Mineral self-organization on a lifeless planet

Abstract

It has been experimentally demonstrated that, under alkaline conditions, silica is able to induce the formation of mineral selfassembled inorganic-inorganic composite materials similar in morphology, texture and nanostructure to the hybrid biomineral structures that, millions of years later, life was able to self-organize. These mineral self-organized structures (MISOS) have been also shown to work as effective catalysts for prebiotic chemical reactions and to easily create compartmentalization within the solutions where they form. We reason that, during the very earliest history of this planet, there was a geochemical scenario that inevitably led to the existence of a large-scale factory of simple and complex organic compounds, many of which were relevant to prebiotic chemistry. The factory was built on a silica-rich high-pH ocean and powered by two main factors: a) a quasi-infinite source of simple carbon molecules synthesized abiotically from reactions associated with serpentinization, or transported from meteorites and produced from their impact on that alkaline ocean, and b) the formation of self-organized silica-metal mineral composites that catalyze the condensation of simple molecules in a methane-rich reduced atmosphere. We discuss the plausibility of this geochemical scenario, review the details of the formation of MISOS and its catalytic properties and the transition towards a slightly alkaline to neutral ocean.

Prebiotic Organic Chemistry of Formamide and the Origin of Life in Planetary Conditions: What We Know and What Is the Future

“…There are no data on the pH value resulting from serpentinization reactions occurring under early Hadean reducing atmospheric conditions, i.e., at low concentrations of CO 2 , but they probably reached a higher pH value. At these high pH values, the concentration of silica in the Hadean seas and lakes could reach up to several grams per liter, mobilizing silica at a large scale and explaining the ubiquitous presence of silica and silicified rocks [5]. Both thermodynamics and kinetical reasons sustain the idea that minerals play a crucial role in the complex chemical routes to the first living organisms.…”

“…The rationale behind the model described above of a hospitable Hadean time has been exposed [5]. We just need to outline two consequences of serpentinization that are relevant for the role of prebiotic chemistry of formamide in the Hadean time.…”

“…The geochemical testing/validation of any proposed chemical pathway intended to explain how life appeared on this planet is now unavoidable. Starting from the new information provided by the crystals of zircon, we have devised a geochemical model for the first six hundred million years of the history of our planet [5]. Water condensed on the surface of the planet before 4.4 billion years ago, i.e., soon after solidification of the first outer surface of an undifferentiated mantle, the first ultramafic rock crust.…”

“…The crust of the planet under these physicochemical conditions should have been a global factory of simple and complex organic compounds. Furthermore, once the first felsic protocontinents emerged among the alkaline seas, the high pH waters became enriched in silica and provided the chemistry to trigger the formation of mineral self-organized structures (MISOS) [5,6].…”

Similarities between terrestrial planets at the time life appeared on Earth

“…We include this qualifying "perhaps" because high-altitude water is readily dissociated by ultraviolet light with subsequent loss of hydrogen to space. Some authors believe that Venus' atmosphere may have dried out before its water had a chance to condense [3]; many others disagree [10].…”