Formation of Calcium–Aluminium-rich Inclusions (4,567 Ma) to Acasta Gneiss (4,031 Ma)
proponents or Body
Preston Cloud (coined 1972); International Commission on Stratigraphy (ICS)
key evidence
Detrital Jack Hills zircons (up to 4,404 Ma), Moon-forming impact, Acasta Gneiss
Core Principles & Analysis
Coined by geologist Preston Cloud in 1972 after Hades, the Hadean spans from Earth's accretion (~4,567 Ma) and the Moon-forming giant impact (~4,500 Ma) to the crystallization of the oldest known intact rock unit, the 4,031 Ma Acasta Gneiss in Canada.
Although Earth initially had a global magma ocean beneath a steam-and-CO₂ atmosphere, detrital zircon crystals dated to 4,404 ± 8 Ma from the Jack Hills of Western Australia show oxygen-18 ratios indicating liquid surface water and continental crust within 160 million years of Earth's formation.
The eon concluded around 4.0–3.8 Ga amid the hypothesized Late Heavy Bombardment of the inner Solar System and the transition to the Archean Eon, when the earliest cratonic nuclei and microbial biosignatures appear.