|Regional usage||Global (ICS)|
|Time scale(s) used||ICS Time Scale|
|Time span formality||Formal|
|Lower boundary definition||Defined chronometrically|
|Lower boundary GSSP||N/A|
|Upper boundary definition||Defined chronometrically|
|Upper boundary GSSP||N/A|
The Calymmian Period (from Ancient Greek: κάλυμμα, romanized: kálymma, meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
- Boring Billion – Earth history between 1.8 and 0.8 billion years ago
- Jotnian – Oldest known sediments in the Baltic area that have not been subject to metamorphism
- "Calymmian 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.