Chemical Gardens: The Effects of Organic Compounds on Inorganic Precipitates

Chemical gardens are inorganic, self-organizing precipitates that form when metal salts are added to a solution of another precipitating ion, e.g. adding iron (II) chloride crystals to sodium silicate solutions. The self-assembly of these inorganic membranes, the maintenance of gradients across them, and the effects of organic compounds on their mineralogy / morphology are of particular interest in understanding similar geological structures at hydrothermal systems in Earth’s early oceans, as well as in putative hydrothermal vents elsewhere in our solar system (such as on Saturn’s moon, Enceladus). Chemical gardens provide a method of recreating these geological “hydrothermal chimneys” which are mineral rich, energetic environments. Previous research (Barge et al, 2012) has explored various morphologies evidenced when the metal salt FeCl2•4H20 is incorporated into sodium silicate and potassium phosphate solutions. While inorganic compounds were included in previous research, organic compounds have yet to be introduced. The current project seeks to build upon previous work by introducing organics to inorganic chemical garden precipitate systems, to determine if/how the organics can affect self-assembling morphologies or crystal growth. Thus far we have observed that amino acids affect chemical garden morphology, density and growth. Scanning Electron Microscope (SEM) imaging of the tubules and structures show that they appear quite robust with varied gradients across their membranes. This work also has applications for life detection: Though chemical gardens are not alive, the structures themselves appear quite biological in SEM images. Chemical garden experiments containing amino acids produce membranes as thin as 0.5 microns, thinner than most chemical garden inorganic membranes reported in the literature. These results show that inorganic precipitation systems analogous to geological environments can produce self-assembling membranes that might have relevance to prebiotic processes at hydrothermal vents on early Earth and other worlds, and that organics can interact with minerals and affect their growth