Rhyacian

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

== Etymology and history == The name Rhyacian is derived from the Greek word rhyas, meaning "stream of lava", and refers to the layered intrusions of the Bushfeld Complex in South Africa. The term was proposed by the Subcommission on Precambrian Stratigraphy as a subdivision of the Proterozoic Eon, and was ratified by the International Union of Geological Sciences in 1990. In 2012, there were suggestions to replace the Rhyacian with an alternate name, bearing a time interval of 2250 to 2060 Ma, and decided on the basis of its stratigraphy. The name Jatulian was proposed in reference to the Lomagundi-Jatuli excursion event, while the term Eukaryian was chosen due to the period's existing signs of the earliest eukaryotic fossils. , a replacement for the Rhyacian has not been officially adopted by the IUGS. The term Jatulian, however, has been used in the regional stratigraphy of Fennoscandia.