To install click the Add extension button. That's it.

The source code for the WIKI 2 extension is being checked by specialists of the Mozilla Foundation, Google, and Apple. You could also do it yourself at any point in time.

4,5
Kelly Slayton
Congratulations on this excellent venture… what a great idea!
Alexander Grigorievskiy
I use WIKI 2 every day and almost forgot how the original Wikipedia looks like.
What we do. Every page goes through several hundred of perfecting techniques; in live mode. Quite the same Wikipedia. Just better.
.
Leo
Newton
Brights
Milds

From Wikipedia, the free encyclopedia

Ediacaran Period
635–541 million years ago
Mean atmospheric O
2
content over period duration
c. 8 vol %[1][2]
(40 % of modern level)
Mean atmospheric CO
2
content over period duration
c. 4500 ppm[3]
(16 times pre-industrial level)
Mean surface temperature over period duration c. 17 °C[4]
(3 °C above modern level)
Events of the Ediacaran Period
view • discuss • edit
-660 —
-640 —
-620 —
-600 —
-580 —
-560 —
-540 —
-520 —
-500 —
 
* * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * *
* * * * * * * * * * * * * * * * * * *
Treptichnus pedum
Large negative peak δ 13Ccarb excursion
Baykonur glaciation
Gaskiers glaciation
Archaeonassa-type trace fossils
Nantuo (Marinoan) glaciation
Stratigraphic scale of the ICS subdivisions and Precambrian/Cambrian boundary.

The Ediacaran Period ( /diˈækərən/), spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. 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 Ediacara biota in 1946, the type section is located in the bed of the Enorama Creek[8] within Brachina Gorge[9] 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.

YouTube Encyclopedic

  • 1/5
    Views:
    4 181
    8 205
    3 592
    2 873
    360
  • The Ediacara biota and first mass extinction of metazoan life
  • Animal Dawn - Research Tuesday - Presentation
  • Ediacaran Sea
  • Catching the second Ediacara wave - PDU2 Adelaide 2016
  • Charnia

