Coupled Evolution of the Martian Atmosphere and Crust Through Geologic Time

Details Coupled Evolution of the Martian Atmosphere and Crust Through Geologic Time Coupled Evolution of the Martian Atmosphere and Crust Through Geologic Time

Sep 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt........24h&link_type=abstract

Thesis (PHD). UNIVERSITY OF COLORADO AT BOULDER , Source DAI-B 59/03, p. 1016, Sep 1998, 222 pages.

Mathematics

Logic

2

Mars

Scientific paper

This dissertation investigates the coupled evolution of the Martian atmosphere and crust throughout geologic time and the implications for Martian sample analysis and exobiology. Abundant geological and atmospheric evidence suggests that Mars has changed significantly throughout time. Removal of volatiles from the atmosphere may have been the trigger for the dramatic transition from that scenario to the present cold, harsh climate. Previous modeling work has shown that loss to space enriches the residual atmosphere in the heavier isotopes. Furthermore, stable isotope measurements from secondary mineral deposits within the Martian meteorites indicate exchange with an isotopically-enriched atmosphere. To investigate the Martian climate history, we developed an atmospheric evolution model for argon and neon considering a mass balance between the mantle, atmosphere, and loss to space by sputtering. Sputtering loss is particularly relevant for noble gases which have few mechanisms of escape. Due to substantial loss, our model is only capable of explaining <25% and <2.5% of the atmospheric abundance of argon and neon, respectively. Thus, sources of volatiles are required in addition to volcanic outgassing. We examined the impact of a Martian paleomagnetic field on sputtering loss. A strong magnetic field could limit sputtering loss by deflecting the solar wind around the upper atmosphere. We found that a magnetic field that persists until 1-2 Ga could affect the loss of light noble gases from the atmosphere. Nonetheless, our model predicts additional sources to balance the atmospheric volatile budgets. Therefore, we investigated outgassing from the Martian crust via groundwater circulation. We found that a crustal reservoir 5-25 km thick could satisfy the atmospheric argon budget. Recently, putative evidence of life has been purported for the Martian meteorite ALH84001. We examined the stable isotope measurements from carbonate and organic deposits found in ALH84001. Due to atmosphere-crust exchange, δ13C and δ18O measurements indicate that the carbonates may have formed at T ~ 50-300oC and, thus, may not harbor evidence of life. Further, we investigated abiotic organic synthesis in Martian hydrothermal systems and found that this could account for the δ13C measurement from organics in ALH84001. Abiotic organic synthesis in hydrothermal systems, however, may still play an important role in the possible origin of life on Mars.

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