Zirconian
| Zirconian Era 4404–4031 million years ago |
The Zirconian is the second Era within the Hadean Eon in a proposed revision of the Precambrian time scale. It lasted 373 million years from the end of the Chaotian Era to the beginning of Eoarchean Era. The Zirconian follows the Chaotian Era and its beginning is chronometrically set at 4.404 ± 0.008 Gya. This corresponds to the age of the first occurrence of Hadean zircons in the Jack Hills in Western Australia. The end of the Zirconian Era and the transition to the Acastan Period occurred with the appearance of the oldest rock at 4.031 ± 0.003 Gya.
Etymology
The term Zirconian is derived from the mineral zircon, since it is the only substance that is preserved from this early period. An alternative proposal for the name of this era is "Jack Hillsian Era".Meaning
The first 196 million years after the formation of Earth, left no solid trace, except for the formation of the Moon. This time is termed the Chaotian Era. The first datable solid Earth minerals, zircons, mark the start of the Zirconian Era. The oldest known crystal could be dated to 4,404 ± 8 Mya. It was in metasedimentary rock on Erawandoo Hills in the Jack Hills of Narryer Gneiss Terrane in Western Australia. The 4.4 Gya is the limiting age, and zircons this old are very rare. But from 4.2 to 4.1 Gya they are already common. The bulk of the zircons in Narryer Gneiss Terrane date much later, from 3.75 to 3.5 Gya.Occurrence
The zircons are limited only to Archean cratons. In the Yilgarn craton quartzites of Southern Cross Terrane also contains zircons with an age of 4.35-3.13 Gya).Possibly the Nuvvuagittuq Greenstone Belt of the Superior Craton is of Zirconian age, its proposed age of 4.28 Gya is however still controversial. The end of the Zirconian Era is at 4.031 Gya, marked by the Acasta Gneiss of Slave craton and it is likely that its protolith is older. In 2006, a single zircon crystal in Acasta Gneiss was dated to 4.2 Gya