Collaborative Research: Biogeochemistry of the Snowball Earth

该项目建议测量脂肪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冰川事件(约750-580 Ma)的起源和影响，这是一种以前未报道的方法。人们提出了多种假说来解释与这些冰川有关的异常地球化学和沉积学特征(d13C负异常、铁建造、异常碳酸盐岩相等)。因为现有的数据，特别是碳酸盐的d13C记录，在它们记录的环境变化方面是模棱两可的，所以许多假设仍然存在。尽管在中国(江格等人，2003)中发现了一个类似甲烷渗漏的地点，并从世界各地进行了数以千计的d13C分析，但我们现在对雪球地球的生物地球化学了解比霍夫曼等人更多。(1998)发表了他们的开创性论文。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。上一次冰川事件与动物门的出现和多样化的巧合并没有逃脱人们的注意，并在这段时间段引发了许多持续的兴趣。我们对冰川的有机地球化学研究也可能为这一重要问题提供一些线索。每个主要的滚雪球假说都预测了新元古代海洋在冰川事件之前、期间和之后的截然不同的环境条件。从适当年龄的富含有机物质的岩石中提取的类脂生物标记物，将提供有关当时海洋中现有生物群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。这些数据应该让我们能够区分争论不休的滚雪球假说，并推动当前的辩论向前推进。收集这类数据的限制不是分析性的或程序性的，因为实验室方法很简单。相反，问题是找到适当年龄和地层位置的有机质丰富的地层(有机质浓度为mg/g)，私人投资者认为他们已经克服了这个问题。私人投资者从巴西和中国的冰前、同生和后冰川单元收集了一系列有机丰富、保存完好、热不成熟的岩石。他们的样本集提供了一个很好的机会来寻找脂质生物标记物，测试相互竞争的假说，并进一步了解导致后生动物进化和多样化的地球生物地球化学。该项目的学术价值如下。关于雪球地球的生物标记物分析的应用是新颖的，由于适当样本的稀有，以前没有尝试过。私家侦探已经组装了必要的样本，并准备好进行分析。这些结果将有可能区分冰川的多种假说，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科学家的指导，这构成了提案的核心(所要求的大部分资金用于学生支持)。P.I.S将通过这项研究扩大代表不足群体的参与。特别是，南加州大学的研究生RA申请将支持艾莉森·奥尔科特，她在NSF研究生奖学金竞赛中获得荣誉称号，从而增加了女性在地球科学领域的存在；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，Walker，2003)，因此将有助于加强公众对科学，特别是地球科学的参与和支持。

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.