The Effect of Temperature on Fatty Acid Vesicle Formation in Simulated Deep-ocean Conditions

Ice-covered worlds may harbor life beneath the ice within reservoirs of liquid water, or at water-rock interfaces in hydrothermal vent communities as have been observed in similar locales on Earth. One theory of life's emergence on Earth holds that initial metabolic and replication reactions took place in protobiotic cell membranes. These may have been composed of n- monocarboxylic acids (fatty acids) alone, rather than more complex phospholipid structures. Our experiments in the lab confirm that aqueous decanoic acid self-assembles into bilayer vesicles at standard temperature and pressure (25°C, 1 atm) in the pH range between 7 and 8.5, as indicated by stepwise increases in fluorescence induced by ultraviolet excitation of dye conjugated to decanoic acid solution. Life's chemical evolution in primordial oceans on Earth or elsewhere could have occurred over a range of temperatures, however. We explore the pH range for vesicle formation for temperatures from 0° C to 50° C. The role of pressure in the formation of protobiotic cell membranes is similarly important to whether life may have formed in deep-ocean environments on Earth, or on icy worlds in the solar system. Hydrostatic pressure has been shown to retard denaturation at above-optimal temperatures, but could affect the pH range for formation of protobiotic cell membranes.