Atmosphere-Surface Interactions on Mars: Δ17O Measurements of Carbonate from ALH 84001

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Science  05 Jun 1998:
Vol. 280, Issue 5369, pp. 1580-1582
DOI: 10.1126/science.280.5369.1580

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Oxygen isotope measurements of carbonate from martian meteorite ALH 84001 (δ18O = 18.3 ± 0.4 per mil, δ17O = 10.3 ± 0.2 per mil, and Δ17O = 0.8 ± 0.05 per mil) are fractionated with respect to those of silicate minerals. These measurements support the existence of two oxygen isotope reservoirs (the atmosphere and the silicate planet) on Mars at the time of carbonate growth. The cause of the atmospheric oxygen isotope anomaly may be exchange between CO2 and O(1D) produced by the photodecomposition of ozone. Atmospheric oxygen isotope compositions may be transferred to carbonate minerals by CO2-H2O exchange and mineral growth. A sink of17O-depleted oxygen, as required by mass balance, may exist in the planetary regolith.

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