Search

The osmotic rupture of a cell, its osmotic lysis or cytolysis, is a phenomenon that active biological cell volume regulation mechanisms have evolved in the cell membrane to avoid. How then, at the origin of life, did the first protocells survive prior to such active processes? The pores of alkaline hydrothermal vents in the oceans form natural nanoreactors in which osmosis across a mineral membrane plays a fundamental role. Here, we discuss the dynamics of lysis and its avoidance in an abiotic system without any active mechanisms, reliant upon self‐organized behaviour, similar to the first self‐organized mineral membranes within which complex chemistry may have begun to evolve into metabolism. We show that such mineral nanoreactors could function as protocells without exploding because their self‐organized dynamics have a large regime in parameter space where osmotic lysis does not occur and homeostasis is possible. The beginnings of Darwinian evolution in proto‐biochemistry must have involved the survival of protocells that remained within such a safe regime. [ABSTRACT FROM AUTHOR]

The self‐organization of complex solids can create patterns extending hierarchically from the atomic to the macroscopic scale. A frequently studied model is the chemical garden system which consists of life‐like precipitate shapes. In this study, we examine the thin walls of chemical gardens using microfluidic devices that yield linear Ni(OH)2 precipitate membranes. We observe distinct light‐scattering patterns within the compositionally pure membranes, including disorganized spots, dendrites, and parallel bands. The bands are tilted with respect to the membrane axis and their spacing (20–100 μm) increases with increasing flow rates. Scanning electron microscopy reveals that the bands consist of submicron particles embedded in a denser material and these particles are also found in the reactant stream. We propose that dendrites and bands arise from the attachment of solution‐borne nanoparticles. The bands are generated by particle‐aggregation zones moving upstream along the slowly advancing membrane surface. The speed of the aggregation zones is proportional to the band distance and defines the system's dispersion relation. This speed‐wavelength dependence and the flow‐opposing motion of the aggregation zones are likely caused by low particle concentrations in the wake of the zones that only slowly recover due to Brownian motion and particle nucleation. [ABSTRACT FROM AUTHOR]

Considering the growing importance of the field of chemobrionics since the term was coined in 2015 and the increase in the number of published papers, it has become necessary to catalogue all the papers published to date. Here, we present the chemobrionics database, which lists all the chemical gardens synthesised according to their anion, cation and experimental protocol. The aim of this database is to encourage the study and dissemination of chemical gardens in order to find new experimental avenues in the field of chemobrionics. As this is such a fruitful field, the database is continuously updated. [ABSTRACT FROM AUTHOR]

Originating from the concept of classical chemical gardens, a new field coined 'chemobrionics' has recently emerged. In the present work, two chemobrionic systems grown from a hydrogel/liquid interface at different time scales (for 1, 7, 14 or 28 days) were investigated, i. e., a calcium‐based hydrogel with a phosphate counterion solution (Ca‐gel) and a phosphate‐based hydrogel with a calcium counterion solution (P‐gel). The initial pH changes of the systems were investigated, and the obtained tubular structures were studied using optical microscopy, SEM, AFM, PXRD and TGA. One of the important findings is that the tubes obtained in the Ca‐gel system were straight and long, which could be explained by the larger pH difference observed between the hydrogel and the counterion solution in this system (ΔpH∼2.1) compared to the P‐gel system (ΔpH∼0). The Ca‐gel structures remained overall more amorphous even though increased crystallinity was observed in both systems with increased time spent in counterion solution. Both systems contained hydroxyapatite phases, with additional calcite phases observed for the P‐gel structures and traces of κ‐carrageenan for the Ca‐gel structures. Our study provides a promising method for controlling tubular macrostructures through adjusting the reaction conditions such as maturation time and pH. [ABSTRACT FROM AUTHOR]

