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Science 1 October 1999:
Vol. 286. no. 5437, pp. 90 - 94
DOI: 10.1126/science.286.5437.90
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Reports

The Age of the Carbonates in Martian Meteorite ALH84001

Lars E. Borg, 1*dagger James N. Connelly, 2 Larry E. Nyquist, 1 Chi-Y. Shih, 3 Henry Wiesmann, Young Reese 3

The age of secondary carbonate mineralization in the martian meteorite ALH84001 was determined to be 3.90 ± 0.04 billion years by rubidium-strontium (Rb-Sr) dating and 4.04 ± 0.10 billion years by lead-lead (Pb-Pb) dating. The Rb-Sr and Pb-Pb isochrons are defined by leachates of a mixture of high-graded carbonate (visually estimated as ~5 percent), whitlockite (trace), and orthopyroxene (~95 percent). The carbonate formation age is contemporaneous with a period in martian history when the surface is thought to have had flowing water, but also was undergoing heavy bombardment by meteorites. Therefore, this age does not distinguish between aqueous and impact origins for the carbonates.

1 SN2/NASA Johnson Space Center Houston, TX 77058, USA.
2 Department of Geological Sciences, University of Texas at Austin, TX 78713, USA.
3 Lockheed Engineering and Science, 2400 NASA Road 1, Houston, TX 77258, USA.
*   Present address: Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA.

dagger    To whom correspondence should be addressed. E-mail: lborg{at}unm.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Magnetofossils from Ancient Mars: a Robust Biosignature in the Martian Meteorite ALH84001.
K. L. Thomas-Keprta, S. J. Clemett, D. A. Bazylinski, J. L. Kirschvink, D. S. McKay, S. J. Wentworth, H. Vali, E. K. Gibson Jr., and C. S. Romanek (2002)
Appl. Envir. Microbiol. 68, 3663-3672
   Full Text »    PDF »
Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001.
D. J. Barber and E. R. D. Scott (2002)
PNAS 99, 6556-6561
   Abstract »    Full Text »    PDF »
Special Feature: Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures.
K. L. Thomas-Keprta, S. J. Clemett, D. A. Bazylinski, J. L. Kirschvink, D. S. McKay, S. J. Wentworth, H. Vali, E. K. Gibson Jr., M. F. McKay, and C. S. Romanek (2001)
PNAS 98, 2164-2169
   Abstract »    Full Text »    PDF »
Special Feature: Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin.
E. I. Friedmann, J. Wierzchos, C. Ascaso, and M. Winklhofer (2001)
PNAS 98, 2176-2181
   Abstract »    Full Text »    PDF »
A Low Temperature Transfer of ALH84001 from Mars to Earth.
B. P. Weiss, J. L. Kirschvink, F. J. Baudenbacher, H. Vali, N. T. Peters, F. A. Macdonald, and J. P. Wikswo (2000)
Science 290, 791-795
   Abstract »    Full Text »


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