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Orosirian Period
2050–1800 million years ago

The Vredefort crater is believed to have formed in this period.

The Orosirian (pronunciation: /ˌɒrˈsɪəriən/; 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).[1] Instead of being based on stratigraphy, these dates are defined chronometrically.

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. 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.


The supercontinent Columbia formed at the end of this period.


  • "Orosiriagn Period". GeoWhen Database. Retrieved July 8, 2011.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
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  1. David Huddart; Tim Stott (16 April 2013). Earth Environments: Past, Present and Future. John Wiley & Sons. pp. 1599–. ISBN 978-1-118-68812-0.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>