Hadean; Hadean eon
Geological term for the earliest eon of Earth's history, before the Archean. Used in academic and scientific contexts.
The Hadean eon refers to the period from about 4.6 billion to 4 billion years ago when the Earth was formed.
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.