作为序言,我说我不知道远程银河动态足以知道超新星可能可能在奥陶纪足够近地球影响伽马射线爆发,我也不了解地球化学知道有办法在化石记录中发现此类事件。话虽这么说,我会尽量回答的问题是:我们需要调用一个外星事件来解释奥陶纪末冰川作用?的分类单元选择性灭绝事件支持伽马线暴假说?让我们看看不同的假设的冰川作用发生时,最初的难题:如何一个冰期时mid-Ordovician美元p_{二氧化碳}$ *认为* 14次四级?* * Brenchley et al . 1994 * *建议奥陶纪海洋环流变化从一个系统在热盐水水域底部与冷底水系统(即温盐而不是haline循环),引发phytoplanktonic开花,然后减少大气美元p_{二氧化碳}美元,引发了一场eutrophization的海洋。* * * * 1999(坎普等。认为赞成构造派生美元p_{二氧化碳}$下降:阿巴拉契亚和加里东造山带造山运动来增加风化减少p_美元{二氧化碳}$。当然,两个假设并不是相互排斥的,因为风化的增加也意味着增加营养物质在海水中,因此提高初级生产力。另一个问题是,群体灭绝在冰川作用:最近的研究表明,acritarchs(最多样化的浮游植物群以这一时期)没有遭受这些事件(2008 * * * * Vecoli);相对底栖生物集团如海百合或者腕足类(见* *希恩2001 * *审查);一些中上层鱼组织如笔石动物的和鹦鹉螺目动物也受事件期间,其他没有(例如放射虫)。 In summary there is no clear pattern, but there is also no reason to think that there was a preferential extinction of surface organisms over deeper-living ones. So, does that answer the question: no; but it seems to me that GRB doesn't explain better the event that unfolded during the late Ordovician than other hypotheses (namely the ocean eutrophization and the continental weathering). Does it discard the hypothesis of a GRB: no; but since there is no direct evidence that it indeed happened at that time, and that we can explain the Ordovician events without, it seems, to me, more parsimonious to think that it didn't. References: Brenchley et al., 1994. [Bathymetric and isotopic evidence for a short-lived Late Ordovician glaciation in a greenhouse period.](http://geology.gsapubs.org/content/22/4/295.short) Geology, 22: 292-298. Kump et al., 1999. [A weathering hypothesis for glaciation at high atmospheric $p_{CO_2}$ during the Late Ordovician](http://dx.doi.org/10.1016/S0031-0182(99)00046-2). Palaeogeography, Palaeoclimatology, Palaeoecology, 152: 173-187. Sheehan, 2001. [The Late Ordovician Mass Extinction.](http://usuarios.geofisica.unam.mx/cecilia/CT-ST/Sheehan2001OrdovicianExtintion.pdf) Annual review of Earth and Planetary Science, 29: 331-364. Vecoli, 2008. [Fossil microphytoplankton dynamics across the Ordovician–Silurian boundary](http://dx.doi.org/10.1016/j.revpalbo.2006.11.004). Review of Paleobotany and Palynology, 148: 91-107.