The Tonian (from Greek tonas, "stretch") is the first geologic period in the Neoproterozoic Era and lasted from 1000 Ma to 850 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry.

Events leading to the breakup of supercontinent Rodinia started in this period.

The first radiation of acritarchs occurred during the Tonian.

[edit] References

• "Tonian Period". GeoWhen Database. http://www.stratigraphy.org/geowhen/stages/Tonian.html. Retrieved January 5, 2006. 
• James G. Ogg (2004). "Status on Divisions of the International Geologic Time Scale". Lethaia 37: 183–199. doi:10.1080/00241160410006492. http://www.stratigraphy.org/precambrian/Ogg_2003.pdf. 

Preceded by Archean eon	2.5 Ga - Proterozoic eon - 542 Ma										Followed by Phanerozoic eon
	2.6 Ga - Paleoproterozoic era - 1.6 Ga				1.6 Ga - Mesoproterozoic era - 1.0 Ga			1.0 Ga - Neoproterozoic era - 542 Ma
	Siderian	Rhyacian	Orosirian	Statherian	Calymmian	Ectasian	Stenian	Tonian	Cryogenian	Ediacaran

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