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Published October 11, 2011 | Published
Journal Article Open

Carbonates in the Martian meteorite Allan Hills 84001 formed at 18 ± 4 °C in a near-surface aqueous environment

Abstract

Despite evidence for liquid water at the surface of Mars during the Noachian epoch, the temperature of early aqueous environments has been impossible to establish, raising questions of whether the surface of Mars was ever warmer than today. We address this problem by determining the precipitation temperature of secondary carbonate minerals preserved in the oldest known sample of Mars' crust—the approximately 4.1 billion-year-old meteorite Allan Hills 84001 (ALH84001). The formation environment of these carbonates, which are constrained to be slightly younger than the crystallization age of the rock (i.e., 3.9 to 4.0 billion years), has been poorly understood, hindering insight into the hydrologic and carbon cycles of earliest Mars. Using "clumped" isotope thermometry we find that the carbonates in ALH84001 precipitated at a temperature of approximately 18 °C, with water and carbon dioxide derived from the ancient Martian atmosphere. Furthermore, covarying carbonate carbon and oxygen isotope ratios are constrained to have formed at constant, low temperatures, pointing to deposition from a gradually evaporating, subsurface water body—likely a shallow aquifer (meters to tens of meters below the surface). Despite the mild temperatures, the apparently ephemeral nature of water in this environment leaves open the question of its habitability.

Additional Information

© 2011 National Academy of Sciences. Edited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved September 2, 2011 (received for review June 10, 2011). Published online before print October 3, 2011. We thank N. Kitchen for assistance with the isotopic analyses. We thank two anonymous reviewers for valuable comments that have improved this work. I.H. was funded by a Texaco Postdoctoral Fellowship (Division of Geological and Planetary Sciences, Caltech). J.M.E. acknowledges funding from National Aeronautics and Space Administration and National Science Foundation-Division of Earth Sciences. Author contributions: I.H. and J.M.E. designed research; I.H. performed research; I.H. contributed new reagents/analytic tools; I.H., W.W.F., and J.M.E. analyzed data; and I.H., W.W.F., and J.M.E. wrote the paper.

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Published - Halevy2011p16154P_Natl_Acad_Sci_Usa.pdf

Published - pnas.1109444108_SI.pdf

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August 22, 2023
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