The correct order of formal eons from oldest to youngest is:
hadean, archaean, proterozoic, phanerozoic.
The geological time scale include divisions of time. The eons are the primary divisions of time (the Hadean, the Archean, the Proterozoic and the Phanerozoic). The Hadean, the Archean and the Proterozoic are together known as the Precambrian supereon. Eons are divided into eras, which are in turn divided into periods, epochs and ages.
