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The Tonian was the first geological period in the Neoproterozoic era. It lasted from 1000 million years ago (mya) to 720 mya. The supercontinent Rodinia began breaking in this period. Acritarchs radiated during the Tonian.
- "Tonian Period". GeoWhen Database. Archived from the original on May 12, 2006. https://web.archive.org/web/20060512164244/http://www.stratigraphy.org/geowhen/stages/Tonian.html. Retrieved January 5, 2006.