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

在喜热微生物群落存在的情况下形成的热液沉积物类似于地球上最早的生态系统之一。对现存生命的分子系统学研究表明，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░C)，这种微生物定义了生命的温度上限。生命是在高温下进化的，还是高温微生物是唯一在“后期轰击”时期的大规模撞击事件中幸存下来的群体，这一点仍然存在争议。无论是哪种情况，对热液沉积物作为重要古生物储存库的潜力的研究都支持了NSF的目标，即了解地球早期生命的产品是如何保存在地质记录中的。为了最大限度地利用古热液沉积对高温群落的古生物学解释，需要了解高温生物成因特征最初被保存并随后被沉积后成岩作用改变的过程。生物起源特征是保存在岩石记录中的生命的产物，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负责保存高温生物成因特征的有机沉积过程，并记录原始生物成因特征在早期成岩作用中是如何改变的。为了提供一个框架，可以在其中适当地解释硅质热液沉积(热泉，特别是浅成热液沉积)中化石中的高温群落的古生物学，将用分子系统学和各种电子束成像方法来表征占据硅质沉积温泉的现存群落。将使用光谱成像、衍射和低剂量透射成像和分析(EELS/EDS)电子显微镜来研究表现出形态保真度的超嗜热微化石，以确定石化的机制。为了建立保存在天然硅质热液矿床中的独特的高温生物标志物类型的基线调查，将对有机保存的高温遗骸样品进行总有机碳(TOC)、13C、脂比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。野外实验将在新西兰的一个地热发电站进行，该实验将在新西兰的一个地热发电站进行，旨在从自然热水流体中依次产生生物成因和非生物成因的硅质热液矿床。从微观到宏观直接比较生物成因和非生物成因热液沉积，将为区分硅质热液沉淀物的生物成因提供一套可靠的标准。在岩石记录中识别和自信地评估极端嗜热群落的生物起源特征的能力有所提高，这将促进对地球上生命的早期化石记录的解释，甚至可能是火星上的生命记录。

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.