前寒武纪
前寒武纪（英語：Precambrian）是地質年代中，對於顯生宙之前數個宙（eon）的非正式涵蓋統稱，原本正式的名稱是隱生宙或隱生元（Cryptozoic eon），但後來拆分成冥古宙、太古宙與元古宙三個時代。開始於大約45億年前的地球形成時期，結束於約5億4200萬年前大量肉眼可見的硬殼動物誕生之時。
| 前寒武紀 |
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| 地质时代表 |
| （單位：百萬年前） |
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儘管前寒武紀佔了地球歷史中大約八分之七的時間，但人們對這段時期的了解相當少。這是因為前寒武紀少有化石紀錄，且其中多數的化石，如疊層石，只適合用來作生物地層學研究。此外，許多前寒武紀時期的岩石已經嚴重變質，使其起源變得晦澀不明。而其他的要不是已經腐蝕毀壞，就是還埋藏在顯生宙地層底下。
大約在45億年前左右，原始的地球從環繞太陽的物質之中聚集而成。不久之後可能又因為小行星（大小如火星）的撞擊，而分離出月球（參見大碰撞說）。一開始地球表面皆為岩漿覆蓋，穩固地殼則大約出現於44億年前。目前已知最古老的岩石發現於澳洲西部，放射性分析顯示一塊鋯石結晶已有大約44億400萬年歷史。
前寒武紀的生命
目前並未明瞭生物究竟起源於何時。在格陵蘭西岸海外群島曾發現一些古老石頭，內含38億年前的碳，可能是早期的有機物。此外在澳洲西部有一些保存良好的細菌，年代已超過34億6000萬年。目前已知最早的複雜多細胞生命型態，可能出現於大約6億年前；而世界各地有許多5億4200萬年前到6億年前之間的軟體無殼動物化石，稱為埃迪卡拉生物群（Ediacaran biota）。至於硬殼動物則出現於前寒武紀結束之後。
大約在5億4400萬年前，也就是前寒武紀的結尾，出現了許多不同型態的動物。這些動物群統稱為小殼化石，目前所知有限。寒武紀的極早期發生了寒武紀大爆發（生命型態的快速分化與數量增加），導致伯吉斯動物群（Burgess fauna）的出現。
前寒武紀各時期
前寒武纪中包含有成鐵紀、層侵紀、造山紀、固結紀、蓋層紀、延展紀、狹帶紀、拉伸紀、成冰紀與埃迪卡拉紀。之後的下一個時期寒武紀，則是顯生宙裡的第一代（era）第一紀（period）。地球上已知最早的鋯石結晶經測試已有44億年歷史。其他隱生宙岩石紀錄有些來自月球或隕石。
| 宙 | 代 | 纪 | 重大事件 | 年代 n亿年前 | ||
|---|---|---|---|---|---|---|
| 元古宙 | 新元古代 | 埃迪卡拉纪 | 埃迪卡拉生物群（狄更遜水母等）、埃迪卡拉紀末期滅絕事件 Good fossils of the first multi-celled animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm-like Trichophycus, etc. First sponges and trilobitomorphs. Enigmatic forms include many soft-jellied creatures shaped like bags, disks, or quilts (like Dickinsonia). Taconic Orogeny in North America. Aravalli Range orogeny in Indian Subcontinent. Beginning of Petermann Orogeny on Australian Continent. Beardmore Orogeny in Antarctica, 633–620 Ma. | 6.3~5.4 | ||
| 成冰纪 | 「成冰紀冰河時期」形成雪球地球。該時期的化石依然稀有。 Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. | 8.5~6.3 | ||||
| 拉伸纪 | Rodinia supercontinent persists. Trace fossils of simple multi-celled eukaryotes. First radiation of dinoflagellate-like acritarchs. Grenville Orogeny tapers off in North America. Pan-African orogeny in Africa. Lake Ruker / Nimrod Orogeny in Antarctica, 1000 ± 150 Ma. Edmundian Orogeny (c. 920 - 850 Ma), Gascoyne Complex, Western Australia. Adelaide Geosyncline laid down on Australian Continent, beginning of Adelaide Geosyncline (Delamerian Orogeny) in that continent. | 10~8.5 | ||||
| 中元古代 | 狭带纪 | Narrow highly metamorphic belts due to orogeny as Rodinia forms. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny (c. 1080 Ma), Musgrave Block, Central Australia. | 12~10 | |||
| 延展纪 | Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. | 14~12 | ||||
| 盖层纪 | Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1600 Ma, Mount Isa Block, Queensland | 16~14 | ||||
| 古元古代 | 固结纪 | First complex single-celled life: protists with nuclei. Columbia is the primordial supercontinent. Kimban Orogeny in Australian Continent ends. Yapungku Orogeny on Yilgarn craton, in Western Australia. Mangaroon Orogeny, 1680–1620 Ma, on the Gascoyne Complex in Western Australia. Kararan Orogeny (1650-Ma), Gawler Craton, South Australia. | 18~16 | |||
| 造山纪 | 东亚呂梁構造期(25-18億年前)。The atmosphere becomes oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny. Penokean and Trans-Hudsonian Orogenies in North America. Early Ruker Orogeny in Antarctica, 2000 - 1700 Ma. Glenburgh Orogeny, Glenburgh Terrane, Australian Continent c. 2005–1920 Ma. Kimban Orogeny, Gawler craton in Australian Continent begins. | 20.5~18 | ||||
| 层侵纪 | 地球在成铁纪和层侵纪之间进入休伦冰河时期（Huronian / Makganyene glaciation）。布什维尔德大火成岩省的杂岩（Bushveld Igneous Complex）形成. | 23~20.5 | ||||
| 成铁纪 | 大氧化事件: 帶狀鐵礦形成. 在澳大利亞洲, 格勞爾克拉通 發生斯利福德造山運動2440–2420 Ma. | 25~23 | ||||
| 太古宙 | 新太古代 | 大部分当今的大陆核心趋于稳定；可能发生地幔翻涌；第一次冰河期。南极洲Insell造山运动, 2650 ± 150 Ma。在现在的安大略和魁北克地区，Abitibi greenstone belt开始形成，并于2600Ma稳定下来。 | 28~25 | |||
