Paleomagnetic evidence of a low-temperature origin of carbonate in the martian meteorite ALH84001

Science

Volumn 275, Issue 5306, 1997, Pages 1629-1633

  Kirschvink, Joseph L ^a   Maine, Altair T ^a   Vali, Hojatollah ^b  

^a CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^b MCGILL UNIVERSITY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

CARBONIC ACID;

ARTICLE; ASTRONOMY; BIOGENESIS; CARBON DIOXIDE FIXATION; LOW TEMPERATURE; MAGNETIC FIELD; PRIORITY JOURNAL;

ALHA 84001; CARBONATE; LIFE ON MARS; MAGNETIC FIELD; METEORITE; PALAEOMAGNETISM;

MARS;

EID: 0030620642     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.275.5306.1629     Document Type: Article

References (35)

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25. This separation was done using a 150-μm-thick diamond-impregnated copper watering saw. The flat surface of the carbonate-bearing grain was first glued to a thin Pyrex cover slip such that it was parallel to the surface of the quartz-glass triangle. The magnetic moment of this new assembly was indistinguishable from that measured prior to addition of the cover slip and the additional cement, confirming that they were both nonmagnetic. The other surface of the Pyrex cover slip was then bound to the surface of a cylindrical brass stub with a temperature-sensitive adhesive that had been filtered in acetone to remove ferromagnetic contaminants. The orientation of the quartz fiber was marked on the brass surface. Shortly after we began our first cut, the bond between the cyanoacrylic cement and the cover slip gave way. This left a small notch in the sample at the boundary between the pyroxene grains (Fig. 1A). By remeasuring the NRM of the sample after this step, we were able to calculate by difference the NRM vector that had been held by the material removed in the cut. Next, we fixed the flat surface of the carbonate-bearing layer directly to the brass stub with the adhesive, which held properly during the remainder of the watering process. This last cut was adjusted slightly so that most material was removed from the larger grain, leaving a 2.2-mg fragment of the small pyroxene grain on the brass stub (Fig. 1D). While it was still bound to the stub, we then used the cyanoacrylate to cement a second quartz-glass triangle and fiber assembly to the this new fragment, with a relative orientation identical to that of the first sample. It was then freed from the brass stub by heating briefly to 110°C, and washed with filtered acetone to dissolve traces of the adhesive. The sawing procedure left a 1.6-mg fragment of the carbonate-bearing grain attached to the larger pyroxene grain. After measurement of the NRM, we were able to break this free with a nonmagnetic ceramic scalpel blade, and by remeasuring the NRM vector, were able to recover by difference the NRM vector of this small chip. The al weight of the pyroxene grain was 12.7 mg, implying that a total of 3.4 mg of the sample was lost in both sawing operations.
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35. We thank D. McKay and E. K. Gibson for our sample of ALH84001, P. Carpenter for assistance with the SEM, and G. R. Rossman for help with the delicate sawing operation. H.V. acknowledges financial support from the U.S. National Research Council. We made extensive use of the software provided by C. Jones (cjones@mantle.colorado.edu) for the analysis and presentation of paleomagnetic data. B. C. Murray, J. Eiler, and D. A. Evans made helpful suggestions on the manuscript. This is contribution no. 5897 from the Division of Geological and Planetary Sciences of the California Institute of Technology.