Photoelectrons from Minerals and Microbial World

The Earth surface is a multiple open system. Semiconducting minerals, including most metal oxides and sulfides, absorb visible light of the solar spectrum. Microorganisms evolve varied pathways to get carbon and energy sources. It is obvious that the interaction among solar light, semiconducting minerals, photoelectron/photohole, organics, inorganics, valence electrons and microorganisms occurs continuously on our planet. In a recent study, Lu et al. (2012) presented evidence demonstrating solar energy mediated by semiconducting mineral photocatalysis, acting as energy source, promoted the growth of some non-photosynthetic bacteria and revealed that the ternary system of microorganisms, minerals and solar light has played a critical role in the history of life on our planet. In simulated system, under simulated solar light semiconducting minerals, such as metal oxides and metal sulfides, generates photoelectrons which could be used by non-phototrophic microorganisms to support their metabolisms. The growth of microorganism was closely related to photon quantity and energy, and the microorganism growth and mineral light absorption spectra were fitted well under different light wavelengths. The overall energy efficiency from photon to biomass was 0.13‰ to 1.9‰. Further studies revealed that in natural soil systems, semiconducting mineral photocatalysis could influence the microbial population. Solar energy utilization pathway by nonphototrophic microorganisms mediated by semiconducting mineral photocatalysis provides a new concept to evaluate the origin and evolution of life. Semiconducting minerals are ubiquitous on Earth’s surface and widely participate in redox reactions following photoelectron-photohole pairs excited by solar light. As photoholes can be easily scavenged by environmental reductive substances and microorganisms possess multiple strategies to utilize extracellular electrons, the highly reductive photoelectrons serve as potential energy source for microbial life. The discovery of this pathway extends our knowledge on the use of solar energy by nonphototrophic microorganisms, and provides important clues to evaluate life on the early Earth. Microorganisms, minerals and solar light constitute a complex but important ternary system through Earth history. The discovery of the novel energy conversion pathway in this system demonstrates how nonphototrophic microorganisms directly or indirectly utilized photoelectrons as the solar energy source. The fully comprehending of nonphototrophic bacteria solar energy utilization conducted by semiconducting minerals in present environment will greatly help us to better understand the energy transform mechanism among interfaces of lithosphere, pedosphere, hydrosphere and biosphere.     

World's largest known Precambrian fossil black smoker chimneys and associated microbial vent communities, North China: Implications for early life

Black smoker chimneys and biological vent communities have been identified at many sites on the deep seafloor, particularly along oceanic spreading centers. We report the largest and oldest known, microbe-rich sub-meter-sized black smoker chimneys and mounds from a 1.43 billion-year old sulfide deposit in a continental graben in northern China. These chimneys are especially well preserved, with characteristic morphology, internal textures and internal cylindrical mineralogical zonation. Four main types of chimneys are distinguished on textural and mineralogical criteria, exhibiting either Zn–Fe-sulfide or Pb–Zn–Fe-sulfide internal cylindrical mineralogical zones. The chimneys mark vent sites in submarine grabens indicating focused flow-venting processes. The fossil chimneys have mineralogical and geological evolutionary features similar to their counterparts on the modern seafloor and other submarine hydrothermal vents. Black smoker vent fluids and seafloor tectonism played important roles for formation of the massive sulfide deposits in the Mesoproterozoic.We also report the first known, remarkably diverse assemblage of fossil microbialites from around and inside Precambrian vent chimneys, demonstrating that Proterozoic life flourished around submarine hot vents and deep within the chimney vent passages. Filamentous, spherical, rod, and coccus-shaped fossil microbes are preserved preferentially on sulfide precipitates. Based on the depth and setting of the fossil biota, the organisms that produced the microbialites were likely sulfate-reducing chemosynthetic and thermophyllic microbes. Textural and mineralogical evidence shows that biomineralization processes enhanced chimney growth and sulfide precipitation.Close association of microorganisms with sulfide chimneys in modern deep-sea hydrothermal vents and younger ophiolites has sparked speculation about whether life may have originated at similar vents. However, little is known about fossil equivalents of vent microfossils and black smoker chimneys from Earth's early evolution. The fossilized microorganisms from the Gaobanhe black smoker chimney sulfide deposits include thread-like filaments with branching and twisted forms and preserved organic carbon, representing fossilized remnants of microbial mats metabolized at high temperatures characteristic of venting fluids. The preservation of fossil microorganisms provides evidence that microbial populations were closely associated with black smoker chimneys in Earth's early history. The microbial population clearly constitutes the site for mediating mineral formation. These ancient microbial fossils lead to a much better understanding of early life on the deep seafloor. The discovery of the Mesoproterozoic microfossils within black-smoker hydrothermal chimneys indicates that hydrothermal activity around sea-floor vents supported dense microbial communities, and supports speculation that vent sites may have hosted the origin of life.     

