title: The Last Possible Outposts for Life on Mars.
abstract: The evolution of habitable conditions on Mars is often tied to the existence of aquatic habitats and largely constrained to the first billion years of the planet. Here, we propose an alternate, lasting evolutionary trajectory that assumes the colonization of land habitats before the end of the Hesperian period (ca. 3 billion years ago) at a pace similar to life on Earth. Based on the ecological adaptations to increasing dryness observed in dryland ecosystems on Earth, we reconstruct the most likely sequence of events leading to a late extinction of land communities on Mars. We propose a trend of ecological change with increasing dryness from widespread edaphic communities to localized lithic communities and finally to communities exclusively found in hygroscopic substrates, reflecting the need for organisms to maximize access to atmospheric sources of water. If our thought process is correct, it implies the possibility of life on Mars until relatively recent times, perhaps even the present.
authors.affiliation: 1 Carl Sagan Center at the SETI Institute , Mountain View, California, USA .|2 NASA Ames Research Center , Moffett Field, California, USA .
authors.forename: Alfonso F
authors.initials: AF
authors.lastname: Davila
authors.affiliation: 3 School of the Environment, Washington State University , Pullman, Washington, USA .|4 Center of Astronomy and Astrophysics, Technical University Berlin , Berlin, Germany .
authors.forename: Dirk
authors.initials: D
authors.lastname: Schulze-Makuch
mesh_terms: D005075:Biological Evolution; D017753:Ecosystem; D018559:Exobiology; D005118:Extraterrestrial Environment; D018535:Mars