The Rhyacian (; Greek: Ρυαξ (rhyax), 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 other similar intrusions formed during this period.
The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted until 2200 Mya
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.
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