Manganese (Mn) oxides are ubiquitous in nature and occur as both biological and abiotic minerals, but empirically distinguishing between the two remains a problem. Recently, electron paramagnetic resonance (EPR) spectroscopy has been proposed for this purpose. It has been reported that biogenic Mn oxides display a characteristic narrow linewidth in contrast to their pure abiotic counterparts, which is explained in part by the large number of cation vacancies that form within the layers of biogenic Mn oxides. It was, therefore, proposed that natural samples that display a narrow EPR linewidth, ΔHpp < 580G, could be assigned to a biogenic origin. However, in poorly crystalline or amorphous solids, both dipolar broadening and exchange narrowing simultaneously determine the linewidth. Considering that the spectral linewidth is governed by several mechanisms, this approach might be questioned. In this study, we report synthetic chemical garden Mn oxide biomorphs that exhibit both morphologically life-like structures and narrow EPR linewidths, suggesting that a narrow EPR line may be unsuitable as reliable evidence in assessment of biogenicity. [ABSTRACT FROM AUTHOR]

[Display omitted] Chemical gardens are tubular inorganic structures exhibiting complex morphologies and interesting dynamic properties upon ageing, with coupled diffusion and precipitation processes keeping the systems out of equilibrium for extended periods of time. Calcium-based silica gardens should comprise membranes that mimic the microstructures occurring in ordinary Portland cement and/or silicate gel layers observed around highly reactive siliceous aggregates in concrete. Single macroscopic silica garden tubes were prepared using pellets of calcium chloride and sodium silicate solution. The composition of the mineralized tubes was characterized by means of various ex-situ techniques, while time-dependent monitoring of the solutions enclosed by and surrounding the membrane gives insight into the spatiotemporal distribution of the different ionic species. The latter data reflect transport properties and precipitation reactions in the system, thus allowing its complex dynamic behavior to be resolved. The results show that in contrast to the previously studied cases of iron- and cobalt-based silica gardens, the formed calcium silicate membrane is homogeneous and ultimately becomes impermeable to all species except water, hydroxide and sodium ions, resulting in the permanent conservation of considerable concentration gradients across the membrane. The insights gained in this work may help elucidate the nature and mechanisms of ion diffusion in Portland cements and concrete, especially those occurring during initial hydration of calcium silicates and the so-called alkali-silica reaction (ASR), one of the major concrete deterioration mechanisms causing serious problems with respect to the durability of concrete and the restricted use of many potential sources of raw materials. [ABSTRACT FROM AUTHOR]

Addition of CaCl2 into a highly alkaline phosphate buffer results in the generation of submerged transparent chemobrionic bubbles mimicking jellyfish that are stable and malleable. A compartmentalized O2‐generating reaction triggered the growth of regular vertical chemical gardens from the bubble through a gas micro‐rocket propelled mechanism. The bubbles can mechanically separate to yield two daughter bubbles in a process reminiscent of cytokinesis or natural jellyfish regeneration, and then re‐grow through new injection of CaCl2. Finally, loading of E. coli bacteria genetically engineered to exert green fluorescence inside the bubbles was demonstrated in a biomimetic analogue of "symbiosis". [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the biomimetic precipitation processes that follow the chemical-garden reaction of brines of CaCl2 and sulfate salts with silicate in alkaline conditions under a Mars-type CO2-rich atmosphere. We characterize the precipitates with environmental scanning electron microscope micrography, micro-Raman spectroscopy, and X-ray diffractometry. Our analysis results indicate that self-assembled carbonate structures formed with calcium chloride can have vesicular and filamentary features. With magnesium sulfate as a reactant a tentative assignment with Raman spectroscopy indicates the presence of natroxalate in the precipitate. These morphologies and compounds appear through rapid sequestration of atmospheric CO2 by alkaline solutions of silica and salts. [ABSTRACT FROM AUTHOR]

Chemical garden (CG) from copper(II) sulfate, nitrate and chloride (CG CuSO4, CG Cu(NO3)2, CG CuCl2) were grown, and characterized from the structural and compositional point of view by using scanning electron microscopy, X‐ray powder diffraction, elemental analysis, thermogravimetric analysis coupled with mass spectrometry, and DR (diffuse reflectance) UV‐Vis‐NIR spectroscopy. The main crystalline phases, controlled by the anion of the starting salt, were brochantite and kobyashevite for CG CuSO4, gerhardtite, rouaite and anthonyite for CG Cu(NO3)2, and atacamite for CG CuCl2. The materials were then exposed to ammonia vapors to test the effectiveness of their entrapping property. All materials proved to be very efficient and rapid in the uptake of ammonia, which invariably results in the formation of a Cu(II)/NH3 complex. However, after a few tens of minutes, CG Cu(NO3)2 and CG CuCl2 release water and get wet, thereby resulting unsuitable for applications. Only CG CuSO4 remains dry for at least 25 hours. This makes it a valid candidate for building devices for trapping ammonia, and possibly other gases capable of interacting with Cu(II). The entrapment of ammonia by this material was also characterized by 1H and 29Si MAS‐NMR XAS spectroscopies. [ABSTRACT FROM AUTHOR]