| 中太古代 | 最早的疊層石（大概由蓝藻群落形成）. 最早的 宏化石. 南极洲洪堡造山运动。 第一個超大陸瓦巴拉大陸。在现在的安大略和魁北克地区，Blake River Megacaldera Complex开始形成，并持续至大约2696Ma. | 32~28 | ||||
| 古太古代 | 已知最早的产氧细菌。最早的 (确认) 微化石。现存最古老的克拉通（比如加拿大地盾和皮尔布拉克拉通）或许形成于此阶段。南极洲雷纳造山运动。 | 36~32 | ||||
| 始太古代 | 地球表面凝固，大氣壓约10到100帕。 单细胞生命（细菌与古菌）和最早的 (疑似) 微化石出现。 | 38~36 | ||||
| 冥古宙 |
早雨海世 | 原始生命的间接光合作用证据(例如干酪根)。 该代与内太阳系的后期重轰炸期末期部分重叠。 | 38.5~38 | |||
| 酒海紀 | 本代的名称来源月球地質年代，由神酒海和其他更大的月海的撞击事件所组成。 | 39.20~38.5 | ||||
| 盆地群代 | 已知最古老的岩石(4030 Ma). 在地球大撞击晚期结束之后，最初的生命形式与自我复制 的RNA分子大約在40億年前開始出現，南极洲内皮尔開始出現造山运动, 4000 ± 200 Ma. | 41.5~39.2 | ||||
| 隐生代 | 地球形成（45.67~45.70亿年）；月球形成（45.33亿年），可能来自大碰撞；已知最古老的矿物（锆石，44亿年前）。 | 45.7~41.5 | ||||
參考文獻
- James Monroe and Reed Wicander. . Belmont: Wadsworth Publishing Company. 1997.
- Pamela J.W. Gore. . . （原始内容存档于2007-01-02）.
- Simon A. Wilde, John W. Valley, William H. Peck, and Colin M. Graham. . Nature. 2001, 409: 175–178. doi:10.1038/35051550.
- Manfred Schidlowsk. . Nature. 1988, 333: 313 – 318. doi:10.1038/333313a0.
- Paleontologists often refer to faunal stages rather than geologic (geological) periods. The stage nomenclature is quite complex. For an excellent time-ordered list of faunal stages, see . . （原始内容存档于2006-02-11）.
- Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in 放射性定年法 and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the 國際地層委員會 2004 time scale. Dates labeled with a * indicate boundaries where a 全球界线层型剖面和点位 has been internationally agreed upon: see List of Global Boundary Stratotype Sections and Points for a complete list.
- The 元古宙, 太古宙 and 冥古宙 are often collectively referred to as the Precambrian Time or sometimes, also the Cryptozoic.
- Defined by absolute age (Global Standard Stratigraphic Age).
- The age of the oldest measurable craton, or continental crust, is dated to 3600–3800 Ma
- Though commonly used, the Hadean is not a formal eon and no lower bound for the Archean and Eoarchean have been agreed upon. The Hadean has also sometimes been called the Priscoan or the Azoic. Sometimes, the Hadean can be found to be subdivided according to the lunar geologic time scale. These eras include the Cryptic and Basin Groups (which are subdivisions of the Pre-Nectarian era), Nectarian, and Early Imbrian units.
- These unit names were taken from the Lunar geologic timescale and refer to geologic events that did not occur on Earth. Their use for Earth geology is unofficial.
- Bowring, Samuel A.; Williams, Ian S. . Contributions to Mineralogy and Petrology. 1999, 134 (1): 3. Bibcode:1999CoMP..134....3B. doi:10.1007/s004100050465. The oldest rock on Earth is the Acasta Gneiss, and it dates to 4.03 Ga, located in the Northwest Territories of Canada.
- (PDF). . （原始内容存档 (PDF)于2020-09-02）.
- Valley, John W., William H. Peck, Elizabeth M. King (1999) Zircons Are Forever, The Outcrop for 1999, University of Wisconsin-Madison Wgeology.wisc.edu （页面存档备份，存于） – Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago Accessed Jan. 10, 2006
- Wilde S.A., Valley J.W., Peck W.H. and Graham C.M.（2001）Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature, v. 409, pp. 175-178.
- Wyche, S., D. R. Nelson and A. Riganti (2004) 4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton, Australian Journal of Earth Sciences Volume 51 Zircon ages from W. Australia - Absract Accessed Jan. 10, 2006
外部連結
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维基共享资源中相关的多媒体资源：前寒武纪 |
- PALEOMAP Project: Late Precambrian Supercontinent and Ice House World （页面存档备份，存于）
- UCMP Berkley （页面存档备份，存于）
本文来源：维基百科：前寒武纪
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