Characterization of Iron–Phosphate–Silicate Chemical Garden Structures

Abstract

Chemical gardens form when ferrous chloride hydrate seed crystals are added or concentrated solutions are injected into solutions of sodium silicate and potassium phosphate. Various precipitation morphologies are observed depending on silicate and phosphate concentrations, including hollow plumes, bulbs, and tubes. The growth of precipitates is controlled by the internal osmotic pressure, fluid buoyancy, and membrane strength. Additionally, rapid bubble-led growth is observed when silicate concentrations are high. ESEM/EDX analysis confirms compositional gradients within the membranes, and voltage measurements across the membranes during growth show a final potential of around 150-200 mV, indicating that electrochemical gradients are maintained across the membranes as growth proceeds. The characterization of chemical gardens formed with iron, silicate, and phosphate, three important components of an early earth prebiotic hydrothermal system, can help us understand the properties of analogous structures that likely formed at submarine alkaline hydrothermal vents in the Hadean-structures offering themselves as the hatchery of life.

From Chemical Gardens to Chemobrionics

“…For example, in the microbead study noted above it was observed that with decreasing growth velocities the tube changed from a smooth to a brick-like texture, and bead-mediated tube growth occurred only if the product of bead radius and loading concentration exceeded a critical value. 34 There are many other examples of morphology transitions in the chemical-garden literature (e.g., Leduc, 12 Barge et al, 37 Haudin et al, 38 etc.) and the precise causes of these changes are still only partially understood.…”

“…Injection methods have induced chemical gardens to grow directly around one electrode placed near the injection point, thus immersing one electrode in the inner solution. 37 In addition, inorganic membranes have been forced to grow from pellet dissolution in an open cylindrical morphology so that an electrode could be placed inside the structure. 130 Another technique is to produce precipitate membranes between different aqueous solutions by introducing the two solutions on either side of a porous dialysis membrane template in a fuel-cell setup so that the precipitate only forms on this template.…”

Genericity of confined chemical garden patterns with regard to changes in the reactants

“…9 They are model systems to understand properties of self-organized materials [10][11][12][13][14][15][16][17][18] and fuel cells 19 and to study possible mechanisms for the origin of life. 20,21 A large variety of water-soluble metallic salts can display growths of similar tubular structures. However, the rate of growth, the size and the shape of the excrescences may vary significantly depending on the precipitating cation of the metallic salt and the concentration and the chemical composition of the alkaline solution.…”

Simulating a Model of Metabolic Closure

“…However, if we are concerned with events that need to have happened only once in many millions of years then we can consider vastly lower probabilities to be reasonable for the appearance of the first selfmaintaining system. 7 In a small-enough volume the chance appearance of a few molecules of a seed intermediate such as STU (resulting perhaps from collisions at very unlikely velocities between S, T, and U molecules) could be 6 In their recent paper on osmotic structures resembling Leduc's osmotic gardens, Barge et al (2012) do not give estimates of the internal volumes of their structures. They have informed us (Barge, personal communication, 8 March 2012) that although these volumes are very difficult to estimate with any accuracy they are certainly orders of magnitude larger than the volumes we are considering here.…”

“…For many years his work was believed to have little relevance to life, but it is now being rehabilitated in efforts to recreate the conditions that led to the emergence of life at the end of the Hadean aeon (Barge et al 2012). However, despite this and other current attempts to create artificial life, most theories of life itself can be traced to the pioneering work of Schrödinger (1944).…”