Chemical gardens are self‐assembled tubular precipitates formed by a combination of osmosis, buoyancy, and chemical reaction, and thought to be capable of catalyzing prebiotic condensation reactions. In many cases, the tube wall is a bilayer structure with the properties of a diaphragm and/or a membrane. The interest in silica gardens as microreactors for materials science has increased over the past decade because of their ability to create long‐lasting electrochemical potential. In this study, we have grown single macroscopic tubes based on calcium carbonate and monitored their time‐dependent behavior by in situ measurements of pH, ionic concentrations inside and outside the tubular membranes, and electrochemical potential differences. Furthermore, we have characterized the composition and structure of the tubular membranes by using ex situ X‐ray diffraction, infrared and Raman spectroscopy, as well as scanning electron microscopy. Based on the collected data, we propose a physicochemical mechanism for the formation and ripening of these peculiar CaCO3 structures and compare the results to those of other chemical garden systems. We find that the wall of the macroscopic calcium carbonate tubes is a bilayer of texturally distinct but compositionally similar calcite showing high crystallinity. The resulting high density of the material prevents macroscopic calcium carbonate gardens from developing significant electrochemical potential differences. In the light of these observations, possible implications in materials science and prebiotic (geo)chemistry are discussed. [ABSTRACT FROM AUTHOR]

In this study, a gel/liquid interface is utilized for growing a new (calcium‐phosphate)/carrageenan garden. The hydrogels are made from carrageenan loaded with either sodium phosphate or calcium chloride, while the interfaced solution contains a source of the salt not used in the hydrogels (i. e. the sodium‐phosphate hydrogel with the calcium‐chloride solution and vice versa). The physical and chemical properties of tubes grown from both systems of the same amount of carrageenan have been reported. Interestingly, when varying the amounts of carrageenan (and thus controlling the stiffness of the phosphate‐hydrogel system), it is possible to control the thickness and height of the tubes. [ABSTRACT FROM AUTHOR]

The aim of this study is to highlight novel CuS‐carrageenan nanocomposites grown from the interface between sulfide solutions (liquid phases) and Cu‐ι‐carrageenan gels. Several parameters including pH, copper and carrageenan concentration of the hydrogel that influence the growth of the nanocomposite have been examined. The most effective parameter is the initial pH of the liquid phase, hence, three growing samples at pH 7, 10 and 13 were selected for further studies and referred as LPH7, LPH10 and LPH13. Three CuS‐carrageenan nanocomposites obtained from the three pH conditions were purified and examined in detail using several characterization techniques such as X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The structure, composition, properties as well as the growth mechanism of the nanocomposite have been studied. Additionally, the electrical conductivity of the nanocomposite was exploited to be used as a sensor of relative humidity and temperature. [ABSTRACT FROM AUTHOR]

Chemical gardens are characterised by the self‐assembly of mineralised abiotic architectures. Utilising the fundamental building blocks of bone mineral, namely calcium and orthophosphate ions, chemical gardens that recapitulate microstructural and compositional features of hard tissue can be grown. Interplay between orthophosphate and pyrophosphate species is highly relevant to natural mineral deposition processes, though this has yet to be explored in the context of generating biologically relevant chemical gardens. Here, tubular calcium orthophosphate‐pyrophosphate chemical gardens were grown from the interface between calcium loaded hydrogels ([Ca2+]=1 M) layered with different orthophosphate‐pyrophosphate solutions ([Pi]+[PPi]=0.7 M). We determine the effect of solution pyrophosphate content on chemical garden morphology and growth rate. Extracted structures were analysed by means of powder X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and X‐ray fluorescence spectroscopy (XRF), revealing orthophosphate‐pyrophosphate solution dependent differences in precipitated mineral crystallinity, composition and microstructure, respectively. Lastly, the potential application of the structures is discussed in the context of tissue engineering and regenerative medicine. [ABSTRACT FROM AUTHOR]

