The habitability and climate history of mars from remote sensing and analog studies

Abstract

Life emerged in what is by definition a “habitable” environment on the early Earth. While 99.9% of the early crust on Earth has been destroyed due to plate tectonics and erosion, Mars retains a large portion of its ancient crust, with minimal metamorphism (80 % surface >3.8 Ga). Unlike the cold, dry and oxidized surface environment of Mars today, ancient Mars shows evidence of extensive lakes, channels, and even oceans or seas and aqueous minerals representing sedimentary and hydrothermal environments. Weathering profiles on Mars, which track the climate evolution and redox state of atmosphere, are widespread in the southern highland. In Chapter 2, I investigate geological characteristics, stratigraphy and relative age of 200 weathering profiles on Mars. My results suggest reducing atmospheric conditions favouring Fe-mobility and chemical weathering profiles occurred at least episodically throughout the Noachian and into Hesperian on Mars. In Chapter 3, I examine the weathering profiles of two ancient explosive volcanoes on Mars. Weathering of glassy, porous and chemically reactive pyroclastic deposits might be an important part linking clay formation, climate and sedimentary process. In Chapter 4, I present many new discoveries of fluviolacustrine carbonate deposits on Mars. The diverse chemistry of fluviolacustrine carbonates suggests various aqueous environments potentially similar to Archean lakes and seas with significant dissolved iron, and are consistent with the occurrence of the CO2-rich anoxic Martian atmosphere predicted by climate models. These results indicate diverse and active surface processes on early Mars, but the duration of these aqueous activities may have been geologically short, accounting for only a small fraction of the prolonged Martian history. In contrast, the early Martian subsurface was perhaps more stable over long periods of harsh surface conditions, providing a continuously habitable environment. In Chapter 5, I explore the mineralogy of the Mangai serpentine mine using multiple-scale spectroscopy to understand the serpentinization and carbonation process that may have been active within the Martian subsurface. Different degrees of serpentinization and carbonation processes through multiple stages of hydrothermal activity in these Mars-analog rocks shed additional light on the possible sequestration of Martian H2O and CO2 within the crust. In Chapter 6, I map the geomorphology features of the landing site of Tianwen-1’s rover Zhurong. I present evidence that extensive pitted cones in the landing site area formed through diapiric upwelling of fluidized sediments and gas (i.e. mud volcanism) with intriguing astrobiological implication and serves as a natural deep drill for understanding the subsurface habitability of Mars. In summary, this thesis provides new insights into the habitability of Mars over time, from climate-surface interactions to the deep subsurface hydrothermal system, from orbital kilometer scales down to microscopic scales of analog rocks studied in the laboratory.