The Origin of Abiotic Hydrocarbons in Seafloor Serpentinization Systems

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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.