Transcription

Good morning, my name is Simon Darroch and I am a postdoctoral fellow in Paleobiology and have been since September. So many of you will be familiar with the Cambrian explosion of animals. This dramatic period, 542 million years ago, when most of the major branches of animal life that we currently recognize dramatically appear in the rock record. In this rendition we have a few early members of the arthropods, the sponges, and the jellyfish, happily swimming around in a Cambrian ocean. What is less well appreciated though is that these were not the first complex life forms on this planet. Now, before the… before the Cambrian period, we have what’s called the Ediacaran period. And in Ediacaran aged rocks we find this bizarre enigmatic collection of, basically weirdies, aliens from outer space and we have no idea where these things fit in the tree of life. So what were the Ediacarans? Well, at various points in the history they’ve been allied with the Cnidarians, so they were all jellyfish. At some stage we thought they were lichens, I mean why not. Some of us still think they’re all fungi and they’ve also been called a failed experiment in history of complex life, the Vendobionts. But all we really know for sure is that they existed between 650 and 542 million years ago. They're entirely soft bodied, they have no skeletonized or mineralized hard parts, they’re probably not closely related to modern animals and they all went extinct at the Cambrian boundary. So, rather than answer this question what were the Ediacarans, which will take me 6 hours, and I'll never give you a straight answer anyway, I’m still going to address this question, of where do they go and what happened to them? So to do that, we have to look a bit, a little bit at Ediacarans in time and space. So in this simple figure on the left hand y axis here, is time, with the Cambrian, the base of the Cambrian at the very top and the base of the Ediacaran on the bottom. And arranged along the top, and color coded, the various different kinds of Ediacaran groups that we recognize and all I really want you to notice is in this middle Ediacaran period here, what we call a white sea assemblage, we have most of these groups represented in the fossil record, this is the time of very high diversity. Once again the latest Ediacaran, we lose a lot of these groups. So the disappearance of the Ediacara biota seems to be quite gradual and if you were to kind of put the beginning of this supposed extinction horizon in here somewhere, you’d probably place it somewhere here, between these two assemblages. So to get a closer look at this, I've been working in Southern Namibia where these latest Ediacaran rocks are exposed at the surface. And here are some Ediacaran fossils, from the … Ediacaran, they don’t look like much so I’ve arrowed them so you know what you’re looking at, like floppy disks. What’s unique about these Ediacaran fossils, is in the same slabs we have this weird collection of pits and bubbles and trails and once you polish these up and section them out, all these represent, are most like the traces left by something like, a sea anemone. These are trace fossils called, Conichnus. Now this is the first example in the rock record of where we have Ediacaran fossils. So, basically aliens from outer space and represents … the modern, an animal group we’d recognize in the same place. And it's also important cause sea anemones, as filter feeders, or what we call ecosystem engineers, and these are the earliest ecosystem engineers. So ecosystem engineers are organisms that create, modify or significantly change their habitat. I’ve got three examples up here. Up on the far left, these are oysters, and just like sea anemones, oysters are filter feeders and they, they kind of clean and scrub out the water column. Beavers obviously create vast new habitats and redirecting rivers. On the far right, this is a polychaete worm, quite apart from being a voracious predator, polychaetes burrow until they mix and churn the sediment. And what’s important to realize is that modern animals, Cambrian type animals do all of these things, the Ediacara biota by in large, don’t. So we’re sneaking up on this hypothesis that, perhaps evolving animals, evolving Cambrian-style ecosystem engineers, gradually marginalize the Ediacara biota and drove their extinction. And what's cool about this hypothesis is it comes to the very definite prediction. And that is that this latest Ediacaran communities should show evidence for low diversity and some sort of ‘stressed’ ecology. And that’s what I’ve been doing in southern Namibia. I’ve been to this place called Farm Swartpunt, collecting a bunch of new fossils and at this stage we got 107 individuals, at least two new species. We’ve got some familiar characters here, those are rather beautiful frondos organisms called Pteridinium and Swartpuntia, and we more or less expected to find these things here. We also found a bunch of new things and a bunch of things we didn't expect to see. There were Bradgatia, Ernietta and some holdfast type things called Aspidella. But what's fascinating is that even with all the extra diversity and all the extra species we found, these latest Ediacaran communities are still appear stressed and they still have very low diversity. And this would appear to corroborate this idea that they’re being engineered away by early members of the Cambria evolutionary fauna. So when we talk about the end of the Ediacara biota, there’s a certainly a mass extinction but it appears more gradual than mass extinctions we typically think about, but their disappearance is total and none of them make it through to the Cambrian. But also as well as, rather than being a mass extinction that is caused by, say a bolide impact, or a period of mass volcanism, as much as you might kind of think the end of the dinosaurs, instead this is a mass extinction is precipitated by evolutionary innovation and appearance of animal groups. So mass extinctions can also be caused by biology and not just by abiotic factors. I think this is a powerful lesson for us as human beings because we are after all powerful ecosystem engineers and here is a lesson from the fossil record but what might happen, but what might come to pass, if we continue to modify our environments. Thank you. [applause] We have a question, you finished on time. That wasn’t 8 minutes? Ah, okay. No, it was 6. Any questions? Yes? So I’m just curious ... I mean being an extant biologist, some things are just rare. I mean they’re not being driven into anything or forced that you can tell, that there’s no particular stress, they’re just rare because they have a small window of where they actually can survive. So how do you tell that from what you’re seeing? Um, well. Repeat the question. The question is, some things in life are rare, so how can you tell that these aren’t just hiding somewhere where you can’t find them. That’s a very good question. And it’s taking many years of careful laboratory experiments to work out how these things are preserved, and as far as we can tell where ever you go in the world, if these things were there, then they should be being preserved. The conditions required for the fossilization of Ediacara biota don’t go away at the Cambrian boundary. And as much as we look in the same places, the right preservation window, we’re not seeing that. So it does seem like they are gone forever.

