Siderian

The Siderian Period (pronunciation: /saɪˈdɪəriən/; Greek: sideros, meaning "iron") is the first geologic period in the Paleoproterozoic Era and lasted from 2500 Ma to 2300 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.

The laying down of the banded iron formations (BIFs) peaked early this period. BIFs were formed as anaerobic algae produced waste oxygen that combined with iron, forming magnetite (Fe₃O₄, an iron oxide). This process cleared iron from the oceans, presumably turning greenish seas clear. Eventually, without an oxygen sink in the oceans, the process allowed the build up of an oxygen-rich atmosphere. This event is known as the oxygen catastrophe, which according to some geologists triggered the Huronian glaciation.

For the time period from 2420 Ma to 2250 Ma, an alternative period based on stratigraphy rather than chronometry, named the Oxygenian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of February 2017^[update], this has not yet been officially adopted by the IUGS.

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