A map of the world as it appeared during the mid-Ediacaran, c. 600 Ma
Name formalityFormal
Name ratified1990
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Chronological unitPeriod
Stratigraphic unitSystem
Time span formalityFormal
Lower boundary definition
  • Worldwide distinct cap carbonates.
  • Beginning of a distinctive pattern of secular changes in carbon isotopes.
Lower boundary GSSPEnorama Creek section, Flinders Ranges, South Australia
31°19′53″S 138°38′00″E / 31.3314°S 138.6334°E / -31.3314; 138.6334
Lower GSSP ratifiedMarch 2004[1]
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[2]
Atmospheric and climatic data
Mean atmospheric O2 contentc. 8 vol %
(40 % of modern)
Mean atmospheric CO2 contentc. 4500 ppm
(16 times pre-industrial)
Mean surface temperaturec. 17 °C
(3 °C above modern)

The Ediacaran period ( /ˌdiˈækərən, ˌɛdi-/ EE-dee-AK-ər-ən, ED-ee-)[3] is a geological period of the Neoproterozoic era that spans 96 million years from the end of the Cryogenian period at 635 Mya, to the beginning of the Cambrian period at 538.8 Mya.[4] It is the last period of the Proterozoic eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian period marks the start of the Phanerozoic eon where recognizable fossil evidence of life becomes common.

The Ediacaran period is named after the Ediacara Hills of South Australia, where trace fossils of a diverse community of previously unrecognized lifeforms (later named the Ediacaran biota) were first discovered by geologist Reg Sprigg in 1946.[5] Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.[6][7][8] Although the period took namesake from the Ediacara Hills in the Nilpena Ediacara National Park, the type section is actually located in the bed of the Enorama Creek[9] within the Brachina Gorge[10] in the Ikara-Flinders Ranges National Park, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E / -31.331611; 138.633361, approximately 55 km (34 mi) southeast of the Ediacara Hills fossil site.

The Ediacaran marks the first widespread appearance of complex multicellular fauna following the end of the Cryogenian global glaciation known as the Snowball Earth. The relatively sudden evolutionary radiation event, known as the Avalon Explosion, is represented by now-extinct, relatively simple soft-bodied animal phyla such as Proarticulata (bilaterians with simple articulation, e.g. Dickinsonia and Spriggina), Petalonamae (sea pen-like animals, e.g. Charnia), Aspidella (radial-shaped animals, e.g. Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry, e.g. Tribrachidium). Most of these organisms appeared during or after the Avalon explosion 575 million years ago and died out during the End-Ediacaran extinction event 539 million years ago. Forerunners of some modern animal phyla also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha, as well as mollusc-like Kimberella. Hard-bodied organisms with mineralized shells or endoskeletons, which can be fossilized and preserved, were yet to evolve and would not appear until the superseding Cambrian Explosion some 35 million years later.

The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations. The Shuram excursion also occurred during this period, but its glacial origin is unlikely.

  1. ^ Knoll, Andrew H.; Walter, Malcolm R.; Narbonne, Guy M.; Christie-Black, Nicholas (3 March 2006). "The Ediacaran Period: a new addition to the geologic time scale" (PDF). Lethaia. 39: 13–30. doi:10.1080/00241160500409223. Retrieved 6 December 2020.
  2. ^ Brasier, Martin; Cowie, John; Taylor, Michael. "Decision on the Precambrian-Cambrian boundary stratotype" (PDF). Episodes. 17. Retrieved 6 December 2020.
  3. ^ "Ediacaran". Dictionary.com Unabridged (Online). n.d.
  4. ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Retrieved 20 April 2022.
  5. ^ Sprigg, Reg. C. (1947). "Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia". Transactions of the Royal Society of South Australia. 71 (2): 212–224.
  6. ^ Cite error: The named reference Knoll2004a was invoked but never defined (see the help page).
  7. ^ Knoll, A. H.; Walter, MR; Narbonne, G. M; Christie-Blick, N (30 July 2004). "A new period for the geologic time scale" (PDF). Science. 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353. S2CID 32763298.
  8. ^ Knoll, A. H.; Walter, M. R.; Narbonne, G. M. & Christie-Blick, N. (March 2006). "The Ediacaran Period: A new addition to the geologic time scale" (PDF). Lethaia. 39: 13–30. doi:10.1080/00241160500409223. Archived from the original (PDF) on 21 February 2007.
  9. ^ "Geological time gets a new period: Geologists have added a new period to their official calendar of Earth's history—the first in 120 years". London: BBC. 17 May 2004. Accessed 27 December 2010.
  10. ^ South Australian Museum Newsletter April 2005 Archived 17 February 2011 at the Wayback Machine Accessed 9 August 2010.

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