Biology
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p44b..02n&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P44B-02
Biology
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [1041] Geochemistry / Stable Isotope Geochemistry, [5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The importance of impact events during the early history of Mars is obvious through a simple examination of the character of the martian surface. This ancient, heavily cratered terrain has been shown to be associated with extensive phyllosilicate deposits. This geologic link could suggest that the extensive phyllosilicate-forming alteration may have occurred during early martian history through impact-induced hydrothermal alteration. However, examination of the oxygen isotopic composition of water on Mars suggests that the extensive phyllosilicate deposits were formed primarily through low temperature (<30°C) interactions, and that high temperature weathering in impact-induced hydrothermal systems have not been a dominant process on Mars. The average oxygen isotopic composition of water on Earth is dictated by the nature of water-rock interactions. If these interactions occur at higher temperatures then the water will contain a higher proportion of 18O, while lower temperature interactions will result in water with a lower proportion of 18O. Water on Earth today contains a higher proportion of 18O because of plate tectonics and hydrothermal interaction at mid-ocean ridges. The oxygen isotopic composition of water on early earth, however, may have been quite different, containing a smaller proportion of 18O suggesting much less hydrothermal interaction. Because there are not yet any direct measurements of the oxygen isotopic composition of water on Mars, it needs to be inferred through examination of carbonates preserved in martian meteorites and the isotopic composition of atmospheric CO2. This can be done because the oxygen incorporated into carbonates and CO2 is easily exchanged with liquid water if it is present. Independently, both measurements provide an estimate for the δ18O of water on Mars to be near -16‰. This composition is consistent with low temperature weathering of the silicate crust, and indicates that impact hydrothermal systems did not play an important role in the early alteration of the planet. However, our understanding of impact-induced hydrothermal systems remains unclear. If most of the water mobilized by an impact event remained at relatively low temperatures (<30°), low-temperature interactions could predominate in these environments. These conditions would be consistent with the isotopic constraints suggested in this study.
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