The Origin of Abiotic Hydrocarbons in Seafloor Serpentinization Systems

几十年来，地球上形成生命最初组成部分的高链碳氢化合物的起源和合成一直是一个主要的研究课题。海底的热液喷口被认为是最有可能形成生命的地方之一，但到目前为止，构建细胞或培育早期生命形式所需的长链和复杂碳氢化合物的机制还只是推测。这项研究建立在加勒比海开曼隆起的超基性热液喷口的有趣的初步数据基础上，这些数据表明，该地区热液喷口流出的大部分碳氢化合物不是通过生物过程产生的，而是通过非生物过程产生的（即通过水岩相互作用和其他不涉及生物体及其副产品的物理过程）。研究前提是，热液体系喷口流体中发现的非生物甲烷和长链烃是在含橄榄石的次生流体包裹体中形成的，受超镁铁质岩石蚀变反应的支配，这些次生流体包裹体在矿物宿主的后续蚀变过程中被浸出。这是一个惊人的、非常规的、新颖的假设，如果得到证实，将改变我们对热液喷口系统地下有机碳化合物形成的理解。为了验证这一假设，我们将分析来自不同海底超基性热液系统的基岩天然样品中次生流体包裹体中低分子量碳氢化合物的丰度和碳同位素组成。采用气相色谱-同位素比质谱法分析流体包裹体的流体和气体含量。利用扫描电子显微镜上的x射线色散光谱和拉曼共聚焦光谱对流体包裹体中形成的矿物进行纳米级表征，将限制有机化合物合成过程中调节化学环境的流体-岩石相互作用。热力学模型和计算将用于帮助解释流体包裹体中的流体-矿物平衡和有机合成。这项工作的更广泛影响包括对研究生和本科生进行重要的学生培训，波多黎各大学邀请本科生实习生在夏季期间到主要研究人员的伍兹霍尔热液实验室工作三个月。这些学生将体验到完整的研究经验，从选择项目到使用最先进的仪器收集分析数据，再到数据分析和结果展示。将在当地学校系统开展更多的教育推广活动，包括访问K-12教室，并在当地一所独立高中开设为期一天的关于热液喷口的短期课程。

The origin and synthesis of higher chain hydrocarbons on Earth that formed the first components of life have been a major topic of research for decades. Hydrothermal vents on the seafloor have been proposed as one of the most likely places where life could have formed, but up to now, mechanisms by which long-chain and complex hydrocarbons that would be required to build a cell or nurture incipient life forms have only been speculated upon. This research builds off intriguing preliminary data from ultra-mafic hydrothermal vents on the Cayman Rise in the Caribbean Sea that indicate a significant proportion of the hydrocarbons coming out of hydrothermal vents in this region is generated not by biological processes, but abiotically (i.e., via water-rock interaction and other physical processes that do not involve living organisms or their byproducts). The research premise is that abiotic methane and longer chain hydrocarbons found in vent fluids in hydrothermal systems, dominated by the alteration reactions of ultramafic rocks, are formed in olivine-hosted secondary fluid inclusions that are leached during subsequent alteration of the mineral host. This is a startling, unconventional, and novel hypothesis that, if validated, will transform how we understand organic carbon compound formation in the subsurface of hydrothermal vent systems. To test this hypothesis, the abundance and carbon isotopic composition of low molecular weight hydrocarbons in secondary fluid inclusion in natural samples of basement rocks from a variety of seafloor ultra-mafic hosted hydrothermal systems will be analyzed. The fluid and gas contents of the fluid inclusions will be analyzed using gas chromatography-isotope ratio mass spectrometry. Cutting-edge nanometer-scale characterization of minerals formed in the fluid inclusions using X-ray dispersive spectroscopy on a scanning electron microscope and Raman confocal spectroscopy will allow constraints to be placed on fluid-rock interactions that regulate the chemical environment during organic compound synthesis. Thermodynamic models and calculations will be used to aid in the interpretation of the fluid-mineral equilibria and organic synthesis in the fluid inclusions. Broader impacts of the work include significant student training at the graduate and undergraduate level, with undergraduate interns being invited from the University of Puerto Rico to come work at the Woods Hole hydrothermal laboratory of the principle investigators for three months during the summer. These students will experience the full-bodied research experience from the selection of a project through collecting analytical data using state-of-the-art instrumentation to data analysis and presentation of results. Additional educational outreach will be carried out in the local school system via visits to K-12 classrooms and the development of a one-day short course on hydrothermal vents to be given at a local independent high school.