Characterizing the Climate and Hydrologic Cycle of Early Mars: Assessing the Role of Rainfall, Groundwater, and Transient Atmospheric HeatingPalumbo, AshleycreatorHead, JamesAdvisorLee, Jung-EunReaderRussell, JamesReaderPieters, CarleReaderWordsworth, RobinReaderBrown University. Department of Earth, Environmental, and Planetary Sciencessponsor2020xix, 416 p.born digitalThesis (Ph. D.)--Brown University, 2020thesesThe nature of the early martian climate remains unsolved. Geologic evidence, including valley networks, paleolakes, and groundwater release, suggest that the long-lived (Noachian-spanning) early climate was “warm and wet” (WW), with above-freezing global mean annual temperature (GMAT) and rainfall-dominated erosion. In contrast, climate modeling studies suggest that the long-lived climate was “cold and icy” (CI), with below-freezing GMAT, water as snow/ice in the highlands, and fluvial activity confined to periods of punctuated heating and snow/ice melting. Our goal is to combine geologic observations with climate models in an effort to understand the nature of the early climate. We introduce nine chapters that cover three topics: (1) testing aspects of a WW climate, including presence and distribution of rainfall, (2) exploring implications of punctuated heating mechanisms, including volcanism- and impact cratering-induced heating, and (3) determining the required climate for groundwater release. Key contributions from each chapter: Role of rainfall: 1) Previous hypotheses for the nature of martian rainfall are not supported by mathematical relationships; continuous Noachian rainfall may not be required. 2) In a WW climate with GMAT ~275 K, rainfall is negligible and precipitation is snowfall-dominated. 3) The distribution of valley networks and paleolakes is more consistent with the predicted distribution of snowmelt in a CI climate with punctuated heating than in a WW climate. 4) A rainfall-dominated climate requires GMAT >~285 K, similar to present-day Earth; annual snow accumulation and melting also occurs, contributing to fluvial activity. Punctuated heating: 5) Volcanism-induced heating could cause snow/ice melting, both (1) local to the edifice and (2) globally in the summer. 6) Impact cratering-induced heating and related effects could cause smoothing of plains, crater degradation, and aqueous alteration. Groundwater release: 7) A groundwater-fed ocean could form in a climate with GMAT <273 K; WW conditions are not required. 8) Groundwater system recharge after ocean formation is an unsolved issue. 9) GMAT >~286 K for thousands of years is required for groundwater release at identified groundwater-fed paleolakes. In summary, we should not discount the possibility that the long-lived Noachian climate was CI with periods of punctuated heating that lasted for thousands of years.Mars (Planet)Climate modelingHydrologyPlanets--Geology (Planetary geology)Planetary scienceEnglishRPB20200720In CopyrightCollection is open for research.dissertations