Cycles of H2O, C, N, S and vital metals in early-Earth and Mars analog environments: geological control on life in extreme conditions and its insights into origin of life and search for life on extraterrestrial planets

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The understanding of habitability and sustainability in hydrothermal and hyper-arid environments on modern Earth is important not only for detecting the limit of our current biosphere but also to inferring the origin and evolution of life on early Earth and searching for life on extraterrestrial planets. The habitability and sustainability in these extreme conditions are mainly determined by the availability of the useful forms of life-constituting elements (e.g., H, C, N, S) and vital metals (e.g., Fe, Ca, Cu, Zn), which are further dependent on the sources and recycling pathways of these elements. By far, our knowledge on the sources and recycling pathways of these elements in extreme conditions is very poor. This knowledge gap has become a focused concern in the interdisciplinary research across geochemistry, mineralogy, microbiology, astrobiology, planetary science and environmental science that aim to unravel the origin of life and search for extraterrestrial intelligence. Our previous research, based on geochemical study of the fracture waters in the deep subsurface environments in the Canadian Shield and South Africa, has demonstrated that sufficient energy sources dominated by sulfate coupled by H2 and methane can be supplied in situ by fluid-rock interaction in these dark, long isolated environments. Such a geological control on energy and nutrient sources for microbial metabolism well explains the unique ecological structure in the deep terrestrial subsurface, and has important applications to the search for life on extraterrestrial rocky planets, such as Mars. Natural questions sprouted from this study are, what control the recycling of vital metals in the deep terrestrial subsurface, and beyond, what control the life-essential elements in the surface environments analogue to early Earth and Mars. In this Discovery application, our overall objective is to employ robust stable isotope tools to investigate the sources and recycling processes of the major life-constituting elements and vital metals listed above. We will study four different types of analog environments: (1) submarine hydrothermal vents, focusing on the understudied nitrogen cycle; (2) fracture waters in the deep subsurface in the Canadian Shield and South Africa, focusing on the unexamined metal cycles; (3) terrestrial hydrothermal vents, represented by the hot springs in the Tengchong hydrothermal fields in SW China, and (4) hyper-arid environment, represented by the dessert in the Qaidam Basin in NW China; the latter two will be focused on a comprehensive study on H2O, C, N, S and vital metals. The results of this study are expected to fill some important gaps in the framework of the cycles of crucial life elements in various extreme conditions, help to understand the spatial variations in biodiversity, and shed lights into the origin of life on Earth and search for extraterrestrial life.