Paleoproterozoic

Paleoproterozoic
2500 – 1600 Ma Pha. Proterozoic Archean Had.
Paleoproterozoic stromatolites
Chronology
−2500 — – −2400 — – −2300 — – −2200 — – −2100 — – −2000 — – −1900 — – −1800 — – −1700 — – −1600 — – P r o t e r o z o i c A Neoarchean P a l a e o p r o t e r o z o i c Mesoproterozoic Siderian Rhyacian Orosirian Statherian   An approximate timescale of key Paleoproterozoic events. Axis scale: millions of years ago.
Proposed redefinition(s)	2420–1780 Ma Gradstein et al., 2012
Proposed subdivisions	Oxygenian Period, 2420–2250 Ma Gradstein et al., 2012 Jatulian/Eukaryian Period, 2250–2060 Ma Gradstein et al., 2012 Columbian Period, 2060–1780 Ma Gradstein et al., 2012
Etymology
Name formality	Formal
Alternate spelling(s)	Palaeoproterozoic
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Era
Stratigraphic unit	Erathem
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 Paleoproterozoic Era^[4] (also spelled Palaeoproterozoic) is the first of the three sub-divisions (eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from 2,500 to 1,600 million years ago (2.5–1.6 Ga). It is further subdivided into four geologic periods, namely the Siderian, Rhyacian, Orosirian and Statherian.

Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year.^[5] It was during this era that the continents first stabilized.^{[clarification needed]}