The Siderian Period

The Siderian (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 Earth was a suffocating place until oxygen in the atmosphere slowly began to climb from almost nonexistent levels about 2.5 billion years ago.

Breathable air is thought to have been created by cyanobacteria, single-celled microbes living in the sea.

These bacteria harnessed the energy of the sun through photosynthesis-the biochemical process used by plants-producing oxygen as a by-product. The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation.

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.

The Huronian glaciation began in the Siderian 2400 Ma and ended in the late Rhyacian 2100 Ma.