Vertical tube‐shaped iron‐oxide accumulations, named rusticles, obtained from the wrecks of the HMAS Sydney II and the HSK Kormoran at 2480 m ocean depth were chemically analysed along with surrounding seawater. Rusticles consisted of a porous aggregation of iron oxides and high levels of toxic metals and metalloids. Their growth rate is approximately 1 cm per year, predominantly over the areas of the hulls that remained underwater during their service years. A connection between the quality of antifouling paints and rusticle growth and composition was found. A mechanism explaining the formation of rusticles is proposed based on corrosion of carbon steel in deep‐seawater, water chemistry, surface complexation of iron oxides and chemical garden formation mechanisms. This study provides a complete rationalisation of the process of rusticle formation and deep‐water corrosion that is applicable to the long‐term integrity of offshore infrastructure. [ABSTRACT FROM AUTHOR]

Chemical gardens, which are self‐organizing, abiotic, inorganic precipitates in far‐from‐equilibrium systems, are of interest for prebiotic chemistry/origin of life research and, under certain reaction systems, can be considered hydrothermal vent analogs. While the presence of different additives to chemical gardens, including phosphate and amino acids, have been explored, the reactivity of organic molecules in chemical garden systems is not well understood. Here we explored the reactivity of two metabolically important alpha‐keto acids (pyruvic acid and glyoxylic acid) and ammonia in the presence of iron‐silicate chemical gardens. While reactivity was not observed in the case of pyruvic acid, we found that glyoxylic acid formed alpha‐hydroxy acids and amino acids. We found that the observed organic reactivity can be attributed to the silicate in the exterior solution as opposed to the solid iron‐containing chemical garden structure. These results have implications for the reactivity of hydrothermal vent chimneys and their surrounding environments in iron‐ and silica‐rich systems. [ABSTRACT FROM AUTHOR]

The far‐from equilibrium precipitation reaction of chemical gardens can lead to the formation of biomimetic and complex structures providing a new route for the rational architectural design of functional materials. Inspired by recent developments in the field of chemical gardens, we put forward a new scientific question: "Is it possible to create an electrochemical garden?" By implementing state‐of‐the‐art electrochemical techniques and using the phenomenon of metal corrosion, we sculpture self‐organized structures on a zinc disc‐electrode surface by a mechanism similar to that of chemical gardens. A deeper search in the formation mechanism reveals that ion‐selective membranes are the driving force for the growth of an electrochemical garden. At last, electrochemical instabilities, introduced under proper conditions, result in the emergence of current oscillations in the region where electrochemical gardens were discovered. Current oscillations sculpture the electrode surface with a variety of self‐organized precipitate structures. [ABSTRACT FROM AUTHOR]

Cadmium(II) acetate in tablet form, immersed in ethanol solutions with a high concentration of heptanethiol (30–80 mM), was able to develop self‐assembled sail‐shaped structures. The solution in which the self‐assembled structure is formed is totally organic (both solute and solvent), thus representing a unique case among organic Chemical Gardens. The constituting material for this new Chemical Garden (CG) is made of a single phase, namely a cadmium heptanethiolate with a microcrystalline structure consisting of a central cluster [CdnSn]. The morphological and structural features were studied using different techniques (SEM‐EDS, elemental analysis, ATR‐FTIR, 113Cd MAS NMR, XRPD). A crystalline cell for the Cd(II) heptanethiolate cluster was obtained that completely differs from that of the solid phase precipitated by mixing an ethanol solution of Cd(II) acetate with heptanethiol. It follows that the conditions under which the formation of Cd(II) heptanethiolate occurs (slowly from solid, quickly from solution) play a critical role in determining the nature and structure of the precipitating phase. [ABSTRACT FROM AUTHOR]

Abstract Tubular structures self‐assemble from precipitating magnesium salts under the chemical garden chemobrionic growth process. Two experimental procedures, the dissolution of magnesium salt pellets and the injection of magnesium salt solutions into silicate solutions, were explored to reproduce in the laboratory the geochemical conditions under which similar structures may form from mineral‐rich fluids at some seafloor hydrothermal vents driven by serpentinization. X‐ray diffraction and Raman microspectroscopy applied to the materials formed indicated the presence of layers of magnesium silicate and magnesium oxide/hydroxide. Quantum mechanical calculations based on density functional theory were performed on models of hydrated magnesium silicate surfaces and related minerals to explain the Raman spectroscopy results. We examine the precipitate morphology, chemical structure, and crystal or mineral structure in our experiments and how these change with the reaction conditions. This is a fascinating example in geochemistry of a self‐organizing nonequilibrium process that creates complex structures.

