Calymmian

Calymmian
1600 – 1400 Ma Pha. Proterozoic Archean Had.
Paleoglobe of the Earth at the start of the Calymmian, c. 1590 Ma[citation needed]
Chronology
−1600 — – −1580 — – −1560 — – −1540 — – −1520 — – −1500 — – −1480 — – −1460 — – −1440 — – −1420 — – −1400 — – P ♇ M e s o p r o t e r o z o i c Statherian Calymmian Ectasian     ← Breakup of the supercontinent Columbia Events of the Calymmian Period. Axis scale: millions of years ago.
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[1]
Upper boundary definition	Defined chronometrically
Upper GSSA ratified	1991[1]

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.

The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.

The supercontinent Columbia started to break up during the Calymmian some 1500 Mya.

The Volyn biota have been dated to 1500 Mya.