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

Abstract

Iron‐silica self‐organized membranes, so‐called chemical gardens, behave as fuel cells and catalyze the formation of amino/carboxylic acids and RNA nucleobases from organics that were available on early Earth. Despite their relevance for prebiotic chemistry, little is known about their structure and mineralogy at the nanoscale. Studied here are focused ion beam milled sections of iron‐silica membranes, grown from synthetic and natural, alkaline, serpentinization‐derived fluids thought to be widespread on early Earth. Electron microscopy shows they comprise amorphous silica and iron nanoparticles of large surface areas and inter/intraparticle porosities. Their construction resembles that of a heterogeneous catalyst, but they can also exhibit a bilayer 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.

Tubular Structures of Calcium Carbonate: Formation, Characterization, and Implications in Natural Mineral Environments

“…Notably, previous studies on silica gardens reported that metal cations were removed from the internal solution by incorporation into the inner surface of the membrane through precipitation as hydroxides. [3,10,[41][42][43][44] However, due to the higher solubility of calcium hydroxide compared to other metal cations (Table 1), it seems safe to conclude that precipitation of Ca(OH) 2 does not play a significant role in the evolution of calcium carbonatebased chemical gardens as prepared in the present work (a 2À groups in different mineral phases as follows: calcite: 155/280, 713, and 1086 cm À 1 , [55] vaterite: 300, 740/750, and 1080/1090 cm À 1 , [56] gaylussite: 165/255, 718, and 1071 cm À 1 . [57] b) IR spectra collected from CaCO 3 tubes at distinct times of aging (as indicated) after grinding to a fine powder.…”

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

“…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 iron‐silicate chemical garden system in particular – where precipitates grow from a ferrous chloride salt submerged into a sodium silicate solution – is relevant for prebiotic chemistry since Earth's early oceans were rich in Fe 2+ , and hydrothermal vents could have vented silica (SiO 2 (aq)) into the early oceans, forming iron silicate (e. g. greenalite ((Fe 2+ /Fe 3+ ) 2–3 Si 2 O 5 (OH) 4 )) and iron oxyhydroxide minerals (e. g. ferrous/ferric hydroxide, and/or green rust) [8,18–21] . 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] .…”

“…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 [23] …”

“…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.…”