Martian Global-Scale Flooding Triggered by Atmospheric Collapse

Abstract Mars experienced an enigmatic epoch of intense liquid water surface erosion ~3.6 billion years ago [1-4], which is particularly puzzling because it followed a period of gentler fluvial erosion [3] despite the waning of processes typically thought to sustain surface water (e.g., volcanism, impacts, thicker atmosphere) [1]. Mars was likely cold 3.6 billion years ago, with most of its surface water frozen in southern ice sheets [5-7], seemingly at odds with a liquid surface water optimum. However, here I report model results showing that burial of a southern H2O ice cap [7] by thick CO2 ice sheets when Mars’ CO2 atmosphere collapsed ~3.6 billion years ago [5,8] would have melted a substantial portion of Mars’ water inventory, leading to direct fluvial erosion and a more active global water cycle. Melting driven by one or more atmospheric collapse-inflation cycles [5,8,9] can produce previously unexplained drainage patterns that span from near the south pole [10,11] to the equator [12-14]. The model predicts potential habitats for early martian life in periodic, long-lived (potentially ≥10^7 year) subglacial melt and ice-covered, Mediterranean-Sea-sized [12,13] lakes.