Part of the Paleoarchean Era
Acastan Period - Isuan Period - Vaalbaran Period
The Isuan Period is the second, and final, period of the Paleoarchean Era, and the second of the Archean Eon. The Isuan begins at the time from which the oldest supracrustal rocks - the Isua greenstone belt - are known and ends at the time from which the oldest macroscopic fossils - stromatolites - are known. Though the earth had a firm crust by the Isuan, it is believed that it was incomplete, and lava existed at the surface in numerous locations. Life is thought to have existed throughout this era, though it may have been ended by the Late Heavy Bombardment, which ended early in the Isuan if it had not already concluded by the end of the Acastan Period. Even if life had gone extinct during the bombardment, it had reemerged before the end of this period. The oceans, having vaporized during the bombardment, are believed to have reformed during the Acastan. The supercontinent of Vaalbara began to assemble at around 3600 MYA during this period.
The Isuan is not further subdivided into epochs.
Isuan Timescale:
Isuan Period - 3810-3490 MYA