From left to right: Four main Proterozoic events: Great Oxidation Event and subsequent Huronian glaciation; First eukaryotes, like red algae; Snowball Earth in Cryogenian period; Ediacaran biota[1]
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitEon
Stratigraphic unitEonothem
Time span formalityFormal
Lower boundary definitionDefined Chronometrically
Lower GSSA ratified1991[2]
Upper boundary definitionAppearance of the Ichnofossil Treptichnus pedum
Upper boundary GSSPFortune Head section, 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 (IPA: /ˌprtərəˈzɪk, ˌprɒt-, -ər-, -trə-, -tr-/ PROH-tər-ə-ZOH-ik, PROT-, -⁠ər-oh-, -⁠trə-, -⁠troh-)[3][4][5] is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 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 "supereon".

The Proterozoic is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic and Neoproterozoic.[7] It covers the time from the appearance of free oxygen in Earth's atmosphere to just before the proliferation of complex life on the Earth during the Cambrian Explosion. The name Proterozoic combines two forms of ultimately Greek origin: protero- meaning "former, earlier", and -zoic, meaning "of life".[8]

Well-identified events of this eon were the transition to an oxygenated atmosphere during the Paleoproterozoic; the evolution of eukaryotes via symbiogenesis; several global glaciations, which produced the 300 million years-long Huronian glaciation (during the Siderian and Rhyacian periods of the Paleoproterozoic) and the hypothesized Snowball Earth (during the Cryogenian period in the late Neoproterozoic); and the Ediacaran period (635 to 538.8 Ma), which is characterized by the evolution of abundant soft-bodied multicellular organisms such as sponges, algae, cnidarians, bilaterians and the sessile Ediacaran biota (some of which had evolved sexual reproduction) and provides the first obvious fossil evidence of life on Earth.

  1. ^ Smithsonian National Museum flickr.
  2. ^ Plumb, K. A. (June 1, 1991). "New Precambrian time scale". Episodes. 14 (2): 139–140. doi:10.18814/epiiugs/1991/v14i2/005.
  3. ^ "Proterozoic – definition of Proterozoic in English from the Oxford dictionary". Archived from the original on July 24, 2012. Retrieved 2016-01-20.
  4. ^ "Proterozoic". Merriam-Webster 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. Retrieved 25 June 2021.

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