Rhyacian is the second geological period in the Palaeoproterozoic that began 2.3 billion years ago, and ended at 2.05 billion years ago. Before it was the Siderian It is followed by the Orosirian.
Huronian (Makganyene) global glaciation began at the start of the Rhyacian. It lasted until 2200 million years ago. 
The first known
eukaryotes began to evolve in the Rhyacian period. The multicellular Francevillian Group Fossils, at 2.1-Gyr-old are from the Rhyacian period. 
↑ Kopp et al.; Kirschvink, JL; Hilburn, IA; Nash, CZ (August 2005). "The Palaeoproterozoic Snowball: A climate disaster caused by the evolution of oxygenic photosynthesis". PNAS 102 (32): 11131–6. doi: 10.1073/pnas.0504878102. PMC 1183582. PMID 16061801.
↑ El Albani, Abderrazak; Bengtson, Stefan; Canfield, Donald E.; Bekker, Andrey; Macchiarelli, Reberto (July 2010). "Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago". Nature 466 (7302): 100–104. doi: 10.1038/nature09166. PMID 20596019.