2300 – 2050 Ma
A reconstruction of the Earth as it may have appeared in the early Rhyacian, c. 2.2 Ga.
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitPeriod
Stratigraphic unitSystem
Time span formalityFormal
Lower boundary definitionDefined Chronometrically
Lower GSSA ratified1991
Upper boundary definitionDefined Chronometrically
Upper GSSA ratified1991

The Rhyacian Period (/raɪˈeɪsi.ən/; Ancient Greek: ῥύαξ, romanizedrhýax, meaning "stream of lava") is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The Bushveld Igneous Complex and some other similar intrusions[specify] formed during this period.

The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period.

For the time interval from 2250 Ma to 2060 Ma, an alternative period based on stratigraphy rather than chronometry, named either the Jatulian or the Eukaryian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of March 2020, this has not yet been officially adopted by the IUGS. The term Jatulian is, however, used in the regional stratigraphy of the Paleoproterozoic rocks of Fennoscandia.

This is when the eukaryotes are thought to have originated from the symbiosis between asgardarchaea and alphaproteobacteria, as well as the sexual reproduction found within the eukaryotes only, thus the alternative name Eukaryian.

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