Saturn's satellite Enceladus is proposed to have a soda‐type subsurface ocean with temperature able to support life and an iron ore‐based core. Here, it was demonstrated that ocean chemistry related to Enceladus can support the development of Fe‐based hydrothermal vents, one of the places suggested to be the cradle of life. The Fe‐based chemical gardens were characterized with Fourier‐transform (FT)IR spectroscopy and XRD. The developed chemobrionic structures catalyzed the condensation polymerization of simple organic prebiotic molecules to kerogens. Further, they could passively catalyze the condensation of the prebiotic molecule formamide to larger polymers, suggesting that elementary biochemical precursors could have emerged in Enceladus. [ABSTRACT FROM AUTHOR]

In an early earth or planetary chimney systems, hydrothermal fluid chemistry and flow durations play a large role in the chimney's ability to drive electrochemical reactions for the origin of life. We performed continuous electrochemical impedance spectroscopy (EIS) characterization on inorganic membranes representing prebiotic hydrothermal chimney vents in natural seafloor systems, by incorporating an electrode array into a chimney growth experiment. Localized potential and capacitances profiles in the chimney reveal a dynamic system where redox processes are driven by transport phenomena, increasing rapidly due to disequilibrium until achieving equilibrium at about 100 mV and 1000 μF/cm2. The impedance in the chimney interior is three orders of magnitude lower (100 Ohms/cm2 vs 100 KOhms/cm2) than at the ocean or the ocean/chimney interface. The calculated peak dissipation factor (DF) values are more than ten times higher (40.0 vs 3.0) and also confirm the elevated chemical reactivity in the chimney interior. [ABSTRACT FROM AUTHOR]

Precipitation reactions occurring under fluid flow can self‐organize a variety of complex spatiotemporal patterns. Herein, we investigate the structures formed when a CoCl2‐containing water‐in‐oil microemulsion is injected into an aqueous NaOH solution. The reacting liquids are confined to the thin gap of a horizontal Hele‐Shaw cell and injection is carried out from a central port. Dark‐field detection of the patterns reveals borders that can deviate from smooth circles by either jagged or sinusoidal deformations. The interior of the patterns shows speckle‐like features that can arrange along either spike‐like tracks or concentric circular segments. The area ratio of light scattering regions increases with increasing flow rates but decreases sharply with increasing NaOH concentration. The latter transition is interpreted as a shift from patterns dominated by the physical breakdown of the microemulsion to patterns strongly affected by the precipitation of α‐Co(OH)2. [ABSTRACT FROM AUTHOR]

Recognizing fossil microorganisms is essential to the study of life's origin and evolution and to the ongoing search for life on Mars. Purported fossil microbes in ancient rocks include common assemblages of iron-mineral filaments and tubes. Recently, such assemblages have been interpreted to represent Earth's oldest body fossils, Earth's oldest fossil fungi, and Earth's best analogues for fossils that might form in the basaltic Martian subsurface. Many of these putative fossils exhibit hollow circular cross-sections, lifelike (non-crystallographic, constant-thickness, and bifurcate) branching, anastomosis, nestedness within 'sheaths', and other features interpreted as strong evidence for a biological origin, since no abiotic process consistent with the composition of the filaments has been shown to produce these specific lifelike features either in nature or in the laboratory. Here, I show experimentally that abiotic chemical gardening can mimic such purported fossils in both morphology and composition. In particular, chemical gardens meet morphological criteria previously proposed to establish biogenicity, while also producing the precursors to the iron minerals most commonly constitutive of filaments in the rock record. Chemical gardening is likely to occur in nature. Such microstructures should therefore not be assumed to represent fossil microbes without independent corroborating evidence. [ABSTRACT FROM AUTHOR]

