Hadean

Hadean
Hadean
Chronology
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 —	Precambrian Hadean Archean Proterozoic Phaner; ozoic Eoarchean Paleoarchean Mesoarchean Neoarchean Paleoproterozoic Mesoproterozoic Neoproterozoic Paleozoic Mesozoic Cenozoic
	(in millions of years)
Etymology
Synonym(s)	Priscoan Period; Harland et al., 1989;
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Definition
Chronological unit	Eon
Stratigraphic unit	Eonothem
First proposed by	Preston Cloud, 1972
Time span formality	Formal
Lower boundary definition	(4567.30 ± 0.16) Ma;
Lower GSSA ratified	October 5th, 2022
Upper boundary definition	Ten oldest U-Pb zircon ages
Upper boundary GSSA	Along the Acasta River, Northwest Territories, Canada; 65.1738°N 115.5538°W
Upper GSSA ratified	2023

The Hadean (/heɪˈdiːən, ˈheɪdiən/ hay-DEE-ən, HAY-dee-ən) is the first and oldest of the four known geologic eons of Earth's history, starting with the planet's formation about 4.54 Bya, now defined as (4567.30 ± 0.16) Mya set by the age of the oldest solid material in the Solar System found in some meteorites about 4.567 billion years old. The supposed interplanetary collision that created the Moon occurred early in this eon. The Hadean ended 4.031 billion years ago and was succeeded by the Archean eon, with the Late Heavy Bombardment hypothesized to have occurred at the Hadean-Archean boundary.

Hadean rocks are very rare, largely consisting of granular zircons from one locality (Jack Hills) in Western Australia. Hadean geophysical models remain controversial among geologists: it appears that plate tectonics and the growth of continents may have started in the Hadean. Earth in the early Hadean had a very thick carbon dioxide- and methane-rich prebiotic atmosphere, but eventually oceans made of liquid water were formed.

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