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

了解现代地球上热液和超干旱环境的可居住性和可持续性不仅对探测我们当前生物圈的极限很重要，而且对推断早期地球生命的起源和演化以及寻找地外行星上的生命也很重要。这些极端条件下的可居住性和可持续性主要取决于构成生命的有用元素（如氢、碳、氮、硫）和重要金属（如铁、钙、铜、锌）的可用性，而这些元素的来源和循环途径又进一步取决于这些元素的来源和循环途径。到目前为止，我们对这些元素在极端条件下的来源和回收途径的了解非常少。这一知识缺口已成为地球化学、矿物学、微生物学、天体生物学、行星科学和环境科学等跨学科研究的焦点，旨在揭示生命的起源和寻找地外智慧。我们通过对加拿大地盾和南非深层地下环境裂缝水的地球化学研究表明，在这些黑暗、长期孤立的环境中，流体-岩石相互作用可以原位提供以硫酸盐为主的H2和甲烷偶联的充足能源。这种对微生物代谢能量和营养来源的地质控制很好地解释了地球深层地下独特的生态结构，对寻找火星等地外岩石行星上的生命具有重要的应用价值。从这项研究中产生的自然问题是，是什么控制着地球深层地下重要金属的回收，以及在类似于早期地球和火星的地表环境中，是什么控制着生命必需元素。在“发现”号的应用中，我们的总体目标是使用强大的稳定同位素工具来研究上述主要生命构成元素和重要金属的来源和循环过程。我们将研究四种不同类型的模拟环境：(1)海底热液喷口，重点研究尚未研究的氮循环；(2)加拿大地盾和南非深层地下裂缝水，重点是未检测的金属循环；(3)以腾冲热液田温泉为代表的陆相热液喷口；(4)以柴达木盆地沙漠为代表的超干旱环境；后两者将侧重于对H2O， C， N， S和重要金属的综合研究。该研究结果有望填补各种极端条件下关键生命元素循环框架的一些重要空白，有助于了解生物多样性的空间变化，并为地球生命起源和寻找地外生命提供线索。

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.