Ribose frees boron from calcium-bearing minerals in UNSW tests of an origin-of-life loop

On early Earth, boron's problem was staying dissolved in water. Ribose and boron compounds form complexes when they meet ^[4], and the UNSW group's idea is that this pairing kept ancient ribose from caramelizing ^[1][15]. Calcium works against that. It pulls boron out of solution and locks it into rock, where nothing can use it ^[5]. Studies over the past two decades have explored ribose-boron chemistry, but the researchers wrote that some of those "experiments may therefore not reflect realistic early Earth environments" ^[6].

Their answer was to test real rocks. Kernite, colemanite and ulexite contain sodium, calcium or both ^[7]. Running them beside lab-grade borax shows how the accompanying metal changes the amount of boron that ribose can free. The field test used a piece of "puffy evaporative crust" from the high-altitude Puga hydrothermal system in Ladakh, India, chosen as a stand-in for early Earth ^[9]. With ribose, the water held about 60% more boron ^[10][14]. The figure comes from a single piece of crust from a single site ^[9].

The two side experiments are the ones I would show a skeptic. If any dissolved organic matter freed boron equally well, browned ribose and other sugars would have matched fresh ribose. Both raised boron solubility, but less than fresh ribose ^[11][12]. That narrows the effect to fresh ribose and, in the explanation ScienceAlert gives, to the geometry of the ribose molecule ^[12].

As ScienceAlert describes them, the experiments did not measure whether the freed boron then saved any ribose. The loop is presented as the team's proposal: ribose pulls boron into water, boron protects ribose, and more ribose could mean more dissolved boron and more surviving ribose ^[15]. What the experiments measured was boron going into water. The sugar's fragility is the other half of the loop. Heat and other factors turn ribose into a tar-like "brown goop" ^[3], and the case that boron prevents this here rests on the complexes the two form ^[4].

In my view the result removes one practical objection to RNA-first accounts, in which ribose, the R in RNA and the material of its backbone ^[2], had to last long enough to matter. Calcium-rich water no longer obviously starves the chemistry of boron, as long as some sugar is already present. Where that starting sugar came from is a separate question. Some ribose may have arrived on space rocks such as Bennu before Earth's own chemistry began making it ^[16].