Siderian

The Siderian (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.

Abundance of 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 created the oxygen-rich atmosphere of today. This event is known as the Oxygen Catastrophe.

Oxygen Catastrophe was followed by Huronian glaciation, one of the most extensive glaciations in Earth's history. The Huronian glaciation began in the Siderian 2400 Ma and ended in the late Rhyacian 2100 Ma.