The Tonian (from Greek tonas, "stretch") is the first geologic period in the Neoproterozoic Era and lasted from 1000 Mya to 850 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry.
The first radiation of acritarchs occurred during the Tonian.
- "Tonian Period". GeoWhen Database. Archived from the original on May 12, 2006. Retrieved January 5, 2006.
- James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia 37 (2): 183–199. doi:10.1080/00241160410006492.
|Preceded by Archean Eon||Proterozoic Eon||Followed by Phanerozoic Eon|
|Paleoproterozoic Era||Mesoproterozoic Era||Neoproterozoic Era|
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