Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures.
McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.
Thomas-Keprta
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KL
Lockheed Martin, 2400 NASA Road 1, Mail Code C23, Houston, TX 77058, USA. kthomas@ems.jsc.nasa.gov
Clemett
S J
SJ
Bazylinski
D A
DA
Kirschvink
J L
JL
McKay
D S
DS
Wentworth
S J
SJ
Vali
H
H
Gibson
E K
EK
McKay
M F
MF
Romanek
C S
CS
D018407:Bacterial Physiological Phenomena; D002244:Carbon; D003460:Crystallization; D052203:Ferrosoferric Oxide; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D018535:Mars; D010087:Oxides / Q000737:chemistry*; D014867:Water
D010087:Oxides; D014867:Water; D002244:Carbon; D007501:Iron; D052203:Ferrosoferric Oxide