生命起源、早期演化阶段与海洋环境演变

近年的研究表明,地球生命可能起源于距今39~36亿年之间。除了碳元素以外,水、氮、氢、磷等元素也是生命起源的必备条件,黏土矿物和金属硫化物是有机质合成的重要催化剂,有热液活动的碱性热水环境是最有利生命发生的孵化场。自原核生物在约3.5 Ga出现之后,生命就一直表现为与环境的协同进化关系。大气圈氧化是地球史上最重大的地质事件之一,它不仅改变了地球表层环境条件、加速了表生地质过程和新矿物的产生,而且改变了海洋化学条件和元素循环。大气圈氧化事件的根本在于产氧蓝细菌的出现,元古宙中期海洋化学性质的整体转换也与微生物过程密切相关。新元古代多细胞生物的繁盛和末期后生动物的出现及其在寒武纪初期的快速多样化是生物圈演化的重大飞跃。这个过程也与海洋氧化增强及其导致的海洋化学变化密切相关,其中硫化水域消失和减弱以及海水中微营养元素可得性增加可能是重要因素,这也与微生物过程直接相关。     

微生物成矿

微生物对生命元素如碳、氮、硫、氧和金属离子的代谢作用能显著的改变微生物周边的外部环境和其内部环境。在一系列的生物地球化学过程中,微生物参与了矿产的沉积(生物成矿)或参与了矿石和岩石的溶解(生物风化)。生物成矿作用有两个途径：一个叫生物诱导成矿,通过这个过程,微生物分泌出代谢产物导致了之后的矿物颗粒的沉积;另一个叫生物控制成矿,在这个过程中,微生物在控制矿物成核和生长上起到了显著作用。微生物成因的矿物总体来说颗粒都很小和／或有着独特的同位素特征。最普遍的生物成因矿物有碳酸盐、硫化物和铁的氧化物。细胞表面和其分泌的胞外聚合物的结构可以为离子的浓缩、聚合和矿化提供模板,并起到重要作用。地球材料的仿生合成帮助我们了解了在人工条件下的生物成矿机制。此外,在地质环境中生物成因的矿物还可以作为一种生物信号,用来重建地球和其他行星的起源和演化。     

Thirty Years of the Seafloor CORK Borehole Observatories: Development,Applications and Future Perspective

In the past 50 years, we have witnessed remarkable progress in our understanding of the Earth and ocean system, as a result of the internationally integrated deep ocean drilling programs, the Deep Sea Drilling Program (DSDP), the Ocean Drilling Program (ODP), and the Integrated Ocean Drilling Program (IODP). One of the legacies of the deep ocean drilling programs is the development and applications of the CORK, Circulation Obviation Retrofit Kit. Earth and ocean sciences have been shifting from a traditional discontinuous, expeditionary mode toward a mode of sustained in situ observations today. The seafloor CORK observatories offer Earth, ocean and life scientists new opportunities to study multiple, interrelated deep marine subsurface processes, over time scales ranging from seconds to decades. Here, we first provided a concise examination of the development history of the CORKs, then described the first installations of ODP CORKs, the evolution of different models of CORK, and finally, summarized the scientific lessons learned in the installation and operation effort of the CORKs. In the end, we offered our perspectives on using CORKs to study geological, hydrogeological, microbiological, and biogeochemical processes in the deep marine subsurface biosphere, particularly pertaining to China’s efforts in establishing and enhancing its deep-sea and deep-biosphere research and monitoring programs.     

Highly alkaline,high-temperature hydrothermal fluids in the early Archean ocean

Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (∼350 °C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO₂ condition, and predict a generation of SiO₂-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.     

浅海热液活动的地球化学示踪研究进展及展望

海底热液活动是海洋地质的前沿和热点研究领域之一,相比于深海热液活动较高的关注度和取得的较多的研究成 果,浅海热液活动研究一直处于“不温不火”的状态。但浅海热液系统一般靠近人类活动的区域,对人类生活具有一定的 影响,深入开展浅海热液活动的研究有助于深刻理解热液流体循环过程、热液成因机制及相关动力学过程。文章在简要介 绍国内外浅海热液活动地球化学研究的主要成果和最新进展的基础上,提出了今后对浅海热液活动的研究应主要集中于以 下几个方面：浅海热液流体及气体的来源;浅海热液系统模式及与构造环境的关系;浅海热液活动对人类的影响。     

