Of, relating to, or being the period of time during which Earth formed, from the start of the solar system (4.6 billion years ago) until accretion, impact, and cooling led to stable Earth-Moon orbits and the formation of the earliest rocks on Earth (3.8 billion years ago).
Designating or of the time on earth when the solar system was forming and the earth was still in a molten state; Precambrian, esp. early Precambrian.
Origin of hadean
After Hades (from the intense heat during part of this period)