title: Past, present, and future life on Mars.
abstract: Although the Viking results indicated that the surface of Mars is dry and lifeless, there is direct geomorphological evidence that Mars had large amounts of liquid water on its surface in the past. From a biological perspective the existence of liquid water, by itself, motivates the question of the origin of life on Mars. One of the martian meteorites dates back to this early period and may contain evidence consistent with life. The Mars environment 3.5 to 4.0 Gyr ago was comparable to that on the Earth at this time in that both contained liquid water. Life had originated on Earth and reached a fair degree of biological sophistication by 3.5 Gyr ago. To determine if life similarly arose on Mars may require extensive robotic exploration and ultimately human exploration. Intensive exploration of Mars will require a continued presence on the Martian surface and the development of a self sustaining community in which humans can live and work for very long periods of time. A permanent Mars research station can obtain its life support requirements directly from the martian environment enabling a high degree of self-sufficiency. In the longer term, it is possible that in the future we might restore a habitable climate on Mars, returning it to the life-bearing state it may have enjoyed early in its history.
authors.affiliation: Space Science Division, NASA Ames Research Center, Moffett Field, CA, USA.
authors.forename: C P
authors.initials: CP
authors.lastname: McKay
mesh_terms: D001272:Atmosphere / Q000032:analysis / Q000737:chemistry; D002245:Carbon Dioxide; D004783:Environmental Microbiology; D019418:Evolution, Chemical; D019419:Evolution, Planetary; D018559:Exobiology / Q000639:trends*; D005118:Extraterrestrial Environment; D019015:Geologic Sediments / Q000382:microbiology*; D018535:Mars; D019110:Meteoroids; D009584:Nitrogen; D010100:Oxygen; D012988:Soil Microbiology; D013026:Space Flight / Q000295:instrumentation*; D018531:Spacecraft / Q000295:instrumentation; D014867:Water
chemical_list: D014867:Water; D002245:Carbon Dioxide; D009584:Nitrogen; D010100:Oxygen