A period in the early history of the Universe between the recombination epoch and the reionization epoch (some 300 000 years to at least 150 million years after the Big Bang), before any stars had formed. During this period the Universe was composed of 75% neutral hydrogen, 25% helium, and trace elements. There was no light in the Universe during the dark ages as there were no stars to emit it. This period ended with the reionization epoch, when the first stars and galaxies formed.