The Siderian (IPAEng|saɪˈdɪəriən, _el. sideros, meaning "iron") is the first
geologicperiod in the PaleoproterozoicEra and lasted from 2500 Ma to 2300 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
banded iron formations (BIFs) peaked early this period. BIFs were formed as anaerobic algaeproduced waste oxygenthat 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 created the oxygen-rich atmosphere of today. This event is known as the Oxygen Catastrophe.
Huronian glaciationbegan in the Siderian 2400 Ma and ended in the late Rhyacian2100 Ma.
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