Benefiting from their adaptability to extreme environments, subsurface microorganisms have been discovered in sedimentary and igneous rock environments on Earth and have been advocated as candidates in the search for extraterrestrial life. In this article, we study iron-mineralized microstructures in calcite-filled veins within basaltic pillows of the late Ladinian Fernazza group (Middle Triassic, 239 Ma) in Italy. These microstructures represent diverse morphologies, including filaments, globules, nodules, and micro-digitate stromatolites, which are similar to extant iron-oxidizing bacterial communities. In situ analyses including Raman spectroscopy have been used to investigate the morphological, elemental, mineralogical, and bond-vibrational modes of the microstructures. According to the Raman spectral parameters, iron minerals preserve heterogeneous ultrastructures and crystallinities, coinciding with the morphologies and precursor microbial activities. The degree of crystallinity usually represents a microscale gradient decreasing toward previously existing microbial cells, revealing a decline of mineralization due to microbial activities. This study provides an analog of possible rock-dwelling subsurface life on Mars or icy moons and advocates Raman spectroscopy as an efficient tool for in situ analyses. We put forward the concept that ultrastructural characteristics of minerals described by Raman spectral parameters corresponding to microscale morphologies could be employed as carbon-lean biosignatures in future space missions.

中文翻译：

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海洋玄武岩中古代生命的痕迹以铁矿化超微结构的形式保存下来：对检测地外生物特征的意义。

得益于对极端环境的适应能力，地下微生物在地球的沉积岩和火成岩环境中被发现，并被提倡作为寻找外星生命的候选者。在本文中，我们研究了意大利拉丁纪晚期 Fernazza 群（中三叠世，239 Ma）玄武岩枕状岩脉中方解石填充矿脉中的铁矿化微观结构。这些微观结构代表了不同的形态，包括丝状、球状、结节和微指状叠层石，它们与现存的铁氧化细菌群落相似。包括拉曼光谱在内的原位分析已用于研究微观结构的形态、元素、矿物学和键振动模式。根据拉曼光谱参数，铁矿物保留了异质超微结构和结晶度，与形态和前体微生物活动相一致。结晶度通常代表着向先前存在的微生物细胞减小的微尺度梯度，揭示了由于微生物活动导致的矿化的下降。这项研究提供了火星或冰冷卫星上可能存在岩石地下生命的模拟，并提倡拉曼光谱作为原位分析的有效工具。我们提出了这样的概念：由对应于微尺度形态的拉曼光谱参数描述的矿物超微结构特征可以用作未来太空任务中的贫碳生物特征。