Orosirian

The Orosirian Period ( /ˌɒroʊˈsɪəriən/; Ancient Greek: ὀροσειρά, romanized: oroseirá, 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.

Orosirian
2050 – 1800 Ma Pha. Proterozoic Archean Had.
A map of Earth as it appeared during the early Orosirian, c. 2 Ga^[citation needed]
Chronology
−2050 — – −2000 — – −1950 — – −1900 — – −1850 — – −1800 — – Paleoproterozoic Rhyacian Orosirian Statherian   ← Beginning of the Boring Billion ← Supercontinent Columbia forms ← Sudbury Basin structure created by asteroid impact? ← End of the Great Oxidation Event ← Vredefort impact structure created by asteroid impact Events of the Orosirian Period Vertical axis scale: Millions of years ago
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
Upper boundary definition	Defined chronometrically
Upper GSSA ratified	1990

The later 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. Early in 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.

For the time period from about 2060 to 1780 Mya, an alternative period based on stratigraphy rather than chronometry, named the Columbian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of February 2022^[update], this has not yet been officially adopted by the IUGS.

Paleogeography

The supercontinent Columbia may have formed at the end of this period.

Further reading

• "Orosirian Period". GeoWhen Database. Retrieved July 8, 2011.
• James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492.