The spontaneous formation of ribonucleotides on prebiotic Earth is considered an essential step in the origin of life. Phosphorylation of ribose to form ribose 5'-phosphate with boric acid has been reported as a key step in ribonucleotide synthesis. However, the probability of phosphorylation of ribose with mineral phosphate, which is the most abundant form of phosphate on Earth, remains unclear. Carbonate and formate were both widely available compounds on prebiotic Earth and are known to increase the solubility of mineral phosphates. Therefore, the present study investigates the phosphorylation of ribose with apatite in the presence of carbonate or formate. Ribose was phosphorylated preferentially at 5'-hydroxyl when slightly alkaline ribose solution was dried down with hydroxyapatite, urea, boric acid, and formate or carbonate at 80°C for 24 h. Conversely, the yield was limited to less than 10% in the absence of formate and carbonate at the same pH. Dissolution of apatite was substantially increased in the presence of carbonate and formate, allowing the phosphorylation of ribose. These results suggest that ribose 5'-phosphate may have been spontaneously formed in boron-rich evaporative environments on prebiotic earth, expanding the availability of ribonucleotides on prebiotic Earth in addition to the conventional process through ribonucleosides.

Although zirconium (Zr), niobium (Nb), hafnium (Hf), and tantalum (Ta) in seawater are potential tracers for water masses, their determination is still a challenge in analytical chemistry. We have refined our preconcentration method using 8-hydroxyquinoline chelating resin (TSK-8HQ) and reinvestigated concentration profiles of the four elements in dissolved (d) and total dissolvable (td) fractions at five different stations from 47 °N, 160 °E to 51 °N, 160 °W in the subarctic North Pacific Ocean. The new method has saved analytical time and reduced systematic errors compared with previous methods. The concentration ranges were 30–276 pmol/kg for dZr, 1.0–2.6 pmol/kg for dNb, 0.09–0.78 pmol/kg for dHf, and 0.006–0.026 pmol/kg for dTa in the subarctic North Pacific Ocean. The concentrations of Zr and Hf increased from surface water to deep water, whereas those of Nb and Ta were nearly constant over the water depth. The profiles of dZr, dNb, and dHf were consistent with those in previous studies. However, we found that dTa is uniformly distributed at 0.015 ± 0.005 pmol/kg (mean ± sd, n = 75), which is approximately one-fifth of that in a previous study. It is likely that the previous dTa data were affected by a systematic error. Negligible differences between td and d fractions suggest that the particulate concentrations of these elements are lower than those reported in a previous study.