Contents

Ediacaran and Vendian

The Ediacaran Period overlaps, but is shorter than the Vendian Period, a name that was earlier, in 1952, proposed by Russian geologist and paleontologist Boris Sokolov. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian.[10][11]

Paleontological substantiation of this boundary was worked out separately for the siliciclastic basin (base of the Baltic Stage of the Eastern European Platform[12]) and for the carbonate basin (base of the Tommotian Stage of the Siberian Platform).[13] The lower boundary of the Vendian was suggested to be defined at the base of the Varanger (Laplandian) tillites.[11][14]

The Vendian in its type area consists of large subdivisions such as Laplandian, Redkino, Kotlin and Rovno Regional stages with the globally traceable subdivisions and their boundaries, including its lower one.

The Redkino, Kotlin and Rovno regional stages have been substantiated in the type area of the Vendian on the basis of the abundant organic-walled microfossils, megascopic algae, metazoan body fossils and ichnofossils.[11][15]

The lower boundary of the Vendian could have a biostratigraphic substantiation as well taking into consideration the worldwide occurrence of the Pertatataka assemblage of giant acanthomorph acritarchs.[14]

Upper and lower boundaries

The 'golden spike' (bronze disk in the lower section of the image) or 'type section' of the Global Boundary Stratotype Section and Point (GSSP) for the base of the Ediacaran System
The 'golden spike' (bronze disk in the lower section of the image) or 'type section' of the Global Boundary Stratotype Section and Point (GSSP) for the base of the Ediacaran System
The 'golden spike' marking the GSSP
The 'golden spike' marking the GSSP

The Ediacaran Period (c. 635–542 Mya) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum (Seilacher, 1955)).[5]

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 that is referred to as a "cap carbonate," because it caps glacial deposits.

This bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower boundary GSSP of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.

The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossil Treptichnus pedum (Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.

Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and ichnofossils are disputable.[14][16]

Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation)[vague] and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere[clarification needed] in the world.

The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ l3Ccarb in the upper layer of the ocean.[14][17]

Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram[18] Formation that is clearly away from any glacial evidence[19] strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events.[20] Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.[21]

As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.[14][22]

Subdivisions

The Ediacaran period is not yet formally subdivided, but a proposed scheme[23] recognises an Upper Ediacaran whose base corresponds with the Gaskiers glaciation, a Terminal Ediacaran Stage starting around 550 million years ago, a preceding stage beginning around 557 Ma with the earliest widespread Ediacaran biota fossils; two proposed schemes differ on whether the lower strata should be divided into an Early and Middle Ediacaran or not, because it's not clear whether the Shuram excursion (which would divide the Early and Middle) is a separate event from the Gaskiers, or whether the two events are correlated.

Absolute dating

The dating of the rock type section of the Ediacaran Period in South Australia has proven uncertain. Therefore, the age range of 635 to 542 million years is based on correlations to other countries where dating has been possible. The base age of approximately 635 million years is based on U–Pb (uraniumlead) isochron dating from Namibia[24] and China.[25]

Applying this age to the base of the Ediacaran assumes that cap carbonates are laid down synchronously around the world and that the correct cap carbonate layers have been selected in such diverse locales as Australian and Namibia. This is controversial because an age of about 580 million years has been obtained for glacial rocks in Tasmania which some scientists tentatively assign to those just beneath the Ediacaran rocks of the Flinders Ranges.[26] The age of the top is the same as the widely recognised age for the base of the Cambrian Period[27] 542± 0.3 Mya,[28] producing a misalignment, as the end of the Edicarian Period should mark the start of the Cambrian Period.

Biota

The fossil record from the Ediacaran Period is sparse, as more easily fossilized hard-shelled animals had yet to evolve. The Ediacaran biota include the oldest definite multicellular organisms (with specialized tissues), the most common types of which resemble segmented worms, fronds, disks, or immobile bags.

