Collaborative Proposal: Biogeochemistry of the Snowball Earth

该项目建议测量脂质生物标志物的丰度和碳同位素组成，以帮助阐明新元古代低纬度冰川事件的起源和影响（约2000年）。750-580 Ma），以前没有报道的方法。人们提出了多种假说来解释与这些冰川作用相关的异常地球化学和沉积学特征（负d13 C异常、铁形成、异常碳酸盐岩相等）。如此多的假设之所以存在，是因为现有的数据，特别是碳酸盐的d13 C记录，在它们记录的环境变化方面是模棱两可的。尽管在中国发现了一个类似甲烷渗漏的地点（Jiange等人，2003年）和来自世界各地的许多地方的成千上万的d13 C分析，我们现在对雪球地球的地球化学的了解比霍夫曼等人（1998年）发表他们的开创性论文时少之又少。需要新的和不同类型的数据来推动我们对这一迷人事件的理解。末次冰期事件与动物门的出现和多样化的巧合并没有逃过人们的注意，并激发了人们对这一时期的持续兴趣。我们对冰川作用的有机地球化学研究也可能对这一重要问题有所启发。主要的雪球假说各自预测了新元古代海洋在冰川事件之前、期间和之后的非常不同的环境条件。从适当年龄的富含有机物的岩石中提取的脂质生物标志物将提供有关当时海洋中现有生物区系和代谢途径的宝贵信息。碳同位素数据也将告诉我们甲烷循环的作用。这些数据应该使我们能够区分相互竞争的雪球假说，并将当前的辩论向前推进。收集这种数据的局限性不是分析性的或程序性的，因为实验室方法是直接的。相反，问题在于找到具有适当年龄和地层位置的富含有机质的地层（有机质浓度为mg/g），这是一个研究人员认为他们已经克服的问题。研究人员已经从巴西和中国的冰前、冰后和冰同时期收集了一系列富含有机质、保存完好、热未成熟的岩石。他们的样本集提供了一个很好的机会来寻找脂质生物标志物，测试竞争的假设，并进一步了解地球的地球化学，导致后生动物的进化和多样化。生物标志物分析的应用与雪球地球是新颖的，并没有尝试以前由于适当的样品稀少。私人侦探已经收集了必要的样本，并配备了进行分析的设备。研究结果将有可能区分冰川作用的多种假设，也可能阐明导致动物进化的一些环境变化。广泛的影响是对研究生、本科生和国际博士后的指导科学家，这构成了该提案的核心（所需资金的大部分用于学生支持）。P.I.s将通过这项研究扩大代表性不足的群体的参与。特别是，南加州大学的研究生RA请求将支持Alison Olcott，她在NSF研究生奖学金竞赛中获得了荣誉奖，从而增加了地球科学领域的女性存在;目前，大多数在南加州大学进行第一次研究经验的本科生助理也是女性。如果得到支持，这项研究将有助于解决最近引起公众关注的一个问题（例如，步行者，2003年），并因此将有助于加强公众参与和支持一般的科学，特别是地球科学。

Project proposes to measure the abundance and carbon-isotopic composition of lipid biomarkers to help elucidate the origins and effects of Neoproterozoic low-latitude glacial events (ca. 750-580 Ma), an approach not previously reported. Multiple hypotheses have been proposed to explain the unusual geochemical and sedimentological features associated with these glaciations (negative d13C anomalies, iron-formation, unusual carbonate lithofacies, etc.). So many hypotheses persist because the existing data, particularly the d13C record of carbonates, are equivocal in terms of the environmental changes that they record. Despite the discovery of one methane-seep-like locality in China (Jiange et al., 2003) and thousands of d13C analyses from a multitude of localities world-wide, we know little more now about the biogeochemistry of snowball Earth than when Hoffman et al. (1998) published their seminal paper. New and different kinds of data are required to move our understanding of this fascinating event forward. The coincidence of the last glacial event and the advent and diversification of animal phyla has not escaped attention, and fuels much of the continuing interest in this time interval. Our organic geochemical studies of the glaciations may also shed some light on that important question.The major snowball hypotheses each predict very different environmental conditions in the Neoproterozoic oceans leading up to, during, and immediately after the glacial events. Lipid biomarkers, extracted from organic-rich rocks of appropriate age, would provide valuable information about existing biota and metabolic pathways in the oceans at that time. Carbon-isotopic data will also tell us about the role of methane cycling. These data should allow us to differentiate between the contending snowball hypotheses and move the current debate forward. The limitation to collecting such data is not analytical or procedural, for the laboratory methods are straightforward. Rather, the issue is finding organic-rich strata (with mg/g concentrations of organic matter) of appropriate age and stratigraphic position, a problem which P.I.s believe they have surmounted.P.I.s have collected a series of organic rich, well-preserved, thermally-immature, rocks from pre-, syn-,and post-glacial units in Brazil and China. Their sample set provides an excellent chance to find lipid biomarkers, test competing hypotheses, and further our knowledge of the biogeochemisty of Earth leading up to the evolution and diversification of the metazoa.The intellectual merit of the project is as follows. The application of biomarker analyses with respect to snowball Earth is novel and has not been attempted previously due to the rarity of appropriate samples. P.I.s have assembled the requisite samples and are equipped to undertake the analyses. The results will have the potential to distinguish between the multiple hypotheses for the glaciations, and may also illuminate some of the environmental changes leading up to the evolution of animals.The broad impact is the mentoring of graduate students, undergraduate students, and international post-doctoral scientists, which forms the core of the proposal (the majority of the requested funding is for student support). P.I.s will broaden the participation of underrepresented groups with this study. In particular, the graduate student RA request from USC will support Alison Olcott, who received an honorable mention in the NSF graduate student fellowship competition, thus increasing female presence in the field of Earth Sciences; currently, most of the undergraduate assistants undertaking their first research experience at USC are women, as well. If supported, this research will contribute to a question that has captured much recent public attention (e.g., Walker, 2003), and will thus serve to bolster public involvement and support ofscience in general, and geoscience in particular.