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.
2nd century BC
The 2nd century BC started the first day of 200 BC and ended the last day of 101 BC. It is considered part of the Classical era, although depending on the region being studied, other terms may be more suitable. It also considered to be the end of the Axial Age. In the context of the Eastern Mediterranean, it is referred to as the Hellenistic period.