Borate Minerals and Origin of the RNA World

Abstract

The RNA World is generally thought to have been an important link between purely prebiotic (>3.7 Ga) chemistry and modern DNA/protein biochemistry. One concern about the RNA World hypothesis is the geochemical stability of ribose, the sugar moiety of RNA. Prebiotic stabilization of ribose by solutions associated with borate minerals, notably colemanite, ulexite, and kernite, has been proposed as one resolution to this difficulty. However, a critical unresolved issue is whether borate minerals existed in sufficient quantities on the primitive Earth, especially in the period when prebiotic synthesis processes leading to RNA took place. Although the oldest reported colemanite and ulexite are 330 Ma, and the oldest reported kernite, 19 Ma, boron isotope data and geologic context are consistent with an evaporitic borate precursor to 2400-2100 Ma borate deposits in the Liaoning and Jilin Provinces, China, as well as to tourmaline-group minerals at 3300-3450 Ma in the Barberton belt, South Africa. The oldest boron minerals for which the age of crystallization could be determined are the metamorphic tourmaline species schorl and dravite in the Isua complex (metamorphism between ca. 3650 and ca. 3600 Ma). Whether borates such as colemanite, ulexite and kernite were present in the Hadean (>4000 Ma) at the critical juncture when prebiotic molecules such as ribose required stabilization depends on whether a granitic continental crust had yet differentiated, because in its absence we see no means for boron to be sufficiently concentrated for borates to be precipitated.

Evaporite Borate‐Containing Mineral Ensembles Make Phosphate Available and Regiospecifically Phosphorylate Ribonucleosides: Borate as a Multifaceted Problem Solver in Prebiotic Chemistry

“…Performing this chemistry in an evaporite desert addresses the concentration problem. [30] and fit the observed major peaks. Minor peaks also fit the peak positions in the literature.…”

Origin of first cells at terrestrial, anoxic geothermal fields

“…In addition, and in contrast to deep sea vents, terrestrial geothermal fields are conducive to condensation reactions and enable the involvement of solar light as an energy source and a selective factor that would favor the accumulation of nucleotides, which are particularly photostable (6,121,124). Also in contrast to deep sea vents, the geothermal vapor is enriched in phosphorous and boron compounds ( Table 2) that could be essential for the emergence of first RNA-like oligomers (96,97).…”

“…b) The major biochemical building blocks are derivatives of those molecules that preferably partition to the vapor phase upon the geothermal separation, namely simple carbonaceous and phosphorous compounds, ammonia, and sulfide. In addition, the vapor phase of geothermal systems is particularly enriched in borate, the concentration of which can reach 10 mM (Table 2) (54,94,95) and which seems to be important for the stabilization of ribose (96,97). c) Geothermal fields should have offered ample opportunity for the reagents to concentrate and interact upon evaporation.…”

Stochastic Prebiotic Chemistry within Realistic Geological Systems

“…Most studies of borate minerals have been conducted on minerals whose direct geological record does not extend beyond the Mesozoic, for instance ulexite, colemanite and kernite (e.g. in [90] ).…”