Hadean
The Hadean () is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago. , the ICS describes its status as ""informal"". 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", from "priscus", the Latin word for "ancient". Other, older texts simply refer to the eon as the Pre-Archean.
Dating creation
According to Censorinus (quoting Varro), the second period ("mythikón") lasted from 2137 to 776 BC, or if Censorinus' own dates are used: 2376 BC to 776 BC, or finally if Castor's: 2123 BC to 776 BC. Ovid, however, dated the start of the ("mythikón") period to the reign of Inachus, who he dated 400 or so years "after" the flood of Ogyges, meaning around 1900–1700 BC, but agreed with Varro that the "mythikón" ended during the first Olympiad (776 BC). See Ages of Man for more details about Ovid's chronology. Another ancient date for the start of the "mythikón" (mythical) period is found preserved in Augustine's "City of God" xviii.3, which dates it to 2050 BC. The final period according to Censorinus and Varro, the "historikón" (historical) era, began from 776 BC (the first Olympiad) to their own time: