埃迪卡拉纪 635–541百万年前 | |
全时期平均大气O2含量 | 约8 Vol %[1] (为现代的40% ) |
全时期平均大气CO2含量 | 约4500 ppm[2] (为前工业时期16倍)
|
埃迪卡拉纪(英语:Ediacaran),又称艾迪卡拉纪[3]、震旦纪、文德纪,是元古宙最后的一段时期,其后紧接着便是显生宙的开端──古生代的寒武纪。埃迪卡拉纪一般指6.35-5.41亿年前。学者曾用这个名字指称不同阶段,直到2004年5月13日,国际地质科学联合会(英语:International Union of Geological Sciences,IUGS)明确定义其年代,这是这个组织120年来首次对其加时期定义。最古老的动物遗迹可追溯至十亿年前,但最早的动物化石出现于埃迪卡拉纪。
名字来源
埃迪卡拉生物群因为发现于南澳大利亚的埃迪卡拉山而得名。1946年,一位澳洲地质学家(Reg Sprigg)在古代的沙岩板中留意到一曾在这里发现显生宙以前的化石。研究这些化石的科学家(Martin Glaessner)认为这是珊瑚、水母和蠕虫的先驱。以后几十年,南澳大利亚还找到很多的隐生宙化石,其他各大洲也找到一些。这些化石都叫作埃迪卡拉动物。一开始,人们认为埃迪卡拉动物是寒武纪的动物,但经过仔细的观察,埃迪卡拉生物群比寒武纪还久远,应属于埃迪卡拉纪。
本纪曾被一些人称为震旦纪(Sinian)[4]。震旦纪的名称来源于中国,“震旦”是中国的古称。由于古印度人称中国为Cinisthana,在佛经中被译为震旦,故名震旦纪。时至今日,中国学者仍经常这么称呼,中国教科书上一直称此纪为震旦纪。俄国人又把埃迪卡拉纪称为文德纪(Vendian),他们在这一时期的地层中又发现了一些古线虫动物的化石。
埃迪卡拉生物群
埃迪卡拉生物群(英语:Ediacaran biota)是1946年发现于澳大利亚南部埃迪卡拉(英语:Ediacara)山地的末远古系庞德石英岩中的化石群,这类化石群已在世界30多个地点被发现。
埃迪卡拉动物和今天的大多数动物截然不同,它们既没头、尾、四肢,又没嘴巴和消化器官,因此它们大概只能从水中摄取养份。大多的埃迪卡拉动物固着在海底,和植物十分相近,其他的则平躺在浅海处,等待营养顺水流而送上门来。埃迪卡拉动物化石出土越多,反而越没有规律。有一些化石比较像后来动物的先驱。
在埃迪卡拉纪末期,埃迪卡拉动物分成两支,它们有的成功演化成更有活力,更具进攻性的动物,并在之后的寒武纪生命大爆发中大放异彩,成为现今大多数动物门的祖先。而有的则走向灭亡,它们的特征也永远消失于历史舞台上。
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金伯拉虫的历史复原变迁
末期灭绝事件
此为一次可能发生在约5.42亿年前埃迪卡拉纪末期的灭绝事件。该次事件包括疑源类生物的集体灭绝、埃迪卡拉生物群突然消失以及寒武纪大爆发之前的一段地球生命空白期。
有部分生物存活过了这次灭绝事件,因此地球上的生命才得以存续至今。然而,只有极少部分的生物种类在埃迪卡拉纪-寒武纪交界带两侧被同时发现。其中一种是凝集的有孔虫门生物 Platysolenites[5]。 其他明显的幸存者,例如奇翼虫,被重新解释为与埃迪卡拉生物群无关。
古地理
埃迪卡拉纪距今十分久远,对当时的地貌几乎一无所知,不过因为缺乏植物覆盖,表面很有可能是荒凉的沙土地或岩石地。当时的大陆则是由一块主要大陆的和几块较小的组成的潘诺西亚大陆。当时的生物都生存在海洋。
参考资料
脚注
- ↑ http://uahost.uantwerpen.be/funmorph/raoul/fylsyst/Berner2006.pdf
- ↑ Image:Phanerozoic Carbon Dioxide.png
- ↑ Bottjer, David J.; 翻译/姚若洁. 小春蟲背後的演化秘密. 科学人杂志. 2005年9月, 第43期 [2014-11-24].
- ↑ 见大英百科全书条目
- ↑ Kontorovich, A; Varlamov, A; Grazhdankin, D; Karlova, G; Klets, A; Kontorovich, V; Saraev, S; Terleev, A; Belyaev, S; et al. A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3). Russian Geology and Geophysics. 2008, 49 (12): 932. Bibcode:2008RuGG...49..932K. doi:10.1016/j.rgg.2008.06.012.
书目
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- Knoll, A. H.; Walter, MR; Narbonne, G. M; Christie-Blick, N (2004). "A new period for the geologic time scale". Science 305 (5684): 621–622.
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- Sokolov, B.S. (1997). "Essays on the Advent of the Vendian System." 153 pp. KMK Scientific Press, Moscow. (in Russian)
- Sokolov B. S. (1965) "Abstracts of All-Union Symposium on Paleontology of the Precambrian and Early Cambrian." Nauka, Novosibirsk.
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- M. A. Fedonkin, B. S. Sokolov, M. A. Semikhatov, N. M. Chumakov (2007). "Vendian versus Ediacaran: priorities, contents, prospectives". In: "The Rise and Fall of the Vendian (Ediacaran) Biota ". Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493n Moscow: GEOS. August 20–31, 2007.
- 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.
- 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
- Bristow, T. F. and Kennedy, M. J. (2008). "Carbon isotope excursions and the oxidant budget of the Ediacaran atmosphere and ocean". Geology 36 (11): 863–866. Retrieved 2007-05-05.
- 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.
- Le Guerroué, E.; Allen, P. A., Cozzi, A., Etienne, J. L. and Fanning, C. M. (2006). "50 Myr recovery from the largest negative δ13C excursion in the Ediacaran ocean ". Terra Nova 18 (2): 147–153.
- 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.
- 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.
- 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.
- Condon, D., Zhu, M., Bowring, S., Wang, W., Yang, A., and Jin, Y. (1 April 2005). "U-Pb Ages from the Neoproterozoic Doushantuo Formation, China " (abstract). Science 308 (5718): 95–98.
- 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.
- Ogg, J. G. (2004). "Status of Divisions of the International Geologic Time Scale". Lethaia 37 (2): 183–199.
- 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: pp 431–434.
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