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Short description: Second period of the Paleoproterozoic Era
2300 – 2050 Ma
A reconstruction of the Earth as it may have appeared at the end of the Rhyacian Period, 2050 million years ago.
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 boundary GSSPN/A
GSSP ratifiedN/A
Upper boundary definitionDefined Chronometrically
Upper boundary GSSPN/A
GSSP ratifiedN/A

The Rhyacian Period ( /rˈsiən/; Ancient Greek:, meaning "stream of lava") is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago).[1] Instead of being based on stratigraphy, these dates are defined chronometrically.[2]

The Bushveld Igneous Complex and some other similar intrusions formed during this period.[2]

The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period.[3]

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.,[4] 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.[5]

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.[6][7][8]


  1. "Rhyacian Period". GeoWhen Database. 
  2. 2.0 2.1 James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia 37 (2): 183–199. doi:10.1080/00241160410006492. 
  3. Kopp et al. (August 2005). "The Paleoproterozoic Snowball: A climate disaster triggered by the evolution of oxygenic photosynthesis". PNAS 102 (32): 11131–6. doi:10.1073/pnas.0504878102. PMID 16061801. PMC 1183582. Bibcode2005PNAS..10211131K. 
  4. Gradstein, F.M. et al. (editors) (2012). The Geologic Time Scale 2012. 1. Elsevier. pp. 361–365. ISBN 978-0-44-459390-0. 
  5. Bingen, B.; Solli, A.; Viola, G.; Torgersen, E.; Sandstad, J.S.; Whitehouse, M.J.; Røhr, T.S.; Ganerød, M. et al. (2015). "Geochronology of the Palaeoproterozoic Kautokeino Greenstone Belt, Finnmark, Norway: Tectonic implications in a Fennoscandia context". Norwegian Journal of Geology 95: 365–396. doi:10.17850/njg95-3-09. 
  6. Strassert, Jürgen F. H.; Irisarri, Iker; Williams, Tom A.; Burki, Fabien (2021). "A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids". Nature. doi:10.1038/s41467-021-22044-z. PMC 7994803. 
  7. Mänd, Kaarel; Lalonde, Stefan V.; Robbins, Leslie J.; Thoby, Marie; Paiste, Kärt; Kreitsmann, Timmu; Paiste, Päärn; Reinhard, Christopher T. et al. (April 2020). "Palaeoproterozoic oxygenated oceans following the Lomagundi–Jatuli Event". Nature Geoscience 13 (4): 302–306. doi:10.1038/s41561-020-0558-5. Bibcode2020NatGe..13..302M. 
  8. Van Kranendonk, Martin J. (2012). "16: A Chronostratigraphic Division of the Precambrian: Possibilities and Challenges". in Felix M. Gradstein. The geologic time scale 2012 (1st ed.). Amsterdam: Elsevier. pp. 359–365. doi:10.1016/B978-0-444-59425-9.00016-0. ISBN 978-0-44-459425-9.