Stenian

The Stenian Period (/ˈstiːni.ən/ STEE-nee-ən, from Ancient Greek: στενός, romanized: stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from 1200 Mya to 1000 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The name derives from narrow polymetamorphic belts formed over this period.

Stenian
Paleoglobe of Earth during the late Stenian, c. 1040 Ma
Chronology
−1200 — – −1180 — – −1160 — – −1140 — – −1120 — – −1100 — – −1080 — – −1060 — – −1040 — – −1020 — – −1000 — – M e s o p r o t e r o z o i c N ♇ Ectasian Stenian Tonian     ← First appearance of Bangiomorpha pubescens[1] ← Large-scale mountain-building from continent-continent collision of the Grenvillian orogeny[2] ← Development of the North American Midcontinent Rift[3] Events of the Stenian 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[4]
Upper boundary definition	Defined chronometrically
Upper GSSA ratified	1991[4]

Preceded by the Ectasian Period and followed by the Neoproterozoic Era.

The supercontinent Rodinia assembled during the Stenian. It would last into the Tonian Period.

This period includes the formation of the Keweenawan Rift at about 1100 Mya.[5]

Fossils of the oldest known sexually reproducing organism, Bangiomorpha pubescens, first appeared in the Stenian.[1]