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极度干旱环境中的宜居性和可持续性，不仅对于探测我们目前生物圈的极限，而且对于推断早期地球上生命的起源和演化以及寻找地外行星上的生命都很重要。在这些极端条件下的宜居性和可持续性主要取决于构成生命的元素(如H、C、N、S)和重要金属(如Fe、Ca、铜、锌)的可获得性，而这些元素的来源和循环途径又取决于这些元素的来源和循环途径。到目前为止，我们对极端条件下这些元素的来源和回收途径的了解非常有限。这一知识鸿沟已成为地化、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外星智慧。我们之前的研究基于对加拿大地盾和南非深部地下环境中裂隙水的地球化学研究，证明在这些黑暗的、长期孤立的环境中，可以通过流体-岩石相互作用在原地提供足够的能源，其中以硫酸盐为主，加上H2和甲烷。这种对微生物代谢能量和营养源的地质控制很好地解释了地球深部独特的生态结构，在寻找火星等地外岩石行星上的生命方面具有重要应用。从这项研究中衍生出的自然问题是，是什么控制了地球深处及更深的地下重要金属的循环，是什么控制了类似于早期地球和火星的地表环境中的生命必需元素。在Discovery应用程序中，我们的总体目标是使用强大的稳定同位素工具来调查上面列出的主要生命构成元素和重要金属的来源和回收过程。我们将研究四种不同类型的模拟环境：(1)海底热液喷口，重点研究未被研究的氮循环；(2)加拿大地盾和南非深部地下裂隙水，重点是未被研究的金属循环；(3)陆地热液喷口，以中国西南部腾冲热液油田的温泉为代表；(4)以中国西北柴达木盆地甜点为代表的极度干旱环境；后两者将集中于H2O、C、N、S和重要金属的综合研究。这项研究的结果有望填补各种极端条件下关键生命元素循环框架中的一些重要空白，有助于了解生物多样性的空间差异，并有助于揭示地球生命的起源和寻找外星生命。

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.