Chemobrionics is an emerging scientific field focusing on the coupling of chemical reactions and different forms of motion, that is, transport processes. Numerous phenomena appearing in various gradient fields, for example, pH, concentration, temperature, and so on, are thoroughly investigated to mimic living systems in which spatial separation plays a major role in proper functioning. In this context, chemical garden experiments have received increased attention because they inherently involve membrane formation and various transport processes. In this work, a noninvasive external magnetic field was applied to gain control over the directionality of membrane structures obtained by injecting one reactant solution into the other in a three‐dimensional domain. The geometry of the resulted patterns was quantitatively characterized as a function of the injection rate and the magnitude of magnetic induction. The magnetic field was proven to influence the microstructure of precipitate tubes by diminishing spatial defects. [ABSTRACT FROM AUTHOR]

Precipitation reactions under flow in confined media are relevant to the control of pathological biomineralization, processes affecting aquifers, and challenges in the petroleum industry. Here we show that for a simple geometry, such conditions create macroscopic structures including helices, tubes, lamellae, slugs, and disordered patterns. All structures emerge when salt solution is slowly injected into thin capillaries filled with hydroxide solution. For the helices, the pitch is proportional to the pump rate revealing a constant period of 0.63 s. Different morphologies of the insoluble metal hydroxide can co‐exist causing random transitions along the capillary. On average, 15 % of the final system contains residual hydroxide solution. While mechanically stable for flow speeds above 25 mm min−1, structures collapse and sediment for slower injection speeds. Some of the observed features share similarities with precipitate tubes in chemical gardens and the dynamics of liquid–liquid pipe flow. [ABSTRACT FROM AUTHOR]

Chemical gardens and clock reactions are two of the best‐known demonstration reactions in chemistry. Until now these have been separate categories. We have discovered that a chemical garden confined to two dimensions is a clock reaction involving a phase change, so that after a reproducible and controllable induction period it explodes. [ABSTRACT FROM AUTHOR]

Brinicles are self-assembling tubular ice membrane structures, centimeters to meters in length, found beneath sea ice in the polar regions of Earth. We discuss how the properties of brinicles make them of possible importance for chemistry in cold environments—including that of life's emergence—and we consider their formation in icy ocean worlds. We argue that the non-ice composition of the ice on Europa and Enceladus will vary spatially due to thermodynamic and mechanical properties that serve to separate and fractionate brines and solid materials. The specifics of the composition and dynamics of both the ice and the ocean in these worlds remain poorly constrained. We demonstrate through calculations using FREZCHEM that sulfate likely fractionates out of accreting ice in Europa and Enceladus, and thus that an exogenous origin of sulfate observed on Europa's surface need not preclude additional endogenous sulfate in Europa's ocean. We suggest that, like hydrothermal vents on Earth, brinicles in icy ocean worlds constitute ideal places where ecosystems of organisms might be found. [ABSTRACT FROM AUTHOR]

The formation of closed chemical gardens that resemble quasibiological cells at the macroscale (> 1 cm) is demonstrated. The cells are produced by injecting lanthanide salts in alkaline solutions and do not require silicates. The cells can encapsulate chemicals and enzymes and carry out reactions. Injection of a lanthanide chloride solution in a strong alkaline medium (2.5 M NaOH) causes the generation of closed chemical gardens (inorganic cells) separated by a semi‐permeable membrane. The cells can host chemicals (KMnO4 is shown) or enzymes and function as microreactors. [ABSTRACT FROM AUTHOR]

The generation of chemical gardens based on tetrachloroauric acid and silicate is presented. The structures were studied with SEM, XRD and micro‐Raman spectroscopy and a new mechanism that participates in their development was revealed. Specifically, the structures were decorated with metallic Au that is derived during the process of plant‐like growth. Probably, the instability of gold salts and hydroxides on silica templates accounts for their reduction to metallic Au. [ABSTRACT FROM AUTHOR]

Tungstate chemical gardens have been prepared for the first time. The synthesis was carried out using cobalt(II) chloride and sodium tungstate. The reaction occurred in three steps: chimney formation, swelling, and upwelling of the chemical garden. This result opens the door to a new variety of materials. [ABSTRACT FROM AUTHOR]

