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2500 – 538.8 ± 0.2 Ma
Newfoundland, Canada
47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Upper GSSP ratified1992

The Proterozoic (

Mya,[6] the longest eon of the Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozoic, and is the most recent part of the Precambrian

The Proterozoic is subdivided into three

Cambrian Explosion. The name Proterozoic combines two words of Greek origin: protero- meaning "former, earlier", and -zoic, meaning "of life".[8]

Well-identified events of this eon were the

bilaterians and the sessile Ediacaran biota (some of which had evolved sexual reproduction) and provides the first obvious fossil evidence of life on Earth

The Proterozoic record

The geologic record of the Proterozoic Eon is more complete than that for the preceding

epicontinental seas; furthermore, many of those rocks are less metamorphosed than Archean rocks, and many are unaltered.[9]: 315  Studies of these rocks have shown that the eon continued the massive continental accretion that had begun late in the Archean Eon. The Proterozoic Eon also featured the first definitive supercontinent cycles and wholly modern[clarify] mountain building activity (orogeny).[9]
: 315–18, 329–32 

There is evidence that the first known glaciations occurred during the Proterozoic. The first began shortly after the beginning of the Proterozoic Eon, and evidence of at least four during the Neoproterozoic Era at the end of the Proterozoic Eon, possibly climaxing with the hypothesized

Marinoan glaciations.[9]
: 320–1, 325 

The accumulation of oxygen

One of the most important events of the Proterozoic was the

: 324 

Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen 2 billion years ago. Such massive iron oxide formations are not found in older rocks.[9]: 324  The oxygen buildup was probably due to two factors: exhaustion of the chemical sinks, and an increase in carbon sequestration, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.[9]
: 325 

A second surge in oxygen concentrations, known as the

Neoproterozoic Oxygenation Event,[10] occurred during the Middle and Late Neoproterozoic[11] and drove the rapid evolution of multicellular life towards the end of the era.[12][13]

Subduction processes

The Proterozoic Eon was a very tectonically active period in the Earth's history.

The late Archean Eon to Early Proterozoic Eon corresponds to a period of increasing crustal recycling, suggesting subduction. Evidence for this increased subduction activity comes from the abundance of old granites originating mostly after 2.6 Ga.[14]

The occurrence of eclogite (a type of metamorphic rock created by high pressure, > 1 GPa), is explained using a model that incorporates subduction. The lack of eclogites that date to the Archean Eon suggests that conditions at that time did not favor the formation of high grade metamorphism and therefore did not achieve the same levels of subduction as was occurring in the Proterozoic Eon.[15]

As a result of remelting of basaltic oceanic crust due to subduction, the cores of the first continents grew large enough to withstand the crustal recycling processes.

The long-term tectonic stability of those cratons is why we find continental crust ranging up to a few billion years in age.[16] It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the Phanerozoic.[14] Studies by Condie (2000)[17] and Rino et al. (2004)[18] suggest that crust production happened episodically. By isotopically calculating the ages of Proterozoic granitoids it was determined that there were several episodes of rapid increase in continental crust production. The reason for these pulses is unknown, but they seemed to have decreased in magnitude after every period.[14]

Tectonic history (supercontinents)

Evidence of collision and rifting between continents raises the question as to what exactly were the movements of the Archean cratons composing Proterozoic continents.

Wilson cycle).[14]

In the late Proterozoic (most recent), the dominant supercontinent was Rodinia (~1000–750 Ma). It consisted of a series of continents attached to a central craton that forms the core of the North American Continent called Laurentia. An example of an orogeny (mountain building processes) associated with the construction of Rodinia is the Grenville orogeny located in Eastern North America. Rodinia formed after the breakup of the supercontinent Columbia and prior to the assemblage of the supercontinent Gondwana (~500 Ma).[19] The defining orogenic event associated with the formation of Gondwana was the collision of Africa, South America, Antarctica and Australia forming the Pan-African orogeny.[20]

Columbia was dominant in the early-mid Proterozoic and not much is known about continental assemblages before then. There are a few plausible models that explain tectonics of the early Earth prior to the formation of Columbia, but the current most plausible hypothesis is that prior to Columbia, there were only a few independent cratons scattered around the Earth (not necessarily a supercontinent, like Rodinia or Columbia).[14]


The Proterozoic can be roughly divided into seven biostratigraphic zones which correspond to informal time periods. The first was the Labradorian, lasting from 2.0 to 1.65 Ga. It was followed by the Anabarian, which lasted from 1.65 to 1.2 Ga and was itself followed by the Turukhanian from 1.2 to 1.03 Ga. The Turukhanian was succeeded by the Uchuromayan, lasting from 1.03 to 0.85 Ga, which was in turn succeeded by the Yuzhnouralian, lasting from 0.85 to 0.63 Ga. The final two zones were the Amadeusian, spanning the first half of the Ediacaran from 0.63 to 0.55 Ga, and the Belomorian, spanning from 0.55 to 0.542 Ga.[21]

The emergence of advanced single-celled

mitochondria (found in nearly all eukaryotes) and chloroplasts (found in plants and some protists only) and their hosts evolved.[9]
: 321–2 

By the late Palaeoproterozoic, eukaryotic organisms had become moderately biodiverse.

stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1200 million years ago.[9]
: 321–3 

The earliest

benthic organisms had filamentous structures capable of anastomosis.[24]

Classically, the boundary between the Proterozoic and the

Period when the first fossils of animals, including trilobites and archeocyathids, as well as the animal-like Caveasphaera, appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, particularly in ones from the Ediacaran, proving that multicellular life had already become widespread tens of millions of years before the Cambrian Explosion in what is known as the Avalon Explosion.[25] Nonetheless, the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian
, which is currently placed at 538.8 Ma.

See also


  1. ^ Smithsonian National Museum flickr.
  2. .
  3. on July 24, 2012. Retrieved 2016-01-20.
  4. ^ "Proterozoic". Dictionary.
  5. ^ "Proterozoic". Unabridged (Online). n.d.
  6. ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Retrieved 22 April 2022.
  7. ^ Speer, Brian. "The Proterozoic Eon". University of California Museum of Paleontology.
  8. ^ "Proterozoic, adj. and n." OED Online. Oxford University Press. June 2021. Archived from the original on 25 June 2021. Retrieved 25 June 2021.
  9. ^ .
  10. . Retrieved 10 November 2022.
  11. . Retrieved 10 November 2022.
  12. . Retrieved 10 November 2022.
  13. . Retrieved 10 November 2022.
  14. ^ a b c d e Kearey, P.; Klepeis, K.; Vine, F. (2008). Precambrian Tectonics and the Supercontinent Cycle. Global Tectonics (Third ed.). pp. 361–377.
  15. .
  16. ^ Mengel, F. (1998). Proterozoic History. Earth System: History and Variablility. Vol. 2.
  17. .
  18. .
  19. ^ Huntly, C. (2002). The Mozambique Belt, Eastern Africa: Tectonic evolution of the Mozambique Ocean and Gondwana amalgamation. The Geological Society of America.
  20. . Retrieved 19 May 2024 – via Elsevier Science Direct.
  21. .
  22. . Retrieved 29 December 2022.
  23. .
  24. . Retrieved 10 November 2022.

External links