Exploring Evidence for Life on Land ~1100 Ma Ago

虽然有一些关于海洋中前寒武纪生命的记录，包括叠层石、碳酸盐和有机物，但对非海洋环境中的前寒武纪生命知之甚少。非海洋的记录也是暂时不完整的，只有有限的证据在太古代，没有令人信服的报告，在古元古代和弱沉积证据的生活在中元古代。最近在中大陆裂谷系（MCR）的西臂的北岸火山群（明尼苏达州）和微生物垫结构的一些古土壤的顶部，也在相关的沉积物中的未改变的~1100 Ma的古土壤的鉴定表明，在非海洋中元古代记录的这一空白可以填补。特别是，微生物垫，古土壤中的有机碳的存在，并在相关的沉积物中的碎屑表明微生物通过光合作用固定碳。PI将测试的假设，有一个广泛的非海洋生物圈约1100 Ma前，它的证据是保存在整个MCR。这些问题将使用全岩和稳定同位素地球化学、沉积学和质量平衡模型相结合的方法来回答。根据现场的初步结果（即，在古土壤、微生物垫结构和基质层中）和MCR中的碎屑有机碳中，光合作用固碳被推断为那里微生物群落的主要代谢途径。MCR沉积物中丰富的有机碳也使得首次利用正构烷烃生物标志物对全陆地元古宙生物量进行原位初步分析成为可能。最后，如果交代作用可以被忽略，那么MCR两侧古土壤的全岩地球化学数据可以与先前发表的定量质量平衡模型一起使用，以重建当时的大气CO2水平。这项拟议的研究将为一位有前途的年轻科学家的博士后研究奠定基础，同时在各种分析地球化学技术、研究监督和科学推广方面提供持续广泛的跨学科培训。它还将每年为两名本科生提供研究经验，包括实地和实验室工作，以及长期的指导。最后，拟议中的研究将通知教育和推广密歇根大学的使命，既增加了当地的数据和实地考察地球科学类，但更重要的是，通过提供自然历史展览博物馆显示，将整合在密歇根州的铜矿开采历史的基础。同时也是中元古代陆地生命的证据。博物馆展出70？每年有80，000名游客（包括来自地区学校的20，000名学童），其中包括来自邻近底特律大都市区的许多传统上在科学领域代表性不足的群体。

Though there is some record of Precambrian life in the oceans from stromatolites, carbonates, and organic matter, relatively little is known about Precambrian life in non-marine settings. The non-marine record is also temporally incomplete with only limited evidence in the Archean, no convincing reports in the Paleoproterozoic, and weak sedimentological evidence for life in the Mesoproterozoic. Recent identification of unaltered ~1100 Ma old paleosols in the North Shore Volcanic Group (Minnesota) of the western arm of the Midcontinent Rift System (MCR) and of microbial mat structures both at the top of some of the paleosols and also in the associated sediments suggests that this gap in the non-marine Mesoproterozoic record can be filled. In particular, the presence of organic carbon in the microbial mats, paleosols, and as detritus in associated sediments suggests microbes fixing carbon via photosynthesis. The PI will test the hypothesis that there was an extensive non-marine biosphere by ~1100 Ma ago, and evidence for it is preserved throughout the MCR. These questions will be answered using a combination of whole rock and stable isotope geochemistry, sedimentology, and mass-balance modelling. Based upon preliminary results from in situ (i.e., within paleosols, microbial mat structures, and stromatolites) and detrital organic carbon in the MCR, C fixation by photosynthesis has been inferred as the primary metabolic pathway for the microbial community there. The abundance of organic carbon in the MCR sediments also makes it possible to use n-alkane biomarkers to make a preliminary analysis of in situ wholly terrestrial Proterozoic biomass for the first time. Finally, if metasomatism can be discounted, whole rock geochemical data from paleosols on both sides of the MCR can be used with a previous published quantitative mass-balance model to reconstruct atmospheric CO2 levels at the time.Broader Impacts: The proposed research will form the basis of a post-doctoral research for a promising young scientist, while providing continued broad interdisciplinary training in a variety of analytical geochemistry techniques, research supervision, and science outreach. It will aslo provide research experience for two undergraduates a year, including both field and laboratory work, and long-term mentoring. Lastly, the proposed research will inform the education and outreach mission of Univ. of Michigan both by adding local data and a fieldtrip to an earth science class, but more importantly, by providing the basis for an Exhibit Museum of Natural History display that will integrate both the history of copper mining on Michigan?s Upper Peninsula and also the evidence of Mesoproterozoic life on land. The Exhibit Museum serves 70?80,000 visitors per year (including 20,000 school children from area schools), including many groups that are traditionally under-represented in science from the neighboring Detroit metropolitan area.