Nanoscale Anatomy of Iron‐Silica Self‐Organized Membranes: Implications for Prebiotic Chemistry

Abstract

Iron-silica self-organized membranes,s o-called chemical gardens, behave as fuel cells and catalyze the formation of amino/carboxylic acids and RNAn ucleobases from organics that were available on early Earth. Despite their relevance for prebiotic chemistry,l ittle is knowna bout their structure and mineralogy at the nanoscale.S tudied here are focused ion beam milled sections of iron-silica membranes, grown from synthetic and natural, alkaline,s erpentinizationderived fluids thought to be widespread on early Earth. Electron microscopys hows they comprise amorphous silica and iron nanoparticles of large surface areas and inter/ intraparticle porosities.T heir construction resembles that of ah eterogeneous catalyst, but they can also exhibit ab ilayer structure.Surface-area measurements suggest that membranes grown from natural waters have even higher catalytic potential. Considering their geochemically plausible precipitation in the early hydrothermal systems where abiotic organics were produced, iron-silica membranes might have assisted the generation and organization of the first biologically relevant organics.

Iron‐Silicate Chemical Garden Morphology and Silicate Reactivity with Alpha‐Keto Acids

“…[25] Though it is thought that iron-silicate chemical gardens contain iron oxyhydroxides, these minerals are proposed to be present mainly on the inner layers of the structure, with a silica layer on the outside. [17,22] Previous prebiotic chemistry studies with iron-silicate chemical gardens observed different suites of organic products in the interior of the chemical garden than in the outer silicate solution. [16] The membrane itself is expected to have a significantly higher reactivity in comparison to that of the silicate in solution.…”

“…[8,[18][19][20][21] Chemical garden precipitates in the ferrous chloride/ sodium silicate reaction system exhibit a bilayer structure, and are composed of amorphous silica and iron oxyhydroxides. [22] Notably, chemical gardens have been found to have highly reactive nanostructural properties. [22] The specific iron oxyhydroxide minerals precipitated in iron-silicate chemical gardens could vary depending on the experimental conditions, but could include green rust, a highly reactive mineral which may have driven relevant prebiotic reactions in alkaline hydrothermal systems.…”

“…[22] Notably, chemical gardens have been found to have highly reactive nanostructural properties. [22] The specific iron oxyhydroxide minerals precipitated in iron-silicate chemical gardens could vary depending on the experimental conditions, but could include green rust, a highly reactive mineral which may have driven relevant prebiotic reactions in alkaline hydrothermal systems. [23] Previously, we have explored the impact of phosphate or amino acids on iron-silicate chemical gardens; [2,15] we observed that increasing concentrations of these additives affected the visual morphology (and in the case of amino acids, the microscale properties) of the chemical garden, but no clear evidence for reactivity was observed.…”

“…Additionally, glyoxylic acid and pyruvic acid can form various protometabolic cycle intermediates under mild and geologically reasonable conditions. [28] Previous work demonstrating reactions of formamide with metal-silicate (including iron-silicate) chemical gardens as mediators, [16] combined with previous work showing potential iron oxyhydroxide content within iron-silicate chemical gardens [22] and iron oxyhydroxide-driven reactions of pyruvate and glyoxylate, [25] led to interest in testing whether an iron-silicate chemical garden system could drive the alpha-keto acid reaction network in the same way as a precipitated mineral. Here, we tested the growth of iron-silicate chemical gardens in the presence of either pyruvic or glyoxylic acid as well as ammonia, to determine whether the organics affected the chemical garden growth, and whether these chemical garden systems could impact the solution phase chemistry as observed by NMR.…”

The “Water Problem”(sic), the Illusory Pond and Life’s Submarine Emergence—A Review

“…Either way, many of the research challenges for the hypothesized role(s) of fougerite—dosed with various trace elements and anions—are similar. Such research addressing the submarine acid v. alkaline milieu calls for the further employment of tried-and-tested microfluidic and nano-crystallographic techniques [ 192 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 224 , 254 , 296 , 297 , 298 , 299 , 300 , 301 , 302 , 310 , 327 , 328 , 329 , 330 , 331 , 332 , 333 , 334 , 335 , 336 , 337 , 338 ]. We enumerate some possible developments from, expectations of, and tests for, the AVT below:…”