The Habitable Epoch of the Early Universe Abraham Loeb (Harvard) http://arxiv.org/abs/1312.0613 (Submitted on 2 Dec 2013 (v1), last revised 16 Jan 2014 (this version, v2)) 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. --WDS: but it seems a bit hard to believe there were enough atoms besides H, He, and Li at the time, for life to exist... but Loeb thinks by that time massive stars would have had time to form and then supernova, so there would have been heavy elements around...