FIG. 2.

Polyextreme environmental evolution of Mars. Mars became polyextreme very early. Its capability to preserve subaerial habitats, ecotones, and microbial dispersal pathways during the transitional period between the Noachian and Amazonian would have depended on fluctuating interactions between multiple environmental extremes and their relative dominance at any given time, which in part depended on time and obliquity. (A) Evolution of the abundance and diversity of microbial habitats, ecotones, and dispersal pathways over time as a function of increase in polyextremes (number and intensity). The impact is most severe for those at the surface (solid black line); it would have been less severe for those in association with the subsurface (dashed black line) and least severe for those of the deep underground (dotted line), where survivability would have depended primarily on the evolution of geothermal energy and deep water circulation. The straight lines show temporal trends, while evolution would have varied with obliquities. (B) Interactions between extreme environmental parameters. White arrows = promote; black arrows = prevent; left-right black arrows = counter; left-right gray arrow = combine; dotted thin arrows show loop cycles.