Geothermal non-equilibria as prebiotic selector

Life is an out-of-equilibrium process, pointing towards an emergence that must also have been decisively shaped and driven by the non-equilibrium systems present 4 billion years ago. Rocks and their constituent phases likely played an essential role as molecular feedstock. We aim to combine this geological scenario with physical non-equilibria such as thermal gradients, offering unique opportunities for molecular selection.

We have studied how simple heat flows through geological networks of interconnected chambers create chemical niches with complex mixtures of prebiotically relevant substances, each with different concentration ratios (1). These confined spaces could thus enable various prebiotic reactions and boost their yield and selectivity compared to bulk systems. We show this exemplarily with the trimetaphosphate-driven dimerization of glycine. Trimetaphosphate, presumably rare on the early Earth, experiences strong thermophoresis and is accumulated significantly stronger than for instance glycine, increasing product yields by multiple orders of magnitude.

Prebiotic reactions often require a defined set of ion concentrations. One example is the activity of some important RNA enzymes that vanishes without divalent magnesium salt, whereas an excess of monovalent sodium salt reduces enzyme function. However, leaching experiments show that relevant geomaterials such as basalts release mainly sodium and only little magnesium. In heated rock cracks, the superposition of convection and thermophoresis actively enriches magnesium ions against sodium and establishes a habitat for ribozyme function from basaltic leachates (2). Interestingly, the same process can also solubilize one of the most abundant phosphate minerals on the early Earth, Apatite, by fractionation of its acidic-dissolved constituents.Under pH conditions relevant to nascent life, this leaves up to 15 mM of phosphate in solution, facilitating the formation of condensed, more reactive phosphate species.

References

(1) Matreux, T., Aikkila, P., Scheu, B., Braun, D. & Mast, C. B. Heat flows enrich prebiotic building blocks and enhance their reactivity. Nature 628, 110–116 (2024).

(2) Matreux, T. Le Vay, K., et al. Heat flows in rock cracks naturally optimize salt compositions for ribozymes. Nat. Chem. 13, 1038–1045 (2021).