB)
had a temperature of 273-373K (0-100 degrees Celsius), allowing early rocky
planets (if any existed) to have liquid water chemistry on their surface and be
habitable, irrespective of their distance from a star. In the standard LCDM
cosmology, the first star-forming halos within our Hubble volume started
collapsing at these redshifts, allowing the chemistry of life to possibly begin
when the Universe was merely 10-17 million years old. The possibility of life
starting when the average matter density was a million times bigger than it is
today argues against the anthropic explanation for the low value of the
cosmological constant.
