"For about the first microsecond [after the big bang], both protons and antiprotons existed in abundance, because the thermal-energy density was greater than that needed to create such a pair.  After the first microsecond, nearly all of the proton-antiproton pairs annihilated each other, leaving a very small surplus of protons and neutrons, flooded by electrons and positrons."—from William W. Porterfield in Inorganic Chemistry: A Unified Approach, Academic Press,1993, p.3