noun
Hadean; Hadean eon
Geological term for the earliest eon of Earth's history, before the Archean. Used in academic and scientific contexts.
冥王代は地球が形成された約46億年前から40億年前までの期間を指す。
The Hadean eon refers to the period from about 4.6 billion to 4 billion years ago when the Earth was formed.
The Proterozoic eon, which follows the Archean.
From 冥王 (meiou, 'Hades') + 代 (dai, 'era, eon'), a calque of the English 'Hadean eon'. The term is used in geology and planetary science.