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The Tonian (from Greek τόνος (tónos), meaning "stretch") is the first geologic period of the Neoproterozoic Era. It 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 Tonian is preceded by the Stenian Period of the Mesoproterozoic era and followed by the Cryogenian. Rifting
Rifting
leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya. The first large evolutionary radiation of acritarchs occurred during the Tonian. The first metazoans (animals) are found in the late Tonian about 800 Mya. A notable example of this is the poriferan-like species Otavia antiqua. See also[edit]

Boring Billion Riphean (stage)

References[edit]

" 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
Geologic
Time Scale". Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. 

v t e

Proterozoic
Proterozoic
Eon

Paleoproterozoic Era Mesoproterozoic Era Neoproterozoic Era

Siderian Rhyacian Orosirian Statherian

Calymmian Ectasian Stenian

Tonian Cryogenian Ediacaran

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