Ediacaran

Ediacaran
~635 – 538.8 ± 0.2 Ma Pha. Proterozoic Archean Had.
A map of the world as it appeared during the mid-Ediacaran. (600 ma)
Chronology
−640 — – −630 — – −620 — – −610 — – −600 — – −590 — – −580 — – −570 — – −560 — – −550 — – −540 — – N e o p r o t e r o z o i c P Z Cryogenian Ediacaran Cambrian       Ediacaran Biota     ← Treptichnus pedum ← ~Baykonurian glaciation ← Gaskiers glaciation ← Marinoan glaciation ← Palaeopascichnids   Major Glacial period Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.
Etymology
Name formality	Formal
Name ratified	1990
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	Worldwide distinct cap carbonates. Beginning of a distinctive pattern of secular changes in carbon isotopes.
Lower boundary GSSP	Enorama 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 ratified	March 2004[1]
Upper boundary definition	Appearance of the Ichnofossil Treptichnus pedum
Upper boundary GSSP	Fortune Head section, Newfoundland, Canada 47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Upper GSSP ratified	1992[2]
Atmospheric and climatic data
Mean atmospheric O2 content	c. 8 vol % (40 % of modern)
Mean atmospheric CO2 content	c. 4500 ppm (16 times pre-industrial)
Mean surface temperature	c. 17 °C (3 °C above modern)

The Ediacaran Period ( /ˌiːdiˈækərən, ˌɛdi-/ EE-dee-AK-ər-ən, ED-ee-)^[3] is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya.^[4] It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

The Ediacaran Period's 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.^[5][6][7] Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946,^[8] the type section is located in the bed of the Enorama Creek^[9] within Brachina Gorge^[10] in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E / 31.331611°S 138.633361°E / -31.331611; 138.633361.

The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, which is represented by now-extinct relatively simple animal phyla such as Proarticulata (bilaterians with articulation including Dickinsonia and Spriggina), Petalonamae (sea pen-like animals including Charnia), Disc-shaped forms (radial-shaped animals including Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry including Tribrachidium). Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago. Some modern groups of animals also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha. Mollusc-like Kimberella also lived during the Ediacaran. Fossilized organisms with shells or skeletons were yet to evolve in the Cambrian, the superseding period of the Phanerozoic eon.

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.