Rhyacian

EtymologyName formalityFormalUsage informationCelestial bodyEarthRegional usageGlobal (ICS)Time scale(s) usedICS Time ScaleDefinitionChronological unitPeriodStratigraphic unitSystemTime span formalityFormalLower boundary definitionDefined ChronometricallyLower GSSA ratified1990Upper boundary definitionDefined ChronometricallyUpper GSSA ratified1990

The Rhyacian () is the second geologic period in the PaleoproterozoicEra. It spans 250 million years and lasted from 2300 to 2050 million years ago (Ma), following the Siderian Period and preceding the Orosirian Period. These dates are defined chronometrically rather than stratigraphically.