Ediacara biota bear little resemblance to modern lifeforms, and their relationship even with the immediately following lifeforms of the Cambrian explosion is rather difficult to interpret. More than 100 genera have been described, and well known forms include Arkarua, Charnia, Dickinsonia, Ediacaria, Marywadea, Onega, Pteridinium, and Yorgia.

There is evidence that Earth's first mass extinction happened during this period when early animals changed the environment.[29]

Astronomical factors

The relative proximity of the Moon at this time meant that tides were stronger and more rapid than they are now. The day was 21.9±0.4 hours, and there were 13.1±0.1 synodic months/year and 400±7 solar days/year.[30]

Documentaries

A few English language documentaries have featured the Ediacaran period and biota:

See also

References

  1. ^ Image:Sauerstoffgehalt-1000mj.svg
  2. ^ File:OxygenLevel-1000ma.svg
  3. ^ Image:Phanerozoic Carbon Dioxide.png
  4. ^ Image:All palaeotemps.png
  5. ^ a b A. Knoll, M. Walter, G. Narbonne, and N. Christie-Blick (2004) "The Ediacaran Period: A New Addition to the Geologic Time Scale." Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.
  6. ^ Knoll, A. H.; Walter, MR; Narbonne, G. M; Christie-Blick, N (2004). "A new period for the geologic time scale" (PDF). Science. 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353.
  7. ^ Knoll, A. H.; Walter, M. R.; Narbonne, G. M. & Christie-Blick, N. (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 2007-02-21.
  8. ^ "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. 2004-05-17. Accessed 27 December 2010.
  9. ^ South Australian Museum Newsletter April 2005 Accessed 9 August 2010.
  10. ^ B. M. Sokolov (1952). "On the age of the old sedimentary cover of the Russian Platform". Izvestiya Akademii Nauk SSSR, Seriya eologicheskaya. 5: 21–31.
  11. ^ a b c Sokolov, B.S. (1997). "Essays on the Advent of the Vendian System." 153 pp. KMK Scientific Press, Moscow. (in Russian)
  12. ^ Sokolov B. S. (1965) "Abstracts of All-Union Symposium on Paleontology of the Precambrian and Early Cambrian." Nauka, Novosibirsk.
  13. ^ Rozanov, A.Y.; Missarzhevskij, V.V.; Volkova, N.A.; Voronova, L.G.; Krylov, I.N.; Keller, B.M.; Korolyuk, I.K.; Lendzion, K.; Michniak, R.; Pykhova, N.G. & Sidorov, A.D. (1969). "The Tommotian Stage and the problem of the lower boundary of the Cambrian". Trudy Geologičeskogo Instituta AN SSSR. 206: 1–380.
  14. ^ a b c d e M. A. Fedonkin; B. S. Sokolov; M. A. Semikhatov; N. M. Chumakov (2007). "Vendian versus Ediacaran: priorities, contents, prospectives". Archived from the original on October 4, 2011. In: "The Rise and Fall of the Vendian (Ediacaran) Biota" (PDF). Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493n Moscow: GEOS. August 20–31, 2007. (82mb)
  15. ^ Khomentovsky, V. V. (2008). "The Yudomian of Siberia, Vendian and Ediacaran systems of the International stratigraphic scale". Stratigraphy and Geological Correlation. 16 (6): 581–598. Bibcode:2008SGC....16..581K. doi:10.1134/S0869593808060014.
  16. ^ Comments By B. S. Sokolov, M. A. Semikhatov, And M. A. Fedonkin. (2004) Appendix 2 in: "The Ediacaran Period: A New Addition to the Geologic Time Scale." Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy. pp. 32–34
  17. ^ Bristow, T. F.; Kennedy, M. J. (2008). "Carbon isotope excursions and the oxidant budget of the Ediacaran atmosphere and ocean" (PDF). Geology. 36 (11): 863–866. Bibcode:2008Geo....36..863B. doi:10.1130/G24968A.1. Retrieved 2007-05-05.
