1000–720 million years ago
The Tonian (from Greek tonas, "stretch") is the first geologic period in the Neoproterozoic Era and lasted from 1000 Mya to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry.
The first large radiation of acritarchs occurred during the Tonian. The first Metazoans (Animals) are found in the late Tonian some 800 MYA. A notable example of this is the poriferan-like species Otavia antiqua.
- "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.