Abstract: Tubular structures self‐assemble from precipitating magnesium salts under the chemical garden chemobrionic growth process. Two experimental procedures, the dissolution of magnesium salt pellets and the injection of magnesium salt solutions into silicate solutions, were explored to reproduce in the laboratory the geochemical conditions under which similar structures may form from mineral‐rich fluids at some seafloor hydrothermal vents driven by serpentinization. X‐ray diffraction and Raman microspectroscopy applied to the materials formed indicated the presence of layers of magnesium silicate and magnesium oxide/hydroxide. Quantum mechanical calculations based on density functional theory were performed on models of hydrated magnesium silicate surfaces and related minerals to explain the Raman spectroscopy results. We examine the precipitate morphology, chemical structure, and crystal or mineral structure in our experiments and how these change with the reaction conditions. This is a fascinating example in geochemistry of a self‐organizing nonequilibrium process that creates complex structures. [ABSTRACT FROM AUTHOR]

Black smokers and Lost City-type springs are varieties of hydrothermal vents on the ocean floors that emit hot, acidic water and cool, alkaline water, respectively. While both produce precipitation structures as the issuing fluid encounters oceanic water, Lost Citytype hydrothermal vents in particular have been implicated in the origin of life on the Earth. We present a parallel-velocity flow model for the radius and flow rate of a cylindrical jet of fluid that forms the template for the growth of a tube precipitated about itself and we compare the solution with previous laboratory experimental results from growth of silicate chemical gardens. We show that when the growth of the solid structure is determined by thermal diffusion, fluid flow is slow at the solid-liquid contact. However, in the case of chemical diffusive transport, the fluid jet effectively drags the liquid in the pores of the solid precipitate. These findings suggest a continuum in the diffusive growth rate of hydrothermal vent structures, where Lost City-type hydrothermal vents favour contact between the vent fluid and the external seawater. We explore the implications for the road to life. [ABSTRACT FROM AUTHOR]

'Do cement nanotubes exist?' is a question that has recently been asked. The answer is yes, they do exist. The evidence is in the literature, in tens of papers showing in detail chemical garden-type tubes in cement from the nanoscale upwards that were published in the 1970s and 1980s. Here, we present a nano-review of the literature. [ABSTRACT FROM AUTHOR]

Rio Tinto in southern Spain has become of increasing astrobiological significance, in particular for its similarity to environments on early Mars. We present evidence of tubular structures from sampled terraces in the stream bed at the source of the river, as well as ancient, now dry, terraces. This is the first reported finding of tubular structures in this particular environment. We propose that some of these structures could be formed through self-assembly via an abiotic mechanism involving templated precipitation around a fluid jet, a similar mechanism to that commonly found in so-called chemical gardens. Laboratory experiments simulating the formation of self-assembling iron oxyhydroxide tubes via chemical garden/chemobrionic processes form similar structures. Fluid-mechanical scaling analysis demonstrates that the proposed mechanism is plausible. Although the formation of tube structures is not itself a biosignature, the iron mineral oxidation gradients across the tube walls in laboratory and field examples may yield information about energy gradients and potentially habitable environments. [ABSTRACT FROM AUTHOR]

To model ion transport across protocell membranes in Hadean hydrothermal vents, we consider both theoretically and experimentally the planar growth of a precipitate membrane formed at the interface between two parallel fluid streams in a 2D microfluidic reactor. The growth rate of the precipitate is found to be proportional to the square root of time, which is characteristic of diffusive transport. However, the dependence of the growth rate on the concentrations of hydroxide and metal ions is approximately linear and quadratic, respectively. We show that such a difference in ionic transport dynamics arises from the enhanced transport of metal ions across a thin gel layer present at the surface of the precipitate. The fluctuations in transverse velocity in this wavy porous gel layer allow an enhanced transport of the cation, so that the effective diffusivity is about one order of magnitude higher than that expected from molecular diffusion alone. Our theoretical predictions are in excellent agreement with our laboratory measurements of the growth of a manganese hydroxide membrane in a microfluidic channel, and this enhanced transport is thought to have been needed to account for the bioenergetics of the first single-celled organisms. [ABSTRACT FROM AUTHOR]

A chemical garden based on iron salt that grows in organic solvents and ions is demonstrated for the first time. This prototype chemical garden develops in an inverted orientation, thus providing evidence that downward growth is feasible. [ABSTRACT FROM AUTHOR]