Exploring Evidence for Life on Land ~1100 Ma Ago

探索陆地生命的证据 ~1100 Ma 前

• 批准号: 1050760
• 负责人: Nathan Sheldon
• 金额: $ 23万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-03-01 至 2015-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1050760&HistoricalAwards=false
• 关键词: Exploring; Evidence; Life; Land; 1100

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.

虽然从叠层石、碳酸盐和有机物中有一些前寒武纪生物在海洋中的记录，但对非海洋环境下的前寒武纪生物的了解相对较少。非海相记录在时间上也不完整，太古宙证据有限，古元古代没有令人信服的报告，中元古代生命的沉积学证据也很薄弱。最近在中大陆裂谷系（MCR）西支的北岸火山群（明尼苏达州）中发现的~ 1100ma未改变的古土壤，以及部分古土壤顶部和相关沉积物中的微生物席结构，表明这一非海相中元古代记录的空白可以被填补。特别是，微生物席、古土壤和相关沉积物中的碎屑中有机碳的存在表明微生物通过光合作用固定碳。PI将验证一个假设，即大约1100 Ma以前存在一个广泛的非海洋生物圈，并且证据保存在整个MCR。这些问题将通过整体岩石和稳定同位素地球化学、沉积学和质量平衡模型的结合来回答。根据MCR中原位（即古土壤、微生物席结构和叠层石）和碎屑有机碳的初步结果，推断光合作用对碳的固定是微生物群落的主要代谢途径。MCR沉积物中有机碳的丰度也使得首次利用正构烷烃生物标志物对原位全陆元古代生物量进行初步分析成为可能。最后，如果不考虑交代作用，MCR两侧古土壤的全岩石地球化学数据可以与先前发表的定量质量平衡模型一起用于重建当时的大气CO2水平。更广泛的影响：拟议的研究将为一位有前途的年轻科学家提供博士后研究的基础，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，以及长期指导。最后，拟议的研究将通过增加当地数据和实地考察地球科学课程，为密歇根大学的教育和推广任务提供信息，但更重要的是，通过为自然历史博物馆的展览提供基础，该展览将整合密歇根铜矿开采的历史。还有陆地上中元古代生命的证据。展览博物馆可容纳70人？每年8万名游客（包括来自当地学校的2万名学童），包括来自邻近底特律大都会地区的许多传统上在科学领域代表性不足的群体。