蛇纹岩化对洋中脊超基性岩热液硫化物成矿的影响:来自青藏高原德尔尼铜矿床的启示

洋中脊超基性岩热液成矿系统通常与洋底核杂岩构造有关,多发育大型矿床,具有巨大的资源前景。然而,受大洋调查取样手段的限制,超基性岩蛇纹岩化对成矿的影响仍需进一步研究。德尔尼铜矿床是地质历史上该类矿床的典型案例,对于理解其成矿模式,以及大洋硫化物勘探具有指导意义。本文选取德尔尼铜矿床块状硫化物样品进行黄铁矿的S同位素分析,结果表明其δ³⁴S值主要分布在-0.4‰～+6.3‰。结合前人研究发现,形成于深部网脉状、条带状矿石中的δ³⁴S值为负值,而经历表层喷流和破碎作用的块状和角砾状矿石中的δ³⁴S值为正值,二者呈对称分布,这主要是由于还原条件下岩浆排气产生的SO_2和H_2S动态平衡并逐渐沉淀S^2-,表明蛇纹岩化提供的还原环境对热液系统演化产生了重要影响。然而,磁黄铁矿和矿床Ni的分布指示成矿物质中超基性岩的贡献较小,主要物质来源是洋中脊深部的基性岩浆,通过热液循环将物质运移至海底并喷流成矿。对比现今超基性岩赋矿的高温热液硫化物矿床,德尔尼铜矿床形成温度更低,代表了超基性岩赋矿热液硫化物中的中温端元,表明在距离拆离面一定距离(约2～4km)的位置也可能形成大型的热液硫化物矿床,这对于现今洋中脊热液硫化物勘探具有一定的指导意义。     

浅海热液活动的地球化学示踪研究进展及展望

海底热液活动是海洋地质的前沿和热点研究领域之一，相比于深海热液活动较高的关注度和取得的较多的研究成 果，浅海热液活动研究一直处于“不温不火”的状态。但浅海热液系统一般靠近人类活动的区域，对人类生活具有一定的 影响，深入开展浅海热液活动的研究有助于深刻理解热液流体循环过程、热液成因机制及相关动力学过程。文章在简要介 绍国内外浅海热液活动地球化学研究的主要成果和最新进展的基础上，提出了今后对浅海热液活动的研究应主要集中于以 下几个方面：浅海热液流体及气体的来源；浅海热液系统模式及与构造环境的关系；浅海热液活动对人类的影响。     

Intracellular and extracellular mineralization of a microbial community in the Edmond deep-sea vent field environment

Microbial biomineralization in submarine hydrothermal environments provides an insight into the formation of vent microfossils and the interactions between microbes, elements and minerals throughout the geological record. Here, we investigate microbial biomineralization of a deep-sea vent community in the Edmond vent field and provide ultrastructural evidence for the formation of microfossils and biogenic iron-rich minerals related to Archaea and Bacteria. Environmental scanning electron microscopy (ESEM) analysis shows that filamentous and spiral microbes are encrusted by a non-crystalline silica matrix and minor amounts of iron oxides. Examination by transmission electron microscopy (TEM) reveals acicular iron-rich particles and aggregates that occur either intracellularly or extracellularly. A culture-independent molecular phylogenetic analysis demonstrates a diverse range of Bacteria and Archaea, the majority of which are related to sulfur metabolism in the microbial mats. Both Archaea and Bacteria have undergone silicification, in a similar manner to microorganisms in some terrestrial hot springs and indicating that silicification may be driven by silica supersaturation and polymerization. Formation mechanisms of intracellular and extracellular iron oxides associated with microbes are discussed. These results enhance our understanding of microbial mineralization in extreme environments, which may be widespread in the Earth's modern and ancient hydrothermal vent fields.     

Geochemical Cycles of Bio-essential Elements on the Early Earth and Their Relationships to Origin of Life

Abstract: The bio-essential elements are demanded for the metabolic action of all living organisms. These elements are continuously supplied to biosphere through the elemental cycle on the surface Earth. The geochemical cycle of bio-essential elements was most likely different in the pre-biotic era (ca. 4.4 to 4.0 Ga) compared to the modern Earth. The difference was probably made by the absence of continents and biological mediation in the pre-biotic environments. Geochemical cycle models of bio-essential elements (P, B and Mo) on the pre-biotic Earth are proposed in this study, and these models are examined using available geochemical data.
The input flux of phosphorous in pre-biotic oceans was probably dominated by submarine hydrothermal activities associated with carbonatized oceanic crusts. Such input flux by submarine hydrothermal activities is not known in the present-day oceans, and probably a unique flux in the pre-biotic oceans. Boron chemistry of pre-biotic oceans was also controlled by submarine hydrothermal input flux. The Mo exchange between the pre-biotic ocean and lithosphere may have restricted only at the submarine hydrothermal areas. These suggest that the submarine hydrothermal discharging areas were only locations to obtain bio-essential elements for the earliest life. This model is consistent with the previously proposed model for hydrothermal origin of life.     

