LEXEN: Interactions Between Hyperthermophilic Communities and Silica Mineralization: Implications for Paleobiology

LEXEN：超嗜热群落与二氧化硅矿化之间的相互作用：对古生物学的影响

• 批准号: 9809471
• 负责人: Sherry Cady
• 金额: $ 30万
• 依托单位: SETI Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-10-15 至 2000-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9809471&HistoricalAwards=false
• 关键词: LEXEN; Interactions; Between; Hyperthermophilic; Communities

9809471CadyHydrothermal deposits that form in the presence of heat-loving microbial communities are analogs for one of Earth's earliest ecosystems. Molecular phylogenetic studies of extant life suggest that these earliest ecosystems were inhabited by hyperthermophiles (optimum growth temperatures 80░C), microorganisms that define life's upper temperature limit. It remains debatable whether life evolved at high temperatures, or whether high temperature microorganisms were the only groups to survive the massive impact events of the 'late bombardment' period. In either case, study of the potential for hydrothermal deposits to serve as important paleobiological repositories supports NSF's goal to understand how the products of early life on Earth are preserved in the geological record. To maximize paleobiological interpretations of hyperthermophilic communities from ancient hydrothermal deposits requires an understanding of the processes by which hyperthermophilic biogenic signatures are initially preserved and subsequently altered by post-depositional diagenetic effects. Biogenic signatures, the products of life that are preserved in the rock record, include microfossils, stromatolites, and chemofossils. The primary objectives of the project are to identify the organosedimentary processes responsible for the preservation of hyperthermophilic biogenic signatures in high-temperature ecosystems, and to document how primary biogenic signatures are altered during early diagenesis.To provide a framework within which the paleobiology of hyperthermophilic communities fossilized in siliceous hydrothermal deposits (thermal spring and especially epithermal deposits) can be properly interpreted, extant communities that occupy silica-depositing thermal springs will be characterized by molecular phylogeny and various electron beam-imaging methods. Hyperthermophilic microfossils that display morphological fidelity will be investigated using spectroscopic imaging, diffraction, and low dose transmission imaging and analytical (EELS/EDS) electron microscopy to identify the mechanisms of fossilization. To establish a baseline survey of the types of unique hyperthermophilic biomarker compounds preserved in natural siliceous hydrothermal deposits, samples with organically preserved hyperthermophilic remains will be analyzed for total organic carbon (TOC), 13C, lipid ratios, and biomarkers. The organosedimentary interactions responsible for the morphological development of high-temperature siliceous sinter stromatolites will be investigated from the submicroscopic to macroscopic scale. Field experiments, designed to produce sequentially biogenic and abiogenic siliceous hydrothermal deposits from natural hydrothermal fluids in a 'water tunnel' will be conducted at a geothermal power station in New Zealand. Direct comparison of biogenic and abiogenic hydrothermal deposits from the submicroscopic to macroscale will provide a robust set of criteria for distinguishing the biogenicity of siliceous hydrothermal precipitates. An improved ability to recognize and confidently assess in the rock record the biogenic signatures of hyperthermophilic communities will advance interpretations of the early fossil record of life on Earth and, potentially, on Mars.

[8094771]在嗜热微生物群落存在的情况下形成的热液沉积物与地球上最早的生态系统之一类似。现存生命的分子系统发育研究表明，这些最早的生态系统中居住着嗜热微生物（最适生长温度为80℃），这些微生物定义了生命的最高温度极限。生命是在高温下进化的，还是高温微生物是在“晚期轰击”时期的大规模撞击事件中幸存下来的唯一群体，这仍然是有争议的。无论哪种情况，热液沉积物作为重要的古生物储存库的潜力的研究支持了NSF的目标，即了解地球上早期生命的产物是如何在地质记录中保存下来的。为了最大限度地从古热液沉积物中对嗜热生物群落进行古生物学解释，需要了解嗜热生物特征最初被保存并随后被沉积后成岩作用改变的过程。生物成因特征，即保存在岩石记录中的生命产物，包括微化石、叠层石和化学化石。该项目的主要目标是确定在高温生态系统中保存超嗜热生物成因特征的有机沉积过程，并记录早期成岩作用如何改变初级生物成因特征。为了提供一个框架，使在硅质热液矿床（温泉，特别是浅热液矿床）中化石的超嗜热群落的古生物学可以得到适当的解释，将利用分子系统发育和各种电子束成像方法来表征占据硅质热液矿床的现存群落。研究人员将利用光谱成像、衍射、低剂量透射成像和分析电子显微镜（EELS/EDS）对具有形态保真度的超嗜热微化石进行研究，以确定化石的形成机制。为了建立天然硅质热液矿床中保存的独特的超嗜热生物标志物化合物类型的基线调查，将对有机保存的超嗜热遗骸样品进行总有机碳（TOC）， 13C，脂质比率和生物标志物的分析。高温硅质烧结叠层石形态发育的有机-沉积相互作用将从亚微观到宏观尺度进行研究。将在新西兰的一个地热发电站进行现场实验，旨在从“水洞”中的天然热液中依次开采生物和非生物热液硅质热液矿床。从亚微观到宏观的生物成因和非生物成因热液矿床的直接比较将为区分硅质热液沉积的生物成因提供一套强有力的标准。在岩石记录中识别和自信地评估超嗜热生物群落的生物特征的能力的提高，将推进对地球上，甚至可能是火星上早期生命化石记录的解释。