MINERAL SURFACES, AMINO ACIDS, AND THE ORIGINS OF LIFE

The chemical origins of life occurred in several steps, each of which increased molecular complexity and patterning of Earth’s near-surface environment. The first step, abiotic synthesis of amino acids, sugars, lipids and other essential molecular bio-building blocks, has been well documented through experiments that mimic environments on Earth and in space. However, the second step, which includes selection, concentration and assembly of those molecules into the functional membranes and polymers of life, is less well understood. Our research team investigates how mineral surfaces might have played a role in the critical transition from a dilute, indiscriminate prebiotic soup to micro-environments that were concentrated in molecules poised to foster life. Studies on adsorption of biomolecules onto common mineral surfaces, including competitive molecular adsorption, batch adsorption, molecular stability and decomposition, and potentiometric titration experiments, coupled with extended triple-layer surface complexation and density functional theory modeling, point to at least four plausible roles that such interactions may have played in life’s origins. (1) Minerals are able to concentrate molecules from dilute solutions by factors of 1000 or more, thus potentially overcoming the problem of a dilute prebiotic soup. (2) Molecules bound to mineral surfaces may be much more stable than those in solution, thus countering a strong objection to the hypothesis that life’s origins occurred at or near a hydrothermal system. (3) Some minerals are able to select and concentrate specific molecules, notably chiral (right- versus left-handed) amino acids, thus providing a possible mechanism for the origins of biological handedness. (4) Finally, mineral surfaces may juxtapose and align molecules to facilitate polymerization and other modes of biomolecular assembly. Our work also underscores the importance of including realistic prebiotic contributions in any origin of life scenario. Any geochemical model for life’s origins must thus incorporate such physico-chemical complexities as cycles, gradients, fluxes, and interfaces.