演題者：Ellie Hara (University of Colorado Boulder)
講演タイトル：Cyanide dynamics in serpentinizing systems: implications for prebiotic chemistry
2/20 (火) 10:00-11:30 JST @Zoom（Zoom IDとパスワード情報についてアウトリーチ担当の冬月までsebastian.d_at_sophia.ac.jpまでご連絡ください。）
While cyanide has been considered essential in some origin of life (OoL) scenarios, cyanide is notably absent from the alkaline hydrothermal vent theory (AVT) which postulates that life started from a proto-metabolism powered by a pH, temperature and chemical gradients. This thesis investigates cyanide storage and availability in subsurface serpentinites and how such interactions could contribute to further developing existing theories on the OoL. It has been proposed that cyanide would concentrate in the Hadean ocean as ferrocyanide complexes ([Fe(CN)6]4-). These complexes form spontaneously when cyanide comes into contact with Fe(II), which is thought to have been present in the early Earth’s ocean due to buffering with mafic and ultramafic rocks. However, once cyanide is locked into this complex it is unable to react. First, I demonstrated that in alkaline conditions, carbon monoxide can undergo a ligand exchange with cyanide in ferrocyanide. This process provides a facile mechanism for cyanide release that could provide continual sources of cyanide should carbon monoxide and ferrocyanide be available. I then tested how cyanide would be stored in ultramafic rock-hosted systems with abundant reactive iron minerals such as ferrous brucite. I found that cyanide was stored not only as aqueous ferrocyanide but also on the brucite mineral surface as iron-cyanide complexes. This suggests that ferroan brucite and by extension other iron bearing minerals commonly found in serpentinites may serve as a substantial and currently overlooked cyanide reservoir on early Earth. Finally, I assessed FeNi brucite’s ability to facilitate cyanide synthesis at a low-temperature and low-pressure environment. While no cyanide synthesis occurred, FeNi brucite did demonstrate the ability to facilitate methane oxidation to methanol when it was reacted with nitrite and methane at 70°C. This is the first known example of mineral-facilitated methane oxidation at low temperatures and pressures. Through this thesis, I have demonstrated how cyanide could be stored and released in subsurface serpentinites, along with demonstrating that brucite, a common component of serpentinites, can facilitate methane oxidation. I propose that these findings provide sufficient evidence that cyanide is a plausible and important reagent that should be integrated into the existing AVT.
Ellie Hara is a geochemist with a focus on mineral-mediated carbon and nitrogen redox reactions to interrogate the role of minerals in the origins of life on Earth. She holds a B.S. in Geology from University of Southern California and earned a PhD in Geology from University of Colorado Boulder under the direction of Prof. Alexis Templeton.