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. 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.