Continental evaporites and the search for evidence of life on Mars

Abstract

Continental evaporites are deposits that originate from the evaporation of saline waters in the low areas of saline lakes from all continents, except Europe, and mainly consist of chloride, sulphate and potash minerals. In recent years, the discovery on the Martian surface of hydrated salt minerals, including sulphates and chlorides, interpreted as deriving from the desiccation of preexisting large bodies of water, such as lakes, has provided further convincing evidence of liquid water activity on the surface of Mars and, consequently, it has reinforced the plausibility of finding life. Because evaporites require short-term aqueous processes for their formation, they can trap and preserve over geologic times a biological record made up of halophilic extremophiles-such as microalgae, bacteria, and their remains-that recent research on Earth has shown to be characterized by unexpectedly high biodiversity. This record may consist of varying types of fossils, including morphological fossils, chemofossils and biominerals. As a consequence, continental evaporite environments and their saline deposits are now a primary target for the near future astrobiology missions devoted to the search for fossil Martian life. Lacustrine evaporite deposits and minerals have, therefore, been identified as primary targets for the NASA-ESA joint programme of the Mars sample return, planned for the end of the current decade.

Bacterial Diversity in Microbial Mats and Sediments from the Atacama Desert

“…Further, Bacteroidetes has been reported as a dominant phylum in hypersaline systems, including microbial mats [40,43], hypersaline water and sediment samples [7,19,44,45], and (endo)evaporitic samples [8,9,14,46,47]. LL2 and Puj display a very high amount of sequences related to this phylum, but in LL2, the family Rhodothermaceae dominates where the conductivity doubles that of Puj.…”

The Role of Terrestrial Analogs in the Exploration of the Habitability of Martian Evaporitic Environments

“…These changes depend on the recurrent phases of persisting aridity and rainfall/ fl ooding (or other hydrological factors in fl uencing the groundwater) that can change the concentration of salts in the water. Drought/rainfall alternations can profoundly alter the physical environments; a striking example is represented by the extremely rugged surfaces (clin kerlike textures, Stoertz and Ericksen, 1974 ) developed in different salares of the Atacama Desert (Barbieri and Stivaletta, 2011 ) (Fig. 1 ).…”

The persistence of a chlorophyll spectral biosignature from Martian evaporite and spring analogues under Mars-like conditions

“…Sulphate evaporite minerals and spring deposits on Earth have been proposed as relevant analogues for the search for extant life on Mars due to their potential for biosignature preservation (Barbieri & Stivaletta 2011;Gómez et al 2012;Berard et al 2013). Evaporites have been found to preserve biosignatures in the form of amino acids and their degradation products (Aubrey et al 2006), and by the entrapment of halophiles in fluid inclusions in modern systems (Foster et al 2010), and on geologically relevant timescales from 3500 years to 250 million years (Vreeland et al 2000;Schubert et al 2009).…”