Research Article Iron-Sulfide-Bearing Chimneys as Potential Catalytic Energy Traps at Life’s Emergence Randall E. Mielke, Kirtland J. Robinson, Lauren M. White, Shawn E. McGlynn, * Kavan McEachern, Rohit Bhartia, Isik Kanik, and Michael J. Russell Abstract The concept that life emerged where alkaline hydrogen-bearing submarine hot springs exhaled into the most ancient acidulous ocean was used as a working hypothesis to investigate the nature of precipitate membranes. Alkaline solutions at 25–70°C and pH between 8 and 12, bearing HS - – silicate, were injected slowly into visi-jars containing ferrous chloride to partially simulate the early ocean on this or any other wet and icy, geologically active rocky world. Dependent on pH and sulfide content, fine tubular chimneys and geodal bubbles were generated with semipermeable walls 4–100 lm thick that comprised radial platelets of nanometric mackinawite [FeS] – ferrous hydroxide [ *Fe(OH) 2 ], accompanied by silica and, at the higher temperature, greigite [Fe 3 S 4 ]. Within the chimney walls, these platelets define a myriad of micropores. The interior walls of the chimneys host iron sulfide framboids, while, in cases where the alkaline solution has a pH > 11 or relatively low sulfide content, their exteriors exhibit radial flanges with a spacing of *4 lm that comprise microdendrites of ferrous hydroxide. We speculate that this pattern results from outward and inward radial flow through the chimney walls. The outer Fe(OH) 2 flanges perhaps precipitate where the highly alkaline flow meets the ambient ferrous iron-bearing fluid, while the intervening troughs signal where the acidulous iron-bearing solutions could gain access to the sulfidic and alkaline interior of the chimneys, thereby leading to the precipitation of the framboids. Addition of soluble pentameric peptides enhances membrane durability and accentuates the crenulations on the chimney exteriors. These dynamic patterns may have implications for acid-base catalysis and the natural proton motive force acting through the matrix of the porous inorganic membrane. Thus, within such membranes, steep redox and pH gradients would bear across the nanometric platelets and separate the two counter-flowing solutions, a condition that may have led to the onset of an autotrophic metabolism through the reduction of carbon dioxide. Key Words: Dendrites—Framboids—Greigite—Hydrothermal chimneys—Mackinawite—Origin of life. Astro- biology 11, xxx–xxx. 1. Introduction B ecause there is no autonomous metabolism outside of cells, compartmentation of some kind has been recognized as essential to the emergence of life (Traube, 1867; Leduc, 1911; Cairns-Smith, 1982; Russell et al., 1989; Cartwright et al., 2002; Martin and Russell, 2003; Koonin and Martin, 2005; Baaske et al., 2007; Allen, 2010). That such compartments must have been inorganic is forced on us by the difficulty of imagining how appropriate organic molecules from disparate sources could be selected and continuously delivered to the site of the emergence of autogenic metabolism in an atmosphere domi- nated by CO 2 and N 2 on a turbulent water world subject to high tides, hard UV, and cosmic radiation (Turcotte et al., 1977; Canuto et al., 1982; Wood et al., 1990, 2006; Kasting et al., 1993; Bahcall et al., 2001; Elkins-Tanton, 2008; Russell and Kanik, 2010). In the alkaline hydrothermal (chemiosmotic) theory for the emergence of life, such compartments were considered to have comprised iron monosulfide botryoids, geodes, and chimneys comparable to those discovered at the Silvermines and Tynagh base metal sulfide deposits in the Lower Carboniferous rocks of Ireland (Larter et al., 1981; Boyce et al., 1983; Banks, 1985; Russell et al., 1989, 1994). However, the study of these and other mineralizing systems has taught us that the ratio between hydrothermal metal sulfide ore deposits and hydrothermal convection cells that could potentially generate such deposits was remarkably low and depended not only on conditions at the potential site of Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California. *And the NASA NAI Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana. ASTROBIOLOGY Volume 11, Number 10, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089/ast.2011.0667 1 AST-2011-0667-ver9-Mielke_2P.3d 11/21/11 4:34pm Page 1