现代海底热液成矿作用研究现状及发展方向

现代海底热水成矿作用研究的重大进展表现在两个方面：（１）大批活动的和窒息的热液活动区和硫化物矿床在洋脊、岛弧、弧后盆地及板内火山活动中心等海底环境相继发现。在沉积物饥饿洋脊，矿床规模较小，Ｃｕ－Ｚｎ为主，沉积物覆盖洋脊，矿床规模巨大，Ｐｂ－Ｚｎ为主。弧后扩张或弧间裂陷盆地，形成Ｐｂ－Ｚｎ→Ｚｎ－Ｐｂ－Ｃｕ→Ｃｕ－Ｚｎ矿床谱系。岛弧环境硫化物矿床不具规模，板内火山活动中心以氧化物－硫化物矿化为特色。（２）现代海底热水成矿作用观察和研究为古代ＶＭＳ矿床成因研究提供了重要信息，对现有成矿理论产生重要影响。现代成矿观念强调：①海底成矿作用虽可产生于不同环境，但均与张裂断陷事件密切相关。矿床规模和分布特点受张裂速率制约；②成矿物质主体来源于热水循环的火山－沉积岩和下伏基底物质；③硫化物堆积发生于丘堤－烟囱联合构成的机构和结壳下部，通过开放空间的硫化物充填和先成矿石淋滤迁移来实现。④热液流体呈双扩散对流循环。现代海底热水成矿作用的未来研究方向可概括为强度方向和广度方向。广度研究将加大力度去发现新的矿床，强度研究将采用地球物理方法并配以必要的钻探，深入揭示矿床的三维结构和热液体系及成矿机制。     

现代海底热液微生物群落及其地质意义

现代海底黑烟囱周围生活着密集的生物群落,它们一般以黑烟囱喷口为中心向四周呈带状分布。热液生态系统的初级生产者嗜热细菌和古细菌,其初级能量来源于地球深部上升喷出流体提供的化学能,它们氧化热液中硫化物（如H2S、FeS）和甲烷获得能量,还原CO2制造有机物,而不依赖光合作用。作为食物链源头的细菌类和古细菌类与其他动物有2种生存关系:①直接作为其他动物的食物;②与其他动物之间的共生关系。这些嗜热微生物不仅依存于海底热液活动,同时在热液成矿作用中起着重要的作用。它们可能来源于地下深部生物圈,海底黑烟囱是研究深部生物圈的窗口,对其周围嗜热微生物的研究,对于理解生命起源和生物成矿都有重要的理论意义。     

Deep-sea smokers: windows to a subsurface biosphere?

Since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from "smoker" vents on the East Pacific Rise, the widely accepted upper temperature limit for life (based on pure culture data) has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees C. Many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees C. We have postulated not only higher temperatures than these (under deep-sea hydrostatic pressures), but also the existence of a biosphere subsurface to accessible seafloor vents. New geochemical information from the Endeavour Segment of the Juan de Fuca Ridge indicative of subsurface organic material caused us to re-examine both the literature on hyperthermophilic microorganisms cultured from deep-sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the Endeavour Segment. Here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of Endeavour smoker fluids, a case in keeping with rapidly evolving geophysical understanding of organic stability under deep-sea hydrothermal conditions.     

深海底热液活动研究热点

深海底热液活动是现代海洋地质科学研究的前沿热点, 我国这方面的研究工作刚刚开展, 亟需对现有研究成果进行总结。本文对海底热液活动的调查研究过程和现状进行了回顾, 重点分析了热液喷溢动力过程的理论研究成果, 从实测事件数据的研究成果中找出了影响热液柱的形态和分布的各种因素, 并对热液烟囱和极端温度微生物等海洋学研究热点进行了分析, 为深海热液活动调查和理论研究提供基础。      

