title: Subsurface water and clay mineral formation during the early history of Mars.
abstract: Clay minerals, recently discovered to be widespread in Mars's Noachian terrains, indicate long-duration interaction between water and rock over 3.7 billion years ago. Analysis of how they formed should indicate what environmental conditions prevailed on early Mars. If clays formed near the surface by weathering, as is common on Earth, their presence would indicate past surface conditions warmer and wetter than at present. However, available data instead indicate substantial Martian clay formation by hydrothermal groundwater circulation and a Noachian rock record dominated by evidence of subsurface waters. Cold, arid conditions with only transient surface water may have characterized Mars's surface for over 4 billion years, since the early-Noachian period, and the longest-duration aqueous, potentially habitable environments may have been in the subsurface.
authors: Institut d'Astrophysique Spatiale, Université de Paris-Sud XI, 91405 Orsay Cedex, France. ehlmann@caltech.edu
authors: Bethany L
authors: BL
authors: Ehlmann
authors: John F
authors: JF
authors: Mustard
authors: Scott L
authors: SL
authors: Murchie
authors: Jean-Pierre
authors: JP
authors: Bibring
authors: Alain
authors: A
authors: Meunier
authors: Abigail A
authors: AA
authors: Fraeman
authors: Yves
authors: Y
authors: Langevin
mesh_terms: D000538:Aluminum Silicates / Q000032:analysis* / Q000737:chemistry* / Q000145:classification; D000077215:Clay; D018559:Exobiology; D005118:Extraterrestrial Environment / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis*; D007053:Ice / Q000032:analysis; D018535:Mars; D017640:Silicates / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D007053:Ice; D017640:Silicates; C060346:basalt; D000077215:Clay