Particle Era

As the universe continued to cool, the particle era consisted of the formation of two particle families - hadrons and leptons. Hadrons are made up of quarks. Hadrons then formed two additional families - baryons and mesons. Baryons are "normal stable everyday matter" consisting of three quarks. Mesons are "short lived unstable particles" made of one quark and one anti-quark. All of the new mesons quickly annihilated each other leaving only protons and neutrons which would make up the nuclei of future atoms.

The formation of hadrons was followed by the formation of leptons. Leptons consist of electrons, neutrinos, muons and taus. Muons and taus are very unstable and quickly decay. During this period most of the matter in the universe consisted of leptons and their anti-particles. The lepton era drew to a close when the majority of leptons and anti-leptons annihilated one another, leaving a comparatively small surplus of leptons to populate the future universe. The lepton epoch ended at about 10^-3 seconds.