| 前寒武纪 | |
|---|---|
| ~4600 – 541.0 ± 1.0百万年前 | |
| 同义名 | Cryptozoic |
| 天体 | 地球 |
| 适用区域 | 国际地层委员会 |
| 适用时标 | ICS |
| 地质年代单位 | 前宙 |
| 年代地层单位 | 前宇 |
| 名称是否正式 | 非正式 |
| 下边界定义 | 地球形成 |
| 下边界GSSP位置 | N/A |
| GSSP批准时间 | N/A |
| 上边界定义 | Treptichnus pedum遗迹化石出现 |
| 上边界GSSP位置 | 加拿大纽芬兰 47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W |
| GSSP批准时间 | 1992 |
前寒武纪（英语：Precambrian）是地质年代中，对于显生宙之前数个宙（eon）的非正式涵盖统称，原本正式的名称是隐生宙或隐生元（Cryptozoic eon），但后来拆分成冥古宙、太古宙与元古宙三个时代。开始于大约45亿年前的地球形成时期，结束于约5亿4200万年前大量肉眼可见的硬壳动物诞生之时。
尽管前寒武纪占了地球历史中大约八分之七的时间，但人们对这段时期的了解相当少。这是因为前寒武纪少有化石纪录，且其中多数的化石，如叠层石，只适合用来作生物地层学研究[1]。此外，许多前寒武纪时期的岩石已经严重变质，使其起源变得晦涩不明。而其他的要不是已经腐蚀毁坏，就是还埋藏在显生宙地层底下[1][2]。
大约在45亿年前左右，原始的地球从环绕太阳的物质之中聚集而成。不久之后可能又因为小行星（大小如火星）的撞击，而分离出月球（参见大碰撞说）。一开始地球表面皆为岩浆覆盖，稳固地壳则大约出现于44亿年前。目前已知最古老的岩石发现于澳大利亚西部，放射性分析显示一块锆石结晶已有大约44亿400万年历史[3]。
前寒武纪的生命
目前并未明了生物究竟起源于何时。在格陵兰西岸海外群岛曾发现一些古老石头，内含38亿年前的碳，可能是早期的有机物[4]。此外在澳大利亚西部有一些保存良好的细菌，年代已超过34亿6000万年。目前已知最早的复杂多细胞生命型态，可能出现于大约6亿年前；而世界各地有许多5亿4200万年前到6亿年前之间的软体无壳动物化石，称为埃迪卡拉生物群（Ediacaran biota）。至于硬壳动物则出现于前寒武纪结束之后。
大约在5亿4400万年前，也就是前寒武纪的结尾，出现了许多不同型态的动物。这些动物群统称为小壳化石，目前所知有限。寒武纪的极早期发生了寒武纪大爆发（生命型态的快速分化与数量增加），导致伯吉斯动物群（Burgess fauna）的出现。
前寒武纪各时期
前寒武纪中包含有成铁纪、层侵纪、造山纪、固结纪、盖层纪、延展纪、狭带纪、拉伸纪、成冰纪与埃迪卡拉纪。之后的下一个时期寒武纪，则是显生宙里的第一代（era）第一纪（period）。地球上已知最早的锆石结晶经测试已有44亿年历史。其他隐生宙岩石纪录有些来自月球或陨石。
| 宙 | 代 | 纪[5] | 重大事件 | 年代[6] n亿年前 | ||
|---|---|---|---|---|---|---|
| 元古宙[7] | 新元古代[7] | 埃迪卡拉纪 | 埃迪卡拉生物群（狄更逊水母等）、埃迪卡拉纪末期灭绝事件 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 | “成冰纪冰河时期”形成雪球地球。该时期的化石依然稀有。 Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. | 8.5~6.3[8] | ||||
| 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[8] | ||||
| 中元古代[7] | 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[8] | |||
| 延展纪 | Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. | 14~12[8] | ||||
| 盖层纪 | Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1600 Ma, Mount Isa Block, Queensland | 16~14[8] | ||||
| 古元古代[7] | 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[8] | |||
| 造山纪 | 东亚吕梁构造期(25-18亿年前)。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[8] | ||||
| 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[8] | ||||
| 成铁纪 | 大氧化事件: 带状铁矿形成. 在澳大利亚洲, 格劳尔克拉通 发生斯利福德造山运动2440–2420 Ma. | 25~23[8] | ||||
| 太古宙[7] | 新太古代[7] | 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[8] | |||
| 中太古代[7] | 最早的叠层石（大概由蓝藻群落形成）. 最早的 宏化石. 南极洲洪堡造山运动。 第一个超大陆瓦巴拉大陆。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[8] | ||||
| 古太古代[7] | 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[9]。南极洲雷纳造山运动。 | 36~32[8] | ||||
| 始太古代[7] | 地球表面凝固，大气压约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 [7][10] |
早雨海世[7][11] | 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 | |||
| 酒海纪[7][11] | 本代的名称来源月球地质年代，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[7][11] | 已知最古老的岩石(4030 Ma)[12]. 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分子大约在40亿年前开始出现，南极洲内皮尔开始出现造山运动, 4000 ± 200 Ma. | 41.5~39.2 | ||||
| 隐生代[7][11] | 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）[13]。 | 45.7~41.5 | ||||
参考文献
- ↑ 1.0 1.1 James Monroe and Reed Wicander. The Changing Earth 2nd ed. Belmont: Wadsworth Publishing Company. 1997.
- ↑ Pamela J.W. Gore. The Precambrian. [12/6/06].
- ↑ Simon A. Wilde, John W. Valley, William H. Peck, and Colin M. Graham. Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature. 2001, 409: 175–178. doi:10.1038/35051550.
- ↑ Manfred Schidlowsk. A 3,800-million-year isotopic record of life from carbon in sedimentary rocks. 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 The Paleobiology Database. [2006-03-19].
- ↑ 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 国际地层委员会 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.
- ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 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.
- ↑ 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 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.
- ↑ 11.0 11.1 11.2 11.3 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. Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada. 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.
- ↑ Geology.wisc.edu (PDF). [2016-09-09].
- Valley, John W., William H. Peck, Elizabeth M. King (1999) Zircons Are Forever, The Outcrop for 1999, University of Wisconsin-Madison Wgeology.wisc.edu – 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
外部链接
- PALEOMAP Project: Late Precambrian Supercontinent and Ice House World
- UCMP Berkley