Pumice as a Remarkable Substrate for the Origin of Life

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.

Community Structure and Biogeochemical Impacts of Microbial Life on Floating Pumice

“…These findings support a recent contention that floating pumice may have served as an initial cradle for the emergence of life on early Earth (14).…”

“…Anecdotes of such pumice islands have been reported for the oceans, and indeed such formations have been considered potential vectors of biogeographic dispersal for marine and terrestrial biota (11,12). Moreover, floating pumice has been proposed as a substrate for early chemical evolution and the origin of life because of its combination of chemically reactive surfaces and small interior voids that could protect early protobiological molecules and provide a stable environment for various reactions (13,14). However, to our knowledge, floating pumice has never been characterized from a microbiological perspective using modern genetic techniques, nor have its biogeochemical impacts been examined quantitatively.…”

Contributions of Professor Martin Brasier to the study of early life, stratigraphy and biogeochemistry

“…For example, their work led to the discovery of sulphurmetabolizing microfossils from the 3.4 Ga Strelley Pool Chert (Wacey et al 2011); the description of putative microbial mat fabrics in seafloor cherts of the 3.46 Ga Apex Chert described in this book (Hickman-Lewis et al 2016) and the hypothesis of Archean volcanic pumice as a possible prebiotic substrate for life (Brasier et al 2011b). Much of this early Archean research had implications for the emerging field of astrobiology, a discipline that excited Martin and inspired several of his studentsleading, for example, to work discussing the protocols for testing for signs of life in Martian samples Brasier & Wacey 2012) and to developing biogenicity criteria tailored for samples from both the early Earth and extraterrestrial materials (McLoughlin et al 2007).…”

Origins of life: From the mineral to the biochemical world

“…In the line of Bernal's original thinking, several authors have remarked that a number of minerals naturally develop a range of porous structures, from the microporosity of zeolites whose dimensions are comparable to the sizes of small molecules (nanometer range), to the micrometer-sized weathering channels that develop in feldspars (technically, they are called macropores) [52]; all of them may have been effective for compartmentalization, and it has even been said that "the first cell wall might have been an internal mineral surface" [53]. The macroporosity of pumices has also been evoked in this respect [54], and a special mention must be made of clay minerals [55], whose expandable interlayers may have provided size-tailored microporosity for a variety of molecules. All of these pores could constitute a rather safe haven for developing prebiotic experiments in organic molecules self-organization, protecting them from dilution, and maybe also from photochemical degradation due to the hard UV photons that reached the surface of the Earth at the time (renewed interest is currently devoted to this possibility in the frame of the exploration of the surface of Mars, where the irradiation is rather similar to what it was on the primordial Earth).…”