The Orosirian ( /ˌɒrɵˈsɪəriən/; Greek: oroseira - ὀροσειρά, meaning "mountain range") is the third geologic period in the Paleoproterozoic Era and lasted from 2050 Mya to 1800 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The latter half of the period was an episode of intensive orogeny on virtually all continents.
Two of the largest known impact events on Earth occurred during the Orosirian. At the very beginning of the period, 2023 Mya, a large asteroid collision created the Vredefort impact structure. The event that created the Sudbury Basin structure occurred near the end of the period, 1850 Mya.
| Preceded by Archean Eon | 2.5 Ga - Proterozoic Eon - 542 Ma | Followed by Phanerozoic Eon | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2.5 Ga - Paleoproterozoic Era - 1.6 Ga | 1.6 Ga - Mesoproterozoic Era - 1.0 Ga | 1.0 Ga - Neoproterozoic Era - 542 Ma | |||||||||
| Siderian | Rhyacian | Orosirian | Statherian | Calymmian | Ectasian | Stenian | Tonian | Cryogenian | Ediacaran | ||