SREL Reprint #2741

Magnetofossils from Ancient Mars: a Robust Biosignature in the Martian Meteorite ALH84001

Kathie L. Thomas-Keprta1, Simon J. Clemett1, Dennis A. Bazylinski2, Joseph L. Kirschvink3,
David S. McKay4, Susan J. Wentworth1, Hojatollah Vall5, Everett K. Gibson, Jr.4,
and Christopher S. Romanek6

1Lockheed Martin, Houston, Texas 77058
2Department of Microbiology, Iowa State University, Ames, Iowa 50011
3Division of Geological and Planetary Sciences, California Institute of Technology,
Pasadena, California 91125
4National Aeronautics and Space Adminstration/Johnson Space Center, Houston, Texas 77058
5Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec H3A 2A7, Canada
6Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina 29802

Abstract: 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. One of the strongest lines of evidence is the presence of tens-of-nanometer-size magnetite (Fe3O4) crystals found within carbonate globules and their associated rims in the meteorite. Approximately one-quarter of these magnetites have remarkable morphological 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. 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, although this work is now in question.

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.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).