Roles of solar energetic particles in habitability of the early Earth and in formation of amino acids and their enantiomeric excesses were examined by simulation experiments. SEPs are mainly composed of high energy protons, and it was suggested that high-flux SEPs were generated from the young Sun and entered into Earth atmosphere. It was shown that such SEPs were major energy to form amino acid precursors, in the case that primitive Earth atmosphere was slightly reducing. SEPs were produced N₂O, which is greenhouse effect gas and could be keep the early Earth habitable. SEPs could generate spin-polarized muons, which may have formed enantiomeric excesses of amino acids.

Steroids are indispensable components of the eukaryotic cellular membrane and have important roles in the process of endocytosis. Steroids are characteristic of eukaryotic organisms and hence have been utilized as biomarkers for eukaryotes in the Precambrian geological record. It is generally inferred that steroids biosynthesis evolved within eukaryotes, while the steroid biosynthesis in a small number of bacteria is a result of horizontal gene transfers from eukaryotes. However, more bacteria have been found to possess a steroid biosynthesis pathway and the traditional understanding of the steroid evolution is now called into question.Our current study suggests that the entire eukaryotic steroid biosynthesis pathway is derived from bacteria. Almost all genes that are involved in the steroid biosynthesis up to cholesterol are inferred to have evolved within the bacterial domain. However, the evolutionary trajectory for individual genes seems to be different from one another. Hence, the evolution of the eukaryotic isoprenoid biosynthesis pathway is inferred to have been a multi-step process that was triggered by the rise of molecular oxygen at Great Oxidation Event.

Stable sulfur isotope ratios are useful not only for understanding microbial activity in the modern and past sulfur cycle, but also for making habitat inferences based on the isotopic fractionation of sulfur from its microbial metabolism. Along with sulfur reduction, sulfur disproportionation is an important sulfur metabolism that increases the sulfur isotopic fractionation between sulfate and sulfide in the sedimentary record. A quadruple sulfur isotopic signature has been proposed to distinguish between sulfur reduction and sulfur disproportionation, but its usefulness as an indicator has not yet been evaluated due to the paucity of research results. In this study, we analyzed quadruple sulfur isotopic fractionations of thermophilic sulfur disproportionation bacteria isolated from the Nakabusa hot spring, and compared it with the previous study in which the bacteria were cultured at low temperatures to discuss the characteristics of the sulfur disproportionation bacteria and the effectiveness of the indicator under high temperature conditions.

Since ¹³⁸La is shielded from β decay paths, it can be synthesized only by supernovae. Therefore, ¹³⁸La can be used as a tracer for supernova-induced isotope anomalies in the early Solar System. Yet, the very low abundance of ¹³⁸La (0.09%) makes it difficult to conduct a precise isotope measurement. Shen and Lee (2003) found ¹³⁸La anomalies in calcium-aluminum rich inclusions by thermal ionization spectrometry, but the presence of such anomalies in bulk chondrites and achondrites remains to be tested with high-precision. To realize high-precision analysis, we have developed a La separation procedure by column chromatography and tested the precision of La isotope analysis by MC-ICP-MS.

We conducted a series of shock devolatilization experiments by using a carbonaceous asteroid analog. We have developed a novel experimental method to investigate the chemical composition of produced gases and the mass of each species quantitatively.

Layered silicate, which is a kind of hydrous mineral that may be contained in meteorites, is a mineral produced in the presence of liquid water, and layered silicate is a variety of minerals depending on the content of structural elements and coordination position. Species exist and the mineral species of layered silicates are associated with the production environment. Therefore, it may be possible to estimate the aquatic environment of extraterrestrial celestial bodies from the mineral species of layered silicate contained in meteorite samples. In this study, we focus on ”scanning transmission electron microscope (STXM)” as a method for meteorite sample analysis. STXM is a tool for analyzing the existence of elements in local regions. That is, it is possible to understand information such as which part of the structure the element is coordinated with, and to estimate the type of layered silicate. In this study, X-ray absorption spectra of constituent elements were collected using various layered silicates on the earth as standard samples, and the obtained results were made into a library together with the sample characteristics so that they could be applied to STXM analysis of meteorite samples.