Prime candidate sites for astrobiological exploration through the hydrogeological history of Mars

The hydrogeological evolution of Mars has been proposed to be dominated by the development of the Tharsis Magmatic Complex through superplume activity, with related magmatic-pulse-drive it flood inundations that directly influence the shaping of the northern plains, the evolution of the atmosphere and climate, and subsurface and surface water processes. On the other hand, several possible biological models and terrestrial analogues have been suggested for Mars during the last decade, including the description-of putative microfossils and the proposal of sedimentary units. Here we revisit these scenarios and present a possible bridge that integrates the geological, paleohydrological, and the putative biological histories of the planet. We primarily focus on the Noachian, a time period that arguably has recorded an inner dynamo, plate tectonics, and an ocean that may have covered one-third of the total surface area of Mars, due to its implications on the possible origin and early evolution of life. This stage is followed by a long-lived cold and dry phase, briefly punctuated by transient magmatic-driven hydrological cycles, dominated by a stagnant-lid/superplume regime, which directly influences the processes of natural selection on the putative early biosphere. Based on this hypothesized evolution of the planet, we suggest three martian locations as prime candidate sites for astrobiological exploration, each one corresponding to an inundation period: Meridiani Planum (Noachian/Early Hesperian), Mangala Valles (Late Hesperian/Early Amazonian), and Orcus Patera (Amazonian). (c) 2005 Elsevier Ltd. All rights reserved.