| Orosirian | |||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2050 – 1800Ma | |||||||||||||||||
 A map of Earth as it appeared during the early Orosirian, c. 2 Ga[citation needed] | |||||||||||||||||
| Chronology | |||||||||||||||||
| |||||||||||||||||
| Etymology | |||||||||||||||||
| Name formality | Formal | ||||||||||||||||
| Usage information | |||||||||||||||||
| Celestial body | Earth | ||||||||||||||||
| Regional usage | Global (ICS) | ||||||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||||||
| Definition | |||||||||||||||||
| Chronological unit | Period | ||||||||||||||||
| Stratigraphic unit | System | ||||||||||||||||
| Time span formality | Formal | ||||||||||||||||
| Lower boundary definition | Defined chronometrically | ||||||||||||||||
| Lower GSSA ratified | 1990[1] | ||||||||||||||||
| Upper boundary definition | Defined chronometrically | ||||||||||||||||
| Upper GSSA ratified | 1990[1] | ||||||||||||||||
TheOrosirian (/ˌɒroʊˈsɪəriən/;Ancient Greek:ὀροσειρά,romanized: oroseirá, meaning "mountain range") is the thirdgeologic period in thePaleoproterozoic Era. It spans 250 million years and lasted from 2050 to 1800million years ago (Ma), following theRhyacian Period and preceding theStatherian Period. Instead of being based onstratigraphy, these dates are definedchronometrically.
For the time period from about 2060 to 1780 Mya, an alternative period based on stratigraphy rather than chronometry, named theColumbian, was suggested in the geological timescale review 2012 edited by Gradstein et al.,[2] but as of February 2022[update], this has not yet been officially adopted by theIUGS.
Two of the largest knownimpact events on Earth occurred during the Orosirian. Early in the period, 2023 Mya, a largeasteroid collision created theVredefort impact structure. The event that created theSudbury Basin structure occurred near the end of the period, 1850 Mya.
The later half of the period was an episode of intensiveorogeny on virtually allcontinents.
ThesupercontinentColumbia may have formed at the end of this period.[3]
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