Non-equilibrium conditions must have been crucial for the assembly of the first informational polymers of early life-by supporting their formation and continuous enrichment in a long-lasting environment. Here we explored how gas bubbles in water subjected to a thermal gradient, a likely scenario within crustal mafic rocks on the early Earth, drive a complex, continuous enrichment of prebiotic molecules. RNA precursors, monomers, active ribozymes, oligonucleotides, and lipids are shown to (1) cycle between dry and wet states, enabling the central step of RNA phosphorylation, (2) accumulate at the gas-water interface to drastically increase ribozymatic activity, (3) condense into hydrogels, (4) form pure crystals, and (5) encapsulate into protecting vesicle aggregates that subsequently undergo fission. These effects occurred within less than 30 minutes. The findings unite physical conditions in one location which were crucial for the chemical emergence of biopolymers.They suggest that heated microbubbles could have hosted the first cycles of molecular evolution.Life is a non-equilibrium system. By evolution, modern life has created a complex protein machinery to maintain the nonequilibrium of crowded molecules inside dividing vesicles. Based on entropy arguments, equilibrium conditions were unlikely to trigger the evolutionary processes during the origin of life 1 . External non-equilibria had to be provided for the accumulation, encapsulation, and replication of the first informational molecules. They can locally reduce entropy, give rise to patterns 2 , and lean the system towards a continuous, dynamic self-organization 3 . Non-equilibrium dynamics can be found in many fluid systems, including gravity-driven instabilities in the atmosphere 4 , the accumulation of particles in nonlinear flow 5,6 , and shear-dependent platelet activation in blood 7 . Our experiments discuss whether gas-water interfaces in a thermal gradient could have provided such a nonequilibrium setting for the emergence of life on early Earth.Non-equilibrium systems in the form of heat flows were a very common and simplistic setting, found ubiquitously on the planet 8 . Hydrothermal activity is considered abundant on early Earth and intimately linked to volcanic activity 9 . Water is thereby circulating through the pore space of the volcanic rocks, which is formed by magmatic vesiculation (primary origin) and fractures (secondary origin). These systems have been studied as non-equilibrium driving forces for biological molecules in a variety of processes 10-17 .Gases originating from degassing of deeper magma bodies percolate through these water-filled pore networks. At shallow depths bubbles are formed by gases dissolved in water and formation of vapor where sufficient heat is supplied by the hydrothermal system. The bubbles create gas-water interfaces, which previously have been discussed in connection with atmospheric bubble-aerosol-droplet cycles 18 , the adsorption of lipid monolayers and DNA to the interface 19,20 , or the formation of pep...

Recent progress in the synthesis of nucleotides from prebiotically plausible precursors has opened up new ways to explain the origin of genetic matter. Mechanisms for the polymerization of nucleotides without the help of catalysts are, however, rare. Complementary to the experiments done by Costanzo et al., we found that drying 3',5'-cyclic GMP leads to poly-G RNA strands with lengths of up to 40 nucleotides. We also show that the polymerization to long RNA strands is considerably more efficient under dry conditions than for cGMP polymerization in water. The length depends on the incubation time of dry nucleotides at temperatures of 40-80 °C. No enzymes or other catalysts are needed for successful polymerization.

Unilamellar lipid vesicles can serve as model for protocells. We present a vesicle fission mechanism in a thermal gradient under flow in a convection chamber, where vesicles cycle cold and hot regions periodically. Crucial to obtain fission of the vesicles in this scenario is a temperature-induced membrane phase transition that vesicles experience multiple times. We model the temperature gradient of the chamber with a capillary to study single vesicles on their way through the temperature gradient in an external field of shear forces. Starting in the gel-like phase the spherical vesicles are heated above their main melting temperature resulting in a dumbbell-deformation. Further downstream a temperature drop below the transition temperature induces splitting of the vesicles without further physical or chemical intervention. This mechanism also holds for less cooperative systems, as shown here for a lipid alloy with a broad transition temperature width of 8 K. We find a critical tether length that can be understood from the transition width and the locally applied temperature gradient. This combination of a temperature-induced membrane phase transition and realistic flow scenarios as given e.g. in a white smoker enable a fission mechanism that can contribute to the understanding of more advanced protocell cycles.