title: Hadean
context: The Hadean (/ˈheɪdiən/) is a geologic eon of the Earth pre-dating the Archean. It began with the formation of the Earth about 4.6billion years ago and ended, as defined by the ICS, 4billion years ago.[1] As of 2016, the ICS describes its status as "informal".[2] Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth.[3][4] W. Brian Harland later coined an almost synonymous term, the "Priscoan period", from priscus, the Latin word for "ancient".[5] Other, older texts simply refer to the eon as the Pre-Archean.
question: When was the Hadean era?
answers: 4.6billion years