  18. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A. (2006). "Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram Formation (Nafun Group, Oman)". Precambrian Research. 146 (1–2): 68–92. Bibcode:2006PreR..146...68L. doi:10.1016/j.precamres.2006.01.007.
  19. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A.; Etienne, J. L.; Fanning, C. M. (2006). "50 Myr recovery from the largest negative δ13C excursion in the Ediacaran ocean". Terra Nova. 18 (2): 147–153. Bibcode:2006TeNov..18..147L. doi:10.1111/j.1365-3121.2006.00674.x.
  20. ^ Le Guerroué, E.; Allen, P. A.; Cozzi, A. (2006). "Parasequence development in the Ediacaran Shuram Formation (Nafun Group, Oman): primary origin stratigraphic test of negative carbon isotopic ratios". Basin Research. 18 (2): 205–220. Bibcode:2006BasR...18..205L. doi:10.1111/j.1365-2117.2006.00292.x.
  21. ^ Gong, Zheng; Kodama, Kenneth; Li, Yong-Xiang (2017). "Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion". Precambrian Research. 289: 62–74. Bibcode:2017PreR..289...62G. doi:10.1016/j.precamres.2016.12.002.
  22. ^ A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008). "Treptichnus pedum and the Vendian-Cambrian boundary". 33 Intern. Geol. Congr. August 6–14, 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. P. 183.
  23. ^ Xiao, Shuhai; Narbonne, Guy M.; Zhou, Chuanming; Laflamme, Marc; Grazhdankin, Dmitriy V.; Moczydlowska-Vidal, Malgorzata; Cui, Huan (2016). "Towards an Ediacaran  Time Scale: Problems, Protocols, and Prospects" (PDF). Episodes. 39 (4): 540555. doi:10.18814/epiiugs/2016/v39i4/103886.
  24. ^ Hoffmann, K.H.; Condon, D.J.; Bowring, S.A.; Crowley, J.L. (2004-09-01). "U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation". Geology. 32 (9): 817–820. Bibcode:2004Geo....32..817H. doi:10.1130/G20519.1.
  25. ^ Condon, D.; Zhu, M.; Bowring, S.; Wang, W.; Yang, A. & Jin, Y. (1 April 2005). "U-Pb Ages from the Neoproterozoic Doushantuo Formation, China" (abstract). Science. 308 (5718): 95–98. Bibcode:2005Sci...308...95C. doi:10.1126/science.1107765. PMID 15731406.
  26. ^ Calver, C.R.; Black, Lance P.; Everard, John L.; Seymour, David B. (2004-10-01). "U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania". Geology. 32 (10): 893–896. Bibcode:2004Geo....32..893C. doi:10.1130/G20713.1.
  27. ^ Ogg, J. G. (2004). "Status of Divisions of the International Geologic Time Scale" (PDF). Lethaia. 37 (2): 183–199. doi:10.1080/00241160410006492. Retrieved 2007-05-05.
  28. ^ Amthor, J. E.; Grotzinger, John P.; Schröder, Stefan; Bowring, Samuel A.; Ramezani, Jahandar; Martin, Mark W.; Matter, Albert (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman". Geology. 31: 431–434. Bibcode:2003Geo....31..431A. doi:10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2.
  29. ^ https://www.sciencedaily.com/releases/2015/09/150902123456.htm Science Daily
  30. ^ Williams, George E. (2000). "Geological constraints on the Precambrian history of Earth's rotation and the Moon's orbit". Reviews of Geophysics. 38 (1): 37–60. Bibcode:2000RvGeo..38...37W. doi:10.1029/1999RG900016.

External links

This page was last edited on 31 October 2018, at 07:17
Basis of this page is in Wikipedia. Text is available under the CC BY-SA 3.0 Unported License. Non-text media are available under their specified licenses. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. WIKI 2 is an independent company and has no affiliation with Wikimedia Foundation.