Rhyacian Period Rhyacium rhyaciano Paleoproterozoic Era Ryaciense Riak Siderian Period Riacis rhyaci Rhyaciën Rhyak Riaciano Base of Rhyacian リヤシアン紀 Ryasium Precambrian Supereon Rhyacian 层侵纪 Proterozoic Eon Ryak Rhyac rhyacium rhyacij Rhyacien Rhyacien Base of Orosirian ryacium Orosirian Period a2.1.3.3 Geologic Time Scale (2019) younger bound -2050 Ma Риац older bound -2300 Ma