The Ediacaran period

 

The Ediacaran period was the first new official geologic time period designated after 1891. It was officially named as a new geologic period in May 2004. The Ediacaran covers the time from the last ice ages of the Cryogenian period 600 Ma (million years ago) to the beginning of the Cambrian period 543 Ma (million years ago).

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The geological timeline
Image sources: BBC   ICS

International ratification of the new period reflects our expanding knowledge of Earth’s deep physical and biological history. The last part of the pre-Cambrian was a special time when creatures of uncertain affinity appeared, like soft-bodied jellyfish-like animals and sea-sluggish beasts. One idea is that climate shocks at the Cryogenian—Ediacaran periods triggered the evolution of complex, multi-celled life and the appearance of the first shelled animals.

Already in 1859, Charles Darwin suspected there was something significant that preceded the Cambrian Explosion. What he did not know, however, was that few of the animals of the Ediacaran appear to have survived to the Cambrian. There were simple animals on the Ediacaran side and complex animals on the Cambrian side of the stratigraphic border.

Many of the new life forms in the Ediacaran were simple organisms, probably related to present-day sponges. They are supposed to be living flat on the seafloor and may have had photosynthetic symbionts, as corals have today. Most paleontologists agree that the Ediacaran assemblage includes early cnidariangrade animals, as well as burrows and trails, and perhaps body fossils of early bilaterians (bilateral organisms).

The Ediacaran organisms became probably extinct when the first predators came along among those new and diverse animals that evolved during the Cambrian Explosion. Then the Ediacaran period ended suddenly and the Cambrian period began.

The Ediacaran period was named after the Ediacara Hills in South Australia. The name is of Australian Aboriginal origin and refers to a place where water is present.

In accordance with international rules, the new period has been defined by an event recorded in a single section of rock outcropping termed the global stratotype section and point (GSSP). It is the reference section that defines the standard for recognition of the base of the new period worldwide. The initial GSSP of the Ediacaran period lies at the base of a texturally and chemically distinctive carbonate layer that overlaies glaciogenic rocks in an exposure along Enorama Creek in the Flinders Ranges, South Australia.

However, there was no general agreement on the decision of the name Ediacaran by the International Union of Geological Sciences (IUGS) and the International Commission on Stratigraphy (ICS).

In international geology and stratigraphy there is a long tradition to use the term Vendian, so this name is likely to be used also in the future as an alternative name.

Vendian was introduced in 1952 as name for a sedimentary rock system in the former Soviet Union by the academician Boris Sokolov at the Academy of Sciences of the USSR. Based on Chinese deposits the same period was named Upper Sinian in China.

 

 

Web Links

You say Ediacaran, I say Vendian; by Anna Salleh, ABC Science Online

Geological time gets a new period; from BBC News

Ediacaran period; from the GeoWhen database

Introduction to the Vendian period; from the University of California Museum of Paleontology

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