“四深”微生物的地质作用——从气候环境变化到生态灾难

“四深”微生物是指深海、深地、深空和深时环境的微生物,特别是细菌、古菌、真菌、病毒等。人们对“四深”微生物的了解非常有限,是亟待突破的地球生物学前沿领域。“四深”微生物的研究对理解地球生命起源、界定生物圈的边界条件、促进地球科学与生命科学以及行星科学之间的交叉融合具有不可替代性的贡献。随着我国深海、深空、深地等重大工程计划的推进,一系列与“四深”微生物有关的前沿科学问题不断提出,包括地质微生物与气候环境的相互作用、地质微生物的生物安全与生态安全、地质微生物参与的隐匿地质过程等。特别是,“四深”环境活性氧自由基对微生物的影响、地质病毒对生物演化和地质过程的影响等前沿领域都亟待突破。活性氧自由基能对生物分子、细胞、组织和器官,乃至整个生物圈的演化以及微生物地质作用都产生重要影响。病毒引发了现代和近代诸多全球性疫情爆发,地质病毒则可能对生物的背景灭绝和大灭绝以及一些地质过程产生影响。     

大洋钻探对海底热液活动研究的贡献

大洋钻探为海底热液活动研究提供了大量数据资料和样品。在此基础上,通过研究流体-沉积物／岩石相互作用,热、物质通量和流体流动,分析构造对海底热液活动的控制作用,使人们对海底热液循环有所了解,并对深部热液成因石油的特征,海底热液沉积物的空间结构和物质组成,以及深部生物与海底热液活动的关系有了一些认识。未来通过实施IODP,海底热液活动研究将会取得更多新的成果。     

地质微生物学及其发展方向

地质微生物学是在20世纪末发展起来的新的地学分支,主要研究地质环境中的微生物活动过程及其形成的各种地质地球化学记录。通过对现代及地质历史上的各种地质环境,包括极高温,高压,极端酸性,碱性,高盐度,极高放射性,地球深部等环境中微生物的生存和演化,及其和地质环境的相互作用而形成的各种地球化学记录的研究,探讨微生物在过去、现在和将来对生命活动最重要的元素(C,H,O,N,S,Fe等)在全球或局部尺度上的循环作用,从而对微生物的风化作用、成矿作用、地质环境下的微生物生态链及其环境的研究提供重要的科学证据。微生物与矿物的相互作用、极端环境下的微生物和生态及分子地质微生物学是当前地质微生物学研究的重要方向。     

矿物光电子能量在地球早期生命起源与进化中的作用

地球早期生命起源的第一步是合成简单的有机化合物,但合成有机物所需能量来源问题长期困扰着学术界。早期地球上丰富的硫化物半导体矿物可将太阳光子转化为光电子,提供持续的能量来源。也正是由于矿物光电子能量较高,在非生物途径合成小分子有机物方面具有优势。其中半导体矿物自然硫转化太阳能产生的光电子能量,是目前所发现的最高的矿物光电子能量,不仅能直接还原CO₂分子为甲酸物质,还可催化其他生命基础物质的合成。在全球陆地系统中暴露在阳光下的岩石/土壤表面普遍被一层铁锰氧化物“矿物膜”所覆盖,光照下含半导体矿物水钠锰矿的“矿物膜”产生原位、灵敏、长效的光电流,显示出优异的光电效应。生物光合作用中心Mn₄CaO₅在裂解水产氧过程中产生成分和结构类似水钠锰矿的结构中间体,地球早期“矿物膜”中水钠锰矿可能促进了锰簇Mn₄CaO₅与生物光合作用的起源与进化。早期地球半导体矿物为生命起源基本物质的合成提供直接能量来源,矿物光电子能量在地球早期生命起源与进化中起到了重要作用。     

矿物光电子能量在地球早期生命起源与进化中的作用

地球早期生命起源的第一步是合成简单的有机化合物，但合成有机物所需能量来源问题长期困扰着学术界。早期地球上丰富的硫化物半导体矿物可将太阳光子转化为光电子，提供持续的能量来源。也正是由于矿物光电子能量较高，在非生物途径合成小分子有机物方面具有优势。其中半导体矿物自然硫转化太阳能产生的光电子能量，是目前所发现的最高的矿物光电子能量，不仅能直接还原CO2分子为甲酸物质，还可催化其他生命基础物质的合成。在全球陆地系统中暴露在阳光下的岩石/土壤表面普遍被一层铁锰氧化物“矿物膜”所覆盖，光照下含半导体矿物水钠锰矿的“矿物膜”产生原位、灵敏、长效的光电流，显示出优异的光电效应。生物光合作用中心Mn4CaO5在裂解水产氧过程中产生成分和结构类似水钠锰矿的结构中间体，地球早期“矿物膜”中水钠锰矿可能促进了锰簇Mn4CaO5与生物光合作用的起源与进化。早期地球半导体矿物为生命起源基本物质的合成提供直接能量来源，矿物光电子能量在地球早期生命起源与进化中起到了重要作用。