Princeton's WordNet

1. Hadean, Hadean time, Hadean eon, Hadean aeon, Priscoan, Priscoan eon, Priscoan aeon(noun)

   the earliest eon in the history of the Earth from the first accretion of planetary material (around 4,600 million years ago) until the date of the oldest known rocks (about 3,800 million years ago); no evidence of life