Hadean

The Hadean ( /ˈheɪdiən/) is the first geologic eon of Earth and lies before the Archean. It began with the formation of the Earth about 4,567.17 million years ago and ended roughly 4,000 million years ago, though the latter date varies according to different sources. The name "Hadean" derives from Hades, the Greek name for the underworld. The name is in reference to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term: the "Priscoan period". Other, older texts simply refer to the eon as the Pre-Archean.