Ediacaran

Geological period
o2=8
co2=4500

The Ediacaran Period (IPAEng|ˌiːdiˈækərən, named after the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just preceding the Cambrian Period of the Paleozoic Era. Its status as an official geological period was ratified in March 2004 by the International Union of Geological Sciences (IUGS) and announced on May 13 2004, the first new geological period declared in 120 years.cite journal
author = Knoll, A.H.
coauthors = Walter, M.R., Narbonne, G.M., Christie-blick, N.
year = 2004
title = A new period for the geologic time scale
journal = Science
volume = 305
issue = 5684
pages = 621–622
issn =
doi =
url = http://www.stratigraphy.org/ediacaran/Knoll_et_al_2004b.pdf
accessdate = ] cite journal
author = Ogg, J.G.
year = 2004
title = Status of Divisions of the International Geologic Time Scale
journal = Lethaia
volume = 37
issue = 2
pages = 183–199
issn =
doi =
url = http://taylorandfrancis.metapress.com/index/PUNM6BQLNW1BJMFN.pdf
accessdate = 2007-05-05 ] The type section is in the Flinders Ranges in South Australia. It overlaps, but is shorter than the Vendian period, a name that was earlier proposed in Russia.

Base of the Ediacaran

Although the Ediacaran Period does contain soft bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer, referred to as a "cap carbonate", because it caps glacial deposits and indicates a sudden climatic change at the end of an ice age. This bed is characterized by an unusual depletion of ¹³C, and is considered by many scientists to be of global extent, although this is controversial.

Dating

No dating has been possible at the type section of the Ediacaran Period in South Australia. Therefore the age range of 635 to 542 million years before the present is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years ago is based on U-Pb (uranium-lead) isochron dating from Namibia.cite journal
author = Hoffmann, K.H.
coauthors = Condon, D.J., Bowring, S.A., Crowley, J.L.
year = 2004
date = 2004-09-01
title = U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation
journal = Geology
volume = 32
issue = 9
pages = 817–820
issn =
doi = 10.1130/G20519.1
url = http://geology.geoscienceworld.org/cgi/content/abstract/32/9/817
accessdate = ] and China. cite journal
title=U-Pb Ages from the Neoproterozoic Doushantuo Formation, China
journal=Science
date=1 April 2005
issue=5718
pages=95–98
doi=10.1126/science.1107765
url=http://www.sciencemag.org/cgi/content/abstract/308/5718/95
author=Condon, D., Zhu, M., Bowring, S., Wang, W., Yang, A., and Jin, Y.
year=2005
volume=308
format=abstract
pmid=15731406] Applying this age to the base of the Ediacaran assumes that individual cap carbonates are synchronous around the world and that the correct cap carbonate layers have been correlated between Australian and Namibia. This is controversial because an age of about 580 million years has been obtained in association with glacial rocks in Tasmania which some scientists tentatively correlate with those just beneath the Ediacaran rocks of the Flinders Ranges.cite journal
author = Calver, C.R.
coauthors = Black, L.P., Everard, J.L., Seymour, D.B.
year = 2004
date = 2004-10-01
title = U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania
journal = Geology
volume = 32
issue = 10
pages = 893–896
issn =
doi = 10.1130/G20713.1
url = http://geology.geoscienceworld.org/cgi/content/abstract/32/10/893
accessdate = ] The age of the top is the same as the widely recognised age for the base of the Cambrian Period 542± 0.3 Ma (million years ago).cite journal
last = Amthor | first = J. E.
coauthors = and others
year = 2003
title= Extinction of "Cloudina" and "Namacalathus" at the Precambrian-Cambrian boundary in Oman
journal = Geology
volume = 31 | pages = pp 431–434
id = doi|10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2
doi= 10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2 ]

Biota

The animal fossil record from this period is sparse, possibly because animals had yet to evolve hard shells, which make for easier fossilization. The Ediacaran biota include the oldest definite multicellular organisms with tissues, and the most common types resemble segmented worms, fronds, disks, or immobile bags. They bear little resemblance to modern lifeforms, and their relationship even with the later lifeforms of the Cambrian explosion is difficult to interpret. More than 100 genera have been described, and well known forms include "Arkarua", "Charnia", "Dickinsonia", "Ediacaria", "Marywadea", "Onega", "Pteridinium", and "Yorgia".

Fossils

In October, 2008, in a poster session at the Geological Society of America, scientists presented the discovery of the earliest footprints ever found. The footprints were found near Goldfield, Nevada in 2000 and date back to the Ediacaran period. At approximately 570 million years old, this new fossil, most likely an arthropod, not only provides the earliest suggestion of animals walking on legs, but it also shows that complex animals were alive on earth before the Cambrian period. [ [http://newswise.com/articles/view/544975/ Earliests Animal Footprints Ever Found -- Discovered in Nevada] Newswise, Retrieved on October 5, 2008.]

ee also

* List of fossil sites "(with link directory)"

References

External links

* cite news
url = http://news.bbc.co.uk/1/hi/sci/tech/3721481.stm
title = 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
publisher = BBC
date = 2004-05-17
* cite web
title = Ediacaran Period
work = GeoWhen Database
url = http://www.stratigraphy.org/geowhen/stages/Ediacaran.html
accessmonthday = January 5
accessyear = 2006
* [http://www.ucmp.berkeley.edu/vendian/vendian.html Introduction to the Vendian Period]
* [http://members.tripod.com/~Cambrian/IntrotoEdiacaran Introduction to the Ediacaran Fauna]
* [http://www.abc.net.au/catalyst/stories/s1785092.htm#transcript transcript] – "Catalyst" (Australian Broadcasting Corporation)
* [http://members.rediff.com/mistakenpoint/ Mistaken Point Fauna: The Discovery]