X-ray absorption fine structure (XAFS) is an elemental speciation method that is highly element-selective and provides information on the valence and local structure of almost all elements. The fluorescence XAFS method allows the speciation of elements at lower concentrations and has therefore been applied to the speciation of elements in various natural samples and to the elucidation of chemical elemental processes in laboratory experiments simulating natural conditions. Thus, fluorescence XAFS is now an essential method in space geochemistry and environmental chemistry. This review presents (i) examples of the application of fluorescence XAFS methods to elements that are difficult to detect by conventional methods, and (ii) examples where new chemical species information has been obtained by increasing the energy resolution of the X-ray fluorescence (XRF) detection system to obtain XAFS. In particular, a new spectroscopic technique called High Energy Resolution Fluorescence Detection (HERFD)-XANES has been developed in recent years, which is obtained by detecting XRF with an energy resolution higher than the lifetime width of electron orbitals. By making full use of these techniques, it is possible to understand physicochemical information at the atomic level and various elementary chemical processes based on this information. This information, in turn, will contribute to a better understanding of the Earth’s material cycles and elemental cycles at different scales (=molecular geochemistry).

Environmental DNA (eDNA) is becoming an essential tool for assessing the distribution and biodiversity of organisms, particularly in aquatic ecosystems. This technology involves extracting DNA from water or soil to investigate the presence and diversity of organisms. eDNA techniques are non-invasive and efficient, making them effective for early detection of invasive species and monitoring rare species. Recent advancements in high-throughput sequencing technology have enabled more extensive analysis of eDNA. Furthermore, it has been discovered that not only contemporary organisms but also ancient species spanning hundreds to tens of thousands of years can be analyzed using sediment cores. This allows for a better understanding of ecosystem changes and the impact of human activities on biological communities. Looking ahead, it is anticipated that analyses will expand to include both eDNA and RNA and proteins. By analyzing biomolecules such as DNA in the environment, new approaches will be provided to better understand ecosystem dynamics and functions.