Magnetofossils
from Ancient Mars: a Robust Biosignature in the Martian Meteorite ALH84001
Kathie L. Thomas-Keprta,1 Simon J. Clemett,1
Dennis A. Bazylinski,2 Joseph L. Kirschvink,3 David
S. McKay,4 Susan J. Wentworth,1 Hojatollah Vall,5
Everett K. Gibson, Jr.,4 and Christopher S. Romanek6
Lockheed Martin1 and National Aeronautics
and Space Adminstration/Johnson Space Center, 4 Houston, Texas
77058;
Department of Microbiology, Iowa State University, Ames, Iowa 500112;
Division oft Geological and Planetary Sciences, California Institute of
Technology, Pasadena, California 911253;
Department of Earth and Planetary Sciences, McGill University, Montreal,
Quebec H3A 2A7; Canada5;
and Savannah River Ecology Laboratory, University of Georgia, Aiken, South
Carolina 298026
Evidence of biogenic activity on Mars has profound scientific implications
for our understanding of the origin of life on Earth and the presence
and diversity of life within the Cosmos. Analysis of the Martian meteorite
Allan Hills 84001 (ALH84001) revealed several lines of evidence that has
led some investigators to suggest that microbial life existed on Mars
approximately 4 billion years ago (45). One of the strongest lines of
evidence is the presence of tens-of-nanometer-size magnetite (Fe304)
crystals found within carbonate globules and their associated rims in
the meteorite (57,58). Approximately one-quarter of these magnetites have
remarkable morhological and chemical similarities to magnetite particles
produced by magnetotactic bacteria, which occur in aquatic habitats on
Earth. Moreover, these types of magnetite particles are not known or expected
to be produced by abiotic means either through geological processes or
synthetically in the laboratory. We have therefore argued that these Martian
magnetite crystals are in fact magnetofossils (57, 58). If this is true,
such magnetofossils would constitute evidence of the oldest life forms
known. In this respect, we note there is now considerable uncertainty
concerning when the earliest terrestrial life forms existed. Until recently,
results from the -3.5-billion-year-old Apex cherts of the Warrawoona group
in western Australia held this record (52), although this work is now
in question (12).
SREL Reprint #2741
Thomas-Keprta, K. L., 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. Magnetofossils from ancient Mars: a robust biosignature in the Martian meteorite ALH84001. Applied and Environmental Microbiology 68:3663-3672.
