Tonian
The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 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.
| Tonian | |||||||||||||||
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A map of the world as it appeared during the late Tonian, c. 750 Ma | |||||||||||||||
| Chronology | |||||||||||||||
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| Etymology | |||||||||||||||
| Name formality | Formal | ||||||||||||||
| Usage information | |||||||||||||||
| Celestial body | Earth | ||||||||||||||
| Regional usage | Global (ICS) | ||||||||||||||
| Time scale(s) used | ICS Time Scale | ||||||||||||||
| Definition | |||||||||||||||
| Chronological unit | Period | ||||||||||||||
| Stratigraphic unit | System | ||||||||||||||
| Time span formality | Formal | ||||||||||||||
| Lower boundary definition | Defined chronometrically | ||||||||||||||
| Lower GSSA ratified | 1991 | ||||||||||||||
| Upper boundary definition | Redefined chronometrically with an interim calibrated age of c. 720 Ma. GSSP is in progress. (Previously defined chronometrically as 850 Ma) | ||||||||||||||
| Upper boundary definition candidates | The first appearance of widespread glaciation. | ||||||||||||||
| Upper boundary GSSP candidate section(s) | To be determined | ||||||||||||||
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.
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