Astrobiology

Abstract

The context for the emergence of life on Earth sometime prior to 3.5 billion years ago is almost as big a puzzle as the definition of life itself. Hitherto, the problem has largely been addressed in terms of theoretical and experimental chemistry plus evidence from extremophile habitats like modern hydrothermal vents and meteorite impact structures. Here, we argue that extensive rafts of glassy, porous, and gas-rich pumice could have had a significant role in the origin of life and provided an important habitat for the earliest communities of microorganisms. This is because pumice has four remarkable properties. First, during eruption it develops the highest surface-area-to-volume ratio known for any rock type. Second, it is the only known rock type that floats as rafts at the air-water interface and then becomes beached in the tidal zone for long periods of time. Third, it is exposed to an unusually wide variety of conditions, including dehydration. Finally, from rafting to burial, it has a remarkable ability to adsorb metals, organics, and phosphates as well as to host organic catalysts such as zeolites and titanium oxides. These remarkable properties now deserve to be rigorously explored in the laboratory and the early rock record. Key Words: Pumice—Volcanoes—Biominerals—Origin of life. Astrobiology 11, 725–735.