| Siderian | |
| Color: | Siderian |
| Top Bar: | all time |
| Time Start: | 2500 |
| Time End: | 2300 |
| Caption Map: | A reconstruction of the Earth's continents during the middle Siderian, circa 2.4 Ga. |
| Image Outcrop: | Banded iron formation Dales Gorge.jpg |
| Caption Outcrop: | A Siderian banded iron formation in Dales Gorge, Western Australia |
| Image Art: | Snowball Huronian.jpg |
| Caption Art: | Artist's impression of the Earth during the Huronian glaciation, starting from mid-Siderian |
| Timeline: | Siderian |
| Proposed Boundaries1: | 2630–2420 Ma |
| Proposed Boundaries1 Ref: | Gradstein et al. |
| Proposed Part1: | Neoarchean |
| Proposed Part1 Ref: | Gradstein et al. |
| Name Formality: | Formal |
| Celestial Body: | earth |
| Usage: | Global (ICS) |
| Timescales Used: | ICS Time Scale |
| Chrono Unit: | Period |
| Strat Unit: | System |
| Timespan Formality: | Formal |
| Lower Boundary Def: | Defined Chronometrically |
| Lower Gssa Accept Date: | 1991[1] |
| Upper Boundary Def: | Defined Chronometrically |
| Upper Gssa Accept Date: | 1991 |
The Siderian Period (; Greek, Ancient (to 1453);: σίδηρος|sídēros, meaning "iron") is the first geologic period in the Paleoproterozoic Era and lasted from Ma to Ma. Instead of being based on stratigraphy, these dates are defined chronometrically.
The deposition of banded iron formations peaked early in this period. These iron rich formations were formed as anaerobic cyanobacteria produced waste oxygen that combined with iron, forming magnetite (Fe3O4, an iron oxide). This process removed iron from the Earth's oceans, presumably turning greenish seas clear. Eventually, with no remaining iron in the oceans to serve as an oxygen sink, the process allowed the buildup of an oxygen-rich atmosphere. This second, follow-on event is known as the oxygen catastrophe, which, some geologists believe triggered the Huronian glaciation.[2] [3]
Since the time period from 2420 Ma to 2250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 in a geological timescale review.[4]