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.

Low groundwater flow is essential in impeding radionuclide migration in the geological disposal of high-level radioactive waste (HLW). In the deep subsurface of thick marine sediments, groundwater may actually be ancient seawater altered during deposition and burial, termed “fossil seawater” in this study. In such cases, groundwater flow is extremely slow because it is not affected by infiltration of meteoric water, even after uplift and erosion of strata. Fossil seawater is often found in the deeper parts of the Neogene marine sedimentary Koetoi and Wakkanai Formations of the Tempoku Basin, Horonobe, northern Hokkaido, Japan. Groundwater dating using Cl isotopes and He concentration indicates that this fossil seawater may have barely moved since uplift of the area began. To confirm the low-flow nature of fossil seawater, its chemistry in the Horonobe area and burial diagenesis were investigated by numerical modeling, focusing on the effects of dehydration associated with phase transitions of biogenic silica, smectite interlayer water dehydration, and drainage and upwelling through porosity reduction. Results indicate that groundwater with δ¹⁸O values of >0‰, δ²H values of –30‰ to –20‰, and Cl^– concentrations of ≤80% lower than that of seawater can be formed during burial without mixing with meteoric water. Groundwater formed during burial in the deeper parts of the Koetoi and Wakkanai Formations may thus have been preserved since uplift, confirming that fossil seawater is of extremely low mobility. The results should contribute to understanding the dilution mechanism of porewater in marine sediments and the selection of suitable site for geological disposal of high-level radioactive waste.

Elemental and isotopic analyses of individual submicron-sized particles in chondrite matrix were made by an inductively coupled plasma time-of-flight mass spectrometer (ICP-TOF-MS) and a multiple collector ICP-MS equipped with high-time-resolution ion counters (HTR-MC-ICP-MS). The particles were collected from Allende CV3 chondrite through a laser ablation-in-liquid (LAL) technique. Firstly, the abundances for four major elements (Si, Al, Mg, and Fe) were determined on total 6086 particles, indicating that the Allende matrix is a mixture of submicron-sized particles made mainly of olivine, pyroxene, spinel, Fe–Ni sulfide, and Fe–Ni metal, consistent with the predicted major constituent minerals by a nebular condensation model. The major elemental compositions revealed that Fe–Ni particles are minor components (about 0.3% in number fraction) in the Allende matrix. Then, to estimate the origin of these metallic particles, abundances for Ni and two minor elements (Os and Pt) were measured. Total 10417 particles of Ni–Os–Pt bearing particles were also found in the chondrite matrix. Majority of the particles were enriched in Ni. Os and Pt were present as separated particles, and no particles with presence of both the Os and Pt were found. Finally, with the HTR-MC-ICP-MS technique, ¹⁹⁵Pt/¹⁹⁴Pt value was measured on total 1545 particles. The resulting ¹⁹⁵Pt/¹⁹⁴Pt values agree with the solar composition within analytical uncertainties. This lack in isotopic anomalies of the ¹⁹⁵Pt/¹⁹⁴Pt can be explained either by majority of the Pt nuggets being produced from uniform reservoir in the solar system or by Pt being isotopically homogenized prior to the formation of the solar nebula.