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多少百分比的地球历史上有永久冰?

维基百科的评论在这里“永久冰实际上是一个罕见的现象在地球的历史,只发生在20%的时间里,地球是在一个冰室效应”。A "citation needed" tag is attached to this remark.

多少百分比的地球历史上有永久(全年)冰?

回答

已经大量的评论和元说,这个问题没有正确的答案在知识的当前状态。但我们至少可以检查是否我们可以想出一个粗略的估计(因此来看看从这20%估计从哪里来)。首先让我们看看主要已知冰期:- * *当前* *:确实有一个永久的东部南极大陆冰盖,据推测,渐新世早期(即35马,看到e . g。* * DeConto &波拉德2003 * *)。上有相当大的争议eai发病的具体时间,但我们在这里谈论不同的< 10最高产量研究,即< 0.25%的地球历史,所以我们现在可以忽略这种差异。- * *卡鲁冰河世纪* *:Carboniferous-Permian冰川作用被认为从Mississipian张成(360毫安,* * Buggish et al . 2008 * *)萨克马力统(ca。290马;* *科特et al . 2008 * *),给我们一个ca。70年最高产量研究区间。然而也有些研究表明(e . g。* *菲尔丁et al . 2008 * *),这是最有可能的alternance冰川和nonglacial气候而不是一个连续的冰川作用,这意味着永久冰可能是现在不到70最高产量研究。* * - * *奥陶纪冰川作用:它被认为已经开始Katian末与早期Hirnantian (ca。445 ma)和前已经结束或者志留纪(e . g。* *芬利et al . 2010 * *)或在志留纪的开始(ca。440马;库珀看到e . g。* * &萨德勒2012 * *)。因此一个间隔1到5的最高产量研究。 This one has been studied extensively as it is thought to be associated with one of the 5 major mass extinctions of the Phanerozoic (see the whole Sepkoski corpus). - **The Cryogenian**: two glaciations are thought to have marked the Cryogenian (see e. g. **Shields-Zhou et al. 2012**), the Sturtian (ca. 720 to 660Ma) and the Marinoan glaciations (ca. 650-635Ma), thus accounting for 75 Myr. - **The Huronian glaciation** lasting presumably from 2.45Ga to 2.22Ga (see a small review in **Van Kranendonk, 2012**). The issue here being that the accuracy of paleoproterozoic event datation does not really allow to go much more into the details as this (both because of the extreme scarcity of the data and the relative low resolution of the dating techniques). Leaving us with a glaciation (or more probably a series of glaciations) that could have lasted up to 230Myr. To this, we can add various minor glaciations that are still highly debated such as the Late Devonian or the Middle to Late Jurassic (e. g. **Dromart et al. 2003**). Whether of not they indeed occur, they hardly account for much of Earth History when aggregated so we can ignore them safely for the purpose of a rough estimate. This leads us to 35 + 70 + 5 + 75 + 230 = 415 Myr which equates to ~ 9 % of Earth History. Which is still far off 20% and I doubt that the minor glaciations put together account for 500Myr. <sub> Buggish, W., Joachimski, M. M., Sevastopulo, G., Morrow, J. R., 2008. [Mississippian $\delta ^{13}C_{carb}$ and conodont apatite $\delta ^{18}O$ records — Their relation to the Late Palaeozoic Glaciation](http://dx.doi.org/10.1016/j.palaeo.2008.03.043). Palaeogeography, Palaeoclimatology, Palaeoecology, 268: 273-292. Cooper, R. A., Sadler, P. M., [The Ordovician Period](http://dx.doi.org/10.1016/B978-0-444-59425-9.00020-2). In Gradstein et al. 2012, The Geologic Time Scale 2012: 489-523. DeConto, R. M., Pollard, D. 2003. [Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric $CO_2$](http://www.nature.com/nature/journal/v421/n6920/abs/nature01290.html). Nature, 421: 245-249. Dromart, G., Garcia, J.P., Picard, S., Atrops, F., Lécuyer, C., Sheppard, S.M.F., 2003. [Ice age at the Middle–Late Jurassic transition?](http://dx.doi.org/10.1016/S0012-821X(03)00287-5) Earth and Planetary Science Letters, 213: 205-220. Fielding, C. R., Frank, T. D., Birgenheier, L. P., Rygel, M. C., Jones, A. T., Roberts, J., 2008. [Stratigraphic imprint of the late Palaeozoic ice age in eastern Australia: A record of alternating glacial and nonglacial climate regime](http://dx.doi.org/10.1144/0016-76492007-036). Journal fo the Geological Society, 165: 129-140. Korte, C., Jones, P. J., Brand, U., Mertmann, D., Veizer, J. 2008. [Oxygen isotope values from high-latitudes: Clues for Permian sea-surface temperature gradients and Late Palaeozoic deglaciation.](http://dx.doi.org/10.1016/j.palaeo.2008.06.012) Palaeogeography, Palaeoclimatology, Palaeoecology, 269: 1-16. Shields-Zhou, G. A., Hill, A. C., Macgabhann, B. A., 2012. [The Cryogenian Period](http://dx.doi.org/10.1016/B978-0-444-59425-9.00017-2). In Gradstein et al. 2012, The Geologic Time Scale 2012: 393-411. Van Kranendonk, M. J., 2012. [A Chronostratigraphic Division of the Precambrian](http://dx.doi.org/10.1016/B978-0-444-59425-9.00016-0). In Gradstein et al. 2012, The Geologic Time Scale 2012: 299-392. </sub>

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